Claude Devant L'universite

Bernard -Lyon

Ecole Doctorale De Chimie

Specialite Chimie

M Jean-Marie

Prof Jean-François Carpentier

M Klaus

Köhler M Régis

Gauvin M Klaus

Köhler M Marc

Lemaire M Christopher

Nicholas M Mostafa

Taoufik Universite

Claude Bernard -Lyon

M Le Professeur

L Collet

J-F Mornex

G Annat

D Simon

M G Gay

Composantes Sante

J Etienne Directeur

: M Le Professeur F-N

Gilly Directeur

D Bourgeois Directeur

F Locher Directeur

Y Matillon

P Farge

Paul Barger

Prof Que Le

Klaus Köhler

Remerciés

Dr Régis Gauvin

Laurent Delevoye

B B Cioslowski

G Stefanov

A Liu

P Liashenko

I Piskorz

R L Komaromi

D J Martin

T Fox

M A Keith

C Y Al-Laham

A Peng

M Nanayakkara

P M W Challacombe

B Gill

W Johnson

M W Chen

C Wong

J A Gonzalez

Gaussian Pople

Revision D G03

THESE Présentée

Ces travaux de thèse ont été rendus possibles grâce à l'étroite collaboration entre la société UOP LCC et le LCOMS. Je tiens particulièrement à remercier le Prof. Jean-Marie Basset de m'avoir accueilli dans son équipe très dynamique. Je le remercie également de m'avoir accordé sa confiance et donné l'opportunité de travailler sur ce sujet aussi intéressant que

COMPOSANTES ET DEPARTEMENTS DE SCIENCES ET TECHNOLOGIE

Régis Gauvin and Dr. Laurent Delevoye for the fruitful collaboration; Dr Jérémie Pelletier for all its useful comments; Olivier Boyron for his help in polymers charachterization; all the students and members of the LCOMS and LCPP, all the members of UCBL, ESCPE Lyon and UCCS Lille, who had provided excellent expertise in their respective fields.

All thoughts go to my family for their constant encouragement and specifically to Angelique. I would also like to take this opportunity to show my gratitude to all the people who offered support and friendship during the last three years.

Abreviations

Introduction

The target of this PhD thesis is the preparation of well-defined supported tungsten catalyst for the production of propylene. It is thus focused on the characterization of catalytic systems and on reactions allowing propylene from light olefins by metathesis. It is divided in six chapters.

Chapter 1 draws up the generalities for propylene production and particularly the olefin metathesis reaction. Then, the state of the art in tungsten surface organometallic chemistry, the existing catalytic systems, the reactions they perform and their mechanisms will be described. After this bibliographic study the goals and the strategy employed for the subject is presented.

Chapter 2 is devoted to the preparation and characterizations of tungsten hydride supported on alumina. The support, the carbynic precursor and the tungsten hydride have been studied. Chapter 3 discloses a complete mechanistic study of the direct conversion of ethylene to propylene reaction using supported tungsten hydride as a catalyst.

Chapter 4 releases the preparation of supported aluminum species. Their reactivity toward ethylene was then investigated to test their influence in the catalytic activity of tungsten hydride supported on alumina.

Chapter 5 reveals the unprecedented activity of the tungsten hydride for the production of propylene from ethylene and/or butenes.

Chapter 6 finally presents the preparation of new model tungsten catalysts supported on silica bearing an oxo ligand.

A general conclusion sums up the whole results and considers the study perspectives.

Chapter 1

Metathesis for propylene production and Surface Organometallic Chemistry of tungsten

Metathesis for propylene production 1.Propylene a key intermediary in chemical industry

Propylene, [115-07-1], CH3-CH=CH2, is one of the principal light olefins. It is mainly obtained as a by-product of ethylene (vide infra) and is a starting material of many significant processes. It was first used for isopropanol synthesis, by combination with water using sulfuric acid or heterogeneous acid catalyst. 1 Until 1965, it was far less used than ethylene, which demand increase constantly and has led to the building of new production units. As a result, propylene became readily available, leading to the development of new applications. Propylene is now used for the synthesis of numerous products, e.g. polypropylene, acrylonitrile, propylene oxide, cumene and acetone (Scheme 1.1). The demand for propylene for production of polypropylene was 17% in 1970 and 64% in 2004 (Figure 1.1). 2 This growing of the demand of polypropylene, replacement of the metal in automotive applications is a major contribution to the global increase of propylene demand. This demand is in constant evolution for all part of the world with the rate of 5% per year (Figure 1.2). 3 Figure

2004

CONFIDENTIAL LCOMS-UOP LCC Scheme 1.1 Propylene as starting material for refinery products and chemicals Since 1992, although the overall demand for ethylene is greater than that for propylene, the rate of growth for propylene has outpaced that for ethylene. For instance, in the US the propylene/ethylene (P/E) demand ratio has increased from 0.43 in 1992 to 0.54 in 2004. A similar phenomenon is seen to an even greater extent in Western Europe and Asia-Pacific, where the P/E demand ratio is 0.77. In 2002, worldwide production for chemical use amounted to 60.10 6 t and was valued at roughly $25.10 9 . Consumption is outpacing production. The supply-side shortage in the United States has so far been accommodated by increasing imported materials. However, dedicated units may be needed to fill demand. 4

Propylene

Routes to propylene

Propylene can be produced by two different paths: by-product technologies or on purpose technology (Scheme 1.2). In the former, which account for most of production, propylene is a by-product, i.e. the production units are not devoted to the production of propylene itself. In the later, propylene is specifically targeted, but that remains the minor path. This section briefly describes the technologies used for the propylene production and the recent advances that have been obtained for the two paths, in order to enhance the P/E ratio or to produce propylene from alternative feedstock.

Scheme 1.2 Commercial routes to propylene 5

Traditional routes: byproduct technologies

Although propylene is a major feedstock in industrial chemistry, it is mostly produced as a byproduct of ethylene by steam cracking and in refinery process (product from fluid catalytic cracking). Steam cracking supplies major part of the chemical industry consumption, whereas refineries only supplies between 20-40%. Most of the propylene produced in refineries is consumed in in-house, non-chemical applications, such as gasoline production (alkylate or polymer gasoline), liquefied petroleum gas production (LPG) or as heating gas. 6 Million Metric Tons CONFIDENTIAL LCOMS-UOP LCC

• Steam cracking

Steam cracking is the principal industrial process used to produce light olefins, e.g. ethylene or propylene, from heavier feedstock such as naphta (C5 to C12 hydrocarbon mixture constituting between 15 and 30% wt of crude oil). 7 In this process, the hydrocarbon feed is mixed with steam and reacted at high temperature (from 750 to 950°C) with a very short residence time (0.1 to 0.6 s). Steam is used to minimize the side reaction of coke formation. The formation of light olefins occurs via a free radical mechanism. This complex mechanism explains the vide range of product of this process. Indeed, numerous reactions, e.g. H abstraction or addition, radical isomerization or decomposition, occur during the propagation step. 8,9 Moreover, the nature of the feedstock has a strong influence on the selectivity. Indeed with complex feedstock, up to 2000 reaction may occur simultaneously. The steam cracker can be operated in different condition, by varying pressure or oil to steam ratio. These parameters can be adjusted to afford higher P/E ratio.

• Fluid Catalytic Craking Fluid catalytic cracking (FCC) is the central technology in modern refining. 10,11 This process upgrade heavy gas oil (the hydrocarbon portion with molecular weight from 200 to 600 or higher) to higher valued gasoline. The total amount of propylene produced depends on the mix of these processes and the specific refinery product slate. For example, in the USA, refiners have maximized gasoline production. This results in a higher level of propylene production than in Europe, where proportionally more heating oil is produced.

In FCC, partially vaporized gas oil is contacted with catalyst. Contact time varies from 5 s to 2 min; pressure usually is in the range of 2.5 to 4 atm, depending on the design of the unit and reaction temperatures are 450 to 580°C. The catalyst employed in FCC has known several significant evolutions. Indeed, during the 60's the replacement of the amorphous silica-alumina catalyst by zeolite Y improve the gasoline selectivity of the process. Then, in the 80's the use of ZSM-5 additives boosts the propylene yield. In 2004, Davison Catalyst starts the commercialization of Apex ® additives and claiming they allow a 15% selectivity in propylene.

• Alternative feedstock

In order to reduce the dependence to oil, processes that produce light olefins from alternative recourses, i.e. coal, natural gas or even biomass, have been developed. An innovative process, namely MTO (Methanol To Olefin) that affords light olefins (i.e. ethylene, propylene and butenes) from methanol has been developed by UOP and HYDRO. This process is claimed to provide a broad range of P/E ratio (from 0.77 to 1.33) that can be adjust

CONFIDENTIAL LCOMS-UOP LCC according market demands. 12 It uses a molecular silico-aluminophosphate synthetic molecular sieve based catalyst and methanol as a feedstock. The main challenge of this method is the purification of the product obtained, due to the presence of oxygen in the methanol, to match polymer grade standards. Methanol can be obtained from alternative natural resources such as coal and natural gas, via syngas (CO/H 2 ), or even biomass.

Hence, it provides a new access to plastic materials such as polyethylene and polypropylene, without recourse to oil. This process is actually tested in Belgium, coupled with the Total petrochemicals' olefin cracking process (OCP), which converts the butenes and higher olefins produced by MTO to ethylene and propylene. 13 Different routes, using the cracking method and focused on alternative feedstock are in development. Indeed, the direct conversion of ethanol to propylene over acidic catalyst has been patented by Toyota Motor Company. 14 The inventors claim very high selectivity in propylene (80-90%). A patent describing the use of SAPO-34 (a silicoaluminophosphate zeolite) to convert ethanol/methanol mixture to propylene have also been filled by China Petroleum & Chemical and Shanghai Research Institute of Petrochemical Technology. 15 Nevertheless in that case the P/E ratios are similar to the ratio obtained for the MTO process. These companies also filled a patent 16 wherein methyl chloride is reacted at high temperature over silico-aluminophosphate zeolite catalyst leading to a propylene ethylene mixture and HCl, contrary to MTO that afford H 2 O. These HCl may be oxidized to Cl 2 which will be recycle for the synthesis of methyl chloride from methane avoiding thus the natural gas reforming to syngas and the subsequent methanol synthesis.

Recent advances: on purpose technologies

The expansion of propylene consumption has enhanced the demand of on-purpose processes, i.e. processes devoted to the production of propylene only. Indeed, they are now economically relevant. Different processes have been developed and some of them are currently running. Outside cracking, propylene can be obtained by propane dehydrogenation or by olefin conversion.

• Propane dehydrogenation

Propane dehydrogenation is an endothermic equilibrium reaction that can be catalyzed using heavy or noble metals. Operating at higher temperature and low pressure increases the propylene yield. With too high temperature, the selectivity moves towards coke formation.

As a result, the reaction is usually performed between 500 and 700°C at atmospheric pressure. A number of processes are commercially available, among them Oleflex (UOP CONFIDENTIAL LCOMS-UOP LCC LCC), Catofin (ABB Lummus) or STAR (Phillips Petroleum), they differs in the nature of the catalyst, the operation and regeneration conditions.

• Olefin metathesis

Propylene can be produced by olefin metathesis. The Olefin Conversion Technology (OCT) provided by ABB Lummus enhances the amount of propylene produced by naphta steam cracker units. This process converts the raw C 2 and C 4 feedstock of the steam cracker to propylene. The C 4 raw feedstock contains both 1-butene and 2-butenes. The reaction occurs over a mixture of WO 3 /SiO 2 and MgO at a temperature higher than 260°C and a pressure of 30-35 bar. The 1-butene of the feed is isomerized to 2-butene, over a MgO catalyst, while the original 2-butene is consumed by the cross-metathesis with ethylene. 17 Another process based on metathesis has been conjointly developed and tested by IFP and the Chinese Petrol Corporation (Taiwan), namely the Meta-4 process. This process uses a Re 2 O 7 /Al 2 O 3 catalyst to convert ethylene and 2-butene at 35°C and 60 bar. 18,19 This technology is not yet commercialized, probably due to the high cost of the catalyst and the necessity of very pure feedstock (high sensibility of the catalyst toward polar functions). 20 The use of olefin metathesis has also been investigated using alternative feedstock.

For example, Mitsui Chemicals of Japan has filed a patent application 21 that describes three methods for producing biomass-derived propylene (see Scheme 1.3). All start by using alcohol (i.e. ethanol or butanol) obtained by selective sugar fermentation: i) dehydrating ethanol to ethylene, dimerizing the produced ethylene to butenes and finally crossmetathesis of both materials to give propylene; ii) making the butenes, not by dimerizing ethylene, but instead dimerizing ethanol to n-butanol and then dehydrating the n-butanol to n-butenes and then metathesizing the ethylene and butenes to give propylene; iii) production of n-butanol and then dehydrating to n-butenes and cross-metathesis with ethylene.

None of these steps are novel; in fact, it is believed that Brazilian petrochemical major Braskem has made biopropylene in commercial development quantities by a similar approaches. 22 The Mitsui patent application is focused on means of removing impurities from the bio-feedstocks, to preclude poisoning of the notoriously sensitive metathesis catalysts.

Chapter 1 21

CONFIDENTIAL LCOMS-UOP LCC Scheme 1.3 Reactions proposed by Mitsui Chemicals' patent to produce propylene from biomass.

Generalities about olefin metathesis

In this thesis, the use of olefin metathesis to provide propylene from light olefin such as ethylene and/or butenes will be investigated. Therefore, in this subsection, the metathesis reaction is presented.

History and mechanism

Olefin metathesis consists in the exchange, usually catalyzed by transition metals, of alkylidene fragments between two olefins. It can be categorized in three types of reactions (Scheme 1.4): i) exchange between two olefins (self-metathesis and cross-metathesis), ii)

ring opening metathesis polymerization (ROMP) and iii) ring closing metathesis (RCM) of a diene.

Ethylene i) ii) iii) Dehydration Dehydration R 2 R 1 + R 2 R 1 R 1 R 1 R 2 R 2 + i) ii) ROMP: iii) RCM: =CHCH 2 CH 2 CH 2 CH= n n + CONFIDENTIAL LCOMS-UOP LCC
In the 60's Banks et al. have first reported an olefin disproportionation reaction. 23 Several processes were developed to allow the conversion of propylene to ethylene and 2butene, as at that time the demand was stronger for ethylene than for propylene. The term "olefin metathesis" has been later introduced by Calderon et al. 24 The main concerns were then, the role of the catalyst and the mechanism of the reaction. Calderon et al. demonstrated that C=C bonds involved in the reaction are the olefinic ones and not those of the substituents. 24 The complete mechanism has been revealed by Hérisson and Chauvin in 1971. 25 The key element of this mechanism is a metallocarbene species that react with an olefin to form a metallacyclobutane. The former evolve to give a new olefin and a new metallocarbene (Scheme 1.5).

Scheme 1.5 Chauvin's mechanism for olefin metathesis

As this mechanism involves equilibrated reactions, the metallacyclobutane can afford new products (productive metathesis) or regenerate the reagents. Degenerative metathesis occurs when the metallacyclobutane decomposes only in products identical to the reagents (R 1 = R 3 ). The degenerative metathesis may be responsible of a slower kinetic rate of the reaction, e.g. when the productive path is less favored than the degenerative path.

This metalacyclobutane mechanism has been extensively examined, for instance, Katz et al. confirmed it by kinetics studies. 26 Then, homogeneous organometallic species, bearing a carbene ligand not substituted with heteroatoms, in the coordination sphere of the metal have been synthesized. [27][28][29][30] These species have shown a good activity in olefin metathesis supporting the hypothesis of the need of a metallocarbene to perform this reaction. Finally, the synthesis of metallacyclobutanes has brought a supplementary proof for this mechanism in homogeneous catalysis. 31 The olefin metathesis is an equilibrated reaction. Indeed, the number and the nature of products' bonds are generally the same that the reagents' (except for the strained cyclic or highly substituted olefins). The reaction is thus quasi-isenthalpic. An interesting effect of this characteristic is the quasi-athermicity of the reaction. Entropic factor dictates the reactivity leading to a statistic distribution of product and reagent. For instance, 2-pentene metathesis at 298 K leads, at thermodynamic equilibrium, to a mixture of 2-pentenes/ butenes/hexenes in a ratio close to 2/1/1. This behavior is not observed in the case of

M R 3 R 2 R 1 + M R 3 R 2 R 1 M R 3 R 2 R 1 + Chapter 1 23
CONFIDENTIAL LCOMS-UOP LCC highly substituted olefins. Indeed, isobutene metathesis reaches only 3% conversion at 298 K (ΔG° = + 17.3 kJ.mol -1 ). Scheme 1.6 Formation of favored and disfavored metallacyclobutanes explaining the E/Z selectivity before reaching thermodynamic equilibrium 32,33 In the case of acyclic olefins, when a mixture of E/Z diastereoisomers is obtained, the ratio obtained at the equilibrium is imposed by thermodynamics. Nevertheless, if the thermodynamic equilibrium is not reached (i.e. in the beginning of the reaction (batch) or at short contact time (continuous flow)), a singular strereoselectivity may be observed. In these conditions, the E/Z ratio is governed by the nature of the catalyst and the substrate and can be explained by Chauvin's mechanism. Thus, outside of thermodynamic equilibrium, a Z olefin (respectively E) gives a Z olefin (respectively E). This can be interpreted by the formation of favored or disfavored metalacyclobutane intermediaries. The (1,3) equatorial (e) disubstituted metallacyclobutanes are the most stable followed by the (1,2) equatorial (e) disubstituted ones (Scheme 1.6). 32,33 1. 3

.2. Catalysts for olefin metathesis

The catalytic systems for olefin metathesis include generally a metal center drawn from the group IV to VIII. These catalysts may be homogeneous or heterogeneous. Herein are presented homogeneous catalysts based on several metals (i.e. Mo, W, Re or Ru), whereas the presentation of heterogeneous systems will focus on WO 3 /SiO 2 as this thesis is related to its chemistry.

M R 3 R 2 R 1 + M R 1 R 2 R 3 M R 3 R 1 R 2 M R 1 + R 2 R 3 + M R 1
R 2 R 1 + M R 1 R 2 R 3 M R 3 R 1 R 2 M R 1 + R 2
The first catalyst used for cyclic and acyclic olefin metathesis has been described by Banks and Bailey. 23 It is composed of WCl 6 /EtAlCl 2 /EtOH. The olefin metathesis catalysts developed after were Zeigler-Natta type system. They were composed of an inorganic transition metal complex and an alkylating agent. In some case, a promoter (e.g. O 2

or an alcohol), is also added to enhance the catalytic activity. The alkylation agent can also be replaced by photochemical activation. In spite of numerous related systems developed, the nature of the active species is not well understood yet.

The proposition of Chauvin that the active species must be a metallocarbene (vide supra) has been pivotal. Afterwards, the investigations were focused on the synthesis of this active species. The first metallocarbene prepared were electrophilic carbene (Fischer's carbene), and therefore inactive in olefin metathesis. 34 Nevertheless, Katz et al.

described 35,36 the first use of a eletrophilic carbene, [(CO) 5 W=C(C 6 H 5 ) 2 ], 27 for olefin metathesis, that is active without co-catalyst at room temperature. Selected catalysts obtained using metallocarbene are summarized on Scheme 1.7. [37][38][39][40] Scheme 1.7 d 0 carbenic complexes active in olefin metathesis

The coordination sphere of all these complexes has been optimized regarding steric and electronic parameters. For instance using electro withdrawing groups (EWG) as ligand weaken the electron density around the metal center. It is believed to favor the approach of the olefin toward the metal and thus the formation of the metallacyclobutane.

Ruthenium-based catalysts have then been documented with Ru IV (d 4 ) based systems showing a high activity for olefin metathesis. [41][42][43][44] Examination of the structurereactivity relationship of these catalysts has disclosed a completely different behavior than for the d 0 electrophilic early transition metal complexes. In the case of ruthenium, the CONFIDENTIAL LCOMS-UOP LCC more σ-donating the ligand, the higher the activity observed in olefin metathesis. 42 The molybdenum and ruthenium catalysts are currently commercially available. Those based on molybdenum are more active than those based on ruthenium, but the latter are more tolerant toward polar functions and are not air-sensitive. This later property makes the ruthenium used in industrial scale, especially in pharmaceutical applications. 45 1.3.3. Tungsten oxide on silica (WO 3 /SiO 2 ) catalyst

Tungsten has provided more heterogeneous catalysts for olefin metathesis than all others metals combined (e.g. Re, Mo). Many studies have discussed the catalyst systems themselves in an attempt to elucidate the nature of the active species and its mode of formation. 31 Herein is presented the WO 3 /SiO 2 system which is the most commonly used among tungsten based catalysis. Tungsten oxide on silica appears to be particularly desirable because of its high resistance to common poisons such as air and water, and its low coke formation. 46,47 It is often prepared by incipient wetness impregnation of ammonium metatungstatehydrate solution on silica. This method is convenient but lead to non-uniform deposition of the impregnated material on the support. 48 The catalyst is then generally activated in dry air at 550°C. When the tungsten loading exceeds 10% wt , WO 3 crystallites are observed on XRD spectra and RAMAN spectroscopy. 49 The heterogeneity of surface species present at the surface has been evidenced by mass transfer limitations of the catalyst. This observed interphase mass transfer effects, although unexpected via calculations, 50 are explainable by assuming that a small number of very active sites are widely separated and, hence, the reaction is limited by site localized diffusional effects. 51 This catalyst also exhibits a significant feature: during the initial contacting of freshly activated tungsten oxide on silica catalyst with propylene there exists a steady increase in catalyst activity. 52 Depending on process conditions, this initiation step may last up to 24 h. At the end of this step the catalyst achieves a stable steady-state activity. This period of increasing activity is known as "break-in". 48,53 This phenomenon has been attributed to the formation of steady-state active sites, i.e. tungsten centers with the appropriate oxidation number. Indeed, the duration of the break-in can be greatly shortened by pretreating the catalyst with hydrogen or carbon monoxide 52 or by activating at temperatures above 630°C. 54 This reduction of the tungsten from WO 3 to WO 2.9 is observed by a characteristic change of color from yellow to blue 55 and accompanied by a slight loss of oxygen in the catalyst. 56 This loss of oxygen is also observed by formation of traces of

Introduction

Employing Tungsten for Surface Organometallic Chemistry (SOMC) has allowed, for the past decade, the access to unprecedented performances for the catalytic transformation of hydrocarbons. By changing the ligands and the nature of the support, novel catalysts were prepared and characterised with significant insights about the organometallic active species and their reactivity being gained. These progresses, although still restrained to the laboratory scale, can potentially affect several main processes involved in the petrochemical industry.

The use of inorganic carriers based on metal oxides such as silica, alumina or silicaalumina has been extensively investigated to generate heterogeneous catalysts with many early transition metals (e.g. Ti, [61][62][63][64][65] Zr, Hf, [87][88][89][90][START_REF] Tosin | Topics in catalysis[END_REF][START_REF] Tosin | [END_REF][93] Ta, 76,81,94-115 etc). A few conclusions, regardless the metal involved, can be drawn on the impact of the support. When considering the surface as ligands, these systems can be assimilated as polynuclear catalysts in which one ligand (i.e. the particules of inorganic carrier) hosts several metals. This is believed to prevent the metal to react with one another thus reducing in fine to the deactivation of the catalyst. It is noteworthy that the nature of the support affects tremendously the metal reactivity. For example, chemisorption of [Zr(CH 2 tBu) 4 ] on alumina provides an efficient olefin polymerization catalyst, 84 while its silica counterpart is inactive under the same conditions. The support employed controls over prominent parameters of the grafted species such as its distribution, its amount, its oxophilicity, its ionic character and its podality among others.

Supported systems such as those obtained by SOMC are notoriously difficult to characterize, but the last decade have seen an important improvement of the tools available to access their molecular structure. Techniques such as IR spectroscopy, mass balance and elemental analysis have long proved their capacity to access overall properties and stoichiometry of grafted species. However, removing the uncertainty around the coordination sphere of the metal remains challenging, hence encouraging the development of new analytical means. For instance spectroscopic techniques such as, SSNMR, EXAFS or even Raman spectroscopy have more recently demonstrated their ability to access the intimate structure of tungsten species obtained by SOMC. In addition, the use of soluble molecular analogues (i.e. polyoligomeric silsesquisiloxane (POSS-OH) [START_REF] Salinier | Advanced synthesis & catalysis[END_REF][START_REF] Salinier | [END_REF] or ( t BuO) 3 Si-OH) and of theoretical models 116 have also allowed to gain an understanding more complete and accurate. The potential contribution of these analytical techniques can be briefly CONFIDENTIAL LCOMS-UOP LCC and non-exhaustively summarized. SSNMR spectrometry is highly relevant to characterizing grafted organometallic species with several 13 C SSNMR and other experiments dedicated to observe the carbon and the hydrogen directly bound to the metal and more: intermediaries ligands complexes. EXAFS permit to know the coordination sphere (i.e. number of atoms and distance) of heavy elements such as transition metal. Raman spectroscopy can also allow to observe vibrations, usually elusive, of metal-oxide bonding.

Herein will be summarized exclusively the well-characterised W complexes grafted to the surface that are relevant to heterogeneous catalysis. For clarity purpose, the discussion is divided in two parts the preparation of the tungsten surface complexes (section 2.2)

and their catalytic performance (section 2.3).

Surface tungsten complexes

In all the W-grafted complexes discussed there, the ligands can be deconstructed similarly in regard to their role in catalysis (Scheme 1.9). For instance, carbyne, carbene or hydride moities intervene directly in the catalytic process and command over the catalytical performance. In contrast, the remaining ligands serve supplementary purposes that can be conveniently distinguished; the surface (silica, silica/alumina, alumina) maintains the metal by one or more bonds to a carrier while the spectator ligands (viz. imido, aryloxy, amido) tune indirectly the active site. For the sake of clarity, the examination of these systems will begin by a concise description of the support with a comparative account of their properties will be given. Secondly, a selection of various W-complexes will be outlined by categorizing the reactive ligands and reporting the relevant examples in term of characterization.

Scheme 1.9 Deconstruction of the grafted complexes: support, active site and ancillary ligands

Surface properties

Several types of inorganic carriers based on metal oxide have been employed to graft tungsten complexes. However, silica, silica-alumina and alumina have all been involved in the formation of the most significant surface complexes in regards of the wealth of their characterization and their prime involvement in catalytic processes. A discussion of their

M O O O O W L x R X Support Active site Ligands Chapter 1 29 CONFIDENTIAL LCOMS-UOP LCC
common properties prior to that of their differences, namely, the type and the reactivity of their hydroxyl, seems judicious.

For all compounds obtained by SOMC, the surface area is a parameter determinant over the total amount of metal potentially immobilizable. This is largely controlled the type of materials employed with two mains options available: non-porous or porous. Both consist in spheroid particles of variable diameters, but porous materials contain controlled-size pores that extend significantly the surface area compared to their non-porous counterparts. It has also been recognized that non porous materials present a few advantages such as their readily availability, their convenient handling and their optimal geometry for the characterization of single site species. Furthermore, the utilization of porous material currently knows great interest but will not be discussed herein. Another common feature to these surfaces is the dehydroxylation treatment that can control the hydroxyl groups distribution. Submitting the carrier to a given temperature under high vacuum induces the elimination of water from the surface and narrows selectively the OH population.

• Specificity of Silica Silica has been extensively employed as an inorganic carrier for the grafting of transition metals drawn from group IV to X. Fumed silica is made of spherical particles of diameters between 5 to 50 μm. For instance, specific surface areas are dependent of the type of silica employed and are typically comprised between 50 and 200 m 2 .g -1 for fumed silica. Regardless the type of silica employed, siloxane and silanol are the two main functionalities with the latter being found almost exclusively at the surface. In the bulk, silica is constituted of tetrahedral SiO 4 units that are generally inaccessible and inert to metal reagents. At the surface, the silanols, due to their higher reactivity, are available to immobilise the metal by forming up to three siloxy groups. As the siloxy substituents modify the structure and properties of grafted early transition metals, thus commanding over their reactivity, the type and the distribution of silanol existing at the surface are determinant.

These parameters can be controlled by the temperature of the dehydroxylation treatment (vide supra). The type (viz geminal, vicinal and isolated) of silanol and their relative proportion at a given temperature can be conveniently determined by combining IR spectroscopy (Figure 1.3) 117 and reactivity studies.

CONFIDENTIAL LCOMS-UOP LCC Silica-alumina has been used as a support for W-SOMC. Its structure is very close from Silica but allows the formation of species impossible on silica avoiding sintering effects (vide infra). Therefore, silica-alumina should be considered as modified silica as silanol are exclusively observed on the surface. 119,120 Both Si-O-Si and Al-O-Si bridges can be found in the bulk; the loading of alumina, and the preparative methods, can be directly correlated with this two groups ratio. Two preparative methods are commonly employed: co-hydrolysis of silica and alumina and the silication of alumina. The silica-alumina has interesting Brönsted acid character.

• Specificity of Alumina

Transition aluminas have been extensively investigated as an inorganic carrier and exhibit significant differences with silica. Among them, γ-alumina is one of the most used in industrial processes due to its high mechanical stability (in large fixed bed reactor the bottom catalyst may carry more than 10 metric tons) and its interesting acidic behavior. The γ-alumina is obtained by heating bohemite above 500°C. This treatment gives a material with specific surface around 200 m 2 .g -1 , less acidic than η-alumina where surface plane 110 is predominant. 121,122 It is made of aluminoxane in the bulk and displays only aluminols at the surface. However, in many aspects, its chemistry is more complicated than either silica or silica/alumina. The combination of all these factors generates a distribution of types of site available for the grafting of metals. Consequently, the deep structure of alumina is still a debated matter with recent progress coming from model provided by theoretical chemistry aiming to provide models in line with experimental data.

The modelisation proposed by Knözinger,123 and more recently by Sautet, 124 have been explaining the IR spectra of γ-Alumina (Figure 1.4). Notably, the bands observed have been correlated to the interaction between the hydroxyl and the geometry of the aluminums beside. The utilization of silica and silica-alumina dehydroxylated at different temperature as a supports in SOMC, leads to well defined structures, as only on type of silanol is involved in the grafting reaction. In contrary, the use of alumina affords more complex structures, as the reactivity of the different aluminol toward organometallic species is variable. Moreover, the acidic character of alumina may lead to the formation of cationic species in unpredictable proportions. 103,125 Theoretical calculations are therefore very profitable to understand these surface species. 116

Al

Preparation and characterizations of supported tungsten complexes

In the following section, the synthesis and the characterizations of selected tungsten-based species obtained by SOMC will be expounded. The discussion will be organized as follow: i) Oxide-supported tungsten carbyne species, ii) Oxide-supported tungsten carbene species and iii) Oxide-supported tungsten hydride species For all surface species the range of analytical techniques usually relevant was employed: IR spectroscopy, DRIFT, SSNMR, mass balance, gas evolution measurement and elemental analysis. Besides, EXAFS, Raman spectroscopy and high-resolution SSNMR spectroscopy (HETCOR, J-resolved 2D SSNMR) will receive particular attention for they had decisively contributed to the identification of the coordination sphere of the grafted tungsten.

Finally, the chemistries of oxide-supported have been closely entangled and directly related to that of their soluble counterparts. When necessary, comparison between the two will be made to account the observations gathered from the grafted species.

• Oxide-supported tungsten carbyne species Oxide-supported tungsten carbyne species have found a key employment as catalytic components for the metathesis of alkynes. bisgrafted cationic complex as major surface species. The difference of reactivity demonstrated by of these two complexes has been investigated by DFT calculation. According to them, the reaction of the Zr precursors is far more exothermic than its W counterpart, which possesses a much higher activation barrier (Ea) 81 kJ.mol -1 . In addition, the rigidity imparted to the complex by the carbyne hinders the coming of the complex close to some type of the aluminol. As a result, the first step consists in the electrophilic cleavage of the W-CH 79 EXAFS experiments shows that (IV) may be the major surface species with the following features: i) about one carbon (1.773 Å) and one oxygen (1.862 Å) atom, the distances of which are consistent with a carbynic carbon atom and σ-bonded OAls, respectively; ii) two carbon atom neighbors at a greater distance (2.110 Å) assigned to two neopentyl ligands; iii) two carbon atoms at 3.314 Å, assigned to the two quaternary carbon atoms of the neopentyl ligands; and iv) a carbon atom at 3.323 Å, corresponding to the quaternary carbon atoms of the neopentylidyne ligand. 135,136 The solid state 13 CP-MAS NMR spectrum of [W(≡C t Bu)(CH 2 t Bu) 3 ] grafted on alumina reveals a broad signal from 50 to 110 ppm. This complexity is explained by theroretical calculation as an interaction between carbynic and methylenic carbons of the carbyne and neopentyl ligand respectively with unreacted aluminols (Scheme 1.12). The 13 C CP-MAS spectrum of this species shows seven resolved peaks, which can be assigned to the aromatic carbons, the isopropyl groups and the carbynic t Bu moiety.

Unfortunately, it has not been possible to detect the resonance of the carbynic atom (a resonance should be expected at ca. 300 ppm), probably due to the fact that i) it is not surrounded by proton and ii) the signal is probably relatively broad due to the interaction with the metal. However the observation of the signal at 51 ppm and the absence of any signal of a methylenic carbon (like in I) at ca. 74 ppm support the above proposed structure. 138 Gauvin et al. have developed an alternative to the direct grafting of the organometallic complex by immobilising dimeric metal compounds on the surface prior to its alkylation. Tunsgten dimeric derivatives of the d 3 -d 3 type involved in metal-to-metal triple bonding are convenient precursors and have found applications in numerous fields, such as in materials, organometallic synthesis, and in catalysis. One of the most versatile entries into this class of compounds relies on the substitution of amido ligands of the W 2 (NR 2 ) 6 species through protonolysis or halogenation. 139 The immobilization of such key compounds onto an inorganic support to generate heterogeneous dinuclear amido de-

V O Si O O O W t Bu Si O O O O O Chapter 1 37 CONFIDENTIAL LCOMS-UOP LCC
rivatives is therefore of great interest capable to act as precursor to form supported carbine bis amido tungsten after treatment with an internal alcyne. 140 The investigation of this grafting of such compounds is complicated by the absence of bonding between the metal and element easily observable such as 13 C or 1 H in NMR spectrometry or even in IR spectrocopy do not allow us to access direct information about the coordination modes of the metals. By contrast, observing the low frequency region (200-600 cm -1 ) by Raman spectroscopy permitted to confirm the immobilisation of W 2 (NR 2 ) 6 on SiO 2-(700) . The modification of the symmetry and the vibration modes involving tungsten centre such as stretching of W≡W observed at 328 cm -1 can attest that the dimeric W is attached to the surface.

• Oxide supported tungsten carbene Most silica supported metallocarbene complexes of tungsten VI have been obtained by grafting their molecular equivalents developed by Schrock et al. 141 on silica, and more specifically SiO 2-(700) . They are typically tetra-coordinated and have a d 0 configuration and they can be described with the following general formula [W(=NR 1 ) (=CHR 2 )(X) 2 ] (R 1 = R 2 = alkyl or aryl , X= neopentyl or pyrollyl). These complexes can be grafted on the surface OH group of silica through different possible competitive ways. Therefore, the nature of surface species are typically investigated as follows: i) monitoring the ligands exchange before and after grafting by combining labelling studies ( 13 C labelled or different types of ligands) and solid state NMR spectroscopy, and ii) using soluble molecular models of silica, based on molecular silanols, i.e. polyoligomeric silsesquisiloxane (POSS-OH) or ( t BuO) 3 Si-OH, to obtain mechanistic insight through monitoring the reaction of molecular silanols by solution NMR. shows similar spectroscopic properties to the silica-grafted moiety. In particular, the syn conformation is assigned to both the surface and the molecular siloxy W(VI) species based on the low 1 J CH coupling constants for the alkylidene signals in the NMR spectra ( 1 J CH = 107 Hz for 13 C solution spectra of the silasesquioxanes vs. 143 It demonstrates that the addition of heteroelements in the coordination sphere of the homogeneous precursor impacts the selectivity of grafting reaction.

W N i Pr i Pr t Bu t Bu O Si O O O Si O O O W N i Pr i Pr t Bu O Si O O O Si O O O N W N i Pr i Pr t Bu
• Oxide supported tungsten hydride The preparation of oxide supported tungsten complexes is generally operated by reaction of a surface OH group with a W-C bound of the relative molecular precursor. A similar method has been undertaken to prepare supported tungsten hydride by grafting of molecular tungsten hydride complexes such as WH 6 (PR 3 ) 3 . Nevertheless, this route is not convenient due to the weak reactivity of W-H bound toward water and therefore toward surface OH groups. 144 In the 70's Zakharov et al. initiate a new method for the preparation of zirconium hydrides supported on silica by the reaction of corresponding organometallic perhydrocarbyl compounds with partially dehydroxylated silica followed by reduction of the surface complexes thus formed at 150°C under H 2 (Scheme 1.15). 145 In the 80's they developed titanium and hafnium hydrides using the same methodology. 146 In the 90's, Vidal et al. have extended these investigations to group V, describing silica supported tantalum trishydride. 96 Scheme 1.15 Preparation of surface zirconium hydride described by Zakharov et al. 145 In the light of these results, the development of this methodology for group VI metals has been envisaged by hydrogenolysis of the corresponding supported organometallic precursor such as I, II, III, or IV. Nevertheless, the energy of W-W and W-O bound are relatively close (675 and 666 kJ.mol -1 respectively) 147 let think that the stabilization of tungsten hydrides on oxides surface may be disfavored, letting the formation of tungsten particles by sintering. In the case of group V, the difference of energy between the metalmetal and metal-oxygen bounds is wide enough to avoid sintering (e.g. Ta-Ta: 390±96 kJ.mol -1 and Ta-O: 799±13 kJ.mol -1 ). 148,149 Therefore, the treatment of I and II (supported on SiO 2-(200) and SiO 2-(700) ) at 150°C for 15h, under H 2 leads to partial or total sintering of the tungsten surface species. The formation of small particles (10 to 20 Å) has been evidenced by TEM, CO adsorption and by resurgence of the Si-OH signal on the infrared spectrum. 150 In sharp contrast, the similar treatment of III and IV (supported on SiAl (500) and Al 2 O 3-(500) ), generate the corresponding hydrides, VI and IX, without sintering. This difference of reactivity highlights the significant role of the support in the stability of species obtained by SOMC. It seems that the presence of aluminum atoms at the surface of the support (i.e. silica-alumina or alumina) prevents the migration of tungsten atoms.

Si-OH) n + Zr(C 3 H 5 ) 4 ( Si-O) n Zr(C 3 H 5 ) 4-n + n C 3 H 6 ( Si-O) n ZrH x + (4-n) C 3 H 6 ( Pentane 0°C H 2 150°C
CONFIDENTIAL LCOMS-UOP LCC However the structures of the resulting tungsten hydride are quite complex. In the case of silica-alumina supported species, VIII, the structure presented on Scheme 1.16 has been proposed based on the chemical reactivity, spectroscopic evidences and analogy with other oxide supported metal hydrides. 134 The tungsten hydrides have been charachterized

by IR spectroscopy (ν (WH) at 1980-1800 cm -1 ) and In the case of alumina, the spectroscopic data are less complex than for the silicaalumina species IX.

Si O O O O W t Bu t Bu t Bu M s O O M s M s x III R= alkyl, H M s = Al or Si x=1,2,3 or 4 Si O O O O W M s O O M s M s x H 2 150°C -3 CH 3 t Bu H H H H R Si O O O O W M s O O M s M s x H H H H H Si O O O O W M s O O M s M s x H H H Si O O O O W M s O O M s M s x H H R H H Si O O O O W M s O O M s M s x H R H + + 70% 30% VIII Chapter 1 41 CONFIDENTIAL LCOMS-UOP LCC
mitted the observation of the qualitative consumption of the alkyl bands simultaneously to the appearance of two large bands at 1903 and 1804 cm -1 ascribed to W-H. Submitting the sample to D 2 under the same condition results in the presence of W-D due to exchange reaction consistently with two corresponding signals at 1388 and 1293 cm -1 . Further characterization of this surface species will be presented in Chapter 2 of this thesis.

Catalytic activity

The SOMC of tungsten has lead to the preparation of a wide range of surface species bearing several ligands. This section will consider the singular catalytic activity of these compounds, and will be divided in three main parts: i) Alkyne metathesis, ii) Olefin metathesis and iii) Non-oxidative coupling of methane, linear and branched alkane metathesis

Alkyne metathesis

Olefin metathesis is now routinely used in organic synthesis. [151][152][153] Some recent and elegant applications are the synthesis of macrocycles by ring closing metathesis of a diene. 154 However, olefin metathesis meets some limitations as it gives mixtures of E and Z isomers, thus decreasing its potential as a highly stereoselective synthetic method. An approach to overcome this difficulty may be found with alkyne metathesis. 155 Indeed, the newly formed C=C bond could then be stereo-selectively reduced to either E or Z, C=C isomers, or converted to another functionality. Up to now, several alkyne metathesis catalysts are known. 155,156 To avoid deactivation by bimolecular dimerization reaction, 129,130 Moore et al. reported the grafting reaction of the molybdenum complex [Mo(≡C t Bu)(NAr( t Bu)) 3 ] on amorphous silica pretreated at 400°C under dry O 2 , the purpose being to induce minimal changes in the electronic structure of the complex and to reduce its mobility. 157 This catalyst showed a high catalytic activity and a good stability.

Using the similar hypothesis, the different tungsten-carbyne surface species presented in last subsection have been identified as potential catalyst for this reaction. Nevertheless, II displays only a stoichiometric activity in alkyne metathesis, probably due to the formation of a biscarbene species by α-H abstraction inactive in this reaction. The modification of the metal coordination sphere by replacing the two neopentyl moieties by ancillary ligands as in surface species V may prevent this phenomenon. 138 Thus, the reaction of V with an excess of pent-2-yne was performed in a batch reactor at room temperature. After reaction 0.65 equiv. per tungsten of a 1/1 mixture of 4,4dimethylpent-2-yne (Me-C≡C-t Bu) and 2,2-dimethylhex-3-yne (Et-C≡C-t Bu) had evolved (Scheme 1.17). These products arise from the interaction between pent-2-yne and the car-CONFIDENTIAL LCOMS-UOP LCC byne ligand, namely the initiation step for alkyne metathesis. The 1/1 ratio is consistent with a comparable stability of both possible metallacyclobutadiene intermediates, 26 which is not influenced by 1,2-or 1,3-interactions due to the planarity of the cycle, at the difference of olefin metathesis. 158 Scheme 1.17 Stoichiometric reactivity of V toward pent-2-yne at room temperature 138 However, at 80°C the reaction of V with an excess of pent-2-yne (61 equiv. per W atom) forms a mixture of but-2-yne and hex-3-yne in a 1/1 ratio (Scheme 1.18). The initial turnover frequency was 0.32 mol.mol W -1 .min -1 . Interestingly, no oligomerization of the alkyne substrate or of the reaction products was evidenced either by GC after extraction of the solid or via the mass balance. This behavior is different from that of similar homogeneous catalysts for which formation of heavy products is problematic. 137 Scheme 1.18 Pent-2-yne metathesis reaction

Olefin metathesis

Olefin metathesis has a crucial role in the chemical industry and academic. While the petrochemical industry has used this technology for forty years, it has gained even more im-

V O Si O O O W t Bu Si O O O O O RT O Si O O O W t Bu Si O O O O O O Si O O O W t Bu Si O O O O O + + t Bu t Bu + [ W ] 80°C Chapter 1 43 CONFIDENTIAL LCOMS-UOP LCC
portance in the recent years with the increasing world demand in propylene (vide supra).

The development of supported catalysts that are easily recyclable and have durable lifetime is thus primordial. SOMC has allowed preparing tungsten species with well-defined coordination sphere, affording a rational approach of the development of heterogeneous catalysts. Several species described in subsection 2.2, i.e. II, VI and VII, have been tested for propylene metathesis in continuous flow reactor at room temperature.

Despite the absence of alkylidene ligand, II exhibits a high activity with an initial rate of 12.7 TON.min -1 and a selectivity of 99.9% in metathesis products. 133 Therefore, this system can be used as a precursor for olefin metathesis and the carbene ligand is probably generated in situ after coordination of olefin either by α-H abstraction from an alkyl ligand leading to a bis-alkylidene surface species 159 or by direct metathesis of an olefin with an alkylidyne, which creates in turn a propagating ligand (Scheme 1.19). Scheme 1.19 Possible formation of the carbene from the alkylidyne ligand 133 In the same conditions, the corresponding tungsten carbene species bearing an imido ligand, VI, gives an initial rate of 8.4 TON.min -1 and a selectivity of 99.4%.-{Rhers 2006}-The replacement of the alkyl by a pyrolyl ligand to form the isoelectronic species namely VII, dramatically increases the performances of the catalyst, with an initial rate of 24.6 TON.min -1 and a selectivity of 99.9%. 143 DFT calculations on the metathesis, the deactivation, and the byproduct formation pathways for the imido tungsten species VI and VII give a rational for the role of pyrrolyl ligand. 160 The greatest benefit of substituting the ancillary alkyl by a pyrrolyl ligand, is in fact not to improve the efficiency of the cata- It has been recently shown that tungsten hydride supported on silica-alumina or alumina, VIII and IX, catalyze the coupling of methane at 350°C, 50 bar in a classical fixed-bed reactor. 166 After an induction period due to modification of the coordination sphere of the metal under methane, the activity remains constant after the initial state (conversion = 0.2%). Ethane is formed selectively (>99% among hydrocarbons) along with an equimolar amount of H 2 ). When the maximum conversion is reached, a stable steady state is observed, showing an essential improvement compared to the tantalum hydride, which suffers from deactivation. The mechanism of the reaction has been proposed according solid-state NMR characterisation of the catalyst (VIII) after reaction with 13 The postulated mechanism involves the formation of tungsten-methylene-hydride as the key intermediate (Scheme 1.22). The following step is C-H bond activation on the hydride via σ-bond metathesis with the formation of a tungsten-methyl-methylidene. A cis migration of the methyl to the methylidene occurs, affording the formation of the C-C bond as already observed on a corresponding tantalum complex. 169 Then, the cleavage of the resulting tungsten-ethyl by hydrogen would take place.

These dual properties of the active site, i.e. tungsten carbene and hydride, afford the occurrence of two noticeable elementary steps on the same metal center: i) C-H bond activation and ii) carbene insertion. While during NOCM reaction catalyzed by supported metal particles, these elementary steps involves two adjacent metal atoms. 164,165,[170][171][172] • Alkanes metathesis The catalytic activation of alkanes remains one of the most important challenges in chemistry in view of their inertness and considerable application potential. 173,174 In the 70's, Hughes and Burnet have evidenced a catalytic reaction, named disproportionation of alkanes, which directly transforms butane, at 399°C and 62.2 bar, into its lower and higher homologues. 175 The catalytic system used in the conversion of butane was based on the succession of reactions: i) dehydrogenation of butane in butenes, ii) butenes metathesis allowing the formation of higher and lowers olefins and iii) their hydrogenation in the corresponding olefins. To achieve these reactions, they used a Pt/Li based dehydrogenationhydrogenation catalyst supported on alumina and WO 3 /SiO 2 as olefin metathesis catalyst mixed together. These mixed catalysts are inoperative for ethane formal disproportionation because of degenerated ethylene metathesis. 96 They introduce the term "alkanes metathesis" in analogy with olefin metathesis. This was the first description of a single site system affording this reaction. The authors have proposed a mechanism where σ-bond metathesis is the only elementary step, due the highly electrophilic character of the silica-supported tantalum-alkyl species, which involve a fourcentered transition state with the presence of an sp 3 carbon in the middle of the metallocycle. 96 The cumulated TON of this system remains modest but corresponds to the productive reaction, whereas degenerate processes also take place as evidenced in the case of 13 C mono-labeled ethane. 98 It was then evidenced that the precursor of silica supported tantalum hydrides, namely [(≡SiO)Ta(=CH t Bu)(CH 2 t Bu) 2 ], was also active for propane metathesis. 101 In light of these results, the activities of supported tungsten species for alkanes metathesis have been investigated. Tungsten carbyne species supported on silica (II), silicaalumina (III) and alumina (IV) have been tested for propane metathesis in batch reactor at 150°C (Table 1.1). [134][135][136] III and IV are active catalyst precursor for the metathesis of propane. Their initial rate is 0.7 TON.h -1 and 1.8 TON.h -1 respectively, while the corresponding silica-supported system, II, is inactive even if its NMR spectroscopic features are identical to these of III, and somewhat different from these of IV. It confirms the essential role of the support in catalytic activity of the metal centre, and particularly the beneficial influence of aluminum. The comparison of the activity of III and IV with [(≡SiO)Ta(=CH t Bu)(CH 2 t Bu) 2 ], reveals that the cumulated TONs after 120 are similar, whereas the initial rate for tantalum complex is higher with 3.0 TON.h -1 , which indicates that the tungsten catalysts are less prone to deactivation.

Table 1.1 Activity of tungsten surface species in propane metathesis at 150°C in batch reactor

Product selectivity [b] Pre-catalysts Initial rate [a] TON at 120 h Methane Ethane Butanes [c] Pentanes [d] Hexanes [e] [(≡SiO)Ta(=CH The comparison with the tantalum-based systems supposes that the tungsten hydride catalysts are more active and as for perhydrocarbyl species the deactivation is slower.

Moreover, tungsten based catalysts lead to a narrowed distribution in the product selectivity. Indeed, the methane selectivity after 120 h is less than 3% for tungsten based catalysts, when it was ca. 10% for the tantalum ones, which is consistent with greater hydrogenolysis capability of tantalum. This significant improvement in activity probably reflects the difference between the intrinsic properties of tungsten and those of tantalum.

Interestingly, in olefin metathesis, it is known that tungsten based are much better than tantalum based homogeneous systems, due to the instability of tantalacyclobutanes. 177,178 In addition high ratio of linear to branched products is observed and the selectivities for higher homologues are as follows C n+1 >C n+2 >> C n+3 . These selectivities are similar to those generally described in olefin metathesis, where 1,3-disubstitued metallacyclobutane intermediates are favored toward 1,2-disubstitued ones. 32 These data have suggested to revisit the σ-bond metathesis based mechanism proposed earlier. 76,96,98,101 Therefore, kinetic studies under dynamic conditions have identified olefins and hydrogen as primary product of the reaction for tantalum and tungsten based catalysts. 107,135,136 It confirms that alkane metathesis mechanism involves elementary steps related to that of olefin metathesis.

For the tungsten hydride supported on alumina the initiation steps of alkane me- 1.24). This tungsten-hydride can operate either dehydrogenation of propane to propylene by σ-bond metathesis followed by β-elimination or perform the reverse reaction, i.e. hydrogenation by olefin insertion followed by cleavage of the tungsten alkyl by hydrogen.

tathesis
Concomitantly the tungsten-carbene can form metallacyclobutane with the propylene to form either 2-butenes or ethylene via the classical Chauvin mechanism. 25 Scheme 1.24 Proposed mechanism for propane metathesis on supported W hydrides for the production of linear products It has to be noted that, while the silica supported tantalum hydride transforms isobutane classically into propane and 2-methyl propane by transfer of one carbon, tungsten hydride supported on alumina, IX, convert isobutane with an unusual selectivity into 2,3dimethylbutane (41.7%) and ethane (41.3%). 179 This reaction is the first example of the transfer of two carbons in alkane metathesis. Hence, for this reaction the selectivities of higher homologues are quite different from those obtained in metathesis of linear alkanes (vide supra) and can be ordered as follows: C n+2 >> C n+1 > C n+3 . The mechanism proposed for this reaction is similar to the mechanism of propane metathesis (Scheme 1.24). Yet again a tungsten carbene-hydride is the key species of the mechanism. Nevertheless, the main difference in the mechanism of isobutane conversion is the sterical crowding of the metallacyclobutane, which presents 1,2-gem-dimethyl substituents (Scheme 1.25). 179 Scheme 1.25 Metallacyclobutane intermediate proposed for the for isobutane metathesis 179 Interestingly, as in NOCM, the key intermediate is a tungsten carbene-hydride.

Moreover this active species displays dual functionality: i) tungsten hydride afford dehydrogenation of alkanes or hydrogenation of olefins and ii) tungsten carbene is involved in olefin metathesis reaction.

W H W H Metathesis Dehydrogenation W H W R H 2 Hydrogenation W R H 2 W R W H W H CONFIDENTIAL LCOMS-UOP LCC

Conclusion

Propylene is a key intermediates in chemical industry especially for the production of polypropylene. The increasing of propylene demand favors the expansion of new technologies for its synthesis. While the traditional routes produces propylene as a by-product, the main developments are yet focused on "on purpose" processes. Among them, olefin metathesis is a promising tool. Nevertheless, while numerous homogeneous and heterogeneous catalytic systems has been investigated in academia, WO 3 /SiO 2 remains the major catalyst employed at the industrial scale for production of propylene by ethylene/2-butene cross-metathesis. The active site of this catalyst is still not well understood, which prevent rational development to improve its activity.

The use of surface organometallic chemistry (SOMC) has afford to produce welldefined surface tungsten species, which are highly active catalysts, or precatalysts for different reactions such as alkyne, olefin and alkane metathesis or non-oxydative coupling of methane. Among this surface species, tungsten hydrides have attracted the attention due to their potential regeneration under H 2 stream. These supported tungsten hydrides are precursor of carbene-hydride species that gives singular reactivity to the tungsten centre. The hydride ligand affords: C-H activation, alkane dehydrogenation and olefin hydrogenation, while the carbene instigates: olefin metathesis or carbene insertion. These remarkable properties have been extended to the transformation of olefins and particularly propylene production. The supported tungsten hydrides have been evidenced as catalyst for the unusual direct conversion of ethylene to propylene. 180 It has been proposed that the hydride ligand may induce dimerization and isomerization reactions. This PhD work has thus been organized as follows. Chapter 2 is devoted to the preparation and characterizations of tungsten hydride supported on alumina. The complex alumina properties have been studied and structural identifications of the carbynic precursor and of the tungsten hydride have been deepened. Chapter 3 discloses a complete mechanistic study of the direct conversion of ethylene to propylene using supported tungsten hydride as a catalyst confirming the results proposed earlier. 180 The optimization of reaction parameters has been undertaken. A particular attention has been given to the determination of the deactivation mechanism according the characterizations presented in Chapter 2. Different methods will also be attempted to regenerate the catalyst. Chapter 4 releases the preparation of isolated supported aluminum alkyl and hydride, which presence has been spotted at the surface of tungsten hydride catalyst in Chapter 2. Their reactivity toward ethylene was then investigated to test their influence in the catalytic activity and deactivation mechanism of tungsten hydride supported on alumina.

Chapter 5 reveals the activity of supported tungsten hydride for the production of propylene from light olefins, taking advantage of singular reactivity of the tungsten carbene-hydride active site and avoiding the deactivation observed in Chapter 3.

Chapter 6 finally presents the preparation of new model tungsten catalysts supported on silica. The preparation of first supported tungsten oxo derivatives using SOMC methodology will be tackled in order to obtain models of the active sites of WO

Introduction

In surface organometallic chemistry, a fundamental understanding of the chemisorptive interaction and reaction of organometallic complex with the oxide surface is crucial to produce well-defined metallic species. The cationic or neutral character of the surface species is a key aspect of its catalytic properties, not easily accessible by classical characterizations techniques. The choice of the oxide support plays a critical role. After years of reseach, it has been shown that silica could be used as a tunable solid ligand, and the chemistry is now understood at a molecular level. 1 Typically one can generate either monosiloxy, bissiloxy, and even in some cases trissiloxy surface complexes. These systems have been characterized by several methods (elemental analysis, IR spectroscopy, Solid-state NMR spectroscopy, and EXAFS), and they have been used as catalyst precursors in several reactions (hydrogenation, polymerization, depolymerization, olefin metathesis, oxidation, and alkane metathesis). Typically, the siloxy substituent of the surface activates the metal center by generating more electrophilic metal centers, but in some instances, it is necessary to use other supports such as alumina to obtain a gain in reactivity.

Several hydrogenation, metathesis, and polymerization supported catalysts have been prepared, for which the alumina support is critical to obtain catalytic activity. For example, chemisorption of [Zr(CH 2 t Bu) 4 ] on alumina provides an efficient olefin polymerization catalyst, while when supported on silica it is inactive. [2][3][4] Alumina has a richer chemistry than silica since it combines a variety of hydroxyl groups, with several modes of coordination, with a Lewis acid character on the aluminum. Various types of aluminum atoms are potentially present on the surface, from tri-to pentacoordinated, originating from the tetrahedral or octahedral cations of bulk γ-alumina. 5 The role of the aluminum Lewis centers for the chemisorptive interaction of the metal-organic complex and more generally the specificity of alumina for this process is still unclear. In some cases the formation of partially or fully cationic species has been proposed based on NMR spectroscopy and theoretical calculations. 11,12 by interaction between some ligands of this monoaluminoxy surface complex and remaining surface hydroxyls. 13 Scheme 2.1 Proposed cationic surface species obtained by chemisorption of [Zr(CH 2 tBu) 4 ] on Al 2 O 3-(500)

Nevertheless, some incertitudes subsist on the interpretation of the NMR spectra of this tungsten surface species. Therefore the proposed interactions between surface hydroxyl and tungsten carbine and alkyl (Scheme 2.2) are not possible as they will certainly evolve to the formation of bis aluminoxy species by addition or σ-bond metathesis of the hydroxyl group to the very reactive carbine or tungsten neopentyl fragment respectively.

The interaction between surface hydroxyl and alkyl fragment observed on the IR spectrum, is only due well-known Wan-der-Valls interactions between surface hydroxyl and less reactive methyl of the neopentyl fragments far from the electron deficient tungsten centre (12 e -complex). 15 The examples of organometallic complexes grafted on dehydroxylated oxides, shows that these weak interactions do not affect the NMR spectrum. 13 In this thesis the catalytic activity of supported tungsten hydrides obtained by treatment under H 2 of the perydrocarbyl tungsten 1 supported on alumina will be studied for the production of propylene from ethylene and/or butenes. It is indispensable to perform further investigations of the catalyst structure, in order to spot the formation of eventual cationic species that may have singular reactivity toward olefins. Indeed, a good description of the catalyst is needed to understand correctly the catalytic activity, mechanism, and deactivation process.

This chapter presents characterizations of this tungsten system. First, the support used for grafting, i.e. Al 2 O 3 , has been studied and particularly the influence of the pretreatment temperature on its properties. Then, the structure of [W(≡C t Bu)(CH 2 t Bu) 3 ], 1, grafted on alumina dehydroxylated at 500°C has been examinated. The preparation and characterizations of the hydride obtained from this surface species is finaly presented.

Results and discussions

Characterizations of the catalyst support

Different oxydes have been studied before being used as a support for the tungsten catalyst. Hence, different aluminas have been expected as potential support for the catalyst.

The nature of their crystalline phase, their pretreatment temperatures and the use of metal

O O O O W t Bu t Bu t Bu Al O O O O W t Bu t Bu x x Al O O O x O H Al O O O x O H t Bu CONFIDENTIAL LCOMS-UOP LCC
the others supports as well as the obtaining of tungsten hydride on these support are presented in Appendix A.

• Preparation

The Al 2 O 3 (RP) is formed of extrudates, they were crushed in a mortar and sieved (40-60 mesh) to limit eventual mass transfers limitation during catalytic tests. The resulting powder was calcinated at 500°C under dry air for 15h. It was then hydrated with a vapor pressure of degassed water at 100°C for 1h prior to treatment under high vacuum (10 -5 Torr) at the desired temperature, i.e. dehydroxylation, for 15h. The resulting material will be referred to as Al 2 O 3-(deshydroxylation temperature) (RP).

These materials were characterized using IR spectroscopy, 1 H and 27 Al solid-state NMR, XRD, elemental analysis and the specific surface was determined using BET adsorption.

• Influence of the pretreatment temperature on the of responds to proton of bonded OH. This bridged OH is present only on Al 2 O 3-(300) and no longer persists for higher dehydroxylation temperature. Around 2.0 ppm, the signal is attributed to proton of terminal OH groups bonded at two (μ 2 ) or three (μ 3 ) Al. At higher field, around 0.1 ppm the signal corresponds to proton of terminal OH groups bonded to one (μ 1 ) Al. As expected, both signals decrease in intensity with dehydroxylation temperature. Quantitative 1 H NMR study, using the method described by Millot et al., 17 provides the OH density at the surface of Alumina for each dehydroxylation temperature (Table 2.1). As expected, the higher the deydroxylation temperature, the lower the OH density is observed. At 800°C the OH density is extremely low with only 21 μmol.g -1 . The 27 Al N.M.R. spectra of Al 2 O 3 (RP) dehydroxylated at 300°C, 500°C and 800°C (Figure 2.1, right) are very similar. Two peaks are observed, assigned to Al from the bulk.

The first one, at 62 ppm, is attributed to tetrahedral Al and the second one, at 4 ppm, corresponds to octahedral Al as described for γ-Al 2 O 3 . 18 These data do not bring information about the surface Al. Nevertheless, they show that the dehydroxylation process does not impact bulk structure of the alumina.

The dehydroxylation temperature has a strong influence on the number of surface OH groups. This influence has been evocated on silica in Chapter 1. It was also discussed that the easiest way to characterize the nature of these different OH groups (Scheme 2. other stretching bands remain at lower frequencies (<3600 cm -1 ) corresponding to H bonded OH groups. These bridged OH disappeared at higher dehydroxylation temperatures. The influence of dehydroxylation temperature on the Lewis acidic character was then studied using pyridine as a molecular probe. Indeed, pyridine is known to adsorb on oxides via Brønsted or Lewis acid sites (Scheme 2.4). [20][21][22][23] The hydrogen bonded pyridine is desorbed over 100°C. CO as a probe on γ-Al 2 O 3 , that the amount of Lewis acid sites increase linearly with dehydroxylation temperature. 24 Furthermore, they prove the formation of two different Al 3+ acidic sites when the dehydroxylation temperature exceed 525°C. The influence of temperature pretreatment on specific surface was then studied. Thus, B.E.T. was performed on four samples of Al 2 O 3 (RP). A 10 grams batch of Al 2 O 3 (RP) was ground, sieved, calcined and rehydrated according to the procedure described above. All of the powder was dehydroxylated at 300°C, a 2 g sample was collected, and the remaining powder was dehydroxylated at 400°C, another 2 g sample was collected and the procedure repeated for 500 and 800°C. According to the results in Table 2.2, the specific surface of alumina does not change with the dehydroxylation temperature. Finally, in order to be sure that pretreatment do not modify crystalline phase of alumina, XRD was performed on Al 2 O 3 (RP) before calcination, and compared to alumina dehydroxylated at 500°C. The same spectra were obtained before and after calcination, showing that the pretreatment does not change the nature of the crystalline phase of the support.

O M O M O M O M O O H N Lewis Acid sites Hydrogen bond sites Brønsted Acid sites M O M O M O M O O H N N O M O M O M O O H N M O M M O M

Characterizations of the [W(≡ ≡C t Bu)(CH 2 t Bu) 3 ] supported on Al 2 O 3- (500) (RP)

The γ-Al 2 O 3 dehydroxylated at 500°C was chosen as support for the characterization of the tungsten complex. Indeed, it is one of the most employed in similar studies, due to its simpler reactivity than Al 2 O 3-(300) and Al 2 O 3-(800) . The first presents water molecules at its surface, which can react with the molecular precursor. 25 The second bears a very few surface OH (see Table 2.1) and show very strained aluminoxanes bridge, these laters may thus be opened by the molecular precursor and lead to mixture of surface species. 8 On Al 2 O 3-(500) , only protonolysis is expected (Scheme 2.5). and 3730 cm -1 (assigned to HO-μ 1 -Al IV , HO-μ 1 -Al VI and HO-μ 1 -Al V respectively) totally disappeared and the band at 3675 cm -1 (assigned to HO-μ 2 -Al VI ) is untouched, while some OH appear as a broad band centered at 3650 cm -1 resulting from interaction with alkyl ligands. 15 Moreover, the characteristic bands in the 3000-2700 cm -1 and 1500-1300 cm -1 regions associated with the ν (CH) and δ (CH) of the perhydrocarbyl ligands around W also appear.

IR spectroscopy

[ Overall, the data are consistent with the formation of a monopodal surface complex by protonolysis with surface hydroxhyl, accompanied with the evolution of one neopentane per tungsten. The presence of carbon remaining at surface after treatment under H 2 at 150°C, demonstrate the presence of a non-hydrogenolyzable carbon species. It can be postulated that this remaining carbon is probably bonded to an aluminum centre resulting from neopentyl transfer on Lewis acidic site of the Alumina (Figure 2.5), as described in group IV or V systems (vide supra).

Scheme 2.6 Formation of cationic species by neopentyl transfer on acidic sites of Al 2 O 3 .

Advanced solid-state NMR spectroscopy will be essential to confirm the structure of the surface complex. shows an intense peak at 32 ppm assigned to the methyl of the t Bu fragments and a broad, albeit weak, signal at 85 ppm, which can tentatively be assigned to the methylene carbons of the neopentyl fragment (CH 2 t Bu). The signal related to carbine is not observed.

100% 13C labeled NMR

Generally, α-carbons (such as carbenic and carbynic carbons but also methylenic ones) are difficult to observe under these conditions (i.e. diluted systems). In order to improve the signal-to-noise ratio, the corresponding 13 C enriched complex, 7,9,26,27 1*/Al 2 O 3-(500) (RP), 99 % enriched on the α-position was prepared starting from 99% 13 C-labeled *CO 2 and using the following reaction sequence : reaction of t BuMgCl with *CO 2 to form t Bu*COOH, followed by a reduction with LiAlH 4 to yield to the corresponding alcohol. By comparison with the 13 C N.M.R. spectrum of the corresponding silica supported W complex, 30 it is clear that the carbyne ligand was left intact during grafting as evidenced by the peak at 315 and 49 ppm assigned, respectively, to the carbynic carbon (≡C t Bu) and the quaternary carbon of the t Bu directly attached to this carbon (≡CCMe 3 ). t Bu) from neutral and cationic species, which is shifted slightly downfield as might be expected for a formally "cation-like" complex. 6 Similarly, different peaks around 32 ppm are attributed to different t Bu groups. The deconvolution of these signals, shows a signal at 26 ppm in addition to the signal at 32 and 30 ppm (Figure 2.9).

The thin signal at 30 and the shoulder at 26 ppm have to be noticed. Indeed, these two signal, are still present on the 13 C NMR spectrum of 1*/Al 2 O 3-(500) (RP) after the treatment at 150°C. On this spectrum, the intense signal at 26 ppm may be attributed to 13 C labeled (99%) carbon of Al-CH 2 t Bu, whereas the signal at 30 ppm is due to terminal methyl of neopentyl bonded to aluminum, Al-CH 2 (CH 3 ) 3 . Similarly to Zr, Hf and Ta chemistry, where partial transfer of alkyl group is observed and confirmed by NMR spectroscopy and theoretical calculation, the grafting of tungsten on alumina lead to a mixture of neutral and cationic surface species. Regarding the mass balance analysis, during the grafting reaction and the treatment under H 2 , the surface species are consist on a mixture of neutral, 1a, and cationic species, 1b, in an approximate 1:1 ratio (Scheme 2.7).

Characterizations of the tungsten hydride on Al 2 O 3-(500) (RP)

In this subsection, the treatment of 1/Al 2 O 3-(500) (RP) under H 2 at 150°C will be studied in detail. The supported tungsten hydrides species, obtained by hydrogenolysis of the neutral (1a) and cationic (1b) species will be characterized by IR, 1 H, 13 C and DQ solid-state NMR and Raman spectroscopies, TEM, theoretical calculations and EXFAS.

Preparation

The previous solid, 1/Al 2 O 3-(500) (RP), was heated in static reactor, at 150 °C in the presence of a large excess of dry H 2 (550 Torr). After 15 h, the gaseous products were quantified by GC, and the resulting solids were obtained after evacuating the gas phase for 15 min. and δ (C-H) . Some OH groups reappear at 3775 cm -1 and some still remain at 3650 cm -1 .

IR Spectroscopy

Note that during the treatment under H 2 , the IR region corresponding to the hydroxyl groups (Al s -OH) is greatly perturbed. While, it is clear that some of hydroxyls previously in interaction with alkyl ligands are transformed into isolated hydroxyls, this observation probably shows that surface restructuration has occurred, and that some hydroxyl groups have reacted with some W species. Additionally, a large broad band appears at 1901 cm -1 in the M-H region (Figure 2.11). This value is in good agreement with the molecular tung-

D 2 exchange

When the solid WH/Al 2 O 3-(500) (RP) is treated with D 2 at 80°C for 1 h, affording WD/Al 2 O 3-(500) (RP), the intensity of ν (WH) band at 1901 cm -1 decrease, at the same time, weak ν (WD) vibrations can be observed at 1388 cm -1 , while expected at 1365 cm -1 (Figure 2.12). Additionally, after treatment under D 2 , a band at 1897 cm -1 , not exchanged under these conditions, can be assigned to Al-H. It has to be noted that Al-H band is usually observed when preparing metal hydride from perhydrocarbyl precursor grafted on alumina: 10 (1915 to 1960 cm -1 ) or when contacting H 2 with dehydroxylated alumina (1866 and 1902 cm -1 ). 25 When

[Ta(=C t Bu)(CH 2 t Bu) 3 ] /Al 2 O 3-(500) 32 (1930 cm -1 ) or [Hf(CH 2 t Bu) 3 ]/Al 2 O 3-(500)

Theoretical calculations

Sautet et al. have performed DFT calculation to understand the mechanism of formation of a tungsten hydride from 1a. The expected mechanism is presented on Scheme 2.9 with the ΔE value calculated for each species. These calculations show that the formation of a tungsten hydride is favored. The first reaction step may be the reaction with a neighbor hydroxyl to form a bipodal transition species. This exothermic reaction (ΔE = -90 kJ.mol - 1 ) is confirmed by IR spectroscopy, which as evidenced perturbation of ν (O-H) signals (Figure 2.11). The resulting species is later hydrogenolysed. The reaction between an aluminoxy ligand and an adjacent hydroxyl group by prototropy of the oxygen bond to tungsten followed by an hydrogen elimination will form an oxo ligand in interaction with a surface aluminum affording a stable surface species (ΔE = -50 kJ.mol -1 ). At that time no calculation have been performed on the cationic surface species 1b.

Nevertheless, the same mechanism should be considered. First the reaction with a neighbor hydroxyl to form a bipodal transition species and the hydrogenolysis of tungsten ligand may leading to a cationic tungsten hydride species (see Scheme 2.10), letting the Al-CH 2 t Bu untouched as the Al-C bond is known to be hydrogenolyzed under sever conditions only. 33 The reactivity of grafted alkyl aluminum toward hydrogenolysis is known to occurs only over 250°C (see Chapter 4).

Scheme 2.10 Formation of a cationic supported tungsten hydride from cationic surface species.

RAMAN spectroscopy

To confirm the presence of an oxo ligand in the coordination sphere of the tungsten, Raman spectrometry was performed on WH/Al 2 O 3-(500) (RP) (Figure 2.13). As Al 2 O 3 does not give any signal in Raman spectrometry, all the signals were attributed to tungsten species.

Al Al O O H W C O H C(CH 3 ) 3 C(CH 3 ) 3 (H 3 C) 3 C H H Al Al O O H W C (H 3 C) 3 C O H C(CH 3 ) 3 C(CH 3 ) 3 Al Al O O O W H H H H H Al Al O O O H W H H H H Al Al O O O H W C(CH 3 ) 3 C (H 3 C) 3 C Al Al O O O W H H H + 4 H 2 -2 C 5 H 12 + 3 H 2 -3 C 5 H 12 + H 2 -C 5 H 12 ΔE = -90 kJ/mol ΔE ‡ = 97 kJ/mol ΔE = -53 kJ/mol ΔE ‡ < 5 kJ/mol ΔE = 4 kJ/mol ΔE ‡ = 34 kJ/mol ΔE = -50 kJ/mol ΔE ‡ = n.c. -H 2 +δ -δ + 4 H 2 -2 C 5 H 12 Al Al O O W H C(CH 3 ) 3 H H Al Al O O W C (H 3 C) 3 C C(CH 3 ) 3 C(CH 3 ) 3 Al O H Al O Chapter 2 79 CONFIDENTIAL LCOMS-UOP LCC

1 H NMR and 1 H NMR spetroscopy after D2 exchange

CONFIDENTIAL LCOMS-UOP LCC and their low concentration at the surface.

Multiple Quanta NMR Spectroscopy

To further assign these various signals, 2D multiple-quantum (MQ) proton spectroscopy under magic angle spinning (MAS) was applied. [35][36][37][38] To probe structural information inherent to proton-proton dipolar couplings, the 1 Autocorrelation peaks are observed on the diagonal of the 2D spectrum (Figure 2.15), in particular for the alkyl protons at 0.9 ppm (ca. 2 ppm in the ω1 dimension, for CHz, with z=2, 3). A weak auto-correlation peak is also observed for a proton resonance at ca. 10.1 ppm (ca. 20 ppm in the ω1 dimension), which unambiguously demonstrate that the tungsten bears almost two hydride, as was found previously in the case of zirconium and titanium surface organometallic chemistry, where [(≡SiO) 2 ZrH 2 ] or [(≡SiO)(MsO)TiH 2 ] species were similarly characterized. 39,40 In order to demonstrate the presence of three hydride on the tungsten, Triple Quantum experiment has been performed, but unfortunately no exploitable signal were obtained. This is probably due to the broadness of the tungsten hydride signal at 10.1 ppm and to the complexity of alumina supported hydride structures, as observed for zirconium, hafnium and tantalum (vide supra).

Steoichiometric reactivity with methane

Regarding the complexity of the characterization of these surface hydrides, stoichiometric reactivity study has been undertaken to confirm the tris-hydride structure given by theoretical calculations.

Methane activation on 500mg of WH/Al 2 O 3-(500) (RP) was studied in continuous flow reactor at 50 barg starting from 25°C to 350°C. The evolution of hydrogen vs. time was monitored by on-line GC analysis. The instant and cumulated evolution of hydrogen vs. time on stream has been plotted. The evolution of hydrogen is observed during a period of 1000 min, the cumulated hydrogen evolution corresponds to 2 H 2 per W (Figure 2.1). The hydrogen evolution could arise from two sources: i) formation of tungsten monohydride by liberation of one H 2 per W from the presumed tungsten trihydride species, as demonstrated by the high evolution of hydrogen before 300 min and similarly to [(≡SiO) 2 TaH 3 ] 41 ii) consecutive C-H bond activation of methane, releasing one H 2 per W and formation of tungsten IV methyl surface species (Scheme 2.11). These results are consistent with trishydride structure proposed by theoretical calculation and IR spectroscopy.

Transmission Electron Microscopy (TEM)

When the tungsten perhydrocarbyl complex grafted on SiO 2-(700) is treated under H 2 at 150°C a sintering of tungsten is evidenced by the resurgence of SiOH signals on IR spectrum and formation of tungsten particles on TEM images. The observation of WH/Al 2 O 3- (500) (RP) by TEM did not reveal the presence of any particles. Nevertheless the contrast for TEM on Al 2 O 3 is known to be quite low. EXAFS has thus been performed to prove the absence of tungsten particles.

Extended X-Ray Adsorption Fine Structure Spectroscopy (EXAFS)

Regarding all the characterizations of WH/Al 2 O 3-(500) (RP), and particularly 13 C NMR spectroscopy and mass balance analysis (presented in subsections 2.2.2 and 2.2.4), a mixture of two major surface species can be proposed: a neutral, and a cationic tungsten hydride. The characterization of WH/Al 2 O 3-(500) (RP) by analysis of the W L III -edge Extended X-Ray Adsorption Fine Structure Spectroscopy (EXAFS) data confirms several features of these surface species (Figure 2.17 and Table 2.3). The difficulty to establish a good fit (ρ = 6.0 %), compared to well-defined species of tungsten alkyl supported on silica (see Chapter 6), corroborates the presence of a mixture of surface species. Due to this mixture of surface species, the EXAFS data have to be considered with caution.

Nevertheless, the results exclude tungsten-tungsten contributions, ruling out the formation of particles, and point out the presence of 0.5(2) oxygen neighbor at short dis- tances (1.74(3) Å), which can be attributed to W=O species, as obtained by theoretical calculations and Raman spectroscopy. which surface exhibits a mixture of neutral and cationic species respectively 1a and 1b.

This later results from a transfer of a neopentyl ligand to an acidic aluminum atom. The structure of these species have been determined using IR spectroscopy, mass balance analysis of grafting and treatment under H 2 at 150°C, and 13 C solid-state NMR spectroscopy. The formation of the cationic species, 1b, is in agreement with the reactivity of group IV, group V and actinides organometallic complexes on alumina but contradict theoretical calculations results of Joubert et al. 13 The treatment of 1/Al

Al O O O O W tBu Al O O O x x Al O O O x O H H H Al O O O x H Al O O O O W x Al O O O x O H H H Chapter 2 85 CONFIDENTIAL LCOMS-UOP LCC
The next chapters are devoted to the role of each species in catalytic activities.

Hence on Chapter 3 the activity of WH/Al 2 O 3-(500) (RP) for the direct conversion of ethylene to propylene will be studied. The catalytic mechanism and the deactivation mechanism will be studied regarding the characterizations obtained here. Chapter 4 will focus on the preparation of well-defined Al-alkyl and Al-H supported on Alumina and presents their activity toward ethylene. Chapter 5 will pay attention to the use of olefins feedstock different than ethylene for the propylene production. On Chapter 6, the preparation of new tungsten supported model catalyst will be presented. A structure-reactivity relationship study of these model complexes to better understand the active site of WH/Al 2 O 3-(500) .

For the sake of clarity, in the following chapters, the neutral and cationic tungsten tris-hydride site will be presented as in Scheme 2.13 when their reactivity is similar.

When their reactivity will differ, the neutral or cationic character will be clearly indicated.

Scheme 2.13 Simplified representation of the neutral and cationic tungsten tris-hydride adopted for the following chapters

Experimental section

General procedures

All experiments were carried out by using standard Schlenk and glove-box techniques.

Solvents were purified and dried according to standard procedures. 42 The trichlorotrimethoxytungsten was prepared from WCl 6 (99 %, Strem, used as received) and methoxytrimethylsilane (99 %, Aldrich, CH 3 OSi(CH 3 ) 3 was distilled over sodium and stored over 3Å molecular sieves) according to published procedure. 43 trometer by using a IR cell equipped with CaF 2 window. Typically, 16 scans were accumulated for each spectrum (resolution 2 cm -1 ). The nitrogen adsorption and desorption isotherms were measured at 77 K using micromeritics automated gas adsorption analyzer.

Before the adsorption measurements, the samples were degassed under vacuum at 200°C for 12 hours. The surface area was calculated by Brunauer-Emmett-Telleller (BET) mode.

Confocal Raman spectra were acquired using the 488nm line of a Ar-ion laser (Melles Griot). The excitation beam was focused on the sample by a 50X long working distance microscope and the scattered light was analyzed by an air-cooled CCD (Labram HR, Horiba Jobin Yvon). The fluorescence was subtracted from the spectra for clarity. Solution NMR spectra were recorded on an Avance-300 Bruker spectrometer. All chemical shifts were measured relative to residual 1 H or 13 C resonance in the deuterated solvent: C 6 D 6 , δ 7.15 ppm for 1 H, 128 ppm for 13 C. All solid-state NMR spectra were recorded under MAS (νR = 10 kHz) on a Brüker Avance 500 spectrometer equipped with a standard 4-mm double-bearing probe head and operating at 500 and 125 MHz for 1 H and 13 C respectively.

The freshly prepared samples were introduced into the 4 mm zirconia rotor in a glove box Chemical shifts were given in ppm with respect to TMS as external reference for 1 H and 13 C NMR and Al(H 2 O) 6 3+ for 27 Al. Two-Dimensional Double-Quantum (DQ) Experiments were performed according to the following scheme: excitation of DQ coherences, t 1 evolution, reconversion into observable magnetization, Z-filter, and detection. Fourteen pC7 basic elements 46 were used for both excitation and reconversion steps, with 70 kHz rf field strength (=7ω R ); the Z-filter delay was 200 μs. A total of 512 increments of 64 scans each was collected with 1.5 s recycle delay, which gave a total experiment time of 14 h. Determination of OH density was performed using 1 H solid-state NMR sprctroscopy following the method described by Millot et al. using SiO 2-(700) as reference. 17 Deconvolution of NMR spectra was achieved using DMFIT#20100301. 47 Procedures related to Extended Xray Absorption Fine Structure Spectroscopy (EXAFS) are described in detail below. XRD on powder have been realized at the Centre de Diffractométrie UCBL using a Bruker D8

Advance. Transmission electron microscopy (TEM) was recorded at the IRCELYON (Institut de Recherche Catalyse et Environement de Lyon). Conventional transmission electron microscopy was performed using a JEOL 100 CX electron microscope. Samples were examined both dry and after dispersion in CH 2 Cl 2 followed by solvent evaporation.

Pyridine adsorption on alumina monitored by IR spectroscopy

The alumina (RP) (40±1 mg) was pressed into a

Monitoring the synthesis of 1/Al 2 O 3-(500) by IR spectroscopy

The oxide (40 mg) was pressed into an 18 mm self-supporting disk, adjusted in the sample holder, and put into a glass reactor equipped with CaF 2 windows. The supports were calcined under N 2 /O 2 and partially dehydroxylated under vacuum at 500°C. The compound 1 was then sublimed under dynamic vacuum at 90 °C onto the oxide disk, which typically turned yellow. The solid was then heated at 80 °C for 2 h, and the excess of 1 was removed by reverse sublimation at 90 °C and condensed into a tube cooled by liquid N 2 , which was then sealed off using a torch. An IR spectrum was recorded at each step.

Preparation of 1/Al 2 O 3-(500) (RP)

A mixture of ter evaporation of the solvent, the resulting brown powder was dried under vacuum. Elemental analysis: W: 5.5% wt , C: 5.2% wt

Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS)

X-ray absorption spectra were acquired at the SRS of the CCLRC in Daresbury (UK), using beam-line 9.3 (project # 50049), at room temperature at the tungsten L III edge, with a double crystal Si(111) monochromator detuned 70% to reduce the higher harmonics of the beam. The spectra were recorded in the transmission mode between 10.05 and 11.45 keV. The supported W sample was packaged within a nitrogen filled dry box in a double air-tight sample holder equipped with kapton windows. This type of cell has already been used and proved to be very efficient for air-sensitive compounds. The spectra analyzed were the results of four such acquisitions and no evolution could be observed between the first and last acquisition. The data analyses were performed by standard procedures using in particular the program "Athena" 48 and the EXAFS fitting program "RoundMidnight", 49,50 from the "MAX" package. The program FEFF8 was used to calculate theoretical files for phases and amplitudes based on model clusters of atoms. 51 The value of the scale factor, S 0 2 = 0.98, was determined from the spectrum of the reference compound, a benzene solution of W(≡C-t Bu)Np 3 (one carbon at 1.76(

Å and three carbon atoms at 2.10(1) Å in the first coordination sphere). The refinements were performed by fitting the structural parameters N i , R i , σ i and the energy shift, ΔE 0 (the same for all shells). The fit residue, ρ (%), was calculated by the following formula:

As recommended by the Standards and Criteria Committee of the International XAFS Society, 52 the quality factor, (Δχ) 2 /ν, where ν is the number of degrees of freedom in the signal, was also calculated and considered.

Monitoring the treatment of 1/Al 2 O 3-(500) (RP) under H 2 by IR spectroscopy

An excess of H 2 was added at room temperature in IR cell containing a self-supported disc of 1/Al 2 O 3-(500) (RP) prepared as described in subsection 3.5. The cell was heated at 150°C for 15h. The gaseous products were quantified by GC and IR spectra were recorded at each step.

ρ = k 3 χ exp (k) -k 3 χ cal (k) [ ] 2 k ∑ k 3 χ exp (k) [ ] 2 k ∑ × 100 CONFIDENTIAL LCOMS-UOP LCC

Introduction

The production of propylene has received growing attention in recent years due to its increasing demand. 1 Propylene is mainly produced as a by-product of ethylene, 2 as discussed in chapter 1. A new process that allows the conversion of ethylene to propylene will be economically relevant. The preparation of the supported tungsten hydride presented in Chapter 2 affords a catalyst with a singular coordination sphere that performs unprecedented reactions such as alkane metathesis 3 or methane non-oxidative coupling. 4 The mechanism of these reactions involves a carbene alkylidene and a carbene hydride species. This chapter will focus on the obtention of propylene from ethylene alone using this supported tungsten hydride.

Scheme 3.1 Reaction of direct conversion of ethylene to propylene

The conversion of three molecules of ethylene to two moles of propylene, as presented in Scheme 3.1, is highly thermodynamically favored. Below 900 K the standard Gibbs free enthalpy is negative, affording a large conversion of ethylene at equilibrium.

Moreover, under 600 K the conversion of ethylene is complete at the equilibrium (Figure 3.1). to the direct transformation of ethylene into propylene. 6 This reaction has also been observed, with a short lifetime, during Fischer-Tropsch synthesis in the presence of small iron nanoclusters formed by the thermal decomposition of [HFe 3 (CO) 11 ]/MgO. 7 This reaction has also been reported to proceed with catalysts based on europium or ytterbium de- CONFIDENTIAL LCOMS-UOP LCC posited on coal in combination with titanium compounds (TiCl 4 , Ti(OiPr) 4 ) 8 as well as with WO 3 on various oxides 9 MO x /SiO 10 or Ru/SiO catalysts. 11 However, the catalytic performances of all these systems were either not quantified or proved to be very low as they were only observed in closed recirculation systems.

A significant example of direct conversion of ethylene to propylene in terms of selectivity and productivity is reported using Zeolites. 12 The proposed mechanism of formation of propylene from ethylene over acidic catalyst implies the trimerization of ethylene.

The cracking of the formed hexenes leads to propylene (Scheme 3.2). they obtain a propylene production rate of 7.00 mmol C3H6 .g -1 .h -1 (79% selectivity) is obtained. Unfortunately, for the sake of comparison, no longer times on stream are mentioned.

Another example of direct conversion of ethylene to propylene has been described using nickel catalyst supported on mesoporous silica. 13,14 In that example the catalyst shows a constant activity at 400°C, during 10 hours on stream, with a propylene production of 1.85 mmol C3H6 .g -1 .h -1 and a selectivity of 49 %. The explanation was given by a mechanism, in which ethylene dimerization on Ni sites afford 1-butene that can be iso-

+H -H -H + + -H 2 β-fission -H 2 β-fission Chapter 3 97 CONFIDENTIAL LCOMS-UOP LCC
merized to 2-butene on acidic sites. 2-butene is supposed to react via cross-metathesis reaction with non-reacted ethylene. Ivamoto claims that Ni(I) are able to perform metathesis reaction by the formation of a nickel carbene (Ni(III)) intermediate. The large pore size of MCM-41 is the major argument presented to exclude an acidic mechanism such as this presented for SAPO-34. Nevertheless, after calcination of impregnated nickel nitrate, it can be agreed that the surface of the catalyst will exhibit silicates with non-negligible acidity and the high temperature of reaction do not exclude cracking of higher olefin to provide propylene as observed by Oikawa et al.

Finally, tungsten hydrides supported on alumina prepared by SOMC have shown outstanding activities for this reaction. Nevertheless, after this high initial activity, a fast deactivation of the catalyst is observed. 15 In Chapter 2, the preparation of WH/Al 2 O 3-(500) has been described. According NMR, IR, RAMAN spectroscopies, mass balance analysis, DFT calculations and EXAFS, it can be assumed that two different tungsten hydride species are present at the surface of this catalyst, i.e. a neutral oxoaluminoxo tungsten trishydride and a cationic bisaluminoxo trishydride, along with aluminum surface species, i.e.

Al-Np and Al-H. These different species may have a different role in the catalytic activity, particularly the cationic tungsten species, highly electrophilic, should react singularly with ethylene. The presence of this different species raises three questions: i) What is the role of these different species in term of activity and mechanism? ii) Is the cationic tungsten species involved in the high initial activity? iii) What is the role of each surface species in the deactivation process?

In this chapter the performance of supported tungsten hydride for this reaction will be presented in details. It will be focused on determination of the reaction mechanism, optimization of parameters in order to increase the activity and determination of the deactivation pathway. The next chapters will be devoted to the role of the different species present at the surface of WH/Al 2 O 3-(500) in its catalytic activity.

CONFIDENTIAL LCOMS-UOP LCC

Results and discussions

Description of the reactor

The catalytic studies were performed in a stainless-steal microreactor (see Schematic representation in Appendix 3) from PID Eng&Tech. The reactor can be divided into three parts. The first one manages liquid and gas flow rates. The flow rate was controlled and monitored by a mass-flow controller for gases and by a piston pump for the liquids. A pressure regulator adjusted the reactor pressure. The second part is the reaction chamber that can be filled in a glove box, and its temperature controlled during the catalytic test.

The reactor is tubular with a diameter of 1 cm and a length of 18 cm. Its volume can be varied by including stainless-steal inserts. The last part is monitoring of different parameters including pressure, flows, temperature that were monitored via indicators/regulators and a Labview interface. After release of the pressure (via a control pressure valve), the gases are also analyzed by online gas chromatography.

In this chapter, the direct conversion of ethylene to propylene is studied. For all experiments the test was carried out at atmospheric pressure. The temperature of the catalytic bed was adjusted to the desired value. Except for the contact time study, the mass of catalyst is adjusted such as the ethylene/tungsten ration reaches R = 1.7 mol C2= .mol W -1 min -1 with a flow rate of 4 mL.min -1 of ethylene. The standard reaction temperature is 150°C.

The ethylene conversion and selectivity were therefore calculated as follows:

Conversion = mol of ethylene converted mol of ethylene introduced Selectivty i = mol of product i formed mol of ethylene converted
The definition of the conversion is the number of moles of ethylene converted divided by the number of moles of ethylene introduced divided. The selectivity for a product i is equal to the number of mol of product i formed divided by the number of mol of ethylene converted.

Direct conversion of ethylene to propylene of over WH/Al 2 O 3-(500)

The catalytic performances of WH/Al 2 O 3-(500) , i.e. the catalyst prepared from γ-Alumina pretreated under vacuum at 500°C (see Chapter 2) have been tested for the direct conversion of ethylene to propylene. This will be the reference experiment for this chapter.

Propylene was obtained selectively (95%) by passing ethylene over WH/Al 2 O 3-(500) in a continuous-flow reactor (P C2H4 = 1 bar, T = 150°C, flow rate 4 mL.min -1 or volume hourly space velocity (VHSV) 400 h -1 ). The reaction presents an initial steep maximal conversion rate of 0.6 mol C2H4 .mol W -1 .min -1 before reaching a pseudo plateau of 0.1 mol C2H4 .mol W -1 .min -1 with an overall TON of 930 after 120 h on stream. The selectivity for propylene increases rapidly up to a plateau at 92%, while that of butenes remains below 6.0%. Higher olefins are present in only trace amounts (less than 1.0 %). These results correspond to a productivity of 9.57 mmol C3H6 .g -1 .h -1 at the maximum and 2.07 mol C3H6 .g -1 .h -1 at pseudo plateau. During the 10 first hours on stream, a fast deactivation rate of the catalyst is observed (2.40%.h -1 ), before reaching a pseudo-plateau with a much lower deactivation rate (0.05%.h -1 ). Despite this phenomenon, the selectivity is constant for all catalytic run. It should be presumed that two different sites are able to achieve the conversion of ethylene to propylene: the first one has an high production rate but deactivate quickly whereas the second one has a lower production rate and deactivate slowly. A study of the reaction mechanism, during the first hours and at pseudo steady state, will thus be performed.

Determination of the reaction mechanism

The complete mechanism of the direct conversion of ethylene to propylene was studied by identification of the products released in early stage of catalysts, influence of contact time and the introduction at pseudo steady state of supposed primary product in ethylene feed. CONFIDENTIAL LCOMS-UOP LCC

Determination of the initiation step

A short initiation period is observed in the early stage of catalysis, showing that the tungsten hydride is only the precatalyst of the direct conversion of ethylene to propylene. The initiation step was elucidated by identifying the products formed, in dynamic reactor, while heating to the reaction temperature of 150°C. CONFIDENTIAL LCOMS-UOP LCC Figure 3.4 shows that whatever the time on stream, the carbon balance is equilibrated, which implies that at each moment, the mass of gas going in and coming out of the reactor is equivalent, within experimental error (± 10%), to the mass of ethylene coming in the reactor respecting Eq.3.1.

Therefore, for this experiment, 360 mg of 6% wt W catalyst were used. Ethane is observed during one hour, after this time the activation is considered as completed. The mass of catalyst contains 0.12 mmol of tungsten. So it needs 3 x 0.12 = 0.36 mmol of Ethylene for the activation. The Ethylene flow rate during the reaction is 4 mL.min -1 corresponding to 0.16 mmol.min -1 . During the activation phase of 100 min, 16 mmol (0.16 x 100) of ethylene pass through the catalytic bed. Thus the ratio of the ethylene consumed by the activation to the ethylene provided during the activation is less than 3% of the feed (0.36 / 9.6 = 3,7%), which is less than the incertitude of the ratio of ethylene to methane.

Regarding these results it is clear that this high initial activity is due to the catalytic activity and neither to the formation of the active species nor to ethylene adsorption.

Study of the early stages of catalysis

A first insight into the mechanism of the direct conversion of ethylene to propylene is given by a careful study of the product selectivity at the early stage of the catalysis where the conversion of ethylene is extremely high for what is believed to be a multistep reaction, but where the formation of the active species is incomplete. Evolution of ethane shows that α-H abstraction leading to the carbenic species occurs only for the first 100 min. At short time on stream butene isomers appear in the gas phase (Figure 3.3). The initial 1-butene/trans-2-butene/cis-2-butene/isobutene isomeric distribution of 5. These results suggest that the primary step is the dimerization of ethylene to 1butene is followed by a fast isomerization of 1-butene to cis-and trans-2-butenes. The newly formed catalyst [W](CH 2 CH 3 )(=CHCH 3 ) can insert ethylene into the ethyl moiety to form an n-butyl species, which affords 1-butene by β-H elimination. 16 Then cis-and trans-2-butenes are obtained after reinsertion of the newly formed 1-butene followed by a second β-H elimination of the sec-butyl species (Scheme 3.4) as proposed by Tolman for the isomerisation of 1-butene to 2-butene by nickel hydride. 17 promotes the isomerization assuming that the oxygen treatment did not affect the isomerization activity of alumina.

Contact time study

In order to understand the propagation mechanism of this reaction, a complete contact time study was performed. The observation of the contact time (VHSV -1 ) influence on the catalyst performances, i.e. conversion and selectivity, reveals two majors information on the catalytic process. 18,19 First, if there is a linear dependence between conversion and contact time, that can be extrapolated to zero at zero contact time, it means that the catalytic process is not affected by mass transfer limitations. The observations can thus be interpreted regarding chemical steps: it is chemical regime. Then, the extrapolated selectivities at zero contact time allow a reliable determination of real primary products. Therefore the reduction of contact time decreases the period when reagents and active sites can interact, reducing de facto the formation of secondary products.

In subsection 2.2, it has been observed that the selectivity is constant with time on stream, whereas the deactivation rate is high in the early stage of the catalysis before reaching a pseudo-plateau. To determine if the mechanism of the reaction is the same dur-

W W W H W W H CONFIDENTIAL LCOMS-UOP LCC
ing this two period, contact time study was performed for different time on stream. Thus four experiments of 46h were carried out at different contact times (Table 3.1) Plotting the conversion vs. inverse space velocity (Figure 3.6) confirms that the chemical regime is maintained, whatever the time on stream, in the range of VHSV studied. At each time on stream there is a strong linear dependence, which can be extrapolated to a zero conversion at infinite VHSV, between conversion and contact time. VHSV -1 (min) In chapter 5, a complete study will show that WH/Al 2 O 3 is a very active catalyst for olefin metathesis. These results thus strongly support the proposal that the first catalytic step of the reaction is ethylene dimerization to 1-butene (the alumina support alone was found to be inactive for this reaction) followed by isomerization to 2-butenes. Propylene is formed in a follow-up cross-metathesis of the resultant mixture of ethylene/2-butene, in agreement with the ability of WH/Al 2 O 3 to catalyze this reaction (see Chapter 5).

To corroborate this hypothesis a contact time study at lower temperature, i.e. 120°C has been performed. The dimerization and metathesis reaction kinetics do not have the same dependency on temperature. The influence of temperature on the selectivity of the reaction has been studied and will be discussed in subsection 2.5.1. It shows that higher selectivity in butenes are observed when lowering the reaction temperature. At 120°C the selectivity is thus even more influenced by contact time. Butenes selectivity clearly increases while contact time decreases (Figure 3.9 left). It is clearer at 120°C than at 150°C as these butenes are less consumed by the metathesis reaction which is less favored by the lower temperature (see subsection 2.5.1). At that temperature, it is also more obvious that 1-butene is a primary product whereas others butenes isomers are secondary products (Figure 3.9 right). These results show that 1-butene is the primary product of the conversion of ethylene to propylene. Its formation occurs by ethylene dimerization. This formation is explained by the insertion of two ethylene molecules in the tungsten hydride bond followed by a β-H elimination retrieving the tungsten hydride. Regarding this results, the dimerization seems to be very slow, compared to other reaction occurring further, as it is very difficult to observe 100% selectivity in 1-butene.

Introduction of 1-butene

To confirm that 1-butene is a primary product in the conversion of ethylene to propylene, the effect of addition of 1-butene was studied at the steady state was studied. So, the conversion of ethylene was run for a 70h experiment after that 1-butene was introduced in the ethylene feed, with increasing amounts from 5% vol to 30% vol . The introduction of 1-butene increases the conversion of ethylene without changing the selectivities. This raising is explained by an isomerization of this added 1-butene to 2butene (cis or trans) and the cross-metathesis of this 2-butene with ethylene. From 0% to Selectivity (%) This result shows that WH/Al 2 O 3-(500) catalyze the reaction of isomerization of 1butene to 2-butene and ethylene/2-butene cross-metathesis. A study of all these reactions will be with more detail in Chapter 5.

1-C 4= 2-trans-C 4= 2-cis-C 4= iso-C 4= 100% C 2= 5% 1-C 4= 15% 1-C 4= 30% 1-C 4= 100% C 2= Conversion (%)

Proposed mechanism

According to numerous examples, 20 olefin cross-meta-thesis is expected to be catalyzed by a tungsten-alkylidene species following a classical Chauvin mechanism. 21 The same tungsten species is also involved in the observed ethylene dimerization reaction according to the classical Cosse-Arlman mechanism, 22,23 which proceeds by a double ethylene insertion into the W-H bond of the tungsten ethylidene hydride; this latter species also catalyzes the isomerization of 1-butene into 2-butenes.

Optimization of the catalytic performances

In order to increase the activity of the catalyst and decrease deactivation, the nature of the support and its pretreatment temperature have been investigated. CONFIDENTIAL LCOMS-UOP LCC

Influence of the support pretreatment temperature

In Appendix 1, the preparation of tungsten hydride supported on alumina dehydroxylated at different temperature (i.e. 300, 400, 500 and 800°C) is presented. All these catalysts have been tested for the direct conversion of ethylene to propylene.

The catalytic results are shown in Figure 3.12. For all the catalyst the conversion profile is similar, with an high initial conversion from 37% for WH/Al This reactivity may be related to the structure of the catalyst. In chapter 2, it was concluded that the WH/Al 2 O 3-(500) bears different surface species. It can thus be postulated that these different species are present at the surface of the catalyst whatever the pretreatment temperature. Nevertheless, their relative amount can vary with this dehydroxylation temperature. Taking into consideration that the number of Lewis acid site of the alumina increases with this pretreatment temperature, 25 it is reasonable to assume that the higher the dehydroxylation temperature, the more the alkyl transfers on the acidic aluminum proceed. 26,27 Therefore WH/Al 2 O 3-(800) should present more cationic species than WH/Al 2 O 3-(500) . A high concentration in cationic species could thus explain the difference of selectivity observed, this cationic species favoring the formation of butenes and oligomers to the detriment of propylene. Noteworthy this catalyst grafted on Al 2 O 3-(800) exhibits the fastest deactivation rate, the cationic tungsten species should be involved in the deactivation mechanism.

Influence of the reaction temperature

The influence of the temperature on the activity and selectivity of the reaction of direct Regarding the ethylene conversion, the experiment at 200°C shows a maximum of 93% after 1.5 h. The conversion rapidly drops and, after 7 h on stream, it is inferior to the conversion observed at 150°C.

The most interesting results concern the selectivity (Figure 3.14). After 15 h on stream, the selectivity of the experiment at 150°C and 200°C propylene is the major product with quite similar selectivity: 92% in propylene, 6% in butenes and 2% in heavier olefins at 150°C and 93% in propylene, 4% in butenes and 3% in heavier olefins at 200°C.

On the contrary for the experiments at 100°C and 50°C the major products are butenes, and the selectivity in propylene decreases with temperature: 55% in butenes, 39% in propylene and 6% in heavier olefins at 100°C and 76% in butenes, 15% in propylene and 9% in heavier olefins at 50°C.

It can also be noted that, the relative selectivity of butenes is highly dependent of the temperature. Even at low temperatures (i.e. 50 and 100°C) the relative selectivity of 2butenes (i.e. cis and trans) is superior to 80%. Thus the isomerization step of the mechanism is fast at low temperature. These results confirm the strong influence of temperature on reaction mechanism. The high selectivity in butenes at low temperature shows that below 150°C the dimerization is favored in comparison with metathesis reaction. When the temperature increases, the 1-butene proportion stays constant but a significant increase of the isobutene proportion is observed. As presented on Scheme 3.7, the isobutene may have two origin: i) a "productive" path, where ethylene inserts in the alkylhydrydo-isobutenyltungsten species, then retrieves the active species by α-hydride abstraction; ii) a "destructive" path, eliminating the isobutenyl ligand and reducing the W (VI)

to inactive W (IV) already described for group 6 metals. 28 Relative selectivity (%) The isobutene formation by reduction of tungsten VI to tungsten IV may be the cause of deactivation of the active species; nevertheless, as its formation is catalytic, other mechanism may be involved in this deactivation.

Chapter 3 115 CONFIDENTIAL LCOMS-UOP LCC

Study of the carbonaceous deposits on the catalyst in function of the temperature of reaction

The deactivation process may not only be caused by the any changes in tungsten active species but also by the formation of carbonaceous species covering the catalyst. Therefore, the catalyst used in the experiments at 50°C, 100°C and 150°C have been studied

after 24 h on stream. Thus, TGA and DSC have been performed on the used catalyst.

The TGA profiles, realized under air, of the catalysts after 24 h on stream at 50°C, 383°C and 449°C and a second between 525°C and 556°C. Interestingly, the carbonaceous species formed at 50°C and 100°C burned at higher temperature than the species formed at 150°C. The DSC profiles for the catalyst which has been tested at 150°C are more simple, confirming the formation of only one species with a melting point of 106°C, corresponding to low density PE or heavy PE waxes (i.e. species containing more than 60 carbon atoms). The crystallization confirms the presence of a single type of carbonaceous deposit.

Characterizations of the aged catalyst, study of the deactivation mechanism

The support (i.e. nature, dehydroxylation temperature) and the reaction condition have

shown an important influence on the selectivity and deactivation of the catalyst. Understanding the mechanism of deactivation may bring the key to regenerate our active species.

In order to better understand the mechanism of deactivation of the catalyst during the direct conversion of ethylene to propylene four experiments have been done in the same standard conditions with different running time (2 h, 24 h, 48 h and 264 h see Figure 3.19). At the end of each experiment, the catalyst was recovered in the glove box to be analyzed in inert conditions.

Drift and NMR spectroscopies studies

The study of the catalyst along time on stream was first performed using DRIFT and NMR spectroscopies.

The DRIFT spectrum (Figure 3.20) of the fresh catalyst exhibits bands between 3500 and 3800 cm -1 corresponding to ν (OH) , bands between 2750 and 3000 cm -1 corresponding with ν (CH) and bands 1360 and 1465 cm -1 corresponding to δ (CH) . Theses can be attributed to the non hydrogenolysed species (Al-CH 2 tBu). Finally the ν (WH) band is present at 1913 cm -1 .

CONFIDENTIAL LCOMS-UOP LCC The DRIFT spectra of the used catalyst are similar whatever the time on stream. It is noteworthy that at 2 h on stream, all the W-H have already inserted ethylene as ν (WH) has completely disappeared whereas bands between 2750 and 3000 cm -1 corresponding to ν (CH) and bands 1360 and 1465 cm -1 corresponding with δ (CH) are observed from 2 h on stream. These bands can be assigned to long chain alkyls formed by multiple insertions in the metal hydride bond. This metal can be the tungsten and/or the aluminum as the ν (AlH) band at 1932 cm -1 , usually hidden by the ν (WH) but evidenced by selective exchange with D 2 is also consumed (see Chapter 2). Thus this aluminum hydride has also inserted ethylene. crystallized and amorphous PE. 29 Even at short time on stream the chain ends (CH 3 ) are not visible on the NMR spectra, confirming chain growth of surface species since the early time of the catalysis

TGA and DSC study

In order to confirm the hypothesis of the formation of PE, the used catalyst were analyzed by TGA and DSC and compared to the fresh catalyst.

Figure 3.22 clearly shows that there is a fast formation of surface carbonaceous species on the surface of the catalyst, even at short time on stream. After 2 h, there is 17% of weight loss when the catalyst is completely calcinated.

On the DTG profiles (Figure 3.22, right) two weight loss peaks could be observed centered on 383°C and 525°C. It is interesting to note that at high time on stream, 264h, the first weight loss peak shifts to 433°C indicating that the species burns 50°C higher.

The longer the time on stream, the more carbonaceous deposits are observed, the harder they are to burn.

CONFIDENTIAL LCOMS-UOP LCC The fusion DSC profile presented on Figure 3.24 (left) shows that the melting point of the formed species increases with the time on stream: starting at 101°C after 2 h and reaching 136°C after 264 h. This is also clear that when the time on stream increases, more than one surface species is formed. This is confirmed by crystallization DSC profile on Figure 3.24 (right) with almost two crystallization peaks after 48h on stream.

The formation of different surface deposits may be explained by the different active sites of the catalyst as represented on scheme 6. It can be assumed that these different sites are sensitive to ethylene partial pressure. Hence, at short time on stream, the ethylene conversion is high, which reduces its partial pressure. Contrariwise, at long time on It is also interesting to compare these results to with the results described in §2.5.2 Thus, in Figure 3.18 and Figure 3.24, it can be observed that at 24h on stream at 100°C the profile is similar the profile at 246h at 150°C. Indeed, the aging of the catalyst is fastened by a decrease of temperature.

Proposed deactivation mechanism

Regarding the last results, it seems that the deactivation of the catalyst is mainly due to the formation of two types of polymers. The drop of initial activity, i.e. before 48h on stream, is accompanied of formation of a low melting point polymer (116°C). This polyethylene species may be formed by multiple insertion of ethylene in the tungsten alky bond. In the literature, only one example of tungsten-based ethylene polymerization catalyst is described, which is a cationic species. 35 (Polymer international 44 1997 517) To the CONFIDENTIAL LCOMS-UOP LCC best of our knowledge, no neutral tungsten species are described as polymerization catalysts. It can thus be proposed that the polyinsertion of ethylene occurs only on cationic tungsten site as presented in Scheme 3.8. Once this long chain is formed on the metal centre, the β-hydride elimination did not occur any more. The resulting species could not perform ethylene dimerization anymore and thus it cannot form 1-butene. The pseudo-plateau conversion may thus be attributed to neutral tungsten species, less reactive in dimerization as less electrophilic, but not affected by deactivation by polymerization.

Scheme 3.8 Mechanism of formation of the polyethylene surface species by poly insertion of ethylene in tungsten carbon bound

This neutral site has an important activity in olefin metathesis, as the introduction of small amount of 1-butene at the end of catalytic test is followed by a large increase in the ethylene conversion. It shows that dimerization is the rate-determining step but also the main step affected by deactivation.

The other surface species such as aluminum hydride or alkyl-aluminum may also play a role in this deactivation process by the formation of the polymer at 135°C (see Chapter 4).

The formation of carbonaceous deposits at the surface of the catalyst during metathesis reaction as been observed many time. [30][31][32] These deposits are assumed to be responsible of the deactivation of the catalyst, such as for WO 3 /SiO 2 , which is reactivated under air at 500°C to calcine these deposits and to retrieve the active species. 33 In the case of WH/Al 2 O 3 the regeneration may be more difficult as the formation of the hydride species cannot occur under air.

Attempts of regeneration of the catalyst

After a certain time on stream the activity of the WH/Al 2 O 3 catalyst for the conversion of ethylene to propylene decreases. The aging of the active site is due to the formation of polyethylene species. Hence, in order to retrieve the initial activity of the catalyst this species must be removed from the catalyst and the tungsten hydride regenerated.

Supported titanium hydrides have already shown a good activity in catalytic hydrogenolysis of parafin waxes at low temperature. 34 The tungsten system may be able to per-

W W W n Chapter 3 123 CONFIDENTIAL LCOMS-UOP LCC
form such a reaction. Indeed, the grafted tungsten is able to perform alkane hydrogenolysis, as during the treatment of 1/Al 2 O 3 under H 2 at 150°C the neopentane is cleaved in ethane and methane 3,24 Treatment of the used catalyst by H 2 should thus regenerate the active species, using the ability of the surface species to break C-C bonds.

Regeneration after catalysis

The regeneration of the catalyst has been studied under a flow of hydrogen at different temperature. After 50 hours on ethylene stream, the following regeneration cycle has been experimented. First, the reactor is purged with argon (4mL.min -1 ). It is then heated to the regeneration temperature. Once the regeneration temperature reached, the gas flow is switched to hydrogen (4mL.min -1 ) until no hydrocarbon is detected on CPG. Finally the reactor is purged with argon (4mL.min -1 ), and cooled to 150°C. Figure 3.25 shows that whatever the temperature used, the regeneration cycles have no influence on ethylene conversion. Indicating that the regeneration of the catalyst did not occur under hydrogen at these temperatures. Thus the regeneration was tested at 300°C.

At 300 °C the active species seems to be irreversibly damaged. There is no more activity after the treatment. On the same sample the treatment commonly used to activate the WO 3 /SiO 2 was tried. The powder was oxidized under dry air at 500 °C the reduced under H 2 at 500 °C. The resulting catalyst exhibits no activity, neither in direct conversion of ethylene to propylene nor in propylene metathesis.

"On-stream" regeneration

As regeneration under hydrogen is not possible, an experiment to avoid the formation of the inactive species was envisaged. Thus, the reactivity of the catalyst for direct conversion of ethylene to propylene using hydrogen as a co-feed was tested. To avoid hydrogenation of ethylene, which is largely thermodynamically favored, small amount of hydrogen has to be used. The experiment was carried following the standard conditions with 8%vol hydrogen added to the ethylene flow rate. (The molar ratio is around 12%). Co-feeding the reactor with hydrogen decrease the selectivity in propylene (Figure 3.28, left). When the efficiency in ethane is plotted (Figure 3.28, right), the first hours on stream displays efficiency in ethane of 16%. Indeed, the formation of the active species converts ethylene to ethane. But after five hours of catalysis, the ethane production remains very high, and confirms that all the hydrogen (12%mol) reduce ethylene, which is largely thermodynamically favored. Hence, an experiment with lower amount of H 2 was necessary to see if the same predominance of ethane was seen. Using 1% of H 2 as co-feed unfortunately gives the same results that the experiment with 8 %. The efficiency is not affected and 1 % of ethane is formed (Figure 3.29). Thus the hydrogenation of ethylene must be highly thermodynamically favored in comparison with regeneration reaction.

Conclusion

The WH/Al 2 O 3-(500) catalyst exhibits an outstanding activity in the direct conversion of ethylene to propylene. This reaction involves a threefold mechanism: dimerization, isomerization and cross-metathesis. The results of this chapter have shown that the dimerization is the rate-determining step of this catalytic mechanism. The ability of the WH/Al 2 O 3-(500) to perform the ethylene/2-butene cross-metathesis will be studied in more detail in Chapter 5. It has also been demonstrated that the two tungsten hydride surface species, i.e. neutral and cationic, may convert ethylene to propylene by the same trifunctional mechanism. Nevertheless, the most active cationic species is quickly deactivated by formation of a polymeric species with a melting point of 116°C. Unfortunately, after deactivation treatment under H 2 do not retrieves the active species.

As selective poisoning experiments of the different surface species of the WH/Al 2 O 3-(500) were not successful, it was decided to prepare isolated surface Al-H, Alalkyls (see Chapter 4) and neutral tungsten oxo-alkyl-alkylidene (see Chapter 6) species, to study their role in this reaction.

Introduction

Metal-hydrides are a class of species that holds a most peculiar position on the fringe of both inorganic and organometallic chemistry. Combining the lightest element of the periodic table to a wide range of transition-and main-group metals, they have found applications in hydrogen storage, 1 in organic synthesis 2 and catalysis. 3 Comparatively, supported maingroup metal hydrides have been overlooked, as they are deemed as less catalytically attractive. However, considering recent advances in catalysis by main-group metals, 4 it seems of interest to take a closer look at this class of compounds, as they may reveal unforeseen reactivity.

Moreover in the course of studies on (silica-)alumina-supported catalysts, the formation of surface aluminum hydrides was encountered on several occasions: Zr-H on alumina, 5 W-H on silica-alumina, 6 Ti-H on silica-alumina, 7 Hf-H on silica-alumina 8 and alumina 9 and finally W-H on alumina (see chapter 2). It is notable that alkyl aluminum, counterpart of the cationic metal species, obtained by alkyl transfer on a Lewis acidic aluminum of the surface, are present at the surface of some metal-hydride catalyst. This species were observed for Zr-Np on alumina, 10 Hf-H on alumina 9 and WH/Al 2 O 3 (see chapter 2).

The chemical pathway leading to these species has only been the subject of assumptions, and their reactivity may be masked by that of the neighboring transitionmetal hydrides. Moreover, they may play a non-negligible role in the catalytic activity of this surface species and especially in the deactivation process. Therefore, it is highly desirable to efficiently and selectively synthesize surface aluminum alkyl and hydrides and to characterize them with the highest possible accuracy. Supported aluminum hydrides have been extensively studied by infrared spectroscopy, 11 but the low concentration of the species hampers their characterization by NMR spectroscopy, not only in 1 H but most crucially, in less responsive 27 Al NMR spectroscopy.

The high yield synthesis of supported aluminum alkyls and hydrides along with their deep characterization by IR spectroscopy, mass-balance analysis and particularly highfield, multinuclear NMR spectroscopy is presented in this chapter. Their reactivity toward ethylene has been tested to understand their potential role in the catalytic activity of WH/Al 2 O 3 .

CONFIDENTIAL LCOMS-UOP LCC

Results and discussions

Preparation and characterizations of Al i Bu/Al 2 O 3-(500)

Choice of the support and precursor

Following on the work on tungsten catalyst supported on alumina, γ-alumina pretreated under vacuum at 500°C (Al 2 O 3-(500) RP), featuring a specific area of 200 m 2 .g -1 was chosen. Such material bears surface hydroxyl groups that may react with incoming organometallic species by protonolysis, with a density of about 2.0 OH.nm -2 (650 μmol.g -1 ).

Furthermore, the thermal treatment creates Lewis acidic sites that are highly electrophilic and therefore, reactive towards organometallics either during the grafting step or in a consecutive pseudointramolecular step where grafted species react with neighbouring surface reactive centers by alkyl group transfer as observed in Chapter 2 for the tungsten species. This dual reactivity pattern stemming from alumina's complexity, coupled to the fact that the incoming reagent and the inorganic carrier are based on the same Al element, confers to the present study a most challenging character when attempting to understand molecular processes at hand and the structure of the formed surface species.

The organometallic precursor Al( i Bu) 3 2 ( i Bu = CH 2 CH(CH 3 ) 2 ), was selected for the grafting. This choice was prompted by its commercial availability, the synthesis of Al(CH 2 t Bu) 3 will have demanded the use of very pyrophoric Al(Me) 3 . Morover Al( i Bu) 3 is well known to form Al( i Bu) 2 H, around 200°C following an β-hydride elimination mechanism by releasing isobutene. 12 This property was another argument to choose 2 as precursor for the preparation of supported alkyls aluminum and aluminum hydrides. ). C-H related bands are observed at 3000-2800 and 1460-1320 cm -1 in agreement with the presence of alkyl groups on the surface. [40-25] and [20-0] ppm, respectively. 14 This means that all three coordination types are presumably present in close vicinity to alkyl fragments, mostly as Al i Bu groups but also as surface Al 2 O 3 -aluminum centers. The major differences between the two spectra, which mostly result from alkyl-bearing aluminum centers, stand in i) an enhanced contribution in the penta-coordinated Al region, and ii) in the significant broadening of the tetra-coordinated aluminum signal. Even if spectral resolution in the Al V region prevents their accurate measurement, it is likely that their electric field gradient, ie. the C Q (quadrupolar coupling) value, is also in the upper range of reported pentacoordinated aluminum. The broadening of the Al IV resonance observed in the HMQC-filtered spectrum accounts for higher C Q values than that encountered in the pristine material. 14 As a high C Q value is diagnostic of high dissymmetry, this indicates severe anisotropy of the Al coordination sphere.

Mass balance analysis

Mass balance analysis indicates formation of 550 μmol.g -1 of isobutane during the grafting step, while hydrolysis of surface alkyl groups leads to evolution of 1200 μmol.g -1 of isobutane, which is consistent with the postulated reaction pattern as the major grafting reaction scheme (Scheme 4.2). These elements point out the introduction of ca. 600 μmol.g -1 of additional Al centers onto the alumina surface, in line with quasi-quantitative consumption of surface hydroxyls. When considering the information extracted from the 27 Al HMQC NMR spectrum, the several types of alkyl aluminum coordination, i.e. tetra-, penta-and hexa-coordinate, can originate from protonolytic grafting, and from transfer of alkyl groups onto acidic Alcenters, accompanied with coordination of the support's oxygen atoms. These pathways are in line with the reactivity of aluminum alkyls with silica surfaces. Anwander et al.

have reported the opening of siloxane bridges at the surface of silica after reaction with Al(Me) 3 (Scheme 4.3). 15 In that system, the resulting SiMe and AlMe group can easily be differentiated by 13 C solid state NMR with a chemical shift of respectively 0.1 and -9.5 ppm. These results have been confirmed by recent studies of reactivity of Al( i Bu) 3 toward silica performed in our laboratory. 16 Scheme 4.3 Reactivity of alkyl aluminum with silica. 15,16

Preparation and characterizations of AlH/Al 2 O 3-(500)

The preparation of aluminum hydrides by thermal treatment of 2/Al 2 O 3-(500) is investigated in this subsection. Once obtained these hydride species have been characterized by IR spectroscopy, mass balance analysis and NMR spectroscopy.

Treatment of 2/Al 2 O 3-(500) under vacuum

The formation of an aluminum hydride was expected by thermal treatment of

Treatment of 2/Al 2 O 3-(500) under H 2

Having introduced alkyl groups onto the surface, it was set out to generate hydride groups from hydrogenolysis of metal-carbon bond. Hydrogenolysis of transition-metal bonds is well documented, and supported transition metal species generated in such a way have been extensively reported. 17 However, main group metal alkyls reactivity toward hydrogen is lesse pronounced, and examples of such reactions usually imply forceful conditions (Scheme 4.4). 18 It was reasonable to assume that the strong polarization of the Al-C bond by the electrodeficient support would ease the heterolytic splitting of H 2 . The unusual asymmetric pattern observed in the non-decoupled 1 H MAS spectra at two magnetic fields is the result of a contribution from (a) the scalar coupling J iso and (b) a second-order coupling arising from the strong dipolar coupling between 1 H and a neighboring quadrupolar nucleus, 27 Al. 25 The spacing of 376 Hz between the innermost lines (see spectrum at 9.4 T) is a direct measure of the 1 H- 27 Al scalar coupling. This J iso value, higher than those reported so far in the literature, 26 denotes the specific characteristic of the present hydride species. The interval between the outermost lines of the multiplet is inversely proportional to the aluminum Larmor frequency ν Al , which explains the larger spreading of the multiplet observed at 9.4 T with respect to that observed at 18.8 T. It is also directly proportional to the quadrupolar constant C Q and the dipolar constant DIS.

From crystallographic data, it is reasonable to consider the AlH distance superior to 1.50 Å13 that leads to a dipolar-coupling constant of about 9 kHz. A fair simulation points to high values of C Q , about 15 MHz (Figure 4.9), much larger that those commonly reported in the literature, 26 but in line with those encountered in silica-supported aluminum alkyls. 15 This large C Q value directly reflects the large electric field gradient that is present around the considered Al-H. Therefore, the large splitting observed in Figure 4.8, which has not been reported previously, accounts for a large local dissymmetry around the aluminum. The first coordination sphere of aluminum is here highly distorted as a consequence of the surface heterogeneity. This is not surprising as heterolytic cleavage of the aluminum-carbon bond by H 2 is expected to yield hydride species on the formerly alkylsubstituted Al IV/V centers, for which we already observed large C Q values. A J-Resolved The 27 Al-1 H correlation spectrum on Figure 4.10 was acquired using the J-HMQC pulse sequence which correlates nuclei via their scalar coupling, a well-suited method for hydride species presenting large 1 J Al-H couplings. 26 The broad signal along the The polymer formed burns mainly around 466°C as the DTG profile features a large peak at this temperature and minor one at 522°C (Figure 4.12). DSC reveals that the melting point of the polymer formed in 135°C (Figure 4.13). This melting point is similar to LHDPE.

• AlH/Al 2 O 3-(500)
When AlH/Al 2 O 3-(500) was tested in continuous flow reactors, no trace of products were found by GC in the gas flow coming out from the reactor. Thus, aluminum hydrides do not perform the dimerization of ethylene either. Interestingly, after 24 h on stream the reactor clogged up. A 960 mg plug of polymeric material and catalyst was collected when the reactor was opened. Indeed, during 24 h on stream 850 mg of polymer was formed.

The resulting material (polymer + catalyst) was analyzed by TGA and DSC.

Catalytic activity of AlH/Al 2 O 3-(500) for ethylene polymerization

As the previous results shows that AlH/Al 2 O 3-(500) is a catalyst for ethylene polymerization at atmospheric pressure, it was decided to performing the reaction at 35 bar of ethylene in autoclave. The polymerization time and the effect of temperature were studied. The results obtained for polymerization of ethylene over AlH/Al 2 O 3-(500) are summarized in Table 4.1. For each runs the polymeric material obtained have a similar melting temperature (T m ): from 134 to 137°C. This temperature is consistent with high density polyethylene HDPE. The average molar mass (M n ) of PE, measured with high temperature size exclusion and spanning from 8.3 to 8.9 10 5 g.mol -1 , is also in line with the formation of HDPE. The molar mass distribution (M w /M n ) remains comparable for all runs, from 2.6 to 3.0, a mass distribution characteristic of single-site polymerization with a high k chain- growth /k chain-transfer ratio. On all this polymers liquid 13 C NMR was performed at 100°C in 1,3,5-trichlobenzene (TCB). The presence of a single signal at 32.2 ppm is characteristic of a linear structure, as no branching carbon is detected (see Figure 4.16). However, the Chapter 4 147 CONFIDENTIAL LCOMS-UOP LCC yield and M n values imply that, at most, only a small fraction (<1.25%) of Al centers produce polymer chains. Such a low fraction of active species has already observed with homogenous catalysts. 28,29 Moreover, from the DFT calculation on the Insertion/Chain Transfer Balance Budzelaar et al. suggested that none of the reported aluminum catalysts so far were the active species and a transition metal contamination could not be excluded. 30 The study of polymerization time at 50°C (Run 1-3) shows that the activity of the catalyst slightly decreases with the polymerization time from 11.0 to 7.7 kg PE .mol -1 (AlH) .h -1 . The study of the reaction temperature indicates that 100°C is the optimal temperature for the ethylene polymerization with an activity of 21.9 kg PE .mol -1 (AlH) .h -1 corresponding to a TOF of 782 h -1 . Yet again this result may be compared with the result of Chapter 3, when WH/Al 2 O 3-(500) was analyzed after exposure to ethylene stream at different temperatures. The formation of carbonaceous deposit reaches a maximum when the ethylene to propylene reaction was performed at 100°C. Moreover the polymeric residue on the used catalyst exhibits similar melting point (134°C) as the polymer obtained from AlH/Al 2 O 3-(500) .

CONFIDENTIAL LCOMS-UOP LCC

Catalytic activity of AlH/Al 2 O 3-(500) for ethylene hydrogenation

As the last results demonstrates that these surface aluminum hydrides are reactive toward double-bond insertion, and as the formation of aluminum hydride have shown that Al-C bonds can be cleaved through H 2 heterolytic cleavage, it is reasonable to expect that the combination of these two elementary steps, i.e. olefin insertion followed by Al-C hydrogenolysis, may be combined into olefin hydrogenation (Scheme 4.6). hydrides, which parallels recent findings in alkaline-earth metal catalysis 31 and main group metal-based frustrated Lewis pairs (FLP). 32 This most probably owes a lot to the peculiar structure of the supported hydrides, as enlighten by their NMR features. Hence, the uncommon highly strained molecular structure of the Al-H may well be the source of this unprecedented reactivity. scans were collected using a 90° pulse excitation of 3 μs. The RA-MP 27 Al decoupling scheme was composed of pulses of 6 μs at an RF field strength of 70 kHz interleaved a delay of 300 μs. The HMQC experiments were set up with an 27 Al spin echo selective to the central transition, with pulses of 8.5 and 17 μs. In the J-HMQC, the recoupling delay was set to 6 msec, with a p pulse on 1 H of 5.3 μs, a recycling delay of 1 s and 768 added transients. For the D-HMQC, the recoupling scheme (SR4) 33 applied for 500 μs. A total of 1536 transients were added with a recycling delay of 1 s. Chemical shifts were given in ppm with respect to TMS as external reference for 1 H and 13 C NMR, and to Al(H 2 O) 6

3+

for 27 Al NMR. Differential scanning calorimetry (DSC) measurements for determination of polymer melting transition were performed on a Mettler DSC1 apparatus. Sample was heated from 40°C to 150 °C at 5°C.min -1 . Two successive heating and cooling of the samples were performed, and data obtained during the second run was considered. High temperature SEC analysis was performed using a Waters Alliance GPCV 2000 chromatograph equipped with three columns (PL gel Olexis 7x300 mm). Polymer was separate from catalyst by extraction with trichlorobenzene at 120°C. Sample (1 mg.mL -1 ) was eluted with trichlorobenzene with a flow rate of 1 mL.min-1 at 150°C. Online detection was performed by refractometry and viscosimetric measurements using Waters equipments. The system was calibrated with polystyrene standards in the range of 500 to 7106 g.mol -1 .

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Preparation and characterizations of Al 2 O 3-(500) RP

γ-Al 2 O 3-(500) RP was used for details of preparation and characterization see section 3 in Chapter 2.

Preparation of 2/Al 2 O 3-(500)

A mixture of Al( i Bu) 3 , 1, (360 mg, 1.614 mmol) and Al 2 O 3-(500) RP (1 g) in pentane (10 mL) was stirred at 25 °C for 4 h. After filtration, the solid was washed three times with pentane and all volatile compounds were condensed into another reactor (volume known > 6 L) in order to quantify isobutane evolved during the impregnation. The resulting white solid was dried under vacuum (10 -5 Torr).

Hydrolysis procedure: 2/Al 2 O 3-(500) was treated with an excess of H 2 O in gas phase (17 Torr). The gaseous products were quantified by GC.

Preparation of

Ethylene to propylene conditions

A stainless-steel half-inch cylindrical reactor that can be isolated from the atmosphere was charged with 2/Al 2 O 3-(500) or AlH/Al 2 O 3-(500) (110 mg; 0.19 mL) in a glovebox.

After connection to the gas lines and purging of the tubes, a 4 ml.min -1 flow of ethylene

(WHSV (C 2 H 2 ) = 2.5 h -1 , SV (C 2 H 2 ) = 1270 h -1
) was passed over the catalyst bed at 150°C. Hydrocarbon products and hydrogen were analyzed online by GC (HP 8890 chromatograph fitted with an Al 2 O 3 /KCl 50 m x 0.32 mm capillary column, FID detector for hydrocarbons with a 3-m molecular sieve column and a catharometer for hydrogen). After 24 hour on stream the catalyst and the material formed was recovered for analysis. 50°C under vacuum until constant mass. Average activity in g PE .mol -1 (AlH) .h -1 was calculated over the whole polymerization time (30 min).

Ethylene polymerization

A

Ethylene hydrogenation

A stainless-steel half-inch cylindrical reactor that can be isolated from the atmosphere was charged with AlH/Al 2 O 3-(500) (200 mg; 0.34mL) in a glovebox. After connection to the gas lines and purging of the tubes, a 4 ml.min -1 flow of H 2 and a 4 ml.min -1 flow of ethylene (WHSV (C 2 H 2 ) = 1.4 h -1 , SV (C 2 H 2 ) = 700 h -1 ) was passed over the catalyst bed at 400°C. Hydrocarbon products and hydrogen were analyzed online by GC (HP 8890 chromatograph fitted with an Al 2 O 3 /KCl 50 m x 0.32 mm capillary column, FID detector for hydrocarbons with a 3-m molecular sieve column and a catharometer for hydrogen).

Introduction

The supported tungsten hydride catalyst has shown unprecedented results for the direct conversion of ethylene to propylene (see Chapter 3). Nevertheless, deactivation occurs during this reaction, and no methods were found for the regeneration of the catalyst. The study of the reaction mechanism reported in Chapter 3 shows that: i) WH/Al 2 O 3 may be able to perform olefin metathesis; ii) butenes are the primary products and iii) ethylene is involved in the deactivation process by polymerization which is assume to occur on cationic tungsten, Al-R and Al-H sites. Taking into account these results, it was decided to use WH/Al 2 O 3 for metathesis reactions involving butenes and with a lower amount of ethylene to produce propylene. The reduction of ethylene partial pressure in the gas feed may generate less deactivation in metathesis.

The production of propylene using olefin metathesis is usually performed by ethylene/but-2-ene cross-metathesis using the reverse reaction of the Philips tri-olefin process. 1 Several examples report the valorizations of butenes cut for the production of propylene:

• Propylene from 1-butene only Liu et al. have reported the preparation of a tungsten oxide catalyst supported on a mixture of γ-Al 2 O 3 and 10% wt of HY zeolite. This catalyst have shown interesting activity for propylene production from 1-butene only, with, after 1 hour on stream, a conversion of 5.7 mmol C3= .h -1 .g -1 (selectivity 53%) at 180°C and 1 bar. 2 The selectivity in ethylene is explained by the isomerization of 1-butene to 2-butene performed on the acidic sites. The newly formed 2-butene reacts further with 1-butene by cross metathesis reaction on tungsten sites (Scheme 5.1). Scheme 5.1 Production of propylene from 1-butene 2

• Propylene from 1-butene/2-butene mixture An example of homogenous system based on Grubbs 1 st generation catalyst has been reported by Meyer et al. 3 This system allow the production of propylene, in high pressure closed reactor, from a mixture of 1-butene and 2-butene (Scheme 5.2). At 20 bar and 60°C, with a molar ratio, R (mol butenes /mol catalyst ), of 14,000 and a 1-butene:2-butene ratio of 1:1, the thermodynamic equilibrium is reached in 60 min with a propylene yield of 25.9%. This system does not provide propylene from 1-butene alone.

CONFIDENTIAL LCOMS-UOP LCC Scheme 5.2 Production of propylene from 1-butene/2-butene mixture 3 • Propylene from 2-butene/isobutene mixture The use of isobutene in olefin metathesis reaction has been described by Banks et al. for the synthesis of isoamylene. 4 In this reaction isobutene is reacted with 2-butene over a WO 3 /SiO 2 catalyst to produce 2-methyl-2-butene (isoamylene) and propylene (Scheme 5.3). When the reactor is fed with a 1:1 ratio, ethylene, propylene, pentenes (n and iso) and hexenes (n plus iso) are produced with the following molar distribution: 10:40:35:15. Scheme 5.3 Production of propylene and 2-methyl-2-butene from 2-butene/isobutene mixture 4 The use of isobutene mixed with butenes is also presented in a BASF patent. 5 In that multistage process the first stage is the reaction of 1-butene, 2-butene and isobutene to give propylene, 2-pentene and 2-methyl-2-butene. The second stage is the separation of propylene and 2-pentene/2-methyl-2-butene. The third stage is reaction of 2-pentene and 2-methyl-2-butene with ethylene to give propylene, 1-butene and isobutene. The latter are separated from propylene in the fourth stage of the process and are recycled in the first stage.

• Propylene from ethylene/2-butene mixture

The Olefin Conversion Technology provided by ABB Lummus enhances the amount of propylene produced by naphta steam cracker units. This process converts the raw C 2 and C 4 feedstock coming from the steam cracker into propylene. The reaction occurs over a mixture of WO 3 /SiO 2 and MgO at a temperature higher than 260°C and a pressure of 30-35 bars. The 1-butene feed is isomerized to 2-butene, over an MgO isomerzation catalyst, and then consumed along with the original 2-butene by the ethylene/2-butene cross metathesis (Scheme 5.4). 6 Scheme 5.4 Production of propylene from ethylene/2-butene metathesis after enrichment of the feed in 2-butene by 1-butene isomerization.

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• Propylene from 2-butene only As for all symmetrical olefins, the reaction of butene-2 with typical olefin metathesis catalyst (MoO 3 /Al 2 O 3 , WO 3 /SiO 2 …) always leads, to the best of our knowledge, to degenerated products, and thus no conversion of butene-2 to higher or smaller olefins is observed (Scheme 5.5). Only cis-trans isomerization occurs by metathesis pathway. No example of systems, are reported to produce propylene from 2-butene only.

Results and discussions

Description of the reactor

The continuous flow reactor described in subsection 2.1 of Chapter 3 and Appendix B was used for the following study.

In this chapter, different reactions involving olefins are presented. As some of these reactions involve two different reagents their conversion can be plotted separately. Nevertheless, for the sake of comparison, the reference in this chapter is the total olefin volumetric, and therefore the molar, flow rate. It is thus appropriate to compare the total carbon conversion, calculated as follow:

The definition of the total carbon conversion is the sum of number of moles of each reagent converted divided by the sum of number of moles of each reagent introduced. The selectivity of a product k is equal to the number of mol of product k formed divided by sum of number of moles of each reagent converted.

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Propylene metathesis

The main drawback of the production of propylene by direct conversion of ethylene over WH/Al 2 O 3 is the deactivation of the catalyst by ethylene polymerization presumably due to the cationic species (see Chapter 3). Before studying new routes of production of propylene, the reactivity of propylene over WH/Al 2 O 3 will first be tested in order to determine its catalytic performances for olefin metathesis. A particular attention will be pointed on the deactivation profile, which will be compared to those of direct conversion of ethylene to propylene.

The catalytic performances of WH/Al 2 O 3-(500) , have been tested for propylene metathesis in continuous flow reactor following the conditions given in Table 5.1. atm. pres. VHSV (h -1 ) 5200 The reaction presents an initial steep maximal conversion rate of 7.8 mol C3= .mol W -1 .min -1 (148 mol C3= .g -1 .h -1 ), reaching 4 mol C3= .mol W -1 .min -1 (74 mol C3= .g -1 .h -1 ) with an overall TON of 88,000 after 260h (Figure 5.1). The conversion profile of the reaction is linear with a low deactivation rate of 0.4%.h -1 , whereas deactivation was very fast in the ten first hours of catalysis for the direct conversion of ethylene to propylene (2.40%.h -1 ).

This difference spots the influence of ethylene in the deactivation of the catalyst. No deac-CONFIDENTIAL LCOMS-UOP LCC tivation by polymerization is observed, probably due to the fact that polymerization of propylene on cationic sites did not occur as observed for cationic tungsten catalysts. 7 It can also be emphasized that the linear deactivation profile observed is characteristic of poisoning by impurities of the feed. 8 The maximum conversion rate of the propylene metathesis is far higher than the maximum rate of direct conversion of ethylene to propylene (7.8 mol C3= .mol W -1 .min -1 vs.

0.6 mol C2H4 .mol W -1 .min -1 ). This high activity has dictated the molar ratio used in this catalytic test (R= 20 mol C3= .mol W -1 .h -1 ), in order to work under thermodynamic equilibrium (38% conversion of propylene). 9 The reaction produces ethylene (49%), trans-2-butene (29%), cis-2-butene (16%), pentenes (5%) and less than 0.2% of hexenes and isobutene (Figure 5.2). The formation of ethylene and butenes, occurs according to the Chauvin mechanism (Scheme 5.6). 10 Scheme 5.6 Intermediates for the production of ethylene and 2-butenes from propylene

The trans/cis 2-butene ratio stays at a constant value of 1.8 (therm. eq. = 2.1), 11 in agreement with that observed in the literature for other d 0 systems, where terminal alkenes Chapter 5 163 CONFIDENTIAL LCOMS-UOP LCC typically give the trans-alkene as the major kinetic product, due to the easier formation of the least sterically hindered metallacyclobutane (A) by an anti approach (Scheme 5.7). 12 Nevertheless, Leconte et al. have pointed out that this model is limited in the case of propylene where (1,3) or (1,2) interactions in the metallacyclobutane A are not very significant. 13 Therefore, as shown in Chapter 3, the active site of the WH/Al 2 O 3 ,which is able to perform olefin isomerization, might also account for the observed ratio by converting cis-2-butene to trans-2-butene.

Scheme 5.7 The stability of the intermediary metallacyclobutane dictates the selectivity of butenes 12,13 These results clearly demonstrate the ability of the WH/Al 2 O 3 to perform olefin metathesis. The formation of 1-butene and pentenes also shows that the 2-butenes produced during the metathesis reaction can be isomerized to 1-butene, which will react with 2butenes to form pentenes and propylene (Scheme 5.8). This finding may be exploited to produce propylene from butenes feeds.

Production of propylene from 1-butene only

Catalytic test

The catalytic performances of WH/Al 2 O 3-(500) , have been tested for 1-butene conversion in continuous flow reactor following the conditions given in Table 5.2. As WH/Al 2 O 3 is a reliable metathesis catalyst, it may be assumed that the main products of the reaction will be the result from 1-butene self-metathesis, i.e. ethylene and 3-hexenes (Scheme 5.9).

Scheme 5.9 1-butene self-metathesis atm. pres. VHSV (h -1 ) 5200 The 1-butene conversion reaches a maximum of 7.2 mol C4= .mol W -1 .min -1 at 1 h on steam and, after 22 h on stream, 3.4 mol C4= .mol W -1 .min -1 with a cumulated TON of 5450 after 22 h. Yet again the conversion profile is quite linear with a deactivation rate of 0.8%.h -1 (Figure 5.3). This deactivation is faster than that observed for propylene metathesis, and may be related, for a part, to the purity of the feed. In contrast to the propylene feed, 1-butene has not been purified on molecular sieve to avoid isomerization to 2butene. Nevertheless, the maximum initial conversion rate is similar for the two gases and yet again no polymerization is observed 1-butene is even more difficult to polymerize. Surprisingly the selectivity of the reaction is not in favor of the expected hexenes and ethylene. An outstanding selectivity of 50% in propylene is observed giving a maximum productivity of 64.8 mmol C3= .g cata -1 .h -1 after 1 h on stream, which is 13 time faster that observed with the system described by Liu et al. (vide supra). 2 Even after 22 h on stream propylene is still the major product with 44% selectivity (productivity of 27.7 mmol C3= .g cata -1 .h -1 ). The other products of the reaction are n-pentenes, n-hexenes and ethylene, with respectively 32%, 15% and 9% selectivity at 22 h on stream (Figure 5.4).

Proposed mechanism

It is reasonable to postulate that initiation of the WH/Al 2 O 3 catalyst occurs with a similar mechanism than that described for the direct conversion of ethylene to propylene: in the early stage of catalysis, butane is observed in the feed, while with ethylene ethane was observed. When an excess of 1-butene is contacted to WH/Al 2 O 3 at 150°C in a batch reactor, after 3 h, 1 equivalent of butane per grafted tungsten is observed in the gas phase. It can be assumed that three 1-butene molecules insert in the trishydride affording a tungsten trisalkyl species, [W]((CH 2 ) 3 CH 3 ) 3 , one of this alkyl ligand is then released following an Herein, a study of the influence of the pressure in activity and selectivity in propylene for this reaction is reported.

The catalytic tests have been performed at 20 barg following the conditions given in Table 5.3. The results are compared to the same experiment performed at atmospheric pressure. The increase of the pressure shows a beneficial impact on the conversion rate, which rises from 45% to 58% at the beginning of the catalysis (Figure 5.5). At 22 h on stream the cumulate TON reaches 9000 at 20 barg while it was 5450 at atmospheric pressure (Figure 5.6). Nevertheless, the selectivity in propylene severely drops in favor of hexenes: from 42% to 24% for propylene and 17% to 35% for hexenes (Figure 5.7).

This change in selectivity is not in favor of the production of propylene as the maximum productivity rate is only 51.5 mmol C3= .g cata -1 .h -1 . For this reaction, increasing reactor pressure has not a valuable effect on propylene productivity.

CONFIDENTIAL LCOMS-UOP LCC

Production of propylene from trans-2-butene only

In last subsection, the activity of WH/Al 2 O 3-(500) for conversion of 1-butene has been studied. The awaited 1-butene self-metathesis was not the only reaction observed, isomerization of 1-butene to 2-butenes afford after metathesis reactions a high selectivity in propylene. This finding suggests that WH/Al 2 O 3-(500) may also convert a symmetrical olefin such as trans-2-butene whereas conventional olefin metathesis catalyst only perform degenerated metathesis (Scheme 5.5). 3

Catalytic test

The catalytic performances of WH/Al 2 O 3-(500) , have been tested for conversion of 2butene in continuous flow reactor following the conditions given in Table 5.4. atm. pres. VHSV (h -1 ) 5200 The trans-2-butene conversion reaches a maximum of 4.9 mol C4= .mol W -1 .min -1 at 2 h on steam and, after 90 h, 2.2 mol C4= .mol W -1 .min -1 with a cumulated TON of 14500. Yet again the conversion profile is quite linear with a deactivation rate of 0.12%.h -1 (Figure

5.8).

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For this reaction the selectivity in propylene is very high 52.5% and remains constant for the entire test. This correspond to a maximum propylene production of 50.5 mmol C3= .g cata -1 .h -1 at 2 h on stream and 21.3 mmol C3= .g cata -1 .h -1 after 90 h on stream. The reaction also produces pentenes (36.5%), hexenes (9.0%) and ethylene (2.0%). The trans to cis 2-pentenes ratio is 2.9:1 and constant with time on stream (thermodynamic equilibrium 1.5:1). This ratio is the same than in the case of 1-butene conversion, it can, yet again, be explain by the interactions of the substituents of the metallacyclobutane intermediate (see Scheme 5.14).

Proposed mechanism

The mechanism of this reaction is very similar to the mechanism described for 1-butene conversion in last subsection. As in the case of 1-butene, butane is observed in the early stage of catalysis and performing the reaction in batch reactor confirms the evolution a stoichiometric butane equivalent per tungsten centre.

Then, as metathesis catalyst should only promote degenerated metathesis, the conversion of trans-2-butene to other olefins must be explained by an isomerization step generating 1-butene from trans-2-butene. At thermodynamic equilibrium the 1-butene:2butenes ratio of 1:33 is reached. This value explains both the lower activity and the higher selectivity in propylene than for the same reaction carried out with 1-butene. As the formation of 1-butene is less favored by thermodynamics, its cross-metathesis with 2-butenes does not occur easily. Moreover, the 1-butene self-metathesis, producing hexenes and ethylene, is statistically less possible. Here also the excess of propylene produced regarding pentene can be interpreted by ethylene/trans-2-butene cross metathesis, as the difference between propylene and pentene (14%) is twice the difference between hexenes and ethylene (7%). This difference is a bit higher than for 1-butene conversion, i.e. 14% vs. 12%, CONFIDENTIAL LCOMS-UOP LCC and may be induced by the high partial pressure of tran-2-butene in the feed. It also explains the higher selectivity of this reaction. To the best of our knowledge, WH/Al 2 O 3 is the first system reported allowing the direct conversion of 2-butene in propylene.

Influence of the pressure

Herein, a study of the influence of the pressure on the conversion of trans-2-butene on WH/Al 2 O 3-(500) has been presented. The catalytic tests have been performed at 20 barg following the conditions given in Table 5.5. The results are compared to the same experiment performed at atmospheric pressure.

Yet again the increase of the pressure shows a benefic impact on the conversion, which rises from 25% to 35% at the beginning of the catalysis (Figure 5.10). At 35 h on stream the cumulate TON reaches 10000 at 20 barg while it was 6000 at atmospheric pressure (Figure 5.11). In contrast to what was observed whit 1-butene, the drop of selectivity in propylene is small, it remains the major product, decreasing from 52.5% to 50%. This change of selectivity is in favor of pentenes, which selectivity slightly increases from 36.5% to 44% (Figure 5.12). Increasing the pressure afford an higher propylene productivity, as after 2 h on stream under 20 bar the productivity rate is 64.8 mmol C3= .g cata -1 .h -1 .

Production of propylene from isobutene/trans-2-butene cross metathesis

As described in last subsection, the conversion of 1-butene/trans-2-butene mixtures on WH/Al 2 O 3-(500) lead to the formation of propylene by cross-metathesis. Moreover, this reaction produces hexenes by self-metathesis of 1-butene. The next step of our study of the valorization of C 4 olefin cut into propylene, is the study of the conversion of isobutene/trans-2-butene. This reaction may also give isobutene self-metathesis. The conversion of isobutene only on this catalyst has been recently studied, 16 and unprecedented results have been found. Therefore this reaction is not thermodynamically favored (13.8% conversion at 150°C). 11 The reaction presented an initial maximal conversion rate of 0.61 mol i-C4= .mol W -1 .min -1 before reaching a pseudo-plateau of 0.22 mol i-C4= .mol W -1 .min -1 , with an overall turnover number (TON) of 235 after 16 h. At the pseudo-steady state, the product selectivities were 2,3-dimethylbutenes 50%. The metathesis of isobutene is usually known as a degenerate process with the classical olefin metathesis catalysts, 17,18 WH/Al 2 O 3-(500) proves to be the first compound capable of catalyzing the productive selfmetathesis of isobutene into 2,3-dimethylbutene. The maximum conversion rate is reached after 2 h on stream with 1.8 mol C4= .mol W -1 .min -1 . This conversion decreases linearly at 0.5%.h -1 to reach 0.8 mol C4= .mol W -1 .min -1 after 57 h with an overall TON of 1000 (Figure 5.16).

CONFIDENTIAL LCOMS-UOP LCC The selectivity of the reaction is in favor of pentenes, 50%, followed by propylene, 40%, linear hexenes, 6%, and ethylene 4% (Figure 5.17). It is noticeable that mostly isopentenes, and only linear hexenes are produced. The propylene production rate for this reaction is thus 17.2 mmol C3= .g cata -1 .h -1 at maximum conversion and 5.8 mmol C3= .g cata -1 .h -1 after 57 h on stream.

During the initiation of the reaction, isobutene probably inserts more easily than 2butenes (α-olefin vs. 2,3-substitued olefin), leading to isobutylidene-hydride after a-H elimination of isobutane as proposed in the case of 1-butene. This tungsten species can react either with isobutene or trans-2-butene to form respectively isopentene or 3-methyl-2-pentenes and tungsten isopropylidene-hydride or tungsten ethylidene-hydride species.

These two newly formed carbenes will react in cross metathesis to afford propylene and isopentenes from isobutene and 2-butene, following the classical Chauvin mechanism (Scheme 5.20). 10 As, in mechanism presented in Scheme 5.18, the intermediate metallacyclobutane D is a priori the less thermodynamically favored intermediate, since it has gemmethyl substituents in the 1-position and two methyl substituents in the 2-and 3-position.

The steric crowding of this intermediate is nevertheless less pronounced that for intermediate C obtained during isobutene self-metathesis. This explains both the lower of this reaction compared to linear olefins and the higher activity compared to isobutene selfmetathesis.

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CONFIDENTIAL LCOMS-UOP LCC Scheme 5.20 Intermediates for the production of isopentenes and propylene from isobutene/trans-2-butene crossmetathesis

As 2,3-dimethylbutene is not observed, the linear hexenes are produced by butene-1 self-metathesis, isobutene self-metathesis did not occur.

Whatever the route employed to produce propylene from butenes, the selectivity in propylene is limited to 55%. The activities of WH/Al 2 O 3-(500) for butenes conversion is related to the nature of the reagent, and therefore related to the sterical hindrance of the intermediate metallacyclobutane.

Ethylene/trans-2-butene cross-metathesis over WH/Al 2 O 3-(500)

The most commonly used process to produce propylene by metathesis is ethylene/trans-2butene cross metathesis, as this reaction should achieve 100% selectivity in propylene (Scheme 5.21). Nevertheless, we have seen that ethylene is responsible of the deactivation of the catalyst by polymerization. This reaction will be studied in order to determine the optimal ethylene to trans-2-butene ratio, affording i) the best conversion rate, ii) the high- (h -1 ) 5200

The maximum conversion rate is reached after 1 h on stream with 7.4 mol C4=+C2= .mol W -1 .min -1 . This conversion decreases linearly at 0.03%.h -1 to reach 5.4 mol C4=+C2= .mol W -1 .min -1 after 45 h with an overall TON of 16000 (Figure 5.18). A very high selectivity in propylene of 97.9% is observed. The other products of the reaction are pentenes (1.6%) and hexenes (0.5%) (Figure 5.19). The propylene production rate for this reaction is thus 133.4 mmol C3= .g cata -1 .h -1 at maximum and 97.9 mmol C3= .g cata -1 .h -1 after 45 h on stream. (500) catalyst is clearly more active for ethylene/trans-2-butene cross-metathesis than for the conversion of ethylene to propylene (7.4 to 5.4 mol C4=+C2= .mol W -1 .min -1 vs. 0.6 to 0.1 mol C2H4 .mol W -1 .min -1 ). It suggests that the metathesis is not the rate-determining step of the ethylene to propylene mechanism, confirming that dimerization of ethylene is the slowest step. Furthermore, the deactivation profile is linear, with 0.03%.h -1 , a value close to the pseudo-plateau of the ethylene to propylene reaction (i.e. 0.05%.h -1 ), while no fast deactivation occurs in the early stage of catalysis. Among all the reactions producing propylene from butenes cross-metathesis, described in this chapter, the ethylene/trans-2butene cross-metathesis exhibits the highest selectivity in propylene (97.8%) and activity (7.4 mol C4=+C2= .mol W -1 .min -1 ). This later can be explained by a less stericaly hindered metallacyclobutane intermediate, the reaction intermediates are the same than for propylene metathesis (A and A' in Scheme 5.6), where the methyl substituents are in 1,2positions where the interactions are minimal in equatorial-equatorial position. The activity is quite similar to the activity of propylene production.

The influence of the nature of aluminas supports provided by UOP on this reaction has been studied. The different tungsten hydride catalysts presented in Appendix A have been tested. No major trend can be determined from these results.

The influence of ethylene proportion in this reaction was then studied to optimize the reaction conditions, but also to see its influence on deactivation rate. The study has been conduct in conditions presented in Table 5.6 and varying the proportion of ethylene from 0%, 10%, 18%, 35%, 45 to 70%mol. in trans-2-butene feed. atm. pres. VHSV (h -1 ) 5200

Conclusion

In this chapter, a study of the propylene metathesis has confirmed the ability of the tungsten hydride to perform olefin metathesis with high activities. Different routes allowing the production of propylene were then investigated. The results are summarized in Table 5.10. Using WH/Al 2 O 3-(500) , the best route, in term of selectivity and productivity in propylene, is high ethylene/2-butene cross-metathesis, with a low deactivation rate (ca.

0.11%.h -1 ).

During this study, it has been observed, for metathesis reaction involving a stoichiometric ratio of reagent, that the number of substituent of the less thermodynamically favored metallacyclobutane governs the conversion rate of metathesis reaction (Scheme 5.22). The different reaction can thus be classified from higher to lower activity: i) Propylene self-metathesis or ethylene/trans-2-butene cross-metathesis where A is the less thermodynamically favored intermediate, ii) 1-butene/trans-2-butene cross-metathesis (metallacyclobutane B), iii) isobutene/trans-2-butene cross-metathesis (metallacyclobutane D) and iv) isobutene self-metathesis (metallacyclobutane C).

Scheme 5.22 Influence of the substituent of the metallacyclobutane on the conversion rate of metathesis reactions.

Chapter 5 185

CONFIDENTIAL LCOMS-UOP LCC

Experimental section

The WH/Al 2 O 3-(500) was prepared following the procedure described in Chapter 2.

The continuous flow reactor used for the catalytic test is presented in subsection 2.1 of Chapter 2 and Appendix B.

Propylene (N35 Air Liquide) and Argon where purified over R3-11 BASF catalyst/MS4Å, 1-butene (Scott) , trans-2-butene (Scott), Isobutene (Linde) where used as recieved to avoid izomerization or dimerization.

Procedure for the catalytic tests:

A stainless-steel half-inch cylindrical reactor that can be isolated from ambient atmosphere was charged with the desired amount of WH/Al 2 O 3-(500) in a glovebox. After connection to the gas lines and purging of the tubing, the desired gas or mixture of gas was passed over the catalyst bed at 150°C at desired pressure and flow rate. For experience under pressure, the reactor was filled with argon at the desired pressure before feeding it with piston pump. Hydrocarbon products were ana-

Introduction

WO 3 /SiO 2 is an efficient catalyst for olefin metathesis used in industrial processes since the the discovery of banks and Bailey in the 1960s. [1][2][3][4] However, as already explained in chapter 1, the structure of the actual active species is still a matter of debate, which prevents efficient and rational development. [5][6][7][8][9] Several observation suggest the existence of isolated metal centers as the active site, and based on the validity of Chauvin mechanism both in homogeneous and heterogeneous systems, 10 it is reasonable to expect that carbene species are involved, possibly bearing an oxo ligand in the metal's coordination sphere 11,12 (Scheme 6.1 left). Owing to the strategic importance of olefins as building blocks for the world chemical industry, development of efficient processes is of utmost relevance. More specifically, tailored heterogeneous catalysts with known structureactivity relationships may improve lifetimes and activity by increasing the numbers of active sites. 13 Moreover, interesting similarities between the active site of WO 3 /SiO 2 and the neutral active site of WH/Al 2 O 3 catalyst described in Chapter 2 must be noted. Hence the active tungsten seems to bear an oxo ligand in its coordination sphere. Moreover, mechanistic considerations, reported in Chapter 3, indicate that the active site of the catalyst for the direct conversion of ethylene to propylene must be an alkyl-alkylidene tungsten species (Scheme 6.1 right). Consequently, the preparation of new surface species with similar coordination sphere will confirm the characterizations of the neutral active site of WH/Al 2 O 3 and deepen the understanding of its catalytic activity.

This chapter details the preparation of new, well-defined single site supported catalysts, as models of the active site of tungsten oxide supported on silica and tungsten hydride supported on alumina. These new surface species were prepared according to SOMC methodology using the strategy described in Scheme 6.1 (centre).

In order to establish a reliable structure-reactivity relationship of the grafted tungsten complexes, it was decided to explore the influence of the coordination sphere of the tungsten atom by changing: i) the nature of M, i.e. the oxide support (M = Si or Al) ii) the nature of the double bonded ancillary ligand Y (Y = O or N-Ar); iii) the nature of the single bonded ancillary ligand X (X = alkyl or an electron-withdrawing group (EWG)). Regarding this last parameter, one should mention that only the alkyl X ligand can afford the alkyl-alkylidene tungsten species needed for the direct conversion of ethylene to propylene (see Chapter 3). When this ligand will be replaced by an EWG, it is a priori expected that the dimerization site will not be available any more, but nevertheless the electrophil- When considering the design of single-site heterogeneous catalysts with a controlled coordination sphere, SOMC has emerged as a powerful approach. The reaction of molecular species with an oxide surface may be understood by comparison to their known reactivity in solution, and therefore targeted species may be obtained through judicious selection of the molecular precursors. The support and the homogeneous organometallic precursors were chosen carefully to match the described model (Scheme 6.1 centre).

As a result, the support used for the grafting of these organometallic species were catalyst. 16 These complexes were not selected as candidates for grafting, as the formation of metal-support bond by protonolysis will lead to the evolution of HCl or ArOH respectively for chlorine or aryloxy complexes. These acidic products may be consecutively added to the carbene to form a σ-alkyl species 17 inactive in olefin metathesis. ]. 18 The mechanism of formation of this oxo has been investigated trough theoretical calculations. The authors describe a silyl migration, leading to a tungsten IV species, induced by the highly exothermic addition of oxygen on that species. 19 Nevertheless, the poor yield of the reaction (1.7%), which has only be reported on NMR tube, discard this complex as a precursor for grafting.

Osborn and Kress described tungsten oxotrisalkyl complexes [W=O(CH 2 t Bu) 3 X] (X = Cl, Br, ONp) that are efficient metathesis catalysts with high, sustained activity upon activation by Lewis acids and photoinitiation. [20][21][22] These oxo alkyls appear as promising candidates for this purpose.

The key step in grafting, namely formation of the metal-support bond by protonolysis of a metal-alkyl, must occur irreversibly with high selectivity. This rules out using of halide (i.e. Cl, Br, I) or alkoxides as the X species in [W=O(CH 2 t Bu) 3 X], as competition between W-C and W-R bond protonolysis may occur upon grafting. A typical example is the formation of binuclear [W 2 O 3 (CH 2 t Bu) 6 ] upon hydrolysis of [W=O(CH 2 t Bu) 3 Cl]. 23,24 Fluorine may be envisaged as an X, since tungsten fluorine bond is stronger than the other tungsten halide bond (W-F = 131±15 kcal.mol -1 ; W-Cl = 101±10 kcal.mol -1 ). 25 The following new tungsten oxo complexes, i.e. [W=O(CH 2 t Bu) 4 ] (3) and [W=O(CH 2 t Bu) 3 F] (5), seem to meet all these constraint, and have thus been prepared.

In contrast to these oxo-alkylidene tungsten derivatives, numerous examples of compounds bearing the isoelectronic imido ligand have been described (Y=N-R). Indeed, due to their easier synthesis, enhanced stability and high activity in olefin metathesis in absence of cocatalysts, this approach proved to be rewarding both for homogeneous and heterogenized systems. 26 It was also decided to use the tungsten imido alkylidene complex [W=N(2,6-i PrC 6 H 3 )(CH 2 t Bu) 2 (=CH t Bu)] (4), as its grafting on silica was already studied in the laboratory. 27,28 This supported complex will be compared with isoelectronic oxo (Y=O) complexes.

The first part of this chapter will be focused on the preparation and characterizations The second part of the chapter describes the grafting and characterizations of these complexes. The most obvious pathway for the immobilizationof these organometallic species is the protonolysis of a W-C bond with the remaining silanols or aluminols of the pretreated support. The grafting of 3 and 4 will afford species bearing X as an alkyl ligand and Y as an oxide or imido ligand, whereas the grafting of 5 and 6 is expected to give surface species bearing X as a fluoride and Y as an oxide or imido ligand according to the defined strategy (Scheme 6.1 centre). However, the fate of the W-F was particularly studied, and the resulting species do not have the expected structure.

The third part of this chapter discloses the catalytic activity of the different catalyst obtained for ethylene to propylene and propylene metathesis. The structure-reactivity relationship will be studied and particularly the deactivation pathway of the active species.

Results and discussions

Preparation of the molecular precursors

Four different organometallic precursors of the model species have been prepared, in this subsection their synthesis and characterizations are presented. The preparation of organometallic complexes containing a fluorine ligand acting as an electron-withdrawing group, X = F, are presented in this subsection. The phenyl substituent of the imido ligand was chosen, without bulky sustituents in ortho and ortho' position, to be as close as possible to the oxo ligand in term of steric hinderance. The synthesis of 5 was adapted from the synthesis of [W=N (2,6-i The NMR study of 5 confirms its structure (Figure 6. On the 1 H NMR spectrum, the only protons affected by scalar couplings are the methylenic ones in β of the tungsten atom (Figure 6.4): i) coupling with 18 rated by three bonds, with a coupling constant 3 J F-H = 10.6 Hz ii) 14.31% of these protons have a coupling with 183 W, spin ½, separated by two bond with a coupling constant 2 J W-H = 10.1 Hz iii) 3 J N-H and 3 J H-H are to small to be observed. Thus the resulting multiplet has the intensity 3.5:43:7:43:3.5, which is in line with the observed signal. Then, on the 13 C{ 1 H} NMR spectrum, the only carbons affected by scalar couplings, as the spectrum is proton decoupled, are the metylenic ones in α of the tungsten atom (Figure 6.5): i) coupling with 18 F, spin ½, separated by two bonds, with a coupling constant 2 J F-C = 6.8 Hz ii) 14.31% of these carbons have a coupling with 183 W, spin ½, separated by one bond with a coupling constant 1 J W-C ≈ 46 Hz iii) 2 J N-C is to small to be observed. Thus the resulting multiplet has the intensity 3.5:3.5:43:43:3.5:3.5, which is in line with the observed signal. Thus, the study of the scalar coupling of the nuclei bounded to the tungsten confirms the presence of three equivalent neopentyl moieties, one imido ligand and a single fluorine atom bounded to the tungsten.

• [W=O(CH 2 t Bu) 3 F] (6)
For the synthesis of [W=O(CH 2 t Bu) 3 F], 6, which has not been reported yet, AgBF 4 was also used as a fluorinating agent. A first method employed was the reaction of a stoichiometric equivalent of AgBF 4 with [W=O(CH 2 t Bu) 3 Cl] with formation of an AgCl precipitate (Scheme 6.5). The BF 3 moiety still in interaction with the complex was then eliminated by precipitaiton of BF 3 N(C 2 H 5 ) 3 formed by addition of an excess of triethylamine. The removing of BF 3 was easier for this complex than for its imido equivalent 5.

This may be due to a weaker interaction between BF 3 and the oxo ligand. 35 Scheme 6. CONFIDENTIAL LCOMS-UOP LCC ppm on the 1 H and 13 C NMR spectra, respectively. On 19 F{ 1 H} NMR spectrum, only a singlet with satellites is observed at -0.36 ppm. These satellites results from the strong coupling between tungsten and fluorine, 1 J W-F = 82.2 Hz. The BF 3 has been fully removed as 11 B NMR gives no signal and elemental analysis did not spot the presence of boron.

The latter has confirmed the formula of 6. 33 that undergoes α-hydrogen abstraction leading to the evolution of t BuCH 3 and the formation of the carbenic ligand. 35,36 The oxo ligand is thus less bulky than the arylimido N(2,6-i PrC 6 H 3 ) leaving, 3, stable toward α-hydrogen abstraction as no carbenic ligand is formed during its synthesis.

Le Ny and Osborn have made a complete study of [W=N(R)(CH 2 t Bu) 3 X] systems (X = halide, R = Me, i Pr, t Bu, 2,6-i PrC 6 H 3 ) have also revealed they are stable toward αhydrogen abstraction. 34 They have performed an NMR study to understand their structure.

For all these complexes the neopentyl ligands were demonstrated equivalent and that the complex adopt a trigonal bipyramid geometry. Moreover 14

Grafting of the molecular precursors and characterizations

The reactivity of the molecular precursors 3, 4, 5 and 6 toward partially dehydroxylated oxides is presented in this section.

Reactivity of [W=O(CH 2 t Bu) 4 ] (3) with Al 2 O 3-(500)

Once the molecular precursor prepared and characterized, the grafting onto the oxide surface was performed. The first oxide chosen for the grafting is γ-Al 2 O 3 . Using this support may explain its influence in the active site of the WH/Al 2 O 3 system. In order to achieve the selective synthesis of species singly bound to the support, Al were monitored by FTIR (Figure 6.8). The resulting spectra shows that the ν (OH) vibrations at 3793, 3775, and 3731 cm -1 disappeared (Figure 3), while some OHs appear as a large band centered at 3645 cm -1 . This is very close from what was observed during the grafting of [W(≡C t Bu)(CH 2 t Bu) 3 ] (1) where mostly HO-μ 1 -Al IV reacts with the tungsten complex (Chapter 2). Moreover, the characteristic bands in the 3000-2700 cm -1 and 1470-1110 cm -1 regions associated with the ν (CH) and δ (CH) of the perhydrocarbyl ligands around W also have appeared. • Mass balance analysis

The reaction of 3 and γ-Al 2 O 3-(500) at RT in pentane in absence of light for 15 h generates 0.05 mmol of t BuCH 3 .g -1 of alumina, and the corresponding solid is washed 3 times with pentane before drying under vacuum. Elemental analysis shows the presence of W to the extent of 4.0 wt %, which corresponds to 0.22 mmol of W.g -1 . As only 0.25 equiv of t BuCH3 evolved per grafted W, 0.05 mmol of OH/g of alumina has been consumed.

Moreover, an average of 18.7 C per grafted W is found on the resulting solid by elemental analysis. Overall, the data are consistent with the formation of a mixture of two surface complexes (Scheme 6.9), which contains 25% of 3a (15 C/W) and 75% of 3b (20 C/W) giving an average of 18.75 C/W and for which 0.25 t BuCH 3 /grafted W is expected during grafting (Scheme 6.9). Thus 3a is formed by the expected protonolysis of W-C bond whereas 3b is formed by coordination of the oxide ligand with Lewis acid sites of the alumina. 36 This coordination has been evidenced for homogeneous tungsten oxo complexes using AlBr 3 as a Lewis acid (Scheme 6.10). 21,35 Scheme 6.9 Grafting of 3 on Al

• Conclusion

The grafting of 3 on Al 2 O 3-(500) provide a mixture of two surface species (3a, 3b). As the target of the study was the formation of well-defined single-sites models, it was decided to exclude Alumina and switch to Silica, a support that does not present Lewis acid character. Only silanols are expected to react trough the protonolysis of W-C bounds.

Reactivity of [W=O(CH 2 t Bu) 4 ] (3) with SiO 2-(700)

In order to achieve the selective synthesis of species singly bound to the support, we selected a silica that solely bears isolated silanols surface groups, namely silica heated under vacuum at 700°C (SiO 2 -700). Grafting of 3 was carried out in absence of light at room temperature in pentane (Scheme 6.11 • DRIFT

Infrared studies revealed the disappearance of the isolated silanol peak, and minor quantities of interacting SiOH (3704 cm -1 ), indeed the small amount of untouched OH exibiths

Van der Walls interaction with the alkyls ligands of the grafted complex. 37 Other main spectral features are ν (C-H) and δ (C-H) (2990-2800 and 1460-1480 cm -1 , respectively; Figure 6.9) corresponding to the alkyl fragments of the grafted complex. • RAMAN

In order to gain information on the W=O bond, the vibration band of which is hidden by the silica network's absorption in the infrared spectrum, Raman spectroscopy was applied (Figure 6.10). A characteristic broad line of medium intensity is observed in 3/SiO have observed, on WO 3 /SiO 2 catalysts, a broad band at 970 cm -1 . They demonstrate that this band is not related to WO 3 crystallites. 7 Kim et al. also observed a band at 975 cm -1 on low tungsten loaded WO 3 /SiO 2 catalyst (1% wt W). They attributed this band to surface tungsten oxides. 38 The lines at about 910, 935 and 990 cm -1 result from neopentyl-related modes.

• Mass balance analysis

The resulting material (3/SiO 2-(700) ) was stable to light exposure, and contained 4.1 wt% of tungsten and 4.2 wt% of carbon (C/W = 14.9 ± 0.1, theory=15). Gas phase analysis indicates evolution of 0.9 equivalent of NpH per metal center. Thus mass balance analysis is fully in agreement with the [(≡SiO)(W=O)(CH 2 t Bu) 3 ] (3c) formulation.

• Solid-state NMR study Solid-state NMR data are in line with the 3c proposed structure (Figure 2). The 20,21 No resonances originating from carbenic species were detected. Assignments have been confirmed by 1 H- 13 C HETCOR 2D NMR, indicating the expected correlation between the 1.93 ( 1 H) and 91 ( 13 C) ppm methylenic fragments' signals (Figure 2).

CONFIDENTIAL LCOMS-UOP LCC

• EXAFS

The structure 3c of the supported tungsten complex 3/SiO 2-(700) was further confirmed by analysis of the W L III -edge extended X-ray absorption fine structure (EXAFS) data (Figure 6.12 and Table 6 39 The rather long ≡SiO-W bond distance found here pleads for a trans mutual arrangement of the oxo and siloxy ligands, following from the strong trans influence of terminal M=O. [40][41][42] Moreover, the fit was improved when considering further layers of backscatterers: (i) three C atoms at 3.24(4)Å, assigned to the neopentyl ligands' modification nor gas evolution was detected upon heating under vacuum at 80°C. Thus, generation of carbene species from 3c through thermally induced α-H abstraction does not seem to be operative. However, exposure to 40 equivalent of propylene at the same temperature (80°C) in a batch reactor led to the formation of equilibrated mixture of metathesis products: propylene, ethylene and 2-butene (trans/cis ratio of 2.3), along with 0.9 equivalent of neopentane per tungsten and trace amounts of noehexene, in agreement with the formation of the expected carbenic catalytic active species [(≡SiO)(W=O)(CH 2 t Bu) (=CHCH 2 )] (Scheme 6.12). The coordination of the olefin to the highly electro-deficient tungsten centre increase the sterical crowding of the complex coordination sphere, going from a trigonal bipyramid to an octahedral geometry, and therefore favors the α-H abstraction. 43,44 DFT calculations indicated that generation of this species from alkyl compound 3c is thermodynamically favored (ΔE= -29 kJ.mol -1 for the corresponding species with H-substituted POSS as surface surrogate). ) have been studied. This supported complex was prepared according the literature procedure (Scheme 6.13). 28 This procedure is briefly reported in this subsection, the characterizations obtained, which are fully in line with the described ones are also presented. The grafting of 2 over SiO 2-(700) was carried out at room temperature. The nature of 2/SiO 2-(700) was confirmed by mass balance analysis, DRIFT and Solid state NMR which were fully in line with the literature characterizations. 28 The comparison between the DRIFT spectra of SiO 2-(700) and 4/SiO 2-(700) shows a complete consumption of the silanol band at 3740 cm -1 . Two groups of bands appear between 3100-2700 cm -1 and 1500-1300 cm -1 corresponding to the ν (CH) and δ (CH) of the neopentyl and disisopropylaryl ligands. Moreover, two broad bands also appear at 3700 and 3600 cm -1 . While the former is typical of residual surface hydroxyls in interaction with perhydrocarbyl groups, the latter is attributed to the interaction of other hydroxyls with the arylimido ligand. 28 • IR Study

Infrared studies revealed the disappearance of ν (OH) bands associated to isolated silanols, and small intensity peaks corresponding to interacting SiOH with other functional groups(3695 cm -1 ), as observed in related materials (Figure 6.15). As for 4/SiO 2-(700) a group of bands appear between 3100-2700 cm -1 , corresponding to the ν (CH) of aromatic (>3000 cm -1 ) and aliphatic parts of the ligands, and a band at 1489 cm -1 corresponding to δ (CH) vibrations of the ligands. Contrary to the spectrum of 4/SiO 2-(700) , the spectrum of 5/SiO 2-(700) does not exhibit the signal at 3600 cm -1 . Moreover other features are notable on this spectrum. A weak broad band at 3330 cm -1 and a sharp signal at 1587 cm -1 that can be assigned to respectively ν (NH) and δ (NH) vibration modes. 45 With deuterated silica (SiO 2-(700)D , 80% of SiOD according to IR), a broad band at 2485 cm -1 appears whereas the adsorptions at 3330 cm -1 and 1587 cm -1 decrease (remaining signal due to the 20% of undeuterated SiOH). This confirms the assignment of an amino moiety (NH vs. ND).

This amine group can result from the 1,2 addition of surface silanols across the imidotungsten fragment of 5. This singular reactivity has never been observed for 4 despite the fact 4 also bears an imido ligand. The bulkiness of isopropyl substituent of the aromatic ring might protect the nitrogen of the imido ligand.

• Conclusion

These results confirm the transformation of the imido ligand to an amino ligand and it is clear that 5a is not present at the surface of the catalyst. As the target of this chapter was to obtain species bearing a carbene and a double-bounded ligand (Y), characterizations of this material were not deepened further.

Reactivity of [W=O(CH 2 t Bu) 3 F] (6) with SiO 2-(700)

In order to achieve the selective synthesis of species singly bound to the support, as presented in Scheme 6.15, silica that solely bears isolated silanol surface groups was selected, namely silica heated under vacuum at 700°C (SiO 2-(700) ). Grafting of 6 was carried out in pentane at room temperature. Finally, the opening of a siloxane bridge followed by the formation of a Si-F bond and a bipodal tungsten species was envisaged (structure 6c poss in Figure 6.22). This was the most stable structure calculated with an energy estimated at -7 kcal.mol -1 and a 19 F chemical shift of -180 ppm.

The driving force of opening of the siloxane bridge reaction is the stability of the formation of the highly stable Si-F bound: W-F =1 31±15 kcal.mol -1 vs. Si-F = 166.1 These DFT calculations contradict the hypothesis of the formation of a monografted tungsten surface species bearing à fluorine and an oxide ligand as presented for structure 6a on Scheme 6.15. Further characterizations have to be performed in order to fully understand the structure of the surface species.

• Using POSS as models of SiO 2

The utilization of POSS as soluble model of silica was taken in consideration to solve the structure of the silica-grafted species. Hence, liquid NMR spectroscopy, which affords a better resolution that solid state NMR spectroscopy may bring information about the fluorine location, in particular with coupling constants. Thus, 6 was reacted with one equivalent of POSS OH (R 7 Si 8 O 12 (OH), R = C 5 H 9 ), which is a good model for isolated silanols. 50,51 The resulting product, 6/POSS was analyzed by NMR spectroscopy in C 6 D 6 .

The comparison with 6/SiO 2-(700) shows that all corresponding 1 H, 13 C and 19 The results are consistent with a W coordination sphere comprising one oxygen atom at 1.71(1) Å, two oxygen at 1.9(7) Å and two carbons at 2.12(2) Å, assigned to an oxo ligand, two siloxide's σ-bonded oxygen, and methylenic carbons from neopentyl ligands, respectively. This is consistent with the bond distances found in one fluorine atom at 2.53 (7) Å which can be in interaction with the tungsten as the W-F distance is quite long for a covalent bound. Errors between parentheses; Δk: [2.0 -17.5 Å -1 ] -ΔR: [0.6-3.6 Å]; S 0 2 = 0.98; ΔE 0 = 7.9 ± 1.0 eV (the same for all shells); Fit residue: ρ = 3.4 %; Quality factor: (Dχ) 2 /n = 1.65 (n = 9 / 31). Two multiple-scattering pathway has been considered for this fit.

• Thermal stability and carbene formation Thermal treatment of 6/SiO 2-(700) at 80°C under vacuum cause neither spectral (IR, RMN) modification nor gas evolution. As for 3/SiO 2-(700) , the generation of carbene species from 6c through thermally induced α-H abstraction is not operative. Its exposition, at 80°C, to 40 equivalent of propylene in a batch reactor led to the evolution of 1 equivalent of neopentane and traces of neohexene and the formation of the same equilibrated mixture of metathesis products than observed for 3/SiO 2-(700) (see section 2.2.2), i.e. propylene, ethylene and 2-butene (trans/cis ratio of 2.3). It can be assumed that the catalytic active carbenic species [(≡SiO) 2 (W=O)(=CHR)(≡SiF)] can be generated from 6c by addition of propylene (Scheme 6.17). Scheme 6.17 Expected pathway of formation of a carbenic species from 6c by propylene coordination followed by α-H abstraction

Catalytic activity of the different species prepared

The catalytic activity of 3/SiO 2-(700) , 4/SiO 2-(700) and 6/SiO 2-(700) have been tested for direct conversion of ethylene to propylene and propylene metathesis.

Compared catalytic performances toward direct conversion of ethylene to propylene

The reactivity of the three catalysts toward 700 eq. ethylene have been tested in batch reactor at 80°C. vs. 5 h). 25200 cumulated TON were achieved after 95 hours (Figure 6.25). For both complexes, the selectively remained constant with time on stream, with equimolar quantities of ethene and 2-butenes, no other alkene were detected (Figure 6.26 and Figure 6.27).

After the onset of the catalysis, the trans/cis 2-butene selectivity kept to a constant value of 1.8 (therm. eq. = 2.3), 53 in agreement with that observed in the literature for other d 0 systems; that is, terminal alkenes typically give the trans-alkene as the major kinetic product, due to the easier formation of the least sterically hindered metallacyclobutane by an anti approach (see subsection 2.2 in chapter 5). 54,55 Then, regarding selectivity, along with the expected formation of ethylene (49.3%) and 2-butenes (48.5%), other products were formed, namely isobutene (0.05%), C 5 olefins (0.6%) and C 6 olefins (1.3%) (Figure 6.28); the trans/cis 2-butene ratio is 0.9, twice lower than for 3/SiO 2-(700) and 6/SiO 2-(700) : This can be explained by the difference of steric hindrance between oxo and imido ligand that impacts on the relative stabilities of the tungstacyclobutanes. ) were synthesized following the literature procedure. 24,28 Ethylene (N35, air liquide) and propylene (N35, air liquide) were purified by passing through a mixture of freshly regenerated molecular sieves (3 Å) and R-3-15 catalysts (BASF). Al 2 O 3-(500) was prepared as decribed in chapter 2. SiO 2-(700) was prepared from Aerosil silica from Degussa (specific area of 200 m 2 g -1 ), which was partly dehydroxylated at 700 °C under high vacuum (10 -5 Torr) for 15 h to give a white solid having a specific surface area of 190 m 2 g -1 and containing 0.7 OH nm -2 . Gas-phase analyses were performed on a Hewlett-Packard 5890 series II gas chromatograph equipped with a flame ionisation detector and an Al All chemical shifts were measured relative to residual 1 H or 13 C resonance in the deuterated solvent: C 6 D 6 , δ 7.15 ppm for 1 H, 128 ppm for 13 C and relative to CF 3 COOH for 18 F.

O Si O O O Si O O O W Y X [W] = [W] + [W] [W] H [W IV ] β-
Solid-state NMR spectra were acquired on a Avance II 800 spectrometers ( 1 H: 800.13

MHz, 13 C: 201.21 MHz, 19 F: 752.96 MHz). For 1 H and 19 F experiments, the spinning frequency was 20 kHz, the recycle delay was 5 s and 16 scans were collected using a 90° pulse excitation of 3 μs. The 13 C CP MAS experiment was obtained at a spinning frequency of 20 kHz, with a recycle delay of 5 s and 10312 scans were collected. Optimal resolution was achieved using the PISARRO decoupling scheme 60 at a RF field strength of 70 kHz and with a decoupling pulse unit of 45 μs, corresponding to 0.9*τ R (where τ R is the rotor period). The Hartmann-Hahn conditions were optimized with a ramped radio Chapter 6 229 CONFIDENTIAL LCOMS-UOP LCC frequency (RF) field centered at 50 kHz applied on protons, while the carbon RF field was matched to obtain optimal signal. The contact time was set to 10 ms. The same CP and decoupling conditions were used for the acquisition of the two-dimensional HETCOR spectrum. The number of collected scans was limited to 688, with a recycling delay of 5s and 50 t 1 increments in the 1 H dimension, leading to a total experimental time of 48 hours.

Chemical shifts were given in ppm with respect to TMS as external reference for 1 H and 13 C NMR. Procedures related to Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) are described in Chapter 2. (500mg) and let react for 4 hours. The silica was extracted 3 times with pentane. The solvent was then removed under vacuum to leave a yellow pale solid solid. This crude material was sublimed at 60°C under reduced pressure (3.10 -5 Torr) to yield 580 mg of pure product (31 % yield). Well-defined surface models of the active sites of WO 3 /SiO 2 and WH/Al 2 O 3 catalysts CONFIDENTIAL LCOMS-UOP LCC

Preparation of the organometallic precursors

Reactivity of the organometallic precursors with oxides and characterizations

Preparation and characterization of 3/SiO 2-(700)

A mixture of 3 (500 mg, 1.03 mmol) and SiO 2-(700) (2 g) in pentane (10 mL) was stirred at 25°C overnight. After filtration, the solid was washed 5 times with pentane and all volatile compounds were condensed into another reactor (of known volume) in order to quantify neopentane evolved during grafting. The resulting white powder was dried under vacuum

Preparation and characterization of 5/SiO 2-(700)

A mixture of 5 (500 mg, 0.98 mmol) and SiO 2-(700) (2 g) in pentane (10 mL) was stirred at 25°C overnight. After filtration, the solid was washed 5 times with pentane and all volatile compounds were condensed into another reactor (of known volume) in order to quantify neopentane evolved during grafting. The resulting white powder was dried under vacuum (10 - 5 Torr). Analysis by gas chromatrography indicated the formation of 10 μmol of neopentane during the grafting (> 0.05 NpH/ W). Elemental analysis: W 4.8% wt C 6.5% wt N 0.5% wt . 500°C for 3-4 h followed by evacuation at 700°C temperature for 3-4 h. This procedure was repeated three times before a final dehydroxylation at 700°C for 15 h. The disk was then immersed in a solution of 5 (30mg, 0.059 mmol) in pentane (12 mL) for 3 h, washed 3 times in pentane, dried under vacuum for 30 min, and then an IR spectrum was recorded.

Preparation and characterization of 6/SiO 2-(700)

A mixture of 6 [WO(CH 2 CMe 3 ) 3 F] (500 mg, 1.2 mmol) in pentane (10 mL) and SiO 2-(700)

(2 g) was stirred at 25°C overnight. After filtration, the solid was washed 5 times with pentane and all volatile compounds were condensed into another reactor (of known volume) in order to quantify neopentane evolved during grafting. The resulting white powder was dried under vacuum (10

DFT calculations

All the calculations have been performed using the G03 program. 61 The geometries have been fully optimized without any symmetry constraints at the B3PW91 level with the Sddall basis set.

Catalytic tests

Reactivity toward ethylene in batch reactor

A mixture of solid 3/SiO 2-(700) (100 mg), 4/SiO 2-(700) (107 mg) or 6/SiO 2-(700) (95 mg) and ethylene (550 Torr, 700 equiv) were heated at 80°C in a batch reactor of known volume (500 mL). Aliquot were drawn and analyzed by gas chromatography every 2 hours.

Propylene metathesis

Procedure in a batch reactor: A mixture of 3/SiO 2-(700) (100 mg) or 6/SiO 2-(700) (95 mg) and propene (500 Torr, 40 equiv) were heated at 80°C in a batch reactor of known volume (28 mL). An aliquot was drawn and analyzed by gas chromatography after 24 hours.

Procedure in a flow reactor: A stainless-steel half-inch cylindrical reactor that can be iso- The characterizations and theoretical calculations made on this product prove the presence of different surface species (Scheme 7.2). Indeed, a neutral tungsten oxo tris-hydride is formed from 1a. The opening of strained aluminoxane bridges during the treatment at 150°C or the activation of H 2 on default of alumina also creates surface Al-H. The cationic species 1b is hydrogenated at 150°C but its anionic Al-CH 2 t Bu counterparts is conserved during this treatment. The complexity of the system as not allowed a rigorous determination of the relative amount of each species. A complete study using DFT calculation is necessary to completely solve such a complex systems, the presence of a cationic species. The WH/Al 2 O 3-(500) catalyst exhibits an outstanding activity in the direct conversion of ethylene to propylene, which is the first example of isolated metal system affording this reaction. This reaction involves a threefold mechanism: dimerization, isomerization and cross-metathesis (Scheme 7.3). The different results have shown that the dimerization is the rate-determining step of this catalytic mechanism. The key intermediates in the mechanism is a tungsten carbene-hydride achieving: i) ethylene dimerization ii) butenes isomerisation and iii) olefin metathesis. Nevertheless, the most active cationic species is probably quickly deactivated by formation of a oligomeric species with a melting point of 116°C (Figure 7.1). A polymer with a melting point of 135°C is also observed. Unfortunately, after deactivation treatment under H 2 do not retrieves the active species. 7.2. This imido species deactivate by reduction of the tungsten centre by decomposition of the metallacyclobutane and formation of isobutene, whereas this mechanism do not occurs for the oxo species (Scheme 7.6). This represents a significant step toward the understanding of the WO 3 /SiO 2 system, as that isolated organometallic metal oxo fragments give rise to high performance in propene metathesis.

Silica-alumina and Aluminum Magnesium Hydroxyde

The tungsten hydride was prepared on Silica-Alumina (SiAl) and Aluminum Magnesium Hydroxyde (Pural) (see properties in Table A.2) and compared to Al 2 O 3 . SiAl and Pural have been chosen for their difference of acidity compared to Alumina. The major surface hydroxyl groups on the SiAl are (≡Si-OH), while (Al s -OH) surface species have not been observed (Figure A.5). [1][2][3] Note that the silica-alumina bulk is mainly constituted of (≡Si-O-Si≡) n along with (≡Si-O-Al s ) n moieties since the low Al content (25%) makes the presence of (Al s -O-Al s ) n moities unlikely. Lastly, temperature programmed desorption of ammonia as shown that SiAl is more acidic than alumina. 4 In con- SiAl and Pural) partially dehydroxylated support and of the grafted tungsten hydride.

These spectra confirm the formation of an hydride on each supports with a band at 1953 cm -1 for SiAl and a broad band at 1868 cm -1 for Pural.

RESUME en français

La préparation de nouveaux catalyseurs à base de tungstène par la voie Chimie Organométallique de Surface a été abordée dans cette thèse pour la production du propylène à partir de l'éthylène et/ou de butènes. Deux types de systèmes catalytiques ont été développés. Des hydrures de tungstène supportés, obtenus par réaction de surface entre un complexe de tungstène [W(≡C

RESUME en anglais

The preparation of new tungsten based catalyst using Surface Organometallic Chemistry is described in this thesis. These catalysts have been prepared for the production of propylene from ethylene and/or butenes. Two types of catalyst have been developed. Supported tungsten hydrides, resulting from the surface reaction of [W(≡C t Bu)(CH 2 t Bu) 3 ] with γ-alumina followed by a treatment under H 2 at 150°C have been prepared. The characterizations by several spectroscopic techniques (IR, SSNMR, Raman and EXAFS) and stoichiometric reactivity combined by with theoretical calculations (DFT) have demonstrated the presence of two tungsten hydride surface species: a neutral and a cationic. This catalyst have shown outstanding reactivity for the direct conversion of ethylene to propylene 150°C following a tri-functional mechanism (dimerization, isomerization and crossmetathesis). The deactivation pathway has been attributes to ethylene oligomerization mainly due to the presence of cationic surface species. To circumvent this deactivation, other reactions affording propylene have been developed (butenes conversion, ethylene/2-butene and isobutene/2-butene cross metathesis). The conversion of 2-butene to propylene, until then unreported, has been notably studied. Finally, a second type of catalyst, models of the active site of supported tungsten hydrides and of WO 3 /SiO 2 catalyst, has been prepared and characterized. These new catalysts, bearing an oxide ligand, have been shown to be more active than their imido counterparts.

Faculté

  la Terre UFR Sciences et Techniques des Activités Physiques et Sportives Observatoire de Lyon Ecole Polytechnique Universitaire de Lyon 1 Institut Universitaire de Technologie de Lyon 1 Institut de Science Financière et d'Assurance Institut Universitaire de Formation des Maîtres Directeur : M. le Professeur F. Gieres Directeur : M. le Professeur C. Gautier Directeur : Mme le Professeur H. Parrot Directeur : M. N. Siauve Directeur : M. le Professeur S. Akkouche Directeur : M. le Professeur A. Goldman Directeur : M. le Professeur H. Ben Hadid Directeur : Mme S. Fleck Directeur : M. le Professeur P. Hantzpergue Directeur : M. C. Collignon Directeur : M. B. Guiderdoni Directeur : M. le Professeur J. Lieto Directeur : M. le Professeur C. Coulet Directeur : M. le Professeur J-C. Augros Directeur : M R. Bernard Acknowledgement None of the work contained in this thesis would have been possible without the tight collaboration between UOP LCC and the LCOMS. I would like to acknowledge Prof. Jean-Marie Basset who welcomed me in his dynamic team. I would also thank him for giving me the opportunity to work in a very interesting and promising subject. I am very thankful to Dr. Paul Barger, Dr. Christopher Nicholas and Dr. James Rekoske for their constant interest in the progresses of my work and UOP LCC for the funding. I am very thankful to Dr. Mostafa Taoufik for his supervision and guidance along these three years. His passionate interest for chemistry has been an inexhaustible source of inspiration and an indispensible input to the project. I am also very grateful to Prof. Jean-François Carpentier and Prof. Klaus Köhler for accepting to evaluate this work. I am filled with gratitude to all those who contributed, directly or indirectly, to the advancement of this research; Dr. Nicolas Merle for his teaching of technical skills; Dr.

2 :Chapter 4 : 3 11 CONFIDENTIAL

 24311 Characterizations of the tungsten hydride supported catalyst Chapter 3: Catalytic activity of WH/Al 2 O 3 for direct conversion of ethylene to propylene Well-defined aluminum alkyl and hydride grafted on γ γ-Al 2 O 3role in deactivation of WH/Al 2 O Introduction LCOMS-UOP LCC

Figure 1 . 2

 12 Figure 1.2 Global propylene consumption and prevision by regions 3

Figure 1 . 3

 13 Figure 1.3 Diffuse reflectance infrared spectra of silica dehydroxylated at a) 200°C and b) 700°C and interpretation according reference 117

31 CONFIDENTIAL

 31 LCOMS-UOP LCC Indeed γ-alumina, like η-alumina, is a spinels compound: Al atoms from the bulk are either tetrahedral or octahedral. At the surface, aluminols and aluminium possessing a Lewis acid character or aluminol possessing weak Brønsted acid character are both present.

Figure 1 . 4

 14 Figure 1.4 Diffuse reflectance infrared spectra of γ-alumina dehydroxylated at 500°C and interpretation according reference 124

Figure 1 .

 1 Figure 1.6 13 C CP MAS NMR spectrum of VIII obtained after 13 CH 4 activation at 150°C

  Scheme 1.22 Proposed mechanism for the NOCM reaction catalyzed by supported tungsten hydride

Chapter 1 51 CONFIDENTIAL

 51 LCOMS-UOP LCC

2 . 4 . 3 . 85 3. 1 . 3 . 2 . 3 . 3 . 3 . 4 . 3 . 5 . 3 . 7 . 4 .

 24385132333435374 Conclusion.................................................................................................................................. Experimental section ..........................................................................................................General procedures................................................................................................................... Pyridine adsorption on alumina monitored by IR spectroscopy .......................................... Synthesis of 99% 13 C-labeled t Bu*CH 2 Cl................................................................................ Monitoring the synthesis of 1/Al 2 O 3-(500) by IR spectroscopy ................................................ Preparation of 1/Al 2 O 3-(500) (RP) ............................................................................................... 3.6. Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS)................................... Monitoring the treatment of 1/Al 2 O 3-(500) (RP) under H 2 by IR spectroscopy ..................... 3.8. Treatment of 1/Al 2 O 3-(500) (RP) under H 2 ................................................................................ 3.9. Reaction of WH/Al 2 O 3-(500) (RP) with D 2 ................................................................................. 3.10. Hydrolysis of WH/Al 2 O 3-(500) (RP).......................................................................................... 3.11. Activation of methane on WH/Al 2 O 3-(500) (RP) in continuous flow reactor........................ Reference and Notes ...........................................................................................................90

  doping elements have been studied for the preparation catalyst. Moreover silica-alumina and alumina-magnesium oxide have also been studied for there specific acido-basic character (see Chapter 1). Previous work realized on the immobilization of 1, on Al 2 O 3 have been performed using AEROXIDE ® Alu C purchased from Evonik. Nevertheless, after analysis by XRD, this alumina was identified as a mixture of γand δphase. As γ-Al 2 O 3 was intensively studied by experimental and theoretical approach (see Chapter 1), and to avoid eventual problems of characterization, it was decided to use an alumina with supposed single γ-phase. In this paragraph, only the characterizations of Alumina E7102 from Rhone-Poulenc, referred to as Al 2 O 3 (RP), support are presented. The characterizations of Al

  Al 2 O 3 (RP) properties The influence of the temperature on Al 2 O 3 (RP) has been fully studied and is presented in this paragraph. First, Solid state N.M.R. was performed on Al 2 O 3 (RP) dehydroxylated at 300°C, 500°C and 800°C (Figure 2.1).

Figure 2 .

 2 Figure 2.1 1 H (left) and 27 Al (right) N.M.R. spectra of Al 2 O 3 (RP) dehydroxylated at 300°C (top), 500°C (middle) and 800°C (bottom) 1 H N.M.R. spectra of Al 2 O 3 (RP) dehydroxylated at 300°C, 500°C and 800°C (Figure 2.1, left) show the presence of three types of proton at the surface of the alumina,which is in agreement with literature data.16 At low field, around 4.3 ppm, the signal cor-

3 ) 19 Scheme 2 . 3

 31923 Scheme 2.3 Different hydroxyl groups at the surface of alumina IR spectra (Figure 2.2) in the ν (OH) region of Al 2 O 3-(300) -(500) and -(800) (RP) show the presence of three types of OH groups. Two absorption bands at highest frequencies, in the

Figure 2 . 2

 22 Figure 2.2 IR spectra (transmission) of the same 30 mg pellet of Al 2 O 3 (D) dehydroxylated at a) 300°C; b) 500°C and c) 800°C

67 CONFIDENTIAL

 67 Scheme 2.4 Pyridine adsorption on oxides

Figure 2 . 3

 23 Figure 2.3 IR spectra (transmission) of pyridine adsorbed on the same 40 mg pellet of Al 2 O 3 (RP) dehydroxylated at a) 300°C, b) 500°C and c) 800°C and treated at 150°C to remove H bonded pyridine.

Figure 2 . 4

 24 Figure 2.4 DRX spectrum of Al 2 O 3 (RP) after calcination and dehydroxylation at 500°C (grey bars: ICDD Ref γ-Al 2 O 3 PDF# 00-047-1308)

Figure 2 . 4 presents

 24 the XRD spectrum of Al 2 O 3-(500) (RP), by comparison with the reference, it is clear that this is a γ-Al 2 O 3 . This alumina was chosen for this reason.

5

 5 Scheme 2.5 Grafting of 1 by protonolysis reaction

Figure 2 .

 2 Figure 2.5 left: IR spectra of a) Al 2 O 3-(500) (RP) and b) 1/Al 2 O 3-(500) (RP); right: subtraction of the two spectra in the ν(OH) region. Upon sublimation of an excess of 1, [W(≡C t Bu)(CH 2 t Bu) 3 ], the alumina disk partially dehydroxylated at 500 °C (Al 2 O 3-(500) (RP)) turns brown and yields the solid 1/Al 2 O 3-(500) (RP). The IR spectrum of Al 2 O 3-(500) (RP) displays the five bands at 3795, 3775, 3733, 3650 and 3600 cm -1 (Figure 2.5) corresponding to the ν (OH) vibrations of different types of surface hydroxyls (vide supra). Upon sublimation of 1, the ν (OH) vibrations at 3795, 3776

71 CONFIDENTIAL

 71 LCOMS-UOP LCC2.2.3. Solid-state NMR spectroscopyThe solid-state MAS1 H NMR spectrum of 1/Al 2 O 3-(500) (RP) (Figure 2.6 left) exhibits only one broad signal at 1.0 ppm, tentatively assigned to the perhydrocarbyl ligand resonances, and particularly to the methyl and methylene of the neopentyl-like ligands. The solid-state CP/MAS 13 C NMR spectrum of solid 1/Al 2 O 3-(500) (RP) (Figure 2.6 right)

Figure 2 .

 2 Figure 2.6 solid-state NMR spectra of 1/Al 2 O 2-(500) (RP): left 1 H-MAS; right 13 C CP-MAS

1 *Figure 2 . 7

 127 Figure 2.7 Preparation of the 99% 13 C labeled [W(≡*C t Bu)(*CH 2 t Bu) 3 ] Using labelled 1*/Al 2 O 3-(500) (RP), the spectrum displays the following features (Figure 2.8): a broad and weak signal at 316 ppm, a broad intense signal at 103 ppm along with a shoulder at 90 and 112 ppm, broad signal around 48 ppm, and a signal at 32 ppm and a thin signal at 30 ppm.

Figure 2 .

 2 Figure 2.8 solid-state 13 C HP-DEC NMR spectra of 1*/Al 2 O 2-(500) (RP)

Figure 2 . 9 7

 297 Figure 2.9 Deconvolution, using DMFIT, of the 13 C HP-DEC NMR spectrum of 1*/Al 2 O 2-(500) (RP) in the 20-60 ppm range a) five different peaks have been obtained, in red the fit obtained b) plain line experimental spectra, tick line fit obtained

Figure 2 .

 2 Figure 2.10 13 C HPDEC N.M.R. spectrum of 99% 13 C-labeled complex 1*/Al 2 O 3-(500) a) before and b) after treatment under H 2 at 150°C

Figure 2 .When 1 /

 21 Figure 2.11 left: IR spectra of a) Al 2 O 3-(500) (RP), b) 1/Al 2 O 3-(500) (RP) and c) WH/Al 2 O 3-(500) (RP); right: zoom on the W-H region. When 1/Al 2 O 3-(500) (RP), is heated under H 2 for 15 h at 150 °C, the pale yellow solid turns brown and leads to the solid WH/Al 2 O 3-(500) (RP) (Figure 2.11). Monitoring by IR spectroscopy (spectrum c) shows the disappearance of 95% of the bands associated with ν (C-H)

CONFIDENTIAL 1 Scheme 2 . 8

 128 Scheme 2.8 Structure of the tungsten trishydride isolated by Dobbs et al.

WD/Al 2 O 3 -Figure 2 .

 232 Figure 2.12 Diffuse reflectance infrared spectra of: a) WH/Al 2 O 3-(500) (RP); b) after treatment at 80°C with D 2 (WD/Al 2 O 3-(500) (RP)) and c) after a final treatment at 80°C with H 2 .

9

 9 Scheme 2.9 Theroretical calculation of the expected mechanism of formation of supported tungsten hydride from neutral surface species. (Sautet et al.; unpublished results)

Figure 2 .

 2 Figure 2.13 Raman spectrum of WH/Al 2 O 3-(500) (RP)The observed bands are very broad, showing, as expected by heterogeneity of alumina surface, a distribution of structures of surface species. The broad signal around 800 cm -1 may be assigned to Al-O-W modes. The bands at 335 and 1089 cm -1 , are assigned, respectively to bending and symmetric stretching mode of the W=O. These values are high for a W=O, which are reported to be at 300 cm -1 (bending) and 1020 cm -1 (symmetric stretching) for surface tungsten oxo species on Al 2 O 3 .34 . The coordination of the oxo ligand proposed by theoretical calculation may induce this shift of the signal. Theoretical investigations about Raman shift may explain this high value. No signal assignable to W-O-W, characteristic of WO 3 crystalline particles are observed. Finally, no signals imputable to WH or OH are detected.

Figure 2 .

 2 Figure 2.14 Solid state 1 H-MAS NMR spectra of WH/Al 2 O 3-(500) (RP) left comparison with WD/Al 2 O 3-(500) (RP) The 1 H MAS NMR spectrum (Figure 2.14) of the solid WH/Al 2 O 3-(500) (RP) exhibits two intense signals at 1.9 and 1.0 ppm, which are, respectively, characteristic of residual hydroxyl groups and neopentyl fragments (see 13 C NMR spectrum in Figure 2.10). Moreover, there is a weak broad signal at 10.1 ppm, which disappears when WH/Al 2 O 3-(500) (RP) is contacted with D 2 at 80°C for 1h (WD/Al 2 O 3-(500) (RP)). This value is in agreement with the 1 H NMR of the tungsten trishydride isolated by Dobbs et al. (vide supra) reported to give a signal at 10.01 ppm. The broadness of the signal can be explained by the 1 J W-H coupling and eventually the distribution of products regarding their close environment. In contrast to IR spectroscopy, the 1 H MAS NMR spectrum of the surface species does not show a resonance indicating the presence of Al-H species (ca. 3.3 ppm, see Chapter 4), probably due to the broadness of the signal induced by the quadrupolar moment of trigonal Al centers

81 CONFIDENTIAL

 81 Figure 2.15 left: DQ Solid state 1 H-MAS NMR spectra of WH/Al 2 O 3-(500) (RP)

8 (

 8 After base-line substraction) ns= 256 CONFIDENTIAL LCOMS-UOP LCC

Figure 2 . 83 CONFIDENTIAL

 283 Figure 2.16 Instant (left) and cumulated (right) hydrogen evolution during activation of methane on WH/Al 2 O 3- (500) (RP)

Figure 2 .

 2 Figure 2.17 W L III -edge k 3 -weighted EXAFS (left) and Fourier transform (right) of WH/Al 2 O 3-(500) (RP). Dashed lines: experimental, solid lines: spherical wave theory.

Chapter 2 87 CONFIDENTIAL

 87 LCOMS-UOP LCC and tightly closed. Compressed air was used for both bearing and driving the rotors.

Figure 3 . 1

 31 Figure 3.1 Thermodynamics' data for the ethylene to propylene reaction: left: Δ r G° vs. temperature; right conversion at equilibrium vs. temperature. Data calculated from tables 5

Scheme 3 . 2

 32 Scheme 3.2 Mechanism proposed by Oikawa et al. for the conversion of ethylene to propylene over acidic catalyst During their investigation Oikawa et al. shed light upon the importance of the pore size and the acidity of the catalyst to obtain a good selectivity and conversion respectively. They have identified SAPO-34 as the most efficient catalyst for direct ethylene to propylene conversion. Its pore size is similar to the kinetic diameter of the propylene, giving thus a good selectivity in this molecule, and its acid strength is intermediate, affording the best conversion rate. When the reaction is performed at 450°C, after 1 hour on stream,

Chapter 3 99 CONFIDENTIAL

 99 LCOMS-UOP LCC

Figure 3 . 2

 32 Figure 3.2 Conversion of ethylene ( ), TON ( ) and selectivity vs. time on stream

Figure 3 . 3 15 Scheme 3 . 3 Formation of the active species 2 . 3 . 2 . 1 Figure 3 . 4

 331533232134 Figure 3.3 Selectivity of the ethylene to propylene reaction in the early stage of catalysis vs. time on stream

5 RelativeFigure 3 . 5

 535 Figure 3.5 Relative selectivity of the butenes vs. time on stream

Scheme 3 . 4

 34 Scheme 3.4 Proposed mechanism for the formation of 1-butene and 2-butene.After exposition of WH/Al 2 O 3-(500) to an excess of dry O 2 , in order to poison all the tungsten active site of the catalyst, isomerization of 1-butene was tested in continuous flow reactor in similar condition. No activity was observed, confirming that tungsten

Figure 3 . 6

 36 Figure 3.6 Conversion vs. inverse space velocity for 2 to 46 hours on stream with linear fits.

Figure 3 . 7 Figure 3 . 7

 3737 Figure 3.7 Selectivity in butenes (left) and propylene (right) at 150°C for different reaction time vs. inverse space velocity

Figure 3 . 9

 39 Figure 3.9 Selectivity in propylene (left) and butenes (right) at different reaction time vs. inverse space velocity

Figure 3 .

 3 Figure 3.10 Conversion of ethylene vs. Time with a co-feed of 1-butene (percentage of 1-butene in the feed of ethylene)

Scheme 3 . 5

 35 Scheme 3.5 Proposed mechanism for the direct conversion of ethylene to propylene

2. 4 . 1 .

 41 Influence of the nature of the support As indicated in Chapter 2 and Appendix 1, the tungsten hydride was prepared on alumina (WH/Al 2 O 3-(500) ) but also on Aluminum Magnesium Hydroxyde (WH/Pural (500) ) and Silica-Alumina (WH/SiAl (500) ). SiAl and Pural have been chosen for their difference of acidity compared to Alumina. Therefore, this paragraph presents a study of the influence of the acidity of the supports for grafted tungsten hydride on catalytic performances in direct conversion of ethylene to propylene. The results of the catalytic tests are shown in Figure 3.11. For WH/Al 2 O 3-(500) , the maximum of conversion is ca. 35 % at 1.5 h on stream, and ca. 12 % at 15 h on stream.

Figure 3 . 11 (

 311 Figure 3.11 (Top) Conversion vs. Time on Stream; (Midlle) Cumulated T.O.N.vs. Time on stream; (Bottom) Selectivity at pseudo steady state (15 h on stream) in propylene, butenes and heavier olefins for each support.

2 O 3 -

 23 (500) to 47% for WH/Al 2 O 3-(300) followed by a hyperbolic deactivation. It is noticeable that the higher the dehydroxylation temperature of the support, the faster the deactivations. The cumulated T.O.N. clearly shows that the activity of the catalyst is dependent of the support dehydroxylation temperature. The selectivity in propylene is quite similar for WH/Al 2 O 3-(300) , WH/Al 2 O 3-(400) and WH/Al 2 O 3-(500) reaching 92%, whereas it is only 55% for WH/Al 2 O 3-(800) , where the formation of heavier olefins is observed.

Scheme 3 . 6 Figure 3 . 12 (

 36312 Scheme 3.6 Surface species of WH/Al 2 O 3-(500)

  conversion of ethylene to propylene on WH/Al 2 O 3-(500) will be discussed in this subsection. The diminution of the reaction temperature may impact the dimerization and crossmetathesis rates, modifying thus selectivities and deactivation process. Four experiments have been performed with different reaction temperatures (i.e. 50°C, 100°C,The results of the catalytic tests are shown in Figure3.13 and Figure3.14. For the experiment at 50°C the ethylene conversion reaches a maximum of 50 % whereas for the experiment at 100°C the maximum is 45 %. Both of these values are slightly superior to the 35 % observed at 150°C. On the other hand there is a more important decrease in the rate of conversion for the experiments at 50°C and 100°C compared to the experiment at 150°C. Thus after 24 h on stream the conversion is only 0.3% for the reaction at 50°C and 2% for the reaction at 100°C.

Figure 3 .

 3 Figure 3.13 (Top) Conversion vs. Time on Stream; (Bottom) Cumulated T.O.N.vs. Time on stream for each reaction temperature.

Figure 3 .

 3 Figure 3.14 (Top) Selectivity at pseudo steady state (15 h on stream) in propylene, butenes and heavier olefins for each reaction temperature. (Bottom) Relative selectivity at pseudo steady state (15 h on stream) of the butene for each reaction temperature.

7 3 Figure 3 .

 733 Scheme 3.7 Possible mechanisms for the formation of isobutene.

Figure 3 .

 3 Figure 3.15 Cumulated TON for isobutene vs. time on stream for the reaction at 150°C

  100°C and 150°C are presented on Figure 3.16, left. The differential thermo-gravimetric profiles, indicating the degradation temperature of the carbonaceous species present at the surface of the catalyst, have been plotted for each reaction temperature (Figure 3.16, right). The amount of carbonaceous deposits on the catalyst after 24h on stream, i.e. the weight loss at the end of the TGA experiment, has been plotted vs. the reaction temperature (Figure 3.17). Moreover, DSC profile for fusion and crystallization are presented (Figure 3.18 left and right, respectively).

Figure 3 .

 3 Figure 3.16 left: TGA profile of the catalyst after 24 h on stream at 50°C, 100°C and 150°C; right: Differential thermo-gravimetric profiles of the catalyst for each reaction temperature.

Figure 3 .

 3 Figure3.17 displays that whatever the reaction temperature, there is an important weight loss of the used catalyst. It clearly indicates that carbonaceous species are formed at the surface of the catalyst during reaction. It is noteworthy that the maximum amount of carbonaceous deposit is for the 100°C reaction with 57% of catalyst weight, followed by 36% at 50°C and 27% at 150°C. Thus lowering the working temperature favored the formation of surface carbonaceous species.It is interesting to compare these results with the selectivity of at each reaction temperature on Figure3.14 (top), where we can observe that the formation of heavier products (e.g. butenes, pentene at 85% in selectivty…) is favored at low temperature (i.e. ≤ 100°C).

116Figure 3 .

 3 Figure 3.17 Amount of carbonaceous deposits on the catalyst after 24h on stream vs. reaction temperature

Figure 3 .

 3 Figure 3.18 left: Fusion DSC profiles for each reaction temperature; right: Crystallization DSC profiles for each reaction temperature

Figure 3 .

 3 Figure 3.19 Conversion of ethylene vs. Time on stream for the ethylene to propylene reaction

Figure 3 .

 3 Figure 3.20 DRIFT spectra of the fresh catalyst and of the catalytic bed at different time on stream.

Figure 3 .

 3 Figure 3.21 13 C CPMASS NMR spectra of the catalyst after 48 h on stream

Figure 3 .

 3 Figure 3.22 left: TGA profiles for of the catalyst for each time on stream; right: Differential thermo-gravimetric profiles of the catalyst for each time on stream

Figure 3 .

 3 Figure 3.23 left: Weight loss of the fresh and used catalyst vs. time on stream; right: Conversion of ethylene vs. Time on stream for the ethylene to propylene reaction (idem Figure 3.19)

  conversion onto propylene has decreased leading to a higher ethylene partial pressure. It explains why the species with a high melting point (>130°C) is observed in DSC only after 24 h on stream.

Figure 3 .

 3 Figure 3.24 left: Fusion DSC profiles for each time on stream; right: Crystallization DSC profiles for each time on stream

Figure 3 .

 3 Figure 3.25 Conversion of ethylene vs. time on stream. Three regeneration temperatures have been experimented: 150°C, 200°C and 250°C.

Figure 3 .

 3 Figure 3.26 Conversion of ethylene vs. time on stream. Regeneration cycle at 300°C.

Figure 3 .

 3 Figure3.27 left: Conversion of ethylene and efficiency in propylene (conversion of ethylene x selectivity in propylene) for the 8% H 2 co-feed ethylene to propylene experiment; right: Efficiency in propylene for the reference ethylene to propylene experiment and efficiency in propylene for the 8% H 2 co-feed ethylene to propylene experiment vs. time on stream.

Figure 3 .

 3 Figure 3.28 left: Selectivity for the 8% H 2 co-feed ethylene to propylene experiment; right: Efficiency (conversion of ethylene x selectivity in ethane) in ethane for the 8% H 2 co-feed ethylene to propylene experiment

Figure 3 .126

 3 Figure 3.29 Comparison of efficiency (conversion of ethylene x selectivity in propylene) in propylene for the 1 % H 2 co-feed and reference ethylene to propylene experiment

Scheme 3 . 9

 39 Scheme 3.9 Global mechanism proposed for the direct conversion of ethylene to propylene on WH/Al 2 O 3-(500)

2 . 4 . 3 . 3 . 1 . 3 . 2 . 3 . 3 . 3 . 4 . 3 . 5 . 4 .

 24331323334354 Conclusion................................................................................................................................ Experimental section ........................................................................................................150 General procedures................................................................................................................. Preparation and characterizations of Al 2 O 3-(500) RP ............................................................ Preparation of 2/Al 2 O 3-(500) ...................................................................................................... Preparation of AlH/Al 2 O 3-(500) ................................................................................................ Catalytic application of 2/Al 2 O 3-(500) and AlH/Al 2 O 3-(500) ...................................................... 3.5.1. Ethylene to propylene conditions ....................................................................................... 3.5.2. Ethylene polymerization..................................................................................................... 3.5.3. Ethylene hydrogenation...................................................................................................... Reference and Notes .........................................................................................................153

Figure 4 . 1

 41 Figure 4.1 Diffuse reflectance infrared spectra of a) Al 2 O 3-(500) , b) 2/Al 2 O 3-(500)

Figure 4 .

 4 Figure 4.2 left: 1 H NMR spectrum of 2; right: 1 H MAS NMR spectrum of 2/Al 2 O 3-(500)The13 C CP MAS NMR spectrum features a broad signal at 28 ppm, with broad shoulder at 26 ppm (Figure4.3), which compares well with isobutyl groups signature in the molecular precursor where signals at 28 ppm and 26 ppm are observed at room temperature with no detectable AlCH2 due to the quadrupolar aluminum (spin5/2). This signal can however be observed at 23.4 ppm by thermal decoupling at -50°C.13

Figure 4 .

 4 Figure 4.3 left: 13 C{ 1 H} NMR spectrum of 2; right: 13 C MAS NMR spectrum of 2/Al 2 O 3-(500) The 27 Al MAS NMR spectrum is uninformative, as the bulk atoms signal masks the resonances from the grafted aluminum nuclei (Figure 4.4 a). Taking advantage of the presence of alkyl protons, one can make use of a correlation pulse sequence such as HMQC in order to gather information on their neighboring aluminums. The 27 Al MAS NMR spectrum of 2/Al 2 O 3-(500) obtained with a dipolar filtering revealing only aluminum centers spatially close to protons is shown in Figure 4.4 b. The recoupling period set to a small value (500 μsec) keeps the bulk alumina at a low signal level. The spectrum features a broad signal spreading from 100 to 0 ppm, resulting from different aluminum coordinations. In the literature, tetra-penta-and hexa-coordinated aluminum sites are generally

Figure 4 .

 4 Figure 4.4 (a) 27 Al Hahn-echo MAS and (b) D-filtered HMQC 27 Al MAS NMR spectra of 2/Al 2 O 3-(500) (208.50 MHz, spinning frequency of 20 kHz; spectrum b is the projection of the 2D correlation spectrum, acquired with 1536 transients and with SR4 recoupling scheme of 500 ms applied on 1H channel).

CONFIDENTIAL

  Scheme 4.2 Reaction of 2 toward Al 2 O 3-(500) affording 2/Al 2 O 3-(500)

2 /CONFIDENTIAL

 2 Al 2 O 3-(500) under vacuum. Surprisingly, by treating 2/Al 2 O 3-(500) gradually from 25°C to 350°C, only a small ν(AlH) signals band at 1940 cm -1 is observed on the IR spectra from 200°C (Figure 4.5) and only 60 μmol.g -1 of isobutene are observed. At higher temperatures neither IR spectroscopy nor gas phase analysis show an evolution of the system. Most of the Al 2 LCOMS-UOP LCC alkyls remains on the surface as ν(CH) and δ(CH) signals are still present on the spectrum and only 5% of the surface isobutyl of 2/Al 2 O 3-(500) has evolved as isobutene. The properties of this surface aluminum alkyl are thus different from its homogeneous precursor preventing the occurrence of β-H transfer and concomitant generation of isobutene and AlH.

Figure 4 . 5

 45 Figure 4.5 IR spectra of 75mg pellet of 2 grafted on Al 2 O 3-(500) by sublimation treated under vacuum from RT to 350°C (2 h at each temperature)

  Scheme 4.4 Hydrogenolysis of triethylaluminum and transition state proposed by Podall et al.18

Figure 4 . 6

 46 Figure 4.6 IR spectra of 65mg pellet of 2 grafted on Al 2 O 3-(500) by sublimation treated under hydrogen excess (550 Torr) from RT to 350°C (2 h at each temperature) Regarding these preliminary results, 2/Al 2 O 3-(500) was treated 4h at 400°C under a low H 2 pressure (550 Torr) and afforded AlH/Al 2 O 3-(500) , along with formation of 4800 μmol.g -1 of C (alkane mixture) in the gas phase, which corresponds to 2.0 isobutyl per initially grafted Al. The formation of the corresponding quantity of hydride is indicated by the stoichiometry of the hydrolysis, as 1200 μmol of H 2 are released upon exposure of

  to excess water. On the infrared spectrum of AlH/Al 2 O 3-(500) , the characteristic,11 and noticeably intense, ν(AlH) signals appeared at 1940 cm -1 , while those of the i Bu groups almost completely vanished (Figure4.7). Performing the reaction under D 2 leads to the formation of a ν(AlD) band with the expected isotopic shift (1400 cm -1 ) (seeAppendix 3)

Figure 4 . 7

 47 Figure 4.7 Diffuse reflectance infrared spectra of a) 2/Al 2 O 3-(500) and b) AlH/Al 2 O 3-(500)

Figure 4 . 24 1940

 424 8 (c) is a J-HMQC filtered1 H MAS spectrum obtained with an27 Al RA-MP decoupling,19 revealing the 1 H chemical shift region of hydride species. The spectrum reveals the presence of a 1 H site at a chemical shift of 3.3 ppm, in a major proportion. This chemical shift lies below the expected range for molecular aluminum hydrides,[20][21][22][23] but is similar to what was observed in related materials.

Figure 4 .

 4 Figure 4.8 1 H MAS NMR spectra of AlH/Al 2 O 3-(500) recorded at (a) B 0 =9.4 T and (b) B 0 =18.8 T at a spinning frequency of nR=20 kHz. (c) J-HMQC filtered 1H MAS spectrum with 27Al RA-MP decoupling (B0=18.8 T, ν R =20 kHz). d) J-resolved projection (see Appendix 3) (B 0 =18.8 T, ν R =20 kHz). Central peak (*) results from the incomplete inversion produced by the 27Al π pulse leading to refocusing of the heteronuclear scalar coupling.

  an27 Al π pulse is used to express the heteronuclear J coupling during a 1 H spin-echo, was performed on AlH/Al 2 O 3-(500) . The signal presented in the frequency domain in Figure 4.8 (d), clearly evidences a doublet characteristic of a terminal aluminum hydride and separated by 381 Hz, in line with the scalar coupling J iso measured on the 1 H MAS spectrum.

Figure 4 .9 1 H

 41 Figure 4.9 1 H MAS spectra of 2 at 9.4 T (a) and 18.8 T (c).The positions of the lines in the multiplet were calculated with DMFIT4 using the expression of the complete shift given by eq. 23 in reference27 . The second-order shift itself, defined as Δ = -3/10 C q D'/v s , was 390 Hz and 195 Hz at 9.4 T and 18.8 T, respectively. These values of D correspond to C Q =15MHz and D'=9kHz.

2. 3 .

 3 Catalytic activity of 2/Al 2 O 3-(500) and AlH/Al 2 O 3-(500) The exposure of AlH/Al 2 O 3-(500) to 550 Torr of ethylene at 100°C leads to formation of polyethylenic fragments and vanishing of Al-H bands, as shown by IR follow-up (Figure 4.11).

Figure 4 .

 4 Figure 4.11 Diffuse reflectance infrared spectra of AlH/Al 2 O 3-(500) a) before and b) after exposition to excess of ethylene (550 Torr) at 100°C

• 2 /When 2 /

 22 defined aluminum alkyl and hydride grafted on γ-Al 2 O 3 -role in deactivation of WH/Al 2 O 3 CONFIDENTIAL LCOMS-UOP LCC Considering the results obtained, AlH/Al 2 O 3-(500) was then tested for in autoclave for ethylene polymerization. Finally AlH/Al 2 O 3-(500) was tested for catalytic ethylene hydrogenation. 2.3.1. Catalytic activity of 2/Al 2 O 3-(500) and AlH/Al 2 O 3-(500) in ethylene to propylene conditions The two materials have been tested in similar conditions that the WH/Al 2 O 3-(500) , i.e. in continuous flow reactor at 150°C and 4 mL.min -1 of ethylene. Al 2 O 3-(500) Al 2 O 3-(500) was tested in continuous flow reactors, no trace of products were found by GC in the gas flow coming out from the reactor. Thus, aluminum alkyls do not perform the dimerization of ethylene. After 24 h, a 355 mg plug of polymeric material and catalyst was collected when the reactor was opened. During 24 h on stream 205 mg of polymer was formed. The resulting material (polymer + catalyst) was analyzed by TGA and DSC.

Figure 4 .

 4 Figure 4.12 left: TGA profile of the material recovered after 24 h on stream over 2/Al 2 O 3-(500) ; right: relative differential thermo-gravimetric profile.

Figure 4 .

 4 Figure 4.13 Fusion and crystallization DSC profile of the material recovered after 24 h on ethylene stream over 2/Al 2 O 3-(500)

Figure 4 .

 4 Figure 4.14 left: TGA profile of the material recovered after 24 h on stream over AlH/Al 2 O 3-(500) ; right: relative differential thermo-gravimetric profile.

Figure 4 .

 4 Figure 4.15 Fusion and crystallization DSC profile of the material recovered after 24 h on ethylene stream over AlH/Al 2 O 3-(500)TGA indicates that 90% of the material is burned during the analysis (Figure4.14).The polymer formed burns mainly around 473°C as the DTG profile features a large peak at this temperature and minor one at 538°C. DSC reveals that the melting point of the polymer formed in 135°C (Figure4.15). This melting point is similar to LHDPE.

3 CONFIDENTIAL

 3 defined aluminum alkyl and hydride grafted on γ-Al 2 O 3 -role in deactivation of WH/Al 2 O LCOMS-UOP LCC • Conclusion This values have to be compared to the results presented in Chapter 3, when WH/Al 2 O 3- (500) was analyzed after different time on ethylene stream. At low time on stream, polymers with low melting point are formed (i.e. 101-116°C). At higher time on stream two melting point are observed one at 116°C and one at 135°C. 2/Al 2 O 3-(500) and AlH/Al 2 O 3- (500) provide after 24 h on stream a polymer with a single melting point of 135°C. It can be assumed that the formation of the polymeric species with a melting point of 116°C is promoted by tungsten surface species of WH/Al 2 O 3-(500) .

Figure 4 .

 4 Figure 4.16 13 C NMR in a TCB at 100°C of the material obtained after Ethylene polymerization over AlH/Al 2 O 3-(500)

Scheme 4 . 6

 46 Scheme 4.6 Postulated mechanism of ethylene hydrogenation over AlH/Al 2 O 3-(500) Therefore, exposure of ethylene and H 2 to AlH/Al 2 O 3-(500) in a continuous flow reactor (H 2 and C 2 H 4 : 4 mL.min-1, 400°C) lead to sustained conversion into ethane, while Al 2 O 3-(500) proved inactive under identical conditions.

Figure 4 .

 4 Figure 4.17 Conversion of ethylene ( ), and TON ( )

3 . 5 .

 35 AlH/Al 2 O 3-(500) Monitoring the treatment of 2/Al 2 O 3-(500) under vacuum or H 2 at different temperature: Al 2 O 3 RP (75mg, 65 mg) was pressed into an 17 mm self-supporting disk, adjusted in the sample holder, and introduced into a reactor equipped with CaF 2 windows. The supports were calcined under air and partly dehydroxylated under vacuum (10 -5 Torr) at 500°C. 2 was then sublimed under vacuum onto the Alumina disk. The solid was reacted at RT for 2 h, and the excess of the molecular complex was removed by reverse sublimation at 60°C and condensed into a tube cooled by liquid N 2 , which was then sealed off using a blow torch. The resulting pellet was treated either under vacuum or under 550 Torr of H 2 and heated two hours at 100, 150, 200, 250, 300 and 350°C. An IR spectrum was recorded and gas phase was analyzed by GC at each step. Preparation of AlH/Al 2 O 3-(500) : 2/Al 2 O 3-(500) was heated at 400 °C in the presence of a large excess of dry, deoxygenated H 2 (750 Torr). After 4 h, material 2 was obtained as a white solid, and the gaseous products were quantified by GC. Hydrolysis procedure: AlH/Al 2 O 3-(500) was treated with an excess of H 2 O in gas phase (17 Torr). The gaseous products were quantified by GC. CONFIDENTIAL LCOMS-UOP LCC Catalytic application of 2/Al 2 O 3-(500) and AlH/Al 2 O 3-(500)

  80 mL autoclave was charged into a glovebox with 20 mL of toluene and 100 mg of AlH/Al 2 O 3-(500) . The reactor was then heated to 100°C. Under magnetic stirring, the wanted ethylene pressure was established and kept constant over 30min. The reaction was quenched by removing ethylene and pouring the mixture into a EtOH (40 mL), H 2 O (140 mL) and HCl (20 mL, 37%) solution. After 2h of stirring, the resulting solid polymer was filtered off and washed successively with water (80 mL) and EtOH (80 mL) and dried at

Scheme 5 . 5

 55 Scheme 5.5 Degenerated 2-butene metathesis

Figure 5 . 1

 51 Figure 5.1 Conversion of propylene ( ) and cumulated TON ( ) vs. time on stream for propylene metathesis on WH/Al 2 O 3-(500) at 150°C

Figure 5 . 2

 52 Figure 5.2 Selectivity vs. time on stream for propylene metathesis on WH/Al 2 O 3-(500) at 150°C

Scheme 5 . 8

 58 Scheme 5.8 Successive reactions leading to the formation of pentenes from propylene

Figure 5 . 3

 53 Figure 5.3 Conversion of 1-butene ( ) and cumulated TON ( ) vs. time on stream on WH/Al 2 O 3-(500) at 150°C

Figure 5 . 4

 54 Figure 5.4 Selectivity vs. time on stream for 1-butene conversion on WH/Al 2 O 3-(500) at 150°C

3 2. 3 . 3 .

 333 Scheme 5.10 Hypothetical formation of the active species as deduced from butane evolution

Figure 5 . 5

 55 Figure 5.5 Conversion of 1-butene on WH/Al 2 O 3-(500) at 150°C at atmospheric pressure ( ) and 20 barg ( ) vs. time on stream

Figure 5 . 6 Figure 5 . 7

 5657 Figure 5.6 Cumulated TON vs. time on stream for conversion of 1-butene on WH/Al 2 O 3-(500) at 150°C at atmospheric pressure ( ) and 20 barg ( )

Figure 5 . 8

 58 Figure 5.8 Conversion of 2-butene ( ) and cumulated TON ( ) vs. time on stream on WH/Al 2 O 3-(500) at 150°C

Figure 5 . 9

 59 Figure 5.9 Selectivity vs. time on stream for 2-butene conversion on WH/Al 2 O 3-(500) at 150°C

Scheme 5 .

 5 Scheme 5.16 Reactions occurring during the conversion of trans-2-butene on WH/Al 2 O 3

Figure 5 .Figure 5 .Figure 5 .

 555 Figure 5.10 Conversion of 2-butene on WH/Al 2 O 3-(500) at 150°C at atmospheric pressure ( ) and 20 barg ( )vs. time on stream

Scheme 5 .Figure 5 .

 55 Scheme 5.18 Intermediates for the production of 2,3-dimethylbutene from isobutene by self-metathesis As known in the classical olefin metathesis mechanism 10 isobutene can react with the hydrido-tungsta-carbene giving the corresponding metallacyclobutanes intermediates C and C' (Scheme 5.18). The metallacyclobutane C is a priori the less thermodynamically favored intermediate, since it has gem-methyl substituents in the 1,2-positions gen-

Figure 5 .

 5 Figure 5.17 Selectivity vs. time on stream for isobutene/trans-2-butene cross metathesis on WH/Al 2 O 3-(500) at 150°C

  Scheme 5.21 Ethylene/trans-2-butene cross-metathesis

Figure 5 .Figure 5 .

 55 Figure 5.18 Total carbon conversion ( ) and cumulated TON ( ) vs. time on stream for ethylene/trans-2butene cross metathesis on WH/Al 2 O 3-(500) at 150°C

1 . 2 . 2 . 1 .

 1221 lyzed online by GC (HP 8890 chromatograph fitted with an Al 2 O 3 /KCl 50 m x 0.32 mm capillary column, FID detector). Introduction ......................................................................................................................190 Results and discussions ....................................................................................................193 Preparation of the molecular precursors...........................................................................

2. 3 . 3 . 3 . 1 . 3 . 2 .

 333132 Catalytic activity of the different species prepared ............................................................. 2.3.1. Compared catalytic performances toward direct conversion of ethylene to propylene ..... 2.3.2. Compared catalytic performances toward propylene metathesis ....................................... 2.4. Conclusion................................................................................................................................ Experimental section ........................................................................................................228 General procedures................................................................................................................. Preparation of the organometallic precursors .....................................................................

3 . 4 . 4 .

 344 Catalytic tests........................................................................................................................... 3.4.1. Reactivity toward ethylene in batch reactor ....................................................................... 3.4.2. Propylene metathesis .......................................................................................................... Reference and Notes .........................................................................................................235

SiO 2 and

 2 Al 2 O 3 in order to obtain species having respectively M = Si and Al regarding the notation of Scheme 6.1. The variation of support will thus provide models of the active site of the WO 3 /SiO 2 when M = Si and the active site of WH/Al 2 O 3 when M = Al.Bearing in mind the active sites of WO 3 /SiO 2 or WH/Al 2 O 3 catalyst, and in the view of developing realistic model surface species, it was targeted, as tungsten molecular precursors, oxo carbenes or their alkyl precursors that are amenable to carbene generation upon α-H abstraction. Then, tungsten oxo-alkylidene derivatives and their alkyl precursors where considered (Y=O).The first example of such complexes was provided by Schrock et al., who reported the synthesis of [W=OCl 2 (=CHR)(PR' 3 ) n ] derivatives which catalyze olefin metathesis in presence of a Lewis acid.14,15 Later they developed a bisaryloxy complex [W=O (OAr)(=CHR)(PR' 3 )] which catalyses ROMP of norbornadiene derivatives without co-

  methylenic group giving rise to a singlet at 1.83 ppm and 85.60 ppm ( 1 J W-C = 48.1 Hz) on the 1 H and 13 C NMR spectra, respectively. Alkylation results in significant shielding as the CH 2 signals in 1 H and 13 C NMR are 2.46 and 100.9 ppm in [W=O(CH 2 t Bu) 3 Cl], respectively (Figure 6.1).

Figure 6 . 1

 61 Figure 6.1 Compared 1 H (left) and 13 C (right) NMR spectra of [W=O(CH 2 t Bu) 3 Cl] (top) and 3 (bottom) (C 6 D 6 , 295K, 1 H: 300 MHz, 13 C: 75 MHz)

  3). As the obtained species, 5, contains five NMR active nuclei (i.e. 1 H (Nat. Ab. = 99.98%, 13 C (Nat. ab. = 1.11%), 14 N (Nat. ab. = 9.63%),18 F (Nat. ab. = 100%) and 183 W (Nat. ab. = 14.31%)), a particular attention has been turned to the study of the scalar coupling of the nuclei bounded to the tungsten.

Figure 6 .

 6 Figure 6.3 liquid NMR spectra of 5: left 1 H NMR; centre 13 C{ 1 H} NMR and right 19 F{ 1 H} NMR

Figure 6 .

 6 Figure 6.4 left: zoom on the 1 H NMR spectra of 5; right: interpretation of the multiplet pattern

Figure 6 .

 6 Figure 6.5 left: zoom on the 13 C{ 1 H} NMR spectra of 5; right: interpretation of the multiplet pattern Finally, the 18 F{ 1 H} NMR spectrum presents, as expected, only one fluorine signal with a chemical shift at 34.8 ppm (Figure 6.6). It is affected by scalar couplings: i) coupling with 14 N, spin 1, separated by two bonds, with a coupling constant 2 J N-F = 49 Hz, forming a spin 1 triplet ii) 14.31% of these fluorines have a coupling with 183 W, spin ½, separated by one bond with a coupling constant 1 J W-F ≈ 50 Hz. Thus the resulting multiplet has the intensity 2:31:34:31:25, which is in line with the observed signal.

Figure 6 .

 6 Figure 6.6 left: zoom on the 19 F{ 1 H} NMR spectra of 5; right: interpretation of the multiplet pattern

Figure 6 .

 6 Figure 6.7 liquid NMR of 6: left 1 H NMR; centre 13 C{ 1 H} NMR and right 19 F{ 1 H} NMR

Figure 6 .

 6 Figure 6.8 left: IR spectra of a) Al 2 O 3-(500) and b) 3/Al 2 O 3-(500) ; right: subtraction of the two spectra in the ν(OH) region.

Figure 6 . 9

 69 Figure 6.9 Diffuse reflectance infrared spectra of a) SiO 2-(700) and b) 3/SiO 2-(700)

Figure 6 .

 6 Figure 6.10 Selected region of Raman spectrum of 3/SiO 2-(700) .

Figure 6 .

 6 Figure 6.11 Solid state NMR data (18.8T) of 3/SiO 2-(700) : a) 1 H MAS, b) 13 C CP MAS and c) 1 H-13 C HETCOR CP MAS.

Figure 6 .

 6 Figure 6.12 Tungsten L III -edge k 3 -weighted EXAFS (left) and corresponding Fourier transform (right) with comparison to simulated curves for the W-containing surface species in 3/SiO 2-(700) . Solid lines: experimental; dashed lines: spherical wave theory.

Figure 6 .

 6 Figure 6.13 DFT calculated isomers of 3/POSS • Thermal stability and carbene formation Hybrid material 3/SiO 2-(700) proved to be thermally stable. Neither spectral (IR, RMN)

Figure 6 .

 6 Figure 6.14 Diffuse reflectance infrared spectra of a) SiO 2-(700) and b) 4/SiO 2-(700)

Figure 6 .Figure 6 .

 66 Figure 6.18 Selected region of Raman spectrum of 6 and 6/SiO 2-(700) .• Mass balance analysisThe resulting material (6/SiO 2-(700) ) contained 4.43 wt% of tungsten and 3.27 wt% of carbon (C/W = 11.3 ± 0.1, theory=10). Gas phase analysis indicates evolution of 1.0 equivalent of NpH per metal center. The mass balance analysis is similar to the one obtained for 3/SiO 2-700 , which is in favor of a monografted species such as: [(≡SiO)(W=O)(CH 2 t Bu) 2 F] (6a).

Chapter 6 217 CONFIDENTIAL 49 Figure 6 .Figure 6 .F

 2174966 Figure 6.20 Calculated structure of 6a poss : Energy = 0.0 kcal.mol -1 ; 19 F chemical shift = -18 ppm

  Scheme 6.16 Proposed structure for the surface species of 6/SiO 2-(700)• EXAFSThe structure of the supported tungsten complex 6/SiO 2-(700) was further studied by analysis of the W L III -edge extended X-ray absorption fine structure (EXAFS) data.

Figure 6 .

 6 Figure 6.23 Tungsten L III -edge k 3 -weighted EXAFS (left) and corresponding Fourier transform (right) with comparison to simulated curves for the W-containing surface species in 6/SiO 2-(700) . Solid lines: experimental; dashed lines: spherical wave theory.

Figure 6 .Figure 6 .

 66 Figure 6.24 Conversion vs. time of 3/SiO 2-(700) , 4/SiO 2-(700) and 6/SiO 2-(700) in propene metathesis (80°C, 20 mL.min -1 )

Figure 6 .

 6 Figure 6.26 Selectivity of propylene metathesis vs. time for 3/SiO 2-(700)

Figure 6 .Figure 6 .

 66 Figure 6.27 Selectivity of propylene metathesis vs. time for 6/SiO 2-(700)

Figure 6 .

 6 Figure 6.29 Selectivity in isobutene during propylene metathesis vs. time for 4/SiO 2-(700)

2 O 3 /

 23 KCl on fused silica column (50 m X 0.32 mm). Elemental analyses were performed at the CNRS Central Analysis Department of Solaize (metal analysis), in the LSEO (Dijon, for C, H analysis) or at Pascher Mikrolabor. IR spectra were recorded on a Nicolet 6700 FT-IR spectrometer by using a DRIFT cell equipped with CaF 2 windows. The samples were prepared under Ar within a glove-box. Typically, 64 scans were accumulated for each spectrum (resolution 4 cm -1 ). Confocal Raman spectra were acquired using the 488nm line of a Ar-ion laser (Melles Griot). The excitation beam was focused on the sample by a 50X long working distance microscope and the scattered light was analyzed by an air-cooled CCD (Labram HR, Horiba Jobin Yvon). The fluorescence was subtracted from the spectra for clarity. Solution NMR spectra were recorded on an Avance-300 Bruker spectrometer.

( 2 .

 2 000 g, 3.8 mmol) and AgBF 4 (0.740 g, 3.8 mmol) were stirred in 20 mL of toluene for one hour at room temperature. The reaction mixture was filtered to remove the insoluble AgCl, and NEt 3 (1.1 mL, 7.70 mmol) was added. The resulting solution was stirred for 16 h at room temperature and the reaction mixture was filtered over celite. The solvent was then removed under vacuum to leave a yellow pale solid. After this treatment boron was still spotted in11 B NMR. A solution of the product in pentane was thus added to SiO 2-(700)

3. 3 . 1 .

 31 Preparation and characterization of 3/Al 2 O 3-(500)A mixture of 3 (500 mg, 1.03 mmol) and Al 2 O 3-(500) (2 g) in pentane (10 mL) was stirred at 25°C 15 hours in absence of light. After filtration, the solid was washed 5 times with pentane and all volatile compounds were condensed into another reactor (of known volume) in order to quantify neopentane evolved during grafting. The resulting white powder was dried under vacuum (10 -5 Torr). Analysis by gas chromatography indicated the formation of 55 μmol of neopentane during the grafting (0.25 ±0.1 NpH/ W). Elemental analysis: W 4.0% wt C 4.9% wt .

( 10 - 5

 105 Torr). Analysis by gas chromatography indicated the formation of 403 μmol of neopentane during the grafting (0.9±0.1 NpH/ W). Elemental analysis: W 4.2% wt C 4.1% wt . 1 H MAS NMR (800 MHz) δ 1.93, 1.01 ppm. 13 C CP MAS NMR (200 MHz) δ 91, 34, 31 ppm.

Figure 6 .

 6 Figure 6.30 Raman spectrum of 3/SiO 2-(700)

3. 3 . 4 .

 34 Monitoring the synthesis of 5/SiO 2-(700)D by IR spectroscopy. The SiO 2 (25 mg) was pressed into a 17 mm self-supporting disk, adjusted in the sample holder, and introduced into a quartz reactor equipped with CaF 2 windows. Deuterated silica (SiO 2-(700)D ) was prepared by heating this pellet under D 2 O (>90% D, 22mmHg) at Chapter 6 233 CONFIDENTIAL LCOMS-UOP LCC

lated from ambient atmosphere was charged with catalyst 3 / 2 % 1 / 1 Scheme 7 . 1

 321171 Scheme 7.1 Different surface species identified on 1/Al 2 O 3-(500) (RP) The treatment of 1/Al 2 O 3-(500) (RP) under H 2 at 150°C afford WH/Al 2 O 3-(500) (RP).

Scheme 7 . 2

 72 Scheme 7.2 Proposed surface species of WH/Al 2 O 3-(500) (RP)

Scheme 7 . 3 3 Figure 7 . 1 3 CONFIDENTIAL

 733713 Scheme 7.3 Proposed mechanism for the direct conversion of ethylene to propylene on WH/Al 2 O 3

  Scheme 7.4 Influence of the substituent of the metallacyclobutane on the conversion rate of metathesis reactions. The characterizations of WH/Al 2 O 3 have shown that cationic and neutral surface species are present at the surface. Moreover, oxo ligand has been evidenced on the tungsten site. In order to have a better understanding of structure of the WH/Al 2 O 3 active site, but also of the WO 3 /SiO 2 active site, single site tungsten-oxo complexes supported on ox-

Figure 7 . 2

 72 Figure 7.2 Conversion vs. time for 3/SiO 2-(700) , 4/SiO 2-(700) , 6/SiO 2-(700) in propylene metathesis (80°C, 20 mL.min -1 )

Scheme 7 . 6

 76 Scheme 7.6 Catalyst deactivation by β-H transfer in the metallacyclobutane All this work has opened several outlooks. First, the investigation of group VI metals can be widened to the molybdenum. The preparation of supported molybdenum hydrides can be studied. Their catalytic activity should then be tested in all the reaction studied for tungsten hydride. A study of mechanism and deactivation pathway could broaden the understanding of metal hydride chemistry. The synthesis of [W=O(CH 2 t Bu) 4 ] (3), which is quite tedious, should be revisited, e.g. using commercial [W=OCl 4 ] as starting material with a selected alkylation agent. It grafting has been extensively studied on SiO 2-(700) leading to a monopodal species, the use of SiO 2-(200) should be investigated in order to form bipodal species, very close from WO 3 /SiO 2 active site (Scheme 7.7).

Figure A. 1

 1 Figure A.1 DRIFT spectra of Alumina RP and UOP A-E dehydroxhylated at 500°C

Figure A. 6

 6 Figure A.6 DRIFT spectra of hydrogenolysed species resulting from the grafting of [W(≡C t Bu)(CH 2 t Bu) 3 ] on Al 2 O 3 (500) RP and UOP A-E Morover, the [W(≡CtBu)(CH 2 tBu) 3 ] complex was grafted on Silica-Alumina (SiAl) and Aluminum Magnesium Hydroxyde (Pural) partially dehydroxylated at 500°C. The grafting was performed by mechanical mixture at 66°C, using the same methodology described in the past report. The resulting species were treated at 150°C under hydrogen to form tungsten hydrides. At each steps, the resulting materials were characterized by DRIFT and mass balance analysis. Figure A.7 presents the DRIFT spectra of each (i.e.

  1.1 Evolution of the propylene demand for chemicals between 1970 and 2004 2

					Others
	1970			Acrylonitryle	6%
	21% Others	17% Polypropylene		Cumene	10%
				3%
				Isopropyl
	11% Acrylonitryle		Propylene oxide 13%	alcohol Butyraldehydes 3%
				7%
					Polypropylene
				Propylene	64%
	9% Cumene	18% Isopropyl alcohol	Butyraldehydes 11%	oxide 7%

  High oxidation state tungsten alkyldynes have been initially reported by Schrock in 1978 with the preparation of [W(≡C t Bu) Ta, etc) W alkyl complexes are prone to α-elimination causing in fine the rearrangement of the coordination sphere. In the present case, the Wcarbyne species is the sole product while [W(CH 2 tBu) 6 ] cannot be observed. Hence, this suggests that the electron-deficient tungsten atom undergoes two eliminations by forming 'agostic' bonds with hydrogens in the α-positions; at the beginning, by one neopentyl ligand, and following elimination of one neopentane, on the corresponding the alkylidyne complex formed. of neopentane or ii) by σ-bond metathesis between O-H bond of a surface silanol and W-C bond of a neopentyl ligand. Scheme 1.11 Different structures proposed for surface species obtained by grafting [W(≡C t Bu)(CH 2

			3 Me 3 SiOMe		6 t BuCH 2 MgCl
		WCl 6	Filtration	WCl 3 (OMe) 3	Filtration	t Bu	W	t Bu
			Crystallization		Sublimation
						35-45% Overall yield
	(CH 2	t Bu) 3 ] .
		The first significant advance in the area of W-based SOMC was the synthesis and
	the characterization of [(≡SiO)W(≡C t Bu)(CH 2 Regardless the silica employed, the metal, assumed to keep its (VI) oxidation state, t Bu) 2 ]. The results obtained were later
	transposed to silica/alumina and alumina. is coordinated to four ligands with one neopentylidene moities. The three remaining
	To obtain [(≡SiO)W(≡C t Bu)(CH 2 ligands depend on the silica employed with the SiO 2-(200) being bipodal (I) and the SiO 2-t Bu) 2 ], the W precursor is reacted with silica to re-
	sult in at least one of the neopentyl group being displaced by the silanol moieties. Al-(700) monopodal (II) with the neopentyl ligands filling (Scheme 1.11).
	CONFIDENTIAL LCOMS-UOP LCC

126

Due, in part, to their high reactivity, a rich chemistry has since been elaborated.

127,128

Schrock has developed latter [W(≡C t Bu)(O t Bu) 3 ], which is the most extensively used catalyst in alkyne metathesis. Nevertheless, a recurring problem hindering these systems is the rapid deactivation that can occur by the mean of either formation of W-metallacyclopentadienyl or through a bimolecular dimerization resulting to a W≡W triple bond.

129,130

The heterogenisation of W-carbyne species can be suggested in response of the latter (vide supra). though different synthetic methods are available, the most efficient preparation of [W(≡C t Bu)(CH 2 t Bu) 3 ] begins with displacing three chlorines in WCl 6 to afford [W(OMe) 3 Cl 3 ] that is then alkylated by t BuCH 2 MgCl (Scheme 1.10). 131 As with other Chapter 1 33 CONFIDENTIAL LCOMS-UOP LCC highly electrophilic metals (e.g. 127 Scheme 1.10 Synthesis of [W(≡C t Bu)(CH 2 t Bu) 3 ] Weiss et al. initially completed the grafting on silica of [W(≡C t Bu)(CH 2 t Bu) 3 ] but wrongly recognized a W-carbene surface species, [(≡SiO)W(=CH t Bu)(CH 2 t Bu) 3 ] of the Schrock-type resulting from the carbyne ligand with silanol of silica. 132 Since, this reaction have been reproduced in the laboratory with both SiO 2-(200) and SiO 2-(700) , to afford two species I and II , respectively.

133

At that stage, the identification of the ligands nature (carbene vs carbyne) was inconclusive. Submitting

13

C enriched I and II to

13

C SSNMR, 2D 1 H-

13

C HETCOR and J resolved 2D SSNMR undoubtedly disproved the presence of carbyne while confirming that of a neopentylidyne and neopentyl ligands. In the

13

C spectra, two signals at 95 ppm and 318 ppm, can be attributed to the methylene of a neopentyl, and to the carbyne of a neopentylidene, respectively. Besides, the J-resolved 2D SSNMR spectra of I and II, contains a triplet (CH 2 t Bu, 1 J C-H = 110 Hz) at 95 ppm assigned to the methylene carbon of the neopentyl fragment but no signal consistent with a carbene moieties. The low 1 J CH value for the methylene is indicative of a weak agostic interaction of these protons with the metal center.

The mechanism of the grafting has not been fully demonstrated, indeed it can occurs either i) by reaction of the carbyne ligand with silanol followed by α-H abstraction with t Bu t Bu evolution t Bu) 3 ] on oxides On silica-alumina dehydroxylated at 500°C (SiAl (500) ), [W(≡C t Bu)(CH 2 t Bu) 3 ] reacts with OH groups to give selectively a monografted [(≡SiO)W(≡C t Bu)(CH 2 t Bu) 2 ] (III). Moreover, the 1 H and 13 C solid-state NMR spectra of this solid display the same signals as those observed for (II). 134 The alumina equivalent [(Al s O)W(≡CtBu)(CH 2 tBu) 2 ] (IV) can be obtained by treatment of γ-alumina dehydroxylated at 500°C by [W(≡C t Bu)(CH 2 t Bu) 3 ]. Due to the more complicated surface of alumina (vide supra), understanding the structure of IV required to confront extensive characterizations (mass balance analysis, IR spectroscopy, NMR spectroscopy and EXAFS) and density functional theory calculations. The evolution of 1 equiv of t BuCH 3 per grafted W and the disappearance of the highest ν(OH) band, while the lowest are let unreacted, suggest that IV is a monopodal species mostly coordinated to a tetrahedral aluminum. It should be noted that this selectivity of grafting is specific to [W(≡C t Bu)(CH 2 t Bu) 3 ]. In contrast, the grafting of [Zr(CH 2 t Bu) 4 ] on similar alumina consumes all present isolated hydroxyl and gives {[(AlsO) 2 Zr(CH 2 t Bu)] + [( t BuCH 2 )(Als)] -}, a

  Bu)(CH 2 -t Bu)(OAr) 2 ] (Ar = 2,6-i Pr 2 C 6 H 3 ) was prepared by a similar pathway as that used for the preparation of [W(≡C t Bu)(CH 2 t Bu) 3 ]: WCl 6 is derivatised to produce W(OAr) 3 Cl 3 that is then alkylated by 4 equivalent t BuCH 2 MgCl to lead to the target. 137 [W(≡C-t Bu)(CH 2 -t Bu)(OAr) 2 ] was grafted on SiO 2-(700) to lead to V. All characterisa-

	tions: IR spectroscopy, solid-state NMR spectroscopy ( 1 H SSNMR, 13 C CP-MAS) and
	mass balance analysis were consistent with a monopodal [(≡Si-O)W(≡C-t Bu(OAr) 2 ]
	(Scheme 1.13).
		Al O O O t Bu x	O W t Bu O	t Bu Al O x O O H	t Bu O O Al x O	O W	t Bu Al O x O O O H
	Scheme 1.12 Interactions proposed by Joubert et al. to explain the complexity of 13 CP-MAS NMR spectrum of
	[W(≡C t Bu)(CH 2	t Bu) 3 ] grafted on alumina 79

The preparation of tungsten-based complexes by SOMC related to I and II was undertaken by replacing the neopentyl ligands with spectator aryloxy groups. Related soluble analogues have been reported by Schrock with the view to examine the modification caused to the steric and electronic parameters of the metal centre. A precursor [W(≡C-t Bu CONFIDENTIAL LCOMS-UOP LCC t Scheme 1.13 Proposed structure for the surface species V, obtained by grafting of [W(≡C-t Bu)(CH 2 -t Bu)(OAr) 2 ] on SiO 2-(700)

  1 J CH = 107 Hz for J-

	resolved 2D 1 H-13 C HETCOR solid-state NMR spectrum of the 13 C labeled silica grafted
	compound).
		The structural assignment for VI is also supported by the EXAFS data, which are in
	agreement with a W atom bound to one nitrogen at 1.734(7) Å, a bond length consistent
	with an imido ligand, two carbons at 1.873 and 2.16(2) Å, consistent with neopen-
	tylidene and neopentyl ligands, respectively, and one oxygen at 1.95(3) Å, consistent with
	a siloxy substituent. Moreover, an oxygen atom from a siloxane bridge is close enough
	(CH 2	t Bu)(2,5-Me 2 NC 4 H 2 )

(i.e. 2.

43

(1) Å) to the metal for allowing interaction. Scheme 1.14 Structures proposed for surface species VII and VIII More recently the replacement of the pending alkyl by amido ligands, (2,5-Me 2 NC 4 H 2 ), which is readily achieved by grafting bis(amido) complexe on silica

([W≡N(2,6-i PrC 6 H 3 )(=CH t Bu)(2,5-Me 2 NC 4 H 2 ) 2 ]

) has been reported. The grafting of 2,5dimethylpyrrolyl compounds is more complex yielding the expected monosiloxy alkylidene surface complex as the major products, [(≡SiO)W(≡NAr)(=CH t Bu)(2,5-Me 2 NC 4 H 2 )] VIIa, along with a surface complex resulting from the protonation of the alkylidene ligand in place of the silanolysis of the W-N bond, [(≡SiO)W(≡NAr) 2 ] VIIb.

Chapter 2 Characterizations of the tungsten hydride supported catalyst 1. Introduction ........................................................................................................................61 2. Results and discussions ......................................................................................................63 2.1. Characterizations of the catalyst support ...............................................................................

  3 /SiO 2 and tungsten hydride supported on alumina. A deep structure-reactivity relationship study confirms the mechanism and the deactivation pathway presented in Chapter 3. Preparation ........................................................................................................................................... • Influence of the pretreatment temperature on the of Al 2 O 3 (RP) properties........................................

		Chapter 1 57
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	CONFIDENTIAL LCOMS-UOP LCC CONFIDENTIAL LCOMS-UOP LCC CONFIDENTIAL LCOMS-UOP LCC	CONFIDENTIAL LCOMS-UOP LCC

•

2.2. Characterizations of the [W(≡ ≡C t Bu)(CH 2 t Bu) 3 ] supported on Al 2 O 3-(500) (RP) .................... 2

  .2.1. IR spectroscopy .................................................................................................................... 2.2.2. Mass balance analysis........................................................................................................... 2.2.3. Solid-state NMR spectroscopy ............................................................................................. 2.2.4. 100% 13C labeled NMR ......................................................................................................

2.3. Characterizations of the tungsten hydride on Al 2 O 3-(500) (RP) .............................................. 2

  .3.1. Preparation............................................................................................................................ 2.3.2. IR Spectroscopy.................................................................................................................... 2.3.3. D 2 exchange.......................................................................................................................... 2.3.4. Theoretical calculations........................................................................................................ 2.3.5. RAMAN spectroscopy ......................................................................................................... 2.3.6. 1 H NMR and 1 H NMR spetroscopy after D2 exchange........................................................ 2.3.7. Multiple Quanta NMR Spectroscopy ................................................................................... 2.3.8. Steoichiometric reactivity with methane .............................................................................. 2.3.9. Transmission Electron Microscopy (TEM).......................................................................... 2.3.10. Extended X-Ray Adsorption Fine Structure Spectroscopy (EXAFS)................................

  Marks et al. have reported the reactivity of [Cp*TaMe 4 ] with the surface of dehydroxylated γ-Al 2 O 3 . 9 In that case also, the transfer of a methyl group on Lewis acidic site to form cationic species [Cp*TaMe 3 ] + [MeAl s ] -, via pathways analog to those established for group IV organometallic and actinides complex, has been evidenced. Group IV and group V organometallic complexes react with dehydroxylated Al 2 O 3 to form cationic species. One can wonder if group VI complex, i.e. [W(≡C t Bu)(CH 2 t Bu) 3 ], 1, react toward γ-Al 2 O 3-(500) to give cationic species? Joubert et al. have evidenced using DFT approach, that this reaction give selectively a monografted neutral surface complex [(Al s O)W(≡C t Bu)(CH 2 t Bu) 2 ]. The calculation show that the reaction between 1 and sur-

2-4, 6-9 Recently Delgado et al. have described the reactivity of hafnium complex, [Hf(CH 2 t Bu) 4 ], with γ-Al 2 O 3-(500) . 10 This reaction provides several surface species: a neutral monoaluminoxy, [(Al s O)Hf(CH 2 t Bu) 3 ], a neutral bisaluminoxy [(Al s O) 2 Hf(CH 2 t Bu) 2 ] and a cationic bisaluminoxy [(Al s O)(Al s O)(Al-O-Al)]Hf(CH 2 t Bu)] + [ t BuCH 2 Al s ] -species. The cationic species is formed by transfer of a neopentyl fragment on Lewis acidic site of alumina giving t BuCH 2 Al s . The treatment of these species under H 2 at 150°C provides a mixture of a neutral, [(Al s O) 3 HfH], and a cationic mono hafnium hydride, [(AlsO)(AlsO)Hf(H)] + [(CH 2 t Bu)Al s ] -. In this study, theoretical calculations were very helpful to interpret the spectroscopic characterizations of all these species. These catalysts CONFIDENTIAL LCOMS-UOP LCC have shown high activity, without co-catalyst, for olefin polymerization, due to the cationic species present at the surface. face hydroxyl, is less exothermic and has a considerably higher activation barrier than the one of [Zr(CH 2 t Bu) 4 ], which chemisorption on Al 2 O 3-(500) afford mainly cationic species (Scheme 2.1). The authors claim that the transfer of an alkyl group onto adjacent aluminum centre is disfavored, and hence cationic species are not formed. They interpret the complexity of the experimental NMR and IR data

  1

		t Bu
						t Bu
	Al O O O x	O Zr O	Al O	O O	Al O x	O

x O Chapter 2 63 CONFIDENTIAL LCOMS-UOP LCC Scheme 2.2 Interaction between surface hydroxyl and [(Al s O)W(≡C t Bu)(CH 2 t Bu) 2 ] surface complex proposed by Joubert et al.

Table 2 .

 2 1 Surface OH density for Al 2 O 3 (RP) dehydroxylated at 300°C, 400°C, 500°C and 800°C determined by 1 H NMR.

	Al 2 O 3 dehydroxylation temperature (°C) 300	400 500	800
	OH density (μmol.g -1 ) ±10%	1300 1200 660	21

Table 2 .

 2 2 B.E.T. measurement for Al 2 O 3 (RP) dehydroxylated at 300°C, 400°C, 500°C and 800°C

	Al 2 O 3 dehydroxylation temperature (°C) 300	400	500	800
	Specific surface (m 2 .g -1 ) ±10%	203	205	200	195

  [W(≡C t Bu)(CH 2 t Bu) 3 ] (311 mg, 660 μmol) and Al 2 O 3-(500) (RP) (2 g) was stirred at 66 °C for 4 h under argon atmosphere. All volatile compounds were condensed into another reactor (of known volume) in order to quantify neopentane evolved during the grafting. Pentane (10 mL) was introduced into the reactor by distillation, and the solid was washed three times with pentane via filtration-condensation cycles. After evaporation of the solvent, the resulting brown powder was dried under vacuum.Elemental analysis shows the presence of W to the extent of 5.5% wt , which corresponds to 289 μmol W .g -1 , confirming that a partial consumption of surface hydroxyls (46%, of the 660 μmol W .g -1 on Al 2 O 3-(500) (RP)). Moreover, 14.5 C/W are found by ele-

			t Bu 2.2.2. Mass balance analysis
	A mixture of 1,		t Bu		t Bu		t Bu	t Bu
					O	H		O	W		+ t BuCH 3
						s		[Al]	s
		4										0.6
	Absorbance	1 2 3	a) b)								Absorbance	-0.2 0 0.2 0.4	3733 cm -1 3775 cm -1 3650 cm -1 3795 cm -1
		0 4000	3500	3000	2500	2000	1500				-0.4	3800	3700	3600	3500
					Wavenumber (cm -1 )						Wavenumber (cm -1 )
	CONFIDENTIAL LCOMS-UOP LCC

Al] W t Bu t Bu mental analysis. And during grafting 327 μmol tBuCH3 .g -1 have evolved, which correspond to 1.1 t BuCH 3 /W. Upon treatment of 1/Al 2 O 3-(500) (RP) with an exess of H 2 at 150°C for 15h, the evolution of a mixture of methane and ethane (ca. 20:1) corresponding to 670 μmol tBuCH3 .g -1 and 2.3 t BuCH 3 per grafted tungsten are observed. Elemental analysis after hydrogenolysis shows the presence of 2.5 carbons per grafted tungsten, showing that ca. 0.5 neopentyl per grafted tungsten remains at the surface of the material. This remaining neopentyl fragment was confirmed by hydrolysis experiments.

  CONFIDENTIAL LCOMS-UOP LCC Nonetheless, several species are possibly present as evidenced by the broadness of the resonance at 316 ppm. Several peaks around 103 ppm are attributed to different types of methylene carbon (CH 2

										Chapter 2 73
	* CO 2	(2) hydrolysis (1) tBuMgCl/ Et2O	tBu	C O *	OH		LiAlH 4 Et 2 O	yield 80% tBu*CH 2 OH
	tBu*CH 2 OH	Vielsmeier reagent DMF / reflux 20 h	tBu*CH 2 Cl	Mg, Et 2 O/THF 12 h at 110 °C	tBu*CH 2 MgCl
					yield 65%			yield 44%
										tBu
	WCl 3 (OMe) 3	+	6 tBu*CH 2 MgCl		Et 2 O 12 h at 25	°C	tBu	*	W *	tBu * *
										tBu

Table 2 .

 2

	3 EXAFS data for WH/Al 2 O 3-(500) (RP) errors between parentheses; fit residue: ρ = 6.0 %
	Type of neighbour Number of neighbours Distance (Å) σ 2 (Å 2 )
	W=O	0.5(2)	1.74(3)	0.001(1)
	W-O	0.6(2)	1.87(3)	0.001(1)
	W-C	1.1(6)	2.16(3)	0.006(4)
	W--O	1.0(3)	2.72(2)	0.002(1)
	W--O	1.8(13)	3.17(9)	0.04(4)
	2.4. Conclusion
	The grafting of [W(≡C t Bu)(CH 2	t Bu) 3 ], 1, on Al 2 O 3-(500) (RP) leads to 1/Al 2 O 3-(500) (RP),

-CH 2 t Bu counterparts

2 O 3-(500) (RP) under H 2 at 150°C afford WH/Al 2 O 3-(500) (RP)

with evolution of a methane:ethane mixture corresponding to 2.5 Np/W and letting 0.5

Np/W at the surface. The characterizations and calculations made on this product prove the presence of different surface species (Scheme 2.12). Indeed, a neutral tungsten oxo tris-hydride is formed from 1a. The opening of strained aluminoxane bridges during the treatment at 150°C or the activation of H 2 on default of alumina surface may also creates surface Al-H. The cationic species 1b is hydrogenated at 150°C but its anionic Alis conserved during this treatment. The complexity of the system as not allowed a rigorous determination of the relative amount of each species. A complete study using DFT calculation is necessary to completely solve such a complex systems, the presence of a cationic species. Scheme 2.12 Proposed surface species of WH/Al 2 O 3-(500) (RP)

  , and isotopic labeled CO 2 (99%13 C, Cambridge Isotope Laboratories, Inc.) were used as received. Methane (N50, Air liquide), H 2 and D 2 (N30, Air liquide) were purified over R3-11 BASF/MS4Å catalysts. Pyridine (Aldrich, 99%) was dried on solid KOH and distilled under argon, degassed and stored over 3Å molecular sieves. Aqueous solution of HCl and H 2 SO 4 were prepared from a concentrated HCl solution (37 %wt, Aldrich) and H 2 SO 4 solution (36 %wt, Aldrich) respectively. t BuCH 2 MgCl or 99% 13 C-labeled t Bu*CH 2 MgCl was prepared from t BuCH 2 Cl (98 %, Aldrich, used as received)

	stored under argon)or 99% 13 C-labeled t Bu*CH 2 (synthesis is described in detail below) respectively and Mg
	turnings (Lancaster) using 1,2-dibromoethane as activator. Concentration of the resulting
	solution was titrated using benzyl alcohol solution in p-xylene and 2-2'-biquinoline as in-
	dicator. [W(≡C t Bu)(CH 2	t Bu) 3 ], 1, was prepared according literature procedures. 44,45 99%
			H							H						H						H
		H			H				H			H			H			H			H			H
			W						W					W					W
		O			O				O			O			O			O			O			O
	O	Al O x	O	O	Al O x	O	O	Al O x	O	O	Al O x	O	O	Al O x	O	O	Al O x	O	O	Al O x	O	O	Al O x	O
						H										H						H
					H			H						H			H			H		H
						W										W						W
															Neutral
	CONFIDENTIAL LCOMS-UOP LCC

1,2-dibromoethane (99%, Aldrich), benzyl alcohol (99%, Aldrich), p-xylene (99%, Aldrich), 2-2'-biquinoline (98%, Lancaster), t BuMgCl (2M solution in Et 2 O, Aldrich), LiAlH 4 (95%, Aldrich, stored under argon), MgSO 4 (Laurylab), NaHCO 3 (Prolabo), Vielsmeier reagent (95%, Aldrich, 13 C-labeled [W(≡*C t Bu)(*CH 2 t Bu) 3 ], 1*, was prepared according the same procedures but using 99% 13 C-labeled t Bu*CH 2 MgCl as alkylation agent. Alumina E7102 from Rhone-Poulenc extrudates were crushed in a mortar and sieved (40-60 mesh). The resulting powder was calcinated at 500°C under dry air for 15h. It was then hydrated with a vapor pressure of degassed water at 100°C for 1h prior to treatment under high vacuum (10 -5 Torr) at the desired temperature, for 15h. Gas-phase analyses were performed on a Hewlett-Packard 5890 series II gas chromatograph equipped with a flame ionisation detector and an Al 2 O 3 /KCl on fused silica column (50 m X 0.32 mm). Elemental analyses were performed at the CNRS Central Analysis Department of Solaize (metal analysis) or in the LSEO (Dijon, for C, H analysis). IR spectra were recorded on a Nicolet 5700 FT-IR spec-

Synthesis of 99% 13 C-labeled t Bu*CH 2 Cl

  CH 3 ) 3 C*COOH) 1.17 (9 H, d,3 J CH = 4.4 Hz, (CH 3 ) 3 C*COOH);13 C{ 1 H} NMR (δ, 295 K, CD 2 Cl 2 , 75 MHz) 185.2 (s, (CH 3 ) 3 C*COOH) 38.4 (d, 2 J CC = 55.8 Hz, (CH 3 ) 3 C*COOH) 26.9 (s, (CH 3 ) 3 C*COOH) This t Bu*COOH solution in Et 2 O (85 mmol in Et 2 O at 0.9M) was added dropwise to a suspension of LiAlH 4 (6.5 g, 170 mmol) in Et 2 O (100 mL) at 0°C over 2 h while stirring. After addition the solution was slowly warmed to RT before being hydrolyzed with aqueous HCl solution at 0°C. The aqueous phase is then extracted 3 times with Et 2 O. The organic phases are added, dried over MgSO 4 and concentrated. The concentration of the solution of t Bu*CH 2 OH in Et 2 O is determined by 1 H NMR, confirming a quantitative yield of the reaction. 1 H NMR (δ, 295 K, CD 2 Cl 2 , 300 MHz) 3.22 (2 H, d, 1 J CH = 140 Hz, (CH 3 ) 3 C*CH 2 OH) 2.09 (1 H, s, (CH 3 ) 3 C*CH 2 OH) 0.84 (9 H, d, 3 J CH = 4.8 Hz, (CH 3 ) 3 C*CH 2 OH); 13 C{ 1 H} NMR (δ, 295 K, CD 2 Cl 2 , 75 MHz) 73.3 (s, (CH 3 ) 3 C*CH 2 OH) 32.4 (d, 2 J CC = 37.7 Hz, (CH 3 ) 3 C*CH 2 OH) 26.0 (s, (CH 3 ) 3 C*CH 2 OH) A part of the resulting t Bu*CH 2 OH solution (55 mmol in Et 2 O at 5M)

	99% 13 C-labeled *CO 2 (2 L, 85 mmol) was added in a 1L round bottom flask to t BuMgCl
	(85 mmol) in frozen Et 2 O (200 mL) by trapping using liquid N 2 bath. Acetone was added
	slowly to the liquid N 2 bath until the reaction media reach -77°C. After 1 h under constant
	stirring the solution was slowly warmed to RT while continuing stirring. The reaction me-
	dia is hydrolyzed at -20°C using aqueous H 2 SO 4 solution. The aqueous phase is then ex-

18 mm self-supporting pellet, adjusted in a sample holder, and introduced into a glass (quartz) reactor equipped with CaF 2 windows. The supports were calcined under air at 500°C, hydrated with a vapor pressure of degassed water at 100°C for 1h prior to treatment at the desired temperature. Under static vacuum, pyridine was adsorbed on Al 2 O 3-(300) , Al 2 O 3-(300) and Al 2 O 3-(800) at room temperature. The reactor was then put under dynamic vacuum and heated to 100°C. IR spectrum was recorded after 2 hours.

3.3. tracted 3 times with Et 2 O. The organic phases are added, dried over MgSO 4 and concentrated. The concentration of the solution of t Bu*COOH in Et 2 O is determined by 1 H NMR, confirming a quantitative yield of the reaction. 1 H NMR (δ, 295 K, CD 2 Cl 2 , 300 MHz) CONFIDENTIAL LCOMS-UOP LCC 10.71 (1 H, s, (was diluted with DMF (10 mL) and added dropwise to a solution of Vilsmeier reagent [ClCH=N(CH 3 ) 2 ] (7.5 g, 55 mmol) in DMF (10 mL) over 1 h while stirring. After addition the solution was refluxed overnight. The product was purified by distillation affording 3.9 g of t Bu*CH 2 (65% yield). 1 H NMR (δ, 295 K, CD 2 Cl 2 , 300 MHz) 3.22 (2 H, d, 1 J CH = 150 Hz, (CH 3 ) 3 C*CH 2 Cl) 0.90 (9 H, d, 3 J CH = 4.6 Hz, (CH 3 ) 3 C*CH 2 Cl) 13 C{ 1 H} NMR (δ, 295 K, CD 2 Cl 2 , 75 MHz) 57.3 (s, (CH 3 ) 3 C*CH 2 Cl) 36.6 (s, (CH 3 ) 3 C*CH 2 Cl) 27.1 (s, (CH 3 ) 3 C*CH 2 Cl)

3.8. Treatment of 1/Al 2 O 3-(500) (RP) under H 2 2g of 1/Al 2 O 3-(500) (RP) was

  heated at 150 °C in the presence of a large excess of anhy-

	drous H 2 (550 torr) to afford WH/Al 2 O 3-(500) (RP). After 15 h, the gaseous products were
	quantified by GC: mixture of methane and ethane (ca. 20:1) corresponding to 1340 μmol
	of t BuCH 3 . Elemental analysis W: 5.5% wt , C: 0.9% wt
	3.9. Reaction of WH/Al 2 O 3-(500) (RP) with D 2
	An excess of D 2 (600 Torr, 460 equiv.) was added at room temperature to 200 mg of
	WH/Al 2 O 3-(500) (RP). After a 1 h treatment at 80°C the reactor was evacuated. 150 mg of
	the resulting material, WD/Al 2 O 3-(500) (RP), was collected in the glove box for DRIFT and
	NMR characterizations. The remaining material was then treated 1h with an excess of H 2
	at 80°C. The resulting material was analyzed by DRIFT spectroscopy.

3.10. Hydrolysis of WH/Al 2 O 3-(500) (RP)

100 mg of WH/Al 2 O 3-(500) (RP) was treated with an excess of H 2 O in gas phase (17 Torr).

After 1 hour the gaseous products were quantified by GC. The main hydrolysis product is neopentane (15 μmol).

3.11.

Activation of methane on WH/Al 2 O 3-(500) (RP) in continuous flow reactor

	and subsection 2.1 in Chapter 2
	4. Reference and Notes
	(1) Basset, J. -M.; Psaro, R.; Roberto, D.; and Ugo, R. Modern surface organometallic chemistry, Basset, J.
	-M.; Psaro, R.; Roberto, D.; and Ugo, R., Ed.; Wiley-VCH ; 2009.
	(2) Tullock, C. W.; Mulhaupt, R.; and Ittel, S. D. Die Makromolekulare Chemie, Rapid Communications.
	1989, 10, 19-23.

In a glove box, WH/Al 2 O 3-(500) (RP) (375 mg; 5.5 wt% W) was loaded into a stainless steel half inch cylinder fixed-bed reactor. Methane was passed at 3 mL.min -1 over the catalyst bed at 50 barg starting from 25°C to 350°C. Hydrocarbon products and hydrogen were analyzed online by GC (HP 8890 chromatograph fitted with an Al 2 O 3 /KCl 50 m x 0.32 mm capillary column, FID detector for hydrocarbons with a 3-m molecular sieve column and a catharometer for hydrogen). See description of the reactor in Appendix B (3) Tullock, C. W.; Tebbe, F. N.; Mulhaupt, R.; Ovenall, D. W.; Setterquist, R. A.; and Ittel, S. D. Journal of Polymer Science Part A: Polymer Chemistry. 1989, 27, 3063-3081. (4) Collette, J. W.; Tullock, C. W.; MacDonald, R. N.; Buck, W. H.; Su, A. C. L.; Harrell, J. R.; Mulhaupt, R.; and Anderson, B. C. Macromolecules. 1989, 22, 3851-3858.

Table 3 .

 3 1 Conditions for the four experimental runs, Pressure: 1 Bar, Temperature: 150 °C

	Runs	1	2	3	4
	VHSV (h -1 )	463	928	1855	3800
	VHSV -1 (min)	0.130	0.065	0.032	0.016

  It is notable that whatever the time on stream, the global selectivity and butenes partial selectivity vs. VHSV -1 have the same profiles. Indeed, the mechanism of the conversion of ethylene to propylene stays the same regardless deactivation of the catalyst.

																Chapter 3 105
	space velocity.
																Time on stream:
																2 h
																5h
																15 h
																20 h
																30h
																46 h
			0	0.01	0.02	0.03	0.04	0.05	0.06	0.07	0.08	0.09	0.10	0.11	0.12	0.13	0.14
	Selectivity in ∑C 4= (%)	8 10 12 14 16							2 h 5h 15 h 20 h 30h 46 h Time on stream:	Selectivity in C 3= (%)	80 85 90				30h 20 h 15 h 5h 2 h 46 h Time on stream:
		6	0 0.02 0.04 0.06 0.08 0.10 0.12 0.14				0 0.02 0.04 0.06 0.08 0.10 0.12 0.14
					VHSV -1 (min)								VHSV -1 (min)
														CONFIDENTIAL LCOMS-UOP LCC

Figure 3.8

Relative selectivity of 1-butene, trans-2-butene, cis-2-butene and iso-butene at 150°C at 46 h on stream vs. inverse space velocity (the values for other time on steam have been omitted for clarity)

  -butene in the ethylene feed, selectivity in pentenes, produced by crossmetathesis between 1-butene and butene-2 and in hexenes, produced by self-metathesis of 1-butene, remains constant. It shows a fast isomerization of 1-butene to 2-butene. It confirms that ethylene dimerization is the rate determining step of the mechanism.

														Chapter 3 107
	15% of 1
	35
	30
	25
	20
	15
	10
	5
	66	68	70	72	74	76	78	80	82	84	86	88	90	92
							Time on stream (h)
										CONFIDENTIAL LCOMS-UOP LCC

/Al 2 O 3-(500) and reaches

  only 167 after 15 h on stream. The selectivity at 15 h is 75 % in propylene, 17 % in butenes and 8 % in heavier olefins.

	WH/SiAl (500) reveals a conversion rate lower than WH/Al 2 O 3-(500) even if its deacti-
	vation profile is similar. The maximum of conversion is ca. 27 % at 1.5 h on stream, and
	ca. 4 % at 15 h on stream. The cumulated T.O.N. is 100 at 15 h while the selectivity at
	15 h is 89 % in propylene, 6 % in butenes and 5 % in heavier olefins.

The cumulated T.O.N. is 230 at 15 h while the selectivity at 15 h is 92 % in propylene, 6 % in butenes and 2 % in heavier olefins.

Regarding the WH/Pural (500) ; it is noteworthy that, the conversion profile is drastically different than the conversion profile of the Al 2 O 3 supported species. In the beginning of catalysis, the conversion of ethylene rises extremely rapidly, reaching a maximum superior to 80 % at 1 h on stream. At this maximum of conversion the selectivity in propylene has already reached 75% and stays constant with time on stream. Nevertheless, after this maximum, the conversion drops with the same velocity sinking to 14 % in 2 hours on stream. After 15 h on stream, this Pural supported hydride shows the lowest conversion rate, with 3 %. As the initial conversion is very high, the cumulated T.O.N. for this species is the highest for the 6 first hours, then, it is outclassed by the WHIt is interesting that for both of these Silica-alumina and Pural supported catalyst the selectivity in propylene is lower, and that formation of higher olefins is favoured. Regarding the tri-functional mechanism (ie. dimerization, isomerization and metathesis) this can Chapter 3 109 CONFIDENTIAL LCOMS-UOP LCC be explain that the ratio of the metathesis rate to dimerization rate is lower for WH/Pural (500) and WH/SiAl (500) than for WH/

Al 2 O 3-(500

  ) . Moreover, these two catalysts deactivates faster than the Al 2 O 3 supported one.

.132 2.1. Preparation and characterizations of Al i Bu/Al 2 O 3-(500)

  Choice of the support and precursor................................................................................... 2.1.2. Reactivity of Al( i Bu) 3 toward Al 2 O 3-(500) ............................................................................ 2.1.3. NMR characterizations....................................................................................................... 2.1.4. Mass balance analysis......................................................................................................... Al 2 O 3-(500) under vacuum............................................................................ 2.2.2. Treatment of 2/Al 2 O 3-(500) under H 2 .................................................................................... 2.2.3. NMR characterizations....................................................................................................... 2

	2.2. Preparation and characterizations of AlH/Al 2 O 3-(500) ..........................................................
	2.2.1. Treatment of 2/

1. Introduction ......................................................................................................................131 2. Results and discussions ........................................................................................................................................................... 2.1.1.

.3. Catalytic activity of 2/Al 2 O 3-(500) and AlH/Al 2 O 3-(500)

............................................................ 2.3.1. Catalytic activity of 2/Al 2 O 3-(500) and AlH/Al 2 O 3-(500) in ethylene to propylene conditions • 2/Al 2 O 3-(500) ........................................................................................................................................ • AlH/Al 2 O 3-(500) ................................................................................................................................... • Conclusion ......................................................................................................................................... 2.3.2. Catalytic activity of AlH/Al 2 O 3-(500) for ethylene polymerization ...................................... 2.3.3. Catalytic activity of AlH/Al 2 O 3-(500) for ethylene hydrogenation........................................

  (AlO-H) region (Figure4.1). Thus, the grafting proceeds on all types of AlOH groups, without distinction, in contrast for instance to [W(≡C t Bu)(CH 2 t Bu) 3 ], 1, which mostly reacts with hydroxyls on tetrahedral aluminum (see chapter 2 and reference10

	Chapter 4 133
	This is confirmed by infrared spectroscopy. The spectrum of 2/Al 2 O 3-(500) is almost
	devoid of bands in the ν
	200°C
	Scheme 4.1 Formation of diisobutyl aluminum hydride from 2 12 2.1.2. Reactivity of Al( i Bu) 3 toward Al 2 O 3-(500) Al2O3-500 reacts smoothly at room temperature with a pentane solution of Al( Al H + Al β-hydride H elimination
	CONFIDENTIAL LCOMS-UOP LCC

i Bu) 3 , 2, to afford a surface-modified alumina bearing Al i Bu moieties, 2/Al 2 O 3-(500) .

/Al 2 O 3-(500) (

  , where Al VI -i Bu species were assumed to be present in much weaker proportion than the tetra-and pentacoordinated aluminum alkyl centers. In the Al VI case, the quadrupolar broadening is clearly reduced, indicating a comparatively more symmetrical environment. Interestingly, as the Al IV/V -H gives 1 H NMR signals in the [3.4-3.2] ppm range, the Al VI -H hydrides resonate at lower fields([3.6-3.4] ppm). The NMR characteristics for the identified types of hydrides are gathered in Figure4.10. 18.8T, at a spinning frequency of 20 kHz, evolution delay of 2 ms, number of transients of 768, relaxation delay of 1s, number of t 1 increments of 100).

						Chapter 4 143
	portion of Al VI -H is small in AlH/Al 2 O 3-(500) (estimated to be less than 10%), as in
	100 2/Al 2 O 3-(500) AlH/Al 2 O 3-(500) is the first example of material bearing isolated aluminum hydride 50 0 -2 8 6 4 2 0 δ( 27 Al) / ppm Al O O O H H-Al IV ( 1 H)= 3.4-3.2 ppm ( 27 Al)= 90-60 ppm CQ>15 MHz A l O O H O O H-Al V Al H O O O O O H-Al VI ( 1 H)= 3.6-3.4 ppm ( 27 Al)=20 ppm 10 CQ=8 MHz
	supported on Alumina, which was prepared by heterolytic splitting of H 2 on Al-C of sup-
	ported alkyl aluminum (Scheme 4.5).
			250°C to 400°C
			H 2 550 torr	H	H	H
	Al s	Al s	Al s	Al s	Al s	Al s
		2/Al 2 O 3-(500)			AlH/Al 2 O 3-(500)
	CONFIDENTIAL LCOMS-UOP LCC

27

Al dimension shows only those aluminum centers bearing hydride ligands. This spectrum confirms the major presence of highly distorted (i.e. with large C Q values) Al IV/V -H in AlH/Al 2 O 3-(500) . The narrow 1 H chemical shift range for the hydride signal prevents definitive conclusion regarding the absolute proportion of A lV in AlH/Al 2 O 3-(500) . The pro-

Figure 4.10 27 Al-1 H J-HMQC MAS NMR spectrum of AlHScheme 4.5 Treatment of 2/Al 2 O 3-(500) under H 2 at 400°C afford AlH/Al 2 O 3-(500) CONFIDENTIAL LCOMS-UOP LCC

Table 4 .

 4

	Run [a] T (°C)	Polymerization	Yield	Activity [b] M n	[c]	M w /M n T m (°C)	Cristalinity (%)
			time (h)	(mg PE )
	1	50	0.5	660	11.0	8.9	2.6	135	45
	2	50	1	1155	9.6	8.3	2.6	134	53
	3	50	4	3270	7.7	8.7	2.6	135	56
	4	100	0.5	1314	21.9	8.7	2.7	136	53
	5	150	0.5	953	15.8	7.4	3.0	137	53

1 Ethylene polymerization results for AlH/Al 2 O 3-(500)

[a] All polymerization experiments were conducted under 35 bar of ethylene, using 100 mg of AlH

/Al 2 O 3-(500)

  Average activity in kg PE .mol -1 (AlH) .h -1 calculated over the whole polymerization time. [c] Average molecular weight (x 10 5 g.mol -1 ) determined by HTSEC in 1,2,4-trichlorobenzene at 150 ˚C, measured with a relative calibration based on standard polystyrene. [d] Determined by DSC (second heating).

(1200 μmol (AlH) .g -1 ) in 20 mL of toluene;

[b]

AlH/Al 2 O 3-(500) have

  . These species are formed by heterolytic splitting of H 2 on Al-C bond of alkyl aluminum. The use of High field NMR, and particularly27 Al-1 H J-HMQC sequence, has proved the presence of aluminum hydride on all types of surface aluminum, with a large scalar coupling constant 1 J Al-H of 380 Hz and a 1 H chemical shift of 3.3 ppm.

													Chapter 4 149
	2.4. Conclusion
	In order to observe the role of alkyl aluminum and aluminum hydride present at the sur-
	face of WH/Al 2 O 3 , isolated alkyl aluminum, 2/Al 2 O 3-(500) , and isolated aluminum hydride,
	AlH/Al 2 O 3-(500) , supported on alumina have been prepared.
	Supported aluminum alkyl, 2/Al 2 O 3-(500) , was prepared by reaction between Al( i Bu) 3
	and the surface of Al 2 O 3-(500) . The isobutyl fragment is located on all types of surface alu-
	minum, i.e. tetra-penta-and hexa-coordinated. 2/Al 2 O 3-(500) has shown an activity in eth-
	ylene polymerization in continuous flow reactor at 150°C.
	Treatment of 2/Al 2 O 3-(500) under hydrogen afford the corresponding aluminum hy-
	drides, AlH/Al 2 O 3-(500)
	0	2	4	6	8	1 0	1 2	1 4	1 6	1 8	2 0	2 2	2 4
						Time on stream (h)
										CONFIDENTIAL LCOMS-UOP LCC

As 2/Al 2 O 3-(500) , AlH/Al 2 O 3-(500) has shown an activity in ethylene polymerization in continuous flow reactor in the same conditions that direct conversion of ethylene to propylene. The resulting polymers have a melting point of 135°C, whereas two melting point, i.e. 116 and 135°C, are observed for the polymers formed on WH/Al 2 O 3-(500) during the ethylene to propylene conversion. These results proves that alkyl aluminum and aluminum hydride are involved in the deactivation of WH/Al 2 O 3-(500) during direct conversion of ethylene to propylene, and that tungsten species may promote the formation of the polymers with a melting point of 116°C. been tested for ethylene polymerization at 35 bar with a maximum activity of 21.9 kg PE .mol -1

(AlH) .h -1 at 100°C.

Finally, it has been found that AlH

/Al 2 O 3-(500) was

  able to perform catalytically ethylene hydrogenation by double bond insertion in Al-H followed of H 2 heterolytic splitting over Al-C at high temperature (400°C).150 Well-defined aluminum alkyl and hydride grafted on γ-Al 2 O 3 -role in deactivation of WH/Al 2 O 3

CONFIDENTIAL LCOMS-UOP LCC 3.

Experimental section 3.1. General procedures

  All experiments were carried out under controlled atmosphere, using Schlenk and glovebox techniques for the organometallic synthesis. For the synthesis and treatments of the surface species, reactions were carried out using high-vacuum lines(10 -5 Torr) and glovebox techniques. Gas-phase analyses were performed on a Hewlett-Packard 5890 series II gas chromatograph equipped with a flame ionisation detector and an Al 2 O 3 /KCl on fused silica column (50 m X 0.32 mm). IR spectra were recorded on a Nicolet 6700 FT-IR spectrometer by using a DRIFT cell equipped with CaF 2 windows. The samples were prepared under Ar within a glove-box. Typically, 64 scans were accumulated for each spectrum (resolution 4 cm -1 ). Solution NMR spectra were recorded on an Avance-300 Bruker spectrometer. All chemical shifts were measured relative to residual 1 H or13 C resonance in the deuterated solvent: C 6 D 6 , d 7.15 ppm for 1 H, 128 ppm for13 C. Solid-state NMR spectra were acquired on a Avance II 800 spectrometers ( 1 H: 800.13 MHz, 13 C: 201.21 MHz). For

1

H experiments, the spinning frequency was 20 kHz, the recycle delay was 5 s and 16

Table 5 .

 5

	1 Experimental conditions
	Propylene flow rate (NmL.min -	20
	1 )
	Mass of catalyst (mg)	135
	Tungsten loading (% wt )	5.5
	Temperature (°C)	150
	R (mol C3=. .mol W	-1 .min -1 )	20
	P C3=

Table 5 .

 5

	2 Experimental conditions
	1-butene flow rate (NmL.min -1 )	20
	Mass of catalyst (mg)	135
	Tungsten loading (% wt )	5.5
	Temperature (°C)	150
	R (mol C4=. .mol W	-1 .min -1 )	20
	P C4=

Table 5 .

 5

3 Experimental conditions

Table 5 .

 5

	4 Experimental conditions
	Trans-2-butene flow rate (NmL.min -1 )	20
	Mass of catalyst (mg)	135
	Tungsten loading (% wt )	5.5
	Temperature (°C)	150
	R (mol C4=. .mol W	-1 .min -1 )	20
	P C4=

Table 5 .

 5

	5 Experimental conditions
	2-butene flow rate (NmL.min -1 )	20
	Mass of catalyst (mg)	135
	Tungsten loading (% wt )	5.5
	Temperature (°C)	150
	R (mol C4=. .mol W	-1 .min -1 )	20
	P C4= (barg)		20
	VHSV (h -1 )		5200

CONFIDENTIAL LCOMS-UOP LCC

Table 5 .

 5

	8 Experimental conditions
	Trans-2-butene flow rate (NmL.min -1 )	10
	Ethylene flow rate (NmL.min -1 )	10
	Mass of catalyst (mg)	135
	Tungsten loading (% wt )	5.5
	Temperature (°C)		150
	R (mol C4=+C2=. .mol W	-1 .min -1 )	20
	P C4=+C2=		atm. pres.
	VHSV

Table 5 .

 5

	9 Experimental conditions
	Total flow rate (NmL.min -1 )	20
	Mass of catalyst (mg)	135
	Tungsten loading (% wt )	5.5
	Temperature (°C)		150
	R (mol C4=+C2=. .mol W	-1 .min -1 )	20
	P C4 C4=+C2=.

Table 5 .

 5 10 Productivity of the different routes to propylene

	Reaction	Propylene selectivity (%)	Productivity at 20h on stream (mmol C3= .g cata -1 .h -1 )
	1-butene conversion	42.5	28.1
	Trans-2-butene conversion	52.1	26.9
	1-butene/trans-2-butene cross-metathesis	49.9	36.0
	Isobutene/trans-2-butene cross-metathesis	40.0	10.5
	Ethylene/trans-2-butene
	cross-metathesis	97.7	115.9
	(45% ethylene)
	Ethylene/trans-2-butene
	cross-metathesis	96.4	142.8
	(35% ethylene)

  ) .......................................................................................................................... • [W=N(2,6-i PrC 6 H 3 )(CH 2 t Bu) 2 (=CH t Bu)] (4)..................................................................................... Bu) 3 F] (5) .............................................................................................................• [W=O(CH 2 t Bu) 3 F] (6)........................................................................................................................ .2.1. Reactivity of [W=O(CH 2 t Bu) 4 ] (3) with Al 2 O 3-(500) ............................................................ • IR study.............................................................................................................................................. • Mass balance analysis ........................................................................................................................ • Conclusion ......................................................................................................................................... 2.2.2. Reactivity of [W=O(CH 2 t Bu) 4 ] (3) with SiO 2-(700) .............................................................. • DRIFT ................................................................................................................................................ • RAMAN............................................................................................................................................. • Mass balance analysis ........................................................................................................................ • Solid-state NMR study....................................................................................................................... • EXAFS............................................................................................................................................... • DFT Calculations ............................................................................................................................... • Thermal stability and carbene formation ........................................................................................... • Conclusion ......................................................................................................................................... 2.2.3. Reactivity of [W=N(2,6-i PrC 6 H 3 )(CH 2 t Bu) 2 (=CH t Bu)](4) with SiO 2-(700) .......................... 2.2.4. Reactivity of [W=N(C 6 H 5 )(CH 2 t Bu) 3 F](5) with SiO 2-(700) ................................................. IR Study ............................................................................................................................................. • Mass balance analysis ........................................................................................................................ • Conclusion ......................................................................................................................................... SiO 2-(700) ............................................................ IR study.............................................................................................................................................. • RAMAN............................................................................................................................................. • Mass balance analysis ........................................................................................................................ • Solid-state NMR study....................................................................................................................... • DFT calculations................................................................................................................................ • Using POSS as models of SiO 2 .......................................................................................................... • EXAFS............................................................................................................................................... • Thermal stability and carbene formation ........................................................................................... • Conclusion .........................................................................................................................................

	...
	2.1.1. Alkyls complexes: [W=O(CH 2 • [W=O(CH 2 t Bu) 4 ] (32.1.2. Fluorinated complexes: [W=N(C 6 H 5 )(CH 2 t Bu) 4 ] (3), [W=N(2,6-i PrC 6 H 3 )(CH 2 t Bu) 3 F] (5) and [W=O(CH 2 t Bu) 2 (=CH t Bu)] (4) ... t Bu) 3 F] (6)............ • [W=N(C 6 H 5 )(CH 2 t 2.2.5. Reactivity of [W=O(CH 2 t Bu) 3 F] (6) with

2.2. Grafting of

the molecular precursors and characterizations.............................................. 2• •

Reactivity of the organometallic precursors with oxides and characterizations

  3.2.1. Preparation of t BuCH 2 Na ................................................................................................... 3.2.2. Preparation of 3 .................................................................................................................. .2.4. Preparation and characterization of 6 ................................................................................. Method 1 ............................................................................................................................................ • Method 2 ............................................................................................................................................ ............... 3.3.1. Preparation and characterization of 3/Al 2 O 3-(500) ................................................................ 3.3.2. Preparation and characterization of 3/SiO 2-(700) .................................................................. 3.3.3. Preparation and characterization of 5/SiO 2-(700) .................................................................. 3.3.4. Monitoring the synthesis of 5/SiO 2-(700)D by IR spectroscopy. ........................................... 3.3.5. Preparation and characterization of 6/SiO 2-(700) .................................................................. DFT calculations ................................................................................................................

	Chapter 189
	3.3. 3.3.1. Preparation and characterization of 6/POSS......................................................................
	3.3.2.
	CONFIDENTIAL LCOMS-UOP LCC

3.2.3. Preparation and of 5............................................................................................................ 3•

  of the metal center may be strengthened and this may provide better metathesis catalysts. This structure-reactivity relationship strategy study will thus afford new catalysts and is expected to confirm the necessity of a carbene-hydride or carbene-alkyl sites for performing direct conversion of ethylene to propylene. Scheme 6.1 left: Expected isolated active sites of the WO 3 /SiO 2 metathesis catalyst; centre: template used for the preparation of model species; right: Expected active site of the WH/Al 2 O 3 ethylene to propylene catalyst.

	Chapter 6 191
	CONFIDENTIAL LCOMS-UOP LCC

icity

  BuCH 2 Na, was prepared, by analogy with (C 6 H 5 )CH 2 K,29,30 by transmetallation of t BuCH 2 Li 31 with t BuONa.NMR features indicate the presence of equivalent neopentyl moieties, with the

	Scheme 6.2 Synthesis of 3
	2.1.1. Alkyls complexes: [W=O(CH 2 [W=N(2,6-i PrC 6 H 3 )(CH 2 t Bu) 2 (=CH t Bu)] (4) t Bu) 4 ] (3),
	The Alkyls complexes, i.e. complexes that my afford model species with X = alky are pre-
	sented herein.
	• [W=O(CH 2	t Bu) 4 ] (3)
	The tungsten oxo-tetraalkyl complex [W=O(CH 2	t Bu) 4 ], 3, has not been reported yet even
	though Kress et al. reported the synthesis of [W=O(CH 2	t Bu) 3 (OCH 2	t Bu)] mistakenly at-
	tributed to 3 starting from [W=OCl 4 ]. 20,21 Thus a new route to the desired complex 3 was
	investigated. The reaction of [W=O(CH 2	t Bu) 3 Cl], prepared from [W 2 O 3 (CH 2	t Bu) 6 ], 24 with
	several alkylating agents was studied. Among ( t BuCH 2 ) 2 Mg dioxane, t BuCH 2 MgCl or
	t BuCH 2 Li, only unconventional t BuCH 2 Na afforded a tractable product, [W=O(CH 2	t Bu) 4 ],
	3, as a colourless, light-and highly moisture-sensitive oil in a 35% yield.
	The alkylating agent, t CONFIDENTIAL LCOMS-UOP LCC

  Bu)], 4, is known and several preparation methods, are described in the litterature.32,33 It was found that the most convenient method, in term of number of steps, yield and purification, was the following. The synthesis begins with the reaction of WOC1 4 with (2,6-i PrC 6 H 3 )NCO, followed by a first alkyla-

					Chapter 6 195
	W O Cl equatorial positions, while the axial sites are occupied by alkyl moieties (Figure 6.2)., t Bu t Bu t Bu W O O t Bu t Bu t Bu W O t Bu Pentane Pentane t Bu t Bu 1/2 1) Me 3 SiCl (2eq) 2) HCl/Et 2 O O t Bu t Bu which is consistent with equivalent neopentyl ligands on the NMR time scale at room t BuCH 2 Na W t Bu t Bu temperature.
					3
					35% yield
	Figure 6.2 DFT calculated structure of 3
		• [W=N(2,6-i PrC 6 H 3 )(CH 2	t Bu) 2 (=CH t Bu)] (4)
	[W=O(CH 2 The compound [W=N(2,6-i PrC 6 H 3 )(CH 2 t Bu) 3 Cl] t Bu) 2 (=CH t tion with three equivalent of neopentylmagnesiumchloride affording [W=N(2,6-i PrC 6 H 3 ) [W=O(CH 2 t Bu) 3 Cl]
	(CH 2	t Bu) 3 Cl] which is alkylated a second time using the more nucleophilic neopentyllith-
	ium to afford 4.
		[W=O(CH 2	t Bu) 4 ]	[W=O(CH 2	t Bu) 4 ]
	Scheme 6.3 Synthesis of 4
		2.1.2. Fluorinated complexes: [W=N(C 6 H 5 )(CH 2 (6)	t Bu) 3 F] (5) and [W=O(CH 2	t Bu) 3 F]
					CONFIDENTIAL LCOMS-UOP LCC

  PrC 6 H 3 ) (CH 2 t Bu) 3 F] described by Le Ny et al.34 Thus, 5 has been synthesized by reaction of WOC1 4 with C 5 H 5 NCO, followed by alkylation with neopentylmagnesiumchloride. The chlorine atom has been substituted by a fluorine using AgBF 4 (Scheme 6.4). Et 3 N was not efficient to fully remove BF 3 , it has only been fully removed by reaction with SiO 2-(700) , as11 B NMR gives no signal and elemental analysis did not spot the presence of boron. This

	method, in spite of its drastic impact of the reaction yield (31%), afford pure
	[W=N(2,6-i PrC 6 H 3 )(CH 2	t Bu) 3 F], 5, as a pale yellow solid.
	Scheme 6.4 Synthesis of 5

  F, spin ½, sepa-

									Chapter 6 197
	O	1)	N C O		N		1) AgBF 4		N	t Bu
	W Cl Cl Cl Cl	2) 3 eq. of t BuCH 2 MgCl	t Bu	W Cl	t Bu	2) (CH 3 CH 2 ) 3 N excess 3) treatment with SiO 2-(700)	t Bu	W F	t Bu
							CONFIDENTIAL LCOMS-UOP LCC

t Bu

  Hz) on the 1 H and13 C NMR spectra, respectively. As expected for this complex bering the more electronegative fluorine ligand both signal are shifted upfield in comparison with the chlorine ligand (vide supra). The quaternary carbon of the neopentyl moeties gives a singlet at 35.5 ppm whereas the terminal methyl groups give a singlet 1.26 ppm and 32.6

	O	AgBF 4	O	t Bu	N(C 2 H 5 ) 3 excess	O	t Bu
	5 Synthesis of 6 from [W=O(CH 2 An original method, was then applied, starting from the [W 2 O 3 (CH 2 t Bu) 3 Cl] the [W=O(CH 2 t Bu) 3 Cl] precursor, reducing the synthesis of 3 of one step (Scheme 6.6). t Bu) 6 ], which is Hence, during the reaction of two equivalent of AgBF 4 with [W 2 O 3 (CH 2 t Bu) 6 ], an Ag 2 O precipitate is observed. After removing the BF 3 moiety with an excess of triethylamine, [W=O(CH 2 t Bu) 3 F] (6) was obtained as a white solid in a 80% yield from the dimeric complex. Scheme 6.6 Synthesis of 6 from [W 2 O 3 (CH 2 t Bu) 6 ] NMR features of 6 (Figure 6.7) indicate the presence of equivalent neopentyl moie-ties, with the methylenic group giving rise to a doublet with satellites at 2.24 ppm ( 2 J W-H = 10.1 Hz, 3 J F-H = 8.6 Hz) and a doublet with satellites at 94.8 ppm ( 1 J W-C = 46.0 Hz; 3 J F-C = F t Bu t Bu W F t Bu t Bu BF 3 6 + AgCl + BF 3 N(C 2 H 5 ) 3 W Cl t Bu t Bu 6 6.3 W W O O t Bu t Bu W O t Bu t Bu W O F t Bu t Bu t Bu O t Bu N(C 2 H 5 ) 3 excess AgBF 4 1/2 W F t Bu t Bu + 1/2 Ag 2 O + BF 3 N(C 2 H 5 ) 3 BF 3

t Bu t Bu t Bu

WH/Al 2 O 3-(500) (

  Scheme 6.1 right). Bu Well-defined surface models of the active sites of WO 3 /SiO 2 and WH/Al 2 O 3 catalysts

					2 O 3-(500) was used. This
	synthesis may afford a surface site with the expected desired structure (Scheme 6.8), close
	3 to that of the active site of the Scheme 6.8 Expected reactivity of 3 toward Al 2 O 3-(500) O Al H + x (500) W O t Bu	t Bu	-t BuCH 3	x t Bu O t Bu Al	W	x t Bu Al O
	• IR study
	An excess of [W=O(CH 2	t Bu) 4 ], 3, was sublimed at 60°C under dynamic vacuum on an
	alumina disk (40 mg) partially dehydroxylated at 500°C (Al 2 O 3-(500) ). These operations
	CONFIDENTIAL LCOMS-UOP LCC

t Bu t

  ).

										t Bu
	O Al x Scheme 6.11 Grafting of 3 on SiO 2-(700) + (500) t Bu W O t Bu H	t Bu t Bu	-t BuCH 3 R.T.	O Al O	W	t Bu t Bu t Bu	+	t Bu	Al O W
						x				x
			3				3a			3b
								Br	Al Br Br
		O							O	t Bu
	t Bu	W Br	t Bu	+ AlBr 3			t Bu	W Br	t Bu
	CONFIDENTIAL LCOMS-UOP LCC

t Bu t Bu t Bu

2-(700) at

  This is close to the values observed for WO 3 /SiO 2 systems. Tomas et al.

																		Chapter 6 205
	around 958 cm -1 .										O
			O	H			O		t Bu	O	t Bu		t Bu		W O		t Bu	O
		O	Si O	O	O	Si	O	+	t Bu	W	t Bu	-t BuCH 3		O	Si O	O	O	Si	O
					SiO 2-(700)			3							3c
																	1470 cm -1
											Kubelka Munk
												100
								2960 cm -1
												50
	3747 cm -1									0
										2870 cm -1
				3704 cm -1
	b)
	a)
	4000	3800		3600		3400	3200	3000	2800	2600	2400	2200	2000		1800	1600	1400
										Wavenumber (cm -1 )
													CONFIDENTIAL LCOMS-UOP LCC

t Bu

  .1). The results are consistent with a W coordination sphere com-

	prising one oxygen atom at 1.71(1) Å, one oxygen at 1.97(3) Å and three carbons at
	2.12(3) Å, assigned to an oxo ligand, a siloxide's σ-bonded oxygen, and methylenic car-
	bons from neopentyl ligands, respectively. This is consistent with the bond distances
	found in [W 2 O 3 (CH 2	t Bu) 6 ] 24 where the W=O terminal (1.676-1.736 Å), W-O bridging (1.913-
	1.987 Å) and W-C (2.113-2.150 Å) bond lengths are in the same range. W-O distances for
	σ-bonded siloxide ligands are usually shorter, e. g. (1.876-1.882 Å) in the case of
	[W=O( t Bu 3 SiO) 2 (C 2 H 5 ) 2 ].

  Bu) 6 ];24 (ii) ca. one silicon at 3.60(4) Å, corresponding to a 171 ± 9° W-O-Si angle: combined with the trans arrangement of the oxo and siloxy ligands, this indicates a quasi-linear O=W-O-Si framework; and (iii) ca. one oxygen atom at 2.98(8) Å, assigned to siloxane bridges of the silica surface.28

		Chapter 6 207
	quaternary carbons, corresponding to a 126 ± 8° W-C-C angle, in agreement with the
	123.7-127.4° range found for [W 2 O 3 (CH 2	t
		CONFIDENTIAL LCOMS-UOP LCC

Table 6 .

 6

	Type of neighbour	Number of neighbours	Distance (Å)	DFT calculated distance (Å)	σ 2 (Å 2 )
	W=O	1.1(3)	1.71(1)	1.755	0.0018(9)
	W-OSi≡	1.2(6)	1.97(3)	1.990	0.002(2)
	W-CH 2 CMe 3	3.1(15)	2.12(3)	2.150-2.153	0.003(2)
	W-CH 2 CMe 3	3.1	3.24(4)	3.321-3.324	0.004(3)
	W-OSi≡	0.8(4)	3.60(4)	3.637	0.004(4)
	W--O(Si≡) 2	0.8(7)	2.98(7)	-	0.007(8)
	Errors between parentheses; fit residue: ρ = 3.4 %
	• DFT Calculations
	These structural propositions have been corroborated by DFT calculations (G03 program,
	B3PW91 level with the Sddall basis set) using polyhedral oligomeric silsequioxane
	(POSS) as a model of SiO 2-(700) . Of the two possible structures (A and B on Figure 6.13),
	the most stable one (A with ΔE=65 kJ) consists of a distorted trigonal bipyramid with mu-

1 EXAFS parameters for 3/SiO 2-(700) and DFT calculated distances for 3/POSS

tually trans oxo and siloxide as axial ligands, and with equatorial positions occupied by alkyl moieties as observed in EXAFS. Moreover, the calculated bond lengths and angles are in very good agreement with the EXAFS data, giving a clear picture of the surface organometallic fragment (Table

6

.1).

A B

  Well-defined surface models of the active sites of WO 3 /SiO 2 and WH/Al 2 O 3 catalysts

	t Bu		O W O		t Bu			O	Propylene coordination	t Bu	O O W		t Bu t Bu		O	α-H abstraction	t Bu	O O	W	O
	O	Si O	O	O	Si	O			O	Si O	O	O	Si	O	t BuCH 3 +	O	Si O	O	O	Si	O
					3c												t BuCH=CH 2
				H															N
	O	O Si O	O SiO 2-(700) O Si	O O	+	t Bu	t Bu					-t BuCH 3	O	Si O O	O	W O	Si	O O
												4								4/SiO 2-(700)

t Bu i Pr i Pr t Bu t Bu W N i Pr i Pr t Bu CONFIDENTIAL LCOMS-UOP LCC

  The formation of amino species is confirmed by the analysis of gas evolved during grafting, as less than 0.05 equivalent of neopentane per grafted tungsten is detected. The grafting occurs thus only by addition of a proton of a silanol on the imido ligand to form an amido. Comparable reactivity has been observed for [Mo≡N(CH t Bu)(CH 2

		Chapter 6 213
	• Mass balance analysis
		t Bu)] that reacts
	with SiO 2-(700) to form [≡SiO-Mo=NH(CH t Bu)(CH 2	t Bu)] 46 but to our knowledge it is the
	H first example of the addition of a silanol to an imido. Moreover elemental analysis of N t Bu
	O Si O 5/SiO 2-(700) gives a tungsten loading of 4.8% wt , 0.5% wt of nitrogen and 6.5% wt of carbon O O SiO 2-(700) Si O O O -t BuCH 3 Si O O O Si O O 5 O W N t Bu t Bu t Bu W F t Bu + O corresponding to 1.3 N/W and 20.6 C/W, i.e. three neopentyl and a phenylimido ligands F per tungsten.
		Expected structure 5a of
		5/SiO 2-(700)
		CONFIDENTIAL LCOMS-UOP LCC

  F signals were found in the molecular analogue. In particular, methylenes of the neopentyl moieties appear at 2.20 ppm as a singlet with satellites ( 2 J W-H = 11.7 Hz) and with the same pattern at 91.7 ppm ( 2 J W-C = 46.7 Hz), in the 1 H and 13 C{ 1 H} NMR spectrum respectively. The notable absence of scalar coupling with19 F supports the disappearance of the fluorine from the tungsten coordination sphere. Moreover, in the 19 F{ 1 H} spectrum, a singlet at -149.6

	ppm, consistent with the signal at -121 ppm for 6/SiO 2-(700) is observed. Yet again, no
	coupling with 183 W can be noticed, which confirms the cleavage of the W-F bound, which
	confirms the cleavage of the W-F bound, in agreement with DFT calculation. Similar re-

activity has been observed during reaction of WF 6 with Me 3 SiOMe, which leads to the formation of WF 5 OMe and Me 3 SiF.

52

Nevertheless, there is a difference of

19

F chemical shift in solid-state NMR between fluorinated silica ([≡Si-F] at -156 ppm)

49

and 6/SiO 2-(700)

  Bu 3 SiO) 2 (C 2 H 5 ) 2 ].39 Moreover, the fit was improved when considering further lay-CONFIDENTIAL LCOMS-UOP LCC ers of backscatterers: (i) two C atoms at 3.28(4)Å, assigned to the neopentyl ligands' quaternary carbons, corresponding to a 126 ± 8° W-C-C angle, in agreement with the 123.7-127.4° range found for [W 2 O 3 (CH 2 t Bu) 6 ];24 (ii) less than two silicon at 3.61(3) Å, (iii) ca.

										t Bu
									O		t Bu
										W
								O	Si O O	O	O	Si F	O O
										6c
						EXAFS						FOURIER TRANSFORM
	4
												Experimental
												Simulated
	k 3 . χ χ (k) 0											2 I F (R) I 4
	-4
												0
	2	4	6	8	10	12	14	16		0	2	4
						k ( Å -1 )						R ( Å )
	[W 2 O 3 (CH 2	t Bu) 6 ] 24 where the W=O terminal (1.676-1.736 Å), W-O bridging (1.913-1.987 Å)

and W-C (2.113-2.150 Å) bond lengths are in the same range. W-O distances for σbonded siloxide ligands are usually shorter, e. g. (1.876-1.882 Å) in the case of [W=O( t

Table 6

 6

	.2 EXAFS parameters for 6/SiO 2-(700)
	Type of neighbour	Number of neighbours	Distance (Å)	σ 2 (Å 2 )
	W=O	1.1(2)	1.71(1)	0.0023(9)
	W-OSi≡	1.9(7)	1.99(3)	0.003(2)
	W-CH 2 CMe 3	2.1(6)	2.12(2)	0.002(1)
	W-CH 2 CMe 3	2.1	3.28(4)	0.005(3)
	W-OSi≡	1.5(7)	3.61(3)	0.005(3)
	W--F	1.1(8)	2.53(7)	0.019(14)

  Bu) 2 )(≡SiF)], has been evidenced by IR, NMR, and EXAFS spectroscopies, mass balance analysis and DFT calculations. The use of POSS as a model of silica has been particularly useful to attest the disappearance of W-F bound during grafting.

																Chapter 6 221
	The grafting of [W=O(CH 2	t Bu) 3 F] (6) on SiO 2-(700) has been performed. The singular reac-
	tivity of the W-F bound, by opening siloxane bridges, leading to 6c,
	[(≡SiO) 2 (W=O)(CH 2	t
	O	O Si O O O	t Bu O W	t Bu Si O O F	Propylene coordination	O	t Bu O O Si O W O	O	t Bu Si F	O O	α-H abstraction t BuCH 3 +	O	Si O O	O W O O	Si F	O O
												t BuCH=CH 2
			6c					6c
				• Conclusion
												CONFIDENTIAL LCOMS-UOP LCC

/SiO 2-(700) and 4/SiO 2-(700) is very low regarding the WH/Al 2 O 3 catalyst

  (seeChapter 3). It can be assumed that the silica do not provide the same electronic character to the tungsten centre.

	2.3.2. Compared catalytic performances toward propylene metathesis
	In a further step, catalytic performances of 3/SiO 2-(700) , 4/SiO 2-(700) and 6/SiO 2-(700) were
	probed in countinuous flow reactor (reactor as described in subsection 2.1 of Chapter 3
	and Appendix 2, 20 NmL C3H6 .min -1 ; R = 30 mol C3H6 .mol W	-1 .min -1 ) at 80°C.
	The oxo derivatives exhibit very similar activities. For 3/SiO 2-(700) an initial conver-
	sion rate of 4.9 mol C3H6 .mol W	-1 .min -1 (ca. 16% conversion) was reached (Figure 6.24), and
	22000 cumulated turnover numbers (TON) were achieved after 95 hours (Figure 6.25).

Noteworthy, after 24h, neopentane is observed for 3/SiO 2-(700) and 6/SiO 2-(700) , which may be characteristic of to the formation of a carbenic species (see section 2.2.5 and Scheme 6.17). After 24h, 3/SiO 2-(700) and 4/SiO 2-(700) have converted ca. 0.5% of ethylene to propylene (cumulated T.O.N. ≈ 20) while no propylene is produced over 6/SiO 2- (700)

. It confirms the necessity of a dimerization site to produce butenes, which can later react by cross metathesis with ethylene. Hence, 3c and 4a have an alkyl ligand (X regarding Scheme 6.1 centre), while 6c have siloxy ligand that did not afford olefin insertion.

Nevertheless, the activity of 3

For 6/SiO 2-(700) , the maximum conversion rate is a bit higher, with 5.5 mol C3H6 .mol W -1 .min -1 (ca. 18% conversion, Figure

6

.24). It is though reached after a longer time

(20 h

CONFIDENTIAL LCOMS-UOP LCC

  Well-defined surface models of the active sites of WO 3 /SiO 2 and WH/Al 2 O 3 catalysts These species are assumed to form a carbene at 80°C when they are contacted to an olefin. The obtained species although not fully characterized yet are thus very close to the expected active site of the WO 3 /SiO 2 .Well-defined surface models of the active sites of WO 3 /SiO 2 and WH/Al 2 O 3 catalysts

	hydride transfer Three novel tungsten complexes, i.e. [W=O(CH 2 2.4. Conclusion and [W=O(CH 2 t Bu) 3 F] (6) , have been successfully synthesized. Their reactivity toward Reductive elimination + Y = O, not observed Y = NAr, operative t Bu) 4 ] (3), [W=N(C 6 H 5 )(CH 2 t Bu) 3 F] (5) partially dehydroxylated oxides have been investigated and compared to the reactivity of [W=N(2,6-i PrC 6 H 3 )(CH 2 t Bu) 2 (=CH t Bu)] (4). The grafting of these species have afforded new, well-defined, oxo alkyl tungsten W O t Bu t Bu t Bu 3 t Bu W N W O F t Bu t Bu 6 3. Experimental section 3.1. General procedures All experiments were carried out by using standard Schlenk and glove-box tech-surface species 3c and 6c. Chapter 6 227 t Bu niques. Solvents were purified and dried according to standard procedures. 59 C 6 D 6 (SDS) t Bu 4 W O t Bu was distilled over Na/benzophenone and stored over 3Å molecular sieves. t Bu t Bu O t Bu [W=O(CH 2 t Bu) 3 Cl] and supported [(≡SiO)W=N(2,6-i PrC 6 H 3 )(=CHtBu)(CH 2 t Bu)] (2/SiO 2-W t Bu O Si O O O Si O O O W N i Pr i Pr t Bu t Bu Si O O O O Si O O F O (700)
				O	3c			O	Si O O	O	O	Si	O O	O	6c
	O t Bu	O Si O	O W O	Si	O O		4/SiO 2-(700)	O	Si O O	O	W O	Si F	O O
														R
												Y
													W
												O		X	O
	O	O O Si O	W O	CH 2 Si O O	O O	M O M= Si or Al O M O Y= O or N-Ar Model species O O X= Alkyl or EWG	O O	R O Al x	O W	x	R O Al	Al	O O	x
	Postulated isolated					Expected active site of
	active sites of the						the ethylene to
		WO 3 /SiO 2								propylene catalyst
	Scheme 6.19 General overview of the species presented in this chapter
	CONFIDENTIAL LCOMS-UOP LCC CONFIDENTIAL LCOMS-UOP LCC					CONFIDENTIAL LCOMS-UOP LCC

The new supported complexes, 3/SiO 2-(700) and 6/SiO 2-(700) , present a very high activity in propylene metathesis, under mild conditions and without need of a co-catalyst.

These systems shows a sustained conversion, in contrast to the parent imido-derived material, 4/SiO 2-(700) . This imido species deactivate by reduction of the tungsten centre by decomposition of the metallacyclobutane and formation of isobutene, whereas this mechanism does not occur for the oxo species. This represents a significant step toward the understanding of the WO 3 /SiO 2 system, as that isolated single site organometallic metal oxo fragments give rise to high performance catalyst for propylene metathesis. i Pr i Pr t Bu t Bu

  3.2.1. Preparation of t BuCH 2 Nat BuCH 2 Na was prepared from t BuCH 2Li 31 following a procedure analogous to that used for C 6 H 5 CH 2 K.29,30 A mixture of neopentyl chloride (20 g) and ca. 6 g (excess) of finely chopped Li wire (1% Na) in ca. 200ml of heptane was stirred and refluxed under argon for 10 days. The LiCl and excess Li was filtered off and the neopentyl lithium isolated from the filtrate by reducing the volume under vacuum, yield 12 g (60%) of white crystalline t BuCH 2 Li.1 H NMR (δ, 295 K, C 6 D 6 , 300 MHz): 8.88 (2H, s) 10.68 (9H, s). A mixture of 5.0 g of t BuCH 2 Li in 100 mL of THF was added dropwise to a stirred and -78°C cooled solution of 6.1 t BuONa in 100 mL of THF. The solution was stirred at this temperature for 1-2 hours and turned yellow. Subsequently, the solution was slowly warmed to RT, the solution was filtered to remove the t BuOLi precipitate and the solvent was removed under vacuum. 5g (80%) of t BuCH 2 Na as a yellow fine powder was obtained. Bu)3 Cl] (1.500 g, 3.34 mmol) was dissolved in 10 cm 3 of Et 2 O and a solution of NpNa (0.314 g, 3.34 mmol) in 10 cm 3 of Et 2 O was added dropwise in absence of light while stirring at -78°C. After one hour, the volatiles were removed under vacuum. Pentane was added and the reaction mixture was filtered to remove insoluble NaCl. Pentane was evaporated to afford a colourless oil. The crude material was distillated twice at 60°C under reduced pressure (3.10 -5 Torr) to yield 0.570 g of pure product (35 % yield).1 H NMR (δ, 295 K, C 6 D 6 , 300 MHz): 1.83 (8 H, s, CH 2 C(CH 3 ) 3 ), 1.17 (36 H, s, CH 2 C(CH 3 ) 3 ).13 C{ 1 H} NMR (δ, 295 K, C 6 D 6 , 75 MHz): 85.6 (s, CH 2 C(CH 3 ) 3 , 183 W satellites: 1 J W-C = 48.1 Hz), 34.5 (s, CH 2 C(CH 3 ) 3 ), 32.9 (s, CH 2 C(CH 3 ) 3 ). As the product was a heat, light and air sensitive oil, elemental analyses were not successful.Freshly distilled phenylisocyanate(3,214 g, 27 mmol) was added to a suspension of crude [W=OCl 4 ] (9.000 g, 26 mmol) 200 mL of heptane. This mixture was heated to reflux for 4 days and a dark brown precipitate is formed. The volatiles are removed under vacuum and Et 2 O (20mL) is added to afford a green solution. This solution if filtered to remove the insoluble impurities and Et 2 O is then removed under vacuum affording 8.4g (65%) of dark green crystalline [W=N(C 6 H 5 )Cl 4 ] (Et 2 O). To the rapidly stirred dark green solution of [W=N(C 6 H 5 )Cl 4 ] (Et 2 O) (10.6 g, 21.6 mmol) in toluene at -78 °C was added dropwise 30 mL of 2.17 M ether solution of neopentylmagnesium chloride. The mixture was allowed to warm slowly to room temperature with continuous stirring. The volatiles were removed under vacuum. The product was extracted with pentane, and the extract was treated with activated carbon and stirred for 30 minutes. The mixture was filtered through a bed of celite, and the solvent was removed from the filtrate under vacuum. The yellow brown residue was collected on a frit, washed with chilled pentane and dried to give 3.8 g of [W=N(C 6 H 5 )(CH 2 t Bu) 3 Cl] as a brown powder (33 % yield). [W=N(C 6 H 5 )(CH 2 t Bu) 3 Cl]

	3.2.2. Preparation of 3
	[W=O(CH 2	t

CONFIDENTIAL LCOMS-UOP LCC

3.2.3. Preparation and of 5

  1 H NMR (δ, 295 K, C 6 D 6 , 300 MHz): 7.72 (2 H, d, 3 J HH =8.2 Hz),7.26 (2 H, t, 3 J HH =7.7 Hz), 7.02 (1 H, d, 3 J HH =7.1 Hz), 2.22 (6 H, m, CH 2 C(CH 3 ) 3 , 2 J WH =10.1 Hz,3 J FH =10.6 Hz ), 1.25 (27 H, s, CH 2 C(CH 3 ) 3 ); 13 C{ 1 H} NMR (δ, 295 K, C 6 D 6 , 75 MHz): 128.9, 128.0, 127.6, 126.6, 90.7 (m, CH 2 C(CH 3 ) 3 , 1 J WC = 46 Hz, 2 J FC =6.82 Hz), 35.7 (s, CH 2 C(CH 3 ) 3 ), 34.0 (s, CH 2 C(CH 3 ) 3 ); 19 F{ 1 H} NMR (δ, 295 K, C 6 D 6 , 280 MHz): 34.84 (m, 1 J WF =50 Hz, 2 J NF =49 Hz). Anal. Calcd for C 21 H 38 FNW: C, 49.71; H, 7.55; F, 3.74; N, 2.76; W, 36.23% Found: C, 48.86; H, 7.38; F, 4.54; N, 2.74; Bu)3 Cl] (1.500 g, 3.34 mmol) and AgBF 4 (0.65 g, 3.34 mmol) were stirred in 20 mL of toluene for one hour at room temperature. The reaction mixture was filtered to remove the insoluble AgCl, and NEt 3 (1.1 mL, 7.70 mmol) was added. The resulting solution was stirred for 16 h at room temperature and the reaction mixture was filtered over celite. The solvent was then removed under vacuum to leave a white solid. The crude material was sublimed at 60°C under reduced presure (3.10 -5 Torr) to yield 1.13 g of pure product (78 % yield). Bu) 6 ] (2.000 g, 2.37 mmol) and AgBF 4 (0.9 g, 4.74 mmol) were stirred in 20 mL of toluene for one hour at room temperature. The reaction mixture was filtered to remove the insoluble Ag 2 O, and NEt 3 (1.1 mL, 7.70 mmol) was added. The resulting solution was stirred for 16 h at room temperature and the reaction mixture was filtered over celite. The solvent was then removed under vacuum to leave a white solid. The crude material was sublimed at 60°C under reduced pressure (3.10 -5 Torr) to yield 1.68 g of pure product (82 % yield). H NMR (δ, 295 K, C 6 D 6 , 300 MHz): 2.24 (6 H, m, CH 2 C(CH 3 ) 3 , 2 J WH =10.1 Hz, 3 J FH =8.6 Hz), 1.26 (27 H, s, CH 2 C(CH 3 ) 3 ). 13 C{ 1 H} NMR (δ, 295 K, C 6 D 6 , 75 MHz) 94.9 (m, CH 2 C(CH 3 ) 3, 1 J WC = 46 Hz, 2 J FC =6.3 Hz), 35.5 (s, CH 2 C(CH 3 ) 3 ), 32.6 (s, CH 2 C(CH 3 ) 3 ). 19 F{ 1 H} NMR (δ, 295 K, C 6 D 6 , 280 MHz): -0.38 (m, 1 J WF =82.2 Hz). Anal. Calcd for C 15 H 33 OFW: C, 41.69; H, 7.69; F, 4.42 %. Found: C, 41.47; H, 7.89; F, 4.72%.

			Chapter 6 231
	3.2.4. Preparation and characterization of 6
			• Method 1
	[W=O(CH 2	t • Method 2
	[W 2 O 3 (CH 2	t
	W, 34.90%
			CONFIDENTIAL LCOMS-UOP LCC

1

  -5 Torr). Analysis by gas chromatrography indicated the formation of 290 μmol of neopentane during the grafting (1,0±0.1 NpH/ W). Elemental analysis of: W 4.43 % wt C 3.27 % wt . 1 H MAS solid state NMR (800 MHz) δ 2.0, 1.1 ppm. 13 C CP/MAS solid state NMR (200 MHz) δ 95, 38 and 34 ppm. 18 F MAS solid state NMR (750 MHz) δ -121.2 ppm CONFIDENTIAL LCOMS-UOP LCC A pentane solution of [(c-C 5 H 9 ) 7 Si 7 O 12 SiOH] (75 mg, 82 μmol, 1 mL pentane) was added at -78°C to a stirred pentane solution of 6 (36 mg, 82 μmol, 1 mL pentane). The mixture was allowed to warm slowly to room temperature with continuous stirring. And the volatile where removed under vacuum to afford 6/POSS. 1 H NMR (δ, 295 K, C 6 D 6 , 300 MHz): 2.20 (m, CH 2 C(CH 3 ) 3 , 2 J WH =11.7 Hz), 1.26 (s, CH 2 C(CH 3 ) 3 ), 1.87-1.22 (m, c-CH(CH 2 ) 4 ), 1.11 (m, c-CH(CH 2 ) 4 ). 13 C{ 1 H} NMR (δ, 295 K, C 6 D 6 , 75 MHz) 91.7 (m, CH 2 C(CH 3 ) 3, 1 J WC = 46.7 Hz), 35.5 (s, CH 2 C(CH 3 ) 3 ), 32.0 (s, CH 2 C(CH 3 ) 3 ), 27.7, 27.5, 27.1, 27.0 (m, c-CH(CH 2 ) 4 ), 22.7, 22.1(m, c-CH(CH 2 ) 4 ). 19 F{ 1 H} NMR (δ, 295 K, C 6 D 6 , 280 MHz): -149.6 (s).

	6/SiO 2-(700)
	200 400 600 800 1000 1200 1400
	Raman Shift (cm -1 )
	Figure 6.31 Raman spectrum of 6 and 6/SiO 2-(700)
	3.3.1. Preparation and characterization of 6/POSS

Table 7 .

 7 2 Productivity of the different routes to propylene

	Reaction	Propylene selectivity (%)	Productivity at 20h on stream (mmol C3= .g cata -1 .h -1 )
	1-butene conversion	42.5	28.1
	Trans-2-butene conversion	52.1	26.9
	1-butene/trans-2-butene cross-metathesis	49.9	36.0
	Isobutene/trans-2-butene cross-metathesis	40.0	10.5
	Ethylene/trans-2-butene cross-metathesis (45% ethylene)	97.7	115.9
	Ethylene/trans-2-butene cross-metathesis (35% ethylene)	96.4	142.8

Using WH/Al 2 O 3-(500) , the best route, in term of selectivity and productivity in propylene, is ethylene/trans-2-butene cross-metathesis, with a low deactivation rate (ca. 0.11%.h -1 ). Moreover, during this study, it has been observed, for metathesis reaction in-

Table A .

 A 2 Properties of the different supports

	Support	Supplier	Reference	BET surface area (m 2 .g -1 )	Composition
	Silica-Alumina (SiAl)	Akzo Nobel	HA-S-HPV	390	Si/Al = 3
	Aluminum Magnesium Hy-droxyde (Pural)	Sasol	Pural ® MG50 595050	150	MgO/Al 2 O 3 = 1

  t Bu)(CH 2 t Bu) 3 ] et la γ-alumine suivi d'un traitement sous H 2 à 150°C ont été préparés. Les caractérisations par différentes techniques spectroscopiques (IR, RMN solide, Raman et EXAFS) et réactivité stoechiométrique ainsi que les modélisations par calculs théoriques (DFT) ont montré la présence à la surface de deux espèces trishydrures : neutre et cationique. Ce catalyseur s'est révélé particulièrement actif pour la conversion directe de l'éthylène en propylène à 150°C selon un mécanisme trifonctionnel (dimérisation, isomérisation et métathèse croisée). L'accent a été mis sur la détermination du mode de désactivation par oligomérisation de l'éthylène, due principalement à la présence en surface d'espèce cationique. Pour palier à ce problème, d'autres réactions permettant la production de propylène avec de meilleures activités ont été développées (conversion des butènes, métathèse croisée éthylène/2-butène, 2-butène/isobutène). La conversion directe de 2-butène en propylène, inconnue jusqu'à lors, a notamment été étudiée. Enfin, un second type de systèmes catalytiques, modèles du site actif de l'hydrure de tungstène supporté et du catalyseur industriel WO 3 /SiO 2 , a été préparé et caractérisé. Ces nouveaux catalyseurs, portant un ligand oxo, se sont montrés bien plus actif en métathèse des oléfines que leurs homologues portant un ligand imido. Ces derniers se désactivent rapidement par décomposition de métallacyclobutane entraînant une réduction du tungstène non observée dans le cas des systèmes oxo. ___________________________________________________________________________ TITRE en anglais Novel generation of tungsten-based catalysts grafted on oxides for propylene production. ___________________________________________________________________________

  These later deactivates quikely by metallacyclobutane decomposition leading to the reduction of the tungsten non observed in the case of oxo systems.

___________________________________________________________________________ DISCIPLINE Chimie __________________________________________________________________________ MOTS-CLES Propylène, tungstène, hydrures, oxydes, aluminium, métathèse, éthylène, butènes, oxo. ___________________________________________________________________________ INTITULE ET ADRESSE DE L'U.F.R. OU DU LABORATOIRE : Laboratoire de Chimie Organométallique de Surface ; UMR 5265 : Chimie, Catalyse, Polymères et Procédés ; CNRS -UCBL -CPE Lyon ; 43 Bd du 11 Novembre 1918 ; B.P. 2077 ; 69616 VILLEUR-BANNE Cedex

Remerciements

Contents

CONFIDENTIAL LCOMS-UOP LCC

CONFIDENTIAL LCOMS-UOP LCC

The first reaction expected when contacting 1-butene to an olefin metathesis catalyst is the self-metathesis. Nevertheless, the resulting product distribution reveals the occurrence of other reactions. As presented in Chapter 3, WH/Al 2 O 3 is not only an olefin metathesis catalyst, the alkyl alkylidene species is in equilibrium with an hydride alkylidene species allowing olefin isomerization. 1-butene can insert in the W-H bound, following the Cosse-Arlman mechanism, 14,15 either by 1,2-insertion or by 2,1-insertion, the later, may be followed by a β-hydride elimination of the hydrogen allowing the formation of 2butene (Scheme 5.11). This reaction is equilibrated and thermodynamics is in favor of the formation of 2-butenes with a 1-butene:2-butenes ratio of 1:33. 11 It can be assumed that these elementary steps occurs on both cationic and neutral sites. During the initiation of the metathesis reaction, the butylidene-hydride tungsten species can react either with 1-butene or 2-butene to form respectively 1-pentene or 2hexenes and propylidene-hydride or ethylidene-hydride species. These two newly formed carbenes will react in cross metathesis to afford propylene and pentenes from 1-butene and 2-butene, following the classical Chauvin mechanism (Scheme 5.12). 10 Scheme 5.12 Intermediates for the production propylene and 2-pentenes from 1-butene and 2-butene If only the self-metathesis of 1-butene and 1-butene/2-butenes cross-metathesis take place, the relative proportion of hexenes to ethylene and propylene to pentenes should be Chapter 5 167 CONFIDENTIAL LCOMS-UOP LCC 1:1. The excess of propylene vs. pentenes and the deficit of ethylene vs. hexenes can be explained by the cross metathesis between 2-butenes resulting from isomerization and ethylene resulting from 1-butene self-metathesis (Scheme 5.13). Therefore, as this reaction gives 2 mol of propylene per mol of ethylene, it explains the difference in selectivities with the difference between propylene and pentenes (12%) being twice the difference between hexenes and ethylene (6%). As observed for propylene metathesis, the trans to cis ratio of 2-pentenes is in favor of the trans isomer, i.e. 2.9:1 (constant with time on stream), and superior to thermodynamic ratio (1.5:1). 11 In this case the pentenes produced by metathesis are mostly trans, regarding the stability of the intermediate metallacyclobutane B (Scheme 5.14). Scheme 5.14 The stability of the intermediary metallacyclobutane dictates the selectivity of pentenes 12,13 A catalytic cycle that involves all these reactions, i.e. i) isomerization of 1-butene to 2-butenes, ii) 1-butene self metathesis, iii) 1-butene/2-butenes cross metathesis and iv) ethylene/2-butenes cross metathesis, can be proposed (Scheme 5.15). This mechanism highlights the importance of the dual functionality of the active site, since tungsten carbene-hydride is required. From the data obtained it appears that 1-butene isomerization is the fastest of all other reactions occurring in this system.

CONFIDENTIAL LCOMS-UOP LCC

Production of propylene from 1-butene/trans-2-butene mixtures

The reactions of butene-1 and trans-2-butene separately with WH/Al 2 O 3-(500) have been presented in previous subsections. Herein is described the reactivity of a mixture of these two gases with the WH/Al 2 O 3-(500) and the influence of the 1-butene/trans-2-butene ratio.

The study has been conducted according to the conditions presented in Table 5.6 and varying the proportion of butene-1 from 0%, 33%, 50%, 66% to 100% in butene-2 feed. As expected, the selectivity in propylene is slightly better when 1-butene is a minor component of the feed. This selectivity decreases when the molar percentage of 1-butene increases, raising the selectivity in hexenes and ethylene, produced by self-metathesis of 1-butene. Operating with 33% of 1-butene in the feed gives the best selectivity in propylene with 55% (Figure 5.14). The maximum conversion rates span from 5.0 to 9.2 mol C4=+C2= .mol W -1 .min -1 , whereas the deactivation rate is quite constant for all ratio: ca. 0.11%.h -1 (Figure 5.20).

The selectivity in propylene increases with proportion of ethylene in the feed, starting from 52.5% when no ethylene was in the feed to 98.7% when 70% of ethylene was added in the trans-2-butene feed (Figure 5.21). The maximum propylene production rate is obtained when the reactor is fed with 35% of ethylene in the 2-butene feed, with 142.8 mmol C3= .g cata .h -1 at 20 h on stream. This optimum, observed at substoichiometric proportion of ethylene, can be explained by the occurrence of trans-2-butene conversion to propylene as seen in subsection 2.4, concomitantly to the ethylene/trans-2-butene crossmetathesis. As no trend could be established between ethylene ratio and deactivation rate, it can be assumed that ethylene is not a major element for the deactivation of the catalyst for metathesis reaction and therefore the rate of metathesis reaction is much higher than the rate of insertion of ethylene responsible of deactivation. It confirms the results obtained in Chapter 3, where it has been seen that ethylene was deactivating the cationic tungsten sites, which are the most active dimerization sites, whereas the neutral sites were still performing the reaction but at a slower rate.

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Reference and Notes

( AlH/Al 2 O 3-(500) have been tested for ethylene polymerization at 35 bar with a maximum activity of 21.9 kg PE .mol -1 (AlH) .h -1 at 100°C (Table 7.1). Moreover, it has been found that AlH/Al 2 O 3-(500) was able to perform catalytically ethylene hydrogenation by double bond insertion in Al-H followed of H 2 heterolytic splitting over Al-C at high temperature (400°C). CONFIDENTIAL LCOMS-UOP LCC grafting on oxide supports. Furthermore, the grafting of the oxo complexes described on this thesis on silica-alumina should lead to active catalyst as surface aluminum can coordinate to the oxo ligand of the tungsten increasing the electrophilic character of the tungsten centre. Moreover this coordination may favor the α-H abstraction to form a tungsten carbene (Scheme 7.8). was mixed with distilled water to obtain a kind of slurry. This slurry was put in the oven at 120°C for 2 days. The resulting blocks were crushed in a mortar and sieved (40-60 mesh). Others alumina were received as extrudates. These extrudates where identically crushed and sieved (40-60 mesh).

CONFIDENTIAL LCOMS-UOP LCC trast, Pural, due to its MgO sites, is reported to be more alkaline than Alumina. 4,5 The drift spectra of these materials are presented in Figure A.7

Characterizations of the hydrides

The tungsten molecular precursor, i.e., [W(≡C t Bu)(CH 2 t Bu) 3 ] has been grafted and hydrogenolysed following the standard procedure. Table A.3 presents the tungsten loading of these prepared tungsten hydride. stream. These results are reported on Table 5. As the catalyst prepared with Al 2 O 3 (500) UOP E was not active, its deactivation was not modeled. The selectivity in propylene of all these systems is very high, between 96.3 and 97.8%. For all these tests, with the same amount of catalyst, Al 2 O 3 (500) RP exhibit the highest activity and selectivity and the lowest deactivation rate.