These De L'universite De Lyon Délivrée Par L'universite

Claude Bernard Lyon

Ecole Doctorale

Diplome De Doctorat

Directeur De

M Christophe

M Chloé Thieuleux

M Christian Bruneau

M Christian

Bruneau M Bert Sels

M Bert

Sels M Antoine Gédéon

M Christophe Copéret

M Chloé Thieuleux

M Daniele

Claude Universite

Bernard -Lyon

M A Bonmartin

M Le Professeur

G Annat

D Simon

J-F Mornex

M G Gay

Composantes Sante

Mr Michael Limbach

Mr Richard Dehn

Mr Stephan

N° d'ordre Année 2011

My special thanks to my friend Samantaray Manoja Kumar for his help in the synthesis of homogeneous catalysts

Introduction

The main objective of this study was to selectively form low cyclic oligomers, in particular dimer via RO-RCM of cyclooctene, using well-defined, heterogeneous Ru-NHC catalysts.

Chapter 1: Reviews the history of olefin metathesis in terms of catalysts developments and olefin metathesis applications. Also deals with the introduction to the mesoporous organicinorganic hybrid materials.

Chapter 2: Describes the synthesis of well-defined, heterogeneous Ru-NHC catalysts and their catalytic performances in RO-RCM of cyclooctene for selective formation of low cyclic oligomers. The influence of the length and rigidity of the tether in terms of reactivity, stability and selectivity in RO-RCM of cyclooctene has been discussed in this chapter.

Chapter 3: Describes the synthesis of unsymmetrical homogeneous catalysts analogues to the hybrid, heterogeneous Ru-NHC catalysts and their catalytic performances in RO-RCM of cyclooctene. Comparison of the catalytic performances between homogeneous and heterogeneous systems has been studied in order to understand the influence of the unsymmetrical nature of the NHC ligands in the RO-RCM of cyclooctene for selective formation of low cyclic oligomers.

Chapter 4: In this chapter, synthesis, characterization and catalytic performances of GH-II type heterogeneous (symmetrical and unsymmetrical) Ru-NHC complexes adsorbed on silica support, in RO-RCM of cyclooctene has been invetigated. The influence of the silica support (SP Grace) on catalytic performances has been discussed.

Chapter 5: Gives an overall conclusion and possible perspectives.

Chapter 1 Bibliography

Introduction

In 2005, three researchers were awarded with the Nobel Prize in Chemistry: Dr. Yves Chauvin, Professor Robert H. Grubbs and Professor Richard R. Schrock "for the development of the metathesis method in organic synthesis, in which carbon-carbon double bonds are broken and formed catalytically". 1 Their discoveries had great influence on the development of biologically active heterocyclic compounds leading to development of new drugs, academic research, polymer science and industrial applications.

The metathesis history is immense and composed of olefin metathesis, 2 enyne metathesis, 3 and alkyne metathesis reactions. 4 Since it would be impossible to cover all aspects of this very versatile reaction, we will thus mainly focus on olefin metathesis reaction, some key Ru based catalyst developments, mechanism of olefin metathesis reaction and some selected examples of supported catalyst systems.

Type of olefin metathesis reactions

The application of olefin metathesis catalysts for performing various transformations with different olefinic substrates and conditions has resulted in the several well-known olefin metathesis reactions, mainly divided in the following reaction types.

1. Ring-opening metathesis polymerization (ROMP) 5 2. Acyclic diene metathesis polymerization (ADMET) 6 3. Ring-closing metathesis (RCM) 7 4. Self and Cross metathesis (CM) 8

Ring-opening metathesis polymerization (ROMP)

The enthalpic driving force for irreversible ring-opening of ROMP monomers, (norbornene and cyclooctene), is the ring-strain release. 9 Consequently, olefins such as cyclohexene with little ring strain cannot be polymerized easily. Exceptionally, cyclooctene represents an unusual case, as the polymerization is favoured both entropically and enthalpically: it is thus polymerizable at any temperature. 10 Although, the pathway back to the cyclic compound(s) has to overcome a significant thermodynamic barrier, backbiting to give cyclic oligomers (cyclic dimers, trimers….) remains possible. The formation of cyclic oligomers from cyclic olefins is termed as ring opening-ring closing metathesis (RO-RCM) 11 (Scheme 1).

ROMP vs. RO-RCM

Concentration-dependence is a key feature of these ring-chain equilibria between cyclic oligomers and polymers. With high monomer concentrations ROMP predominates while dilution plays a major role in shifting the equilibrium towards the formation of smaller, cyclic species (RO-RCM) thus favoring backbiting over polymerization. 12 Höcker observed a steady increase in the proportion of cyclic oligomers prior to formation of a measurable amount of polymer 13 and proposed an initial bias toward either cyclic oligomers or linear polymer. 14 The favored pathway was proposed to correlate with the degree of ring strain and the reactivity of the catalyst. Metathesis of high-strain cycloolefins by catalysts of relatively low activity was reported to initially yield high molecular weight polymers, from which cyclic oligomers were subsequently extruded by cyclodepolymerization (i.e. backbiting). At the opposite extreme, metathesis of low-strain cycloolefins by highly reactive catalysts gave cyclic oligomers as the kinetic products, with cyclodimers and cyclotrimers being predominant. These cyclic species underwent conversion into high-molecular weight linear polymer through a stepwise chain growth mechanism once the equilibrium concentration of each cyclic oligomer was exceeded.

Acyclic diene metathesis polymerization (ADMET)

ADMET is a condensation polymerization reaction and is essentially the self-metathesis of a diene, usually a terminal diene, to form polymer (Scheme 2). 15 This involves usually equilibrium processes in which the functional groups react in a stepwise fashion to form dimer from two monomers, then trimer, tetramer, and so on to high polymer. Scheme 2: Acyclic diene metathesis polymerization (ADMET).

Ring-closing metathesis (RCM)

The driving force for RCM is primarily entropic, as one substrate molecule gives two molecules of products (Scheme 3). Furthermore, this reaction is practically irreversible due to the release of volatile small molecules and can therefore proceed to completion.

+ M R n n n
Scheme 3: Ring closing metathesis (RCM).

RCM vs. ADMET

In both reactions, the loss of ethylene creates a powerful, but indiscriminate, driving force for intra-and intermolecular metathesis.

The key competing reaction in RCM is oligomerization, which can be decreased by lowering the concentration of the diene or by using slow addition of the substrates. Higher temperature also favors ring closure.

ADMET is usually conducted in the absence of solvent to favor polymerization and linear chain extension over cyclization, since high concentration favors intermolecular over intramolecular reactions. Oligomeric cyclics however have also been observed in ADMET polymerization. 16 Acyclic diene metathesis is theoretically capable of cyclizing unimolecularly by the RCM reaction. Thus, monomers that will cyclize to a 5-, 6-, or 7membered ring yield RCM over ADMET products. Monomers that would hypothetically cyclize to give 3-and 4-membered rings or larger than a 7-membered ring, are more rapidly polymerized than cyclized in ADMET conditions (concentrated solutions).

Cross metathesis (CM)

On the other hand, cross metathesis (CM) reaction is more challenging, as it lacks the entropic driving force of RCM and the ring-strain release of ROMP to get the desired cross-products.

This reaction can be used for chain extending, chain shortening and functionalization using functional olefins (Scheme 4).

Industrial applications

The olefin metathesis reaction has opened new perspectives in three important fields of industrial chemistry i.e. petrochemicals, polymers synthesis and fine chemicals. 17

Petrochemistry

The applications of metathesis can be found in Shell Higher Olefin Process (SHOP), to produce linear higher olefins from ethylene. The Phillips triolefin process was used to produce ethylene and 2-butene from propylene. Later, a reverse process was used to produce propylene, known as the Olefins Conversion Technology (OCT).

Polymer synthesis

The first commercially made polymer was Norsorex, a polynorbornene compound. A process using a RuCl 3 /HCl catalyst produces an elastomer which proved useful for oil spill recovery and as a sound or vibration barrier. Degussa-Hüls AG is manufacturing Vestenamer® 8012, a polyoctenamer via ROMP of cyclooctene using tungsten based catalyst. The polymer is used in the rubber industry to manufacture tires, molded rubber articles and roller coatings. The endo-dicyclopentadiene (DCPD), an inexpensive, readily available byproduct of the petrochemical industry, which is now subjected to ROMP to produce linear polymer, also gives cross linked polymers with cyclopentene under specific conditions. These poly-DCPD polymers are used to produce bathroom modules, lawn and garden equipment, construction machinery, body panels for trucks etc. The poly-DCPD was put on the market under the trade names TeleneR and MettonR. In the TeleneR process, molybdenum based precatalyst is activated by a mixture of Et 2 AlCl, alcohol and SiCl 4 while the MettonR process utilizes a WCl 6 + WOCl 4 precursor, which is initiated by the addition of EtAlCl 2 . Ciba Specialty Chemicals first investigated the ruthenium initiators for producing the poly-DCPD. However, Materia made it as poly-DCPD resin, which was used in conjunction with glass and thermoplastic microspheres to produce high quality foam products. Later a Japanese company, using ruthenium technology produced a polymer which is used for various applications including bathroom devices.

Fine chemical industry

The development of well-defined and functional-group tolerant ruthenium catalysts has influenced the research in fine chemical research area for the synthesis of complex molecules. 18 Olefin metathesis has been used as one of the key steps in the synthesis of various agrochemicals and pharmaceuticals such as macrocyclic peptides, cyclic sulfonamides, novel macrolides, or insect pheromones. [START_REF] Bicchielli | Recent Applications of Alkene Metathesis in Fine Chemical Synthesis, Green Metathesis Chemistry, Great Challenges in Synthesis[END_REF] Several ruthenium based metathesis initiators became commercially available at industrial relevant scale during the last couple of years, few examples -(phenylthio)methylene Ru complex 1 st and 2 nd generation analogues, 20 Hoveyda-derived air stable ZhanR-catalysts, 21 indenylidene based catalysts by Evonik 22 for pharmaceutical applications etc.

Olefin Metathesis: Historical overview

The discovery

Derived from the Greek words meta (change) and thesis (position), metathesis is the exchange of parts between two substances. Olefin metathesis is a chemical reaction in which two olefins come together in presence of a catalyst and through alkylidene exchange between the two olefins, form two new olefins (Scheme 5). The story of olefin metathesis began almost six decades ago, in 1955, the first carbon-carbon double-bond rearrangement reaction, in the titanium-catalyzed polymerization of norbornene was reported by Anderson and Merckling. 23 After few years, Banks and Bailey reported novel transformation -disproportionation of olefins -conversion of propene into ethene and butene upon treatment with a mixture of triisobutylaluminum and molybdenum oxide on alumina. 24 Later, Calderon and co-workers reported further work using other cycloolefins with a mixture of tungsten hexachloride and ethyl aluminum chloride (WCl 6 /EtAlCl 2 /EtOH) as initiator and suggested that the polymerization of cyclic alkenes and the disproportionation of acyclic alkenes are the same type of reaction and named this metal-catalyzed redistribution of carboncarbon double bonds as olefin metathesis. 25 These catalytic systems had limited applications in organic synthesis, because of the harsh reaction conditions and prolonged initiation periods.

R 2 R 2 R 1 R 1 R 2 R 2 R 1 R 1 R 1 R 1 R 1 R 1 R 2 R 2 R 2 R 2 + + Catalyst
The mechanism underlying metathesis was not yet discovered and remained a mystery.

Chauvin mechanism and first well-defined systems

In 1971, the first generally accepted mechanism for olefin metathesis was proposed by Prof.

Yves Chauvin and his student Jean-Louis Hérisson. 26 Of course, the synthesis of (CO) 5 W=C(CH 3 ) (OCH 3 ) by Prof. Fischer was an important detail for Prof. Chauvin that led him to his hypothesis. 27 In this mechanism, olefin metathesis proceeds via generation of the metallacyclobutane intermediate, by the coordination of the olefin(s) to a metal alkylidene, via a series of alternating [2 + 2]-cycloadditions and cycloreversions. The mechanism has also experimental support by Prof. Grubbs, T. J. Katz, Schrock and others and is now generally accepted as the mechanism for metathesis. 28

R 1 R 1 R 2 R 2 R 2 R 1 + [M] R [M] R R 1 R 1 [M] R 1 R 2 R 2 R 1 R [M] R 1 R 2 R 2 + R 1 R 2 [M] R [M] R = metal alkylidene
Scheme 6: Chauvin's mechanism of Olefin Metathesis.

However, an equilibrium mixture of olefins is obtained, due to the reversibility of all individual steps in the catalytic cycle. For the metathesis to be productive, it is necessary to shift the equilibrium in one direction.

Importantly, this mechanism, with a metal alkylidene initiating metathesis, indicated that metal-alkylidene complexes can act as catalysts for the metathesis reaction with olefins. The attempts to synthesize metal alkylidenes and eventually metallacyclobutanes led to the first single component metathesis catalysts, based upon tungsten, titanium and tantalum-[(CO) 5 WdCPh 2 , 29 bis(cyclopentadienyl) titanocyclobutanes, 30 tris(aryloxide)

tantalacyclobutanes 31 and various dihaloalkoxide-alkylidene complexes of tungsten]. 32 Later, Prof. Schrock and his group produced stable molecular molybdenum-and tungstenalkylidene complexes of the general formula [M (=CHMe 2 Ph) (=N-Ar) (OR 2 )], R being bulky groups (figure 1). 33 Unfortunately, the use of these highly active, early transition-metal catalysts was restricted due to their high sensitivity toward oxygen and moisture and to their limited functional group tolerance. 34,35 Even though, the problem of functional group tolerance can be handled using functional group protection strategy, it is time consuming and a tedious job.

M

Although, the structure and reactivity relationship was well-defined using above well-defined systems, it was important to develop catalysts which react preferentially with olefins in the presence of heteroatomic functionalities.

Why Ru? : Functional group tolerance

Now, if we look at titanium, tungsten, molybdenum, and ruthenium, these catalysts react more selectively with olefins as the metal centers were varied from left to right and bottom to top on the periodic table. 35 Titanium and tungsten are more reactive towards esters, ketones than olefins, while molybdenum being more reactive towards olefins than these systems, cannot tolerate aldehydes or alcohols. In comparison to the early transition metals, the later transition metals, such as ruthenium show preferential and increased reactivity towards olefins. 36

From ill-defined to well defined Ruthenium alkylidene complexes

First, in the 1960s the ROMP of norbornene derivatives with RuCl 3 (hydrate) in refluxing ethanol and under aqueous emulsion conditions was carried out but albeit with low yields. 37 Later, in 1980s, RuCl 3 (hydrate) investigation showed that the ROMP reactions are slower when performed in organic solvents, 38,[START_REF] Zenkl | Several other groups subsequently published related results[END_REF] in contrast to the reactions in aqueous solution. 41 Importantly, addition of acyclic olefins led to their incorporation at the ends of the polymer chains during ROMP 42 suggesting that the active species was a ruthenium alkylidene.

Furthermore, the addition of ethyldiazoacetate to Ru(H 2 O) 6 -(p-toluenesulfonate) 2 to generate Ru-alkylidene, produced a species with higher activity than that of Ru(H 2 O) 6 -(ptoluenesulfonate) 2.

43

This catalysts, showed promising reactivity towards the ROMP of monomers being less strained than norbornene (cyclooctene for instance).

Based on this, the first metathesis active Ru-alkylidene complex 1, 44 was prepared applying similar methodology to that used for the synthesis of tungsten alkylidenes. 45 Further development led to catalysts 2, which showed an improved activity towards low strain cyclic monomers. The catalytic activity of these complexes increases with the basicity of the phosphines in the order PPh 3 , P i Pr 3 < PCy 3 . The catalyst 2 showed functional group tolerance 46 and was air-stable as a solid, retaining its activity even when exposed to water, alcohols, or acids. Because of difficulties in the synthesis of this catalysts, further developments resulted in the preparation of the benzylidene complex 3, commonly known as Grubb's 1 st generation catalyst (Grubbs-I). 47 in the same period, the bis(substituted)N-heterocyclic carbene (NHC) complex 4 was reported by Prof. Hermann and co workers, 48 which showed slightly better activity than Grubbs-I. However, due to less labile nature of NHC ligands, the dissociation of one NHC ligand was difficult. To address this issue further development work to prepare monosubstituted NHC derivative of Grubbs-I complex was carried out, which resulted in catalyst 5 with unsaturated NHC backbone, as reported by Prof.

Ru

Nolan's group and Prof. Grubbs group. 49 Soon after, Prof. Grubbs reported more active catalyst 6 with saturated NHC backbone, known as Grubbs 2 nd generation catalyst (Grubbs-II). 50 Remarkably, Grubbs-II was effective with loadings as low as 0.05 mol % for RCM reactions and 0.0001 mol % (monomer: catalyst= 1,000,000) for ROMP. 51 The slow initiation step of Grubbs-II catalyst was improved by replacement of the phosphine with weakly bound ligands such as pyridine. This 18-electron bis-pyridine adduct referred as the Grubbs 3 rd generation catalyst (Grubbs-III) had a very high initiation rate. The monopyridine complex could be formed by decoordination of one pyridine under vaccum (Figure 5). 52 The discovery of the Grubbs complexes triggered the search for other active ruthenium based metathesis catalysts. Another breakthrough example is the Hoveyda 1 st generation catalyst 9

Ru

Ru

(GH-I) (Figure 6), which was discovered in 1999 during mechanistic studies of Ru-catalyzed styrenyl ether to chromene transformations. 53 This catalyst was found to be exceptionally robust and was isolated in high yield by air-driven silica gel chromatography. Importantly, it forms the same active species as those of Grubbs-I. The 2 nd generation analogue 10 (GH-II) (Figure 6) was a more active catalyst, with similar efficiencies to those of Grubbs-II, but providing selectivity levels for CM and RCM better than the latter. 54 In due course, Prof.

Blechert developed an improved synthesis and patented the catalysts with a number of phenyl vinyl ethers and various substitution patterns on the aromatic ring, for example complex 11

(Figure 6). 55 Studies indicated that the presence of steric bulk adjacent to the chelating unit were critical. 56 Electronic effects in the isopropoxystyrene ligand sphere were investigated by Grela et. al. The introduction of a strong electron-withdrawing group led to complex 12 (Figure 6), which was equally stable but spectacularly more reactive than GH-II. 57 A decrease in electron density of the isopropoxy oxygen atom was expected to reduce its chelating ability, thereby facilitating formation of the 14-electron catalytically active species, while suppressing reassociation to the Ru center. These findings clearly demonstrated that small variations in the ligand structure could result in considerably different catalytic activities. 58 Ru Cl Over the last decade, a constant improvement in the Grubbs, Schrock and Hoveyda classes of catalysts, allowed the widespread use of olefin metathesis in organic syntheses as it could replace advantageously many of the traditional synthetic tools. 59

Cl

NHC -N-heterocyclic carbene in Ru Metathesis catalysts:

The N-heterocyclic carbenes (NHC) are singlet carbenes with excellent stability. 60 They can act as two electron donor ligands towards almost any element in the periodic table and they derive their excellent stability from their unique electronic structure. The carbene carbon atom is sp 2 -hybridised featuring two -bonds to the adjacent nitrogen atoms ("pull" stabilization due to large electronegativity of nitrogen) and an electron lone pair in the remaining sp 2hybrid orbital. Two N C donor interactions from the electron lone pairs of nitrogen into the "empty" p-orbital of the carbene carbon atom complete the electron configuration on the carbene carbon atom ("push" stabilization) and gives the NHC its stability (Figure 7) Due to their electronic structure, NHCs are strong -donor but only weak -acceptor ligands.

They bind strong to many transition metals and afford metal-carbon bonds that are usually less labile than the related metal-phosphine bonds. 61, , 62 63 This decreased lability of carbenes, improve the air and thermal stability of the corresponding organometallic complexes making them more resistant to oxidation. The electronic and steric properties of NHC can be easily modified, by changing the substituents to fine-tune the catalytic properties of the corresponding organometallic complexes.

The stability of cyclic diaminocarbenes NHCs such as imidazolin-2-ylidenes, 1, 2, 4-triazolin-5-ylidenes and benzimidazolylidenes (Figure 7) 64,65 was assigned to their steric bulk which prevents dimerization. For unsaturated NHCs, a further stabilization was associated with their 4n+2 aromatic Hückel configuration. 66 Later, it was found that steric protection was not a decisive factor and sterically less demanding carbenes can be isolated. 67 For instance, the saturated imidazolin-2-ylidenes (or imidazolylidenes), were isolated and were thought to be more electron donating than their unsaturated counterparts. However, studies showed that the basicity of NHC ligands had little to do with the saturated or unsaturated nature of the imidazole backbone. 68,69 While imidazolin-2-ylidenes dimerized under special circumstances, 70 in case of saturated systems the steric constraints of the Nsubstituents determined their existance as either monomeric carbenes or as the enetetramine dimers (Wanzlick equilibrium). The free carbene with sustituents directly bonded (like t Bu or arger) to the N-atoms were stable while smaller groups led to dimerization (Figure 8). 71 l

N N R R N N R R N N C R R Wanzlick equilibrium imidazolinylidene Figure 8: Wanzlick equilibrium.
Profs. Öfele and Wanzlick and Prof. Lappert et. al. reported the synthesis of carbene coordinated organometallic complexes 13, 14 (Figure 9). 72, , , 73 74 75 However, the isolation of the first stable naked NHC 15 (Figure 9) 76 Although, four, 79 six and seven membered 80,81 NHC ligands can be prepared, the fivemembered NHC ligands are the most commonly used.

The heterocyclic carbene precursors can be easily prepared via various synthetic routes. 82 Although, many are stable enough to be isolated, their in-situ generation and their subsequent coordination with the desired metal source is more straightforward and popular.

Most common methods used for the preparation of the Ruthenium precatalyst complexes using NHC as ligands comprise

1) The deprotonation of imidazolium or imidazolinium salts with a strong base, such as potassium hexamethyldisilazane (KHMDS) or potassium tert-butoxide (KO t Bu), to generate free NHCs 83, , , 84 85 86 which, on subsequent coordination to the appropriate ruthenium precursor, affords the targeted organometallic complex. This is usually achieved by displacing one (or more) phosphine or pyridine ligands.

2) The use of Ag 2 O to form the corresponding heterocyclic carbene-Ag complexes (when the in situ generated carbenes tend to dimerize), 87 and their subsequent transmetallation with the metal precursor to afford the desired organometallic complex.

Today, several homogeneous metathesis catalysts are commercially available and as a result, new perspectives are opening up in the amazing research field of olefin metathesis, attracting a vast amount of interest both from industry and academia. [START_REF] Ivin | Olefin Metathesis and Metathesis Polymerization[END_REF] The most successful and wellstudied ruthenium catalysts bear either symmetrical or unsymmetrical imidazoles or imidazolin-2-ylidenes. We will focus on the ruthenium complexes with symmetrical and unsymmetrical imidazolylidene and imidazolin-2-ylidenes ligands.

Ruthenium complexes with symmetrical imidazolylidene and imidazolin-2-ylidenes ligands:

In the above section, we have looked at the development of some popular Ru complexes bearing symmetrical N, N-dimesityl saturated and unsaturated NHC ligands. However several other Ru based complexes with other symmetrical NHCs were successfully prepared and studied First, sterically demanding NHCs were used and the influence of the bulkiness on the catalytic activity of the corresponding complexes (complexes 16-18, Figure 10) was investigated. [START_REF] Jafarpour | [END_REF] Second, NHCs with ortho fluorinated N-bound aryl rings (complexes 19, 20,

Figure 10) were investigated as new ligands and the differences in reactivity was found in the case of Grubbs and Hoveyda type catalysts. This was explained based on the presence of fluorine-ruthenium interactions. 90 Third, NHCs without o-substituents on the N-bound aryl rings were used to generate complexes 21-23 (Figure 10) 91 and an increased efficiency for the formation of tetrasubstituted olefins starting from sterically demanding substrates Fourth, catalysts with N-arylsubstituted NHC without ortho-substituents on the N-aryl groups were prepared and they were found to be prone to degradation compared to complexes bearing ortho-substituted N-aryl NHCs. 92,93 Such a lack of stability was attributed to an easier rotation of the N-aryl groups in the former. Such rotation allowed the complex degradation through C-H bond activation because of the close vicinity of the ortho C-H bond to Ru. To restrict such a rotation and to make the decomposition pathway unfavorable, NHC substituted catalysts with the bulky substituents on the backbone (complexes 24, 25, Figure 10) were prepared and were efficient catalysts in RCM, CM and ROMP. 94,95 Fifth, saturated and unsaturated symmetrical NHCs 96 were prepared to investigate the putative presence of intramolecular -interactions and their influence on the electronic density at the ruthenium center with the corresponding complexes (complex type 26, Figure 10) and the catalytic ability of the later complexes was also investigated. 97 Further, catalysts with pH-responsive NHC ligand (complex 27) was used to favor the removal of residual ruthenium from RCM reaction mixtures by acidification and subsequent filtration. Sixth, catalysts with bulky NHC ligands (complexes 28, 29, Figure 10)

were synthesized to increase the diastereoselectivity of ring rearrangement metathesis reactions. 98, Although, complexes 28 and 29 showed improvements in the diastereoselectivty, were found to less stable in solutions. Complex 30 was found to be an efficient RCM catalyst. 99 Seventh, catalysts bearing saturated NHCs with two aliphatic side groups 100 (complexes 31, 32, Figure 10) were successfully isolated and were found to be highly active in ROMP but less active in model RCM and CM reactions. This low efficiency was explained based on the increased steric bulk of the alkyl groups relative to that of the usual aromatic groups.

N N F F F F Ru Cl Cl PCy 3 Ph N N F F F F Ru Cl Cl O iPr N N F F F F Ru Cl Cl O iPr N N Ru Cl Cl

Ruthenium complexes with unsymmetrical imidazolyl-and imidazolin-2-ylidenes:

The first synthesis of Ru-complexes with unsymmetrical NHC ligands was reported by Prof. Fürstner et. al. in 2001. 101 Complexes 33-35 (Figure 11) were found to be efficient in the formation of tetrasubstituted olefins via. RCM of N,N-dimethallyl-N-tosylamide. Prof. Mol and co-workers attempted the synthesis of complex 37 (Figure 11) to enhance the steric bulk and the electron donating ability of the NHC. Although, the attempts to prepare symmetrical NHC complex failed, probably due to the increased bulkiness of the adamantyl ligand, the unsymmetrical complex 38 (Figure 11) was isolated in good yield. 102 The very low activity in ROMP of norbornene was explained based on the steric hindrance of the adamantyl substituent on the NHC. Unsymmetrical complex 36 (Figure 11) was synthesized to immobilize on various supports. 103 However, rearrangement of the complex during immobilization on silica gel was observed and attributed to the terminal hydroxyl groups.

Complexes 38, 39 (R = Me, Et) (Figure 11) were synthesised with the intentions to increase catalyst activity and improve E/Z selectivity in CM reactions and improvement of diastereoselectivity in RCM reactions. 104 These catalysts indeed showed improved E/Z ratios in selected CM reactions and selectivities in a diastereoselective RCM reaction than symmetrical catalysts. With the same idea, several various N-alkyl-N-aryl-substituted NHCs ruthenium complexes were synthesized and evaluated. (complexes 40, 41 for insatance, Figure 11). 105, , 106 107 Consecutively, Prof. Grubbs and co-workers reported the synthesis of ruthenium complexes containing unsymmetrical NHCs with fluorinated N-aryl groups (complexes 43, 44 Figure 11). 108,109 These complexes showed higher E/Z selectivity in CM reactions. The influence of unsymmetrical NHC ligand on the initiation rate of the irreversible reaction with butyl vinyl ether was also studied. For phosphine-containing catalysts, a dissociative phosphine mechanism was suggested, while an associative mechanism was indicated for phosphine-free catalysts. In 2008, phosphine-containing complexes 42 (Figure 11), coordinated with unsymmetrical bis (N-aryl)-substituted NHCs, were also reported. 110

Prof. Collins and co-workers prepared another family of ruthenium catalysts with unsymmetrical chiral monodentate NHC ligands (complexes 45, 46, Figure 11). 111,112 These catalysts showed high reactivities and high enantiomeric excess in representative ARCM reactions. In 2008, Prof. Buchmeiser, Blechert and Grisi reported the synthesis of complexes 47, 48 113,114 (Figure 11). The pyridine derivatives of complex 47 were studied in alternating copolymerizations reactions. Further study using complexes 48 with different substitutions for asymmetric induction in ARCM, showed that the chiral substitution on the NHC backbone was a key for asymmetric induction.

Prof. Hoveyda and co-workers have reported the first catalysts in which the chiral information of the NHC ligand was transferred directly to the ruthenium center, using binaphtholate moieties (complex 49, Figure 11). 115 These complexes were isolated in high diastereo-and enantiomeric purity without resolution. They were found to be recylable and stable towards air and moisture but their activity was low due to the less electronegative nature and the increased steric bulk of the ligand compared to the initial chlorido ligand. The activity was enhanced by increasing the electronegativity of the naphtholate using trifluoromethylsubstituted chiral NHC ligand. The most significant drawback of binaphthyl-based catalysts was their lengthy, chiral auxiliary directed synthesis. Such an issue was addressed by synthesis of biphenolate, NHC-coordinated complexes. Recently, several reports dealing with the utilization of these unsymmetrical catalysts particularly to improve the E/Z selectivities, diastereoselectivities, alternative copolymerization and selective ethenolysis were also published.

Mechanism of olefin metathesis reactions with Ru-NHC complexes

The mechanism using ruthenium 1 st and 2 nd generation complexes was deeply investigated, and was shown to proceed via an initial dissociation of a phosphine ligand to form a 14electron intermediate, 118 which coordinates to the olefinic substrate to form a 16-electron complex. The complex, through the coupling of the olefin and the ruthenium alkylidene forms a metallacyclobutane ring within the ruthenium coordination sphere. The Ru(IV) metallacycle breaks down in a productive way to form a new olefin and a new alkylidene complex, or in an unproductive way to regenerate the starting compound (Scheme 7)

Ru PCy 3 Cl L Cl Ph Ru Cl L Cl Ph Ru Cl L Cl Ph R 1 R 2 Ru Cl L Cl R 1 R 2 Ph -PCy 3 +PCy3 A B C E K 1 K -1 K 2 K -2 + alkene -alkene K 3 K -3 K 3 K -3 K 2 K -2 + alkene -alkene 3, L = PCy 3 6, L = H 2 IMes D Ru R 2 L Cl Cl Ph R 1
Scheme 7: Proposed dissociative mechanism for Grubbs catalysts. This dissociative pathway is strongly supported by experimental investigations, 119 computational investigations, 120 direct isolation of a ruthenium coordinated to olefin. Prof.

Chen et. al. confirmed the identification of the 14-electron active species (B) 121 using mass spectrometry 122 while recently Piers et. al. directly observed the ruthenacyclobutane (D) which also provided evidence for trans binding mechanism. 123 Apart from the catalyst initiation, the site of olefin coordination and metallacyclobutane formation were also studied. The experimental evidences showed both mechanisms: olefin binding either cis 124 or trans 125 to the L-ligand (Scheme 8). Several computational 126 and experimental 127 investigations supported the trans olefin binding. It was also important to note that, calculations by Prof. Cavallo et. al. indicated that it was difficult to generalize the conclusion due to the influence of several factors (electronic, steric and even solvent) which could alter the reaction pathway. 128 However, in the presence of steric effects, the reaction mechanism was pushed toward the bottom-bound pathway while in the absence of such steric effects, the side-bound reaction pathway was favored. The trans olefin coordination has emerged as the most reliable mechanism in the case of Grubbs catalysts.

The increased activity of the Grubbs-II (G-II) vs. Grubbs-I (G-I) catalysts has also been studied experimentally and theoretically. Initially, faster initiation (dissociation of phosphine) of G-II was attributed to the higher electronic trans-influence of the NHCs (higherdonation properties) as compared to G-I and this was assumed to be the reason for higher reactivity of G-II. However, mechanistic studies 129,130 and gas-phase experiments 131 proved it wrong. In fact the initiation rate (k1) of G-I was 2 orders of magnitude higher than that of G-II. 132 In contrast, the catalytic activity of G-II was about 2 orders of magnitude higher than that of G-I.

Such a contradiction led to the proposal that the coordination of the alkene substrate (k2) vs.

the phosphine ligand (k-1, return to the resting state of the catalyst), on the intermediate B, (Scheme 7), is about 4 orders of magnitude higher for G-II relative to G-I. 121,122 Such an increased affinity of the NHC substituted ruthenium center for -acidic olefins relative todonating phosphines must be the reason for higher activity of G-II. In the case of another breakthrough catalyst namely Grubbs-Hoveyda catalysts (GH-II, complex 10), the proposed catalytic mechanism was slightly different from that for the G-II complexes in terms of initiation, but gave same propagating species (III, Scheme 9) after a single turnover. Initially, 14-electron intermediate II was formed through the dissociation of the benzylidene ether chelating group (Scheme 9). The further coordination of the alkene substrate, followed by metathesis, led to the formation of the catalytically active species III and the release of the isopropoxystyrene derivative. Therefore, once the olefin was completely consumed, the catalyst may return to its resting state by rebinding of isopropoxystyrene (release/return mechanism). 133 However, recent reports by Plenio et. al. showed that the return phenomenon was not common as previously thought. 134 Importantly, an activity enhancement similar to that of Grubbs complexes was observed when the phosphine ligand was replaced by the NHC ligand in the Hoveyda-Grubbs 2 nd generation catalyst.

Immobilization of Ru alkylidene complexes

Heterogenization of homogeneous complexes is expected to provide the advantages of homogeneous catalysis, (i.e. high catalytic performances and reliable structure activity relationship) and heterogeneous catalysis, (i.e. catalyst recycling and ease of separation from the reaction mixture). 135 Several strategies have been therefore developed for immobilization of olefin metathesis catalysts on solid supports. 136 The main strategies are 1) surface organometallic chemistry (SOMC), 2) supported homogeneous catalysts i.e. grafting of silylated organometallic complexes/or parent precursors onto supports and 3) adsorption of complexes onto supports. However, we will mainly discuss here about the first two strategies.

Surface organometallic chemistry (SOMC) 137

In this approach, the organometallic complex is directly attached to the oxide support like silica or alumina: via either a covalent/ionic bond or a Lewis acid-Lewis base interaction. In these systems, the surface is considered as a ligand and is thus directly involved in the coordination sphere of the metal. This approach requires a detailed understanding of the structure of the surface and a control care of the grafting step.

Various well-defined alkylidene systems supported on silica (Figure 12) were prepared in our laboratory and a complete characterization of the supported surface species allowed the understanding of their mechanism of formation and of their reactivity with alkanes and alkenes. 138,139 The alkylidene complexes based on Re (complex 51, Figure 12),

Supported homogenous catalysts 145

In this approach, immobilization of homogeneous catalysts is carried out by attaching the complex itself or one of its ligands via a organic linker, with usually a covalent bond to a support/carrier (oxide, polymer, dendrimer). Using this approach, several reports for the immobilization of olefin metathesis catalysts on various supports were published. 145,147 The Grubbs type catalysts were mainly immobilized through (a) halide ligands, (b) the alkylidene ligand, (c) phosphine or NHC ligands. 13). 148 Monolith-supported version of this catalyst was also used in a continuous flow setup (60, Figure 13). Prof. Blechert's group used trialkoxysilyl-substituted fluorinated carboxylates for immobilizing Grubbs catalysts on silica. 149 Based on similar strategy Grubbs-Hoveyda complex was immobilized on SBA- 15. 150 These catalysts displayed good performances in RCM and Ru leaching was extremely low, (i.e. <100 ppb/g). Application of these catalysts in a continuous flow reactor was also achieved, with high TON (up to several thousands). However, their performances are still very low compared to their homogeneous analogues and deactivation was still a problem.

Immobilization through the alkylidene ligands

In principle, the idea of catalyst immobilization through its alkylidene ligand is based on the release of the active complex during catalysis and its return onto the support at the end of the reaction (boomrang concept). Although, immobilization of Grubbs I 151 or Grubbs II 152 catalysts can be achieved by reaction with a macroporous polystyrene or poly-DVB resin having pendant vinyl groups, the fast decrease of the catalyst activity was observed, preventing effective recycling. Prof. Hoveyda et. al. provided full evidence for the general applicability of the boomerang concept, 153 which was further confirmed by work of Prof.

Barrett et. al. and Prof. Nolan et. al. 154 Because of this, further investigations were directed at immobilizing these types of complexes through the alkylidene ligands on different supports like polyethyleneglycol (PEG) (61, Figure 14), 155 dendrimer (62 Figure 14), 156 polymer , 157 Wang resin, 158 silica via organic linkers (64, Figure 14) 159 and via polymer linkers. 160 Even though these immobilized systems are claimed to be active because of the so called boomerang-concept, recent work by Pleino et. al. showed that it was probably not so obvious and that the catalyst could be purely homogeneous with no return in its original form. 161 Overall, these supported systems have never out-performed the homogeneous systems but they have definitely reduced the Ru leaching in organic samples.

Immobilization through phosphine ligands

The first attempt to immobilize the Grubbs I catalyst by exchanging its phosphine ligands was reported by the group of Prof. Grubbs et. al., using phosphine incorporated polystyrenedivinylbenzene polymers (PS-DVB). 162 However these systems showed much lower performances than their homogeneous counterparts. Improvement in the performances was observed when using MCM-41 supported phosphine ligands (67, Figure 15) 163 probably because of the larger pores, which do not limit the diffusion of reactants (problem usually encountered with polymers). Prof. (71). 170 These catalysts have been mainly used in RCM and related reactions with good catalytic performances, recyclability and lower Ru-contamination but the performance is not as good as those of their homogeneous counterparts. Grubbs catalyst directly on silica gel was also reported. 174 There are also reports on immobilization of an ionically tagged catalyst into an ionic liquid. 175 Although, organic polymers have been mainly used, the inorganic silica materials are often considered as better supports (in terms of thermal and chemical stability) for the immobilization of homogeneous catalysts. In recent years, tremendous efforts are directed towards the use of mesoporous materials for immobilization of catalysts. 176

3. Hybrid organic-inorganic mesoporous silica materials 177

Introduction

A hybrid material is defined here as a material which contains two different components at the molecular level. When these components are inorganic and organic, the solid is considered as organic inorganic hybrid material (OIH material). We will mainly focus on this latter class solid in the following paragraphs. For the development of OIH materials, the sol-gel process is one of the methods of choice because it allows formation of oxide based materials at temperature compatible with introduction of organics. The sol-gel process is based on the hydrolysis and condensation of the metal alkoxide precursors to form the corresponding oxide. In the particular case of silica based solids their functionalization with organics implies the cohydrolysis and cocondensation of tetraalkoxysilane precursor with organosilanes; the stability of the Si-C bond being an advantage to produce organically modified silica network ion one step. Depending on the predominant pore size, the porous materials are classified by IUPAC into three classes: 178 (1) microporous, having pore sizes below 2.0 nm, ( 2) macroporous, with pore sizes exceeding 50.0 nm, (3) mesoporous, with intermediate pore sizes between 2.0 and 50.0 nm.

The sol-gel process 179

The word "sol-gel" corresponds to the abbreviation of "solution-gelification". The sol-gel process is a versatile chemical process initially used for the preparation of inorganic materials such as glasses and ceramics of high purity and homogeneity. It involves the transition of a system from a liquid "sol" into a solid "gel" phase.

Sols are dispersions of colloidal particles in a liquid. Colloids are solid particles with diameters of 1-100 nm. A gel is an interconnected, rigid network with pores of submicrometer dimensions and polymeric chains whose average length is greater than a micrometer. This process involves hydrolysis of metal alkoxide M(OR) 4 (tetramethyl orthosilicate (TMOS) or tetraethyl orthosilicate (TEOS)), with water under acidic or basic conditions to the form silanol groups Si-OH. These silanol groups condense to form siloxane Si-O-Si groups. As the hydrolysis and condensation reactions continue, viscosity increases until the "sol" ceases to flow and form the "gel". For example, the main reaction occuring during the formation of a silica gel are presented in scheme 12.

Si(OCH Tremendous progresses in both fundamental understanding of the sol-gel process and the development of new organic-inorganic hybrid materials has been made and extensively reviewed.

In 1992, the first highly ordered mesoporous molecular sieves M41S (pore size in the range 2-10 nm), were reported by Mobile oil company. 180 The long chain cationic surfactants were used as the template (structure directing agents) during the hydrothermal sol-gel synthesis.

Depending on the starting components and varying synthesis conditions, different mesoporous silica based oxides with an ordered structuration of their porous network were formed, the structuration being hexagonal (MCM-41), cubic (MCM-48) or laminar (MCM-50) (Figure 17). 181 the second mechanism is based on a cooperative assembly between the silica precursor and the surfactant, the latter being introduced in the low concentration if compared to the TLCT concentrations. 183 Recently, the hard sphere packing (HSP) mechanism is described for the synthesis of cubic mesoporous materials. 184 In 1998, silica based Santa Barbara Amorphous type materials (SBA) or SBA-15 185 with larger 4.6 to 30 nanometer pores with hexagonal porous network were produced at the University of California using the cooperative self assembly mechanism. These materials are generally prepared using non-ionic triblock copolymers based on poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO). Such materials have thick silica walls as compared to the thinner walled MCM-41 structures made with conventional cationic surfactants and this characteristic is responsible for their greater hydrothermal stability.

Organically functionalized mesoporous silica

Organic-inorganic hybrid silica based materials are considered to posssess both the properties of their organic and inorganic building blocks and thus offer the possibility to combine enormous functional variations. Such materials, with the advantages of a thermally stable and robust inorganic part are particularly applicable to heterogeneous catalysis. Different strategies were used for the synthesis of organic functionalized porous hybrid materials based on organosilica units: 1) the classical post functionalization (grafting approach), 2) the direct synthesis of organic inorganic hybrid materials with the selective localization of the organic units either in the pores or in the walls of the silica matrix.

Grafting

Grafting is the modification of the inner surfaces of solids (in particular mesostructured silica) by reaction of organosilanes (R'O) 3 SiR, or less frequently chlorosilanes ClSiR 3 or silazanes HN(SiR 3 ) 3 , with the free hydroxyl groups of the oxide surfaces (Scheme 13). The process of grafting is frequently called immobilization. However, such a grafting generally leads to a nonhomogeneous distribution of the organic groups within the pores depending upon the size of the organic residue and the degree of occupation. In extreme cases (e.g. with very bulky organic groups), this can lead to complete closure of the pores (pore blocking). Moreover, the control over the condensation of the organic part on the silica surface is not secured (surface species being mono-, bi-or tripodal -Scheme 18).

Direct synthesis

In this one-pot synthesis method, the materials containing organic residues anchored covalently to their pore walls are formed by the co-hydrolysis and co-condensation of tetraalkoxysilanes [(RO) 4 Si (TEOS or TMOS)] and organotrialkoxyorganosilane precursors (R'O) 3 SiR in the presence of structure-directing agents (i.e. surfactants) (Scheme 14).

Scheme 14: Co-condensation method (direct synthesis), for the synthesis of organically functionalized mesoporous silica phases. R=organic functional group 191

Via this synthetic procedure, the organic units are regularly distributed along the pore channels of the silica matrix (different from classical grafting approach) with a control over the condensation of the organic surface species.

These two methodologies (grafting vs. direct synthesis) present their own advantages and disadvantages: the post-grafting approach is convenient to introduce rapidly all kinds of organic moieties in solids but it does not permit either the control of the distribution of the functional groups in the final material or the nature of the surface species (Figure 18). This lack of control, during the grafting step, can be a major problem for obtaining homogeneous functionalized material, and this could explain the poorer activity of supported homogeneous catalysts, prepared by this method, compared to their homogeneous analogues.

O O S i O O S i O O O S i O O O R O S i O R O R O S i O O RO S i O O O S i S i O O O O d 1 O S i O R O R O S i O O d 2 d 3 O O S i O O S i O O O S i O O O R O S i O R O R O S i O O RO S i O O O S i S i O O O O d 1 O S i O R O R O S i O O d 2 d 3

Figure 18:

Grafted material: a simplified view of the surface oxide after the grafting reaction.

In contrast, the direct synthesis provide highly mesostructured functionalized materials containing regularly distributed organic moieties along their channel pores 186 and being fused within the inorganic framework (Figure 19). However, the experimental procedures are more difficult to handle and optimization is often needed when the organosilane precursor is changed.

Scheme 19: Hybrid organic-inorganic material: a simplified view of the inner surface of the channel pores.

We reported recently immobilization of Grubbs-type catalyst in SBA-15 hybrid material. 187 Herein the active species remains attached to the support during reaction as the catalyst is permanently grafted via one of the NHC substituent. This catalyst was mainly used in selfmetathesis with impressive catalytic performances, recyclability and no Ru-contamination.

Prof. Pleixats et. al. also reported the immobilization of Grubbs-Hoveyda type catalysts in mesoporous silica, 188 in this case the catalysts is anchored via an alkylidene ligand into the mesoporous silica via direct synthesis approach and then further transformed into catalyst. In this case the active species is released in the solution during the reaction and thus needs to be recaptured after the reaction. These catalysts were tested in the RCM reactions with good activity and recyclability but leaching of Ru was not mentioned. An extension of this work was also performed by directly synthesizing the mesoporous material using silylated Grubbs-Hoveyda ruthenium-alkylidene complex via direct synthesis approach. 189 However, catalyst prepared by this method showed lower performances compared to those prepared by earlier method.

Aim

Here the main objective of the study was to selectively form low cyclic oligomers (in particular cyclooctene dimer) in RO-RCM of cyclooctene using metathesis catalysts. The strategy was to develop well-defined, mesoporous, hybrid, organic-inorganic, heterogeneous materials containing Ru-NHC units along the pore channels of their silica matrix. The idea was to use the pore confinement to constrain the formation of cyclic structures over polymers,

i.e. to favor backbiting over polymerization.

+ Dimer Trimer

x + C 32 C 40 higher oligomers and / or polymers + +

Scheme 15: Metathesis of cyclooctene

In the literature, metathesis of cyclic alkenes or acyclic dienes had already been investigated, and that cyclic oligomers were obtained along with polymers, albeit in low yields (Scheme 16). 190 They were obtained via back-biting of the growing chain on the propagating carbene.

Although it is a challenge to control back-biting over polymerisation for the selective formation of specific cyclic structure, it could be addressed by using a cavity to constrain the formation of cyclic structures over polymers. Indeed, such confinement effects are known in heterogeneous catalysis, and can be obtained when the active sites is included in a cavity of given controlled size (shape selective catalysis). 191 Our group has already developed 187 and protected 192 new well-defined heterogeneous catalysts containing Ru-NHC units regularly distributed through the pore channels of the inorganic matrix. These Ru-NHC heterogeneous catalysts were used in the self-metathesis of ethyl-oleate and showed very high catalytic performances (in terms of rate and TON).

Ru L 2 Ar Cl Cl N N R Si O O O Ru L 2 Ar Cl Cl L 1 [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] N N R Si O O O X Ru L 2 Ar Cl Cl N N R Si O O O Ru L 2 Ar Cl Cl L 1 [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] [Ru] N N R Si O O O X
Scheme 17: Mesoporous heterogeneous inorganic matrix containing Ru-NHC units in the pore channels.

Thus, we decided to use and optimize the properties of such mesoporous well-defined Ru-NHC systems to generate selective catalysts for the formation of cyclic oligomers over polymers, in the RO-RCM of cyclooctene.

Chapter 2

Synthesis of hybrid organic-inorganic, heterogeneous Ru-NHC catalysts and their catalytic performances in

RO-RCM of cyclooctene

In the present chapter we have described the following points:

1. The synthesis of hybrid organic-inorganic heterogeneous unsymmetrical Ru-NHC catalysts i. Five well-defined, heterogeneous unsymmetrical Ru-NHC catalysts with different tethers namely propyl (short-flexible), benzyl (semi-rigid), hexyl (long-flexible), phenyl mesityl (long-rigid) and dimethyl phenyl (short-rigid) were prepared and fully characterized. 2. The catalytic performances of these catalysts in the RO-RCM of cyclooctene for the selective formation of cyclic oligomers (in particular dimer of cyclooctene) were studied. 3. A kinetic investigation was perfomed to determine the nature of products (primary vs.

secondary products) during the RO-RCM of cyclooctene and dimer of cyclooctene.

Five targeted heterogeneous catalysts are listed below:

Heterogeneous Ru-NHC catalysts N N Ru Cl Cl L M-RuPr R = SiMe 3 O O O SiOR O O O Si M-RuBn R = SiMe 3 O O O SiO R O O O Si N N Ru Cl Cl L N N Ru Cl Cl L M-RuHex R = SiMe 3 O O O SiOR O O O Si 4 M-RuMs R = SiMe 3 O O O SiOR O O O Si N N Ru Cl Cl L M-RuPhMs R = SiMe 3 O O O SiOR O O O Si N N Ru Cl Cl L

Introduction

Low molecular weight cyclic oligomers (C15-17 cyclic alkenes) are important intermediates in the fragrance and perfume industry to prepare macrocyclic musks. 1 Our objective was thus the selective formation of low molecular weight cyclic oligomers (in particularly dimer-C16) from cyclooctene through the tandem Ring Opening -Ring Closing Metathesis (RO-RCM) reactions, which to date remains a challenge. One of the key problems is the competitive polymerization of cyclooctene via Ring Opening Metathesis Polymerisation (ROMP), which is favoured both entropically and enthalpically at any temperature. RO-RCM of cyclooctene has been reported previously using Re 2 O 7 /Al 2 O 3 catalysts preactivated with tin compounds for the synthesis of macrocyclic dienes. 3 Recently, heterogenized methyltrioxorhenium (MTO) species were used for the synthesis of low molecular weight cyclic oligomers. 4 However, higher activity and better selectivity in lower cyclic-oligomers still remain a challenge.

One parameter to favour the selective formation of specific cyclic structure is the control of back-biting over polymerisation. One approach in the context of heterogeneous catalysis can consist in using confinement effects (shape selective catalysis) 5 to impose constrain for the preferred formation of cyclic structures over polymers.

Our research group has recently developed a new class of heterogeneous catalysts based on regularly distributed surface M-NHC units (M = Ir, Ru, Au) through the pore channels of the mesostructured inorganic matrix. 6 Such well-defined and fully controlled Ru-NHC based materials -obtained by sol-gel process via a templating route -display unprecedented high activity and stability in the self-metathesis of ethyl oleate. 7 Thus, we decided to use these mesoporous materials as catalysts, tuning advantage of their structuration to generate confinement effects as well as a favorable interaction of the Rucenter with the surface to yield mostly cyclic structures over polymers. In this context, we prepared several Ru-NHC hybrid heterogeneous catalysts with different length and flexibility of tethers [M-RuPr (short-flexible tether), M-RuBn (semi-rigid tether), M-RuHex (longflexible tether), M-RuPhMs (long-rigid tether) and M-RuMs (short-rigid tether)] (Figure 1)

and we tested their catalytic performances for the selective formation of cyclic oligomers (particularly cyclic dimer) in RO-RCM of cyclooctene.

Results and discussion

General strategy for the synthesis of hybrid materials containing Ru-NHC units

2D hexagonal mesostructured materials were prepared by sol-gel process via a templating Using this templating route, we synthesized five different hybrid materials as shown in Figure 3. In general, after removal of the surfactant, these materials are quantitively transformed into imidazolium units by reaction with mesityl-imidazole in toluene under reflux for 48 h. The materials are further treated with 2.0 M acid solution at 45 °C for 2 -3 h, in order to transform the surface alkoxy silane groups into silanols. Materials are further extracted with aqueous pyridine/HCl solution for the removal of trace amounts of surfactant. 9 Then, the materials silanol surface groups are passivated into trimethylsilyl units using Me 3 SiBr in presence of triethylamine. This material is then treated with KHMDS to generate a NHC-carbene unit, and contacted with the Grubbs-I complex, thus yielding the targetted Ru-NHC heterogeneous catalyst (Figure 4). The effect of tether length and flexibility were indeed observed and is discussed below, first in terms of chemical structures of Ru-NHC sites (first and second coordination sphere) and then in terms of low cyclic oligomers selectivity and productivity.

O O O Si O O O Si O R O O O Si O O O Si O R R = H or Et R = H or Et T X T N N + Y X - O O O Si O O O Si O R R = H T N N + Y X - O O O Si O O O Si O R R= H T N N + Y X - T = organic linker X = halogen or N N O O O Si O O O Si O R R = SiMe 3 T N N + Y X - O O O Si O O O Si O R R = SiMe 3 T N N Y Ru Ph Cl Cl L Y = mesityl

Interaction of surface functionality with Ru-NHC -Effect of flexibility and length of tether

A key feature of the Ru-NHC pre-catalyst is the presence of a coordinated PCy 3 ligand, which is liberated to generate the active 14 electron species (Scheme 2). For Ru-NHC pre-catalysts the ratio P/Ru is 1. The elemental analysis of the supported pre-catalysts also revealed the ratio P/Ru of ca. 1. We thus investigated the nature of the supported pre-catalysts by 31 P NMR in order to get a better understanding of the structure of these Ru-NHC supported systems, in particular because proton and 13 C solid-state NMR, even using 13 C labelled samples, failed to provide much information about their structures. It is noteworthy that for M-RuPr, M-RuBn and M-RuMs no signal was observed in the 32-36 ppm region in the 31 P NMR spectra as expected for PCy 3 coordinated to Ru-NHC species. This result indicated that the Ru centre was not coordinated to PCy 3 and thus probably stabilized by surface functionalities, e.g. siloxane oxygen (Figures 6a-c). The only -largesignal observed at 49 ppm corresponds to a pentavalent phosphorous compound, probably a tricyclohexylphosphine oxide resulting from side-reactions of PCy 3 with surface functionalities. 10,11 For M-RuHex (long-flexible tether), the major signal still appears at 49 ppm, but it is possible to observe a weak signal at 32 ppm (Figure 6d), suggesting that either some Ru centres have kept a coordinated PCy 3 or phosphonium species are generated. 11 In contrast, for M-RuPhMs (long rigid tether) a strong signal at 36 ppm appears along with the signal at 49 ppm (Figure 6e), suggesting that besides the formation of pentavalent phosphorus compound, a large number of Ru centres (most) are coordinated to PCy 3 . The shoulder peak at around 25 ppm is probably due to the presence of a phosphonium surface species (Figure 6e).

O O O Si T Ru NHC L Ph O O O Si O R O O O Si O O O Si O R Ru NHC L Ph T T T O O O Si T O O O Si O R R u NHC Ph = Propyl (shor t f lex ible tether ), Hexyl ( long felxible tether ) Benzyl (semi-r igid t et her) = L = PCy 3 , R = SiMe 3 L = PCy3
Long r igid tether This result shows that the nature of the tether has indeed a major influence on the structure of supported Ru-NHC pre-catalysts, the interaction with surface functionalities being more prominent with the shorter flexible tethers than with the long rigid tethers i.e.; Pr ~ Bn ~ Ms > Hex >> PhMs (Figure 5). a)

N N Ru Cl Cl L M-RuPr R = SiMe 3 O O O SiOR O O O Si b) M-RuBn R = SiMe 3 O O O SiO R O O O Si N N Ru Cl Cl L c) M-RuMs R = SiMe 3 O O O SiOR O O O Si N N Ru Cl Cl L d) N N Ru Cl Cl L M-RuHex R = SiMe 3 O O O SiOR O O O Si

Evaluation of catalytic performances as a function of the tether

All the catalytic reactions were carried out in toluene with a ratio cyclooctene / Ru = 10,000 using 20 mM solution of cyclooctene in toluene at room temperature unless otherwise noted. Conversion and selectivities were monitored using eicosane as internal standard.

Sample at 0 min was taken before the addition of catalyst and considered as reference point.

All selectivities are defined as follows: S i = (number of mole of cyclooctene converted in product i) / (total number of cyclooctene converted).

The response ratio (cyclooctene and dimer) with respect to eicosane (internal standard) were measured and used to monitor their concentration as a function of time during the catalytic test (Appendix section 5.1). For the higher cyclic oligomers (trimer, tetramer & pentamer), the concentrations were measured with respect to the internal standard assuming that the response factor of n-mers is n times the response factor of cyclooctene (use of FID detector and assuming that there is no segregation in the injector as observed for the dimer).

Oligomers greater than pentamers were not detected by GC with the present method and only in small amounts by direct injection in MS.

Catalytic Performances of Ru-NHC containing hybrid material M-

RuPr for the selective RO-RCM of cyclooctene

The reaction was performed under standard conditions, i.e. with a ratio of cyclooctene / Ru = 10000 and ~21 mM cyclooctene. Results concerning conversion of cyclooctene, product selectivities and mass balance in the cyclo-oligomerisation of cyclooctene are summarized in Figures 7, 8 (details can be found in the appendix -Table 4). In the case of M-RuPr (flexible propyl tether), high conversion of cyclooctene (83% within 7 h) was obtained with an initial rate of ca. 1360 mol/mol Ru/h; the conversion reaching ca.

Conversion (%) vs. Tim e [h]

96% after 20 h (Figure 7).

The mass balance was high at all reaction times: it increased from 79% at low conversion to reach a steady maximum of 87-90% (Figure 8). The main detected products were the dimers and trimers of cyclooctene along with smaller amounts of tetramers and pentamers; higher oligomers up to octamers were detected in small amount (<2%) by mass spectrometry only via direct introduction of the reaction mixtures. The selectivity in dimer was observed to vary from 50% to 54% up to 60-65% conversion of cyclooctene and then decreased slowly to 32-33% from 65-95% conversion of cyclooctene. Concomitantly the selectivity in trimer (17-31%), tetramer (7-16%) and pentamers (3-8%) increased throughout the catalytic test (Figure 8). The correlation between the decrease of selectivity in dimer and the increase of selectivity in higher oligomers along with a constant mass balance of ca. 87-90% is consistent with the conversion of dimer into other oligomers at higher conversions.

Overall, it is noteworthy that M-RuPr displayed the selective formation of lower cyclic oligomers, in particular dimer, with constant mass balance even at higher cyclooctene conversions and the current data suggested that nearly no polymers are formed during the catalytic test and that low cyclic oligomers are mainly obtained with high selectivity.

Moreover, the selectivity at low conversions indicates that all oligomers are possibly formed as primary products, but also via secondary processes. With respect to initial rates, the reactivity of the catalysts for cyclooctene conversion is of 10, Table 1).

Comparison of catalytic

order: M-RuPr > M-RuMs > M-RuBn > M-RuPhMs > M-RuHex (Figure
This result indicates that the catalysts with shorter tethers are more active than those with the longer ones.

In terms of final conversion, the performances of M-RuPr and M-RuBn were observed to be similar (Table 1) where as the performances of M-RuMs are similar to those of M-RuHex, the latter catalysts showing an initiation period and a rapid deactivation with a maximum conversion of 60-65%. M-RuPhMs was found to be the worst catalysts: it displayed an initiation period and a lower maximum conversion (ca. 20-25% after 95-100 h). For this specific catalysts it is noteworthy that (long rigid tether), 31 P NMR (Figure 6e) showed the presence of coordinated phosphine on Ru. This result could explain the presence of an initiation period (the phosphine decoordination from Ru). The faster deactivation of M-RuMs because stabilising interactions between the Ru-NHC active site and the surface functionalities are not favored.

Overall, the trend in terms of stability is: M-RuPr (short-flexible) > M-RuBn (semi-rigid) > M-RuHex (long-flexible) > M-RuMs (short-rigid) > M-RuPhMs (long-rigid), showing that the stability depends mainly on the flexibility and then on the length of the tether.

In terms of selectivity, catalysts with flexible tethers (M-RuPr, M-RuBn and M-RuHex)

showed similar performances, in particular dimer selectivity of 50-54% and mass balance of 85-90%. In contrast, catalysts with rigid tethers and in particular M-RuMs displayed much lower selectivity of dimer (30-35%) and mass balance (65-70%); M-RuPhMs being slightly more active than M-RuMs with the dimer selectivity of 40-45% and a mass balance of 75-80% (Figure 11, 12). Thus presence of a long rigid tether and a phosphine coordinated to Ru seems to be detrimental to catalytic performance, thus illustrating the influence of the interactions between the metal centre and the passivated silica surface.

The slow increase in the selectivity of trimer, tetramer and pentamers throughout the catalytic test was also observed for all the catalysts (Figures for selectivity of all the cyclic products and mass balance can be found in the appendix section), where as the decrease of selectivity in dimer was observed only after conversion of cyclooctene reached 60-65% (Figure 11), for the catalysts M-RuPr and M-RuBn. Overall, catalysts with short flexible tethers were found to be better in terms of rate and selective formation of dimer in RO-RCM of cyclooctene. We can observe here that the rate of conversion is roughly proportional to the concentration of cyclooctene, thus indicating that the reaction is 1 st order with respect to cyclooctene (Figure 13). The experimental data show that product selectivities, at similar conversion (13-15%) and mass balance (81-85%) (Figure 14), are also affected by cyclooctene concentration: Selectivity of dimer increases with the decrease of cyclooctene concentration whereas the selectivity of other products (trimer up to pentamer) decreases. This further supports that dimer is indeed a primary product, where as other oligomers are also formed via secondary processes (COM of dimer).

Kinetic Investigation

Nature of products (primary vs. secondary)

To have a closer look at the the effect of concentration of cyclooctene variations on the formation of each cyclic oligomer (dimer to pentamer), i.e. to have better understanding of the nature of the products (primary and secondary processes involved in their formation). We decided to plot products productivity dimer, trimer, tetramer and the pentamer oligomers We can therefore see a linear increase in the product productivities with conversion (for the first 50-60% conversion), thus suggesting that they were all primary products. However, comparison of the slopes for the reactions carried out at different concentrations of cyclooctene, indicated that the dimer and the trimer formations, were not as much affected by concentrations of cyclooctene if compared to tetramer and pentamer formations (Figure 14 -18).

Productivity of pentam er vs. conversion of cyclooctene

y = 0 R 2 = #N/A y = 2.1271x R 2 =

RO-RCM of dimer

Because of the decrease in the productivity of dimer during the RO-RCM of cyclooctene, we decided to perform the RO-RCM of cyclooctene dimer as a key experiment for understanding the formation of cyclic products. The reaction was carried out with a ratio of dimer / Ru = 5000 and ~10 mM dimer solution in toluene. These conditions were chosen because they correspond to the maximum possible concentration of dimer to be reached considering a selective and quantitative conversion of ~20 mM cyclooctene in its cyclic dimer. The conversion of dimer was found to be slow for the first 1-2 h with the initial rate of ca. 80 mol/mol Ru/h and it slowly increased from 2 -8 h (Figure 19, 20) before slowing down to reach a maximum conversion of 38-39% (Figure 19). At low conversion, RO-RCM of the dimer gave cyclooctene, trimer and tetramer as primary products with high selectivities in trimer and tetramer (Figure 21). The pentamer selectivity was null at low conversion (Figure 21, which is consistent with its formation as at least a secondary product (tetramer + cyclooctene or trimer + dimer). This preliminary data, in particular the formation of cyclooctene, was consistent with a relatively fast back-biting reaction vs. polymerisation.

Conversion (%) vs. Tim e [h]

At low conversions we have observed the increase and decrease of selectivities for trimer, tetramer and pentamer (Figure 21) but this could not give a clear insight in the nature of those products. In contrario, the selectivity for cyclooctene was found to be decreasing from 8-3%

and remained almost constant throughout the reaction (Figure 21) thus indicating that the cyclooctene was observed as a primary product. In order to have a deeper understanding of the influence of cyclooctene formed during the metathesis of dimer, we carried out further experiments with addition of cyclooctene during the dimer metathesis reactions.

Effect of cyclooctene concentration

Effect of cyclooctene addition on the rate of reaction

The influence of cyclooctene during the metathesis of cyclooctene dimer (C16) is studied here by addition of cyclooctene during the metathesis of dimer. The reactions were performed using M-RuPr with a ratio of cyclooctene / Ru = 5,000 and ~10 mM dimer of cyclooctene with no addition of cyclooctene (0 mM), 2 mM cyclooctene and 4 mM cyclooctene. The results are summarized in Figures 222324. (Details can be found in the appendix-Tables 16171819). First, the decrease of the rate of the conversion of dimer was observed as the concentration of cyclooctene increased (Figure 22-24). This is consistent with the fact that the conversion of cyclooctene was faster than this of the dimer.

Conversion (%) vs. Time [h]

Conclusion

We have developed here five well-defined, heterogeneous Ru-NHC catalysts with different tether length and flexibility.

Investigation of the structure of the Ru-NHC active sites by 31 P NMR of the five materials showed that the flexibility of the tethers and thus the presence of interactions with the silica surface functionalities is an important factor for the stability of active Ru site.

Catalytic performances showed that catalysts with short-flexible tethers (M-RuPr and M-RuBn) were better catalysts for RO-RCM of cyclooctene as they provided selectively low cyclic oligomers with high rate.

The higher catalytic performances observed for M-RuPr and M-RuBn compared to those of M-RuHex, RuMs and M-RuPhMs could also be explained by the stabilization of the Ru active species by surface functionalities as suggested by 31 P NMR observations. Further kinetic investigation of the reaction of cyclo-oligomerization with M-RuPr showed that this reaction was 1 st order in cyclooctene, and that dimer and trimer were primary products, while the tetramer and pentamer were secondary products. At this stage the observed selectivity towards lower cyclic oligomers could be attributed either to confinement of pores or to nature of the unsymmetrical NHC ligands (see next chapter).

Experimental section

Synthesis and characterization of hybrid materials General Information:

All the passivation steps and experiments for introduction of metal complex were carried out under 'Ar' using standard Schlenk techniques, using dry and degassed solvents. Toluene was freshly distilled over NaK under 'Ar' in presence of benzophenone ketyl. Dichloromethane was freshly distilled over P 2 O 5 . tetraethoxysilane (TEOS) was distilled over Mg under Ar.

Triethylamine, Pluronic acid P123, Me 3 SiBr (TMSBr), [K(N(SiMe 3 ) 2 ] (0.5 M in toluene), hexamethyldisilazane and Grubbs I catalyst (Cl 2 (PCy 3 ) 2 Ru(=CHPh)) were bought from Sigma-Aldrich. Chlorobenzyltriethoxysilane and 3-chloropropyltriethoxysilane from ABCR. Pluronic P123 from BASF was used for the synthesis of the benzyl chloride containing material to ca. 30 g. Elemental analyses were performed at the microanalysis center in Pascher, Germany.

Nuclear Magnetic Resonance Spectroscopy:

Liquid state NMR spectra were recorded using a Bruker AC 300 and solid state NMR spectra were recorded under MAS on a Bruker Avance 300 and 500 MHz spectrometer with a conventional double resonance 4 mm CP-MAS probe.

The MAS frequency was set to 10-10.5 kHz for all of the experiments reported here. The samples were introduced in a 4 mm zirconia rotor in the glove box and tightly closed.

29

Silicon NMR

T 3 Q 2 Q 3 Q 4 -65 ppm -90 ppm -101 ppm -111 ppm OSi Si SiO C OSi OSi Si SiO OR OR OSi Si SiO OR OSi OSi Si SiO OSi OSi

(3-iodopropyl) triethoxysilane

Pyridine/Water/2M HCl 70 °C, 16 -18 h

N N + M-HPrIm R = H O O O SiOR O O O Si N N Ru Cl Cl L M-RuPr R = SiMe 3 O O O SiO R O O O Si N N + M-PPrIm R = SiMe 3 O O O SiO R O O O Si N N + M-EHPrIm R = H O O O SiO R O O O Si N N + M-PrIm R = H or Et O O O SiOR O O O Si M-PrI R = H or Et O O O SiOR O O O Si I Cl - Cl - Cl - Cl -

Synthesis

We have synthesized M-HPrIm as described in the previous work. Isotherm of type IV, characteristic of mesoporous materials with a narrow pore size distribution, S BET : 1010.3 7 m 2 /g, Vp: 1.1 cm 3 /g and Dp BJHads .: 6.2 nm.

Synthesis of material M-EHPrIm

To the material M-HPrIm (5.6 g) was added a solution of pyridine (42.0 mL), water (42.0mL) and 2 M aqueous HCl (7.0 mL), and the reaction mixture was heated to 70 °C. After stirring for 16-17 h, the solid was filtered and washed successively with water (3 × 200 mL), acetone (3 × 200 mL) diethyl ether (2 × 100 mL). The solid was then dried for 14-16 h under high vacuum (10 -5 mm Hg) at 135 °C, affording 5.1 g of material.

Elemental analysis: Si: 36.2%; N: 1.22%

Synthesis of material M-RuPr

To the suspension of material M-PPrIm (3.15 g, 1.0 equiv) in toluene (10.0 mL) was slowly added at room temperature 3.4 mL of a 0.5 M toluene solution of [K(N(SiMe3)2] (1.2 equiv).

After stirring for 30 min., slowly added the solution of Cl 2 (PCy 3 ) 2 Ru(=CHPh) (1.41 g, 1.2 equiv) in toluene (20.0 mL) at room temperature and stirred overnight. The solid was then filtered and washed successively with toluene (2 × 20 mL) and dichloromethane (4 × 20 mL) till the filtrate was colourless. The material was dried under high vacuum (10 -5 mm Hg) at room temperature for 14-16 h to yield 3.1 g of light beige solid.

Elemental analysis: Si: 37.2%; N: 1.04%; Ru: 0.63%, P : 0.17%.

M-BnCl R = H or Et

O O O SiOR O O O Si M-BnIm R = SiMe 3 O O O SiOR O O O Si N N + Cl Cl - M-HBnIm R = H or Et O O O SiOR O O O Si N N + Cl - M-PBnIm R = SiMe 3 O O O SiOR O O O Si N N + Cl - M-RuBn R = SiMe 3 O O O SiOR O O O Si N N Ru Cl Cl L Scheme 5: Synthesis of M-RuBn.

Synthesis

Synthesis of this catalyst has already been depicted in the previous work. Isotherm of type IV, characteristic of mesoporous materials with a narrow pore size distribution, S BET : 971.7 5 m 2 /g, Vp: 1.0 cm 3 /g and Dp BJHads .: 6.5 nm.

Synthesis of M-RuBn

To the suspension of material M-PBnIm (1.5 g, 0.693 mmol, 1.0 eq) in toluene (8.0 mL, 5. Elemental analysis: Si: 35.0%; N: 0.87%; Ru: 0.84%; P: 0.24%.

Synthesis

Original synthesis and development work for M-HexIm was carried out in Montpellier in LCMOS (ICG), in collaboration with our laboratory (ANR PNANO "Nanobiocat") and this work was already published in the CPE patent. Isotherm of type IV, characteristic of mesoporous materials with a narrow pore size distribution, S BET : 656.2 2 m 2 /g, Vp: 0.79 cm 3 /g and Dp BJHads .: 8.4 nm.

Synthesis of M-HHexIm

The material M-HexIm (1.6 g, DYA-207) was stirred in a 2 M aqueous HI solution (160.0 mL), at 45 °C for 2 h. The solid was then filtered and washed successively with water (2 × 100 mL), acetone (2 × 100 mL) & diethyl ether (2 × 100 mL). The solid was dried under high vacuum (10 -5 mm Hg) for overnight (14-16 h) at 135 °C, affording 1.3 g of material.

Synthesis of M-PHexIm

To the suspension of material M-HHexIm (1.05 g) in toluene (80.0 mL), triethylamine (13.6 mL) and trimethylsilylbromide (6.3 mL) were added at room temperature. After stirring the reaction mixture overnight, the solid was filtered under 'Ar' and washed successively with toluene (2 × 50 mL) and dichloromethane (2 × 50 mL). The solid was dried under high vacuum (10 -5 mm Hg) for overnight (14-16 h) at 135 °C, affording 1.1 g of material.

Synthesis of M-RuHex

To the suspension of material M-PHexIm (0.92 g, 0.409 mmol, 1.0 eq) in toluene (6.0 mL, 5.5 rel vol), 0.5 M toluene solution of [K(N(SiMe 3 ) 2 ] (1.0 mL, 0.490 mmol, 1.2 mol eq) was slowly added at room temperature. After stirring for 30 min., a solution of Cl 2 (PCy 3 ) 2 Ru(=CHPh) (0.40 g, 0.490 mmol, 1.2 mol eq) in toluene (4.0 mL, 3.6 rel vol) was slowly added at room temperature and stirred overnight. The solid was then filtered and Overall yield for the synthesis of PhMs precursor was 14%. Isotherm of type IV, characteristic of mesoporous materials with a narrow pore size distribution, S BET : 581.9 2 m 2 /g, Vp: 1.3 cm 3 /g and Dp BJHads .: 9.9 nm.

Synthesis of M-RuPhMS

M-RuPhMs R = SiMe 3 O O O SiOR O O O S i N N Ru Cl Cl L M-PPhMs R = SiMe 3 O O O SiOR O O O S i N N + Cl - M-EHPhMsIm R = H O O O SiOR O O O S i N N + Cl - M-HPhMsIm R = H O O O SiOR O O O S i N N + Cl - M-PhMsIm R = H or Et O O O SiOR O O O S i N N + Cl -

M-PhMs R = H or Et

water (3 × 100 mL), acetone (3 × 100 mL) and diethyl ether (3 × 100 mL). The solid was then dried for 14-16 h under high vacuum (10 -5 mm Hg) at 135 °C, affording 0.5 g of product.

Synthesis of M-PPhMsIm

To the suspension of material M-EPhMsIm (0. Attribution: -111 ppm (Q 4 ), -102 ppm (Q 3 ), -81 ppm (T 3 ), 12 ppm (-OSi(Me) 3 ).

Synthesis of M-RuPhMs

To the suspension of M-PPhMsIm (0.38 g, 1.0 equiv) in toluene (2.0 mL) was slowly added a 0.5 M toluene solution of [K(N(SiMe 3 ) 2 ] (0.4 mL, 1.2 mol equiv) at room temperature.

After stirring for 30 min, a solution of Cl 2 (PCy 3 ) 2 Ru(=CHPh) (0.16 g, 1.2 mol eq) in toluene (4.0 mL) at room temperature was slowly added to the reaction mixture. After stirring the reaction mixture for 20 h, the solid was filtered and washed successively with toluene (2 × 20mL) and dichloromethane (3 × 20 mL) till the filtrate was colourless. The material was dried under high vacuum (10 -5 mm Hg) at room temperature for 22-24 h to yield 0.35 g of a light greenish solid.

Elemental analysis: N:1.13%; Ru:1.40%., P: 0.40%.

M-RuMs

R = SiMe 3 O O O SiOR O O O Si N N Ru Cl Cl L M-EMsIm R = H or Et O O O Si OR O O O Si N N M-EMsImBn R = H or Et O O O SiOR O O O Si N N + M-MsIm R = H or Et O O O SiOR O O O Si N N Cl - M-EHMsImBn R = H or Et O O O SiOR O O O Si N N + Cl - M-EMsImBn R = SiMe 3 O O O SiOR O O O Si N N + Cl -
Scheme 9: Synthesis of M-RuMs.

Synthesis of M-EMsIm

To the material M-MsIm (1.08 g), was added a mixture of pyridine (7.5 mL), water (7.5 mL) and 2 M aqueous HCl (1.25 mL). The reaction mixture was heated to 70 °C. After stirring the reaction mixture for 20-24 h, the solid was filtered and washed successively with water (3 × 200 mL), acetone (3 × 200 mL) and diethyl ether (3 × 100 mL). The solid was then dried for 14-16 h under high vacuum (10 -5 mm Hg) at 135 °C, affording 0.7 g of material.

M-EMsImBn

To the material M-EMsIm (0.63 g) were added toluene (10.0 mL) and benzyl chloride (0.62 g, 0.56 mL, 20 mol eq.). The reaction mixture was heated up to 110 °C. After stirring the reaction mixture for 70-72 h, the solid was filtered and washed successively with toluene (3 × 100 mL), acetone (3 × 200 mL) and diethyl ether (3 × 100 mL). The solid was then dried for 14-16 h under high vacuum (10 -5 mm Hg) at 135 °C, affording 0.6 g of material.

Synthesis of M-EHMsImBn

To the material M-EMsImBn (0.6 g) was added 60 mL of a 2 M aqueous HCl. The reaction mixture was heated up to 45 °C. After stirring the reaction mixture for 2 -2.5 h, the solid was filtered and washed successively with water (3 × 200 mL), acetone (3 × 200 mL) and diethyl ether (3 × 100 mL). The solid was then dried for 5-6 h under high vacuum (10 -5 mm Hg) at 135 °C, affording 0.4 g of material.

Synthesis of M-PMsIm

To the suspension of material M-EHPhMsIm (0.4 g) in toluene (28.0 mL), were added triethylamine (4.2 mL, 200 mol eq) and trimethylsilylbromide (2.0 mL, 100 mol eq) at room Attribution: 128-134 ppm (aromatic carbon atoms), 15-17 ppm (CH 3 of mesityl unit), 0 ppm to (-OSi(Me) 3 ).

Synthesis of M-RuMs

To the suspension of M-PMsIm (0.2 g, 1.0 equiv) in toluene (2.0 mL), was slowly added a 0.5 M toluene solution of [K(N(SiMe 3 ) 2 ] (0.17 mL, 1.2 mol equiv) at room temperature. After stirring for 30 min, a solution of Cl 2 (PCy 3 ) 2 Ru(=CHPh) (0.07 g, 1.2 mol eq) in toluene (2.0 mL) at room temperature was slowly added to the reaction mixture. After stirring the reaction mixture overnight, the solid was filtered and washed successively with toluene (2 × 20mL)

and dichloromethane (3 × 20 mL) until the filtrate was colourless. The material was dried under high vacuum (10 -5 mm Hg) at room temperature for 12-16 h to yield 0.15 g of a light greenish solid. Elemental analysis: Si: 36.9%; N:0.86%; Ru: 0.71%, P: 0.19%. Attribution: 49 ppm (phosphine oxide (probably due to further reaction of liberated PCy 3 ), no signal for the PCy 3 bound to Ru. peaks around 100 and 0 ppm are spinning side bands.

Catalytic performances of hybrid materials

General information for catalytic tests:

All metathesis experiments were carried out under an inert atmosphere, in a glove-box.

Toluene was dried over NaK and distilled under nitrogen prior to use. Cyclooctene (ciscyclooctene) was purchased from Aldrich, distilled over Na prior to use. Catalysts G-II and GH-II were purchased from Aldrich and catalyst (Nolan) was synthesized according to the literature procedures.

Cyclooctene metathesis experiments with heterogeneous Ru-complexes (Ratio

Cyclooctene/ Ru of c.a. 10,000).

Representative procedure for heterogeneous catalysts: Eicosane was dissolved in 20mM toluene solution of cyclooctene. Sample was taken for GC analysis as a reference.

Heterogeneous Ru-catalyst was added to the above solution of cyclooctene, at room temperature. The progress of the metathesis reaction was monitored by sampling at suitable intervals. (The samples were immediately quenched by an excess of ethyl acetate). The samples were analysed by GC with a HP5 column.

Appendix:

GC standardization (Response factor using internal standard

Standardization of GC was performed to calculate the response of cyclooctene & dimer with respect to eicosane (standard). Standard solutions were prepared with different concentrations of cyclooctene & dimer keeping the eicosane concentration constant at 8.14 mM. Response ratio for the cyclooctene was 0.368 & for the dimer 0.786 (see Figure 5, 6 and Table S1).

Gas phase analyses (metathesis) were performed on Agilent Technologies 7890A GC apparatus equipped with a FID detector and a HP5 Fame column (30 m × 0.32 mm). Split ratio of GC was set to 50:1. Sample injection was 1 microliter with 10 microliter syringe.(details can be found in Appendix -Table S1).

Catalytic performance of M-RuBn

Catalytic performance of M-RuHex

Selectivity (%)

Sel-dimer (%) Sel-trimer (%) Sel-tetra (%) Sel-penta (%) Mass balance (%)

Figure 62: Selectivity of cyclic products (%) vs. conversion of cyclooctene (%) using M-RuHex. Representative plots for the productivity of products in RO-RCM of cyclooctene using different concentration of cyclooctene using M-RuPr. Chapter 3

Catalytic performance of M-RuPhMs

Catalytic performance of M-RuMs

Kinetic investigation

RO-RCM of cyclooctene

Productivity of dimer vs. conversion of cyclooctene

Synthesis and catalytic performances of homogeneous unsymmetrical and symmetrical

Ru-NHC catalysts 1. Introduction

We have observed that RO-RCM of cyclooctene, using Ru-NHC based heterogeneous catalysts, showed selectivity towards formation of cyclic oligomers. It was thus important to know whether the observed selectivity was due to pore confinement/surface interaction which could impose constrain to favour formation of cyclic oligomers over higher oligomers and /or polymers or to the chemical structure of Ru-NHC sites (dissymmetry of the NHC ligand).

Note that, several reports can be found in the literature concerning synthesis and use of unsymmetrical Ru-NHC for ROMP, RCM and CM reactions. 1 Recently, the research groups of Prof. Chen 2 and Prof. Buchmeiser Herein, we will discuss the synthesis and catalytic performances of unsymmetrical Ru-NHC catalysts analogues to those contained in our hybrid heterogeneous catalysts, in view of understanding the origin of the selectivities in RO-RCM of cyclooctene.

Results and discussion

General strategy for the synthesis of homogeneous complexes

Homogeneous unsymmetrical Ru-NHC complexes were prepared using the respective unsymmetrical imidazolium salts (Scheme 1). Although several methods were used for the synthesis of symmetrical and unsymmetrical imidazolium salts, 4 we chose to prepare them by quaternisation of mesityl imidazole with alkyl halides in 80-90% isolated yields. For the synthesis of Grubbs-type catalysts, the imidazolium salt was treated with KHMDS (potassium bis(trimethylsilyl)amide) in toluene at RT to generate the corresponding naked carbene. The carbene was further reacted with the Grubbs-I complex at RT yielding the targetted Ru-NHC complex. The detailed synthesis of such complex is described in the experimental section.

R 1 N N + R 2 X - R 1 N N R 2 .. N N R 1 R 2 Ru Cl

Structural feature of homogeneous catalysts

Three unsymmetrical homogeneous silylated complexes, namely RuPr Si , RuBn Si and RuPhMs Si (Figure 1a) were prepared as analogues of the Ru-NHC sites contained in our hybrid heterogeneous catalysts M-RuPr, M-RuBn and M-RuPhMs. Note that non-silylated unsymmetrical complexes RuPr and RuBn were also synthesised to get insight in the influence of the silane groups over the selectivity and the activity during the RO-RCM of The only distinctive feature of these Ru-NHC homogeneous catalysts compared to the classical Ru-NHC catalysts (G-II and N-II) is the coordination of unsymmetrical NHC ligands on Ru. All these unsymmetrical complexes were obtained in high yield and fully characterized by liquid state NMR and mass spectrometry.

In the specific case of RuBn, an X-ray structure was obtained. Note that the RuBn Si is already reported by our group and the X-ray structure was elucidated. 5 The structural analysis of RuBn reveals a square pyramidal coordination with a nearly linear Cl( 2 indicating the presence of the -interactions, which is also a characteristic feature of symmetrical catalysts reported earlier. 6,7 Attempts to crytallize RuPr, RuPr Si and RuPhMs Si complexes are still under progress. The synthesis and the characterisation of these catalysts is described in the experimental section. All the catalysts showed high catalytic activities leading to full conversion of cyclooctene in 24 h (Figure 3). The symmetrical catalysts showed higher activity than the unsymmetrical catalysts, in terms of initial rates with the following order of reactivity: G-II (TOF 9721 h -1 ) > N-II (TOF 4181 h -1 ) > RuPr Si (TOF 1090 h -1 ) > RuBn Si (TOF 570 h -1 )> RuPhMs Si (TOF 513 h -1 ) (Figure 3, Table 1). However, it is noteworthy that these catalysts displayed very different mass balance and product selectivities. The symmetrical catalysts (G-II and N-II) exhibit a rather low mass balance (30-40%) up to 90% conversion before a sharp increase up to 80% at high conversion (Figure 4). This is consistent with the formation of polymers (or higher oligomers) first and then their conversion into smaller oligomers via backbiting when cyclooctene is consumed (i.e. at very high conversion). In sharp contrast, the unsymmetrical catalysts led to a high mass balance reaching a constant value of 80% after 10% conversion and remained constant throughout the reaction (Figure 4). This experimental data clearly shows that the formation of smaller cyclic oligomers (up to pentamers) was favored. In terms of selectivity, the major product was the dimer along with smaller amounts of trimer, tetramer and pentamer cyclic oligomers for all catalysts, in particular the dimer selectivity reached 50% for unsymmetrical catalysts, but only 30% for symmetrical ones (Figure 5, Table 1). It is also noteworthy that for unsymmetrical catalysts the trimer was also produced with a significant yet lower selectivity of 24%, yielding a dimer/trimer ratio of ca. 2:1 (Table 1).

Comparison of Ru

Interestingly, the selectivity of dimer decreased slowly to 28-30% from 65 to 95% conversion of cyclooctene (Figure 5). The decrease in the selectivity of dimer at higher conversion (with mass balance being constant) indicates the conversion of the dimer into higher oligomers.

In conclusion, the unsymmetrical nature of NHC is indeed a key parameter for the favoured formation of lower cyclic oligomers in RO-RCM of cyclooctene, i.e. backbiting is favoured over polymerisation in case of unsymmetrical catalysts but the influence of silicon atom on the selectivity need to be clarified to assess this later comment (vide supra).

These results suggest that the higher dimer selectivity observed in case of hybrid heterogeneous catalysts is not due to pore confinement effect, but it is related to the unsymmetrical nature of the NHC bonded to Ru.

Effect of the silane group on the NHC substituent -Comparison of catalytic performances of unsymmetrical homogeneous catalysts (silylated vs. non-siloxy silylated)

We have investigated here the effect of silane groups present on the NHC substituents by comparison of the catalytic performances of unsymmetrical homogeneous silylated catalysts RuPr Si , RuBn Si with non silylated RuPr, RuBn. Detail results for the individual catalysts can be found in Appendix section. All the catalysts showed high activity, with different initial rates and the order of reactivity was RuPr (TOF 2343 h -1 ) > RuPr Si (TOF 1090 h -1 ) > RuBn Si (TOF 770 h -1 )> RuBn (TOF 505 h -1 ) (Figure 6, Table 2). Note that in case of RuPr Si the silane group lowered the initial rate, in contrast to that was observed for RuBn Si . Such difference could be mainly due to the difference in the initiation periods of each system. However, all the catalysts showed similar performances in term of mass balance which increased to 80% within 10-15% conversion and remained constant throughout the reaction (Figure 7). Selectivities in all products, in particular in dimer and trimer, were found to be similar (Figure 8, Table 2) Overall, the comparison of the catalytic performances of silylated (RuPr Si and RuBn Si ) and non-silylated (RuPr and RuBn) catalysts indicate that there was no influence of silane group, over the selectivity of cyclic products or over the mass balance during the RO-RCM of cyclooctene, at the exception of slight modification in the initial rates. Thus, the origin of low oligomers selectivity arose exclusively from the unsymmetrical nature of the NHC ligand.

Conversion (%) vs. Time [h]

much lower performances of M-RuPhMs compared to those of RuPhMs Si in terms of rate and productivity (final conversion and TON) could be attributed to the absence of surface interactions stabilizing the Ru-NHC active sites.

Interestingly, in terms of mass balance, all heterogeneous catalysts showed almost similar results to those of their homogeneous analogues (Figure 11, Table 3). The only exception was observed for RuPhMs Si , for which a decrease in mass balance (from 80% to 60%) was observed at the end of the reaction (conversion between 95-97%), indicating the formation of higher oligomers and/or polymers (Figure 11). This was mainly due to the higher performances of the homogeneous system vs. the heterogeneous system.

In terms of dimer selectivity, the heterogeneous and homogeneous catalysts were found to be equivalent. Although, we could observe a slightly faster decrease in dimer selectivity for homogeneous systems (Figure 12), being possibly due to either the faster rate of reaction for the homogeneous systems or the adsorption-desorption problem of the dimer in heterogeneous systems, slowing down the metathesis of dimer in these systems. For trimers, tetramers and pentamers, there was an increase in the selectivity throughout the reaction for all systems. Overall, the performances of our heterogeneous systems were found to be almost similar to those of the respective homogeneous analogues, in terms of dimer selectivity and mass balance (Table 3), clearly showing that active sites in both heterogeneous and homogeneous systems were equivalent if not identical, with surface providing stability to active sites of heterogeneous catalysts.

Proposed mechanism

Such dramatic selectivity switch due to the presence of unsymmetrical NHC ligand is reminiscent of what was reported regarding the sequence-selective copolymerization of norbornene and cyclooctene using unsymmetrical phosphine or NHC ligands. 2,3 Such chemoselectivity could be explained by the fact that the alkylidene ligand swings between two non-equivalent "positions" (two different configuration associated to two different steric environments) for each metathesis cycle, thus allowing alternating site reactivity.

This sequence selective ROMP, providing alternated cyclooctene/norbonene copolymer, originates from the catalyst architecture having dual-site configuration, which discriminates between two substrates in the same catalytic reaction (ROMP). Such mechanism can also explain here the observed selectivity towards cyclic oligomers in particular the selective formation of dimers and trimers including their ratio in the RO-RCM of a single substrate, cyclooctene, by alternatively favouring one reaction over another, Ring Opening (ROM) vs.

Ring Closing (RCM) Metathesis (propagation vs. backbiting) (Scheme 2).

For illustration, Ru-NHC complexes enter the catalytic cycle by de-coordinating the phosphine ligand to generate a reactive Such proposed mechanism explains the preferred formation of dimer and trimer products including the observed 2:1 ratio (Table 4), if one considers that all backbiting reactions on remote alkenes from D LESS are equally favored (BB 2 BB 3 ). NHC-units provide selectively small cyclic oligomers -dimer and trimer -over polymers from cyclooctene. This is in sharp contrast with symmetrical homologues, which lead mainly to polymers. This unexpected selectivity is due to a controlled tandem RO-RCM reaction, where one configuration favors intramolecular backbiting and the other one coordination of an additional substrate (intermolecular), thus leading to RO-RCM.

Conclusion

Ru-alkylidene metathesis catalysts bearing unsymmetrical NHC-units provide selectively small cyclic oligomers dimer and trimer -over polymers from cyclooctene. This is in sharp contrast with symmetrical homologues, which lead mainly to polymers.

Silane functionalities in homogeneous systems does not have any effect on their catalytic performances in terms of dimer selectivity and mass balance. The unsymmetrical nature of NHC is thus the key for the selective formation of lower cylic oligomers over higher oligomers and/or polymers.

There is no evidence for pore confinement or/surface effect in the mesoporous, hybrid heterogeneous catalysts over the selectivity in low cyclic oligomers.

The active Ru-NHC sites in both heterogeneous and homogeneous systems are identical (similar performances in terms of selectivity of dimer and mass balance), with surface interactions providing stability to the active Ru-NHC sites in case of heterogeneous catalysts.

The proposed mechanism based on the catalyst architecture having dual-site configuration is consistent with the observed selectivity towards cyclic oligomers in particular the selective formation of dimers and trimers. Figure14: 13 2. Grubbs I ( 0.9 eq) Overnight, R.T.

Synthesis

The catalysts has been synthesized previously. 2. Grubbs I ( 0.9 eq) Overnight, R.T.

Synthesis of RuBn

To 1-mesityl-3-benzyl imidazolium chloride (0. 2. Grubbs I ( 0.9 eq) Overnight, R.T.

Synthesis

The catalysts has been synthesized previously.

. Synthesis of (PhMsIm Si )

To the solution of triisopropoxysilylphenylmesityl imidazole (0.63 g) in toluene (10.0 mL) was added benzyl chloride (0.21 g, 1.2 mol eq), and the reaction mixture was heated to reflux.

After stirring for 24 h the solid was filtered and washed with pentane (20.0 mL). Viscous liquid was dried at 50 °C under vaccum to afford 0.7 g of the PhMsIm Si . The product was characterized by NMR. 1 H NMR (CD 2 Cl 2 , 300 MHz): (ppm) = 1.25 (d, J HH = 6Hz, 18H, (-CH(CH 3 ) 2 ) 3 , 2.24 (s, 6H, -ArCH 3 ), 4.33 (m, 3H, -CH(CH 3 ) 2 ), 5.97 (s, 2H, -CH 2 Ph), 7.26 (s, 1H), 7.46-7.50 (m, 5H), 7.63-7.66 (m, 5H), 7.79 (d, J HH = 9 Hz , 2H), 11.23 (s, 1H). 13 C NMR (CD 2 Cl 2 , 75 MHz): (ppm) = 143. 7 C ar , 140.7 C ar, 139.3 C ar , 136.4 C ar , 136.3 C ar , 136.2 C ar , 133.8 C ar , 129.4 C ar , 129.3 C ar , 129.0 C ar, 127.9 C ar, 125.4 C ar, 123.1 C ar,

Synthesis of RuPhMs Si

To 1-triisopropoxysilylphenylmesityl -3-benzyl imidazolium chloride (0.35 g, 0.60 mmol) in 5 mL of toluene, was added 1.45 mL (0.72 mmol) of a 0.5 M toluene solution of [K(N(SiMe 3 ) 2 ]. After stirring for 20 min, a solution of Cl 2 (PCy 3 ) 2 Ru(=CHPh) (0.55, 0.66 mmol ) in 10 mL of toluene was added. The reaction mixture was stirred for 3 h and filtered over celite. The solvent was removed under vacuum, and the residual solid product was crystallized in toluene and pentane giving 0.16 g of RuPhMs Si . 1 H NMR (CD 2 Cl 2 , 300 MHz):

(ppm) = 19.2 (s, 1H), 7.93 (br, 1H), 7.37 -7.47 (m,5H), 7.25 (t, 1H, J = 7.5 Hz), 6.88 -6.99 (m, 5H), 6.85 (br, 2H), 5.9 (s, 2H), 4.32 (m, 1H, -CH(CH 3 ) 2 ) 2.4-2.3 (m, 4H), 2.0 (s, 6H), 1.64-1.53 (m, 18H), 1.24 (d, 18H, J = 6Hz) 1.11-0.9 (m, 14H), 31 P NMR (CD 2 Cl 2 , 300 MHz): (ppm) = 36.4 (s, 1P). 13 C NMR (CD 2 Cl 2 , 75 MHz): (ppm) = 163.2 (C NHC =Ru, J P-C = 75 Hz), 151. 4 C ar , 141.5 C ar , 140.9 C ar, 138.1 C ar , 136.9 C ar , 135.3 C ar , 135.0 C ar , 131.8 C ar , 129.9 C ar , 129.4 C ar , 128.8 C ar, 128.6 C ar, 128.2.4 C ar, 126.3 C ar, 123.8 C ar, 220 restraints Extinction coefficient: 52 ( 9)

RuBn Si

G-II

N-II

Geometric parameters (Å, º)

Ru1-Cl2 In the BASF company, promising results for the selective formation of low cyclic oligomers in the RO-RCM of cyclooctene were observed using symmetrical GH-II complexes, immobilized on Grace SP silica. 1 To further investigate the role of the surface, we looked at the performances of symmetrical and unsymmetrical GH-II type homogeneous catalysts and their heterogeneous analogues prepared by adsorption on Grace SP silica support.

In the present chapter we will thus describe the following points:

1. The synthesis, characterization and catalytic properties of heterogeneous catalysts RuGH-II/silica (immobilized GH-II on silica).

Introduction

In recent years, several reports concerning the immobilization of olefin metathesis catalysts on various supports were investigated using different strategies. 2 The Grubbs-type catalysts were immobilized via (a) exchange of halide ligands 3 (b) exchange of phosphine and NHC ligands 4 (c) the functionalization of supports by alkylidene ligand. 5 In the latter case, the nonpermanent grafting of the precatalyst to the support allowed the release of the active species into the reaction mixture after the initial catalytic cycle and the recapture of the resting state when the reaction was complete, this phenomenon being called the "boomrang effect".

However, recent work by Pleino et al. has shown that it is probably not the case, and that the catalyst is purely homogeneous. 6 Besides, Sels et al. reported recently an alternative convenient method for the immobilization of Grubbs-Hoveyda catalyst: adsorption of molecular Ru-NHC complex on the silica support. 1 However, till today, the exact nature of the interaction between the molecular catalyst and the silica surface is still unknown. Yet, based on this strategy, BASF showed that higher performances in RO-RCM of cyclooctene under flow conditions could be obtained compared to those of homogeneous equivalents.

Here, the goal is to obtain further insight into the structure of such catalysts through spectroscopy and reactivity studies. Further improvement of these catalysts activity/selectivity will also be attempted.

Results and discussion

Synthesis, characterization and catalytic performances of GH-II

catalyst immobilized on silica (RuGH-II/silica)

Synthesis of immobilized catalyst RuGH-II/silica

A study concerning the "best" BASF system (GH-II adsorbed on Grace SP silica support calcined at 550 °C under 'Ar') was carried out.

The preparation of the supported catalyst required the following experimental procedure: a dichloromethane solution of Grubbs-Hoveyda catalyst was added to the suspension of the dehydroxylated Grace support in dichloromethane. After stirring for 2 h, the solvent was removed under vacuum yielding the targetted RuGH-II/silica catalyst (Scheme 1) as reported by BASF. Here, Ru loading was typically 0.064% wt . However, the low Ru loading and thus the larger amount of support could represent a drawback for catalysis because of adsorption/desorption problems but also for catalyst characterization. Note that such loading is about 10 times lower than that of our hybrid heterogeneous catalyst M-RuPr as discussed in the previous chapter 2 (Table 1). For example, if 5 mg of M-RuPr are needed for a catalytic run, we need 50 mg of RuGH-II/silica to be in the same conditions.

Study of the acidity of support by pyridine adsorption using IR (DRIFT) technique

In order to understand the nature of the interaction of the molecular complex and silica, the acidity of the support was investigated by pyridine adsorption. The acidity was monitored by DRIFT technique, however the expected distinctive peaks corresponding to the C=C frequencies for the hydrogen bonded pyridine (in the region around 1600 cm -1 ) were not observed, indicating that pyridine desorbed at 150 °C (Figure 3, Table 2)

and therefore that the support presented very little acidity. The observed difference in the intensity of Si-OH at 3750 cm -1 was not significant, in particular because of the use of DRIFT technique, which is not quantitative (Figure 2). show any evidence for the presence of adsorbed GH-II complex either (signals corresponding to the C-H frequencies expected around 3000 cm -1 ) (Figure 3). This is probably due to the very high dilution of GH-II complex in the RuGH-II/silica catalyst. IR spectroscopy is thus not the technique of choice to investigate such systems, despite its higher sensitivity compared to NMR spectroscopy. Overall no structural information could be obtained by usual spectroscopic techniques; one alternative option being the use of solid state NMR using DNP. 6, 7). The low mass balance at low conversions could be due to a problem of adsorption/desorption of the reagents because of the presence of large amount of support.

Note however that the RuGH-II/silica displayed almost similar catalytic performances in terms of selectivity of dimer and mass balance than those of M-RuPr. More importantly, in chapter 3, we have seen that the unsymmetrical nature of NHC ligand was the key factor for the observed selectivity towards low cyclic oligomers (dimer and trimer). Thus it was possible to propose that upon adsorption of GH-II, dissymmetrisation of the NHC ligand occured, with one mesityl substituent more strongly interacting with the silica surface than the other (Figure 8). Finally, comparison of the catalytic performances (RuGH-II/silica vs. GH-II), clearly showed that the catalysts had different active sites and thus that, in RuGH-II/silica, the reaction does not take place in the homogeneous phase (i.e. no release of molecular GH-II in the solution which performed catalysis). To further investigate these observations and with the hope to generate improved catalysts, we prepared unsymmetrical GH-II type complexes RuPrGH-II and RuBnGH-II and they were further adsorbed on SP Grace silica support, yielding RuPrGH-II/silica and RuBnGH-II/silica. The preparation and the comparison of the catalytic performances for these systems are discussed in the following section.

Homogeneous and silica-immobilized unsymmetrical NHC-GH-II type complexes

Synthesis of homogeneous catalysts

To determine the influence of the disymmetry of the NHC ligand, we have developed the synthesis of unsymmetrical molecular GH-II type complexes and further adsorbed them on Grace silica. For the synthesis of unsymmetrical GH-II type catalysts, a two-step process was used. First, the imidazolium salt was treated with the Ag 2 O in dichloromethane at RT to generate the silver carbene. The silver carbene was further reacted with the GH-I complex in the presence of CuCl in toluene at 50°C. The targetted Ru-NHC compound was isolated in 65-70% yield via column chromatography. It is noteworthy that synthesis of GH-II type catalysts via this route typically provides low yields of ca. 30-35% and was thus optimized here

. 8 R 1 N N R 2 R 1 N N + R 2 X - Ag X N N R 1 R 2 Ru Cl Cl O Ag 2 O DCM GH-I, CuCl
Toluene, Scheme 2: Methodology for the synthesis of Ru-NHC GH-II type homogeneous catalysts.

Two unsymmetrical catalysts RuPrGH-II and RuBnGH-II (Figure 9) were prepared and their detailed synthesis is described in the experimental section.

Structural feature of homogeneous catalysts

Suitable crystals for X-ray crystallography were obtained for both RuPrGH-II and RuBnGH-II (Figure 9). Structural analysis of RuPrGH-II and RuBnGH-II showed shorter bond lengths for the Ru-C of the NHC ligand, bond distance (1.985 Å for both the catalysts) than that observed for GH-II (1.978 Å). An increase in the (C-N-C) bond angles (4-5°) for the NHC substituents with respect to NHC backbone carbons was observed as compared to GH-II, thus indicating an increased steric hindrance around the metal center. Note that, an increase of the Ru-benzylidene bond distance was observed for RuBnGH-II (1.840 Å) compared to that obtained for GH-II (1.831 Å), the effect being smaller in the case of RuPrGH-II (1.832 Å). The benzylidene protons were located under the mesityl group as reported already on similar compounds. 9

Immobilization of unsymmetrical GH-II type catalysts

The immobilization of unsymmetrical GH-II type catalysts was carried out by adsorption on Grace SP 550 -10020 pretreated at 550 °C under 'Ar'. The same procedure as described in

Catalytic performances of homogeneous and immobilized catalysts

As the selectivity for low cyclic products was attributed to the unsymmetrical nature of NHC (see chapter 3) and as the grace silica surface further induced similar trend when adsorbing

Conclusion

The adsorption of GH-II complex on silica induced the reversal of products selectivity (i.e. here small cyclic oligomers are formed), if compared to GH-II complex which produces mainly polymers and/or higher oligomers.

Immobilized unsymmetrical catalysts (RuPrGH-II/silica and RuBnGH-II/silica)

showed little activity if compared to RuGH-II/silica with no improvement in the selectivity of cyclic oligomers.

In all cases, while surface could bring selectivity, it is detrimental to the reaction rate, probably through retardation of catalyst initiation. Such an effect was further enhanced in case of unsymmetrical GH-II type catalysts because of the initiation mechanism that involved a rotation of the alkylidene ligand in place.

The catalytic performances of unsymmetrical catalysts RuPrGH-II and RuBnGH-II were found to be similar to those of RuPr and RuBn catalysts, in terms of dimer selectivity and mass balance, thus confirming that the unsymmetrical nature of NHC was a key for low cyclic oligomers selectivity in RO-RCM of cyclooctene.

Synthesis

The "best" BASF catalyst (optimized loading and support) was prepared using Grace SP 550 -10020 support pretreated at 550 °C under 'Ar', with a heating ramp of 5 °C/min and plateau kept at 550 °C for 5 h (this support was characterized by pyridine adsorption, see section 3.1.2). To 1.0 g of this "activated" support in dichloromethane (10 mL), was added a dichloromethane solution of GH II type catalyst (4 mg, 0.064%wt of Ru), and the resulting suspension was stirred for 2 h. After removal of dichloromethane at 50 °C under vacuum, the obtained catalysts were stored in the glove box.

Synthesis of RuBnGH-II

To a solution of (1-mesityl-3-benzyl-imidazol-2-ylidene) AgCl (0.42 g, 1.0 mmol ) in 10 mL of toluene, were added CuCl (0.098 g, 1.0 mmol) and GH-I (0.51 g, 0.85 mmol). The reaction mixture was stirred for 2 days at 50°C. The reaction mixture was filtered over Celite. The solvent was removed under vacuum and the solid product was purified by column chromatography using acetone and pentane mixture (25:75) (Watkin, 1994, Prince, 1982) [weight] = 1.0/[A 0 *T 0 (x) + A 1 *T 1 (x)

RuPrGH-II

General conclusion

The main objective of the study was to selectively form lower cyclic oligomers (in particular cyclooctene dimer) in RO-RCM of cyclooctene. The strategy was to develop well-defined, single-site mesostructured heterogeneous materials containing regularly distributed Ru-NHC units along the pore channels of their silica matrix and to use the pore confinement to constrain the formation of cyclic structures over polymers, i.e. to favor backbiting over polymerization.

Towards this goal, we prepared and characterized hybrid, heterogeneous Ru-NHC based catalysts with different tether lengths and flexibilities: M-RuPr (short-flexible tether), M-RuBn (semi-rigid tether), M-RuHex (long-flexible tether), M-RuPhMs (long-rigid tether)

and M-RuMs (short-rigid tether).

The structural investigation of these catalysts by 31 We also showed that these catalysts displayed unprecedented high mass balance and selectivity for low cyclic oligomers (dimer and trimers) compared to those of symmetrical G-II and GH-II homogeneous catalysts. In particular, the mass balance was 85-90% and remained constant throughout the reaction with dimer and trimer selectivities of 50% and 25%, respectively. These data clearly show the preference for the cyclic oligomers formation over polymers, in other words backbiting is favoured over polymerization. Furthermore, among these highly selective catalysts, those with short-flexible tethers (M-RuPr and M-RuBn) are the best ones in particular in terms of rate and stability, thus further illustrating the Finally, we also showed that for the BASF catalyst the selectivity was very similar to that of unsymmetrical systems, and we thus proposed that adsorbing GH-II on silica promotes the disymmetrization of the complex. Attempts to further increase the selectivity of these systems by adsorbing unsymmetrical precursors was carried out, but such systems displayed unfortunately very little activity and no improvement of selectivity.

Overall, we have successfully developed both well-defined single site Ru-NHC based heterogeneous catalysts and their homogeneous analogues for the selective formation of cyclic oligomers. The Ru-NHC alkylidene metathesis catalysts were found to require unsymmetrical NHC ligands to generate a dual catalytic site configuration: one site favors intramolecular backbiting while the other one coordinates an additional substrate (intermolecular) and favors propagation. This original catalyst architecture provided selectivity for the formation of small cyclic oligomer (dimer and trimer) -over polymers from cyclooctene via a tandem RO-RCM reaction. These new results open perspectives in forming selectively macrocycles from other cyclic alkenes via metathesis.

Perspectives

Knowing that the unsymmetrical nature of NHC is key for the selective formation of low cyclic oligomers in the tandem RO-RCM of cyclooctene, it would be interesting to test these catalysts with other cycloolefins (cycloheptene, cyclopentene etc.) as substrates for the formation of the corresponding low cyclic oligomers (dimer, trimer and tetramers), because these molecules are key intermediates in the flavor and perfume industry (synthesis of macrocyclic musks).

With the catalyst architecture having dual-site configuration, it would also be worth looking at the alternating co-RO-RCM for various mixture of cyclic alkenes. For example cyclohexene does not undergo metathesis and thus cannot be used to generate cyclic C 12 diene. However, co-RO-RCM of cycloheptene and cyclopentene could be an attractive solution for this product. Moreover, generation of odd numbered cyclic systems like C 13 (cyclooctene + cyclopentene) and C 15 (cyclooctene + cycloheptene) could also be generated by this approach, taking into account that these reactions depend on several factors like reactivity differences of substrates. Finally, it would also be important to investigate in more details the structure (in particular, how the molecular complex interacts with the surface) of the BASF catalyst (RuGH-II/silica) to obtain deeper understanding of the observed reactivity and selectivity in RO-RCM of cyclooctene. Structure investigation by surface enhanced NMR spectroscopy using dinuclear polarization technique (DNP) could be the way forward. [1][2]

Faculté

  Institut des Sciences Pharmaceutiques et Biologiques Institut des Sciences et Techniques de la Réadaptation Département de formation et Centre de Recherche en Biologie Humaine Directeur : M. le Professeur J. Etienne Directeur : M. le Professeur F-N. Gilly Directeur : M. le Professeur D. Bourgeois Directeur : M. le Professeur F. Locher Directeur : M. le Professeur Y. Matillon Directeur : M. le Professeur P. Farge COMPOSANTES ET DEPARTEMENTS DE SCIENCES ET TECHNOLOGIE Chimie Physique Electronique Institut Universitaire de Technologie de Lyon 1 Institut de Science Financière et d'Assurances Institut Universitaire de Formation des Maîtres Directeur : M. le Dr. F. Demareln Directeur : M. le Professeur F. Fleury Directeur : Mme le Professeur H. Parrot Directeur : M. N. Siauve Directeur : M. le Professeur S. Akkouche Directeur : M. le Professeur ADirecteur : M. le Professeur C. Coulet Directeur : M. le Professeur J-C. Augros Directeur : M. R. Bernard

Scheme 1 :

 1 Scheme 1: General representation of polymerization vs. backbiting (ROMP vs. RO-RCM).

Scheme 4 :

 4 Scheme 4: Cross metathesis (CM) reactions.

Scheme 5 :

 5 Scheme 5: Olefin metathesis reaction.

Figure 1 :

 1 Figure 1: Schrock's Mo and W catalysts.

Figure 2 :

 2 Figure 2: Functional group tolerance of early and late transition metal olefin metathesis catalysts.35

Figure 3 :

 3 Figure 3: Ruthenium catalysts containing phosphine ligands.

Figure 4 :

 4 Figure 4: Ruthenium catalysts containing N-heterocyclic carbene ligands.

Figure 5 :

 5 Figure 5: Grubbs 3 rd generation catalysts.

Figure 6 :

 6 Figure 6: Hoveyda-type catalysts.

Figure 7 :

 7 Figure 7: Push-pull stabilization in NHC and diaminocarbenes.

Figure 9 :

 9 Figure 9: First reported NHC-coordinated organometallic complexes and isolable carbene.

Figure 10 :

 10 Figure 10: symmetrical Ru-NHC catalysts with different NHC ligands.

Scheme 8 :

 8 Scheme 8: Coordination of olefin with Ru.

1 IIIScheme 9 :

 19 Scheme 9: active 14 electron intermediate after first turnover.

Figure 12 :Scheme 10 :

 1210 Figure 12: Well-defined alkylidene systems supported on silica.Recently, the research group of Prof. Marciniec also reported the preparation of heterogeneous catalysts based on Ru-NHC sites immobilized on silica through covalent Ru-O-Si bonds (Scheme 10).144

Figure 13 :

 13 Figure 13: Few examples of catalysts immobilized through halide exchange. 145, 147c

Figure 14 :

 14 Figure 14: Examples of catalysts immobilized via alkylidene. 145

Figure 16 :

 16 Figure 16: Examples of catalysts immobilized via NHC ligand. 145, 147c

Figure 17 :

 17 Figure 17: Different structures of mesoporous MCM41S materials a) MCM-41 (2D Hexagonal), b) MCM-48 (cubic), and c) MCM-50 (lamellar). 191 Two different mechanisms were proposed for the formation of these materials (Scheme 11): 1) the true liquid-crystal templating (TLCT) mechanism, where the presence of the alkoxysilane precursor [normally tetraethyl-(TEOS) or tetramethylorthosilica (TMOS)] is not required for the formation of liquid crystalline phase because the surfactant is already organized in compact mesophases and this high concentration of surfactant is needed, 182 2)

Scheme 11 :

 11 Scheme 11: Formation of mesoporous materials by structure-directing agents: a) true liquid-crystal template mechanism, b) cooperative liquid crystal template mechanism. 191

Scheme 13 :

 13 Scheme 13: Post synthetic functionalization of a mesoporous silica with organosilanes (R'O) 3 SiR. R=organic functional group. 191

Scheme 16 :

 16 Scheme 16: Ring opening-Ring Closing Metathesis (RO-RCM) reaction vs. Ring Opening Metathesis Polymerization (ROMP).

Figure 1 :

 1 Figure 1: Well-defined heterogeneous unsymmetrical Ru-NHC catalysts.

route 8 ,

 8 i.e. via cohydrolysis and co-polycondensation of tetraethyl-orthosilicate (TEOS) and an organotrialkoxysilane RSi-(OR) 3 in the presence of a surfactant (used as structure-directing agent), namely the triblock copolymer, Pluronic 123, EO 20 PO 70 EO 20, [poly(ethyleneoxide)poly(propyleneoxide)-poly(ethyleneoxide)]. The surfactant was then removed by non destructive solvent extraction thus liberating the material porosity (Figure 2).

Figure 2 :

 2 Figure 2: Synthesis of hybrid materials with organic functionalities inside the pores.

Figure 3 :

 3 Figure 3: Hybrid materials with different organic tethers.

Figure 4 :

 4 Figure 4: Methodology for the synthesis of Ru-NHC materials.

Scheme 2 :

 2 Scheme 2: Dissociation of phosphine to generate 14 e -species.

Figure 5 :

 5 Figure 5: Presence or absence of interactions between the surface functionality and the Ru phosphine complex depending on the tether.

Figure 6 :

 6 Figure 6: 31 P NMR for heterogeneous Ru-NHC catalysts, peaks at 0 and 100 ppm are spinning side bands

Figure 7 :Figure 8 :

 78 Figure 7: Conversion of cyclooctene (%) vs. time [h] using M-RuPr. Selectivity (%) vs. Conversion (%) (M-RuPr)

Figure 9 :Figure 10 :Figure 11 :Figure 12 :

 9101112 Figure 9: Comparison of conversion of cyclooctene (%) vs. time [h] using various heterogeneous catalysts.

-primary vs. secondary products 2 . 4 . 1 .Figure 13 :

 24113 Figure 13: Rate [mol/mol Ru/h] vs. Concentration [mM]. Effect of cyclooctene concentration on rate of reaction in COM of cyclooctene.

RateFigure 14 :

 14 Figure 14: Selectivity of isomers (%) vs. Concentration [mM] at 13-15% conversion of cyclooctene Effect of cyclooctene concentration on the selectivity of products in COM of cyclooctene.

(Figure 15 :

 15 Figure 15: Productivity of dimer at 50-60% conversion of cyclooctene.

Figure 16 :

 16 Figure 16: Productivity of trimer at 50-60% conversion of cyclooctene.

Figure 17 :

 17 Figure 17: Productivity of tetramer at 50-60% conversion of cyclooctene.

Figure 18 :

 18 Figure 18: Productivity of pentamer at 50-60% conversion of cyclooctene.

Scheme 3 :

 3 Scheme 3: RO-RCM of cyclooctene dimer.

Figure 19 :Figure 20 :Figure 21 :

 192021 Figure 19: Conversion (%) vs. time [h] using M-RuPr.

Figure 22 :Figure 23 :

 2223 Figure 22: Comparison of Conversion of dimer (%) vs. time [h].

Figure 24 :

 24 Figure 24: Rate of dimer [mol/mol Ru/h] vs. cyclooctene concentration [mM].

Scheme 4 :

 4 Scheme 4: Synthesis of M-RuPr.

Figure 28 :Figure 29 :

 2829 Figure 28: Nitrogen adsorption-desorption isotherm of M-PrI.

Figure 30 :

 30 Figure 30: Solid State 13 C NMR of M-HPrIm.Peaks at 120-140 ppm are attributed to aromatic and imidazolium carbon atoms, 76-66 ppm to surfactant, 60 ppm to -OCH 2 CH 3 , 52 ppm to -CH 2 N of the propyl, 9 and 24 ppm to -CH 2 of the propyl groups respectively, 17 ppm to methyl groups of mesityl.

Figure 31 : 4 . 1 . 1 . 5 .

 314115 Figure 31: Solid State 13 C NMR of M-EHPrIm.Peaks at 120-140 ppm are attributed to aromatic and imidazolium carbons, 52 ppm to -CH 2 N of propyl, 9 and 25 ppm to -CH 2 of the propyl group, 17 ppm to methyl groups of mesityl. (Note: peaks at 76-66 ppm (to surfactant) and 60 ppm (to -OCH 2 CH 3 ) are absent. Indicating at complete removal of the surfactant and ethoxy groups on the surface.)

Figure 32 :

 32 Figure 32: Solid State 13 C NMR of M-PPrIm. Peaks at 120-140 ppm are attributed to aromatic and imidazolium carbons, 51 ppm to -CH 2 N of propyl, 8 and 23 ppm to -CH 2 of the propyl group,17 ppm to methyl groups of mesityl and at 0 ppm to -OSi(CH 3 ) 3.

Figure 33 :

 33 Figure 33: Solid state 29 Si NMR of M-PPrIm. Peaks at 12, -68, -103 and -111 ppm are attributed to -OSi(CH 3 ) 3, T 3 , Q 3 and Q 4 .

Figure 34 :

 34 Figure 34: Solid State 13 C NMR of M-RuPr.Peaks at 120-135 ppm are attributed to aromatic and imidazolium carbons, 52 ppm to -CH 2 N of propyl, 26 ppm to -PCy 3 ,8 ppm to -CH 2 of propyl,18 ppm to methyl groups of mesityl and at 0 ppm to -OSi-(CH 3 ) 3.

Figure 35 :

 35 Figure 35: Solid State 31 P NMR of M-RuPr.Attribution: 49 ppm (phosphine oxide (probably due to further reaction of liberated PCy 3 ) no signal at 36 ppm (PCy 3 bound to Ru).

Figure 36 :Figure 37 :

 3637 Figure 36: Nitrogen adsorption-desorption isotherm of M-BnCl.

5 M

 5 Toluene solution of [K(N(SiMe 3 ) 2 ] (1.66 mL, 0.831 mmol, 1.2 mol eq) was slowly added at room temperature. After stirring for 30 min. slowly added the solution of Cl 2 (PCy 3 ) 2 Ru(=CHPh) (0.68 g, 0.831 mmol, 1.2 mol eq) in toluene (6.0 ml, 4.0 rel vol) at room temperature. After stirring the reaction mixture for overnight, filtered the solid and washed successively with toluene ( 3 × 10mL) and dichloromethane ( 3 × 10mL) till the filtrate was colourless. The material was dried under high vacuum(10 -5 mm Hg) at room temperature overnight(14-16 h) to yield 1.4 g of a light beige solid.

Figure 38 :

 38 Figure 38: Solid State 13 C NMR of M-RuBn.Peaks at 122-141 ppm are attributed to aromatic and imidazolium carbon atoms, 74 ppm to surfactant, 52 ppm to -CH 2 N of propyl, 26 ppm to -PCy 3 ,17 ppm to methyl groups of mesityl and at 0 ppm to -OSi-(CH 3 ) 3, peaks around 215 ppm are spinning side bands.

Figure 39 :Scheme 6 :

 396 Figure 39: Solid State 31 P NMR of M-RuBn.Attribution: 49 ppm (phosphine oxide (probably due to further reaction of liberated PCy 3 ) no signal at 36 ppm (PCy 3 bound to Ru). peaks around 100 and 0 ppm are spinning side bands.

Figure 40 :Figure 41 :

 4041 Figure 40: Nitrogen adsorption-desorption isotherm of M-HexIm.

Figure 42 :

 42 Figure 42: Solid State 13 C NMR of M-PHexIm.Peaks at 120-140 ppm are attributed to aromatic and imidazolium carbon atoms, 30, 24 ppm to -CH 2 of Hexyl groups, 17 ppm to methyl groups of mesityl unit and at 0 ppm to -OSi-(CH 3 ) 3.

Figure 43 :

 43 Figure 43: Solid state 29 Si NMR of M-PHexIm. Peaks at 11, -69, -102 and -111 ppm are attributed to -OSi(CH 3 ) 3, T 3 , Q 3 and Q 4 .

  washed successively with toluene (3 × 10 mL) and dichloromethane ( 3 × 10 mL) under 'Ar' till the filtrate was colourless. The material was dried under high vacuum(10 -5 mm Hg) at room temperature(14-16 h) to yield 0.85 g of light beige solid. Elemental analysis: Si: 35.8%; N: 0.80%; Ru: 0.71%; P: 0.20%.

Figure 44 :

 44 Figure 44: Solid State 13 C NMR of M-RuHex.Peaks at 122-139 ppm are attributed to aromatic and imidazolium carbon atoms, 50 ppm to methoxy groups on the surface, 29, 22, 12 ppm to -CH 2 of hexyl groups, 25 ppm to -PCy 3 moities, around 17 ppm to methyl groups of mesityl unit, and at 0 ppm to -OSi-(CH 3 ) 3.

Figure 45 :

 45 Figure 45: Solid State 31 P NMR of M-RuHex.Attribution: 49 ppm (phosphine oxide-probably due to further reaction of liberated PCy 3 ), 32 ppm (weak signal for PCy 3 bound to Ru or phosphonium species).

Scheme 7 :

 7 Scheme 7: Synthesis of Precursor PhMs.

Scheme 8 : 6 4Figure 46 :Figure 47 :

 864647 Scheme 8: Synthesis of M-RuPhMs.NOTE:Original synthesis and development work for PhMs (precursor) and M-PhMs were carried out in Montpellier in LCMOS (ICG), in collaboration with our laboratory (ANR PNANO "Nanobiocat") and this work was already published in the CPE patent.6

Figure 49 :

 49 Figure 49: Solid State 13 C NMR of M-EPhMsIm. Attribution: 128-142 ppm (aromatic carbon atoms), 54 ppm to -NCH 2 Ph, of 15 ppm (CH 3 of mesityl unit).

  4 g) in toluene (28.0 mL) was added triethylamine (5.1 mL) and trimethylsilylbromide (2.5 mL) at room temperature. The reaction mixture was stirred overnight. The solid was further filtered and washed successively with toluene (3 × 20 mL) and dichloromethane (3 × 20 mL). The solid was dried under high vacuum (10 -5 mm Hg) overnight (16-18 h) at 135 °C, affording 0.4 g of material.

Figure 50 :

 50 Figure 50: Solid State 13 C NMR of M-PPhMsIm.Attribution: 128-142 ppm (aromatic carbons), 15 ppm (CH 3 of mesityl), 0 ppm to (-OSi(Me) 3 ).

Figure 51 :

 51 Figure 51: Solid State 29 Si NMR of M-PPhMsIm.

Figure 52 :

 52 Figure 52: Solid State 13 C NMR of M-RuPhMs. Attribution: 126-140 ppm (aromatic carbon atoms), 26 ppm (PCy 3 moieties), 15 ppm (CH 3 of mesityl unit), 0 ppm to (-OSi(Me) 3 ).

Figure 53 :

 53 Figure 53: Solid State 31 P NMR of M-RuPhMs.Attribution: 49 ppm (phosphine oxide-probably due to further reaction of liberated PCy 3 ) 36 ppm (PCy 3 bound to Ru -first evidence of a coordinated Phosphine on Ru), shoulder peak around 30 ppm (probably due to the phosphonium species).

  temperature. The reaction mixture was stirred overnight. The solid was then filtered and washed successively with toluene (3 × 20 mL) and dichloromethaner (3 × 20 mL). The solid was dried under high vacuum (10 -5 mm Hg) overnight (16-18 h) at 135 °C, affording 0.25 g of material. Elemental analysis: Si: 40%; N: 0.81%.

Figure 54 :

 54 Figure 54: Solid State 13 C NMR of M-PMsIm.

Figure 55 :

 55 Figure 55: Solid State 13 C NMR of M-RuMs. Attribution: 120-134 ppm (aromatic carbon atoms), 54 ppm to -NCH 2 Ph, 26 ppm (-PCy 3 moieties), 17 ppm (CH 3 of mesityl unit), 0 ppm to (-OSi(Me) 3 ), peaks around 210 ppm are spinning side bands.

Figure 56 :

 56 Figure 56: Solid State 31 P NMR of M-RuMs.

Figure 57 :Figure 58 :

 5758 Figure 57: Response ratio of C8 /E.

Figure 59 :

 59 Figure 59 : Conversion of cyclooctene (%) vs. time [h] using M-RuBn.

Figure 61 :

 61 Figure 61: Conversion of cyclooctene (%) vs. time [h] using M-RuHex.

Figure 63 :

 63 Figure 63 : Conversion of cyclooctene (%) vs. time [h] using M-RuPhMs.

Figure 65 :Figure 66 :

 6566 Figure 65 : Conversion of cyclooctene (%) vs. time [h] using M-RuMs. Selectivity (%) vs. Conversion (%) (M-RuMs)

Figure 67 :Figure 68 :Figure 69 :Figure 70 :

 67686970 Figure 67: Productivity of dimer for the reactions carried out with different concentration of cyclooctene using M-RuPr.Productivity of trimer vs. conversion of cyclooctene

  3 have developed unsymmetrical catalysts for sequenceselective copolymerization of norbornene (NBE) with cis-cyclooctene (COE) and cyclopentene (CPE) by Ring Opening Metathesis Polymerization (ROMP). The observed chemoselectivity was attributed to the dual configuration of catalysts provided by the presence of an unsymmetrical ancillary ligand (phosphine or NHC), which allowed discrimination between two substrates in the same catalytic reaction (ROMP).

Scheme 1 :

 1 Scheme 1: Methodology for the synthesis of Ru-NHC homogeneous catalysts.

Figure 1 :

 1 Figure 1: Homogeneous unsymmetrical and symmetrical Ru-NHC pre-catalysts.

2 :

 2 )-Ru-Cl(3) angle (165.56 °). However, RuBn displays a Ru-C(23) bond distance (1.830 Å) shorter than that in N-II (1.841 Å), and an increase in the bond angles (2-4 °) for the NHC substituents with respect to NHC backbone carbon atoms as compared to N-II, indicating a slight increase of steric interactions around the metal center. Selected geometrical features of Ru-NHC pre-catalysts RuBn and N-II. The carbene unit is perpendicular to the C(30)-Ru-P plane, and the carbene aryl moiety is slightly twisted out of the Cl(2)-Ru-Cl(3)-C(23) plane with the phenyl ring of the apical benzylidene ligand and the N-mesityl substituent of the NHC are almost coplanar, clearly

-NHC complexes catalytic performances 2 . 3 . 1 . 1 .Figure 3 :Figure 4 :Figure 5 :

 2311345 Figure 3: Conversion of cyclooctene (%) vs.time [h] using several Ru-NHC complexes.Mass balance (%) vs. Conversion (%)

Figure 6 :Figure 7 :Figure 8 :

 678 Figure 6: Comparison of conversion of cyclooctene (%) vs. time [h] using silylated and non-silylated Ru-NHC complexes.Mass balance (%) vs. Conversion (%)

2 . 3 .Scheme 2 :

 232 Scheme 2: Proposed mechanism for the tandem Ring Opening-Ring Closing Metathesis of cis-cyclooctene, selective formation of dimer and trimer. Mesityl represents the small group while Propyl or Benzyl represent the bulky group. (BB n = backbiting, n = position of alkene from the carbene carbon).

Figure 13 : 1 H

 131 Figure 13: 1 H NMR of RuPr

Figure 15 :

 15 Figure 15: a) High resolution mass spectrum (ESI+) of RuPr. b) Experimental molecule ion spectrum. c) Simulated spectrum.

Figure 16 :Figure 17 :

 1617 Figure 16 : 1 H NMR of RuBn

Figure 18 :

 18 Figure 18: a) High resolution mass spectrum (ESI+) of RuBn. b) Experimental molecule ion spectrum. c) Simulated spectrum.

  122.1 C ar, 65.5 (-CH(CH 3 ) 2 ), 25.3 (-CH(CH 3 ) 2 )17.8 (Ar-CH 3 ).

Figure 19 :

 19 Figure 19: 1 H NMR of PhMsIm Si .

Figure 20 :

 20 Figure 20: 13 C NMR of PhMsIm.

  121.1 C ar, 121.0 C ar, 65.5 (-CH(CH 3 ) 2 ), 55.1 (-NCH 2 Ph), 31.4 (d, J P-C = 16.5 Hz, ipso-C Cy ), 29.5 (meta-C Cy ), 27.7 (d, J P-C = 9.8 Hz ortho-C Cy ), 26.5 (para-C Cy ), 25.3 (-CH(CH 3 ) 2 )18.3 (Ar-CH 3 ). HRMS (ESI+): m/z 1049.4478 [M-Cl] + i.e. calculated 1049.4493.

Figure 21 :

 21 Figure 21: 1 H NMR of RuPhMs Si .

Figure 22 :Figure 23 :

 2223 Figure 22: 13 C NMR of RuPhMs Si .

Figure 24 :

 24 Figure 24: Conversion of cyclooctene (%) vs. time [h] using RuPr Si .

Figure 28 :

 28 Figure 28: Conversion of cyclooctene (%) vs. time [h] using RuPhMs Si .

Figure 30 :

 30 Figure 30: Conversion of cyclooctene (%) vs. time [h] using G-II.

Figure 33 :

 33 Figure 33: Conversion of cyclooctene (%) vs. Time [h] using N-II.

Figure 38 :

 38 Figure 38: Conversion of cyclooctene (%) vs. time [h] using RuBn.

C18

2 .

 2 The synthesis and catalytic performances of unsymmetrical GH-II type catalysts. a. Synthesis and characterization of unsymmetrical GH-II type catalysts (RuPrGH-II and RuBnGH-II) b. Immobilization on silica to obtain RuPrGH-II/silica and RuBnGH-II/silica c. Comparison of the catalytic performances of RuPrGH-II/silica and RuBnGH-II/silica heterogeneous catalysts with their homogeneous homologues, namely RuPrGH-II and RuBnGH-II catalysts.

Scheme 1 :

 1 Scheme 1: Immobilization of the GH-II catalyst on Grace silica support.

7

 7

Figure 1 :

 1 Figure 1: Representative figure describing type of pyridine bonding with the surface.

Figure 2 : 2 . 1 . 3 .

 2213 Figure 2: Comparison of DRIFT spectra for Grace SP 55 support before and after the adsorption of pyridine 2.1.3. Study of the immobilized catalyst (RuGH-II/silica) by IR (DRIFT) technique Investigation of the immobilized catalyst itself by solid state NMR gave no further clue because only very broad signals were observed. Similarly, IR spectroscopy (DRIFT) did not

Figure 3 : 2 . 1 . 4 .Figure 4 :Figure 5 :

 321445 Figure 3: Comparison of DRIFT spectra for Grace SP 550 support before and after the adsorption of catalyst

Figure 8 :

 8 Figure 8: One putative dissymmetrisation of the NHC ligand by the silica surface.

Figure 9 :

 9 Figure 9: Unsymmetrical GH-II type catalysts.

Figure 10 :

 10 Figure 10: a) Selected geometrical features of unsymmetrical GH-II type complexes, b) Ortep X-ray crystal structure of RuPrGH-II (left) and RuBnGH-II (right).

section 2 . 1 .Figure 11 :

 2111 Figure 11: Unsymmetrical immobilized GH-II type catalysts RuPrGH-II/silica and RuBnGH-II/silica.

Figure 18 :

 18 Figure 18: 1 H NMR of RuPrGH-II.

Figure 19 :

 19 Figure 19: 13 C NMR of RuPrGH-II.

Figure 20 :

 20 Figure 20: a) High resolution mass spectrum (ESI+) of RuPrGH-II b) Experimental molecule ion spectrum. c) Simulated spectrum.

  yielding 0.38 g of RuBnGH-II.1 H NMR (CD 2 Cl 2 , 300 MHz): (ppm) = 16.37 (s, 1H, (-HC=Ru)),7.60-7.70 (m, 3H), 7.50 (m, 2H, J = 2.1 Hz),7.19 (brs, 2H), 7.05 (m, 3H), 6.90 (d, 1H, J = 2.1 Hz), 6.94(d, 1H, J = 2.1 Hz ), 6.17 (s, 2H), 5.22 (m, 1H), 4.87 (m, 2H), 2.56 (s, 3H), 2.07 (s, 6H), 1.77 (d, 6H, J = 6.0Hz).13 C NMR (CD 2 Cl 2 , 75 MHz): (ppm) = 287.7 (-HC=Ru), 173.6 (C NHC =Ru), 153.3 C ar , 144.9 C ar , 140.7 C ar , 138.0 C ar , 136.8 C ar , 130.3 C ar , 130.0 C ar , 129.8 C ar , 128.7 C ar , 129.4 C ar , 125.4 C ar , 123.5 C ar , 122.5 C ar, 122.3 C ar, 113.8 C ar, 76.2 (-CH(CH 3 ) 2 ), 56.2 (PhCH 2 -N), 26.8 (-CH 2 ), 22.6 (Ar-CH 3 ), 21.8 (CH(CH 3 ) 2 ) , 18.5 (Ar-CH 3 ). HRMS (ESI+): 557.1721 m/z [M-2Cl + CHO -] + i.e. 557.1744 m/z calculated.

Figure 21 :

 21 Figure 21: 1 H NMR of RuBnGH-II.

Figure 22 :

 22 Figure 22: 13 C NMR of RuBnGH-II.

Figure 23 :

 23 Figure 23: a) High resolution mass spectrum (ESI+) of RuBnGH-II b) Experimental molecule ion spectrum and simulated spectrum.

Figure 24 :Figure 25 :

 2425 Figure 24: Conversion of cyclooctene (%) vs. time [h] using GH-II.

Figure 29 :

 29 Figure 29: selectivity of cyclic oligomers (%) vs. Conversion of cyclooctene (%)using RuBnGH-II. 5.1.4. RuGH-II/silica

Figure 32 :Figure 33 : 5 R

 32335 Figure 32: Conversion of cyclooctene (%) vs. time [h] using RuPrGH-II/silica. Selectivity (%) vs. Conversion (%) (RuPrGH-II/silica)

Scheme 1 :

 1 Scheme 1: Interaction of surface functionality with Ru-NHC active site.

Scheme 1 :

 1 Scheme 1: Alternating co-RO-RCM reaction.

  Thus, suggesting tolerance towards alcohols and water. Further developments led to Ru(H 2 O) 6 (p-toluenesulfonate) 2 , 40 which catalyzed ROMP of functionalized norbornene, including hydroxyl-, carboxyl-, alkoxy-, and carboximide-substituted derivatives, However, the activity of RuCl 3 (hydrate) or Ru(H 2 O) 6 -(p-toluenesulfonate) 2 is limited to more highly strained substrates. Also, RuCl 3 (hydrate) and Ru(H 2 O) 6 -(p-toluenesulfonate) 2 catalyst solutions containing ruthenium olefin adducts were recyclable.

34 35 36 37 38 39 40 41 42 43 44 47 48

																			116,117
		n			N Cl	N Ru Cl PCy 3	Ph	tBuMe 2 SiO			N Cl	N Ru Cl PCy 3	Ph	F 3 C(F 2 C) 5	N Cl	N PCy 3 Ru Cl	Ph
				33 n=1,2,3
	R 2 O R 1	R 1	n	N Cl	N Ru Cl PCy 3	Ph			N Cl	N Ru Cl PCy 3	Ph			R	N Cl	N Ru Cl PCy 3	Ph	N Cl iPr R	N Cl Ru O	R	N Cl iPr	N Ru Cl O
			N Cl	N PCy 3 Cl Ru	Ph		R 1		N Cl	N Ru Cl PCy 3	Ph		R 2	N Cl iPr F F	N Ru Cl O	F F	N Cl	N Ru Cl PCy 3	Ph
		N Cl iPr tBu i Pr	N Me Ru Cl 45 O tBu			R	N Cl tBu i Pr	N Me Ru Cl PCy 3 Ph 46 tBu				N Cl	N Ru Cl PCy 3	Ph Ph H	Ph	H	N Cl R 1	PCy 3 Ru Cl N R 2	Ph H Ph	R 4	R 3	R 2 N X	49 Ru O N iPr O	R 1
						Figure 11: l Ru-NHC catalysts with different unsymmetrical NHC ligands.

2.9.2.1. Immobilization through halide exchange

	Prof. Grubbs et. al. have reported the preparation of carboxylic acid derivatives of the first-
	generation Grubbs catalyst by chloride replacements. 146 Using this methodology, the group of
	Prof. Mol et. al. reported immobilization of Grubbs I catalyst (56, Figure 13) on Merrifield
	resins functionalised with perfluorated dicarboxylates. 147 Prof. Buchmeiser et. al. reported a
	series of first-and second generation Grubbs and Grubbs-Hoveyda-type catalysts
	immobilized on Merrifield supports (57-59, Figure

place. 66 67 66 67 Figure 15: Examples of catalysts immobilized via phosphine. 145 2.9.2.4. Immobilization through NHC ligands As

  Gatard et. al. have reported immobilization of Grubbs I catalysts on dendrimer, by replacing both PCy 3 ligands with a bidendate phosphine attached to the dendrimer.164 However, supported Ru metathesis catalysts with phosphine ligands bound to the support suffer from metal leaching occurring when ligand dissociation takes NHC ligands are strongly attached to Ru, no dissociation is observed and this characteristic could be advantageously used to permanently anchor the Ru complex via NHC ligand to the support. Several Grubbs II and Grubbs-Hoveyda II immobilized catalysts (Figure16) were thus prepared via anchoring of NHC units on different supports. Prof. Blechert et. al.

	used Merrifield resin (PS-DVB 1%) and derivatized it to the corresponding imidazolium
	containing resin before conversion into the corresponding supported Ru-NHC catalyst (68).
	165 Prof. Hoveyda et. al. immobilized the Grubbs-Hoveyda catalyst on monolithic silica rods
	(69) 166 while Prof. Buchmeiser and Fürstner et. al. reported on the immobilization of a
	Grubbs-type catalyst on a ROMP-derived monolith (70). 167 In 2005, Prof. Grubbs et. al.
	reported on the synthesis of a water-soluble Grubbs-type catalyst bound to poly(ethylene
	glycol) (PEG)

. 168 Weck et. al. reported poly (norborn-2-ene)-supported version of a Grubbs- type catalyst. 169 Immobilizations of modified Grubbs II catalyst on SBA silica supports are also reported

2.9.2.5. Other immobilized Ru alkylidene catalysts Kobayashi

  et. al. described a poly(styrene)-supported Ru catalyst bound to the polymer arene ligand, which was found to be active in RCM of various dienes. 171 Prof. Kirschning and Grela et. al. also reported an appealing alternative concept for immobilization of a Grubbs-Hoveyda catalyst based on noncovalent interactions 172 between the support and the catalyst: 173 here the amine tagged Hoveyda type catalysts was immobilized on sulfonic acid functionalized Rasching ring support. Recently, the convenient method for the immobilization of Hoveyda-

Table 1 :

 1 Comparison of selectivity of cyclic products, at 30-40% conversion of cyclooctene and constant mass balance. Also in terms of initial rate and final conversion of cyclooctene Selectivity

(%) Catalyst Initial rate [mol/mol Ru/h]

			Final conversion (%)	Dimer	Trimer	Tetramer Pentamer	Mass balance (%)
	M-RuPr	1360	95-96	53	22	10	4	85-90
	M-RuBn	529	95-96	54	20	8	3	85-90
	M-RuHex	215	60-65	54	24	9	3	85-90
	M-RuPhMs	260	20-25	45	19	8	4	75-80
	M-RuMs	598	60-65	34	17	10	6	65-70

Table 2 :

 2 Representative NMR values for different type of silicon

4.1.2. Synthesis of M-RuBn 4.1.2.1. Reaction scheme

	Cl
	30 eq. Si(EtO) 4	(15 Eq.)	N N Mes
	P123,H 2 O pH =1.5	Tol uene, 48 h, 110 °C
	Si(OMe) 3
			1) HCl, H 2 O ,
			45 °C, 2 -3 h
		BrSiMe 3 ; Et 3 N
		Toluene, R.T.
	1. KN(SiMe 3 ) 2 (1.2 eq)
	30 min., R.T.
	2. Grubbs I (1.2 eq)
	Overnight, R.T.

Table 3 :

 3 GC standardization for the response of cyclooctene (C8) & dimer (C16) with respect to Eicosane (E) as standard.

	[C8]	[C16]	Ratio [C8]/[E]	Ratio [C16]/[E]	(AC8)	(AC16)	Eicosane	R(AC8) /(AE)	R(AC16) /(AE)
	2.86	1.39	0.3511	0.1703	139.4	144.2	1092.9	0.13	0.13
			0.3511	0.1703	138.2	142.8	1084.0	0.13	0.13
	5.72	2.77	0.7022	0.3406	279.2	285.7	1087.2	0.26	0.26
			0.7022	0.3406	282.5	289.6	1102.9	0.26	0.26
	11.43	5.55	1.4045	0.6812	565.9	582.5	1090.3	0.52	0.53
			1.4045	0.6812	570.8	593.4	1111.9	0.51	0.53

Table 4 :

 4 Catalytic performances of M-RuPr in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)	TON	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	0.0	0.0	0
	0.5	6.6	658	51	17	7	3
	1.0	13.6	1359	55	19	8	3
	1.5	20.6	2065	54	19	8	3
	2.0	26.6	2663	53	20	8	4
	2.5	34.0	3400	54	21	9	4
	3.0	40.1	4006	53	22	10	4
	3.5	47.1	4713	53	22	10	4
	4.0	54.1	5408	52	23	10	4
	5.0	65.2	6522	50	24	11	5
	7.0	82.7	8274	44	27	12	6
	18.5	95.5	9550	35	30	15	7
	44.0	96.5	9649	33	31	15	9
	68.0	96.6	9656	33	31	16	8
	96.0	96.6	9658	32	31	16	8
	124.0	96.6	9662	32	31	16	8

Table 5 :

 5 Catalytic performance of M-RuBn in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)		TON	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	0.0		0.0		0
	0.5		3.4		345		24	8	3	0	3
	1.0		5.3		529		34	11	4	2
	2.0		9.5		954		43	14	5	3
	3.0		13.8		1379		49	17	6	3
	4.3		20.9		2087		53	18	7	3
	5.0		24.3		2433		54	19	7	3
	6.0		30.1		3011		54	20	7	3
	7.0		34.9		3489		54	20	8	3
	8.0		39.6		3962		54	21	8	4
	26.0	84.8		8479		43	27	12	6
	32.0	88.8		8883		41	28	13	6
	48.0	93.0		9298		37	29	14	7
	56.0	94.0		9396		36	30	14	7
	73.0	94.9		9493		35	30	15	7
	97.0	95.6		9555		34	30	14	7
			Conversion (%) vs. Time (hr)
					(M-RuBn)
	100
		80
	Conversion (%)	40 60
		20
		0
		0	20	40	60 Time [h]	80	100	120

Table 6 :

 6 Catalytic performance of M-RuHex in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)	TON	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	0.0	0.0	0
	1.0	2.3	226	31	11	4	0
	3.5	6.8	676	50	17	6	2
	6.0	11.9	1190	56	19	7	2
	23.0	47.9	4789	54	24	9	3
	49.0	58.6	5858	52	24	10	4
	72.0	61.7	6165	51	25	10	4
	96.0	62.5	6254	51	24	10	4

Conversion (%) vs. Tim e (hr)

(M-RuHex)

Table 7 :

 7 Result of catalytic performance of M-RuPhMs in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)	TON	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	0.0		0.0		0
	1.0		2.6		260	4		1	0	0	6
	2.0		2.9		294	10		3	2	0	1 6
	3.0		3.7		374	14		5	3	0	2 2
	4.3		3.6		357	23		9	4	3	3 9
	5.0		4.9		487	20		8	4	2	3 5
	6.0		5.2		518	23		9	4	2	3 9
	7.0		5.1		512	28		11	5	4	49
	8.0		6.2		615	27		11	5	3	46
	26.0	12.5		1246	43		18	8	5	74
	32.0	14.3		1430	44		18	8	4	75
	48.0	19.8		1976	42		18	8	4	72
	56.0	21.5		2146	43		18	8	4	72
	73.0	23.6		2363	44		18	8	4	75
	97.0	25.6		2561	45		19	8	4	76
	121.0	26.7		2666	45		19	9	4	77
			Conversion(%) vs. Time [h]
				(M-RuPhMs)
	100
	Conversion (%)	40 60 80
		20
		0
		0	20	40	60 Time [h] 80	100	120	140

Table 8 :

 8 Result of catalytic performance of M-RuMs in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)	TON	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	0.0	0.0	0
	1.0	6.0	598	25	12	7	4
	2.0	10.4	1036	29	14	8	4
	5.3	21.5	2148	32	16	9	5
	16.0	40.2	4022	34	17	10	6
	45.0	58.6	5859	35	19	10	6
	67.0	60.8	6083	35	19	11	6
	91.0	61.5	6153	35	19	10	6
	115.0	61.7	6171	35	19	10	5

Conversion (%) vs. Time [h]

Table 9 :

 9 Rate of reaction for cyclooctene RO-RCM at different concentration using M-RuPr.

	Concentration [mM]	5	9	15	20	21
	Rate [mol/mol Ru/h]	239	624	963	1359	1696

Table 10 :

 10 Selectivity of products in RO-RCM of cyclooctene at different concentration with similar conversion (13-15%) and mass balance (80-85%) using M-RuPr.

	Concentration	Conversion	Mass		Selectivity of products (%)
	[mM]	(%)	Balance (%)	Dimer	Trimer	Tetramer	Pentamer
	0	0	0	0	0	0	0
	5	13.7	85	68	14	4	0
	9	14.2	81	58	18	6	0
	15	15.2	81	53	18	7	3
	20	13.6	85	55	19	8	3

Table 11 :

 11 Productivity of products in RO-RCM of cyclooctene using 5 mM cyclooctene and using M-RuPr.

	Conversion (%)	TON	TON Dimer	TON-trimer	TON-tetramer	TON-pentamer	TON-Sum	Mass balance (%)
	0.0	0	0	0	0	0	0
	0.8	83	49	0	0	0	49	59
	2.4	239	87	13	0	0	100	42
	2.4	244	140	20	0	0	160	65
	3.2	319	216	30	0	0	247	77
	4.7	465	267	43	12	0	322	69
	4.8	480	335	53	15	0	403	84
	6.2	619	397	78	16	0	491	79
	7.3	731	455	90	23	0	568	78
	8.5	846	595	117	28	0	740	87
	10.7	1065	703	141	32	0	875	82
	11.9	1192	810	164	40	0	1014	85
	13.7	1370	925	187	51	0	1164	85
	21.7	2166	1587	322	70	0	1978	91
	24.4	2437	1821	378	97	0	2297	94
	25.1	2514	1866	389	79	0	2334	93
	25.8	2578	1896	404	85	0	2385	93
	25.8	2584	1901	395	94	0	2390	92
	25.7	2570	1909	412	85	0	2406	94

Table 12 :

 12 Productivity of products in RO-RCM of cyclooctene using 9 mM cyclooctene and using M-RuPr.

	Time [h] Conversion (%)	TON	TON-Dimer	TON-trimer	TON-tetramer	TON-pentamer	TON-Sum	Mass balance (%)
	0.0	0.0	0	0	0	0	0	0
	0.5	3.6	365	108	33	8	0	149
	1.0	6.2	624	333	93	34	0	459
	1.5	9.7	968	546	165	51	0	762
	2.0	14.2	1423	829	250	79	0	1158
	2.5	18.4	1844	1055	317	99	0	1471
	3.0	22.9	2288	1281	401	116	0	1797
	3.5	25.7	2572	1535	490	152	69	2246
	4.0	30.5	3054	1806	590	179	68	2643
	4.5	35.0	3503	2036	681	219	70	3005
	5.0	39.0	3898	2311	756	253	68	3388
	5.5	42.0	4202	2440	812	268	82	3602
	6.0	45.1	4506	2660	911	293	98	3962
	6.5	47.9	4786	2861	1001	328	119	4310
	7.0	52.3	5231	3040	1085	355	132	4612
	7.5	55.0	5501	3174	1166	393	133	4866
	8.0	56.2	5621	3273	1287	413	124	5097
	24.0	82.3	8232	4390	2213	794	230	7626
	48.0	85.3	8530	4432	2378	855	265	7930
	72.0	86.1	8611	4466	2419	874	273	8031
	120.0	86.2	8621	4472	2442	843	269	8027

Table 13 :

 13 Productivity of products in RO-RCM of cyclooctene using 15 mM cyclooctene and using M-RuPr.

	Time [h]	Conversion (%)	TON	TON-Dimer	TON-trimer	TON-tetramer	TON-pentamer	TON-Sum	Mass balance (%)
	0.0	0.0	0	0	0	0	0	0
	0.5	4.6	463	160	52	24	0	236
	1.0	9.6	963	463	149	57	26	695
	1.5	15.2	1521	807	273	102	44	1226
	2.0	20.9	2092	1158	408	153	62	1780
	2.5	26.6	2664	1486	521	208	79	2294
	3.0	32.9	3289	1848	674	259	97	2878
	3.5	37.9	3786	2128	808	315	122	3373
	4.0	44.1	4409	2458	962	377	143	3941
	4.5	49.8	4984	2753	1124	440	164	4481
	5.0	54.8	5485	2992	1257	501	191	4942
	5.5	60.8	6078	3266	1451	585	215	5518
	6.0	63.8	6378	3411	1556	640	241	5848
	7.0	72.8	7283	3742	1881	780	311	6714
	8.0	78.3	7832	3878	2094	885	348	7205
	23.0	94.1	9407	3745	2911	1348	569	8572
	50.0	95.4	9539	3599	3022	1425	612	8657
	78.0	95.6	9562	3597	3031	1438	644	8710
	110.0	95.7	9571	3554	2837	1220	487	8098

Table 14 :

 14 Productivity of products in RO-RCM of cyclooctene using 20 mM cyclooctene and using M-RuPr.

	Conversion (%)	TON	TON Dimer	TON-trimer	TON-tetramer	TON-pentamer	TON-Sum	Mass balance (%)
	0.0	0	0	0	0	0	0
	6.6	658	335	113	47	23	518
	13.6	1359	743	264	105	37	1149
	20.6	2065	1115	399	167	60	1742
	26.6	2663	1424	534	218	94	2269
	34.0	3400	1827	721	300	128	2976
	40.1	4006	2134	881	382	154	3550
	47.1	4713	2484	1059	448	191	4182
	54.1	5408	2803	1263	540	226	4832
	65.2	6522	3253	1598	703	312	5866
	82.7	8274	3673	2238	1019	471	7402
	95.5	9550	3316	2875	1472	712	8375
	96.5	9649	3148	2967	1496	883	8494
	96.6	9656	3143	2961	1547	763	8414
	96.6	9658	3124	2970	1566	758	8418
	96.6	9662	3111	2961	1556	768	8397

Table 16 :

 16 Effect of addition of cyclooctene on the rate of metathesis of dimer: addition of 0 mM cyclooctene and using M-RuPr.

	5.3.2. RO-R	CM	of dimer
	T able 15: R es ult of catalyt ic perf	o r m a	nce for	CM of R O -R	d i m e r	using	Pr. M-Ru
	Time [h]	Dimer conversion (%)	Sel-c ycloctene Sel-trimer Se (%) (%)	a Sel-penta ( l-tetr (%) %)	Mass balancel ( %)
	0.5		0.8			16		60	29	0	105
	1.0		1.6			11		38	36	0	86
	1.5		2.5			10		39	24	7	80
	2.0		3.7			10		43	29	7	90
	2.5		4.8			10		46	30	14	101
	3.0		7.7			8		4 0	2 7	1 1
	3.5		8.9			8		4 2	2 8	8
	4.0		10.8			8		4 1	2 9	8
	4.5		13.2			7		3 9	2 5	7
	5.0		14.3			7		4 1	2 7	8
	5.5		15.7			7		4 1	2 8	8
	6.0		17.3			7		4 1	2 8	8
	6.5		18.7			7		4 0	2 6	8
	7.0		19.1			7		4 1	2 7	8
	7.5		20.1			7		4 1	2 7	8
	8.0		21.2			7		4 1	2 7	9
	24.0		31.7			6		4 2	2 7	8
	48.0		37.2			6		4 2	2 6	9
	72.0		39.2			5		4 2	2 6	9
	120.0		39.6			6		42	26	10	83
	176.0		40.1			5		42	26	9	82

Table 17 :

 17 Effect of addition of cyclooctene on the rate of metathesis of dimer: addition of 2 mM cyclooctene and using M-RuPr.

	Time [h]	Dimer conversion (%)	TON Dimer	TON-trimer	TON-tetramer	TON-pentamer	TON-Sum
	0.0	0.0	0	0	0	0	0
	0.5	1.1	55	11	5	0	16
	1.0	1.4	72	21	16	0	38
	1.5	2.0	101	34	18	8	60
	2.0	2.5	123	53	27	11	91
	2.5	3.5	177	81	43	19	143
	3.0	4.6	231	116	61	26	203
	3.5	5.8	292	148	79	34	261
	4.0	7.1	357	181	98	40	320
	5.0	11.0	552	294	158	69	522
	6.0	15.0	748	393	215	89	697
	7.0	17.9	893	475	256	107	838
	8.0	21.7	1086	578	312	133	1023
	26.0	33.9	1694	895	495	214	1604
	56.0	35.9	1797	941	519	231	1691
	82.0	35.8	1788	944	524	225	1692
	109.0	35.8	1792	947	525	234	1706

Table 18 :

 18 Effect of addition of cyclooctene on the rate of metathesis of dimer: addition of 4 mM cyclooctene and using M-RuPr.

	Time [h] Dimer (%)	TON Dimer	TON-trimer	TON-tetramer	TON-pentamer	TON-Sum
	0.0	0.0	0	0	0	0	0
	0.5	1.1	53	10	5	0	15
	1.0	1.1	53	22	10	6	38
	1.5	1.4	70	32	16	9	58
	2.0	1.8	90	50	24	12	87
	2.5	2.6	130	75	38	19	132
	3.0	3.5	177	105	53	25	184
	3.5	4.2	208	134	67	31	232
	4.0	5.1	256	165	84	41	289
	5.0	8.2	409	270	143	62	474
	6.0	10.8	542	359	185	83	626
	7.0	12.8	641	428	221	101	750
	8.0	16.0	800	529	276	125	929
	26.0	34.1	1704	1062	571	265	1898
	56.0	38.5	1927	1191	649	313	2152
	82.0	38.6	1929	1190	636	307	2133
	109.0	38.5	1927	1192	638	313	2144

Table 19 :

 19 Rate of dimer metathesis for reactions carried out with addition of different concentration of cyclooctene using M

-RuPr. Dimer Rate [mol/mol Ru/h] Concentration of added cyclooctene [mM]

	80	0
	72	2
	53	4

Table 1 :

 1 Mass balance of cyclic oligomers and their selectivity at 30-40% conversion of cyclooctene.

	Selectivity (%)

Table 2 :

 2 Comparison of selectivity of cyclic products at 30-40% conversion and constant mass balance.

Selectivity (%) Catalyst Initial rate (mol/mol Ru/h) Dimer Trimer Tetramer Pentamer Mass balance (%)

	RuPr	2343	48	24	11	5	88
	RuPr Si	1090	51	24	10	4	90
	RuBn	505	50	24	10	4	88
	RuBn Si	770	51	23	9	4	87

Table 3 :

 3 Mass balance of cyclic oligomers and their selectivity at 30-40% conversion of cyclooctene

	Selectivity (%)

Table 4 :

 4 Ratio of dimer to trimer in RO-RCM of cyclooctene using homogeneous/heterogeneous catalysts.

		Selectivity (%)	Ratio of dimer/trimer
	Catalyst	Dimer	Trimer	Experimental Expected
	RuPr	48	24	2	2
	RuPr Si	51	24	2.1	2
	M-RuPr	53	22	2.4	2
	RuBn	50	24	2.1	2
	RuBn Si	51	23	2.1	2
	M-RuBn	54	20	2.7	2
	RuPhMs Si	52	25	2.1	2
	M-RuPhMs	45	19	2.4	2
	M-RuMs	34	17	2	2
	M-RuHex	54	24	2.2	2

  High resolution mass spectrum (ESI+) of RuPr

	x10 4 Intens.													+MS, 1.3min #75
									605.2615
	1.5
			281.2396
	1.0
	229.1709									699.3390 735.3150
	0.5
				353.1462
			311.2503
					419.1080
						469.3341						789.3689
	0.0
	200		300		400		500		600		700		800		900 m/z
	b) Experimental molecule ion spectrum				c) Simulated spectrum.
	Intens.							+MS, 1.3min #75	Intens.						C40H59Cl1N2P1Ru1, M ,735.31
				735.3150					2000			735.3150
	6000
					737.3151				1500				737.3152
				734.3165								734.3155
	4000
					736.3181								736.3175
									1000
											733.3143
			733.3161
			732.3171			738.3176					732.3159			738.3186
	2000
									500
						739.3197
														739.3125
	729.3195								729.3175
		730.3233	731.3190				740.3234			730.3208	731.3152				740.3157
								741.3348
	0								0
	728	730	732	734	736	738	740	m/z	728	730	732	734	736	738	740	m/z

C NMR of RuPr a)

Table 5 :

 5 Catalytic performances of RuPr Si in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)		TON	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	0.5	2.1		211		38	13	6	0	57
	1.0	10.9	1089		54	19	7	3	83
	1.5	22.2	2221		53	22	9	4	87
	2.0	33.2	3322		51	24	10	4	90
	2.5	43.8	4383		49	25	12	5	91
	3.0	51.9	5185		47	26	12	5	91
	4.0	70.4	7035		42	27	14	6	90
	5.0	80.3	8035		39	28	14	7	88
	6.0	87.6	8756		36	29	15	7	88
	7.0	91.1	9111		34	30	15	8	87
	8.0	93.5	9350		33	30	16	8	86
	24.0	97.4	9741		28	31	17	8	84
	32.0	97.4	9741		28	31	16	8	83
	50.0	97.4	9739		28	31	17	8	84
			Conversion(%) vs. Time [h]
					(RuPr Si )
		100
		80
	Conversion (%)	40 60
		20
		0
		0	1 0	2 0	3 0 Time [h]	4 0	5 0	6 0

Table 6 :

 6 Catalytic performance of RuBn Si in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)	TON	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	0.5	4.7	475		26	8	2	0	3 6
	1.0	7.7	769		40	13	4	2	59
	1.5	14.2	1417		49	18	6	2	74
	2.0	22.2	2218		51	20	7	3	80
	3.0	38.3	3828		51	23	9	4	87
	4.0	54.2	5425		47	25	11	5	89
	5.0	67.2	6719		43	27	12	6	89
	6.0	77.3	7726		40	28	13	7	87
	7.0	82.5	8248		38	28	14	7	86
	8.5	90.3	9027		34	29	15	8	86
	24.0	97.2	9717		28	30	16	9	83
	50.0	97.3	9727		28	30	15	8	80
			Conversion(%) vs. Time [h]
				(RuBn Si )
		100
		80
	Conversion (%)	40 60
		20
		0
		0	1 0	2 0	3 0	4 0	5 0	6 0
				Time [h]
	Figure 26: Conversion of cyclooctene (%) vs. time [h] using RuBn Si

Table 7 :

 7 Catalytic performance of RuPhMs Si in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)	TON	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	0.5	2.1	211	29	8	2	0	3
	1.0	5.1	513	47	13	4	0
	1.5	9.0	898	54	16	4	2
	2.0	12.4	1237	58	19	6	2
	2.5	17.1	1711	55	21	7	3
	3.0	20.0	1998	57	22	8	3
	4.0	30.9	3093	52	23	9	3
	5.0	38.2	3816	52	25	10	4
	6.0	46.0	4603	50	26	11	5
	7.0	53.0	5301	48	26	11	5
	8.0	58.6	5858	46	27	12	5
	24.0	95.3	9534	30	28	14	6
	32.0	96.6	9659	28	25	11	5
	50.0	97.2	9717	26	20	8	3
		Conversion(%) vs. Tim e(h)
			(RuPhMs Si )

Table 8 :

 8 Catalytic performance of G-II in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)	TON	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	0.2	36.9	3692	25	3	1	1	2 9
	0.3	91.0	9099	20	5	2	1	2 8
	0.5	96.7	9675	24	17	7	3	52
	1.0	97.2	9721	28	29	15	8	79
	1.5	97.3	9730	28	30	16	8	82
	2.0	97.3	9731	28	30	16	8	83
	2.5	97.3	9729	28	30	16	8	82
	3.5	97.3	9733	28	30	16	8	82
	4.5	97.4	9737	28	30	16	8	83
	5.5	97.4	9738	28	30	16	8	82
	6.5	97.3	9734	28	30	16	8	82
	7.5	97.4	9740	28	30	16	8	82
	23.0	97.5	9745	27	30	16	8	81
	32.0	97.4	9745	27	30	16	8	81
	50.0	97.5	9747	27	30	16	8	81
		Conversion (%) vs. Time [h]
			(G-II)

Table 9 :

 9 Catalytic performance of N-II in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)	TON	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	0.2	4.9	486	41	9	4	0	5 4
	0.3	10.8	1084	46	8	2	1	5 7
	0.5	18.6	1864	38	6	2	1	4 6
	1.0	41.8	4181	32	5	2	1	4 0
	1.5	61.6	6163	30	6	2	1	3 9
	2.0	75.7	7574	33	14	5	2	55
	2.5	85.5	8549	31	14	5	2	52
	3.5	94.7	9473	27	13	5	2	48
	4.5	97.0	9696	28	24	10	5	68
	5.5	97.3	9730	28	28	14	7	76
	6.5	97.3	9735	28	29	15	8	80
	7.5	97.3	9734	28	28	15	7	78
	23.0	97.1	9707	26	20	8	4	58
	32.0	96.2	9618	23	10	4	2	39
	50.0	96.7	9668	23	14	6	2	45
		Conversion (%) vs. Time [h]
			(N-II)

Table 10 :

 10 Catalytic performance of RuPr in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)	TON	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	0.5	9.9	989		40	16	7	4	67
	1.0	23.4	2343		50	22	9	4	86
	1.5	40.2	4025		48	24	11	5	88
	2.0	55.3	5526		45	25	12	6	87
	3.0	76.3	7627		40	27	13	7	87
	4.0	88.0	8802		35	28	15	7	86
	5.0	93.1	9313		32	29	15	8	85
	6.0	95.4	9543		31	30	16	9	85
	7.0	96.2	9618		30	30	16	9	84
	8.5	96.9	9689		29	30	16	9	84
	24.0	97.2	9724		28	30	16	8	83
	50.0	97.2	9719		28	30	16	9	83
			Conversion(%) vs. Time [h]
				(RuPr)
		100
		80
	Conversion (%)	40 60
		20
		0
		0	1 0	2 0	3 0	4 0	5 0	6 0
				Time [h]
	Figure 35: Conversion of cyclooctene (%) vs. time [h] using RuPr.

Table 11 :

 11 Catalytic performance of RuBn in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)	TON	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	0.5	2.5	252	13	4	0	0	1 7
	1.0	5.0	505	42	14	5	0	61
	1.5	10.0	1005	53	17	5	2	78
	2.0	16.9	1687	53	19	7	2	82
	2.5	22.4	2237	53	21	8	3	85
	3.0	28.1	2808	52	22	8	3	85
	4.0	40.7	4072	50	24	10	4	88
	5.0	51.2	5118	47	25	11	5	88
	6.0	60.9	6090	45	26	12	5	87
	7.0	68.1	6812	42	27	12	6	87
	8.0	73.8	7376	40	27	13	6	87
	23.0	96.7	9671	29	30	16	8	83
	34.0	97.3	9730	28	30	16	8	81
	52.0	97.5	9746	27	30	16	8	82
		Conversion(%) vs. Time [h]
			(RuBn)

Table 1 :

 1 Loading (% wt ) and surface density of Ru in the catalysts.

	Catalysts	% wt of Ru	Ru (mmol/g)	Surface area (m 2 /g)	Ru (mmol/m 2 )
	RuGH-II/ silica	0.064	0.0064	550	0.000012
	M-RuPr	0.63	0.0623	900	0.000069

Table 2 :

 2 IR bands for different type of pyridine bonding with the surface.

	Position of bands v(C=C) (cm -1 )	Type of bonding	Temperature of desorption [°C]
	1438 / 1485 / 1580	Physisorption	25
	1444/1593	Hydrogen bonding	150
	1490 / 1575 / 1606 / 1619	Lewis acidity	250-500
	1544 / 1638	Bronsted acidity	400

Table 3 :

 3 Comparison of selectivity of cyclic products and mass balance at 30-40% conversion of cyclooctene.

	Selectivity (%)

Table 6 :

 6 Catalytic performances of GH-II in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	1.0	4.3	65	10	3	0	78
	1.5	7.0	53	8	2	0	6 3
	2.0	8.5	52	8	2	0	6 2
	3.0	13.0	45	7	1	0	5 4
	4.0	16.9	43	6	2	1	5 2
	5.0	26.1	37	6	1	0	4 5
	6.0	34.5	34	5	1	1	4 0
	7.0	52.0	35	7	2	1	4 4
	11.0	82.8	24	4	1	1	3 1
	24.0	91.1	19	4	1	1	2 4
	33.0	88.4	17	3	1	0	2 2
	46.0	90.3	17	4	1	1	2 3
	59.0	94.2	20	6	2	1	2 9
	71.0	93.4	20	6	2	1	2 8
	80.0	95.7	20	11	5	2	39
	100.0	96.3	22	13	5	3	43

Table 7 :

 7 Catalytic performances of RuPrGH-II in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)	TON	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	24.0	3.4	310	29	12	3	0
	40.0	7.0	628	47	17	5	2
	48.0	10.3	926	46	18	5	2
	65.0	19.0	1712	49	18	6	2
	88.0	34.7	3121	49	20	6	2
	97.0	41.4	3725	47	19	6	2
	120.0	56.0	5040	44	19	6	2
	168.0	78.6	7073	38	20	6	2
	216.0	89.2	8032	34	23	8	4
	264.0	93.6	8423	31	25	10	5
	312.0	95.1	8562	30	23	8	3
	336.0	95.9	8630	30	27	12	5

Table 9 :

 9 Catalytic performances of RuGH-II/silica in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)	TON	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	0.5	1.9	187	12	7	4	0	2
	1.0	2.7	267	24	14	6	0
	1.5	5.0	501	29	18	8	3
	2.0	4.9	493	30	19	9	4
	2.5	6.3	632	33	20	9	3
	3.0	7.4	737	35	20	9	4
	3.5	8.3	831	38	21	10	4
	4.0	10.2	1021	37	21	8	3
	4.5	11.0	1095	37	21	9	4
	5.0	11.5	1150	40	21	9	3
	5.5	11.9	1189	42	23	9	3
	6.0	13.4	1336	40	22	9	3
	6.5	14.0	1402	41	23	10	4
	7.0	15.0	1498	41	23	10	4
	22.0	31.1	3105	43	20	7	3
	56.0	49.5	4952	40	19	7	3
	126.0	73.2	7324	39	25	6	6

Table 10 :

 10 Catalytic performances of RuPrGH-II/silica in the RO-RCM of cyclooctene.

	Time [h]	Conversion (%)	TON	Sel-dimer (%)	Sel-trimer (%)	Sel-tetra (%)	Sel-penta (%)	Mass balance (%)
	6.0		1.6	164	11	5		4	0	2
	24.0	2.6	259	37	16		7	2
	48.0	3.9	394	41	18		7	3
	79.0	6.1	609	39	17		6	3
	96.0	6.7	670	39	17		7	3
	120.0	6.3	634	43	19		20	3
	144.0	5.9	594	47	21		8	4
	192.0	6.5	653	44	20		8	4
	240.0	8.1	812	36	16		7	3
			Conversion (%) vs. Tim e [h]
			(RuPrGH-II/silica)
	100
	Conversion (%)	20 40 60 80
		0
		0	50	100	150	200	250
				Tim e [h]

  •••+ A n-1 ]*T n-1 (x)] where A i are the Chebychev coefficients listed below and x = F /Fmax Method = Robust Weighting (Prince, 1982) W = [weight] * [1-(deltaF/6*sigmaF) 2 ] 2 A i are: 0.153E + 04 0.229E + 04 0.128E + 04 361.

	C11-H111	0.931	C30-C34	1.507 (5)
	C12-C13	1.389 (6)	C31-C32	1.397 (5)
	C12-H121	0.933	C31-H311	0.936
	C13-C14	1.399 (6)	C32-C33	1.509 (5)
	C13-H131	0.937	C33-H331	0.957
	C14-H141	0.932	C33-H333	0.963
	C15-N16	1.360 (4)	C33-H332	0.955
	C15-N26	1.363 (5)	C34-H341	0.962
	N16-C17	1.464 (5)	C34-H343	0.958
	N16-C24	1.395 (5)	C34-H342	0.960
	C17-C18 wR(F 2 ) = 0.122 C17-H172	1.509 (5) 0.969	C35-H351 ( / ) max = 0.001 C35-H352	0.965 0.965
	S = 1.06 C17-H171	0.978	max = 1.49 e Å -3 C35-H353	0.966
	7089 reflections		min = -2.23 e Å -3
	317 parameters		Extinction correction: Larson (1970), Equation
			22
	0 restraints		Extinction coefficient: 24 (4)
	Geometric parameters (Å, º)
	Ru1-Cl2	2.3393 (10)	C18-C23	1.392 (5)
	Ru1-Cl3	2.3310 (9)	C19-C20	1.388 (6)
	Ru1-O4	2.255 (3)	C19-H191	0.929
	Ru1-C10	1.840 (4)	C20-C21	1.375 (6)
	Ru1-C15	1.985 (4)	C20-H201	0.933
	O4-C5	1.472 (5)	C21-C22	1.386 (6)
	O4-C8	1.383 (4)	C21-H211	0.926
	C5-C6	1.513 (6)	C22-C23	1.382 (6)
	C5-C7	1.522 (6)	C22-H221	0.932
	C5-H51	0.985	C23-H231	0.934
	C6-H62	0.958	C24-C25	1.340 (5)
	C6-H61	0.967	C24-H241	0.933
	C6-H63	0.957	C25-N26	1.388 (5)
	C7-H71	0.965	C25-H251	0.930
	C7-H73	0.966	N26-C27	1.442 (4)
	C7-H72	0.964	C27-C28	1.389 (5)
	C8-C9	1.393 (5)	C27-C32	1.387 (5)
	C8-C14	1.387 (5)	C28-C29	1.393 (5)
	C9-C10	1.453 (5)	C28-C35	1.503 (5)
	C9-C11	1.405 (5)	C29-C30	1.383 (5)
	C10-H101	0.938	C29-H291	0.931
	C11-C12	1.390 (6)	C30-C31	1.389 (6)

Table 1 :

 1 Ratio of dimer to trimer in RO-RCM of cyclooctene using homogeneous/heterogeneous catalysts.

		Selectivity (%)	Ratio of dimer/trimer
	Catalyst	Dimer	Trimer	Experimental Expected
	RuPr	48	24	2	2
	RuPr Si	51	24	2.1	2
	M-RuPr	53	22	2.4	2
	RuBn	50	24	2.1	2
	RuBn Si	51	23	2.1	2
	M-RuBn	54	20	2.7	2
	RuPhMs	52	25	2.1	2
	M-RuPhMs	45	19	2.4	2
	M-RuMs	34	17	2	2
	M-RuHex	54	24	2.2	2

Acknowledgement

Abbreviations

Chemical shift in NMR downfield from TMS, ppm Further analysis of productivity at higher conversion of cyclooctene (> 60%) showed the decrease in the productivity of dimer which was consistent with the fact that dimer is primary product. It is noteworthy that the productivity of trimer was almost unaffected and showed minor increase compared to the increase in productivity of the tetramer and the pentamer products. This indicates that trimer mainly comes from cyclooctene and thus it can be primary product, while tetramer and pentamer are formed via secondary processes involving dimer and are likely secondary products. (Details in appendix section, Figures 67-70). If we compare now the productivity in product formation, i.e. for the trimer, the tetramer and the pentamer (cumulated TON in each product) as a function of dimer conversion, a linear increase is observed thus, indicating that all the low cyclic products are primary products (or formed by processes faster than cyclooctene and dimer metathesis). Moreover, the effect of the concentration of added cyclooctene is noteworthy: comparison of the slope shows that for the tetramer formation, its productivity is not as much affected as for trimer and pentamer formation (Figures 25-27). This is consistent with the fact that the tetramer is mainly produced via the dimer only. While the formation of the trimer and the pentamer are resulting from a reaction involving cyclooctene as reactant (Scheme 2). This explains why such products are apparently primary products and formed via cross metathesis of the dimer and cyclooctene.

Effect of cyclooctene addition on the productivity of cyclic products

Synthesis of M-PhMsIm

To the material M-PhMs (0.8 g, DYA-210) were added toluene (15.0 mL) and benzyl chloride (0.62 mL, 15 equiv.). The reaction mixture was heated up to 110 °C. After stirring, for 70-72 h, the solid was filtered and washed successively with toluene (3 × 100 mL), acetone (3 × 100 mL) and diethyl ether (3 × 50 mL). The solid was then dried for 14-16 h under high vacuum (10 -5 mm Hg) at 135 °C, affording 0.75 g of product.

Elemental analysis: N: 1.23%, Si: 35.6%.

Synthesis of M-HPhMsIm

To the material M-PhMsIm (0.7 g, SK-055) was added 5 mL of a 2 M aqueous HCl. The reaction mixture was heated up to 45 °C. After stirring the reaction mixture for 2 h, the solid was filtered and washed successively with water (3 × 100 mL), acetone (3 × 100 mL) and diethyl ether (3 × 50 mL). The solid was then dried for 5-6 h under high vacuum (10 -5 mm Hg) at 135 °C, affording 0.6 g of product.

Synthesis of M-EHPhMsIm

To the material M-HPhMsIm (0.55 g, SK-058) was added a mixture of pyridine (4.1 mL), water (4.1 mL) and 2 M aqueous HCl (0.7 mL). The reaction mixture was heated up to 70 °C.

After stirring the suspension for 22-23 h, the solid was filtered and washed successively with

Selectivity (%)

Sel-dimer (%) Sel-trimer (%) Sel-tetra (%) Sel-penta (%) Mass balance (%)

Figure 64 : Selectivity of cyclic products (%) vs. conversion of cyclooctene (%) using M-RuPhMs.

In the previous chapter, hybrid heterogeneous Ru-NHC catalysts have promoted the selective formation of cyclic oligomers in RO-RCM of cyclooctene. The particularly high selectivity in low cyclic oligomers could be attributed to various hypotheses: the pore confinement effect and surface interactions or the chemical structure of the Ru-NHC sites bearing unsymmetrical NHC ligands, which could favor backbiting over polymerization.

In order to address these questions, we will first compare the catalytic performances of the classical symmetrical homogeneous Ru-NHC complexes (G-II and N-II) and unsymmetrical homogeneous Ru-NHC analogues (effect of chemical structure).

Then the catalytic performances of the Ru-NHC unsymmetrical complexes will be compared to those of our hybrid heterogeneous catalysts (effect of pore confinement or surface interactions).

Evaluation of catalytic performances

All homogeneous catalysts were tested in RO-RCM of cyclooctene using the typical conditions developed for the heterogeneous systems, i.e. ratio of cyclooctene / Ru = 10,000 and 20 mM solution of cyclooctene in toluene at room temperature. Conversion and selectivities were monitored using eicosane as internal standard. Sample at 0 min was taken before the addition of catalyst and considered as the reference point. All selectivities are defined as follows:

S i .= (number of mole of cyclooctene converted in product i) / (total number of cyclooctene converted).

The response ratio of cyclooctene and dimer with respect to eicosane (internal standard) were measured and used to monitor their concentration as a function of time during the catalytic test. For the higher cyclic oligomers (trimer, tetramer & pentamer), the concentrations were measured with respect to the internal standard assuming that the response factor of n-mers is n times the response factor of cyclooctene (use of FID detector and assuming that there is no segregation in the injector as observed for the dimer).

Oligomers bigger than pentamers have not been detected by GC with the present method.

Unsymmetrical hybrid heterogeneous catalysts vs. unsymmetrical homogeneous homologues

The catalytic performances of both unsymmetrical heterogeneous (M-RuPr, M-RuBn and M-RuPhMs) and homogeneous systems (RuPr Si , RuBn Si , and RuPhMs) were compared to confirm the single site nature of Ru active sites within our heterogeneous systems and also to calibrate the intrinsic catalytic performances of our materials: are they as active as homogeneous systems? In RO-RCM of cyclooctene, M-RuPr displayed almost similar rate when compared to RuPr.

For M-RuBn, the observed rate is slightly lower than that of the corresponding homogeneous analogue RuBn (Figure 9). However, a closer look at the conversion over the first 8 h indicated the presence of a short initiation period and then a slightly higher rate of conversion for homogeneous systems compared to heterogeneous systems (Figure 10). The observation of the absence of initiation period for heterogeneous systems (M-RuPr and M-RuBn) was consistent with fact that no phosphine was coordinated in M-RuPr as well as in M-RuBn, (vide supra, Chapter 2). This lack of coordinated phosphine on Ru centre was attributed to the presence of surface functionalities (SiOSiMe 3 ) interacting with the Ru-NHC active sites. The

Catalytic performances

All metathesis experiments were carried out under an inert atmosphere, in a glove-box.

Toluene was dried over NaK and distilled under nitrogen prior to use. Cyclooctene (ciscyclooctene) was purchased from Aldrich, distilled over Na prior to use. Catalysts Grubbs second generation catalyst was purchased from Aldrich and Nolan catalyst was synthesized according to the literature procedures.

Cyclooctene metathesis experiments with homogeneous Ru-complexes (Ratio Cyclooctene/ Ru of ca. 10,000)

Representative procedure for homogeneous catalysts: Eicosane was dissolved in 20 mM toluene solution of cyclooctene. Sample was taken for GC analysis as a reference.

Homogeneous Ru-catalyst was dissolved in toluene so as to obtain the initial stock solution.

An aliquot of this stock solution was added to the aforementioned solution of cyclooctene, at room temperature. The progress of the metathesis reaction was monitored by sampling at suitable intervals. The samples were immediately quenched by an excess of ethyl acetate. The samples were analysed by GC with a HP5 column. It is also important to note that, in terms of mass balance and selectivity, the observed trend for RuGH-II/silica was exactly the opposite to GH-II, i.e. increasing mass balance and increasing selectivities for dimer (Figure 6,7) and cyclic oligomers up to pentamer (appendix section) with a maximum mass balance of 75-77% and a dimer selectivity up to 39% (Figure

GH-II complex, we attempted to increase the selectivity towards low cyclic oligomers by

adsorbing unsymmetrical NHC-GH-II type molecular complexes on silica. We thus carried out the catalytic tests using homogeneous and immobilized catalysts based on RuPrGH-II and RuBnGH-II under our standard conditions and their catalytic performances were compared to those of previously studied RuPr and RuBn catalysts and RuGH-II/silica immobilized catalyst.

Comparison of catalytic performances of unsymmetrical catalysts

RuPrGH-II and RuBnGH-II vs. RuPr and RuBn

In RO-RCM of cyclooctene, RuPrGH-II and RuBnGH-II displayed low reaction rate with a long initiation period of 24-40 h, allowing only 10-12% conversion in 48 h vs. 95-96% conversion for RuPr and RuBn catalysts, in 6 h and 23 h respectively (Figure 12). However, the mass balance and selectivity in dimer for these unsymmetrical catalysts RuPrGH-II and RuBnGH-II were similar to those of RuPr and RuBn catalysts (Figure 13, 14 and Table 4).

This result further confirmed that the selectivity for cyclic oligomers in RO-RCM of cyclooctene is indeed due to the unsymmetrical nature of NHC. It also shows that changing from Grubbs-type catalysts to Grubbs-Hoveyda type catalysts, mainly affected initiation as expected (replacement of PCy 3 via a RO-tether alkylidene).

Comparison of catalytic performances of unsymmetrical homogeneous vs. immobilized GH-II type catalysts

Furthermore, the immobilized RuPrGH-II/silica (6-8% conversion) and RuBnGH-II/silica (5-6% conversion) displayed much lower initiation rate with almost no conversion within 250 h in sharp contrast to the molecular complexes RuPrGH-II (95-96% conversion) and RuBnGH-II (60-65% conversion) (Figure 15). This result shows that the surface was detrimental to the reaction rate, as previously observed when comparing RuGH-II/silica and GH-II. Note that this detrimental effect was not observed for the hybrid mesostructured catalysts and for which the surface has a stabilising effect.

It is also noteworthy that the mass balance and the selectivity in dimer for RuPrGH-II and RuBnGH-II were almost similar to those of their immobilized counterparts for the observed minimum conversion, indicating that there is probably no modification of the active sites (Figure 16, 17). Furthermore, all the immobilized catalysts showed similar mass balance and selectivity of dimer (Table 5). However, no improvement in the selectivity of cyclic oligomers after immobilization of unsymmetrical catalysts was observed, indicating that the surface did not influence the selectivity in RO-RCM of cyclooctene and that here the catalytic TON could be attributed to homogeneous "active sites" (in sharp contrast with what was observed with RuGH-II/silica).

Synthesis of RuPrGH-II

To a solution of (1-mesityl-3-propyl-imidazol-2-ylidene) AgI (0.42 g, 0.9 mmol ) in 10 mL of toluene, were added CuCl (0.089 g, 0.9 mmol) and GH-I (0.46 g, 0.77 mmol). The reaction mixture was stirred for 2 days at 50 °C. The reaction mixture was filtered over Celite. The solvent was removed under vacuum and the solid product was purified by column chromatography using acetone and pentane mixture (25:75)

Catalytic performances

Catalytic tests:

All metathesis experiments were carried out under an inert atmosphere, in a glove-box.

Toluene was dried over NaK and distilled under nitrogen prior to use. Cyclooctene (ciscyclooctene) was purchased from Aldrich, distilled over Na prior to use. Catalysts Grubbs second generation catalyst was purchased from Aldrich and catalyst (Nolan) was synthesized according to the literature procedures.

Representative procedure for heterogeneous catalysts: Eicosane was dissolved in 20 mM toluene solution of cyclooctene. Sample was taken for GC analysis as a reference.

Heterogeneous Ru-catalyst was added to the solution of cyclooctene, at room temperature.

The progress of the metathesis reaction was monitored by sampling at suitable intervals. The samples were immediately quenched by an excess of ethyl acetate. The samples were analysed by GC with a HP5 column investigation on the M-RuPr catalyst showed that RO-RCM reaction was 1 st order in cyclooctene, and that the dimer and trimer were found to be primary products, while the tetramer and pentamer were secondary products.

RuBnGH-II

To understand the origin of this selectivity towards low cyclic oligomers, we prepared the isostructural homogeneous Ru-NHC complexes with unsymmetrical NHC ligands. We showed that their reactivity and selectivity are similar to those of previously prepared heterogeneous homologues and that the main factor influencing the dimer and trimer selectivity was the unsymmetry on the NHC ligand and not pore confinement.

The collected data allowed us to propose an hypothetical mechanism explaining the observed selectivity towards cyclic oligomers and fitting the experimental observations (the prefered formation of dimers and trimers and their 2:1 ratio, Table 1).This mechanism is based on the catalyst architecture which exhibits dual site configuration (see Scheme 1).

Ru Cl