Une thèse en sciences est aussi bien un voyage scientifique qu'un voyage humain.

Dès qu'on bloque sur un point ou qu'on perd un produit (parce qu'on l'a fait tomber par terre ou dans un bain d'huile), il faut apprendre à gérer la frustration de ne pas comprendre ou d'avoir perdu des semaines de travail. Au final, peu importe le temps que ça prendra, on finira toujours par comprendre la Science, d'autres chercheurs étaient là bien avant nous et le seront après. Par contre, grandir en tant que personne et scientifique et se comprendre soi-même prends du temps, on peut même passer une vie à le faire. J'ai donc beaucoup de personnes à remercier pour ce qu'elles m'ont apporté sur cette voie, durant mes trois ans à l'IRCELYON.

À commencer par les deux personnes par qui cette aventure à commencer : Jérôme Canivet et Alessandra Quadrelli.

Après CPE Lyon, je ne savais pas si je voulais commencer un emploi ou faire une thèse, la seule condition était de trouver un superviseur avec qui je m'entende bien et qui serait présent dans ce voyage. Je sais que dans ta culture un merci signifie « au revoir, je n'ai plus besoin de vous » mais pour moi, merci d'avoir été un superviseur incroyable, d'avoir toujours été à l'écoute, de m'avoir poussé à me dépasser à chaque étape, de m'avoir aidé dès les premiers instants à préparer le dossier pour la bourse de l'École doctorale, d'avoir toujours trouvé la force de répéter les choses deux fois parce que j'étais un doctorant sourd.

Tu m'as aussi toujours laissé l'autonomie dont j'avais besoin pour faire mes erreurs et avancer.

Alessandra

, on se connait depuis les cours d'organométallique en 2014 à CPE et t'es sûrement la personne qui m'a vu le plus changer en huit ans : à travers CPE, mon stage de fin d'étude au LCOMS, ma thèse avec Jérôme et toi. Ton point de vue incisif, percutant et ton soutien pour que je me pose à chaque fois les bonnes questions m'ont poussé à être un meilleur scientifique. Ton engagement pour l'environnement a également attisé ma curiosité pour comprendre la science derrière les enjeux climatiques d'aujourd'hui. Merci pour votre confiance à tous les deux et tout le temps que vous aurez consacré à rendre mes présentations, mes abstracts et mon manuscrit meilleurs. C'était comme avoir un deuxième papa et une deuxième maman. Je souhaite à tous les étudiants qui passeront sous vos ailes de pouvoir bénéficier de l'enseignement et de l'encadrement que j'ai eu la chance d'avoir. 5.1 Chemicals ...............

Je tiens également à remercier Catherine Pinel et Stéphane Daniele pour les heures d'enseignement avec eux et de m'avoir permis de réaliser cette thèse à l'IRCELYON sous la direction de Jérôme et Alessandra avec une des bourses de l'École doctorale. Merci beaucoup à David Farrusseng et à Yves Schuurman de m'avoir permis de réaliser cette thèse au sein de l'équipe Ingénierie.

Ma formation a également été enrichie par le savoir et les compétences de nombreux amis post-doctorants. À commencer par Florian Wisser qui a su répondre avec pédagogie à mes nombreuses questions, de mon premier jour jusqu'à son départ de l'équipe. Il n'y a aucun doute que tous les étudiants que tu encadreras auront la chance de bénéficier de ton enseignement et de ta gentillesse. Je souhaite également remercier Katia Barbera qui m'a très tôt montré comment fonctionnaient le laboratoire, les autoclaves et les appareils de mesure. Merci à vous deux de m'avoir aussi bien accueilli et montré les techniques qui m'ont été utile tout au long de ma thèse. Merci aussi à toi Yoann (Roux), tu jouais très bien les calmes et les pédagogues au laboratoire mais on l'a tous vu le grain de folie que t'avais. Un merci très spécial à Partha (Samanta), arrivé durant mes dernières années de thèse et qui m'a énormément aidé dans mes synthèses de Bpy-MP-3 et de MOF-808. Merci beaucoup pour ta gentillesse, ta pédagogie dans les techniques de laboratoires et à propos des MOFs.

Merci aussi pour ces vacances dans le centre de la France qui ont été une super pause au milieu de l'été ! Merci aussi à Medet (Zhukush) qui m'a supporté dans ma rédaction, qui m'a rassuré et qui a été aux premières loges à chaque fois que je me plaignais, un grand merci à toi pour ta gentillesse (ouais j'utilise beaucoup ce mot, et pédagogie aussi, mais c'est vraiment l'atmosphère dans laquelle j'ai travaillé durant trois ans). Merci Marcelo (Alves-Favaro) et Yorck (Mohr) d'avoir été ces doctorants modèles, de m'avoir montré vos techniques et de m'avoir rassuré quand j'en avais besoin. Merci beaucoup Yorck pour ta franchise constante, on en a tous besoin ! Merci Cécile (Daniel) et Emmanuel (Landrivon) pour toutes ces discussions enrichissantes à propos de tout, d'avoir été là quand j'en avais besoin, de toujours prendre un peu de temps, j'ai beaucoup grandi à votre contact. Merci d'avoir pris le temps pour moi.

Merci aussi à Nolven Guilhaume, Frédéric Meunier, Franck Morfin, Jean-Luc Rousset et Alain Tuel, pour toujours avoir un bonjour et un sourire.

Un grand merci également à tous les autres post-doctorants, doctorants, ingénieurs et techniciens : Ranin Atwi, Mehdi Bessaa, Rémi Beucher, Corentin Colomb, Taha El-Gayyar, Ashta Ghosh, Firat Goc, Clément Got, Paul Hazemann, Aleksandra Lelevic, Chetna Mohabeer et Eddy Moreno.

Le travail des chercheurs à l'Institut ne serait pas possible sans le travail du service administratif avec Christine Babolat, Géraldine Chapuis, Narayman El-Jerrari, Lala Fillon et Marie-Laure Venditti. Merci beaucoup pour votre bonne humeur chaque jour, de toujours avoir la patience de régler les problèmes administratifs que je pouvais avoir, et de le faire avec charme ! Vous allez grave me manquer. C'est rare d'avoir un service aussi efficace, où tous les papiers sont prêts dès qu'on arrive et où on a juste à apposer notre signature. Il est facile d'oublier ce que les efforts des gens quand tout se passe bien, donc j'espère que les gens n'oublient pas. Ne changez rien ! Merci également à Sébastien Albert et David Tatangello pour l'entretien du magasin.

Indépendamment des ruptures de stock, on a toujours su trouver ce dont on avait besoin afin de travailler dans de bonnes conditions et de l'aide quand on avait besoin de quelque chose.

Merci aux services analytiques, pour leur patience et pour avoir accepté d'analyser mes échantillons à chaque fois, de prendre le temps de m'expliquer ce que je ne comprenais pas et de discuter avec moi: Chantal Lorentz, Pascale Mascunan, Yoann Aizac, Françoise Bosselet et Thibaut Cornier.

Un grand merci au jury d'avoir évalué ma thèse et d'avoir donné lieu à une discussion aussi enrichissante. Je souhaiterai remercier particulièrement Vincent Monteil, présent en tant qu'invité et qui a (aussi) été un de mes professeurs, pour ses conseils durant mes Comités de Suivi de Thèse avec Alexandra Fateeva (que je remercie également). Il m'a également conseillé de consulter Olivier Boyron, qui a aimablement analysé mes échantillons de polyéthylène issu de mes catalyses, permettant de comprendre leur composition, merci beaucoup à toi ! Merci à toute l'équipe des Bras Cassés, pour tous les verres et les week-ends qu'on a passés à Fressac, Vaison-la-Romaine ou Vallon-Pont-d'Arc. À tout ce qui a été décrit avant s'ajoute donc une équipe d'amis formidables et aussi fous les uns que les autres : Nicolas Bonnet, Pauline Bredy, Bastien Buey, Corentin Chatelard, Baptiste Chauchon, Ekaterina Galand, Pauline Giraud, Jordan Guillemot, Gaëlle Hisler (de me faire garder les pieds sur terre), Thomas Len (pour toutes les parties d'échecs), Valentin Lhospital (j'espère qu'on va bientôt l'escalader cette grue), Mathieu Lions (merci frère pour toutes les séances d'escalade et t'inquiète tes abdos sont toujours là, par contre, arrête de fumer…), Alisa Ranscht (merci pour toutes les fois où on est allé courir qu'il pleuve, qu'il neige ou qu'il fasse beau), William Rezende-Locatel (merci pour toutes les soirées Demon Slayer et Attaque des Titans), Quentin Rivet (t'es vraiment impec') et Gabriel Trierweiler.

Merci Eugénie (Blaser) pour tous les déjeuners ensemble et les discussions qu'on avait, ta confiance et ton honnêteté. Merci également au Réseau Jeunes de la Société Chimique de France : Noémie Perret, Céline Pagis (d'avoir dès le début de ma thèse donné l'exemple de ce que devait être une soutenance et la satisfaction du travail accompli), Quentin Touloumet et Alexandre Vandeponseele.

Merci aux « colocataires » géniaux que j'ai pu avoir, présents depuis le début : Candice, Elsa, Ghislain (arrivé en cours de route, merci pour toutes les séances de sport) et Pierre.

Les noms qui suivent sont ceux des guerriers qui me supportent depuis la première heure et qui ont toujours été des amis, des piliers et des exemples qui m'ont toujours tiré vers le haut : Abdallah, Alexandre, Anne, Antoine, Isaline, Kusumita, Léon, Marie, Marine (merci pour toutes les séances de sport ma belle et d'avoir toujours répondu présente dans les moments difficiles, parce que cette thèse n'aurait pas été la même sans toi), Rudy et Sofia.

Le noyau dur, ceux qui sont là depuis que je suis tout petit : merci Wathsala et Bastien de toujours être là, pour les repas préparés pendant ma rédaction, d'avoir accepté mon annulation de Noël à la dernière minute, de m'avoir fait témoin pour votre mariage, d'être les meilleurs amis que vous êtes sur qui je peux toujours compter. Dihan, tant que tu seras célibataire, je ne serai toujours que le second gendre idéal mais bon ça nous permettra toujours de sortir tranquillement les soirs d'été et de parler aux inconnus. Merci aussi à Elsa et Sujeewa, mes amis d'enfance.

Enfin, une vie ne suffira pas à remercier papa, maman, loku akki et banthi akki d'avoir toujours été là, de m'avoir soutenu, de m'avoir élevé, d'avoir fait de moi la personne que je suis aujourd'hui avec ses qualités et ses défauts. Merci à mes beaux-frères, Lakshitha ayya et Vincent. Merci aussi aux quatre frites, Alexis, Maxime, Côme et Roxane, de mettre autant d'animation dans nos vies.

Enfin, comme pour de nombreux doctorants (entre millions d'autres), pas merci du tout au COVID-19. La seule raison pour laquelle j'ai réussi à tenir seul dans mon 10 m² pendant cette période est la personne que je suis devenue grâce à toutes les personnes citées avant.

Abstract

Ethylene α-oligomers are typically used in copolymerization with ethylene to modulate the properties of polyethylene. With an increased availability of shale gas, and therefore of ethylene, it has become more viable economically to produce selectively α-oligomers from this gas. Despite a large use of various catalysts in industry, based on Ti, Fe, Ni, etc. with different ligands, homogeneous catalysis could present certain limitations such as the presence of metal particles or a lack of catalyst stability. Heterogeneous catalysts could enable to separate products from the catalyst more easily. At the same time, isolating active sites within a solid matrix can prevent their deactivation. Molecular catalysts heterogenization enables to bridge the gap between homogeneous catalysis and heterogeneous catalysis by preserving catalytic activities and selectivities obtained in homogeneous catalysis, while obtaining isolated active sites.

During this thesis work, two types of porous supports were synthesized and characterized, Metal-Organic Frameworks (MOFs) and Porous Organic Polymers (POPs), with bipyridyl coordination sites: the MOF UiO-67-bpy and the POPs Bpy-MP-1, Bpy-MP-2

and Bpy-MP-3. The bipyridyl sites within their structure were functionalized with nickel(II) chloride complexes in order to obtain isolated active sites. Ill-defined active sites could be obtained with UiO-67-bpy-based catalysts. The series of catalyst synthesized with Bpy-MP-1 and Bpy-MP-2 macroligands were characterized. For the Bpy-MP-1-based catalysts, the bipyridyl sites within the structure coordinate to nickel(II) chloride. However, traces of Pd originating from their Pd-catalyzed synthesis pathway were found within their structure, which can cause side reactions and deactivation of catalyst by interaction between Pd and Ni active sites. Therefore a new POP, obtained by Pd-free radical polymerization, Bpy-MP-3, enabled to prepare a series of catalyst with different loadings of nickel. These series were fully characterized and show that the bipyridyl sites within their structure are functionalized with nickel(II) chloride complexes.

These four series of catalysts were tested for ethylene oligomerization and for each given conditions, the catalyst series obtained with Bpy-MP-3 enabled to obtain TOFs above 10 000 mmol oligomers.mmolnickel -1 .h -1 , higher to the activity obtained with its homogeneous counterpart Ni(bpy)Cl 2 and its other heterogeneous analogues UiO-67-bpy, Bpy-MP-1 et Bpy-MP-2. Despite being highly active for ethylene oligomerization and selective in butene within oligomer products, Bpy-MP-3-based catalysts are also highly active for ethylene polymerization, decreasing the global selectivity and causing the deactivation of the catalyst. Different possible causes were elucidated concerning the origin of the uncontrolled polymerization reaction during this thesis work. The same type of active sites within the catalyst was capable of both oligomerizing and polymerizing ethylene at the same time.

However, the addition of PPh3 during the reaction enabled to stop ethylene polymerization and promote ethylene oligomerization.

Accordingly, the MOF-808-DPPB and the Phos-MP-3 POP, both being phosphinebased rather than bipyridyl-based porous solids, were synthesized and characterized. The ability of the corresponding Ni-based catalysts to oligomerize ethylene, and not polymerize it, is currently under investigation with promising preliminary results. This work highlights the potential of porous solids like MOF and POP to act as macroligands to heterogenize molecular catalysts, as proved for Ni-based complexes active in ethylene oligomerization.

The newly designed heterogeneous catalysts are at least as active and selective than their homogeneous counterparts. The nature of MOF and POP solids allows a wide versatility in solid porous macroligand construction to tune the steric and electronic environment around the active site, at the origin of the catalytic activity and selectivity.

Résumé

Les α-oligomères de l'éthylène sont utilisés notamment en copolymérisation avec l'éthylène afin de moduler les propriétés du polyéthylène. Aujourd'hui, avec une disponibilité accrue en gaz de schiste, et donc en éthylène, il est devenu très intéressant de produire sélectivement des α-oléfines à partir de ce gaz. Malgré une utilisation répandue en industrie avec des catalyseurs présentant des ligands phenoxy-imines ou bipyridyl, la catalyse homogène de cette réaction peut présenter certaines limites comme la présence de résidus métalliques ou un manque de stabilité des catalyseurs. Ainsi, non seulement la catalyse hétérogène présente cette facilité de séparation du catalyseur et du milieu réactionnel mais peut permettre aussi de contrôler la forme des catalyseurs, tout en obtenant des sites actifs bien définis, évitant la désactivation du catalyseur par interaction des sites actifs entre eux. Ainsi, un nouveau support a été synthétisé par une polymérisation radicalaire qui n'inclut pas l'utilisation de Pd, le Bpy-MP-3. Une série de catalyseurs infiltrés avec différents taux de nickel a été synthétisée à partir de ce matériau et caractérisée. Pour les catalyseurs obtenus à partir de Bpy-MP-3, les sites bipyridyls sont coordinnés par des complexes de chlorure de nickel(II).

Ces quatre séries de catalyseurs ont été testées en oligomérisation de l'éthylène. Pour des conditions données, la série obtenue avec le Bpy-MP-3 présente une activité plus importante (supérieure à 10 000 mmololigomères.mmolNi -1 .h -1 ) que son homologue homogène Ni(bpy)Cl 2 et ses analogues hétérogènes UiO-67-bpy, Bpy-MP-1 et Bpy-MP-2. Cependant, tout en étant hautement actif en oligomérisation de l'éthylène et sélectif en butène parmi les oligomères, les catalyseurs à base de Bpy-MP-3 sont également très actifs en polymérisation de l'éthylène, entraînant des limites diffusionnelles au sein des catalyseurs durant la réaction, réduisant la sélectivité globale en oligomères et entraînant la désactivation du catalyseur. Différentes hypothèses ont été testées durant ce travail de thèse sur l'origine possible de cette polymérisation non-contrôlée. Un même type de site actif au sein des catalyseurs à base de Bpy-MP-3 semble être responsable d'oligomériser et de polymériser l'éthylène. En ajoutant des équivalents de triphénylphosphine durant la réaction, cette polymérisation peut être stoppée et l'oligomérisation favorisée. Ces nouveaux catalyseurs hétérogènes synthétisés sont aussi actifs et sélectifs, si ce n'est plus, que leurs équivalents moléculaires. La nature même des MOFs et des POPs permet d'accéder à une large variété de type de macroligands pour moduler l'environnement stérique et électronique des sites actifs, à l'origine de l'activité catalytique et de la sélectivité. understand the influence of metals (Ti, Ni, Fe, CO, etc.), of the ligands (bipyridyl-based, phenoxy-imine, etc.), of the aluminum-based co-catalysts (Et2AlCl, Me3Al, etc.), of the active sites nature (cationic or neutral) on the catalytic activity and selectivity of the catalyst. Among these α-oligomers, 1-butene focuses a lot of attention as a major building block for plastic materials and for chemicals. It can be produced from an available and cheaper gas like ethylene. Furthermore, among all metals, Ni is the best known to dimerize selectively ethylene.

Table of contents

Homogeneous catalysts have been developed and tuned at the molecular level to meet both activity and selectivity requirements for high process efficiency. However, further purification steps are required to separate the catalysts from the products after the reaction, which can alter catalyst stability overtime. Therefore, synthesizing heterogeneous catalysts enables to overcome this separation step and obtain isolated active sites, preventing them from deactivation.

Porous macroligands enable to embed anchoring sites for molecular active sites coordination. Designing a porous heterogeneous catalyst that reproduces, if not exceeds, the activity and the selectivity of the molecular counterpart rises challenges within the pores of the material of diffusion of the reagents and the products, possible physisorption of precursors, side reactions that can occur during catalytic applications and interactions between the active sites.

Based on homogeneous studies and literature results, this PhD work aimed to synthesize a porous macroligand with bipyridyl anchoring sites, that after nickel infiltration could compete with its homogeneous counterpart in terms of TOFs (mmol oligomers.mmolNi -1 .h -1 ) and butene selectivity (above 90%). By using physisorption measurements and spectroscopic techniques, the purpose was to understand the textural properties and the coordination of Ni complexes within the supports in order to optimize the catalysts activity and butene selectivity.

Context

Oligomerization of ethylene is an exothermic reaction that enables to assemble a limited number of ethylene molecules: when the number of carbon atoms C n in a chain of ethylene monomers is comprised between 2 and 100, the product is called an oligomer.

When n is above 100, the product is called a polymer. [1,[START_REF] Sanati | Catalysis[END_REF] In the case of ethylene oligomerization, Linear Alpha Olefins (LAO), carbon chains with no branching and a terminal double-bond (1-butene, 1-hexene, 1-octene, etc.) can be produced (Figure 1). etc. [START_REF] Demirors | ACS Symposium Series[END_REF]4] LAOs are also used to produce surfactants, linear mercaptans (to detect odorless gases), drilling lubricants, polyalphaolefins and more importantly building blocks for chemicals, such as propylene (obtained by ethylene and 2-butene metathesis), alcohols (by hydroformylation then hydrogenation of olefins), alkanes, amines and acids (Figure 2). [START_REF] Greiner | Linear Alpha-Olefins[END_REF][START_REF] Breuil | [END_REF][7][8][9] Figure 2 : Different applications of Linear Alpha Olefins Among all the LAOs that can be produced by ethylene oligomerization (1-butene, 1hexene, 1-octene, etc.), this work is focused on producing selectively 1-butene. Its demand has been on the increase for the past decade (1.1 million of tons in 2006 and an annual growth of 5.3% from 2006 to 2020) and its value overtook ethylene's price (around 500 dollars more per ton). [10,[START_REF]Conférence à l'Académie Des Sciences -H. OLIVIER-BOURBIGOU -De La Conception Des Catalyseurs à Leurs Applications Industrielles En Pétrochimie[END_REF] This phenomenon can be explained by a shale gas booming in many countries (206 560 billions of cubic meters worldwide): ethane availability has significantly increased, which enables to crack it into ethylene in great amounts. [START_REF] Hardy | Issues in Environmental Science and Technology[END_REF][START_REF] Armor | [END_REF][14] It is economically interesting to produce an expensive product, like 1-butene, from an abundant reagent, like ethylene.

Ethylene is a gas that can also be obtained by steam cracking, leading to lighter alkanes or olefins (ethylene, propene, etc.) from naphta (oil distillate) or heavy alkanes, by ethanol dehydration and more recently, from sugarcane [15,16,[START_REF] Breuil | [END_REF]14] Besides, LAOs can be produced by elimination reaction (such as cracking or paraffin dehydrogenation), alcohol dehydration or biomass conversion. [1,16,17] However, ethylene oligomerization, occurring by chain growth, remains the main industrial source of LAOs and the most selective process in 1-butene. [8,[START_REF] Geilen | Ullmann's Encyclopedia of Industrial Chemistry[END_REF] 1.2 Molecular complexes for ethylene oligomerization

Ethylene oligomerization mechanisms and product distributions

Two types of mechanisms have been highlighted for ethylene oligomerization:

-a cycle of activation -coordination -insertion -elimination and/or propagation (also called Cossee-Arlman mechanism) [START_REF] Cossee | [END_REF]20] -a cycle of coordination -oxidative coupling -metallacycle intermediate -elimination and/or propagation (also called metallacycle mechanism) Karl Ziegler's discovery in 1953 of ethylene polymerization (the Aufbaureaktion) with an alkyl aluminum at low pressure initiated the research of organometallic compounds for catalysis. [21][22][23][24] It was a breakthrough since ethylene is a non-polar gas requiring high pressures and temperatures (300 MPa -300 °C) to initiate polymerization without a catalyst.

In 1954, Giulio Natta first synthesized an isotactic polypropylene with a TiCl 3 -based catalytic system. Since Ziegler and Natta's pioneer work on olefin polymerization, Cossee and Arlman highlighted the mechanism occurring for this reaction. However, the same mechanistic principles apply to ethylene oligomerization.

In the case of a Cossee-Arlman mechanism, two types of metal complexes are typically used:

-metal-halide-based complexes (for example, nickel di-halide or titanium-chloride)

-metal-hydride-based complexes (like nickel-hydride)

Metal hydride-based complexes readily react with ethylene and don't need further activation, as it will be described later. [25] Concerning the metal halide-based complexes, which are among the easiest to synthesize and the most stable ones, an activation step is required in order to obtain the catalytic active species for ethylene oligomerization. This step typically involves an alkyl-aluminum activator (also called co-catalyst) that subtracts halides and alkylates the metal center (Figure 3). Ability of an alkyl-aluminum co-catalyst to subtract halides and alkylate a metal complex can be attributed to its Lewis acidity. De Souza et al. proved that, in the case of ethylene polymerization with a nickel-α-diimine complex, the more acidic (Lewis sense) the co-catalyst was, the higher the activity was. [26] Different aluminum activators are used in the literature: triethylaluminum (TEAL or AlEt3), diethylaluminum chloride (DEAC or Et2AlCl), ethylaluminum sesquichloride (EASC or Et3Al2Cl3), ethylaluminum dichloride (EADC or EtAlCl2) and aluminum trichloride (AlCl3) (Figure 4). polymerization with a nickel-α-diimine complex (adapted from De Souza et al.) [26] Metylaluminoxanes (MAO) and Modified Metylaluminoxanes (MMAO) are also alkylaluminum activators, but they require high aluminum equivalents (at least 100 and sometimes more than 1000) in order to observe an activity for ethylene oligomerization. [27][28][29] . [START_REF] Cossee | [END_REF]30,31] Hence, the use of a metallic center enhances ethylene's activation. The reaction continues with the insertion of a coordinated ethylene molecule inside the established metal-carbon bond. The complex formed is stabilized by a β-agostic interaction. [32][33][34] This species can also undergo an isomerization step, depending on the ligand on the metallic center and the reaction conditions. Either the reaction proceeds through n insertions or an oligomer is obtained by β-H elimination (resulting from the transfer of the catalytic activity to another molecule, also called chain transfer). The latter step is also favored with electron rich metals, such as iron or nickel, which favor a more significant retrodonation into anti-bonding orbitals of the carbonhydrogen (C-H) bond. This mechanism is also called "degenerated polymerization", polymerization being mostly characterized by continuous insertions of ethylene monomers (continuous propagation).

From the metal-hydride species obtained after the elimination step, the coordination of a new ethylene molecule would be followed by its insertion in the metal-hydrogen bond and the resulting metal-ethyl species becomes the site of a new catalytic cycle.

In the case of a metallacycle mechanism, the reaction starts with the coordination of two ethylene molecules to the metal center in a coplanar manner (Figure 6). Their oxidative coupling leads to the formation of a metallacyclopentane. Upon this step, two pathways can be considered:

-either a hydrogen transfer followed by a reductive elimination releases a 1-butene molecule -or the insertion of another ethylene monomer enables the creation of a metallacycloheptane intermediate, ending with the production of 1-hexene by transfer-elimination or the insertion of a fourth ethylene monomer leads to the production of 1-octene, with a metallacyclononane intermediate (energetically considered less favorable than the seven atom intermediate) [35][36][37] [27,38,39] This equation represents the relation between the oligomer fraction Tn+2 and the previous oligomer fraction Tn. The general solution to this equation is:

Tn/R = (1-α)α n-1
Equation 2 : General solution of the Schulz-Flory equation with R the total molar amount of olefins produced in a given time and Tn/R the mol% of oligomers with n carbon atoms When T n/R is plotted against the number of carbon atoms n for a given α, resulting in an exponential decreasing function: when the number of carbon atoms of the oligomers that are produced increases, the mol% of the corresponding oligomers decreases. Therefore, systems based on Schulz-Flory distributions enables to target short LAOs.

On the other hand, some systems are based on a Poisson distribution. In this type of distribution, resulting also from the plotting of mol% of oligomers with n carbon atoms against the number of carbon atoms, a Gaussian type curve is obtained. Systems based on Poisson distributions enables to target a range of LAOs, rather than a specific LAO.

Mechanisms and resulting product distributions for ethylene oligomerization have been presented. The next part will describe the major breakthrough catalysts along with the industrial processes resorting to these systems.

Overview of industrial homogeneous catalysts for ethylene oligomerization

Two types of processes have been defined to produce LAOs with high activities:

-full-range processes, that enables to produce a mixture of alpha-olefins -on-purpose processes, that enables to produce selectively one alpha-olefin (1butene, 1-hexene, etc.)

Today's main full-range processes are summed up in 7). This type of catalyst is synthesized with a phosphorus ylide, a [Ni(1,5-cyclooctadiene) 2] (Ni(COD)2) complex and a phosphine. [40] SHOP-based catalysts with a phosphino-enolate component favors the elimination step rather than the propagation step, leading to LAOs up to twenty carbon atoms. Removing the phosphine part with a scavenger would lead to a polymerization catalyst rather than an oligomerization catalyst. [START_REF] Glockner | Ethylene Oligomerization[END_REF][START_REF] Klabunde | [END_REF][43][44][45] The SHOP process enables to produce a broad range of oligomers but mainly C12 to C20+ olefins and one of the challenge remains to make this type of catalyst more selective towards 1-butene. : Full-range processes for ethylene oligomerization [1,[START_REF] Greiner | Linear Alpha-Olefins[END_REF][START_REF] Breuil | [END_REF]8,46] Idemitsu and Alpha-SABLIN processes are Zr-based catalysts activated with alkylaluminum activators. Idemitsu enables to produce 55 000 tons per year of oligomers from C4 to C18 in Japan whereas the Alpha-SABLIN plant (in Saudi-Arabia) reaches a capacity of production of 150 000 tons/year of LAOs. Furthermore, the Alpha-SABLIN requires moderate reaction conditions (between 50 and 100°C, with a feed of ethylene between 20 and 35 bar).

In the case of on-purpose processes, the AlphaButol ® process, initiated by Yves Chauvin and developed by IFPEN, represents one of the most important systems developed for the selective dimerization of ethylene, while minimizing polyethylene production (Table 2). [START_REF] Le | Process for the Synthesis of Butene-1 by Dimerisation of Ethylene[END_REF] This process is based on Ziegler's discovery and resorts to a titanium complex Ti(OR)4 activated with Et3Al, at 50 °C and 20 bars of ethylene. This system is an example of the influence that the aluminum activator amount can have on the orientation of the reaction: for an Al/Ti ratio of 10, polyethylene is the major product whereas, for a ratio of 3, 1-butene is produced with a 93% selectivity and less than 100 ppm of polyethylene. [START_REF]Conférence à l'Académie Des Sciences -H. OLIVIER-BOURBIGOU -De La Conception Des Catalyseurs à Leurs Applications Industrielles En Pétrochimie[END_REF] From the first AlphaButol ® plant in Thaïland in 1987 producing 3 000 tons of 1-butene per year, this process has been implemented in several countries and enables to produce today more than 700 000 tons of 1-butene per year. The AlphaHexol™ process, used by Axens, is also based on a chromium catalyst but resorts to a phenol proprietary ligand, that enables to stabilize the metallacycle leading to 1hexene (99%). [START_REF] Commereuc | Catalytic Composition and Process for Oligomerising Ethylene in Particular to 1-Butene and/or 1-Hexene[END_REF] In 2004, Sasol developed a chromium-based catalyst with a bis(diphenylphosphino)isopropylamine ligand, activated with MAO. This system enabled an ethylene consumption of ethylene of 250 000 gethylene.gCr -1 .h -1 with a selectivity of 99% in 1octene among the octenes (72%) and of 85% in 1-hexene among the hexenes (25%). [36] The first plant installed in Louisiana enables to produce 100 000 tons per year of a 1-hexene/1octene mixture.

Based on Fujita's titanium catalyst with an aryloxy-imine functionalized ligand, Mitsui Chemicals developed a plant at Ichihara Works, consuming 40 kilotons of ethylene per year and with a selectivity in 1-hexene of 94% (Figure 8). 9). [START_REF] Small | [END_REF]50] They proved that for this iron-based type of catalyst, the lower the steric hindrance around the metallic site, the more favorable the reaction towards ethylene oligomerization and not polymerization.

Figure 9 : Iron-based catalyst with a bis(imino)pyridine ligand (adapted from Brookhart et al.) [START_REF] Small | [END_REF] Another major breakthrough has been obtained in ionic liquid IL (Figure 10). [10,[51][52][53][START_REF] Trzeciak | Ionic Liquids (ILs) in Organometallic Catalysis[END_REF] The main advantage of using IL is to obtain a biphasic liquid system where the ionic metal-based catalysts is soluble in IL whereas the organic reagents and products, such as the olefins, are soluble enough in IL in order for a catalytic reaction to happen. Hence, the products dissolved in the upper organic phase (alkane-based) can be recovered while the catalyst is remaining trapped in the lower IL phase.

Figure 10 : Main cations and anions described in literature (adapted from Olivier-Bourbigou et al.) [53] In 1990, IL have been proposed for the first time for the propene dimerization by Chauvin et al. [51] Nickel-based catalyst with different IL (like the 1-butyl-3methylimidazolium][AlEtCl 3] have achieved a 6 600 ghexenes.gNi -1 .h -1 TOF with a [NiBr2L2] complex (L=2-methylallyl) at -15 °C and 10 bars of propylene.

For ethylene oligomerization, Wasserscheid et al. proposed for the first time a nickel complex associated with a biphosphine monoxide ligand (analogous to the one used for the SHOP process), at 25 °C and 50 bars of ethylene during two hours. [START_REF] Wasserscheid | [END_REF] With an [1-butyl-3méthylimidazolium][PF 6] , they achieved a 12 712 molconverted ethylene.molNi.h -1 TOF with a selectivity in 1-hexene of 88%.

Some studies suggest that IL can suffer from mass transfer limitations between the two liquid phases. [START_REF] Small | [END_REF]27,29,56] Today, the Difasol™ process (Axens) developed by IFPEN is an industrial application of the IL. [START_REF]Conférence à l'Académie Des Sciences -H. OLIVIER-BOURBIGOU -De La Conception Des Catalyseurs à Leurs Applications Industrielles En Pétrochimie[END_REF]53,57,58] It has been connected to the Dimersol™ process, the latter dimerizing light olefins (C2 to C4). By using a recycling system, the Difasol™ process dimerizes the reagents that have not reacted in the first place with the Dimersol™ process, with a lower reagents concentration and the same catalyst amount as the Dimersol™ process (Figure 11). The catalyst used is an ionic nickel, without additional ligand, dissolved in an [1-butyl-3methylimidazolium][Cl]/AlCl 3/EtAlCl2 IL. [53] This process has been extended to the selective dimerization of propylene. ) [53] In summary, this section enabled to describe major breakthroughs in biphasic IL systems done for the ethylene oligomerization with molecular catalysts based on different metallic centers (Ti, Cr, Ni, Zr, etc.). With these systems, a broad range of oligomers mixture (full-range processes) or a specific oligomer (1-butene, 1-hexene, etc.) are obtained depending on the metallic center and the reactions conditions. Depending also on the conditions and the ligands that are used, the selectivity of the reaction can be directed towards ethylene oligomerization or polymerization. Several reviews highlight the many other breakthroughs with other metals (V, Co, Pd, W, etc.) and the research challenges that they raise for ethylene oligomerization. [1,[START_REF] Breuil | [END_REF]8] This thesis work is focused on the Ni-based catalysts. Unlike other metals (Ti, Cr or W),

Ni is well-known to oligomerize not only ethylene, but also other olefins such as propylene and butene. [START_REF] Breuil | [END_REF]59] There are two types of active species used for ethylene oligomerization (Figure 12):

-cationic species, highly electrophilic, isolated by Wilke et al. in 1966 [60] -neutral species, less electrophilic and isolated by Keim et al. in 1978 [43] Figure 12: Two types of nickel active species: cationic and neutral

The results shown this far prove that homogeneous and biphasic catalyses are very efficient. One of the possible targets in developing new paradigmatic shifts in ethylene oligomerization (for example through heterogeneous catalysis) is TOFs and selectivities as competitive as those obtained by homogeneous (molecular) catalysis (in the case of ethylene oligomerization, more than 10 000 mol oligomers.molmetal -1 .h -1 and more than 90% of butene), while controlling the amount and the isolation of the active sites. Isolation of active sites prevents them from sintering, possibly leading to the catalyst deactivation. Using heterogenized active sites enables to isolate active sites from each other and, as a consequence, prevent them from sintering, aggregating or interact between them, which could lead to the catalyst deactivation. [61][62][63][64]

Siliceous-based heterogeneous platforms for ethylene oligomerization

In the field of heterogeneous catalysis, inorganic solids are the most established catalysts, with siliceous-based materials at the forefront. This section will review the state of the art for ethylene oligomerization by this class of materials. 22) for ethylene oligomerization. [7,65,[START_REF] Lallemand | Studies in Surface Science and Catalysis[END_REF] The catalysts are obtained from zeolite structures, by cation exchange. Cations are used during zeolite synthesis in order to ensure charge neutrality within the structure. The pristine materials underwent a treatment with an ammonium nitrate solution to replace the cations and then the ammonium ions were replaced by nickel cations. This technic of cation exchange with zeolites (for ethylene oligomerization purposes results in an optimal dispersion of the active sites throughout the support. Given their cationic nature, they ensure the structure's charge neutrality and do not require any further activation with an aluminum-based co-catalyst.

Zeolitic catalysts

However, the activation of the catalyst requires high temperatures in order to desorb any impurities within the pores and to obtain an optimal porosity for the reaction. This activation might be responsible for the occurrence of acidic sites and the reduction of Ni a wider pore width than underwent Ni-AlSBA-15 underwent a less significant deactivation.

However, the Ni exchange technic does not allow control on active site environment.

The exact nature of the active sites is still unknown and the occurring mechanism is not fully solved. [68] Acid sites represent also another type of active sites, responsible not only for isomerization reactions but also for dimerization of the products formed in the first place.

Combined to the microporosity of some catalysts, the production of heavier products (C8 and more) can lead to pore blocking. Working at higher temperatures also favors catalytic cracking of the products.

Surface Organometallic Chemistry

Historically, Surface Organometallic Chemistry (SOMC) represented an innovation in the eighties for heterogeneous catalysis by developing catalysts where organometallic compounds were coordinated to oxide or hydroxide supports.

Basset et al. proposed the synthesis of two catalysts by SOMC for ethylene oligomerization:

-a tantalum-based catalyst, [(≡SiO)Ta V Cl 2 Me 2 ], by grafting TaMe 3 Cl 2 on SBA-15 [69] -a niobium-based catalyst, [(≡SiO)NbMe4], resulting from the grafting and methylation of NbMe2Cl3 on a SiO2 surface dehydroxylated at 700 °C. [70] The niobium-based catalyst enabled to achieve 91.9 wt% of butene selectivity with an activity of 1 050 molethylene consumed.molNb -1 .h -1 under 50 bars of ethylene at 100 °C during one hour in toluene. In similar conditions (30 minutes of reaction instead of one hour), the tantalum-based catalyst's activity reached 375 mol ethylene consumed.molTa -1 .h -1 with 82.7 wt% of hexene products. Both catalysts are active without aluminum-based co-catalyst activation.

However, they suffered from deactivation by polyethylene production, stemming from the complexes geometry and coordination sphere on the surface. [71] Hence, the interactions between the active sites and the free oxide or hydroxide sites may hamper the catalytic activity. [72][73][74][75]

Periodic Mesoporous Silica

Periodic Mesoporous Organosilica (PMOs) is a class of siliceous materials, possibly containing organic moieties and an organized mesoporosity. [75][76][77] They present high surface areas, high porous volume and structural diversity (MCM-48 with a 3D porous structure or MCM-50 with a 2D structure). Aluminum can be introduced into the structure to tune its acidity.

Recently, Shin et al. synthesized a series of eight bpy-SBA-15, with different molar amounts of bipyridyl sites metalated with NiCl 2•H2O (Figure 13). [78] The design of these catalysts was motivated by minimizing polyethylene formation and improving oligomer production, with heterogenized (bpy)Ni(II)Cl2 catalysts.

Figure 13 : From a synthesized SBA-15 PMO, the design of a series of eight bpy-SBA-15

(bipyridyl sites embedded on the surface and within the walls of the structure) and their metalation with NiCl 2•H2O (adapted from Shin et al.) [78] Ethylene oligomerization tests were performed in heptane during 30 minutes with 70 or 700 equivalents of Et 2AlCl and under 30 bar of ethylene, at 150 °C.

First, the series of catalysts were more active than their homogeneous counterpart Ni(bpy)Cl2 for the given conditions, with 406 mololigomers.molNi -1 .h -1 and a selectivity in butene of 51%. Authors observed minimal polyethylene formation with the catalyst characterized with 0.21 wt% of Ni and a 4 nm pore size. It achieved 4 422 mol oligomers .mol Ni -1 .h -1 and a selectivity in butene of 77%, with 700 equivalents of Et 2 AlCl. The catalyst has been recycled seven times, without nickel leaching, suggesting the successful immobilization of the molecular complex within the large pores of the material.

However, catalysts with higher pore sizes (7 and 10 nm) and higher nickel loadings (0.27 wt% and 0.31 wt% of Ni respectively), proved to be less active and less buteneselective in the same conditions. Same conclusions can be drawn for 2.25 wt% and 1.51 wt% nickel loadings.

Added to the fact that the bipyridyl sites are theoretically embedded over the surface and within the walls of the material, which decreases the ratio of active sites per catalyst mass, the mesoporosity of the material does not ensure the possibility of immobilizing the molecular complex within its pores. The large pores of the PMOs (between 20 and 500 Å) make them less suitable for pore confinement of molecular complexes.

Different inorganic and non-porous materials have been also synthesized and tested for catalytic purposes, like clays, aluminum sulfates and oxide surfaces, but they will not be developed in this work since they have not shown particularly high activity in ethylene oligomerization. [7,[79][80][81] In summary, siliceous-based heterogeneous nickel catalyst have shown activity for ethylene oligomerization. The most interesting results were obtained with bipyridine moieties in the solid. At the same time, the performance obtained so far were not competitive with respect to their homogeneous counterpart.

Porous polymers for ethylene oligomerization

Within our research group, the strategy adopted to bridge the gap between homogeneous and heterogeneous catalysis, by keeping advantages of both fields, is to develop a porous solid framework around the molecular catalyst in order to increase the density of active sites by mass unit. The framework itself acts as a ligand (with an influence on the activity and selectivity of the active site) and is qualified of macroligand. On one hand, the porosity of the framework enables to diffuse the metallic precursor to the preinstalled ligand within the solid, to form the catalytic material and, on the other hand, it allows, during the catalysis itself, the diffusion of the reagents towards the active sites and of the products off the pores network (Figure 14).

Figure 14 : The porous macroligands strategy for molecular catalysts heterogenization (adapted from Canivet et al.) [75] Porous frameworks are built from monomers, some of the monomers bearing the anchoring site required to obtain a catalytic active site and the other monomers establishing the rest of the framework. Different ways of assembling the monomers have been established (self-assembly, C-C coupling catalyzed reactions, etc.), leading to the development of different types of frameworks (Metal-Organic Frameworks, Covalent-Organic Frameworks, Porous Organic Polymers, etc.). This way of designing porous frameworks enables to obtain isolated active sites (by diluting the monomers bearing anchoring sites among other monomers within the solid) and avoid interactions between them leading otherwise to the catalyst's deactivation. Besides, using monomers with different organic functions allows the addition of new functionalities after the framework build-up. [75] 1 Different methods have been employed to obtain isolated active sites for ethylene oligomerization in porous frameworks. Hereafter are the most relevant literature data organized by the following synthetic routes (Figure 15):

-by one-pot synthesis (OPS), with Ni active sites already incorporated within the structure of the MOF (route A) [82] -by cation exchange of metal nodes of the MOF with a metal complex (route B) [83,84] -by atomic layer deposition (ALD) in a MOF (AIM) (route C) [85,86] -by post-synthetically modifying (PSM) MOFs by imine condensation of Ni(PyCHO)X2 complexes (X = Cl or Br) (route D) [87][88][89] performances, leading to confirm by PXRD that the as-synthesized MIL-100(Cr) and the MIL-100(Cr)-t (with t representing the temperature the catalyst it has been activated at) are in agreement with the pattern reported in the literature. [97,98] On one hand, for ethylene oligomerization, performed in toluene at 10 °C with 500 equivalents of Et2AlCl and under 10 bars of ethylene during one hour, the authors observed polyethylene production along with oligomer products, with the MIL-100 16): [100] CPO-27 (Ni) No polymeric product could be observed with these nickel-based MOFs, as it was with the MIL-100(Cr). The active nickel sites are isolated enough not to interact between them and lead to the production higher olefins (C 8 or C10).

Ni-ZIF-8

More recently, in 2021, Chen et al. proposed the One-Pot Synthesis of a Ni-ZIF-8 MOF for the selective dimerization of ethylene. [82] From a mixture of Zn(NO3) 2+ imine-like site, remains on the surface of the crystals, and not within the porosity of the material, which enables to dispense from mass-transport limitations within the porosity of the material (Figure 17). The authors also prepared another catalyst by growing a ZIF-8 shell on the Ni-ZIF-8 surface, namely Ni-ZIF-8@ZIF-8, in order to cover-up the surface [82] First, the ZIF-8 itself (with only Zn sites) was not active whereas all the other Ni-ZIF-8 catalysts generates oligomers (whatever the loading or the catalytic conditions), indicating the necessity of Ni sites to observe a catalytic activity. For given conditions, the Ni-ZIF-8 was seven times more active than the Ni-ZIF-8@ZIF-8, hence only some of the Ni active sites on the surface have been deactivated by the ZIF-8 growth.

In

Isolating active sites by cation exchange (route B) MFU-4l

To the best of our knowledge, only [1,4]dioxin). [84] An MFU-4l is soaked in a DMF solution of Ni(NO3)2•6H2O. The longer the pristine material is left to soak, the higher Zn 2+ replace by Ni 2+ . This method resulted in the synthesis In similar conditions, Ni(1%)-CFA-1 achieved 1 800 mol ethylene converted .mol Ni -1 .h -1 with a 88.6% butene selectivity whereas Ni(1%)-MFU-4l enabled to achieve 41 500 molethylene converted .mol Ni -1 .h -1 , with a 97.4% butene selectivity when activated with 500 equivalents of MAO.

H 2BTDD for bis(1H-1,2,3-triazolo[4,5-b],[4',5'-i])dibenzo
In addition, Ni(7.5%)-CFA-1 achieved 1 800 molethylene converted.molNi -1 .h -1 with a 88.6% butene selectivity whereas Ni(1%)-MFU-4l enabled to achieve 41 500 mol ethylene converted.molNi -

Isolating active sites by Atomic Layer Deposition in MOFs (route C) Ni-AIM-NU-1000

Based on previous research work done on Atomic Layer Deposition in MOFs (AIM), Li et al established a method to deposit isolated Ni ions on the Zr nodes of the NU-1000, for catalytic ethylene hydrogenation purposes, at a reduced Ni-H center. [85,101] Upon activation with Et2AlCl, the authors tested the Ni-AIM-NU-1000 for ethylene oligomerization at 45 °C and 2 bar pressure, in a continuous reactor. Polymeric product was formed during the first 10 hours of the process and afterwards oligomers could be observed with a butene selectivity around 42% with a 0.3 s -1 TOF (1 080 h -1 ).

By using the same strategy, a Co-AIM+NU-1000 was developed and its activity appeared to be lower than Ni-AIM+NU-1000.

In a later work, Farha et al. tuned the electronic and steric environment of the Ni-AIM+NU-1000 active sites, with hexafluoroacetylacetonate (Facac -) electron-withdrawing groups and acetylacetonate (Acac -) weakly electron-donating groups. They evaluated the effects of this tuning on the catalytic ethylene oligomerization, in a packed reactor under continuous flow of 100% ethylene gas feed at 2 bar and 45 °C, activated with Et 2AlCl. [102] Despite a twenty times lower activity of these materials compared to Ni-Facac-AIM-NU-1000, the two electronically/sterically tuned catalysts afforded 100% selectivity in butene (Figure 20). A Gibbs free energy profile, with a model where the Zr 6 node is functionalized with a single Ni atom and the Facac -or the Acac -ligand, enabled to prove that with these specific ligands, the butene production is energetically more favorable than chain growth.

At the same time, since comparison of selectivities have not been made at comparable conversions, little can be extrapolated from these data. 2), this Cr-based catalyst leads to a product distribution of 79% of C 8 -C 18 and 21% of C 20 -C 28 , with a 60 h -1 TOF. Polyethylene could only be observed after 24 hours of reaction.

In summary, this functionalization of a hydroxy node ligand of MOFs does not appear particularly performing in terms of catalytic activity with respect to ethylene oligomerization.

Isolating active site by Post-Synthetic Modification (route D)

Ni@(Fe)-MIL-101

Canivet et al. achieved isolation of active sites by the imine condensation of a

Ni(PyCHO)Cl2 complex with the dangling amino groups of the (Fe)-MIL-101-NH2 framework, to yield 10Ni@(Fe)-MIL-101 and 30Ni@(Fe)-MIL-101 catalysts, where respectively 10% and 30% of the amino groups were converted into the corresponding Ni imine. [87,104] These two catalysts were tested for ethylene oligomerization in n-heptane, with 15 bars of ethylene at 10°C during one hour and with 70 equivalents of Et 2AlCl per Ni. 10Ni@(Fe)-MIL-101 and 30Ni@(Fe)-MIL-101 enabled to achieve a similar catalytic activity (respectively 3 166 and 3 215 mololigomers formed.molNi -1 .h -1 , with a selectivity in butene around 94% in both cases), proving that the catalytic sites are accessible (Figure 21). It can also be assumed MixMOF-b and MixMOF-c), synthesized following the same procedure as IRMOF-3, except partial amounts of aminoterephtalic acid were substituted with terephtalic acid. [88] The MOFs were post-synthetically modified by imine condensation of a Ni(PyCHO)Br2 complex with the NH 2 groups, by the same molecular complex immobilization technique as Canivet et al. [87] Upon metalation, the authors tested the different synthesized catalysts for ethylene oligomerization in toluene, under 20 bar of ethylene, at 20 °C during 30 minutes and activated with 100 equivalents of Et 2AlCl. MixMOFs-Ni-b exhibited a catalytic activity of 6.91

x 10 4 goligomers.molNi -1 .h -1 with a selectivity in butene of 79.5% whereas IRMOF-3-Ni-a achieved a catalytic activity of 6.29 x 10 4 goligomers.molNi -1 .h -1 with a butene selectivity of only 35% (Figure 22).

IRMOF-3 was characterized with a higher amino content and the resulting catalysts proved to be as active but less selective in butene than the MixMOFs-Ni-b catalyst, which had a lower amino content. Higher amino content can hamper catalytic activity and site dilution might improve diffusion within the pores and catalytic site selectivity. performed condensation reaction to obtain a dangling bipyridyl coordinating site, which is metalated with a NiCl2 solution. [105][106][107][108] The catalytic tests were performed in heptane, at 21 °C under 15 bar of ethylene, the catalyst being activated with 70 equivalents of Et 2AlCl during one hour. NU-1000-bpy-NiCl2 enabled to achieve an intrinsic catalytic activity for butenes of 1 950 ± 180 h -1 , with a selectivity in butene of 93%.

MIL-125(Ti)-NH 2

Chen et al. work, reported in 2020, the PSM of MIL-125(Ti)-NH2 with 2pyridinecarboxaldehyde, that was metalated afterwards with NiCl 2•6H2O. [89] The result is the Zr6O4(OH)4(bpydc)0.84(bpdc)5.16, with bpydc 2-for 2,2'-bipyridine-5,5'-dicarboxylate), the three of them by One-Pot Synthesis. [90] Zr6O4(OH)4(bpydc)0. ). Along oligomers, polyethylene was also formed with Zr6O4(OH)4(bpydc)6(NiBr2)6. These results enabled to prove that higher metal loadings do not necessary lead to higher activities and the steric crowding (brought by ZrCl4, enables to achieve a phenoxy-imine based MOF. This SHOP-like catalyst embedded within a MOF and with a nitrogen heteroatom instead of a phosphorus one, is suitable for the immobilization of a molecular complex.

The nitrogen physisorption measurements highlighted the microporosity of the material, making it suitable for the immobilization of a molecular complex within its structure. To that purpose, they metalated the DUT-133 with NiCl2 in DMF at 65 °C during two days.

Ethylene oligomerization tests have been led in an autoclave with 1,2-dichlorobenzene and 51 equivalents of Et2AlCl at 21°C and under 15 bars of ethylene. The authors synthesized a NiCl2@UiO-67(bpydc) catalyst, similar to the one developed by Gonzalez et al.

in 2017 and described previously in this section.

For the catalytic tests, the authors compared the 63%NiCl@DUT-133 (63% Ni loading verified by ICP-OES) to NiCl2@UiO-67(bpydc) (with a 5.3% Ni loading verified by ICP-OES) in the same catalytic conditions described before. Gonzalez et al. proved that higher nickel loading do not necessarily result in higher activities: NiCl 2@UiO-67(bpydc) proved to be two times more active and less butene-selective (25 mololigomers.molNi -1 .h -1 with 28% of butene) than 63%NiCl@DUT-133 (12 mol oligomers.molNi -1 .h -1 with 100% butene). In addition, the production of polyethylene by NiCl2@UiO-67(bpydc) confirmed the results obtained by Gonzalez et al.

It could be assumed that, in heterogeneous conditions, a Ni active site coordinated to a phenoxy-imine macroligand would be less active and more selective than a Ni complex coordinated to a bipyridyl site. The phenoxy-imine macroligand seems to favor β-H elimination over propagation step whereas the bipyridyl one favors propagation step, for the given catalytic conditions.

However, Gonzalez et al. proved the ability of Zr nodes to coordinate Ni complexes, which may have a slight activity for ethylene oligomerization. Hence, it is possible in the case of NiCl@DUT-133, ill-defined Ni sites not coordinated to a phenoxy-imine site, participate to the catalytic activity.

Ni(II)-POP-1

In 2017, Kim et al. proposed for the first time the immobilization of a nickel complex within a bipyridyl-based POP, used for ethylene oligomerization. [91] The pristine material, designated as POP-1, was obtained by reaction between a tetra(4-azidophenyl)methane and a 5,5'-diethynyl-2,2'-bipyridine tectons in distilled DMF under nitrogen atmosphere. Nitrogen physisorption measurement enabled to highlight the microporosity of POP-1 and its suitability to immobilize a molecular complex within its structure. TGA analysis enabled to prove the thermal stability of the support up to 300 °C (two times more than for most of the MOFs described before). It can be assumed that, with two different bpy-based macroligands, UiO-67-bpy and POP-1, the resulting Ni-based catalysts produce significant amount of polyethylene.

Independently of the macroligand, the bipyridyl-anchoring site, associated with a Ni complex, not only oligomerizes ethylene but also polymerizes it. In the catalytic conditions or the design of the porous macroligand, investigation has to be made to improve ethylene oligomerization and decrease ethylene polymerization.

Ni@IL-PON, Ni@meso-CTF and Ni@microCTF

Rozhko et al. proposed the use of Porous Aromatic Frameworks (PAFs), a class of materials among COFs, for the oligomerization of ethylene. [93] Three different PAFs were The materials were metalated afterwards with nickel(II) bromide ethylene glycol dimethyl ether (NiBr2•DME) in THF, to afford three catalysts: Ni@IL-PON, Ni@meso-CTF and Ni@microCTF.

CTFs are highly conjugated which make them highly stable structures, compared to MOFs, which was confirmed by TGA analysis showing a stability up to 400 °C. However, their lamellar organization makes them less stable materials compared to POPs. Despite the triazine binding sites, which enable to obtain isolated active sites upon metalation, XPS analysis may have revealed the presence of nickel particles physisorbed on the material, which could be responsible for side reactions.

Afterwards, ethylene oligomerization experiments were conducted in heptane in a batch mode, with equivalents of Et3Al between 75 and 125 during two hours, at 50 °C and under 15 bar of ethylene. The three catalysts Ni@IL-PON, Ni@meso-CTF and Ni@microCTF enabled to achieve respectively 92.5, 75.3 and 63 molethylene converted.molNi -1 .h -1 , with respective selectivities in butene of 58%, 59% and 54%. Lower TOFs and selectivities were obtained with Ni-based COFs, compared to bpy-based MOFs and POPs.

In summary, the literature shows several attempts to obtain very high ethylene oligomerization activities and selectivities towards specific oligomers, by using different methods to obtain isolated active sites. Isolating active sites with materials already containing coordination sites present high activities and selectivities towards butene production.

However, the polyethylene production remains a problem that is still not clearly understood.

Considerations on pressure and temperature effects in heterogeneous conditions

In homogeneous conditions, for ethylene oligomerization, experimental factors such as temperature, ethylene pressure, the reaction time, the nature of the solvent (toluene, heptane, 1,2-dichlorobenzene, etc.), the nature and the amount of co-catalyst (MMAO, Et 2AlCl, EtAlCl2, etc.) can have an effect on the activity and the selectivity of the reaction. In the case where porous macroligands are used for this catalytic reaction, new phenomena can add up: temperature diffusion through the material, ethylene pressure within the pores and close to the active sites, porosity of the framework towards the solvent use, diffusion of the co-catalyst through the pores until the active site, etc. The different MOFs and the POP that were used for ethylene oligomerization enabled to give insight on the phenomena going on within the pores.

As a general trend, the literature review detailed in the previous section shows that, for a given temperature of ethylene oligomerization in liquid phase, increasing the ethylene pressure leads to an increase of activity and butene (or hexene in Chen et al. case with MIL-125(Ti)-NH2) selectivity. [82][83][84][87][88][89]91,100] Increasing ethylene pressure leads to an increase of ethylene concentration, hence an enhancement of ethylene availability at the active site, both for MOF or POP. This increased ethylene availability at the active site promotes the termination step over the propagation step, which favors the production of 1-butene over other oligomers. In addition, it can be assumed that the restraints due to the pores also favors the production of shorter oligomers than longer ones.

On the other hand, for a given pressure in liquid phase ethylene oligomerization reaction, a general trend embracing all the different porous catalysts cannot be outlined when the temperature is increased. However, increasing the temperature leads to a decrease of the oligomerization activity and 1-butene selectivity: ethylene solubility decreases, hence less ethylene available at the active site and among the few oligomers that are formed, higher temperature favors their isomerization, leading to a lower selectivity in αoligomers. [82][83][84][87][88][89]89,91,94,99] Therefore in this thesis, mild conditions will be used to perform ethylene oligomerization reactions in heterogeneous conditions, to obtain high activities (above 10 000 mmololigomers.mmolNi -1 .h -1 ) and high butene selectivities (above 90%): around 25°C with a continuous feed of ethylene around 30 bar.

Recyclability of heterogeneous catalysts for ethylene oligomerization

An important feature for an industrial catalyst (and a catalyst in general) can be recyclability. Among the common options, a catalyst can be neutralized at the end of a process, but this can hamper the economic viability of the process. A convenient alternative would be to separate the catalyst from the reaction medium and use it again afterwards.

In 2015, Madrahimov et al. observed that the reuse of NU-1000-bpy-NiCl2 catalyst for a second cycle (recycling experiment, in heptane, with 15 bars of ethylene at 21°C, 70 equivalents of Et2AlCl, during one hour) led to observe an enhancement of the intrinsic activity for butenes from 1 950 to 6 040 molbutenes.molNi -1 .h -1 with a constant selectivity in butene around 93%. [109] PXRD, GPC and SEM analyses enabled to prove that a polymer layer was created around the crystals during the first cycle and the authors assumed that it was increasing the local solubility of ethylene during the second cycle, hence the enhancement in intrinsic activity for butenes. The authors used the same experiment conditions settled by Canivet et al. in 2013 with the 10Ni@(Fe)MIL-101, who washed the catalyst with anhydrous ethanol before using it for two more cycles without any loss of activity (from 3 166 to 2 972 mol oligomers.molNi -1 .h -1 at the third cycle). [87] In 2017, with the POPbased catalyst Ni(II)-POP-1, Lee et al. also confirmed by SEM and DSC analyses that the "white insoluble polymer around the POP particles" was polyethylene. [91] Authors also experiment. [100] This phenomenon can partly be attributed to the fact that ethylene gets solubilized in the reaction solution but the gradual solubilization (i.e. the higher amount of ethylene consumed at each cycle during the first minute of the reaction) is assumed to be improved by the fact that the solution contains oligomers from the previous cycle. In addition, in 2019, Cheng et al. recycled the Ni-UMOFN catalyst for four consecutive cycles (with 10 bars of ethylene at 25°C, in toluene, with 500 eq. of Et 2AlCl, during one hour) without any significant loss of activity and butene selectivity, by washing the recovered catalyst with dry ethanol before each new cycle. [99] However, in this case the slight decrease of the activity during the fourth cycle (3 929 mol ethylene consumed.molNi -1 .h -1 instead of 4 893 molethylene consumed.molNi -1 .h -1 for the first cycle) could be attributed by elemental and XPS analyses to Al(OH)3 precipitate from aluminum co-catalyst.

Since recycling can be an important feature of a catalyst, specially for a heterogeneous one, wash it before each ethylene oligomerization cycle enables to remove any byproduct (like polyethylene) and avoid increasing ethylene's solubility at each cycle, leading to biased catalytic activity and butene selectivity. Furthermore, byproducts can block the pores of the catalyst and hamper the accessibility of the reagents (ethylene and co-catalyst) to the active sites, leading to catalyst deactivation. In case of polyethylene production, it can be characterized by SEM, GPC and/or DSC. Nitrogen physisorption measurement, after washing and activation, can also be a good indication of pore unblocking: any decrease in BET surface area, compared to the one before the reaction, can be an indication of trapped byproduct.

Comparison between heterogeneous catalysts and their homogeneous counterparts

As it is described later in this section with the correlation between the catalytic activity of heterogeneous catalysts and the Hammett parameter, the choice and the design of the bipyridine-based MOFs and POPs rooted from their homogeneous counterparts.

Heterogeneous catalysts often lack comparison with homogeneous counterparts in the same reaction conditions. [110,111] In the case of ethylene oligomerization, some of the heterogeneous catalysts developed mention the homogeneous catalytic results obtained in previous works, in different conditions. [82,84,90,112] Some other works compared the catalytic activity of the newly designed heterogeneous catalyst with its homogeneous counterpart, in the same conditions (Figure 25). [87,91,100,109] .h -1

The Ni@(Fe)-MIL-101 and the Ni(II)-POP-1, respectively a MOF and a POP, proved to be ten times more active than the Ni(bpy)Cl 2 molecular complex, in the given conditions.

Regarding the comparison of homogeneous and heterogeneous catalysts, in 2018, our research group proved for the first time that bipyridyl-based catalysts follow the same linear correlation between the catalytic activity and the Hammett parameter (σ) of the bipyridine substituent, regardless of their homogeneous (as molecular in solution) or heterogeneous (in POPs) nature. [113] The extension of the Hammett parameter, a factor that has enabled the community of homogeneous catalysis to describe the electronic effects of chemical function on reaction kinetics in solution, to describing solids is the major contribution of this work. In this context, it enables to bridge the homogeneous heterogeneous gap in catalysis. [114] Just as predictable and tunable as its homogeneous counterpart, the porous frameworks used for the study were bipyridyl-based MOFs (MOF-253 and UiO-67-bpy) and POPs (Bpy-MP-1 and Bpy-MP-2, for Bipyridyl-Microporous Polymers 1 and 2), newly prepared by the authors. [115,116] ). [113,117] Hence, Bpy-MP-1 and Bpy-MP-2 syntheses are well established within our research group and will be used in this thesis work (Figure 26). photoreduction as model catalytic reaction, but they also used it to design a catalytically efficient porous catalyst (Cp * Rh@Bpy-MP-1-NH2) for the transfer hydrogenation of α-aryl ketones. [118] For these two reactions, a general trend would be to assess that the lower the Hammett parameter is, the higher the catalytic activity would be. As a consequence, the Bpy-MP-1-NH2-based catalyst showed to be one of the most active catalyst for the transfer hydrogenation of α-aryl ketones, like it could be predicted with the correlation (-0.02 Hammett constant for the meta-amino group in Bpy-MP-1-NH2).

In addition, the same linear correlation followed by heterogeneous catalysts (MOFs and POPs) and their homogeneous counterparts corroborates that their catalytic performances only depend on the local electronic structure. Diffusion limitations within bipyridine-based POPs can be excluded, for carbon dioxide photoreduction and transfer hydrogenation of αaryl ketones, which make them suitable and tunable catalysts for additional reactions.

Conclusion and thesis motivation

Linear Alpha Olefin (LAO) production has become economically viable and profitable thanks to different homogeneous catalytic processes installed throughout the world.

Academic and industrial research enabled to improve these processes by testing different metals (Al, Cr, Ti, Fe, W, Ni, etc.) associated with different types of ligands (diphosphine, imine, etc.). 1-butene is an expensive LAO and producing it from a cheaper and quite available gas, like ethylene, is all the more economically viable.

Among, all these catalyst, Ni is the less expensive and most available one, along with the fact that it selectively oligomerizes ethylene, instead of polymerizing this gas.

Catalysts recyclability and shaping for industrial processes triggered the development of heterogeneous catalysts, more suitable for catalyst-product splitting and for continuous industrial processes. As the vibrant, fairly recent literature reviewed above has shown, porous materials (such as MOFs and POPs) appear to be the most interesting supports for this axis of research compared to purely inorganic materials.

MOFs and POPs appear to be well-suited supports for their high tunability, the infinite variety of possible design and the possibility of modifying them post-synthetically. For ethylene oligomerization many MOFs have already been developed, most of them employing Ni as catalytic active site for its high activity towards ethylene oligomerization and selectivity towards 1-butene. Polyethylene produced in an uncontrolled way tends to be a recurrent pitfall, leading to deactivation.

However, aiming at designing porous catalyst designed to display ethylene dimerization catalytic sites comparable to homogeneous very active and very selective ones, also brings other challenges, such as the diffusion of reagents and products in and out of the pores. The design of a porous macroligand a molecular active site should not generate any loss of activity or selectivity towards the desired products.

Understanding the effect of the macroligand, the catalytic conditions (temperature, ethylene pressure, nature and amount of co-catalyst, solvent, etc.) the diffusion within the pores are key factors to optimize oligomerization, especially dimerization of ethylene, over polymerization.

So far, only one bipyridyl-based POP, metalated with a Ni molecular complex has been developed and tested for ethylene oligomerization and appeared to be, in the given conditions, as competitive as its homogeneous counterpart. This result goes along with the fact that most of the MOF developed are imine-based anchoring sites, coordinating, in most of the cases a Ni molecular complex.

This thesis work is focused on developing heterogeneous microporous macroligands, MOF and POP, with an imine-like anchoring site for a Ni molecular complex, since this macroligand/metal combination is the most known one to achieve the selective dimerization of ethylene. The microporosity is an important feature to ensure the immobilization of the molecular complex within the pores. Developing MOFs and POPs with the same type of anchoring site would bring a better understanding on the effect of a macroligand on catalytic activity, since MOFs are crystalline but less stable than the amorphous POPs. Furthermore, upon immobilization of the Ni molecular complexes within the pores of the synthesized materials, the catalysts will be used for ethylene oligomerization, to achieve competitive TOFs (above 10 000 mololigomers.mmolNi -1 .h -1 ) and butene selectivities (above 90%) compared to the homogeneous counterpart.

General introduction

As presented in the bibliographic chapter, macroligands enables to bridge the gap between homogeneous and heterogeneous catalysis. First, in this chapter, the synthesis and the characterization of MOFs and POPs macroligands bearing bipyridyl (further designated as bpy) binding sites will be described. Subsequently, the infiltration of Ni(II) salts inside these materials will be detailed.

Along this chapter, the principles of powder X-ray diffraction (PXRD), nitrogen and toluene physisorption, inductively coupled plasma -optical emission spectroscopy (ICP-OES), infrared spectroscopy (IR), liquid and solid state nuclear magnetic resonance (NMR) will be detailed and as well as their use for the characterization of the pristine materials and catalysts.

During this thesis work, a particular attention was focused on bipyridine coordination site for their readily and substantial availability. [START_REF] Constable | Advances in Inorganic Chemistry[END_REF][START_REF] Constable | [END_REF] They belong to the class of bidentate ligands of α-diimines developed by Brookhart et al. for ethylene oligomerization or polymerization with activities and selectivities as competitive as other types of ligands. [28,121,[START_REF] Small | [END_REF]122,29,34] The use of bpy motif as ligand allows the direct comparison between bpy-based and/or diimine-based MOFs and POPs in heterogeneous catalysis with their homogeneous counterpart. [98,118,123,124] As it was described in chapter 1, Methods to obtain isolated active sites, using One- However, designing microporous materials can lead to diffusional limitations of the reagents towards the active sites within the micropores and of the resulting products. These diffusional limitations would be decreased with larger pores, like mesopores and/or macropores. However, obtaining active sites in larger pores brings less efficient site isolation, leading to possible active sites interactions and subsequent deactivation of the catalyst.

Pot

UiO-67-bipyridyl framework: synthesis and characterizaion

A series of Zr-based MOF materials have been introduced by Lillerud et al. in 2008, namely UiO-66, 67 and 68 (where UiO stands for Universitetet i Oslo). [125] Zr-based MOF are among the most stable (thanks to the strength of the Zr-O bond) and versatile MOFs. [126] From a general point of view, the series consist on Zr6O4(OH)4 octahedral clusters, where Even though the three of them exhibit chemical and thermal stability as well as high surface areas, UiO-67 has been chosen as a macroligand since its biphenyl linker exhibit the same size as a bipyridyl anchoring site, for further metalation purposes. On one hand, its larger pore opening than UiO-66 enables a better diffusion of reagents and products through the pores and on the other hand, its higher stability and synthesis easiness compared to UiO-68

makes UiO-67 a good candidate for catalytic purposes. [125,127,128] Previously, the synthesis of UiO-67 has been done according to a modified literature procedure ( Figure 28). [127,115,113] Figure 28 : UiO-67 synthesis procedure

After getting focused on the UiO-67, reports have been published where part of or whole of the biphenyldicarboxylic linkers have been replaced by 2,2'-bipyridyl-5,5'dicarboxylic linkers. [90,129,130] To obtain a UiO-67-bpy macroligand, the mixed linker synthesis (instead of PSM) is a common strategy adopted in the laboratory. Different proportions of 2,2'-bipyridyl-5,5'-dicarboxylic acid (x eq. towards ZrCl 4) and 4,4'-biphenyldicarboxylic acid (1-x eq.) are put into self-assembly synthesis, along ZrCl4 and AcOH in DMF (Figure 29). From 1 H NMR spectra, the ratio between the integrals of the bipyridyl hydrogen peaks (from 9.2 to 8.6 ppm) and the sum of all the integrals (bipyridyl and biphenyl, from 9.2 to 7.9 ppm), enables to access the percentage of bipyridyl linkers (x %) inside the structure (Figure 30). When p0 is reached, the cell can be evacuated progressively and the equilibrium pressure is measured at each desorbed nitrogen amount, in order to plot the desorption isotherm.

Gaseous isotherms are classified in six different classes (I to VI) according to IUPAC.

In the case of UiO-67-bpy-based materials, a type I(b) adsorption isotherm can be observed (Figure 32), which is typical of microporous materials.

For further description of UiO-67-based materials microporosity, a monolayer adsorption model of adsorbents on a nonporous surface established by Langmuir in 1918 is used. [131,132] The Langmuir equation resulting from this theory is based on four hypotheses (Equation 3):

-adsorption sites are energetically equivalent and have the same adsorption energy On the adsorption isotherms of the Figure 32, the process starts with the progressive filling of the micropores, below a p/p 0 relative pressure of 0.05, until the isotherm reaches a plateau. The beginning of the plateau corresponds to the partial pressure when all the micropores are filled (by nitrogen adsorbates in this case) and the rest of the plateau corresponds to the filling of the remaining pores and intergrain spaces of the material. This textural behavior of the synthesized UiO-67-bpy materials complies with literature and makes this type of material suitable for the immobilization of a molecular catalyst within its micropores.

Compared to the initial UiO-67 material (Figure 32), the introduction of bipyridyl sites does not decrease the microporosity of the material. In contrast, UiO-67-bpy(68%) and UiO-67-bpy(100%) seem to exhibit a higher amount of micropores than UiO-67. However, UiO- As already demonstrated in the literature, the amount of bipyridyl sites can be modulated without affecting the crystallinity of the material. [133] However, depending on the synthesis conditions, the amount of micropores can vary. [90] In the context of porous systems description and quantification, Brunauer, Emmett and Teller extended Langmuir's monolayer adsorption theory to a multilayer one. [134] They applied By working in this range, the specific surface area obtained with the BET theory can be compared to the specific surface area obtained with the Langmuir theory (Table 3). The higher values of Langmuir surface areas that can be observed compared to BET surface areas is due to the fact that both sides of the micropores that are filled are considered as monolayers.

The UiO-67 syntheses performed by Gonzalez et al. involved using benzoic acid and a reaction time of five days whereas acetic acid and a reaction time of two days were used for this thesis work. In Table 3, higher BET and Langmuir surface areas are obtained with the reaction conditions that has been used in this work compared to those used by Gonzalez et al. [90] This result supports the fact that difference reaction conditions can lead to differences in the final material porosity (which was observed previously on the nitrogen isotherm differences between UiO-67, UiO-67-bpy(68%), UiO-67-bpy(100%) with UiO-67-bpy(5%)

and UiO-67-bpy(10%). [90] Thus, UiO-67-bpy-based materials have been synthesized and their crystallinity have been preserved upon bipyridyl site introduction. They are microporous, which makes this type of material a good candidate for active site isolation by metal infiltration.

Isolating nickel(II) chloride active sites within UiO-67-bipyridyl frameworks

Nickel infiltration within the UiO-67-bpy-based materials were performed according to a method established within our research group. [135] A solution of nickel(II) chloride ethylene glycol dimethyl ether (NiCl2•glyme) was prepared in methanol and the solution was stirred with the porous material at 60°C during two days. NiCl 2 •glyme was chosen for the lability of the ethereal ligand, which also improves the solubility of the Ni salt for the infiltration.

Four different Ni loadings were infiltrated in the synthesized UiO-67-bpy-based materials (Table 4). The nickel amounts were evaluated afterwards by ICP-OES (Inductively Couple Plasma -Optical Emission Spectrometry) and the materials were named according to the weight percent (wt%) of Ni in the catalyst (xwt%Ni@UiO-67-bpy for xwt% of Ni obtained by ICP-OES).

ICP-OES measurement enables to access the concentration of elements within a sample. The liquid sample is nebulized under argon and injected in a plasma torch (between 6 000 and 10 000 °C), where any element is excited or ionized. In this state, each element radiates wavelengths specific to its nature and, by using an external calibration, the intensity of these wavelengths enables to deduce the concentration of the elements within a given sample (from ppm level to weight mass). In our case, in order to evaluate the Ni content, the MOF-based catalysts were dissolved in a H2SO4 + HNO3 mixture at 300 °C and the Ni amount was calculated by using an external calibration.

From the results obtained by ICP-OES, the binding site occupation (BSO) was calculated and enables to evaluate, the rate of bipyridyl sites that has been coordinated by Ni complexes (Equation 5): sites were obtained by metalation with a NiBr 2 complex of pristine materials. They maintained crystallinity and porosity upon metalation. [90] In contrast here, the overloading of UiO-67-bpy(68%) (up to 133%) in the targeted 2.50wt%Ni@UiO-67-bpy(68%) catalyst caused a decrease of crystallinity with the apparition of amorphous phases observable in PXRD at 10° 2θ (Figure 33). On the other hand, 0.95wt%Ni@UiO-67-bpy(64%) retained its crystallinity, with a BSO of 54%. The loss of crystallinity of 2.50wt%Ni@UiO-67-bpy(68%), compared to its pristine material, can be due to ill-defined active sites (chemisorbed and/or physisorbed) within the catalyst.

However, upon nickel infiltration, 0.47wt%Ni@UiO-67-bpy(5%) and 0.72wt%Ni@UiO-67-bpy(10%) achieved low nickel loadings but high BSOs (respectively 340% and 260%), without affecting the crystallinity of the materials (Figure 33). It can be assumed that all the bipyridyl sites has been coordinated with a Ni complex. In this case, high BSOs, that can be due to chemisorbed or physisorbed (within the pores) Ni complexes, did not affect the crystallinity of the pristine materials.

On one hand, achieving low amounts of bipyridyl sites enables to improve mass transport within the material but only gives access to a low ratio of active sites per catalyst mass. In the case of low amounts of bipyridyl sites, even though the material is overloaded with Ni, microporosity of the material is preserved: active sites can be assumed isolated in the micropores and interactions between them are limited. However, active sites that are not Ni(II) chloride complexes coordinated to bipyridyl sites have to be taken into account and further investigations need to be done to evaluate their influence on catalytic reactions. The apparition of ill-defined active sites requires a further control of the metal infiltration technique.

Figure 33 : PXRD diffractograms of four Ni@UiO-67-bpy-based catalysts with different amounts of nickel infiltrated compared to the theoretical pattern of UiO-67 from CCDC-960486 (each diffractogram has been normalized in respect to the highest peak at 5° 2θ)

The four synthesized catalysts (0.47wt%Ni@UiO-67-bpy(5%), 0.72wt%Ni@UiO-67bpy(10%), 0.95wt%Ni@UiO-67-bpy(64%) and 2.50wt%Ni@UiO-67-bpy(68%)) have also been characterized by nitrogen physisorption measurement to evaluate the influence of immobilizing a molecular complex within the micropores on the textural properties of the UiO-67-based materials.

Their nitrogen physisorption isotherms exhibit a type I(b) isotherms (Figure 34), similar to their pristine material, which assess the presence of micropores. The micropores are filled for a partial pressure below 0.1. The Langmuir linear plots that have been obtained for the UiO-67-based catalysts are represented in the Appendix of Chapter 2 (Figure 107), supporting the fact that the catalysts are still microporous upon metalation.

A decrease of the micropore volume V m (Table 3 and Table 5) can be observed for:

-0.72wt%Ni@UiO-67-bpy(10%), from 429 cm 3 .g -1 to 318 cm 3 .g -1 -2.50wt%Ni@UiO-67-bpy(68%), from 982 cm 3 .g -1 to 311 cm 3 .g -1 This decrease proves the incorporation of the Ni complexes within the pores but as it was specified before, this incorporation can be either chemisorbed on bipyridyl sites or physisorbed within the pores of the material. Further experiments need to be done to assess the exact amount of bipyridyl sites effectively coordinated by Ni complexes.

The increase of micropore volume Vm observed for 0.47wt%Ni@UiO-67-bpy(5%) from 395 cm 3 .g -1 to 429 cm 3 .g -1 can be due to an error of measurement. This strategy of diluting bipyridyl sites within the UiO-67 framework has been used and depending on the amount of bipyridyl sites, three different limitations can occur.

First, low amount of bipyridyl sites (5% and 10%) within the framework enables to obtain isolated actives sites within the micropores and avoid interactions between them.

However, this type of materials exhibit a low ratio of active sites per catalyst mass.

Second, high amounts of bipyridyl sites (68% and 100%) within the framework enables to increase the ratio of active sites per catalyst mass. However, upon metalation, an overloading of nickel can decrease the crystallinity of the catalyst.

Finally, we found that ill-defined Ni sites are created within these microporous materials either because of Zr-OH, coordinating Ni or with Ni complexes physisorbed (Figure 35), in line with previous report by Gonzales et al. on similar materials. [90] Figure 35 : NiBr2@UiO-67-bpy catalyst will ill-defined active sites on Zr nodes Therefore, another type of support has been considered: Porous Organic Polymers (POPs). The purpose of developing POP-based catalysts is to obtain isolated bipyridyl-based actives sites within micropores while avoiding the creation of ill-defined active sites. Indeed, fully organic materials without inorganic parts like Zr-OH will limit the uncontrolled chemisorption of Ni complexes.

Bpy-MP-1 and Bpy-MP-2: Sonogashira-coupling POPs

Several types of porous organic frameworks have been developed and described in the literature, depending on the synthesis pathway (Friedel-Crafts reactions, radical polymerization, Sonogashira coupling, etc.). [136][137][138][139][140][141] POPs are amorphous materials and despite their lack of crystallinity compared to MOFs and COFs, they exhibit high surface areas. Their backbone, made of C-C bonds ensures a resistance to harsh conditions (acidic, basic and high temperatures) and enables to avoid hydrolysis, which can occur with MOF materials. Their high versatility enables to incorporate coordination sites like bipyridyl (further designated as bpy).

Bpy-MP-1 and Bpy-MP-2 (Bpy-MP standing for Bipyridyl Microporous Polymer, followed by the order of apparition) are two POP materials, which syntheses are already established within our research group. [113] They are synthesized by Pd-catalyzed Sonogashira-Hagihara coupling of a tridimensional triethynyl tecton and a dihalogen tecton (Figure 36). This synthetic strategy enables to dilute bpy sites within a polymer made predominantly of biphenyl and triethynyl parts and obtain isolated active sites upon metalation. Therefore, site dilution of active sites within a POP can be done to improve mass transport limitations that can occur during catalytic reactions.

Finding traces of metal within POPs made by Pd-catalyzed cross coupling (even at loading as low as 0.05wt%) can become a problem for catalytic purposes: in this case, Pd can coordinate to the bipyridyl sites and/or remain physisorbed within the pores of the POP.

For a given catalytic reaction, the pristine material has to be tested to evaluate the activity of the remaining Pd traces within the POP (like for the ill-defined Ni sites within the UiO-67based materials).

Bpy-MP-1 and Bpy-MP-2 have been synthesized by adapting the strategy proposed by Cooper et al. (Figure 36). [142] Structurally, the MP-1 series node is a tritopic one made from 1,3,5-triethynylbenzene, giving a conjugated structure whereas the MP-2 series node is a tetratopic one made from tetrakis(4-ethynylphenyl)methane, an sp 3 node that breaks the conjugation of the system. This node difference creates a local geometry distinction, planar for the MP-1 series and tetraedral for the MP-2 series. The porosity improvement brought by the tetratopic node of the MP-2 series will be more detailed later with the nitrogen physisorption measurements.

Figure 36 : MP-1 and MP-2 series synthesis from a modified literature procedure [142] This polymerization technique enables to modulate the amount of bipyridyl active sites within an organic framework made of phenyl rings, to improve mass transport limitations and isolation of active sites.

The polymerization process is under kinetic control, which enables to produce an amorphous porous material. [142] The presence of the triethynylbenzene or the tetrakis(4ethynylphenyl)methane nodes ensures the separation between the bipyridyl and the biphenyl tectons. Further investigation has to be led to assess the homogeneous spread of the bipyridyl sites throughout the polymer and that there is no different domains within the POP with different bpy density.

Bpy-MP-1 and Bpy-MP-2 materials have been characterized by ICP-OES analysis to

evaluate the amount of Pd remaining in the material, after Soxhlet washings (chloroform and methanol). Traces of Pd are found to represent a wt% below 0.5 within the worked-up POPs.

Pd active sites within the catalysts, if active for a catalytic reaction, could represent ill-defined active sites, obtained by coordination of Pd on bipyridyl sites or physisorbed within the materials.

IR spectroscopy analysis of Bpy-MP-1 and Bpy-MP-2 materials confirms the presence of non-reacted ethynyl ends within the POPs (Figure 37). At 2 100 cm -1 , a weak signal can be observed for the Bpy-MP-1 material, corresponding to the terminal C≡C stretching vibration and indicating a complete polymerization whereas a higher signal for the Bpy-MP-2 material proves that some unreacted alkyne ends remain within the material. This issue can be addressed by increasing the polymerization time. The strong signal at 2 200 cm -1

indicates the presence of medial C≡C within the polymer structure. MAS NMR. [113,118,135,143,144] Further work is led to obtain the composition of Bpy-MP-2 materials.

Unlike UiO-67-based materials that can be dissolved and analyzed by liquid state NMR to evaluate the experimental amount of biphenyl and bipyridyl linkers integrated to the structure, quantifying Bpy-MP materials monomers can be done by solid state NMR. Bpy-MP-1 materials have been characterized by [START_REF] Armor | [END_REF] C composite-pulse (ComP) multiple crosspolarization (multiCP) MAS NMR, to evaluate the experimental bpy amount within the materials.

In liquid-state NMR, the average of the anisotropic magnetic interactions (orientationdependence of the magnetic atoms dipole) is measured due to the rapid reorientation of the molecules. In solids, reorientations are much slower than in the liquids and the effect of anisotropy results in the acquisition of broad signals in solid-state NMR. These broad signals depend on a factor, 3cos 2 θ-1, representing the dipolar coupling and the anisotropic interactions (θ being the angle between the applied magnetic field B 0 and the dipoles). This factor can be suppressed for θ = 54.74° (called the Magic Angle). Therefore, rotating the solid sample around an axis with an angle of 54.74° compared to B0 enables to suppress these anisotropic interactions and to obtain narrow signals (Magic Angle Spinning or MAS).

For Bpy-MP-1 analysis, solid-state MAS NMR was coupled with [START_REF] Armor | [END_REF] C ComPmultiCP (Composite-Pulse multi-cross polarization) which enables to enhance the signal of a rare nucleus like [START_REF] Armor | [END_REF] C (with a natural isotopic abundance of 1.1%) by transferring to it the magnetic polarization from an abundant nucleus, like 1 H (natural isotopic abundance of 99.98%).

However, this technique is not quantitative, since the transfer of polarization from a 1 H nucleus to a [START_REF] Armor | [END_REF] C nucleus depends on the proton environment of a carbon atom: the higher the number of protons in a carbon atom environment is, the better enhanced the signal of this carbon atom is.

In To make [START_REF] Armor | [END_REF] C ComPmultiCP MAS NMR quantitative, the delay d1 between each pulse of polarization during the analysis has to be higher than the T1 relaxation time of the slowest relaxing nuclei, to ensure that all the nucleus have fully relaxed between each pulse.

The three different materials have been analyzed by [START_REF] Armor | [END_REF] C ComPmultiCP MAS NMR: the Full-Bpy-MP-1 (top), the Bpy-MP-1 (middle) and the MP-1 (bottom) (Figure 39). Signals between 115 and 160 ppm and between 85 and 100 ppm are respectively specific to the aromatic carbon atoms of the backbone and to the carbon atoms of medial alkyne groups.

Further investigation would enable to isolate a signal specific to MP-1 materials and calculate the ratio of biphenyl and bipyridyl sites in the Bpy-MP-1 material. to IUPAC classification of isotherms and as it is described in the literature (Figure 40). [142,145] Prior to measurement, the sample within the cell is degassed under vacuum at 80°C overnight. For a partial pressure p/p 0 below 0.1 nitrogen fills up the micropores, and between 0.1 and until 1.0, the mesopores of the materials. The nitrogen uptake of the Bpy-MP-2 isotherm above 0.9 can be attributed to the capillary condensation that occurs: nitrogen gas condenses between the pore walls below the saturating vapor pressure p0. 6): [146,147] Equation 6 : Statistical thickness tflat (in nm) calculated from the nitrogen volume adsorbed Va (in cm 3 (STP).g -1 ) and the monomolecular layer adsorption volume Vm (in cm 3 (STP).g -1 ) ; 0.354 nm represents the thickness of a monomolecular layer of nitrogen molecules Concerning the surface areas, and as it was described before with the different amounts of nitrogen adsorbed , Bpy-MP-1 exhibit a lower surface area (590 ± 11 m 2 .g -1 ) than Bpy-MP-2 (874 ± 10 m 2 .g -1 ). The tetratopic node of the Bpy-MP-2 enables to open up the pores and increase the surface area of the material. This increase is also observable regarding the mean pore diameter and the total pore volume of the two Bpy-MP materials (Table 6). However, both POP materials exhibit lower specific surface areas than the UiO-67-based materials but their organic structure makes them suitable for catalytic purposes involving harsh conditions (like the use of aluminum-based activators for ethylene oligomerization). The two POPs offer higher mean pore diameters, which theoretically improve diffusion of reagents and products. This feature, coupled with active site dilution, can improve mass transport limitations.

Table 6 : Textural properties of Bpy-MP-1 and Bpy-MP-2 materials compared to UiO-67, obtained by nitrogen physisorption measurements at 77K a average of three batches (the three batches textural properties are detailed in Table 7 and on Figure 108 and Figure 110)

Bpy-MP-1 and Bpy-MP-2 materials both exhibit essentially micropores (below 2 nm)

and their pore size distribution has been evaluated by the method established by Barrett,

Joyner and Halenda (BJH) in 1951. [148] Other methods can also be used (Dollimer and Heal (DH), Cranston and Inkley (CI), Non Localized Density Functional Theory / Grand Canonical Monte Carlo (NLDFT/GCMC) methods). [START_REF] Cranston | Advances in Catalysis[END_REF][START_REF] Dollimore | [END_REF] BJH method has been chosen because it allows to consider a system of open ended cylindrical pores, which is more fitting to the porous network description of Bpy-MP-1 and Bpy-MP-2 materials. A limit to the BJH theory is that the pore size is calculated from the desorption isotherm, since the Kelvin Equation takes into account the meniscus part of the capillary condensation within the pores. pore distribution peak at 1.55 nm (Figure 42). They both exhibit a micropore volume of 0.12 ± 0.01 cm 3 .g -1 , which, correlated with BET results, represents the third of the total pore volume (Table 6). The average pore diameter obtained for Bpy-MP-1 and Bpy-MP-2 materials are respectively 2.82 ± 0.04 nm and 2.42 ± 0.2 nm. The percentage change of pore volume uptake that can be observed around 4 nm for the Bpy-MP-1 pore size distribution can be attributed to a cavitation phenomenon (creation of a gas bubble due to a sudden depression) within the pores and cannot be attributed to a pore diameter. [151] Bpy-MP-1 and Bpy-MP-2 materials are mainly microporous materials (a slight mesoporosity is observed). to IUPAC classification of isotherms (Figure 43). Below a partial pressure of 0.1, the micropores are filled. The move back of the curve that can be observed can be due do to an error of measurement. The toluene uptake in the early stages of the measurement (between 0 and 0.1 and below a toluene volume adsorbed of 15 cm 3 .g -1 ) can be attributed to the fact that Bpy-MP-1 and Bpy-MP-2 are fully organic and physisorption an organic solvent within the micropores is facilitated.

Bpy-MP-1 and Bpy-MP-2 exhibit a H4 type hysteresis loop that can be caused for the same reason as with the nitrogen adsorbent: toluene adsorbents fills the pore up through a bottleneck during adsorption and when the desorption process starts, all the adsorbed molecules within the pore are forced out through the bottleneck. The hysteresis remains until the end of the desorption process.

One major difference compared to nitrogen physisorption measurements is that no capillary condensation has been observed with toluene vapor pressures.

To conclude, Bpy-MP-1 and Bpy-MP-2 are porous towards toluene and, therefore, are suitable materials for catalytic purposes performed in this solvent.

A technique adopted all along this thesis work is to synthesize several batches of the same POP and mix them to obtain a sufficient stock of the same POP. The mixing process is performed in pentane during one hour under stirring. Pentane has been chosen because this organic solvent is easily removable under heating and temperature, which has been done to obtain pristine mixed batches of Bpy-MP-1 and Bpy-MP-2. Three batches of Bpy-MP-1 and three batches of Bpy-MP-2 are used for this process. The synthesis methods adopted are the ones described before (Figure 36). All the different POPs include a theoretical molar amount of bipyridyl sites representing 25% of the monomers. When nitrogen isotherms can be overlaid, with similar surface areas and mean pore diameter, the three batches of the same POP can be mixed to obtain a sufficient stock of the same material (Table 7).

Table 7 : Textural properties of Bpy-MP-1 and Bpy-MP-2 materials, obtained by nitrogen physisorption measurements at 77K a average of three batches Bpy-MP-1 mixed batches exhibit a higher BET surface area (1 154 m 2 .g -1 ) and a higher total pore volume (0.65 cm 3 .g -1 ) than the three separate batches of Bpy-MP-1 (Table 7). On the other hand, the Bpy-MP-2 mixed batches exhibit a lower BET surface area (648 m 2 .g -1 )

and a lower total pore volume (0.36 cm 3 .g -1 ) than the three separate batches of Bpy-MP-2.

These different results can be explained:

-either by the node difference between Bpy-MP-1 and Bpy-MP-2 (using a tritopic node for the Bpy-MP-1 could lead to smaller POP particles and therefore higher intergrain area and higher BET surface area whereas using a tetratopic node, like for the Bpy-MP-2 could lead to higher POP particles, lower integrain area and lower BET surface area) . Granulometry analysis can be done to evaluate this hypothesis.

-or by the fact that the mixed batches were obtained by mixing different batches of POPs in pentane, the solvent modifying the porosity of the material

The nitrogen isotherm of Bpy-MP-1 mixed batches exhibit also a higher amount of micropores and the same type of hysteresis loop than the three separate batches (Figure 108). On the contrary, the nitrogen isotherm of Bpy-MP-2 mixed batched exhibit a lower amount of micropores but the same type of hysteresis loop than the three separate batches (Figure 110).

BJH plot of the Bpy-MP-1 mixed batches exhibit the same distribution peak at 1.55 nm as the three separate batches of Bpy-MP-1 (Figure 109). The micropore volume increased of 75%, from 0.12 ± 0.01 cm 3 .g -1 (average of three batches) to 0.21 cm 3 .g -1 . The average pore diameter of the obtained Bpy-MP-1 mixed batches decreased of 6%, from 2.82 ± 0.04 nm of the separate batches to 2.65 nm.

BJH plot of the Bpy-MP-2 mixed batches has been represented and exhibit the same distribution peak at 1.55 nm as the three separate batches of Bpy-MP-2 (Figure 111). The micropore volume also increased of 92%, from 0.12 ± 0.01 cm 3 .g -1 (average of three batches) to 0.23 cm 3 .g -1 . The average pore diameter of the obtained Bpy-MP-2 mixed batches decreased of 16%, from 2.42 ± 0.04 nm of the separate batches to 2.09 nm.

Therefore, mixing batches enabled to increase the amount of Bpy-MP-1 and Bpy-MP-2 to be able to use a common stock for catalysts synthesis, not alter the microporous properties of the separate batches with a distribution peak in the micropore area (1.55 nm)

and to increase the microporous volume of the pristine materials.

In summary, Bpy-MP-1 and Bpy-MP-2 were synthesized according to a modified procedure literature. IR spectroscopy enabled to evaluate if non-reacted ethynyl ends remained within the POPs. Further investigation is ongoing with [START_REF] Armor | [END_REF] C ComPmultiCP MAS NMR to quantify the bipyridyl amount within the materials. Nitrogen and toluene physisorption measurements enabled to prove that Bpy-MP-1 and Bpy-MP-2 are mostly microporous, which makes them suitable supports for molecular complex immobilization within the micropores and use them for catalytic purposes performed in toluene. The amount of bipyridyl sites can be diluted with biphenyl monomers, to improve mass transport limitations and increase site isolation. Concerning the MP-1 series catalysts, a significant decrease in the volume adsorbed (Figure 44) and the BET surface area (Table 8) of the catalysts can be observed compared to the mother material (Bpy-MP-1 mixed batches). The micropore volume of the catalysts is filled up for a partial pressure below 0.1 is lower than for the pristine material, which is a first indication of the successful nickel infiltration inside the material. The trend is confirmed with the catalysts characterized with a Ni loading between 0.32wt% and 1.77wt%. The MP-1 series catalysts have also been characterized by using the BJH method. For all the catalysts, the distribution peak is at 1.55 nm, supporting the fact the catalysts are still microporous upon metalation of the pristine material. 9), from 648 m 2 .g -1 to 742 m 2 .g -1 . This increase can also be observed for four other Bpy-MP-2-based catalysts and can be explained by the fact that the Ni infiltration is done in methanol, therefore, the solvent can have an effect on the pore opening of the material. 1.70wt%Ni@Bpy-MP-1 and 0.45wt%Ni@Bpy-MP-2 catalysts were characterized by toluene physisorption measurement to evaluate the porosity of the catalysts towards the solvent used for ethylene oligomerization purposes (Figure 46). Compared to their respective pristine materials, 1.70wt%Ni@Bpy-MP-1 and 0.45wt%Ni@Bpy-MP-2 catalysts exhibit the same type I(b) toluene isotherm as Bpy-MP-1 and Bpy-MP-2 materials. However, the volume adsorbed by the catalysts is lower than for the pristine materials, which supports the successful infiltration of nickel within the pores of the pristine materials.

Isolating Ni(II)Cl2 active sites within Bpy-MP-1 and Bpy-MP-2,

Sonogashira-coupling POPs

Below a partial pressure of 0.2, the volume adsorbed reached a plateau that is not observed on the nitrogen physisorption isotherms of the catalysts. It can be explained by the favorable adsorption of toluene within the micropores of the organic materials. Afterwards, for a partial pressure above 0.2, the micropores are filled up and the H4 type hysteresis loop that has been observed for the pristine materials is found again for the catalysts. Therefore, within our research group, the coordination of Ni complexes to bpy sites within the Bpy-MP-1 has been assessed by using two spectroscopic techniques : [START_REF] Armor | [END_REF] C ComPmultiCP MAS NMR and IR. [135] Further investigation has to be done for complex immobilization assessment within Bpy-MP-2-based catalysts.

After establishing that the NMR signals around 155 ppm, determined by [START_REF] Armor | [END_REF] C multi CP MAS NMR, corresponds to the carbon atoms neighboring the bipyridyl anchoring site within Bpy-MP-1, the decrease of this signal was observed upon Ni coordination, due to the 100 paramagnetic effect of this metal. A linear correlation was determined between the Ni loading obtained by ICP-OES and the bpy occupancy extracted from the NMR data (ratio between the integrals of the peak at 155 ppm of the pristine material and the corresponding metalated Bpy-MP-1) (Figure 47). The characterizations were performed on another set of Bpy-MP-1 catalysts than the one described in Table 8. [135] Second, this first correlation was supported by IR spectroscopy: with the increase of the Ni loading for the Ni@Bpy-MP-1 catalysts, the intensity of the C-H deformation band at 1453 cm -1 , corresponding to the C-H bond in ortho position of the bipyridyl active site, was decreasing. A correlation was established by normalizing the intensity at 1453 cm -1 with the intensity of the band at 2209 cm -1 , corresponding to the signal of the internal C≡C vibration within the Bpy-MP-1, a bond that don't change whatever the Ni loading of the catalyst (Figure 48). [135] Therefore, the coordination of the Ni complexes to the bipyridyl sites within the microporosity of the Ni@Bpy-MP-1 catalysts have been assessed by two spectroscopic techniques, [START_REF] Armor | [END_REF] C multi CP MAS NMR and IR. Further investigation has to be done to assess the same result within Ni@Bpy-MP-2 catalysts. For Ni@Bpy-MP-1 catalysts, this result enables to prove that nickel complexes within the catalysts are coordinated to bipyridyl sites and not physisorbed within the materials. There is no ill-defined active sites, like for the UiO-67-based catalysts, within the Ni@Bpy-MP-1 catalysts, upon Ni complexes infiltration.

It can be assessed that the BSOs of Ni complexes, from 14% to 75% that have been calculated for the catalysts from respectively 0,32wt%Ni@Bpy-MP-1 to 1,77wt%Ni@Bpy-MP-1, correspond essentially to the occupation of bipyridyl sites by nickel(II) chloride complexes (Table 8). However, given the fact that Pd traces are found by ICP-OES (average of 0.41wt% in Pd on the six catalysts), it can be assumed that part of the BSO (6%) can be due to Pd. Further investigation has to be done to assess either the chemisorption of Pd on the bipyridyl sites or the physisorption of Pd complexes within the pores of Ni@Bpy-MP-1 and Ni@Bpy-MP-2 catalysts. 0.1% in the final material. On the other hand, triphenylphosphine, used as L ligands to obtain an unsaturated, catalytically active Pd(0) catalyst, remains in the final product, as it can be observed with the multiple peaks at 7.5 ppm (Figure 50 The Bpy-MP-3 series is synthesized by radical polymerization according to a modified literature procedure using divinylic monomers (divinylbenzene, divinylbipyridyl, etc.). The polymer synthesis is performed in a sealed airtight reactor in a pre-heated oven at 100°C. [154- 157] The polymerization process starts with a radical initiator. The most used one in the literature is the azobisisobutyronitrile (AIBN) but two other similar and less expensive radical initiators have been used for this thesis work: 1,1'-azobis(cyclohexanecarbonitrile) (ACHN) and 2,2'-azobis(2-methylpropane) (ATTN) (Figure 51). ACHN was used because it initiates radicals in the same conditions as AIBN and is more easily available. However, ACHN exhibit nitrile functional groups that remains within the synthesized POP after the initiation step. To avoid the creation of ill-defined active sites upon the eventual coordination of Ni complexes on the nitrile groups, the radical initiator ATTN was also investigated. temperatures (more than 80°C), these species decompose into radicals that will react with the vinylic ends of the monomers and initiate the polymerization between the divinylic monomers. The early produced polymer precipitates. Nevertheless, the reaction being performed within a sealed airtight reactor, the solvent is brought up at both high pressure and temperature and remain in a liquid phase, just above its boiling point. This liquid state at high temperature enables to avoid the segregation of the highly cross-linked polymer network that has been formed. Besides, a slight amount (in the range of 1/10 of the organic solvent volume) of water is used in order to decrease the solubility of the mixture and to exacerbate the solvent/polymer splitting, and solvent has an influence on macropores shaping. The ratio solvent/water introduced plays a major role on the final pore size. Afterwards, the obtained monolith is dried under room temperature and pressure in order to free the pores of the solvent guest molecules and obtain a highly cross-linked network structure. This porous network is organized with a hierarchical porous structure, containing micropores, mesopores and macropores, which is linked to the loose swelling behavior obtained upon removal of the solvent/water mixture causing the newly formed polymer to shrink (Figure 52). This Pd-free radical polymerization procedure adapted from Zhang et al. has different advantages. [154,155,158] This new synthesis pathway enables to obtain a structure with a hierarchical porosity (meaning the combination of pores of different size). For catalytic purposes, this feature represents a key to improve mass transport limitations, by modifying the amount of divinylbipyridyl monomer in the synthesis and improve catalytic sites accessibility. The ratio of active sites per catalyst mass can be increased and no metal is needed for the polymerization technique, which enables to avoid ill-defined active sites within the material. Furthermore, it is also possible to modify the functional moieties that can be introduced into the porous framework, whether by using hydrophobic or hydrophilic monomers, characteristics that are passed on to the final material. Hydrophobicity brings another layer of protection of active sites undergoing poisoning and simplifies the fact to activate the materials under harsh conditions (vacuum and high temperature) before using it for catalysis.

Figure 52 : Bpy-MP-3 series synthesis adapted from a modified literature procedure [154] For the polydivinylbenzene (PDVB)-based POP, Zhang et al. studied the influence of solvothermal conditions on the porosity of the polymer. [154] As a general trend, working at high temperature (100°C), with a ratio of H 2O/THF of 0.1 during at least 48 hours enables to produce a polymer with high surface area and high adsorptive capacity towards organic compounds.

In the Bpy-MP-3 series case, the highly cross-linked network, with the solvent used as a porogen (in our case THF), exhibit a non-conjugated system. The Bpy-MP-3 (ACHN) and the Bpy-MP-3 (ATTN) materials were analyzed by nitrogen physisorption measurement and both exhibit type II physisorption isotherms (Figure 53). This type of isotherm complies with Zhang et al. isotherms, describing hierarchical porous structure, with a range of pore size within the structure from micropores to macropores. below a partial pressure of 0.1, the micropores are filled-out ; followed by the mesopores between a partial pressure of 0.1 and 0.9 ; and finally, above 0.9, the nitrogen uptake corresponds to the filling-up of the macropores (it can also correspond to capillary condensation). 10). Both Bpy-MP-3 (ACHN) and Bpy-MP-3 (ATTN) materials do not dwell under nitrogen physisorption measurements like Bpy-MP-1 and Bpy-MP-2 materials do. Bpy-MP-3 materials come back to their initial state and do not present any hysteresis loop (Figure 53). It can be linked to the loose behavior resulting from the shrinkage of the material in the end of the synthesis, an aspect that is not found with Bpy-MP-1 and Bpy-MP-2 materials, synthesized by Sonogashira coupling. have been analyzed by the BJH method (Figure 55). They are microporous with a pore distribution peak at 2.23 ± 0.5 nm. They exhibit a micropore volume of 1.52 ± 0.2 cm 3 .g -1 for Bpy-MP-3 (ACHN) and 1.63 ± 0.3 cm 3 .g -1 for Bpy-MP-3 (ATTN). The average pore diameter obtained for Bpy-MP-3 (ACHN) and Bpy-MP-3 (ATTN) materials are respectively 9.23 ± 2 nm and 8.00 ± 2 nm. Thus, Bpy-MP-3 (ACHN) and Bpy-MP-3 (ATTN) are obtained as Pdfree materials with isolated bipyridyl sites but they exhibit a large pore distribution from micropores to macropores which could lead to different types of active sites within the mesopores and the macropores. material, synthesized without any bipyridyl monomer). The introduction of bipyridyl monomers generates less spherical particles and more fibers than in the case of pure PDVB (Figure 57). [154] Their study also highlighted the fact that the hierarchical structure (meaning the association of both mesopores and macropores, hierarchy that will be described later) observed at a nanoscale support the idea that this type of nanoporous material have high adsorptive capacity towards organic compounds. [113] In conclusion, if the three types of POPs Bpy-MP-1, Bpy-MP-2 and Bpy-MP-3 (ACHN) are structurally close, with a backbone made of alternating alkyne or alkyl and aromatic parts, they are profoundly different texturally, which is assessed by the physisorption and microscopy measurements.

Figure 57 : (top, left) PVDB SEM image [154] ; (top, right) Bpy-MP-3 SEM image ; (bottom, left) Bpy-MP-1 SEM image ; (bottom right) Bpy-MP-2 SEM image [113] Full-Bpy-MP-3 (ACHN) and the MP-3 (ACHN) have been synthesized by radical polymerization respectively with only divinylbipyridyl monomers in the first case and divinylbenzene monomers in the second case (Figure 58). [START_REF] Armor | [END_REF] C multi CP MAS NMR spectra (Figure 60). After establishing that the peaks at 28, 39, 127 and 143 ppm are specific to the common core (alkyl parts between the aromatic components) of the three materials, it can be established that the peak at 155 ppm is specific to the bipyridine parts. Like for the Bpy-MP-1-based materials, further investigation has to be done to isolate a signal specific to MP-3 materials and be able to calculate the ratio of biphenyl and bipyridyl sites in the Bpy-MP-3 material. Bpy-MP-3-onlyTHF (ACHN) exhibits slightly higher adsorptive capacity than Bpy-MP-3 (ACHN), which can be attributed to the fact that mesopores have more room to develop since water does not intervene in macropores shaping (Figure 61). When the pore distribution is determined by the BJH method, it can be observed that the distribution peak is shifted towards mesopores from 2.23 ± 0.5 for Bpy-MP-3 (ACHN) to 4.61 nm for Bpy-MP-3-onlyTHF (ACHN). This textural property is obtained when water equivalents are removed from the synthesis of Bpy-MP-3 (ACHN) structure (Figure 62). Furthermore, by increasing the average pore diameter (from 9.23 ± 2 nm to 13.88 nm), the mass transport limitations of the material may be improved but with more mesopores that means a possibility of the active sites interacting between them, upon metalation (Table 12). To conclude on the modulation of the pore distribution of Bpy-MP-3-based materials, it is possible to shift the pore distribution towards either micropores or macropores by modifying the synthesis conditions that plays a role on the pore shaping, like the solvent ratio of the solvent that is used as it has been proved by Zhang et al. [154] Further investigation has to be done to evaluate the effect on the pore size distribution of Bpy-MP-3-based materials

MP-3 (ACHN) and MP-3 (ATTN), containing no bipyridyl sites, have been infiltrated

with NiCl2•glyme solution to evaluate the ability of the materials to physisorb Ni species. After washings, ICP-OES analysis revealed that no traces of Ni have been found in the material indicating that the Bpy-MP-3 (ACHN) and Bpy-MP-3 (ATTN) are suitable for Ni complexes immobilization and that ill-defined active sites due to Ni physisorption will not likely be found.

Porosity of the different catalysts towards nitrogen have been evaluated. For the sake of reading, only the nitrogen physisorption isotherms of the pristine material, the catalyst with the lowest and the highest loading have been represented (Figure 63 and Figure 64). All the other catalysts nitrogen physisorption isotherms are represented in Appendix of the Chapter 2 (Figure 117 and Figure 118). -from 0.70wt%Ni@Bpy-MP-3 (ACHN) to 2.02wt%Ni@Bpy-MP-3 (ACHN) (Table 15), with BSOs ranging from 9% to 26% respectively -from 0.49wt%Ni@Bpy-MP-3 (ATTN) to 1.90wt%Ni@Bpy-MP-3 (ATTN) (Table 14)

with BSOs ranging from 6% to 24% respectively This lack of significant decrease for the Bpy-MP-3-based catalysts, that can however be observed for Bpy-MP-1 and Bpy-MP-2 based catalysts (Figure 112 and Figure 113), can be explained by the fact that the Ni complexes are spread through the hierarchical porous structure of the materials. The impact on the porosity of the catalysts is reduced and a significant decrease is not observed since the Ni complexes occupy the different pore levels of the material. Furthermore, it was proved that the Bpy-MP-3-based catalysts do not physisorb Ni complexes. Therefore, it can be assumed that the Ni complexes are coordinated to the bipyridyl sites throughout the material, which will be assessed by IR spectroscopy measurement later in this work.

For the MP-3 (ACHN and ATTN) series, catalysts were also characterized by using the BJH method. For all the catalysts, the distribution peak is at 1.55 nm, supporting the fact the catalysts remain microporous upon metalation of the pristine material (Table 15 andTable 14). Ni@Bpy-MP-3 (ACHN) is characterized by the same toluene adsorption behavior as the pristine material, with a decrease in the volume adsorbed, indicating that the Ni complexes have been infiltrated within the material. Concerning the desorption isotherm, a larger hysteresis loop than the pristine material can be observed. This behavior was also observed for the Bpy-MP-1 material with the H4 type hysteresis loop. The toluene adsorbents filled in favorably the different levels of pores (from micropores to macropores) due to the organic nature of the Bpy-MP-3 (ACHN) material. Once, all the pores are filled in, the pores are gradually emptied out but the desorption isotherm do not follow the same way as the adsorption isotherm due to the deformation of the pores by the toluene adsorbent. This deformation can come from the loose feature of the Bpy-MP-3 (ACHN) network. Like it has been suggested for Bpy-MP-1, cycles of toluene adsorption measurement can be done to evaluate if the Bpy-MP-3 (ACHN) comes back to its initial textural state after a first cycle or remains altered.

Different catalysts were also synthesized from the Bpy-MP-3 (ACHN)-based materials, resulting from the pore distribution modulation strategies:

-8.68wt%Ni@Full-Bpy-MP-3 (ACHN) and 2.17wt%Ni@Full-Bpy-MP-3 (ACHN) -

2.38wt%Ni@ Bpy-MP-3-onlyTHF (ACHN)

Their physisorption isotherms were represented in the Appendix of Chapter 2 (Figure 119 and Figure 120). The same isotherm type as the pristine Bpy-MP-3 (ACHN) materials can be observed, with a hierarchical porous structure.

Catalysts with different loadings, from 0.70wt%Ni@Bpy-MP-3 (ACHN) to 2.02wt%Ni@Bpy-MP-3 (ACHN) (Table 15) and from 0.49wt%Ni@Bpy-MP-3 (ATTN) to 1.90wt%Ni@Bpy-MP-3 (ATTN) (Table 14 In the case of X-Ray fluorescence (XRF) spectroscopy, when a sample is irradiated by X-rays, a first fraction will pass through the sample, a second one will be absorbed and a third one will be scattered back. X-ray fluorescence occurs when a fraction of the X-rays are absorbed: X-rays photons that have an energy close to the binding energy of the electrons of an atom, will expel these electrons from their orbital. An electron from an outer orbital will fill in the vacancy produced in the atomic structure. During this process, this electron will release an energy corresponding to the difference of energy between the orbitals. This energy will either give rise to the emission of a X-ray photon or either be transmitted to an other electron that will be expelled (Auger electron), the two emissions being in competition.

In the case of the X-ray photon emitted, its energy is specific to the difference of energy between the orbitals and, therefore, specific to the element it comes from. Finally, the distribution of energy of the emitted photons (fluorescent X-rays) by a sample irradiated by Xrays will compose its spectra. However, the matrix of the sample is a barrier that X-rays have to penetrate before reaching the atoms within a sample. The amount of irradiating X-rays absorbed by the matrix will depend on the energy of the radiation, the path length d of the Xrays within the matrix and the density ρ of the sample.

When a X-ray photon hits an element, two phenomena can occur:

-Rayleigh scatter, which happens when X-ray photons encounter electrons that are strongly bonded and are scattered back, without loss of energy (coherent scatter) -Compton scatter, which happens when X-ray photons loose their energy after colliding with electrons and are scattered back (incoherent scatter)

Compton scatter is more pronounced than Rayleigh scatter with light elements.

However, the heavier the elements are, the lower the Compton scatter is and the higher the Rayleigh one is.

In our case, with POPs (made of light elements carbon, hydrogen, nitrogen, etc. The normalized intensities of the peak at 1450 cm -1 by the intensity of the peak at 1466 cm -1 has been plotted against the wt% in Ni (determined by ICP-OES (Table 14)) within the different characterized Ni@Bpy-MP-3 (ATTN) catalysts (Figure 68). In summary, different bipyridyl-based porous frameworks have been synthesized with the purpose to immobilize nickel(II) chloride complexes within their micropores and use them for ethylene oligomerization. Micropores enable to obtain isolated active sites but can lead to diffusion limitations and immobilizing active sites within mesopores can lead to interactions between them, which is a source of secondary reactions and catalyst deactivation. On the other hand, mesopores enable to improve diffusion of reagents and products within the catalyst.

The MOF UiO-67 and the POPs Bpy-MP-1, Bpy-MP-2 and Bpy-MP-3 were chosen for their microporosity and the possibility to dilute bipyridyl sites within their structure with aromatic linkers or monomers, which enables to improve mass transport limitations. They also enable to obtain a high ratio of active sites per catalyst mass.

The synthesized UiO-67-bpy-based catalysts were highly microporous crystalline catalysts (characterized by PXRD and nitrogen physisorption measurements), suitable for the immobilization of nickel(II) chloride molecular complexes. However, ill-defined nickel sites can be obtained by the coordination of the molecular complexes on the Zr-OH sites of the framework. This type of secondary sites can lead to side reactions and leaching issues (Figure 69). Therefore, bipyridyl-based Porous Organic Polymers (POPs) were synthesized. The target is to find optimal conditions that enable to achieve a TOF above 10 000 mmololigomers.mmolNi -1 .h -1 and a selectivity in butene above 90%. Starting from a screening of Ni-based molecular catalysts, conditions of ethylene oligomerization have been settled in order to study the effects observed on productivity and selectivity when these molecular catalysts are integrated into porous macroligands.

Preliminary homogeneous screening

Effect of the solvent on molecular catalysts' TOFs

Given the fact that bipyridine and imine-based homogeneous catalysts, combined with Ni, selectively dimerize ethylene (with selectivities in butene around 90%),

bis(triphenylphosphine)nickel(II) dichloride and 2,2'-bipyridine nickel(II) dichloride

(respectively designated as Ni(PPh3)Cl2 and Ni(bpy)Cl2) were chosen as benchmark catalysts for functionalizing the new heterogeneous macroligands.

First, based on the work that has been previously established within our research group and among other groups, it has been chosen to lead first homogeneous catalytic tests in mild conditions : 10 μmol of nickel, 50 equivalents of aluminum activator (Et2AlCl) with a continuous feed of ethylene at 30 bars at 25°C, during one hour. [87,84,90,159] Et2AlCl was chosen as aluminum activator, according to the classification provided by De Souza et al.,

for: [87,90,[160][161][162]26] its high alkylating strength, its low catalytic activity towards polymerization of ethylene (since the purpose is to favor oligomerization) and for dimerizing selectively ethylene when associated with a Ni-based catalyst, whether it is in heterogeneous catalysis The reactor was purged three times with ethylene before starting the reaction at a desired pressure. The temperature of the reactor was regulated during the reaction with a thermostated bath (25°C during the reaction). At the end of the reaction, the reactor's bottom was put into an ice bath using cooled ethyl acetate, to increase the products' solubility in the solvent (especially 1-butene, gaseous at 25°C and liquid below -6°C). Afterwards, the products were analyzed by GC-FID (Figure 70). Based on previous studies using MOFs for ethylene dimerization, heptane has been first evaluated as solvent for the catalysis because it is containing an odd number of carbons, 133 in contrast to most ethylene oligomerization products. [87] Afterwards, toluene was tested and with the molecular catalysts Ni(PPh3)Cl2 and Ni(bpy)Cl2, higher TOFs were obtained in toluene than in heptane (respectively 15 600 against 285 mmololigomers.mmolNi -1 .h -1 with

Ni(PPh 3)Cl2 and 26 135 against 685mmololigomers.mmolNi -1 .h -1 with Ni(bpy)Cl2) (Figure 71). In all cases, butene selectivities ranged between 90 and 95%. This difference in TOFs could come from a difference of ethylene solubility in heptane and toluene. According to the solubility data series of ethylene established by the IUPAC in 1994, a difference of molar fraction of the saturating ethylene solubilized in each solvent could be observed at the temperatures used here (Figure 72). [163,164] Further investigation has to be done to evaluate if this difference of molar fraction could lead to a significant difference of ethylene amount dissolved in each solvent. Surprisingly, when the catalysis is performed in heptane and the co-catalyst is in toluene, substantial differences with respect to the alltoluene or the all-heptane systems are observed (Figure 71). We have no explanations for now for this phenomenon.

134

Therefore, the influence of the solvent on the ethylene selective dimerization TOF remains to be investigated.

Molecular catalysts screening

The electronic and steric effects on the Ni active site have been studied by using 2,2'bipyridyl-based ligands bearing different groups (Figure 73). The six complexes were synthesized by mixing one equivalent of NiCl2•glyme molecular complex with 1.05 equivalents of a 2,2'-bipyridyl-based ligand in THF at 65°C during 24 hours, according to a modified procedure literature. [165] NiCl2•glyme molecular complex was chosen for the lability of the ethereal ligand, which also improves the solubility of the nickel salt. According to Budnikova et al., the obtained complexes can be characterized by cyclic voltammetry and the oxidation states of the nickel-bipyridyl-based complexes can be determined, but it has not been done in this work. [166] The experiments were performed under the same conditions as described in the 3.2.1 part (led with a continuous feed of ethylene at 30 bars, 25°C during one hour, 10 μmol of nickel and 50 equivalents of Et2AlCl) (Figure 74). With the catalysts Ni(bpy)Cl2, 4,4'-dimethyl-2,2'-bipyridyl nickel(II) dichloride and 4,4'-ditert-butyl-2,2'-bipyridyl nickel(II) dichloride, no significant effect could be observed on the TOF (ranging between 23 589 and 26 135 mmololigomers.mmolNi -1 .h -1 ) (experiments a, c and e in Figure 74), with selectivities in butene ranging from 92 to 95%. Further tests have to be performed but the data suggest that adding an electron-donating group on the bipyridyl ligand has no effect on the TOF or the butene selectivity.

With the catalyst 6,6'-dimethyl-2,2'-bipyridyl nickel(II) dichloride, no substantial changes in TOF are observed compared to the Ni(bpy)Cl 2 counterpart (23 109 mmololigomers.mmolNi -1 .h - 1 compared to 26 135 mmololigomers.mmolNi -1 .h -1 ) (experiment b in Figure 74), with a selectivity in butene of 89%. This suggest that steric hindrance on the ligand has little effect on the oligomerization TOF and butene selectivity. However, a twofold TOF drop (from 26 135 to 12 577 mmol oligomers.mmolNi -1 .h -1 ) can be observed when the electron density is increased with the phenantroline ligand, along a drop of selectivity in butene down to 84%.

Besides, when iodine replaces chlorine as leaving group in the case of the d experiment, a fourfold drop can be observed (from 26 135 to 5 488 mmololigomers.mmolNi -1 .h -1 ), with a selectivity in butene of 92%. As it was described before in chapter 1, one of the aluminum-based co-catalyst role is to abstract halides; it can be assumed that Et2AlCl abstract chlorine better than iodine. precursor NiCl 2•glyme, already used within our research group was chosen. [135] This precursor is a catalyst for ethylene dimerization in its own right (Figure 75). At the same time, we believe that its utilization should not interfere with the overall catalytic performance of the porous polymer. Indeed, NiCl2•glyme is highly soluble in THF. We therefore think that any unreacted quantity still present after infiltration in the POP would be washed out during the numerous washing that the final material undergoes before its utilization as catalyst. 631 mmololigomers.mmolNi -1 .h -1 (Figure 76). In both cases, the butene selectivity was 93%.

Ni(PPh 3)Cl2 catalyst has not been tested for 3 and 10 μmol of nickel with respectively 50 and 150 equivalents of EtAlCl2. In summary, the catalytic center Ni(bpy)Cl 2 appears appropriate for designing an heterogeneous porous macroligand for ethylene dimerization. The designed catalysts can target a TOF above at least 20 000 mmololigomers.mmolNi -1 .h -1 and a butene selectivity around 90% while minimizing polyethylene production, based on the homogeneous data gathered so far.

Heterogeneous bipyridyl-based MOF and POP catalyst for selective ethylene dimerization

Two types of bipyridyl based porous catalysts were synthesized in this work: the MOF Ni@UiO-67-bpy and three POPs, Ni@Bpy-MP-1, Ni@Bpy-MP-2 and Ni@Bpy-MP-3 (ACHN). Based on the homogeneous screening of part 3.2, unless otherwise stated, the heterogeneous catalytic tests will be performed with 3 μmol of nickel and 150 equivalents of Et 2AlCl (0.6 mL of activator solution dissolved in toluene), in a batch reactor fed continuously with ethylene at 30 bars at 25°C, during one hour in toluene (for a typical run).

Preliminary heterogeneous catalytic tests with Ni@UiO-67-bpy

By using 0.58wt%Ni@UiO-67-bpy(5%) and 0.74wt%Ni@UiO-67-bpy(10%) catalysts, TOFs of 59 and 10 634 and mmol oligomers .mmol Ni -1 .h -1 were respectively obtained, with butene selectivities of 100% in both cases. Compared to homogeneous counterpart Ni(bpy)Cl2 catalyst (26 207 mmololigomers.mmolNi -1 .h -1 and a butene selectivity of 92%), Ni@UiO-67-bpy catalysts are more selective but less active. Apparently, since we observed no polyethylene production, such spurious sites do not occur, at least extensively in our system. At the same time, 0.58wt%Ni@UiO-67-bpy(5%)

has not been analyzed by physisorption and PXRD measurements after ethylene oligomerization, and further investigation would have to be done to corroborate the current hypothesis. In the case of Ni@Bpy-MP-3 (ACHN)-based catalysts, a significant amount (more than 1 g) of polyethylene was produced. Only few milligrams or none resulted from the catalytic experiments with the Ni@Bpy-MP-1 and Ni@Bpy-MP-2 catalysts. The TOFs (in gproduct.gcatalyst -1 .h -1 ) obtained with the three types of catalysts has been plotted against the loading of Ni are reported in the Appendix of Chapter 3 (Figure 121). To evaluate the TOFs relative to the oligomers produced, separately from the TOF relative to the polyethylene formed, the amount of polyethylene was separately estimated.

Heterogeneous catalytic tests with Ni@Bpy-MP-based catalysts

After catalysis, the solid recovered is left to dry at room temperature during one night and put under vacuum at 80°C during one night. The weight of the catalysts and the aluminum Cocatalysts are subtracted from the weight of the dried white solid. The resulting weight is assigned to polyethylene formation. Given the sticky nature of the solid, few milligrams can be lost during the work-up process. The oligomers formed are analyzed after the catalytic test by gas chromatography equipped with a flame ionization detector (GC FID). The solvent of the reaction is used as the internal standard. In terms of product weight, more polyethylene is produced than oligomers, regardless the Ni loading considered. presents TOF (above 10 000 mmololigomers.mmolNi -1 .h -1 and butene selectivity among oligomers (around 90%) as competitive as its homogeneous counterpart (Ni(bpy)Cl2) .

However, the competing polyethylene hampers the ability of the Ni@Bpy-MP-3 (ACHN)

catalyst to exclusively dimerize ethylene to butenes (Figure 79). Above a 1.0 wt% Ni loading, the production of oligomers is hampered and it can be assumed that the pore blocking induced by the polyethylene production hampers the oligomer production. polyethylene showed a melting temperature of about 127°C (Figure 80). This temperature is substantially different from the expected melting temperature of linear polyethylene. As discussed by Boyron et al., α-olefin incorporation in polyethylene induces lowering of the melting temperature and of the melting enthalpy. [167] The DSC analysis reported in Figure 80 therefore suggests some incorporation of oligomers in the polymer. It can be assumed, mechanistically, that the oligomers formed in the early times of the reaction copolymerize with ethylene to yield the final macromolecules. The wide range of polyethylene molecular weight distributions, added to the fact that oligomers are also produced, is a proof that there are several active sites producing polyethylene with different chain lengths. In addition, the significant amount of oligomers trapped inside the polyethylene produced does not allow to determine which step, between insertion of ethylene and chain transfer, is favored for a given active site. When the temperature decreases, the solubility of ethylene is improved but the kinetic of the reaction is also slowed down. The effect of lowering the temperature, performing ethylene oligomerization with 1.26wt%Ni@Bpy-MP-3 (ACHN) catalyst has been first studied (Figure 82). A test at 0°C enabled to confirm that both oligomers and polyethylene productions are decreased and the butene selectivity went down from 79% at 25°C to 65% at 0°C. The effect of the pressure has not yet been evaluated but it can be assumed that traces of polyethylene would also be found at lower pressures, along with oligomers.

Figure 82 : TOF in gproduct.gcatalyst -1 .h -1 of oligomers and polyethylene, compared at 0°C (left) and 25°C (right), with a 1.26wt%Ni@Bpy-MP-3 (ACHN) catalyst ran at 30 bars of ethylene, in toluene with 150 equivalents of Et2AlCl

Afterwards, the effect of the solvent was investigated. Heptane, rather than toluene, has been tested as catalytic solvent with 188 equivalents of Et2AlCl (dissolved in toluene), at 25°C and 30 bars of ethylene, with a 0.94wt%Ni@Bpy-MP-3 (ACHN) catalyst. Polyethylene was produced up to 153 gpolyethylene.gcatalyst -1 .h -1 and oligomers, up to 356 goligomers.gcatalyst -1 .h -1 , with a selectivity in butene of 91%. In the same conditions, a 0.90wt%Ni@Bpy-MP-3 catalyst showed TOFs of 193 g polyethylene.gcatalyst -1 .h -1 and 181 goligomers.gcatalyst -1 .h -1 . Solvent may not have an effect on the Ni@Bpy-MP-3 catalyst selectivity towards oligomerization or polymerization.

Focusing on Et2AlCl, by using a 1.61wt%Ni@Bpy-MP-3 (ACHN) catalyst, no significant activity could be observed for a number of aluminum equivalents under 141, for neither polyethylene nor oligomers (Figure 83). With 61 equivalents of Et2AlCl, a TOF of 133 mmololigomers.mmolNi -1 .h -1 was observed with a selectivity in butene up to 90% (no polyethylene) against a TOF of 37 177 mmol oligomers.mmolNi -1 .h -1 (3.28 g of polyethylene) and a selectivity in butene of 94% with 141 equivalents. Besides, no activity was observed when the catalytic experiment was performed with only 1.61wt%Ni@Bpy-MP-3 (ACHN) catalyst and without Et2AlCl.

A competitive TOF and butene selectivity could only be achieved with a number of cocatalyst equivalent around 140. Higher amounts of co-catalyst have not been tested yet to avoid the production of aluminum salts at the end of the reaction that could hamper the porosity of the catalyst. have been produced with MMAO-12. In the case of EtAlCl2, a significant drop can be observed when the co-catalyst is used under heterogeneous conditions (from 13 300 goligomers.gcatalyst -1 .h -1 with Ni(bpy)Cl2 to 24 goligomers.gcatalyst -1 .h -1 with 1.61wt%Ni@Bpy-MP-3 (ACHN)) (Figure 84). However, no polyethylene production could be observed under heterogeneous conditions: the drop in TOF has been followed by an extinction of polyethylene production and the butene selectivity in heterogeneous conditions reached 99%.

As it was described in chapter 1, EtAlCl 2 has a lower alkylating strength than Et2AlCl and exhibits a higher activity with nickel-α-diimine catalysts, according to De Souza et al. [26] Further investigation has to be done to evaluate the effect of EtAlCl2 on catalysis with

Ni@Bpy-MP-3 catalysts. For the rest of this work, Et2AlCl will be used for its high alkylating strength (towards the production of oligomers) and its lower activity towards ethylene polymerization with nickel-α-diimine catalysts. No polyethylene could be observed at one minute of reaction and the TON in oligomers already reached 1 628 mmol oligomers.mmolNi -1 .h -1 , with a selectivity in overall butene of 77%

(among all products). One of the limitations that can occur is the ability of the reaction to be homogeneously stirred since polyethylene occupies most of the reactor space up to a certain point (around 30 minutes). The decrease in oligomer production observed at 50 minutes may As it was described in the chapter 2, the Bpy-MP-3 (ACHN) porous macroligand has been prepared according to a radical polymerization process, adapted from a modified literature procedure. [154] Despite the different washing steps (Soxhlet and metalation process) that the Bpy-MP-3 (ACHN) goes through, it has been hypothesized that some radicals trapped inside the catalyst and put into contact with ethylene, could induce polymerization.

Therefore, 2,2,6,6-ttetramethylpiperidin-1-yl)oxyl (or TEMPO), a stable radical organic compound has been used to react with the potentially leftover radicals in the material and inhibit the polymerization process, if any, due to free radicals. Five equivalents of TEMPO (compared to Ni) have been introduced under inert conditions to 1.86wt%Ni@Bpy-MP-3 (ACHN) catalyst, activated with 150 equivalents (compared to Ni) of Et2AlCl, at 25°C and 30 bars of ethylene in toluene. A TOF of 233 gpolyethylene.gcatalyst -1 .h -1 has been observed against 75 goligomers.gcatalyst -1 .h -1 , with a selectivity in butene of 68%. When TEMPO is left to react with the 1.86wt%Ni@Bpy-MP-3 (ACHN) catalyst before introducing the co-catalyst and the ethylene, to make sure that in this second experiment TEMPO reacts with the left radicals, both ethylene polymerization and oligomerization are inhibited. The hypothesis of radical responsible for polyethylene production has not been corroborated by this TEMPO experiment.

A second hypothesis is that besides the coordination on the bipyridine sites during produces a small amount of oligomers but it is less likely that these oligomers are afterwards polymerized, given the amount of polyethylene found at the end of a Ni@Bpy-MP-3 (ACHN) catalysis (more than 1 g).

To simulate the potential entrapment of NiCl2•glyme complexes inside Bpy-MP-3 (ACHN) pores, the molecular complex Ni(bpy)Cl2 was added to the process leading to MP-3 (ACHN), with the idea that the pores would build up around it. Neither oligomers nor polyethylene have been produced under the catalytic conditions (25°C, 30 bars of ethylene in toluene, with 0.6 mL of Et2AlCl, during one hour).

Effect of replacing Et2AlCl with Me3Al in the catalytic system

The catalytic system used in this work combines a Ni-based precatalyst with an aluminum-based co-catalyst. The large excess of the co-catalyst is necessary in some cases to reactivate spent Ni sites. More information on the relevance of this, reactivation routes can be useful to address the oligomer versus polyethylene production. For ethylene oligomers production, Me 3Al co-catalyst can be used to obtain such information.

As described in chapter 1, each (re)activated site will start an oligomerization/polymerization cycle until the elimination step, leading to oligomers with odd numbers of carbon in their chain (cycle A in Figure 88). Conversely, oligomers resulting from living Ni catalysts (as opposed to just activated ones) will lead to even numbered carbon chains (cycle B in Figure 88). equivalents of Et 2AlCl, in the same conditions (Figure 89).

Despite the activation by Me3Al, no odd alpha-olefin was observed in the products, only 64% of butene (molar selectivity) against 94% when activation is done with Et 2AlCl. Beside this loss of selectivity, even-numbered oligomers were produced by the 1.41wt%Ni@Bpy-MP-3 (ACHN) and 1.61wt%Ni@Bpy-MP-3 (ACHN) catalysts with respective TONs of 9 g oligomers.gcatalyst -1 and 590 goligomers.gcatalyst -1 (Figure 89). This production of even-numbered oligomers, along polyethylene production (respectively 43 g polyethylene .g catalyst -1 and 306 gpolyethylene.gcatalyst -1 ) indicates that only one type of cycle is prevailing with a Ni@Bpy-MP-3 (ACHN) catalyst type: cycle B. That cycle produces by its own even-numbered oligomers and polyethylene. The activation process takes a negligible part in the final product distribution.

The absence of odd number oligomers seems to suggest that reactivation processes are not predominant. This is equivalent to say that once activated, the Ni site seems to remain a living center for a while. An interesting suggestion of this analysis is that the major expected catalytic cycle -in our Ni@Bpy system -is probably active throughout the catalysis.

Combined with the evidence of the previous paragraph, where no obvious competing sites have been identified, these data lead us to formulate the working hypothesis that one single site, probably Ni@Bpy is responsible for both oligomers and polyethylene production.

Effect of changing pore size distribution in Bpy-MP-3-based catalysts

The relevance of improving the diffusion of the products inside a Ni@Bpy-MP-3

(ACHN) material has also been explored. The hypothesis that is tested hereafter is to address whether a different confinement of the same Ni@Bpy site within the pore might be a parameter steering the oligomers versus polyethylene production. To test this hypothesis two Bpy-MP-3 materials, differing mostly in terms of their poor distribution, have been tested, namely 1.61wt%Ni@Bpy-MP-3 (ACHN), the reference material used so far versus 2.38wt%Ni@Bpy-MP-3-onlyTHF (ACHN). As described in chapter 2, the synthesis using only THF of the latter material has favored the formation of mesoporosity, while the benchmark standard material, which utilizes water and THF leads to co-existing micro-, meso-and macro-porosity.

As shown in Figure 90, the presence of mesoporosity in 2.38wt%Ni@Bpy-MP-3-onlyTHF (ACHN) has induced a substantial drop in oligomers selectivity. These data show that indeed a different pore distribution can influence the oligomers versus polyethylene distribution. These data also suggest that microporosity is beneficial for increasing selectivity towards oligomers (at the expense of overall ethylene conversion rate). This conclusion is in agreement with the data presented earlier in the chapter where Bpy-MP-1 and Bpy-MP-2based material, which are characterized by substantial microporosity, did not lead to polyethylene formation but this higher selectivity was also characterized by lower overall activity. As shown in Figure 90, the oligomer versus polyethylene ratio drastically changes between the 1.61wt%Ni@Bpy-MP-3 benchmark catalyst and the 8.68wt%Ni@Full-Bpy-MP-3 (ACHN) catalyst: while the selectivity in oligomers is about 65% for the benchmark catalyst, it drops to 10% with the Full-Bpy-MP-3 (ACHN). The large difference in Ni content, as well as the scant characterization of the Full-Bpy-MP-3 (ACHN) material so far, does not allow to over interpret these data, but seems to suggest that dense Ni sites might favor polyethylene production versus oligomer one.

Recycling Bpy-MP-3-based catalysts

Recycling the catalyst remains a challenge because of polyethylene production. Since only few milligrams of catalyst are introduced inside the reactor for a run, in the end of the reaction, it is trapped inside the polyethylene produced. Aromatic and halogenated solvents (toluene, xylene, trichlorobenzene, etc.) are used industrially to dissolve polyethylene. It has been tried to dissolve in two separate vials with m-xylene at 130°C: a batch of polyethylene produced from a catalysis and few milligrams of a Bpy-MP-3 pristine material.

Even if the polyethylene gets solubilized in m-xylene at 130°C, the Bpy-MP-3 material remains intact. Nevertheless, to recover the few milligrams of catalyst from the polyethylene batch, the solution needs to be filtrated under hot conditions otherwise, the polyethylene precipitates. Even if Bpy-MP-3 material shows good resistance at high temperature, the ability of Ni not to lixiviate in those conditions remains to be investigated.

In summary, since polyethylene production by the Ni@Bpy-MP-3 does not originate from experimental parameters (such as temperature, co-catalyst nature or amount), it can be assumed that it is caused by a textural effect or an electronic effect. Nevertheless, like it was detailed in the homogeneous screening, ethylene oligomerization is less likely to be influenced neither by electronic nor steric effects (Figure 74). Therefore, this polymerization of ethylene is more likely due to textural effects of the Ni@Bpy-MP-3 (ACHN). This hypothesis can be verified by an ethylene adsorption measurement. This assertion is supported by the fact that in Zhang et al. original publication, the authors proved the ability of the PDVB to adsorb organic compounds (like acetone or pentane). [154] As a consequence, by increasing ethylene solubility, Bpy-MP-3 might have a textural effect rather an electronic effect on the Ni@Bpy active site causing it to dimerize selectively ethylene as well as polymerize olefins close to the active site.

Further investigation has to be done to evaluate the effect of the pore size distribution modulation on the product distribution obtained by ethylene oligomerization with Ni@Bpy-MP-3 (ACHN) catalysts. It can be expected that by increasing the amount of micropores and decreasing the amount of mesopores, the amount of polyethylene can be decreased. twofold reduction with one equivalent of tricyclohexylphosphine (more basic than triphenylphosphine). [168] It can be assumed that, as it was showed by Monteil et al., that the phosphine stabilizes the nickel complex during the polymerization, better than the agostic interaction with the β-hydrogen of the newly formed alkyl chain on the metal complex. This stabilization leads to the cleavage of the alkyl-metal bond. [169] In order to circumvent, or at least minimize, the production of polyethylene using POPbased catalysts, three phosphines have been tested as ancillary ligands for the heterogeneous selective dimerization of ethylene with Ni@Bpy-MP-3 (ACHN) catalysts:

Phosphine

PCy 3 (tricyclohexylphosphine), P(OMe) 3 (trimethylphosphite) and PPh 3 (triphenylphosphine).

Each one represents different combination of the Tolman angle and their π-donating

properties. [170] First, as a benchmark experiment, the 1.86wt%Ni@Bpy-MP-3 (ACHN) catalyst has been tested for ethylene oligomerization without any additional phosphine in the conditions described previously and produced up to 11 839 mmol oligomers.mmolNi -1 .h -1 , with a selectivity in butene of 80%. A production of polyethylene along oligomer production was also observed: 458 gpolyethylene.gcatalyseur -1 .h -1 compared to 237 goligomers.gcatalyseur -1 .h -1 (Figure 92). Comparing activity per gram of catalyst is obviously in favor of pure molecular complexes compared to heterogenized ones, while the same amount of Ni is present in the catalysis reactor. This comparison in gram per gram allows taking into account the mass of polyethylene produced.

two equivalents of P(OMe)3 (corresponding experimentally to 1 μL), polyethylene productions were respectively 281 gpolyethylene.gcatalyseur -1 .h -1 and 209 gpolyethylene.gcatalyseur -1 .h -1 (Figure 92). (ACHN) catalyst used remained as competitive as its homogeneous counterpart with respective TOFs of 27 074 and 14 929 mmol oligomers.mmolNi -1 .h -1 and respective selectivities in butene of 90% and 80%, compared to a TOF in oligomers of 6 854 mmololigomers.mmolNi -1 .h -1 and a butene selectivity of 88% for Ni(bpy)Cl2 with one equivalent of PPh3 (Figure 93). With one equivalent of P(OMe)3, along high polyethylene production, the TOFs went down to 3 066 mmol oligomers.mmolNi -1 .h -1 .

More 2-butene was observed when the catalysis is carried out with one equivalent of PPh 3 added to 1.86wt%Ni@Bpy-MP-3 (ACHN) catalyst. The selectivity in 2-butene represents 39% compared to all oligomers. This result shows that isomerization of 1-butene happens. Isomerization usually occurs after the first insertion of ethylene in the nickel-ethyl bond, along the agostic interaction stabilizing the formed complex. The predominance of 2butene brings a confirmation that PPh 3 intervene at this particular step of the mechanism, stabilizing the complex formed after ethylene insertion. Therefore, it can be assumed that the two most electron-donating phosphine, PCy 3 and PPh3, enable to circumvent the polymerization process by stabilizing the metal-alkyl intermediate. The lower 2-butene/1butene ratio observed with PCy3 compared to PPh3 can be due to PCy3 higher steric hindrance.

By using the same catalyst 1.86wt%Ni@Bpy-MP-3 (ACHN) under the same conditions (activated with 150 equivalents of Et 2AlCl, at 25°C and 30 bars of ethylene, during one hour in toluene), higher equivalents of PCy 3 and PPh3 have been tested (Figure 94). For ten equivalents of PPh3, polymerization prevails again over oligomerization with a TOF of 165 gpolyethylene.gcatalyseur -1 .h -1 against 28 goligomers.gcatalyseur -1 .h -1 . Concerning P(Cy)3, higher equivalents enabled to increase the oligomerization TOF from 79 to 200 goligomers.gcatalyseur -1 .h - Finally, further tests would enable to recycle the 1.86wt%Ni@Bpy-MP-3 (ACHN) catalyst that has been used for ethylene oligomerization (after adding PPh 3).

In summary, this subsection enabled to prove that by using additional phosphine, polymerization of ethylene due to Ni@Bpy-MP-3 (ACHN) catalyst can be circumvented. By comparing the effect of three phosphines P(OMe)3, PPh3 and PCy3, it could be confirmed that the phosphine has an electronic effect on the metal-alkyl intermediate during the ethylene oligomerization process. However, to stabilize it efficiently, the ancillary ligand needs to be sufficiently electron-donating and not hindering, making PPh3 a more promising candidate than P(OMe) 3 and PCy3. Furthermore, preliminary tests tend to show that the phosphine ancillary ligand do not cause leaching of the Ni active site from the Ni@Bpy-MP-3 (ACHN) catalyst

Conclusion of the chapter

For the selective dimerization of ethylene, after studying the effect of a bipyridine ligand on a nickel(II) chloride molecular catalyst, the Ni@Bpy-MP-3 (ACHN) porous catalyst has been tested. Not only is this heterogeneous catalyst as competitive as its homogeneous counterpart, but it is also more active than other Ni-infiltrated macroligands such as Ni@UiO-67-bpy, Ni@Bpy-MP-1 or Ni@Bpy-MP-2.

However, along with this selective dimerization of ethylene, polymerization takes place.

It appears possible that the same active site dimerizing selectively ethylene also polymerizes this gas. The ability of Ni@Bpy-MP-3 (ACHN) to polymerize ethylene might originate from a textural effect of the macroligand rather than an electronic effect. Further investigation has to be done but the production of polyethylene can be due to pore confinement of the oligomers within the micropores of the catalyst. ethylene oligomerization. [43,45] Not only these catalysts proved to be highly active and selective towards α-olefins (98%), but they also shaped the commercially used Shell Higher Olefin Process (SHOP) catalyst. Wilke et al. developed monodentate phosphine-nickelbased catalysts for propylene dimerization as well as Mitsubishi Chemical Corporation, who elaborated a process for dimerizing lower olefins using a phosphite-Ni-based catalyst. [44,171- 173] With the idea of designing phosphorus-based macroligands for selective ethylene dimerization, Bogdanovic et al. proved how the degree of oligomerization can be controlled depending on the chosen phosphine. [174] Introducing a phosphine ligand, and more generally an electron-donating ligand, within the coordination sphere enables to improve both the stability, the activity and to steer the selectivity of the catalyst. [174] Grubbs et al. and Monteil et al. proved that, in molecular catalysis, the addition of one equivalent of PPh3 in a Ni-catalyzed ethylene polymerization reaction enabled to inhibit the reaction. [168,169] This result has been successfully adapted in heterogeneous catalysis: polyethylene production was inhibited by adding one equivalent of PPh 3 (compared to Ni) in the reaction mixture of Ni@Bpy-MP-3 for ethylene oligomerization. Three phosphines PCy3, P(OMe)3 and PPh3 have been used to modulate the TOF and the selectivity of Ni@Bpy-MP-3 catalysts for ethylene oligomerization. PPh 3 proved to be the most efficient to inhibit polymerization of ethylene: it can be assumed that it is due to the coupling of its moderate steric hindrance (compared to PCy3) and its electron-donating ability (more than P(OMe)3).

We also found that the commercially available and phosphine-based catalyst bis(triphenylphosphine)nickel(II) dichloride (Ni(PPh3)Cl2) is highly active for ethylene oligomerization with a TOF above 10 000 mmol oligomers .mmol Ni -1 .h -1 and highly selective towards butene (above 90%).

Based on these results, new phosphine-based microporous heterogeneous macroligands have been developed to immobilize Ni molecular complex within the micropores. After characterization by PXRD, nitrogen physisorption and 31 P solid-state NMR of the pristine materials and the catalysts, they have been tested for ethylene oligomerization. 95). [175] Each cluster made by Zr atoms (green parts), bridged to each other either by a oxo or hydroxo species (red points). The clusters are connected together by 1,3,5benzenetricarboxylic linkers.

MOF-808-phosphine-based framework

Figure 95 : MOF-808 synthesis procedure, adapted from Furukawa et al. [175] The formed cavities can be classified into two groups : a tetrahedral and an adamantane-shaped cavities with respective diameters of 4.8 and 18 Å. [176] Formic acid has been first introduced to tune the pore size of the cavities, since the formate groups point towards the center of the cavities. [177] Unlike the UiO-67-bpy synthesis where bipyridine sites have been incorporated by a Further investigation has to be done to evaluate the MOF-808 pore distribution.

volume adsorbed compared to the pristine material surface area (from 2 301 to 479 m 2 .g -1 )

along with a decrease of the mean pore diameter opening (from 1.47 to 2.13 nm) could be observed (Table 17). These results obtained under nitrogen physisorption measurements justifies the successful incorporation of phosphine sites inside the material and the fact that these bulky anchoring sites point toward the center of the pores (Figure 98).

POPs with phosphine sites

Different phosphine-based POPs have been synthesized for hydroformylation of alkynes, C-C coupling, CO2 conversion, etc.. [START_REF] Kumar | [END_REF] They can be prepared by Pd-catalyzed coupling, Friedel-Craft or condensation reactions.

A phosphine-based POP has been synthesized following the same procedure as the Bpy-MP-3 (ACHN) (described in the chapter 2 of this thesis work). The phosphine-based POP will be designated as Phos-MP-3 (ACHN). The ACHN radical initiator has been used and a withe solid material is obtained (Figure 102).

Figure 102 : Phos-MP-3 series synthesis adapted from a modified literature procedure [154] Phos-MP-3 (ACHN) materials were characterized by nitrogen physisorption measurements and exhibit a type II physisorption isotherm, the same type as the Bpy-MP-3

(ACHN) and the Bpy-MP-3 (ATTN) materials (Figure 103). Below a partial pressure of 0.1, the micropores are filled, followed by the mesopores between a partial pressure of 0.1 and 0.9. Finally, above 0.9, the nitrogen uptake corresponds to the filling-up of the macropores.

The porosity hierarchy of the Bpy-MP-3 (ACHN) is also observed for the Phos-MP-3 (ACHN) materials. However, further investigation has to be done to understand if the bulkiness of the triphenylphosphine site allows them to be incorporated within micropores in order to obtain isolated active sites and furthermore, incorporated in mesopores and macropores or if the triphenylphosphine sites only remain on the surface of the material. to Bpy-MP-3 materials (850 m 2 .g -1 ) (Table 20). This decrease can be explained by observing the lower total pore volume of Phos-MP-3 (ACHN) materials (0.93 ± 0.05 cm 3 .g Like it has been mentioned for the MOF-808-DPPB materials, phosphine groups of the monomers can be oxidized. Freeze-pump cycles have also been performed on the reaction The catalysts have been tested for ethylene oligomerization at 25°C and 30 bar of ethylene, in toluene, during one hour, if not otherwise stated. In the case of 1.38wt%Ni@MOF-808-DPPB catalyst, a TOF of 7 mmol oligomers.mmolNi -1 .h -1 has been reached, without no polyethylene production and a selectivity in butene of 88%. These catalytic results are lower than the results obtained with Ni@UiO-67-bpy catalysts (for example, 59 mmol oligomers.mmolNi -1 .h -1 and 100% butene selectivity was obtained with 0.58wt%Ni@UiO-67-bpy(5%)). The decrease of surface area and mean pore diameter observed for the MOF-808-DPPB, upon the introduction of the phosphine-based linker, may limit the diffusion of the reagents inside the material, hence the dimerization of ethylene.

Although a butene selectivity of 88% shows that when it happens, the Ni coordinated to a phosphine site is selective and as competitive as the molecular catalysts Ni(PPh 3)2Cl2.

However, the slower activity of this ) with a 0.08wt%Ni@Phos-MP-3 catalyst (0.1 μmol of nickel) activated with 2 732 equivalents of Et2AlCl, for two hours of reaction were obtained.

In both cases with 0.05wt%Ni@Phos-MP-3 and 0.08wt%Ni@Phos-MP-3, the catalysts were 100% selective in butene (47% of 1-butene) and no traces of polyethylene was observed. These results confirm the fact that the phosphine-based macroligand hindrance enables to slow down the oligomerization process and improve the butene selectivity. It can be assumed that the phosphine-based macroligand stabilizes the Ni complex to favor the elimination step of the formed oligomer. However, high amounts of aluminum activator were used. Therefore, improving the infiltration of Ni complexes would enable to decrease the amount of aluminum activator that has to be used for the reaction. Unless otherwise stated, all deuterated solvents were purchased from Eurisotop, regular solvents from Carlo-Erba and anhydrous solvents from Sigma-Aldrich

Synthetic procedures

5,5'-divinyl-2,2'-bipyridyl

Synthesis has been performed according to a modified literature procedure. [153] For a typical synthesis, in a quartz tube, a suspension of potassium vinyltrifluoroborate (850 mg, 6.35 mmol), 5,5'dibromo-

Bpy-MP-3

Synthesis has been performed according to a modified literature procedure. [154] 242 mg (1.53 mmol) of divinylbenzene (0,914 g.mL -1 , 80%, passed through a column of basic Al 2O3 in order to remove dissolved oxygen in the solution), 75.3 mg (0.36 mmol) of 5,5'divinyl-2,2'-bipyridyl and 13.6 mg (0.06 mmol) of ACHN were dissolved in 4.4 ml of a deaerated THF:H2O mixture (10:1) under Ar. The solution was stirred for 3 h at room temperature. Afterwards, the solution was transferred into a Teflon lined stainless-steel autoclave. The autoclave was sealed and places in a preheated oven at 100 °C for 48 h.

After the autoclave was cooled to room temperature, the polymer (monolith) was transferred into a Soxhlet thimble and purified by Soxhlet extraction using THF for one night. The white solid was dried at 100 °C under vacuum.

Bpy-MP-1

For a typical Bpy-MP-1 synthesis, 100,0 mg (0,67 mmol, 1 eq.) of 1,3,5-triethynylenzene, 310,3 mg (0,75 mmol, 1,13 eq.) of 4,4'-diiodobiphenyl, 80,0 mg (0,25 mmol, 0,38 eq.) of 5,5'dibromo-2,2'-bipyridyle and 15,54 mg (0,01 mmol, 0,02 eq.) of tetrakis(triphenylphosphine) palladium (0) are added in a flame-dried quartz tube, under inert atmosphere inside the glovebox. After sealing the filled tube with a septum, the overall system is taken outside the glovebox and 12 mL of anhydrous DMF and 6 mL of anhydrous NEt 3 are added under inert atmosphere. The reaction mixture is then left in an oil bath preheated at 100°C for one night.

A yellow precipitate is formed after ten minutes, indicating the beginning of the polymerization. After letting the system come back to room temperature, the obtained solid is further purified by continuous extraction with a Soxhlet apparatus, starting with CHCl3 during 6 hours then MeOH overnight. The yellow solid is then dried under vacuum 80°C. Typical yield: 230 mg.

Bpy-MP-2

For a typical Bpy-MP-2 synthesis, 125,40 mg (0,30 mmol, 1 eq.) of tetrakis(4ethynylphenyl)methane, 183,3 mg (0,44 mmol, 1,5 eq.) of 4,4'-diiodobiphenyl, 47,3 mg (0,15 mmol, 0,5 eq.) of 5,5'-dibromo-2,2'-bipyridyl and 10,3 mg (0,01 mmol, 0,03 eq.) of tetrakis(triphenylphosphine) palladium (0) are added in a flame-dried quartz tube, under inert atmosphere inside the glovebox. After sealing the filled tube with a septum, the overall system is taken outside the glovebox and 12 mL of anhydrous DMF and 6 mL of anhydrous NEt 3 anhydre are added under inert atmosphere. The reaction mixture is then left in an oil bath preheated at 100°C for one night. A yellow precipitate is formed after ten minutes, indicating the beginning of the polymerization. After letting the system come back to room temperature, the obtained solid is further purified by continuous extraction with a Soxhlet apparatus, starting with CHCl3 during 6 hours then MeOH overnight. The yellow solid is then dried under vacuum 80°C. Typical yield: 230 mg.

UiO-67-bpy

Synthesis has been performed according to a modified literature procedure. [118,115] In a glass vial of 60 mL,

MOF-808

Synthesis has been realized according to a modified literature procedure. [176] In a glass vial of 60 mL, ZrOCl 2 (194 mg, 0.602 mmol) and 1,3,5-benzenetricarboxylic acid (42 mg, 0.200 mmol) are dissolved in 9 mL of DMF with 9mL of formic acid. The sealed vial is put inside an ultrasound bath during three minutes. The suspension is heated at 130°C in an oven during 48 hours. After a cooling down to room temperature during 24 hours, the solid is recovered by centrifugation and washed two times with DMF. Then the solid is left to soak in deionized water during one night and washed a second time with deionized water.

After leaving the solid to soak in acetone during one night, it is left to stir in methanol at 50°C during one night. The solid is dried under vacuum at 120°C.

MOF-808-DPPB

In a glass vial of 60 mL, a freshly desorbed MOF-808 (250 mg) is put with 4-(diphenylphosphino)benzoic acid (76.5 mg, 0.250 mmol) in 20 mL of DMF. The mixture is degassed for 20 to 30 minutes with argon and put for stirring at 100°C during 48h.

Afterwards, the mixture is left to cool down to room temperature. The solid is recovered by centrifugation and washed twice with DMF, once with ethanol and left to soak in acetone overnight. Then, the solid is washed twice with methanol.

2,2'-bipyridine nickel(II) dichloride

Synthesis has been performed according to literature procedure. [165] NiCl2•glyme (139 mg, 0.620 mmol) and 2,2'-bipyridyl (103 mg, 0.651 mmol) are stirred in 3 mL of anhydrous THF at 65°C during 24h. After cooling down to room temperature, the solid is recovered by centrifugation and washed three times with THF.

Phos-MP-3

Synthesis has been performed according to a modified literature procedure. [154] 242 mg (1.53 mmol) of divinylbenzene (0,914 g.mL -1 , 80%, passed through a column of basic Al2O3 in order to remove dissolved oxygen in the solution), 108 mg (0.36 mmol) of 4-(diphenylphosphino)styrene and 13.6 mg (0.06 mmol) of ACHN were dissolved in 8.8 ml of a deaerated THF:H 2 O mixture (10:1) under Ar. The solution was degassed with argon by using freeze-pump-thaw cycles. Afterwards, the solution was transferred into a Teflon lined stainless-steel autoclave. The autoclave was sealed and places in a preheated oven at 100 °C for 48 h. After the autoclave was cooled to room temperature, the polymer (monolith)

was transferred into a Soxhlet thimble and purified by Soxhlet extraction using THF for one night. The white solid was dried at 100 °C under vacuum.

Nickel infiltration procedure

The nickel(II) chloride ethylene glycol dimethyl ether complex (NiCl After the reaction, the catalyst is recovered by centrifugation and washed three times with methanol.

Catalytic procedures

Ethylene oligomerization

Synthesis has been realized according to a modified literature procedure. [87] For a typical catalytic run, 3 or 10 μmol of nickel (either molecular or heterogeneous catalysts) are aimed to be put inside a borosilicated insert of 30 mL, followed by 15 mL of toluene and 0.6 of Et2AlCl (0.9M in toluene). The insert is placed inside a stainless steel autoclave. After degassing the reactor three times, it is kept under a constant pressure of 30 bars of ethylene during one hour at 25°C, by using a thermostated bath. The reactor is cooled down afterwards in an ethyl acetate/liquid nitrogen bath at -84°C. The reaction products are analyzed by gas chromatography using the solvent as internal standard. equipped with a 4 mm MAS (magic angle spinning) probe.

Characterization techniques

GC-FID analysis have been lead on an Agilent Technologies 7890A instrument equipped with a ZB-1 column (60 m x 0.32 nm x 5.0 μm, Zebron Phenomenex).

ICP-OES analyses have been lead on an Activa instrument from Horiba Jobin Yvon. Prior to a analysis, POPs were dissolved in a H 2SO4/HNO3 solution heated at 450°C.

FTIR spectra have been recorded with a Nicolet Magna IR 550 FTIR spectrometer (Thermo Fisher Scientific) in diffuse reflection (64 scans). Prior to analysis, the samples were grinded in KBr.

General conclusion

Two types of porous heterogeneous macroligands have been presented in this work: This result is the same order of magnitude as its homogeneous counterpart Ni(bpy)Cl2 with 26 207 mmol oligomers .mmol Ni -1 .h -1 and a butene selectivity of 92%, tested in with the same conditions. However, further investigation is ongoing to evaluate the activity of ill-defined active sites in Ni@UiO-67-bpy catalysts.

MOF

Outlooks

Bpy-MP-1 and Bpy-MP-2 proved to be efficient catalysts for ethylene oligomerization and both materials offer structure versatility that can be used to improve catalysts MP-1-NH2 POP was synthesized during the course of this thesis. It has to be characterized by nitrogen physisorption measurement (to evaluate its porosity towards nitrogen), IR spectroscopy (to evaluate the presence of NH2 grafting sites) and ICP-OES (to evaluate the amount of Pd that can remain within the framework). [87] A Ni(PyCHO)Cl2 complex was grafted by imine condensation within the framework and the synthesized catalyst has to be characterized by nitrogen physisorption measurement and ICP-OES. Theoretically, a Ni loading of 6.33wt% was obtained. However, the formed catalyst, analogous to the one obtained with (Fe)-MIL-101-NH2, exhibited a TOF of 1 093 mmololigomerss.mmolnickel -1 .h -1 and a butene selectivity of 94% when used for ethylene oligomerization at 25°C with an ethylene Concerning Phos-MP-3 materials, Ni infiltration can be improved either by modifying the synthesis condition like the solvent ratio to increase the amount of mesopores and improve the coordination of Ni complexes on phosphine sites or by modifying the phosphine monomers that are used for the synthesis. Therefore, to keep the phosphine's bulkiness and its ability to coordinate nickel(II) chloride complexes, tris(4-bromophenyl)phosphane can be vinylated (according to a modified procedure literature) and used for radical polymerization. [153,154] Finally, Mashima et al. proposed in 2014 the synthesis of an organic (salt-free) reductant (1,4-Bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadienes) that enables to obtain lowvalent transition metals. This reductant was successfully synthesized and will be tested for 201 ethylene oligomerization in molecular catalysis, before being applied under heterogeneous conditions with MOF and POP catalysts.

Thus, the development of novel macroligands based on POP is still at its infancy and clearly benefits from their high synthetic versatility and is only limited by our ability to prepare the targeted monomers for both metal coordination and side-functionality driving textural properties.

Appendix of Chapter 1

Metal-Organic Frameworks

MOFs are porous hybrid structures with an organic part (the linkers) and an inorganic part (the Secondary Building Units, SBUs). They have been developed for the first time by

Robson et al. in 1989. [180] They are a sub-class of Porous Coordination Polymers (PCPs) or also called Porous Coordination Networks (PCNs), a class of material where the repetition unit is a metallic ion coordinated to multidentate organic components. [START_REF] Corma | Llabrés i Xamena[END_REF] The organized structure of the MOFs is formed by a self-assembly process from a mixture of ionic compounds: a metal ion or a metal oxo-cluster that forms the nodes of the structure and polytopic organic molecules, rigid and linking the monomers between them. Hence, the integrity of the organic parts are ensured with covalent bonds whereas the inorganic parts are characterized by ionocovalent ones. [182] This auto-assembly approach enables to tune the size and the volume of the pores. This is linked to the fact that the inorganic parts are characterized by the ability to organize themselves in different dimensions:

-the zero dimension (0D), which is the inorganic cluster or the isolated metallic ion -the dimension one (1D), which is a chain association of SBUs and linkers -the dimension two (2D), which is a superposition of layers -the dimension three (3D), which is an association of polyhedron structures

Since their discovery in 1989, MOFs draw a lot of attention for the versatility of their size, composition, porosity and properties which open many ways of applications:

-for separation, adsorption and gas storage (H 2, CO2, CH4) [183][184][185][186] -for drug encapsulation and delivery [183,[186][187][188][189] -for detecting chemical species (gas, solvents, etc.) by luminescence [183,186,190,191] -for water depollution and toxic products removal [192,193] -for catalysis [START_REF] Corma | Llabrés i Xamena[END_REF]183,186,[194][195][196] Several synthesis pathways can be used for the MOFs:

-solvothermal, by heating from room temperature to around 200°C [197][198][199][200] -microwaves [201,202] -electrochemistry [203][204][205] -sonochemistry [206,207] Organic parts are made of aromatic cycles with terminal carboxylate, phosphonate or sulfate functional groups, facilitating the addition of inorganic components (issued from metallic salts). The latter is characterized by a cationic part bi-, tri-or tetravalent which associated to the linkers, enables to tune the size and the volume of the pores (with a pore diameter below 20 Å for the micropores and above 20 Å for the mesopores). Besides, the aromatic cycles of the linkers can be functionalized with amine, bipyridine, diimine or diphosphine groups by using organic chemistry reactions. As a consequence, the possible combinations between metal nodes (Al, Cr, Fe, Ni, Cu, Zr, etc.) and commercially available linkers (biphenyl-4,4'-dicarboxylic acid, 2-aminoterephtalic acid, benzene-1,3,5-tricarboxylic acid, etc.) enables to design (ideally) an infinite variety of MOF structures. [208] For example, in the case of the UiO series, the Zr6O4(OH)4 octahedron clusters can be bridged by either 1,4benzenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid or 4,4''-p-terphenyldicarboxylic acid leading to respectively UiO-66, UiO-67 and UiO-68, with different surface areas (ranging from 1 580 to 2 500 m 2 .g -1 ) and window openings (from 6 to 10 Å). [125,128] The same logic applies for:

-the IRMOF series, where octahedral Zn-O-C clusters are associated with different ditopic carxoylate linkers in order to yield IRMOF-2 to 16 (with pore size ranging from 3.8 to 28.8 Å) [209] -a series where each MOF among four types of porous two-dimensional layers of copper(II) dicarboxylate are put into reaction with a triethylenediamine linker between the layers, yielding three-dimensional porous coordination polymers [210] -the MIL-88 series, with trimers of iron(III) or trimers of chromium(III) that are each associated with three different dicarboxylate groups in order to extend the pore size (from 14.5 to 27.5 Å) [211] -the MOF-69 series, where different metal centers (Zn, Pb, Co, Cd, Mn and Tb) are associated with different carboxylate linkers, in different modes [212] However crystalline and made of rigid organic parts, MOFs are flexible structures with pivotal points at the junction point of the SBUs and the linkers, in addition to the free rotation of the aromatic cycles around the axe of the carboxylate-carboxylate bond (phosphatephosphate or sulfate-sulfate). This flexibility of the MOFs decreases its reticular energy (which is the energy required to decompose a mole of a crystal solid into its gaseous components) and facilitate the adsorption of gas and solvents within its structure.

When MOFs are synthesized and already contain the catalytic active site, they can be qualified of MOFs obtained by a One-Pot Synthesis (OPS). This one-step synthesis enables to quickly obtain the needed MOF, after washing and drying. This type of MOFs are opposed to those obtained by Post-Synthetic Modification (PSM), which consists on introducing active sites within the structure of a MOF by simple organic reactions. This expression has been used for the first time to describe the possibility to exploit the organic components of the MOFs. [213,214] This approach enables to control the number of chemical functions to introduce inside the crystalline structure of the MOF, without affecting its stability.

Furthermore, since obtaining optimal crystallinity for a MOF already represents a challenge, introducing catalytic active sites by OPS can affect the structure of the final MOF. Therefore, PSM is a powerful tool to obtain isolated active sites. However, as it has been described, different ways exist to modify the properties of a MOF by PSM and a proposed classification consists on identifying the type of bond involved in the modification: [214,215] -covalent PSM -PSM by coordination chemistry or metalation -Post-synthetic deprotection PSM enables on one hand, to obtain new functionalities within a MOF by using organic reactions (nucleophilic addition or substitution, metal coordination, etc.), but on the other hand, it is required that the reaction conditions do not deteriorate its crystallinity, porosity or initial structure. To improve MOF's porosity without affecting its crystallinity, acid modulators are used during the synthesis to add defects within the structure. [94,[216][217][218][219][220] The diversity of structures that be can be obtained with MOFs, added to a well-defined porous structures makes them reliable candidates as macroligands for heterogeneous catalysis purposes. [124] Despite their numerous advantages, MOFs also present some stability issues: the coordination bonds between the metal clusters and the linkers can be degraded due to chemical, thermal, photolytic, radiolytic, electronic and chemical stimuli, as Feng et al.

thoroughly described in their review. [208] Given conditions can affect MOFs' crystallinity and porosity. This study completes Low et al. hydrothermal stability testings of different MOFs (MOF-5, HKUST-1, Al-MIL-101, etc.). [221] At high temperatures, the hydration of the coordination bond between the metal cluster and the linker can lead to its dissociation, resulting in structural transformation (loss of crystallinity and surface area) of the initial MOF.

In addition to the design of a MOF macroligand (for catalytic purposes), particular attention phenyl rings. This spatial dilution prevents active sites from aggregating and interacting between them, possibly leading to catalyst deactivation.

The porous network of the POPs and their swelling behavior facilitate the accessibility of active sites for the reaction substrates. [75,224] The swelling behavior is often observed when physisorption measurements (with nitrogen or solvents) are performed and is observable by the difference between the adsorption and the desorption branches for a given material.

The different features, strengths and drawbacks of PMOs, MOFs, COFs and POPs have been summed up in the following table (

L

  'hétérogénéisation de complexes moléculaires permet d'établir une passerelle entre catalyse homogène et catalyse hétérogène afin de conserver les activités catalytiques et les sélectivités obtenues en catalyse homogène tout en obtenant des sites actifs isolés. Durant ce travail de thèse, deux types de supports poreux, les Metal-Organic Frameworks (MOFs) et les Polymères Organiques Poreux (POPs) présentant des sites de coordination bipyridyl ont été synthétisés et caractérisés : le MOF UiO-67-bpy et les POPs Bpy-MP-1, Bpy-MP-2 et Bpy-MP-3. Les sites bipyridyl au sein de leur structure ont servi de site de coordination pour des cations Ni(II) afin d'obtenir des sites actifs isolés. Différents taux de complexes de chlorure de nickel(II) ont été testés. Les catalyseurs synthétisés à partir du MOF UiO-67-bpy ont donné des sites actifs non-contrôlés. Une série de catalyseurs avec différents taux de nickel ont été synthétisés à partir de Bpy-MP-1 et Bpy-MP-2 et ont été caractérisés. Pour les catalyseurs obtenus à partir de Bpy-MP-1, les sites bipyridyls au sein de la structure sont coordinnés par le chlorure de nickel(II). Cependant, les traces de Pd retrouvées dans les matériaux Bpy-MP-1 et Bpy-MP-2 et liées à leur méthode de synthèse par couplage C-C catalysée au Pd peut entraîner des réactions secondaires, des interactions entre sites actifs de Pd et de Ni et causer la désactivation du catalyseur.

À

  partir de ce dernier résultat, un MOF le MOF-808-DPPB et un POP, le Phos-MP-3, tous deux avec des sites phosphine, et non plus bipyridyl, ont synthétisés et caractérisés. La capacité de ces macroligands à oligomériser sélectivement l'éthylène, et non le polymériser est en cours d'évaluation, avec des résultats préliminaires prometteurs. Ce travail met en valeur le potentiel des solides poreux, tels que les MOFs et les POPs d'être utilisés en tant que macroligands pour hétérogénéiser des complexes moléculaires, comme il a été montré pour des complexes à base de Ni actifs pour l'oligomérisation de l'éthylène.

Chapter 1 :Chapter 2 : 2 . 1 Chapter 3 : 3 . 1 Chapter 4 : 4 . 1 Chapter 5 :

 12213314415 Abbreviations .........................................................................................................................

3 .MP- 3 ,MP- 3 ,

 333 The first chapter of this thesis work presents the stakes of ethylene oligomerization from an industrial and mechanistic point of view. It starts from the analysis of the well-known homogeneous catalysts that enabled to understand the mechanisms of this reaction and continues with the description of applied heterogeneous porous macroligands for ethylene oligomerization, classified according to their synthesis pathways. All these studies settles milestones in the understanding of the catalytic reaction occurring within the pores and establish the starting point for the present work. The second chapter is focused on the synthesis and the characterization of the different Metal-Organic Framework-based and Porous Organic Polymer-based bipyridyl macroligands that were used during the course of this thesis: UiO-67-bpy, Bpy-MP-1, Bpy-MP-2 and Bpy-MP-From the ill-defined active sites that were obtained with UiO-67-bpy upon Ni complexes metalation, continues with Bpy-MP-1 and Bpy-MP-2 synthesized by a Pdcatalyzed pathway and concludes with the design of a new type of porous macroligand: Bpywith a hierarchical porous structure that enables the immobilization of molecular complexes and without ill-defined active sites. The third chapter of this thesis work is focused on testing the different catalysts described in chapter 2 for ethylene oligomerization under mild conditions (25°C and 30 bars of ethylene continuous feed in toluene). A preliminary study in molecular catalysis enabled to set the catalytic conditions, the TOFs and selectivity goals that were to be achieved during the course of this thesis. UiO-67-bpy-based catalysts were tested in those set conditions for ethylene oligomerization. Afterwards, Bpy-MP-1, Bpy-MP-2 and the new macroligand Bpy-MP-3-based catalysts were compared. Bpy-MP-3-based catalysts offered competitive TOFs and butene selectivities but was also active for ethylene polymerization. The chapter ends on trying to understand the origin of ethylene polymerization and how it can be circumvented with phosphine ancillary ligands. The fourth chapter describes two macroligands, MOF-808-DPPB and the POP Phosbearing phosphine anchoring sites instead of bipyridyl sites. Their synthesis and characterization are described as well as their catalytic application for ethylene oligomerization after Ni infiltration. The promising results obtained open new perspectives for the development of phosphine-based macroligands based on POP materials. The chapter 5 gathers experimental details and the chapter 6 gives a brief outlook and perspectives of this work.

Figure 1 :

 1 Figure 1 : Linear products obtained by oligomerization of ethylene

Figure 3 :

 3 Figure 3 : Activation of metal-halide-based complex with an alkyl-aluminum activator

Figure 4 :

 4 Figure 4 : Correlation between the Cl/Al ratio, the Lewis acidity of different alkyl-aluminum activators, the alkylating strength and the catalytic activity observed for ethylene

Figure 5 :

 5 Figure 5 : Cossee-Arlman mechanism for a halide metallic center activated with a Et2AlCl cocatalyst

Figure 6 :

 6 Figure 6 : Metallacycle mechanism for ethylene oligomerization

Figure 7 :

 7 Figure 7 : SHOP catalyst with different groups that enable to tune its activity and selectivity (adapted from Kuhn et al. and Olivier-Bourbigou et al.)[START_REF]Conférence à l'Académie Des Sciences -H. OLIVIER-BOURBIGOU -De La Conception Des Catalyseurs à Leurs Applications Industrielles En Pétrochimie[END_REF]40]

Figure 8 :

 8 Figure 8 : Titanium-based catalyst developed by Fujita et al. and affording 92.3 wt% of hexene after activation with 10 000 equivalents of MAO

Figure 11 :

 11 Figure 11: Dimersol reactors (1) associated with the Difasol reactors (3) after a vaporization/condensation process (2) (adapted from Olivier-Bourbigou et al.)[53]

. 5

 5 Literature overview of the MOFs and POPs used for ethylene oligomerization A comparison work of the different MOFs that have been used and developed for the ethylene oligomerization through the years, along with the techniques (One-Pot Synthesis (OPS), Post-Synthetic Modification (PSM), etc.) in order to tune them would be provided. It is based on the different catalysts' synthetic pathways, to highlight the challenges and the comprehension brought by these publications for the phenomena occurring within the porous macroligands. To the best of our knowledge, only one work has been published concerning the use of an immobilized Ni(II) complex within a bipyridine-based POP for ethylene oligomerization by Lee et al., the results provided by the authors would be compared to those obtained with the MOFs.

Figure 16 :

 16 Figure 16: Nickel-based MOFs synthesized: a) CPO-27(Ni) ; b) [Ni(bdc)(dabco)] n ; c) [Ni3(ndc)3(DMF)2((CH3)2NH)2]n ; d) [Ni(bdc)(dabco)0.5]n ; e) DUT-8(Ni), rigid and flexible ; f) DUT-128

  Ni active sites and observe its catalytic activity. The ethylene oligomerization experiments were performed in toluene during ten minutes, the catalysts being activated with MAO (between 660 and 19 900 equivalents), under 30 bars of ethylene and at 35 °C.

Figure 17 :

 17 Figure 17: Representation of the ethylene oligomerization TOF (top), of the MAO equivalents used (in toluene, at 35 °C and 30 bar of ethylene) (middle) and of the butene selectivity (bottom) with ZIF-8, four different catalysts obtained from ZIF-8 and exhibiting different nickel loadings (0.08, 0.20, 0.40 and 0.70 wt%) and Ni-ZIF-8@ZIF-8[82]

  of three additional catalysts to Ni(30%)-MFU-4l (Figure 18): Ni(10%)-MFU-4l, Ni(3%)-MFU-4l and Ni(1%)-MFU-4l.

Figure 18 :Ni-CFA- 1

 181 Figure 18: Representation of the soaking time effect of MFU-4l in a Ni(NO3)2•6H2O/DMF solution on the number of Zn 2+ replaced by Ni 2+ (top), of the nickel loading on the ethylene oligomerization TOF (led in toluene, at 25 °C and 50 bars of ethylene and activated with 500 equivalents of MAO) (middle) and on the butene selectivity (bottom)

Figure 19 :

 19 Figure 19 : Representation of how the H 2bibtz (1H,1'H-5,5'-bibenzo[d][1,2,3]triazole)) linker and the H 2BTDD linker, used respectively to synthesize CFA-1 and MFU-4l enable to obtain the same scorpionate-like configuration with three coordinating nitrogen atoms embedded within the MOF structure.

Figure 20 :

 20 Figure 20: Ethylene oligomerization catalytic results obtained with Ni-AIM-NU-1000, Ni-Facac-AIM-NU-1000 and Ni-Acac-AIM-NU-1000 in a packed reactor under continuous flow of 100% ethylene gas feed at 2 bar and 45 °C, activated with Et 2AlCl

  that, up to a certain Ni loading, the reaction is not limited by diffusion. No catalytic activity could be observed with only (Fe)-MIL-101-NH2 or with (Fe)-MIL-101-NH2 put into solution with either NiCl 2 or PyCHO and with the filtrated catalytic solution (leaching experiment) reactivated with Et2AlCl.Catalytic activities of 10Ni@(Fe)-MIL-101 and 30Ni@(Fe)-MIL-101 all originate from the nickel-isolated active sites within the frameworks. Hence, Canivet et al. proved that site isolation can be achieved by PSM of a (Fe)-MIL-101-NH 2 MOF with a Ni(PyCHO)Cl2 complex, in different Ni loadings. However, higher loadings do not necessarily mean higher activities.In this study, the most competitive result was obtained in mild conditions (25 °C and 30 bar of ethylene, with 70 equivalents of Et 2AlCl): 10 455 mololigomers.molNi -1 .h -1 , with a butene selectivity above 90%.

Figure 21 : 101 IRMOF- 3

 211013 Figure 21 : Catalytic experiments led with 15 bars of ethylene at 10°C during one hour and with 70 equivalents of Et2AlCl per nickel, with 10Ni@(Fe)-MIL-101 and 30Ni@(Fe)-MIL-101

Figure 22 :

 22 Figure 22: Textural and catalytic activity comparison between the MixMOFs-based, IRMOF-3-based and (Fe)-MIL-101-based catalysts

1 . 5 . 5

 155 same as Canivet et al. and Liu et al.: an imine-like anchoring site coordinating Ni(II)X2 complex (with X = Cl or Br). However, Chen et al. borrowed a different synthetic pathway by synthesizing the MIL-125(Ti)-NH2 MOF, post-synthetically modifying it with a 2-pyridinecarboxaldehyde monomer and then metalating the imine-like site with NiCl2•6H2O. For the same catalytic active site, another macroligand, other than (Fe)-MIL-101-NH2, Mix-MOF or IRMOF-3, is tested for ethylene oligomerization. Ethylene oligomerization performances were performed in cyclohexane, with 800 equivalents of MAO, at 50 °C and under 10 bar of ethylene, during 30 minutes. They achieved a catalytic activity of 1.81 x 10 5 goligomers.molNi -1 .h -1 with a butene selectivity of 19.6 wt% (87.2 wt% of 1-butene). Isolating active sites with materials containing the coordination site (route E) [Al]-Ni-bpydc (MOF) and [Ni]-Ni-bpydc (MOF) Kyogoku et al. initiated the research in 2010 with two MOFs: [Al]-Ni-bpydc (MOF) and [Ni]-Ni-bpydc (MOF). [92] They were respectively synthesized by One-Pot Synthesis of Al(NO 3)3•9H2O with a Ni-bipyridyl-dicarboxylic acid in DMF and of Ni(NO3)2•6H2O with bipyridyl-dicarboxylic acid. Ethylene oligomerization tests were conducted in heptane, at 5 °C during one hour, under 15 bar of ethylene, the catalyst being activated with 70 equivalents of Et 2AlCl. [Al]-Nibpydc (MOF) and [Ni]-Ni-bpydc (MOF) respectively exhibited a 21 goligomers.gcatalyst -1 .h -1 TOF and a 13.4% conversion, with respective selectivities in butene of 89.1% and 92.7%. Ni@UiO-67-bpy Later, in 2017, Gonzalez et al. proved that site dilution within a porous framework enables to improve diffusion of the reagents and the substrates towards the active sites and of the products off the porous framework. The authors synthesized a UiO-67 framework (Zr6O4(OH)4(bpdc)6, with bpdc 2-for biphenyl-4,4'-dicarboxylate) and two UiO-67-bpy frameworks with different amounts of bipyridyl sites (Zr6O4(OH)4(bpydc)6 and

  84(bpdc)5.16 bipyridyl sites are diluted with biphenyl linkers within the framework, compared to Zr 6O4(OH)4(bpydc)6 that only contains bipyridyl sites.Afterwards, they metalated each material with Ni(DME)Br2 (DME for dimethoxyethane), with 1.0 equivalent per bpydc 2-and ICP-OES analysis enables to confirm that all the bipyridine sites of the UiO-67-bpy materials were coordinated by NiBr 2 . More surprisingly, the UiO-67 material, containing no bipyridyl coordinating sites, turned to contain 2.30% Ni for each Zr center (obtained by ICP-OES, which would represent 0.06 wt% of Ni for this catalyst), despite several washings with dimethoxyethane in order to remove any physisorbed Ni complex. Authors assumed that Ni got coordinated to water and hydroxide ligands filling in vacant linker sites on zirconium clusters. Three catalysts were synthesized, with three different amounts of bipyridyl sites and hence, three different loadings of nickel (Figure23): Zr6O4(OH)4(bpydc)6(NiBr2)6 (100% of bipyridyl linkers, all nickel coordinated, wt%(Ni) = 1.72%), Zr 6O4(OH)4(bpydc)0.84(bpdc)5.16(NiBr2)0.84 (14% of bipyridyl linkers, all nickel coordinated, wt%(Ni) = 0.36%) and Zr6O4(OH)4(bpdc)6(NiBr2)0.14 (only biphenyl linkers, wt%(Ni) = 0.06%).

Figure 23 :

 23 Figure 23 : Metalation procedure of UiO-67, UiO-67(bpy14%) and UiO-67(bpy100%) with Ni(DME)Br2

  Metalation was done afterwards by placing the bpy-based POP in a mixture of NiCl2•H2O dissolved in DMF, to achieve a Ni(II)-POP-1 catalyst. Ethylene oligomerization experiments were performed in heptane, with 70 equivalents of Et 2AlCl during one hour, at 20 °C and under 20 bar of ethylene. Ni(II)-POP-1 achieved a catalytic activity of 1 198 mol oligomers .mol Ni -1 .h -1 , with a selectivity in butene of 54%. Like previously for Gonzalez et al., polyethylene was observed to be formed around the POP particles (further discussions will be presented in part 1.7, where the recycling experiments are analyzed).

  synthesized: two Covalent Triazine Frameworks (CTFs), one with a microporous structure and another one with a mesoporous one, and one Imine-Linked Porous Organic Network (IL-PON). CTFs exhibit triazine-anchoring sites, which proved to be active in ethylene oligomerization, whether it is in homogeneous conditions with Brookhart et al. and Gibson et al., or in heterogeneous conditions with Metzger et al. Two different synthetic pathways were used for the synthesis of the three PAFs: for the IL-PON PAF and by ionothermal synthesis, with, on one hand 2,6-pyridinecarboxaldehyde and ZnCl 2 to obtain microporous CTF (microCTF) and on the other hand, 2,6-pyridinecarboxaldehyde with 4,4'-biphenyldicarbonitrile and ZnCl2 to synthesize mesoporous CTF (mesoCTF). Not only ZnCl2 acts as a catalyst for the trimerization of the monomers but also as a template.

  recovered the catalyst for two more cycles and, each time, washed it with dichloromethane before activating it under super critical CO 2 . Despite the fact that the catalyst remained active for ethylene dimerization, polyethylene continued to cover Ni(II)-POP-1 particles during each cycle, hampering the accessibility of the active sites and hence, decreasing the activity. Finally, in 2019, Gonzalez et al. observed that the ethylene consumption of the molecular catalyst [NiCl 2(bpy)] and of the MOF [Ni3(ndc)3(DMF)2((CH3)2NH2]n (with ndc = 2,6-naphtalenedicarboxylate) (with 10 bars of ethylene at 21°C, in toluene, with 17 eq. of Et 2AlCl, during one hour) gradually increased in the first minute of each cycle of a five-cycle

Figure 25 :

 25 Figure 25 : Activity comparison between heterogeneous catalysts and their homogeneous counterpart: Lee et al. experiment conditions with 20 bars of ethylene at 20°C, in anhydrous heptane, with 70 eq. of Et 2AlCl, during one hour; Kaskel et al. experiment conditions with 10 bars of ethylene at 21°C, in toluene, with 17 eq. of Et2AlCl, during one hour; Madrahimov et al. experiment conditions with 15 bars of ethylene at 21°C, in heptane, with 70 eq. of Et2AlCl, during one hour; Canivet et al. experiment conditions 15 bars of ethylene at 10°C, in heptane, with 70 eq. of Et2AlCl, during one hour a 2,2'-bipyridyl nickel(II) dichloride complex b [Ni3(ndc)3(DMF)2((CH3)2NH2]n and DUT-8(NI)_rigid MOFs (with ndc = 2,6-naphtalenedicarboxylate) respectively achieved 59 and 41 mmol ethylene.mmolNi -1

  They synthesized the POPs by Sonogashira coupling in stoichiometric amounts of polyethynyl tectons (1,3,5-triethynylbenzene for Bpy-MP-1 and tetrakis(ethynyl-phenyl)methane for Bpy-MP-2) and halogenated tectons (5,5'-dibromo-2,2'bipyridine and 4,4'-diiodo-biphenyl). Compared to other polymerization techniques of POPs (Friedel-Crafts, alkyne trimerization, etc.), this stoichiometric approach with Sonogashira coupling, introduced by Thomas et al., enabled to avoid unwanted side reactions (like homocoupling of the tectons), access porous frameworks with high porosity and allow Rh infiltration afterwards, by PSM (see Appendix of Chapter 1

Figure 26 :

 26 Figure 26 : Bpy-MP-1 and Bpy-MP-2 based catalysts synthetic pathways

  Synthesis or Post-Synthetic Modification the bipyridyl anchoring site inside a MOFbased, COF-based or POP-based macroligand, coupled with a Ni(II)X 2 complex (X = Cl or Br), the resulting catalysts proved to be active for ethylene oligomerization and selective towards butene. The goal of this chapter is to present the different bipyridyl-based macroligands (MOFs and POPs) that have been synthesized and characterized, in order to infiltrate molecular Ni complexes within their porous network to get heterogenized Ni(bpy) sites and use them afterwards for ethylene oligomerization.

each

  Zr are linked by μ 3 -O and μ 3 -OH bridges. The general formula is Zr6(μ 3 -O)4(μ 3 -OH)4(linker)12, the linker part resulting from 1,4-benzenedicarboxylic acid, 4,4'biphenyldicarboxylic acid and 4,4''-p-terphenyldicarboxylic acid, respectively for UiO-66, UiO-67 and UiO-68 (Figure 27). Because of the different linker size, the access to the internal surface area is determined by the triangular window opening respectively of 6, 8 and 10 Å.

Figure 27 :

 27 Figure 27 : Representation of Zr 6O4(OH)4 octahedral clusters for UiO-66, UiO-67 and UiO-68 with the corresponding linkers, respectively 1,4-benzenedicarboxylic acid, 4,4'biphenyldicarboxylic acid and 4,4'-p-terphenyldicarboxylic acid

Figure 29 :

 29 Figure 29 : UiO-67-bpy synthesis procedure

  In the general formula Zr6(μ 3 -O)4(μ 3 -OH)4(bpdc)a(bpydc)b of a UiO-67-bpy-based material, a and b (the molar amounts of bpdc and bpydc within a node) are obtained by multiplying respectively x % and y % by 6. A TGA analysis has to be done to determine the ratio between Zr and the total amount of linkers.

Figure 30 : 1 H

 301 Figure 30: 1 H NMR spectra resolution of dissolved UiO-67 in DCl/DMSO mixture in order to determine the experimental amount of each linker in the pristine material

Figure 31 :

 31 Figure 31 : PXRD diffractograms of as-synthesized UiO-67 and four UiO-67-bpy-based materials with different amounts of bipyridyl sites compared to the theoretical pattern of UiO-67 from CCDC-960486 (each diffractogram was normalized with respect to the highest peak at 5° of 2θ)

-

  each adsorption site can only be occupied by one adsorbed molecule -no lateral interaction occurs between adsorbed molecules -adsorption occurs on a non-porous flat surface and is complete when a single layer of molecules is formed Equation 3 : Langmuir equation with p the absolute pressure of adsorbent molecules, V a the volume of adsorbed gas (in cm 3 (STP).g -1 ), V m the micropore volume (in cm 3 (STP).g -1 ) and B the ratio between adsorption constant ka and the desorption constant kd When is plotted against p, a linear plot is obtained for a microporous material exhibiting a type I isotherm. The slope of the approximate curve and the intercept enable to access respectively to V m and B. The monolayer volume (V m ) obtained is the micropore volume of the material. The Langmuir model enables to describe materials giving a type I isotherm, like for the UiO-67-based materials. The linear plots that have been obtained for the materials are represented in the Appendix of Chapter 2 (Figure 106), supporting the fact that highly microporous materials have been obtained.

Figure 32 :

 32 Figure 32 : Nitrogen physisorption isotherms at 77 K of a UiO-67 material and four UiO-67bpy-based materials with different amounts of bipyridyl sites (desorption isotherms for UiO-67-bpy-(100%) and UiO-67 have not been plotted during the measurement)

  Langmuir's theory for each layer of adsorbed molecules in this multilayer theory. The equation obtained from this theory enables to access the specific surface area of the material, i.e. the total surface area of the material per mass unit (in m 2 .g -1 ). The equation has been determined based on different hypotheses:-adsorption occurs on several layers and each layer acts as an adsorption site for the next layer : hence, spatial defects between adsorption sites, at molecule scale, are neglected -the top molecule layer is in equilibrium with the gas phase, hence the adsorption rate is equal to the desorption one -no lateral interaction occurs between adsorbed molecules -different adsorption energies are considered : E 0 for the adsorption of the first layer on the bare surface 74 E1 for the adsorption on the first layer already adsorbed E 2, E3, etc. for the adsorption on the second layer and all higher layers. These energies are equal to the condensation energy E L of the adsorbent -adsorption is complete when the saturating vapor pressure of the adsorbent is reached and the thickness of the molecule layer is supposed to be infinite These different hypotheses enabled the authors to establish the BET equation (Equation4) and hence, calculate the BET specific surface area: Equation 4 : BET equation with Vads the adsorbed volume (in cm 3 (STP).g -1 ) , Vm the monomolecular layer adsorption volume (in cm 3 (STP).g -1 ), C a coefficient linked to the heat of adsorption, p the absolute pressure (bar) and p 0 the saturating vapor pressure of the adsorbent (bar) Due to the different hypotheses, the BET theory provides a relevant description only in the relative pressure range p /p 0 of 0.05 and 0.35: below 0.05 the adsorption occurs on a heterogeneous surface and not on a non-porous flat one and above 0.35 the adsorbed amount is limited (and not infinite).

Equation 5 :

 5 Binding site occupation (BSO) (%) calculation from the wt%(Ni) (%) obtained by ICP-OES, the molecular weight of the considered MOF MW(MOF) (in g.mol -1 ), Ni molecular weight MW(Ni) (in g.mol -1 ) and the molar rate of bipyridyl sites in the considered MOF mol%(bpy) (%) Bipyridyl site dilution might reduce transport limitations that can occur within the micropores of a framework during catalytic reactions and might prevent saturation of active sites. Site dilution can be done by tuning the amount of anchoring sites and enables to control the maximum amount of bipyridyl sites that can be coordinated upon metalation. However, Gonzalez et al. proved the ability of the UiO-67 material to chemisorb (on the Zr clusters) or physisorb (within the pores) Ni complexes: further investigation has to be done to evaluate the maximum amount of nickel complexes that a UiO-67 material can retain without coordinating sites (like bipyridyl sites), since uncontrolled active sites can cause side reactions. UiO-67-bpy(64%) and UiO-67-bpy(68%) exhibit a higher ratio of anchoring sites per catalyst mass compared to UiO-67-bpy(5%) and UiO-67-bpy(10%). Like, Gonzalez et al. proved by synthesizing the mixed-linker Zr 6O4(OH)4(bpydc)0.84(bpdc)5.16(NiBr2)0.84 catalyst, site dilution enables to obtain more uniformly dispersed nickel(II) active sites.

Figure 34 :

 34 Figure 34 : Nitrogen physisorption isotherms at 77 K of four Ni@UiO-67-bpy-based catalysts with different loadings of nickel

Figure 37 :

 37 Figure 37 : FTIR spectra of Bpy-MP-1 and Bpy-MP-2 (each spectra has been normalized with respect to the absorbance peak at 820 cm -1 )

  the case of Bpy-MP-1-based materials, three different materials have been synthesized (Figure38): a Full-Bpy-MP-1 material, synthesized by Sonogashira coupling of 1,3,5-triethynylbenzene and 5,5'-dibromo-2,2'-bipyridyl monomers ; a Bpy-MP-1 material, synthesized according to the synthesis described before ; and a MP-1 material, synthesized by Sonogashira coupling of 1,3,5-triethynylbenzene and 4,4'-diiodobiphenyl monomers.

Figure 38 :

 38 Figure 38 : MP-1, Bpy-MP-1 and Full-Bpy-MP-1 synthesized by Sonogashira coupling

Figure 39 :

 39 Figure 39 : 13 C multi CP MAS NMR spectra of Full-Bpy-MP-1 (top), Bpy-MP-1 (middle) and MP-1 (bottom) (adapted from a previous work realized within our research group). Asterisks (*) and hashes (#) enable to respectively designate spinning side bands and impurities

Figure 40 :MP- 2 materials

 402 Figure 40 : Nitrogen physisorption isotherms at 77 K of a microporous Bpy-MP-1 and Bpy-MP-2 materials

Figure 42 :

 42 Figure 42 : BJH plot of Bpy-MP-1 and Bpy-MP-2 material calculated from the desorption isotherm and based on a GCB model

Figure 43 :

 43 Figure 43 : Toluene physisorption measurements of pristine materials Bpy-MP-1 and Bpy-MP-2 at 25°C

From

  the large-scale batches of Bpy-MP-1 and Bpy-MP-2, catalysts with varying weight percentages of Ni were synthesized. Ni infiltration into the materials was performed according to the same procedure as for the UiO-67-bpy-based materials. The NiCl2•glyme is dissolved in an anhydrous methanol solution before being put into stirring with 100 mg of POP at 60°C. Six different amounts of Ni were targeted : 0,29 wt% ; 1,04 wt% ; 2,04 wt% ; 2,99 wt% ; 4,13 wt% ; 4,99 wt%. The exact amounts of Ni were determined by ICP-OES analysis. Furthermore, a linear correlation could be established for POP materials between the Ni amount determined by ICP-OES analysis and the one determined by X-fluorescence analysis. The establishment of this correlation will be described later in this work.At first, porosity of the different catalysts towards nitrogen have been evaluated. For the sake of reading, only the nitrogen physisorption isotherms of the pristine material (made from the combination of three batches), the catalyst with the lowest and the highest loading have been represented: Figure44and Figure45for respectively Bpy-MP-1 and Bpy-MP-2 pristine materials and resulting catalysts. All the other catalysts nitrogen physisorption isotherms are represented in Appendix of Chapter 2 (Figure112and Figure113).

Figure 44 :

 44 Figure 44 : Nitrogen physisorption isotherms at 77 K of the obtained Bpy-MP-1 mixed batches and two resulting nickel infiltrated Bpy-MP-1 catalysts

Table 9 : 98 Figure 45 :

 99845 Figure 45 : Nitrogen physisorption isotherms at 77 K of the obtained Bpy-MP-2 mixed batches and two resulting nickel infiltrated Bpy-MP-2 catalysts

Figure 46 : 1 and

 461 Figure 46 : Toluene physisorption measurements at 25°C of pristine materials Bpy-MP-1 and Bpy-MP-2 compared to the toluene isotherms of 1.70wt%Ni@Bpy-MP-1 and 0.45wt%Ni@Bpy-MP-2 catalysts

Figure 47 :

 47 Figure 47 : (left) 13 C ComPmultiCP MAS NMR spectra of Bpy-MP-1 and Ni@Bpy-MP-1 catalysts with varying amounts of nickel ; (right) correlation between bpy occupancy determined by 13 C ComPmultiCP MAS NMR and the nickel loading in weight percent measured by ICP-OES (figures adapted from Mohr et al.)[135]

Figure 48 :

 48 Figure 48 : (left) IR spectra between 2400 and 1400 cm -1 of Ni@Bpy-MP-1 catalysts with varying amounts of nickel ; (right) linear correlation between the normalized intensity of the C-H band at 1453 cm -1 and the nickel loading of the corresponding Ni@Bpy-MP-1 catalyst (adapted from Mohr et al.)[135]

  a, top). After PTLC purification, no traces of triphenylphosphine remains (Figure 50 b, middle) at 7.5 ppm. Pd traces is supposed to be removed since after PTLC purification a white solid is obtained, compared to the pale yellow solid obtained as crude product. Removal of Pd will be confirmed later by ICP-OES analysis. The monomer needs to be stored under argon and at low temperature to prevent it from oligomerization (Figure 50 c, bottom).

Figure 50 :

 50 Figure 50 : 1H NMR spectra resolution of 5,5'-divinyl-2,2'-bipyridyl at three distinct stages : a) before work-up (top) ; b) purified by PTLC (elution with 35:70:1 petroleum ether/CH2Cl2/NEt3) (middle) ; c) after more than a week left at room temperature (bottom)

Figure 51 :

 51 Figure 51 : Schemes of azobisisobutyronitrile (AIBN), 1,1'-azobis(cyclohexanecarbonitrile) (ACHN) and 2,2'-azobis(2-methylpropane) (ATTN) radical initiators

Figure 53 :

 53 Figure 53 : Nitrogen physisorption isotherms at 77 K of the obtained for Bpy-MP-3 (ACHN) and Bpy-MP-3 (ATTN) materials

Table 10 :

 10 Textural properties of Bpy-MP-3 (ACHN) and Bpy-MP-3 (ATTN) compared to Bpy-MP-1, Bpy-MP-2 and UiO-67 materials, obtained by nitrogen physisorption measurements at 77K a average of four batches b average of three batches On Figure 53, between partial pressure of 0.1 and 0.8, the volume of nitrogen adsorbed increases almost linearly with partial pressure increasing. This textural behavior can be either attributed to a non-porous material or to a material with a hierarchical porous structure. Therefore, Bpy-MP-3 (ACHN) and Bpy-MP-3 (ATTN) were analyzed by the t-plot method,based on a GCB model (Figure54). Two slopes can be observed: the first sharp slope corresponds to the homogeneous filling of the micropores, as it can happen on the flat surface of the model. The second slope corresponds either to the filling up of the mesopores and the macropores or to the filling up of the intergrains.

Figure 54 :

 54 Figure 54 : t-plot of Bpy-MP-3 (ACHN) and Bpy-MP-3 (ATTN) materials based on a Graphitized Carbon Black (GCB) model

Figure 56 :

 56 Figure 56 : Toluene physisorption measurements at 25°C of pristine materials Bpy-MP-1, Bpy-MP-2 and Bpy-MP-3 (ACHN) materials

Figure 58 : 3 (

 583 Figure 58 : Schemes of MP-3 (ACHN), Bpy-MP-3 (ACHN) and Full-Bpy-MP-3 (ACHN)

Figure 59 :

 59 Figure 59 : Nitrogen physisorption isotherms at 77 K of the obtained for MP-3 (ACHN), Bpy-MP-3 (ACHN) and Full-Bpy-MP-3 (ACHN)

Figure 60 :

 60 Figure 60 : 13 C multi CP MAS NMR spectra of Full-Bpy-MP-3 (top), the Bpy-MP-3 (middle) and the MP-3 (bottom). Asterisks (*) and hashes (#) enable to respectively designate spinning side bands and impurities

Figure 61 :

 61 Figure 61 : Nitrogen physisorption isotherms at 77 K of Bpy-MP-3 (ACHN) pristine materials compared to Bpy-MP-3-onlyTHF (ACHN)

Figure 62 :

 62 Figure 62 : BJH plot of Bpy-MP-3 (ACHN) and Bpy-MP-3-onlyTHF (ACHN) materials, calculated from the desorption isotherm and based on a GCB model

Figure 63 :Figure 64 :

 6364 Figure 63 : Nitrogen physisorption isotherms at 77 K of the obtained Bpy-MP-3 (ACHN) mixed batches and two resulting nickel infiltrated Bpy-MP-3 (ACHN) catalysts

Figure 65 :

 65 Figure 65 : Toluene physisorption measurements at 25°C of Bpy-MP-3 (ACHN) and Ni@Bpy-MP-3 (ACHN)

  ) were synthesized. It was proved that Bpy-MP-3based catalysts do not physisorb Ni complexes upon metalation and it is assumed that the Ni complexes that have been infiltrated within the materials are coordinated on the bipyridyl sites 123 Table 15 : Physisorption data and ICP-OES results of the Bpy-MP-3 (ACHN) series catalysts and their pristine material a pristine material made from the combination of four similar batches of Bpy-MP-3 (ACHN) Table 14 : Physisorption data and ICP-OES results of the BpyMP-3 (ATTN) series catalysts and their pristine material a pristine material made from the combination of four similar batches of Bpy-MP-3 (ATTN) . X-fluorescence spectroscopy has been performed for the first time to evaluate the Ni loading within POP-based catalysts, instead of using time consuming and destructive ICP-OES.

  ), Compton scatter is more pronounced than Rayleigh scatter. Due to the matrix effects, intensities obtained for Ni element were normalized by the intensity of the Kβ ray due to Compton scatter within the porous material. By performing this normalization, the effect of the matrix is suppressed on the measured intensities. A calibration curve was established by, first, evaluating the Ni loadings of Bpy-MP-3 (ACHN) by ICP-OES (Table15), second, analyzing them by XRF spectroscopy and third, by plotting the normalized intensity of Ni X-ray emissions by the intensity of the Kβ X-ray emission due to Compton scatter against the wt%(Ni) of the catalysts obtained by ICP-OES (Figure66).

Figure 66 :MP- 1 ,

 661 Figure 66 : Linear correlation between the normalized intensity of Ni X-ray emission by the intensity of the Kβ X-ray emission due to Compton scatter and the loading of nickel within Bpy-MP-3 (ACHN) catalysts, determined by ICP-OES

Figure 67 :

 67 Figure 67 : IR spectra between 2000 and 1300 cm -1 of five Ni@Bpy-MP-3 (ATTN) catalysts with varying amounts of nickel and the pristine material Bpy-MP-3 (ATTN) mixed batches

Figure 68 : 3 ( 3 (

 6833 Figure 68 : IR linear correlation between the normalized intensity of the C-H band at 1450 cm -1 by the CH band at 1466 cm -1 and the nickel loading of the corresponding Ni@Bpy-MP-3 (ATTN) catalysts

Figure 69 : 3 . 131 3. 1

 6931311 Figure 69 : Bipyridyl-based porous frameworks synthesized and characterized during the course of this thesis

(

  with the imine-based Ni@(Fe)-MIL-101 or with Ni@UiO-67-bpy) or in homogeneous catalysis (with nickel oxime complexes or with nickel α-diimine complexes) Unless otherwise stated, all the catalytic tests of this work were performed in a sealed batch reactor, charged with the solvent, the catalyst and the co-catalyst. Ethylene oligomerization led with a continuous feed of ethylene at 30 bars, 25°C during one hour. For these experiments, 10 μmol of nickel and 50 equivalents of Et2AlCl (which represents 0.6 mL of aluminum activator) were used. A minimum amount of aluminum activator (0.6 mL) has been used to obtain an ethylene oligomerization TOF and a butene selectivity comparable with literature and with the aim to minimize the amount of aluminum salt that could remain trapped at the end of the reaction inside the solid catalyst.

Figure 70 :

 70 Figure 70 : GC-FID chromatogram from a typical catalytic ethylene oligomerization run

Figure 71 :

 71 Figure 71 : TOF values for Ni(PPh3)Cl2 and Ni(bpy)Cl2 tested either in heptane or toluene with a continuous feed of ethylene at 30 bars, 25°C during one hour ; 10 μmol of nickel and 50 equivalents of Et 2AlCl were used (0.6 mL of Et2AlCl)

Figure 72 :

 72 Figure 72 : Representation of the molar fraction of saturating ethylene solubilized in each solvent at 1 bar partial pressure of gas for different temperatures

Figure 73 :

 73 Figure 73 : 2,2'-bipyridyl-based ligands bearing different groups

Figure 74 :

 74 Figure 74 : TOF values for a) Ni(bpy)Cl 2 ; b) 6,6'-dimethyl-2,2'-bipyridyl nickel(II) dichloride ; c) 4,4'-dimethyl-2,2'-bipyridyl nickel(II) dichloride ; d) 4,4'-dimethyl-2,2'bipyridyl nickel(II) iodide ; e) 4,4'-ditert-butyl-2,2'-bipyridyl nickel(II) dichloride f) 1,10phenantroline nickel(II) dichloride ; catalytic experiments were done in toluene with a continuous feed of ethylene at 30 bars, 25°C during one hour ; 10 μmol of nickel and 50 equivalents of Et 2AlCl were used

Figure 75 :

 75 Figure 75 : TOF values for a) Ni(bpy)Cl2 ; b) NiCl2•glyme ; catalytic experiments were performed in toluene with a continuous feed of ethylene at 30 bars, 25°C during one hour ; 10 μmol of nickel and 50 equivalents of Et2AlCl were used

Figure 76 :

 76 Figure 76 : TOF values for Ni(PPh3)2Cl2 and Ni(bpy)Cl2 tested in toluene with a continuous feed of ethylene at 30 bars, 25°C during one hour with different amounts of Ni and different equivalents of Et 2AlCl

84 ,

 84 was tested under the following conditions : 59 bar of ethylene, 55 ° C during one hour and with 100 equivalents of Et2AlCl per Ni. The material displayed a fivefold larger activity with respect to our best active system (that is 370 ± 30 gproducts.gcatalyst -1 .h -1 compared to 73 gproducts.gcatalyst -1 .h -1 in our system). The lower TOFs obtained in our case can be explained with the lower ethylene pressure used (30 bars instead of 59 bars) and the lower temperature (25°C instead of 55°C). At the same time, Gonzalez et al. described also the production of polyethylene during the reaction and assigned it to the presence of ill-defined catalytic sites originating from the uncontrolled coordination of Ni complexes on Zr nodes of the UiO-67-bpy-based catalysts.

  POP materials are synthesized by Pd-catalyzed C-C coupling reaction (described in Chapter 2). Before using any nickel-infiltrated bpy-based catalysts and given the fact that Pd traces could be found in the materials, it was necessary to ensure the non-activity of the pristine materials. None of the POPs, put in presence of 0.6 mL of Et 2AlCl (which is the amount used to obtain 150 equivalents of aluminum activator for 3 μmol of Ni), with a continuous feed of 30 bars of ethylene in toluene during one hour at 25°C, oligomerized ethylene. The POP-based catalysts were tested (Ni@Bpy-MP-1, Ni@Bpy-MP-2 and Ni@Bpy-MP-3 (ACHN)) with the purpose to evaluate (i) which macroligand would enable to obtain TOF and selectivities in butene as competitive, if not more, as their homogeneous counterpart, Ni(bpy)Cl 2 and (ii) if there could be any diffusion limitations with increasing Ni loading in each type of catalyst.For all the experiments, the weight of catalyst put into the reactor is based on the theoretical Ni amount, in order to obtain 3 μmol of nickel in the catalysis reaction. Et 2AlCl was used as a co-catalyst and, for each catalyst, it was aimed to introduce 150 equivalents of aluminum activator. A significant deviation can be observed concerning co-catalyst equivalents (112 to 499) because differences were observed between the nominal (expected) Ni loading used to calibrate the polymerization experiments, and the effective ICP-OES determined loading, measured after the oligomerization experiments were performed.

Figure 77 :

 77 Figure 77 : TOFs (in mmololigomers.mmolNi -1 .h -1 ) obtained for the oligomerization of ethylene with Ni@Bpy-MP-1, Ni@Bpy-MP-2 and Ni@Bpy-MP-3 (ACHN) catalysts; the number of aluminum equivalents is indicated beside each point (at 1.6 wt%(Ni), two points are considered with 290 and 474 equivalents)

Figure 78 :

 78 Figure 78 : Butene selectivity obtained for the oligomerization of ethylene with Ni@Bpy-MP-1, Ni@Bpy-MP-2 and Ni@Bpy-MP-3 (ACHN) catalysts

Figure 79 :

 79 Figure 79 : TOF (in gproducts.gcatalyst -1 .h -1 ) for polyethylene and oligomers (C4, C6 and C8), produced with Ni@Bpy-MP-3 (ACHN) catalysts containing different amounts of Ni

Figure 80 :

 80 Figure 80 : DSC thermograms of four different polyethylene batches obtained from a typical run of ethylene oligomerization with a Ni@Bpy-MP-3 catalyst

Figure 81 :MP- 3 ( 1

 8131 Figure 81 : Molecular weight distribution of the polyethylene analyzed by SEC-HT, after a typical run of ethylene oligomerization with a 1.44wt%Ni@Bpy-MP-3 (ACHN) catalyst

Figure 83 : 3 (

 833 Figure 83 : Variation of the number of aluminum equivalents with a 1.61wt%Ni@Bpy-MP-3 (ACHN) catalyst, at 25°C and 30 bars of ethylene in toluene

Figure 84 :

 84 Figure 84 : TOF in gproduct.gcatalyst -1 .h -1 of oligomers and polyethylene, compared at 25°C, with Ni(bpy)Cl 2 and 1.61wt%Ni@Bpy-MP-3 (ACHN) catalysts ran at 30 bars of ethylene, in toluene with 150 equivalents of EtAlCl 2 (left) and Et 2 AlCl (right)

Figure 87 : 3 . 4 . 2

 87342 Figure 87 : Mass selectivities of C4, C6, C8 and polyethylene products, considered at different times with a 1.51wt%Ni@Bpy-MP-3 (ACHN) catalyst, tested at 25°C and 30 bars of ethylene in toluene

3 (

 3 metalation and despite washings, Ni complexes could remain coordinated to the nitrile moieties of the ACHN radical initiator within Bpy-MP-3 (ACHN)-based catalysts. These illdefined active sites can be responsible of uncontrolled side reactions, such as polymerization of ethylene. To test this hypothesis, we have synthesized a bipyridine-free MP-3 (ACHN) material. The resulting Ni@MP-3 (ACHN) material (synthesized with ACHN radical initiator) and one Ni@MP-3 (ATTN) (synthesized with ATTN radical initiator) were obtained. As it was described in chapter 2, Bpy-MP-3 materials can be synthesized either by using the radical initiator 1,1'-azobis(cyclohexanecarbonitrile) (ACHN) or the radical initiator 2,2'-azobis(2methylpropane) (ATTN). In the following part, the resulting catalysts will be named Ni@MP-ACHN) and Ni@MP-3 (ATTN). Therefore, two experiments were performed at 25°C, 30 bars of ethylene in toluene, with 150 equivalents of Et 2AlCl, during one hour.First, Ni@MP-3 (ACHN) material was characterized by using the X-fluorescence correlation and an amount below 0.001 wt% of Ni was find in the material, indicating that no Ni complexes remained physisorbed in the material. This datum suggests that Ni coordination to nitrile moieties, if any, is rather limited.By testing Ni@MP-3 (ACHN) for ethylene oligomerization, 2.87 mmol of oligomers were produced with a selectivity in butene of 98%. No polyethylene traces were found.Compared to NiCl 2•glyme catalyst, that produces 146 mmol of oligomers, Ni@MP-3 (ACHN)

Figure 88 :

 88 Figure 88 : Two-cycle mechanism obtained for ethylene oligomerization activated by Me 3 Al

Figure 89 :

 89 Figure 89 : TOF in gproduct.gcatalyst -1 .h -1 of oligomers and polyethylene, compared at 25°C and 30 bars of ethylene, during one hour in toluene, with a 1.61wt%Ni@Bpy-MP-3 (ACHN) catalyst activated with 150 equivalents of Et2AlCl (left) and 1.41wt%Ni@Bpy-MP-3 (ACHN) catalyst activated with 150 equivalents of Me 3Al (right)

Figure 90 : 3 . 4 . 5

 90345 Figure 90 : TOF in gproduct.gcatalyst -1 .h -1 of oligomers and polyethylene, obtained with three different catalysts: 1.61wt%Ni@Bpy-MP-3 (ACHN) (left), 2.38wt%Ni@Bpy-MP-onlyTHF (middle) and 8.68wt%Ni@Full-Bpy-MP-3, activated with 150 equivalents of Et2AlCl, compared at 25°C and 30 bars of ethylene, during one hour in toluene

  : an ancillary ligand used with Ni@Bpy-MP-3 (ACHN) to overcome ethylene polymerization In 2000, Grubbs et al. proved that by adding additional phosphine, a Ni-based catalyst's activity towards polyethylene production could be reduced : by half with one equivalent of triphenylphosphine, completely neutralized with several equivalents and a

Figure 91 : 3 ( 3 (

 9133 Figure 91: Representation of the Tolman angle value and π-donating properties linked to the CO stretching frequency within Ni(CO)L obtained by IR spectroscopy (L = phosphine ligand) for P(OMe), PPh 3 and PCy3

Figure 93 :

 93 Figure 93 : TOF in mmol oligomers.mmolNi -1 .h -1 obtained with (from left to right): Ni(bpy)Cl2, Ni(bpy)Cl 2 with one equivalent of PPh3, Ni(PPh3)Cl2, 1.86wt%Ni@Bpy-MP-3 (ACHN) with one equivalent of PCy 3 , two equivalents of P(OMe) 3 , one equivalent of PCy 3 and pristine 1.86wt%Ni@Bpy-MP-3 (ACHN), activated with 150 equivalents of Et2AlCl, compared at 25°C and 30 bars of ethylene, during one hour in toluene

Figure 94 : 3 (MP- 3 (

 9433 Figure 94 : TOF in gproduct.gcatalyst -1 .h -1 of oligomers and polyethylene obtained with a 1.86%Ni@Bpy-MP-3 catalyst in four different experiments (from right to left): ten equivalents of PPh 3, one equivalent of PPh3, ten equivalents of P(Cy)3 and one equivalent of P(Cy)3 activated with 150 equivalents of Et2AlCl, compared at 25°C and 30 bars of ethylene, during one hour in toluene

167 While

 167 this textural effect in Ni@Bpy-MP-3 (ACHN) has to be further analyzed, a way has been found to circumvent the polymerization of ethylene by adding an ancillary phosphine ligand. It has been observed in molecular catalysis of ethylene polymerization that the addition of few equivalents of phosphine ligand can inhibit the reaction. This result has been successfully transposed in heterogeneous catalysis. The ancillary phosphine ligand has an electron-donating effect on the Ni-alkyl intermediate of the oligomerization mechanism and enables to stabilize it. This stabilization favors the oligomerization reaction over the polymerization of ethylene. Among different types of phosphine, PPh3 seemed to represent a good candidate since its hindrance and electron-donating ability, enabled to reduce significantly the polymerization process with one equivalent. Further investigation would enable to evaluate if PPh 3 causes Ni active site leaching and how PPh 3 may have influence on the Ni-alkyl intermediate during the catalytic reaction.By using this promising result, the next chapter will describe the effect of covalently introducing a phosphine-anchoring site within MOF and POP porous macroligands. ligands are interesting for olefin oligomerization since attention has been brought on phosphorus/oxygen chelate ligands developed by Keim et al forNi-based

Figure 97 :

 97 Figure 97 : PXRD diffractograms of as-synthsized MOF-808 and MOF-808-DPPB materials compared to the theoretical pattern of MOF-808 from CCDC-1002672 (each diffractogram has been normalized in respect to the highest peak at 4.3° 2θ)

Figure 98 :

 98 Figure 98 : Nitrogen physisorption measurements at 77K of phosphine-infiltrated MOF-808-DPPB material compared to the MOF-808 pristine material

Figure 99 :

 99 Figure 99 : 31 P HPDEC NMR spectra of MOF-808-DPPB. Asterisks (*) enable to designate spinning side bands

Figure 100 :

 100 Figure 100 : 1.38wt%Ni@MOF-808-DPPB diffractogram, compared to its pristine material, MOF-808-DPPB

Figure 101 :

 101 Figure 101 : Nitrogen physisorption measurements at 77K of Ni-infiltrated 1.38wt%Ni@MOF-808-DPPB catalyst compared to MOF-808-DPPB pristine material

Figure 103 :

 103 Figure 103 : Nitrogen physisorption measurements at 77 K of four pristine materials Phos-MP-3 (ACHN)

  -1 ) compared to Bpy-MP-3 materials (ca. 1.35 cm 3 .g -1 ). If, like for the MOF-808-DPPB materials, the triphenylphosphine anchoring sites point towards the center of the pores, it can lead to a lower amount of nitrogen adsorbed and therefore a lower BET surface area and a lower total pore volume for the Phos-MP-3-based materials compared to Bpy-MP-3-based materials. Table 20 : Textural properties of Phos-MP-3 (ACHN) compared to Bpy-MP-3 (ACHN), Bpy-MP-3 (ATTN), Bpy-MP-1, Bpy-MP-2 and UiO-67 materials, obtained by nitrogen physisorption measurements at 77K a average of four batches b average of three batches Phos-MP-3 (ACHN) materials have been analyzed by the BJH method (the plot being represented in the Appendix of the Chapter 3, Figure 125).

Table 21 :

 21 Textural properties of four different batches of Phos-MP-3 (ACHN) materials obtained by nitrogen physisorption measurements at 77K Toluene physisorption measurements have to be done on Phos-MP-3 (ACHN) materials, to evaluate the ability of toluene to diffuse within the porosity of the material.

Figure 105 : 4 . 6

 10546 Figure 105 : Nitrogen physisorption measurements at 77 K of four Ni@Phos-MP-3 (ACHN) catalysts

  This chapter presented the different phosphine-based MOFs and POPs used as porous macroligands for Ni infiltration and further ethylene oligomerization. Based on the results obtained in heterogeneous catalysis with Ni@Bpy-MP-3 catalysts coupled with phosphine ancillary ligands inhibiting polymerization of ethylene and improving ethylene oligomerization, Ni@MOF-808-DPPB and Ni@Phos-MP-3 catalysts were developed. It was expected that by heterogenizing phosphine sites instead of bipyridyl sites, ethylene oligomerization would be favored over polyethylene production.Ni@MOF-808-DPPB is microporous and it is assumed that Ni-phosphine sites are isolated within the micropores of the catalyst. However, further investigation and blank experiments have to be done to evaluate if ill-defined active sites can be formed upon metalation and have an activity for ethylene oligomerization. Furthermore, only one loading of Ni has been tested and testing other Ni loadings with Ni@MOF-808-DPPB catalysts would enable to understand if mass transport limitations can occur within this type of catalyst.Ni@Phos-MP-3 catalysts were successfully synthesized but improvement has to be done to increase the Ni loading within the material. It can be assumed that no ill-defined active site is obtained and Ni@Phos-MP-3 catalysts enabled to achieve promising TOFs for ethylene oligomerization and a butene selectivity of 100%, which is as competitive as their homogeneous counterpart, Ni(PPh 3)2Cl2 in terms of butene selectivity. In both cases, with Ni@MOF-808-DPPB and Ni@Phos-MP-3 catalysts, no polyethylene traces were found. triethylamine (anhydrous, 121-44-8) 1,3,5-benzenetricarboxylic acid (95%, 554-95-0) formic acid (>98%, 64-18-6) From Alfa-Aesar: aluminium oxide Al2O3 (alpha-phase, 99.99%) From Acros Organics (Thermo Fisher Scientific): diethylaluminium chloride (0.9 M in toluene) diethylaluminium chloride (1.0 M in heptane) From Honeywell Fluka (Fisher scientific): Zirconyl chloride hexahydrate ZrOCl 2•H2O (>95, 13520-92-8) From Air Liquide: Ethylene N35, L50 (> 99.95, 74-85-1)

  2•glyme) is dissolved in an anhydrous methanol solution before being stirred with 100 mg of the material (UiO-67-bpy, Bpy-MP-1, Bpy-MP-2, Bpy-MP-3, MOF-808-DPPB or Phos-MP-3) at 60°C during three days. The NiCl2•glyme amount is calculated from the theoretical Ni loading wt%(Ni) wanted.

  and Zr content of POPs and MOFs Fourier transform infrared spectroscopy FTIR Polymerization of Bpy-MP-1 and Bpy-MP-2 Nickel coordination on the POPs' bipyridyl sites Solid-state nuclear magnetic resonance 13 C and 31 P MAS-NMR Bpy-MP-3 bipyridyl proportion compared to divinyl parts Free phosphines proportion in Phos-MP-3 X-ray fluorescence analysis FX Ni and Pd content in POPs

  crystalline and organic-inorganic hybrid MOFs and amorphous organic POPs. First, from the different techniques presented in the literature, it was chosen to incorporate bipyridyl anchoring sites within the structures of already-known MOFs and POPs. This technique enables to control the amount of anchoring sites within the structure and increase the ratio of catalytic sites per catalyst mass. Therefore, a series of UiO-67-bpy MOF materials and series of Bpy-MP-1, Bpy-MP-2 and Bpy-MP-3 POP materials have been synthesized. Different amounts of bipyridyl sites have been successfully incorporated within the structure of the UiO-67-bpy MOF, to improve mass transport limitations that can occur within a porous catalyst during a reaction. The incorporation of different bipyridyl sites amounts did not affect the crystallinity of the material (which was verified by PXRD measurements) whereas it can have an effect on the nitrogen volume adsorbed by the material (evaluated by nitrogen physisorption measurements).Afterwards, a nickel(II) chloride molecular complex was infiltrated within the synthesized UiO-67-bpy materials by using a methanol solution of NiCl 2•glyme. This molecular complex was chosen for the lability of its ethereal ligand, leading to the formation of nickel(II) chloride bipyridyl site embedded within the porous macroligand. Different loadings of Ni have been infiltrated and it has been observed that the different UiO-67-bpy materials were able to bear more Ni sites than expected: based on the results obtained by ICP-OES analysis and from the calculated bipyridyl amount with 1 H NMR, the calculated binding site occupation indicated an overload of the material. A hypothesis that has to be further investigated is the ability of the UiO-67 materials to coordinate nickel(II) chloride complexes on the Zr-OH sites. These ill-defined active sites can lead to side reactions during a catalytic test and even cause the leaching of molecular complexes within the reaction mixture. 0.74wt%Ni@UiO-67-bpy(10%) catalyst enabled to achieve a TOF of 10 634 and mmololigomers.mmolNi -1 .h -1 with a selectivity in butene of 100% (for a reaction in toluene at 25°C and a continuous feed of ethylene of 30 bars, and activated with 150 equivalents of Et 2AlCl).

  -808-DPPB was fully characterized by PXRD, nitrogen physisorption measurements and 31 P solid-state NMR. However, only one nickel loading was tested and further investigation has to be done to evaluate the effect of different amounts of phosphine sites within the material, like it was done with different amounts of bipyridyl sites for UiO-67bpy materials to improve mass transport limitations that can occur. Furthermore, MOF-808-DPPB is a Zr-based MOF like UiO-67-bpy. Therefore, its ability to create ill-defined catalytic sites with Zr-OH centers remains to be investigated.Regarding Phos-MP-3 (ACHN) materials, they were characterized by nitrogen physisorption measurements and31 P solid-state NMR. They exhibited the same hierarchical porous structure as Bpy-MP-3 (ACHN) but Ni infiltration did not go over 0.08wt% of the Phos-MP-3 (ACHN) material. We show that the low Ni loadings of Phos-MP-3 (ACHN) catalysts can be mainly attributed to the coordination on phosphine sites. Both Ni@MOF-808-DPPB and Ni@Phos-MP-3 (ACHN) catalysts have been tested for ethylene oligomerization (25°C and 30 bar of ethylene, in toluene) and enabled to obtain TOFs (respectively 7 and 7 223 mmol oligomers.mmolNi -1 .h -1 ) and butene selectivities (respectively 88% and 100%) that can be improved depending on the Ni loadings. No polyethylene production was observed in both cases. This work highlights the potential of porous solids like MOFs and POPs to act as macroligands and heterogenize molecular catalysts, as proved for Ni-based complexes active in ethylene oligomerization. The newly designed heterogeneous catalysts can be at least as active and selective than their homogeneous counterparts. The nature of MOF and POP solids allows a wide versatility in solid porous macroligand construction to tune the steric and electronic environment around the active sites, at the origin of the catalytic activity and selectivity.

  performances and butene selectivity and to understand the diffusion of the reagents and the products within the pores of the material. Based on the work that was done in 2013 within our research group by Canivet et et al. by grafting for the first time a Ni(PyCHO)Cl2 complex by imine condensation within a (Fe)-MIL-101-NH2 framework and by using POP versatility, a

pressure of 30 MP- 3 ,

 303 bars during one hour in toluene, activated with 148 equivalents of Et 2AlCl. No polyethylene production was observed. This promising result enables to further prove that the result obtained with MOF-based catalyst can be adapted with POP materials, thanks to their versatility of structure and obtain competitive results compared to their homogeneous counterpart.Furthermore, MP-3-based materials offer a new path to synthesize frameworks with different electronic and textural properties. First, the solvent ratio can be modulated to obtain different pore hierarchies within the structure (more mesopores over micropores and viceversa). This synthesis pathway has to be investigated and also its influence on ethylene oligomerization performances. Second, different frameworks can be obtained such as Phenwhere bipyridyl monomer are replaced with more hindered and electron-withdrawing phenantroline monomers, and Bpy-MP-4, where divinylbipyridyl monomers are replaced by monovinylbipyridyl monomers in the synthesis to obtain imine-like active sites that proved to be active for ethylene oligomerization and selective in butene upon Ni coordination.

Figure 112 :

 112 Figure 112 : Nitrogen physisorption isotherms at 77 K of the obtained Bpy-MP-1 mixed batches and six Ni infiltrated Bpy-MP-1 catalysts

Figure 113 :Figure 115 :Figure 116 :Figure 117 :Figure 118 :

 113115116117118 Figure 113 : Nitrogen physisorption isotherms at 77 K of the obtained Bpy-MP-2 mixed batches and six resulting Ni infiltrated Bpy-MP-2 catalysts

Figure 119 :Figure 120 :Figure 122 :Figure 123 :

 119120122123 Figure 119 : Nitrogen physisorption isotherms at 77 K of Full-Bpy-MP-3 (ACHN) compared to two resulting catalysts: 8.68wt%Ni@Full-Bpy-MP-3 (ACHN) and 2.17wt%Ni@Full-Bpy-MP-3 (ACHN)

Table

Table

Table 2 :

 2 On-purpose processes for the selective ethylene oligomerization towards one

specific LAO (selectivities expressed in weigh selectivities) Concerning the AlphaPlus ® process developed by CP-Chem, it resorts to a chromiumethylhexanoate catalyst with a pyrrolyle ligand. The first plant in Qatar enabled to produce 47 kilotons per year and three other plants followed between 2010 and 2014 producing up to 200 kilotons per year, with a weight selectivity in 1-hexene above 99%.

Table 3 :

 3

Textural properties of the UiO-67 and the UiO-67-bpy-based materials obtained by nitrogen physisorption measurements at 77K, compared to the materials obtained by Gonzalez et al. (bpydc 2-= 2,2'-bipyridine-5,5'-dicarboxylate and bpdc 2-= biphenyl-4,4'dicarboxylate)

Table 4 :

 4

Binding site occupation rates of different Ni@UiO-67-bpy-based catalysts calculated from the results of wt%(Ni) obtained by ICP-OES a Ni-wt% calculated from Gonzalez et al. work For the catalysts Zr

6O4(OH)4(bpydc)0.84(bpdc)5.16(NiBr2)0.84 and Zr6O4(OH)4(bpydc)6(NiBr2)6 synthesized

by Gonzalez et al., 93% and 63% of the bipyridyl

  Another Zr-based MOF (among the most stable and versatile ones) than UiO-67-bpy has been synthesized during the course of this thesis: MOF-808.

	MOF-808's general formula is Zr6O4(μ 3 -OH)4(BTC)2(HCO2)6 (BTC standing for 1,3,5-

benzenetricarboxylic acid), first synthesized and characterized in 2014 by Yaghi et al. (Figure

Table 17 :

 17

Textural properties of MOF-808-DPPB compared to MOF-808 pristine materials data, obtained by nitrogen physisorption measurements at 77K

-808-DPPB-based catalysts for

	ethylene oligomerization.
	In the case of Ni@Phos-MP-3, since the infiltration technique led to very low Ni
	loadings (around 0.06wt% in nickel), TOFs of 4 328 mmol oligomers .mmol Ni -1 .h -1 (2
	goligomers.gcatalyst -1 ) with a 0.05wt%Ni@Phos-MP-3 catalyst (0.1 μmol of nickel) activated with 4
	629 equivalents of Et 2AlCl, for one hour of reaction and 7 223 mmololigomers.mmolNi -1 .h -1 (11
	g oligomers .g catalyst -1

Ni-phosphine-based catalyst enables not to produce polyethylene. One Ni loading has been tested and other loadings would enable to understand if any diffusion limitations could occur within MOF

  Hz, 2H), 8.68 (s, 2H).[START_REF] Armor | [END_REF] C at (100 MHz, CDCl3): δ 154.4, 147.5, 133.9, 133.2, 133.1, 121.0,

	2,2-bipyridine (500 mg, 1.60 mmol), Pd(OAc)2 (7 mg, 0.03 mmol), PPh 3 (25 mg, 0.1 mmol) and Cs 2 CO 3 (1,56 g, 4.77 mmol) in THF/H 2 O (24:1, a total of 25 mL) was heated at 85°C for 48h under an N2 atmosphere in a sealed tube. After coming back to room temperature, the mixture was diluted with H 2 O (25 mL) and extracted with CH2Cl2 (20 mL x 3). The organic phases were combined and extracted with aqueous saturated NaCl (50 mL), and dried over Na 2SO4. The solvent was removed under vacuum, using a rotating evaporator. The light orange solid was purified by thin layer chromatography (eluting with 35:70:1 petroleum ether/dichloromethane/NEt3) to yield 5,5'-divinyl-2,2'-bipyridyl as a white solid. 116.7

1 H NMR (400 MHz, CDCl3): δ 5.43 (d, J = 11.15 Hz, 2H), 5.90 (d, J = 17.26 Hz, 2H), 6.77 (dd, J = 17.26 Hz, 11.01 Hz 2H), 7.87 (d, J = 8.27 Hz, 2H), 8.39 (d, J = 8.25

  150,0 mg (644 μmol) of ZrCl4 are dissolved in 20 mL of anhydrous DMF containing 1,1 mL of HOAc and 16,6 μL of dionized water. Then, 117,9 mg (480 μmol) of 2,2'-bipyridine-5,5'-dicarboxylic acid and 39,0 mg (160 μmol) of biphenyl-4,4'-dicarboxylic acid are added. The sealed vial is put inside an ultrasound bath during three minutes. The suspension is heated at 120°C in an oven during 48 hours. After a cooling down to room temperature during 24 hours, the solid is recovered by centrifugation and washed three times with DMF. The solvent is replaced with MeOH during two days (exchange of MeOH every 12 hours). Finally, the solid is dried under vacuum (1.10 -6 bar) at 120°C.

Table 24 :

 24 Characterization techniques and their purpose used in this thesis work5.5 Used instrumentsLiquid nuclear magnetic resonance (NMR) spectra have been recorded on a Bruker Ascend 400 ( 1 H at 400.13 MHz,[START_REF] Armor | [END_REF] C at 100.61 MHz) spectrometer. Solid-state NMR spectra have been recorded at room temperature on a Bruker AVANCE III 500WB spectrometer (11.7 T, 1 H at 500.04 MHz, 13 C at 125.73 MHz and 31 P at 202.41 MHz)

Table 25 :

 25 Structure comparison betweenPMOs, MOFs, COFs and POPs):

Table 25 :

 25 Structure comparison between PMOs, MOFs, COFs and POPs

	Material	Porosity	Properties Crystallinity	Chemical stability	Advantages for catalytic applications	Drawbacks for catalytic applications	Characterization techniques
	PMO	Mesoporous	hybrid organic/inorganic	high	PSM thermal resistance	reduced ratio of active sites per catalyst mass diffusion, 1D channels

could be observed after one hour and a half, with an improved selectivity in butene of

.h-1 , with a 97.4% butene selectivity when activated with 500 equivalents of MAO.In summary, the scant examples with cation exchange approach show some catalytic activities but no major conceptual breakthrough with respect to One-Pot Synthesis approach.

, without any significant change in the case of the polymerization.

Figure 124 : Molecular weight distribution of the polyethylene analyzed by SEC-HT, after a typical run of ethylene oligomerization with a 1.26wt%Ni@Bpy-MP-3 catalyst

Acknowledgements

Chapter 1: Bibliographic study

-by infiltrating nickel complexes in materials containing the coordination site (bipyridine [90][91][92][93] or phenoxy-imine) in the porous polymer structure (route E) [94] Figure 15 : Different synthetic pathways in order to obtain isolated active sites within MOFs MOFs. [95,96] Given the crystalline structure of the MOF, it can be assumed that each Cr III active site is isolated.

The authors activated the catalyst at five different temperatures (150, 200, 275, 300 and 350 °C). They evaluated the effect that it could have on its ethylene oligomerization the maximum amount of bipyridyl sites, all nickel-coordinated) around the active sites of Zr6O4(OH)4(bpydc)6(NiBr2)6 leads to polyethylene production (Figure 24). They also observed an activity of 44 ± 3 g product.gcatalyst -1 .h -1 with Zr6O4(OH)4(bpdc)6(NiBr2)0.14, leading them to suggest that there are two types active sites in Zr6O4(OH)4(bpydc)0.84(bpdc)5.16(NiBr2)0.84 and in Zr6O4(OH)4(bpydc)6(NiBr2)6. Nevertheless, the active sites coordinated to water and hydroxide ligands have a negligible share in the activity.

Figure 24 : Catalytic TOFs and butene selectivity obtained with Ni@UiO-67, Ni@UiO-67(bpy14%) and Ni@UiO-67(bpy100%) in the following conditions: 59 bar of ethylene at 55°C during one hour and with 100 equivalents of Et 2AlCl per nickel

NiCl@DUT-133

In 2020, Arrozi et al. synthesized two imine-based MOFs, PCN-161 and PCN-164, and one phenoxy-imine novel MOF, DUT-133. [94] For PCN-161 and PCN-164, the imine condensation occurring between 4formylbenzoic acid and respectively, 4-aminobenzoic acid and p-phenylenediamine, in presence of ZrCl 4, enables to achieve imine-based MOFs. Based on these syntheses, the authors proposed the DUT-133 framework, isoreticular to PCN-161, where the imine condensation of 4-formyl-3-hydroxybenzoic acid with 4-aminobenzoic acid, in presence of

Chapter 2: Bipyridine-based MOF and POP materials for nickel infiltration

The higher amount of nitrogen adsorbed in Bpy-MP-2 materials compared to Bpy-MP-1 during the measurement can be attributed to the difference of node, tetratopic for Bpy-MP-2 and tritopic for Bpy-MP-1. The tetratopic node leads to the formation of wider pore channels within the material than with a tritopic one. However, both materials display micropores, which make them suitable for active site isolation.

Both isotherms exhibit a hysteresis loop that attributed to the fact that pores reached a critical width and remains altered. The type of hysteresis loop observed for Bpy-MP-1 and Bpy-MP-2 resembles a H4 one, according to IUPAC. For a H4 type, the adsorbent fills the pore up through a bottleneck during adsorption. When the desorption process starts, all the adsorbed molecules within the pore are forced out through the bottleneck, which causes the desorption isotherm to follow a different path than the adsorption one. Afterwards, the desorption isotherm reaches back the adsorption one when the pores are completely emptied out. In the case of Bpy-MP-1 and Bpy-MP-2, the hysteresis remains until the end of the desorption process.

A further experiment to understand this phenomenon would be to do cycles of adsorption and desorption. In the end of the first desorption if the second adsorption isotherm starts where the first desorption isotherm ended, it would mean that the material remained altered and did not come back to its initial state. If the second adsorption isotherm starts where the first adsorption started, it would mean that the pores went back to their initial shape.

For a given material, with an unknown porosity, the nitrogen volume adsorbed obtained from physisorption measurement is plotted against the values from Shull et al.

model, achieving the t-plot of the considered material with an unknown porosity. If the t-plot is a straight line, the amount adsorbed on the considered material is the same as it was adsorbed on the flat surface used for the model. For t-plots that are not straight lines, no classification has been established.

The t-plots of Bpy-MP-1 and Bpy-Mp-2 enables to observe that the first sharp slope corresponds to the homogeneous filling of the micropores, as it can happen on the flat surface of the model (Figure 41). The flat surface model chosen in this case is a Graphitized Carbon Black (GCB), which is close to the organic composition of Bpy-MP-based materials.

When the micropores filling is completed, the second slope starts and adsorption occurs on the surface of the micropores. Two regimes of filling can be observed, which indicates the presence of two types of pores. However, despite Bpy-MP-1 and Bpy-MP-2 materials synthesis easiness by Sonogashira coupling, they require expensive transition metals which can be a drawback since traces of them are found in the worked-up material. ICP-OES analysis confirmed an amount up to 0.5 wt% in Pd. These traces unfortunately require to ensure the non-activity of the pristine material, for the considered catalytic reaction, before infiltration of any other metals for catalytic purposes. Therefore a novel type of bipyridyl-based POP, which synthesis is Pd-free, has been proposed: the Bpy-MP-3.

Bpy-MP-3: a novel type of POP obtained by Pd-free radical polymerization

In this part, the Pd-free synthesis of a novel type of Bpy-MP materials, Bpy-MP-3, made by radical polymerization will be described, from the synthesis of divinylbipyridyl monomers to the solid characterization by nitrogen physisorption and [START_REF] Armor | [END_REF] C multi CP MAS NMR. The POP purity and synthetic reproducibility mainly lies on pure starting monomers. [152] The vinylic monomer 5,5'-divinyl-2,2'-bipyridyl was synthesized according to a modified literature procedure based on Suzuki-Miyaura cross-coupling (Figure 49). [153] Figure 49 : Divinylbipyridyl monomer synthesis adapted from a optimized literature procedure [153] On one hand, given the fact that this reaction is Pd-catalyzed, it requires thorough purification by preparative thin layer chromatography (PTLC) in order to remove metal traces before using it for Bpy-MP-3 polymerization synthesis and meet fixed goals of Pd wt% below

GCB model

Bpy-MP-3 (ACHN) was also characterized by toluene physisorption measurement to evaluate the ability of the materials to adsorb toluene within the pores. It exhibits a type II isotherm with a H3 hysteresis loop, according to IUPAC classification of isotherms (Figure 56). [145] Below a partial pressure of 0. by tuning the solvent ratio or by tuning the nature of the monomers that are used (styrene, divinylphenantroline, vinilbipyridyl, etc.).

In summary, Bpy-MP-3 (ACHN) and Bpy-MP-3 (ATTN) have been successfully

synthesized according to a modified procedure literature. This procedure allows to fully Pdfree structures, in contrast to Bpy-MP-1 and Bpy-MP-2. However, the hierarchical pore distribution, from micropores to macropores of the Bpy-MP-3-based materials may influence the active site isolation upon metalation. In addition, different active sites due to different environment (confinement, interactions) can be obtained, in the micropores, mesopores and macropores, which can lead to different products during a catalytic reaction.

On the other hand, site dilution enables to increase the ratio of active sites per catalyst mass, as it has been proved with Full-Bpy-MP-3 (ACHN) materials, the large pore distribution enables to improve mass transport limitations within the material during a catalytic reaction. Furthermore, Bpy-MP-3-based materials are porous towards solvent like toluene, which make them suitable for liquid-phase catalysis. Further investigation is ongoing with [START_REF] Armor | [END_REF] C ComPmultiCP MAS NMR to quantify the bipyridyl amount within the materials.

Similarly, to Bpy-MP-1 and Bpy-MP-2 materials, four batches of Bpy-MP-3 (ACHN)

and four batches of Bpy-MP-3 (ATTN) have been synthesized and the batches from the same type (ACHN or ATTN) have been mixed to obtain a sufficient stock of the same POP (Table 13). The mixing process is performed in pentane during one hour under stirring. This method found its justification in the fact that the different batches are amorphous materials with the same theoretical molar amount of the same monomers. The nitrogen physisorption isotherms of the different batches have been represented in the Appendix of Chapter 2 (Figure 115 and Figure 116). According to the BJH model, the different batches also follows the same pore distribution. 15 and Table 14).

Isolating Ni(II)Cl2 active sites within Bpy-MP-3-based materials

An average amount (in mmol) of polyethylene produced during the reaction was calculated from the weight of polyethylene produced (in g) and the number average molar mass Mn (in g.mol -1 ). The resulting average amount enabled to calculate an average TOF of polyethylene production (in mmol polyethylene.mmolNi -1 .h -1 ) (Table 16).

Table 16 : TOFs (in mmolproduct.mmolNi -1 .h -1 ) obtained for the oligomerization of ethylene with four different Ni@Bpy-MP-3 (ACHN)-based catalysts, calculated from the number average molar mass Mn (g.mol -1 ), the weight of polyethylene produced and the amount of oligomers (C4, C6 and C8)

When considering all the products (ethylene oligomers, from C4 to C8, and polyethylene), Ni@Bpy-MP-3 (ACHN) catalysts, with TOFs above 100 gproduct.gcatalyst -1 .h -1

(ranging from 161 to 508 gproduct.gcatalyst -1 .h -1 ) are more active than Ni@Bpy-MP-1 and

Ni@Bpy-MP-2 catalysts with TOFs below 100 gproduct.gcatalyst -1 .h -1 (Figure 121). Furthermore,

Ni@Bpy-MP-3 (ACHN) catalysts are more active than Ni@UiO-67-bpy-based catalysts.

Further investigation has to be done concerning the lower activities obtained with

Ni@Bpy-MP-2 catalysts. However, it can be assumed that the wider pore channels created by the tetratopic node of the Bpy-MP-2 material may induce a higher induction period within the pores, compared to the narrower pore channels of the Bpy-MP-1 material, built around a tritopic node, as it was described in chapter 2.

The TOFs (in mmololigomers.mmolNi -1 .h -1 ) and the selectivities obtained with the three types of catalysts have been plotted against the loading of nickel (Figure 77 and Figure 78).

The number of aluminum equivalents is indicated beside each point. It can be observed with increasing Ni loadings, the TOF with Ni@Bpy-MP-1 and Ni@Bpy-MP-2 catalysts remains constant and the selectivity in butene increases whereas Ni@Bpy-MP-3 (ACHN) TOF increases and the butene selectivity remains constant with increasing Ni loading.

be caused by entrapment of oligomers inside the polyethylene or diffusion limitations within the reactor due to polymerization. This behavior does not appear completely controlled since the next experiment stopped at 60 minutes did not show a stunted oligomer production.

Figure 85 : TON in g product.gcatalyst -1 of the parallel catalytic reaction of ethylene oligomerization and polymerization considered at different times with a 1.51wt%Ni@Bpy-MP-3 (ACHN)

catalyst, tested at 25°C and 30 bars of ethylene in toluene

The data reported in Figure 86 were analyzed in terms of oligomer distribution. The C 6 and C 8 mass selectivities remain lower but seems also less erratic than the C 4 and the polyethylene ones (Figure 87). This result can be an addition to the DSC results described before indicating that butene might be more likely to be co-polymerized with ethylene, given its higher amount than hexene and octene products. Figure 96 : MOF-808-DPPB synthesis procedure (adapted from Furukawa et al.) [175] MOF-808-based materials have been characterized by Powder X-Ray Diffraction (PXRD). The introduction of phosphine sites did not affect the relative intensity of the peaks compared to the calculated model of the MOF-808 and the as-synthesized MOF-808 (Figure 97). PXRD measurement at low angles has to be done to observe the effect of phosphinesite introduction on pore occupancy. The amount of phosphine sites can be modulated without affecting the crystallinity of the MOF-808 structure.

Due to the high abundance of 1 H and 31 P (both spin ½), spin-spin heteronuclear coupling can occur between the nuclei, causing splitting of the 31 P signals and giving rise to multiplets. Therefore, 31 P HPDEC is necessary to obtain distinct 31 P signals, with a high signal-to-noise ratio. The minor peak at 34 ppm corresponds to the oxidized phosphines whereas the major peak at -5 ppm comes from the free phosphine sites (Figure 99). [START_REF] Musina | Organophosphorus Chemistry[END_REF] It can be drawn from this analysis that most of the phosphine sites are free (98%), and not oxidized (Table 18).

Table 18 : Intensity ratio of the free-phosphine peak at -5 ppm and the phosphine-oxide peak at 24 ppm of MOF-808-DPPB material, spectrum being represented on Figure 99 In summary, a microporous phosphine-based MOF-808-DPPB has been successfully synthesized and is suitable for the immobilization of a Ni-based molecular complex within the pores. Further investigation are ongoing to modulate the amount of phosphine sites within the material, to improve mass transport limitations that can eventually occur. Asterisks (*) enable to designate spinning side bands 31 P HPDEC NMR analysis of four batches of Phos-MP-3 (ACHN), synthesized in the same conditions, enables to assess that a majority of the phosphine sites (88 ± 0.7 %) are free, compared to the phosphine-oxide sites (Table 22).

Nickel infiltration into MOF-808-DPPB materials

Table 22 : Intensity ratio of the free-phosphine peak at -5 ppm and the phosphine-oxide peak at 24 ppm of four different batches of Phos-MP-3 (ACHN), each spectrum being represented on Figure 104 In summary, Phos-MP-3 (ACHN) materials were synthesized according to a modified procedure literature. Nitrogen physisorption measurements enabled to prove that they are mostly microporous. Further investigation has to be done to evaluate the amount of phosphine sites and their porosity towards toluene. 23). It enabled to establish that a low amount of Ni has been infiltrated within the material (between 0.05 and 0.08 wt% of Ni). No significant changes could be observed concerning the porosity of the materials and its ability to adsorb nitrogen (Figure 105). It was proved that MP-3 (ACHN) materials do not physisorb Ni complexes on the surface.

Nickel infiltration within Phos-MP-3 pristine materials

Furthermore, Phos-MP-3 (ACHN) has to be analyzed by methanol physisorption measurement to evaluate the porosity of the material during the metalation process.

Nitrogen physisorption measurements have been performed at 77 K using a Belsorp Mini X.

Toluene vapor physisorption measurements have been conducted on a Belsorp-Max II at 25°C. Prior to physisorption measurements, the samples have been desorbed of any impurities under vacuum at 100°C (for POPs) and 120°C (for MOFs) for at least 2h.

Powder X-Ray diffractograms have been recorded on a Bruker D8 Advance Diffractometer equipped with a Lynx-Eye detector (CuKα radiation)

Chapter 6: Conclusion and outlooks

To avoid the formation of ill-defined Ni sites by interaction with OH groups at inorganic nodes in MOF, bipyridyl-based POP materials were considered for Ni infiltration: Bpy-MP-1

and Bpy-MP-2. POP materials combine structure versatility (i.e. the ability of changing the amount of bipyridyl sites) with the advantage of structural diversity (i.e. changing the nature of the monomers used for the synthesis). Among, the different synthesis pathways for POPs, The catalysts were tested for ethylene oligomerization. Bpy-MP-3-based catalyst proved to be as competitive as its homogeneous counterpart under given conditions, with TOFs above 10 000 mmol oligomers.mmolnickel -1 .h -1 and butene selectivities among oligomers above 90% (26 178 mmololigomers.mmolnickel -1 .h -1 for example with a butene selectivity of 87%).

Bpy

They also proved to be more competitive than UiO-67-bpy, Bpy-MP-1 and Bpy-MP-2-based catalysts. [91] However, Bpy-MP-3-based catalysts proved also to be highly efficient for ethylene polymerization, decreasing the overall selectivity towards butene. Polyethylene was produced between 1 and 5 g. Investigations were led to determine the causes of this polymerization side reaction.

Neither nickel(II) chloride complexes nor free radicals remained physisorb within the catalyst causing the polymerization of ethylene. Furthermore, despite the versatility of Bpy-MP-3 materials allowing to tune the textural and porous properties of the pristine material, none of the MP-3-type catalysts allows to reduce ethylene polymerization. By using a Me 3Al aluminum activator instead of Et2AlCl, it was proved that the same active sites within the Ni@Bpy-MP-3 catalyst produced both oligomers and polyethylene.

Inspired by literature, it has been observed that the addition of one equivalent of PPh 3 enables to completely inhibit Ni@Bpy-MP-3-catalyzed ethylene polymerization reaction and promote ethylene oligomerization, with a higher selectivity in 2-butene. Other phosphines, such as P(OMe)3 and PCy3 were tested but their electron donation properties and their steric hindrance do not allow to inhibit ethylene polymerization and promote oligomerization.

Accordingly, phosphine-based MOF-808-DPPB and POP Phos-MP-3 (ACHN) were finally synthesized to evaluate the effect of having a phosphine-based macroligand instead of a bipyridyl-based one on the activity and selectivity of ethylene oligomerization.

has to be brought to the catalytic conditions in order to avoid water and any substrate or reagent that might react with the coordination bonds within the MOF, and alter its integrity. ). [222][223][224][225] However, these types of bonds make them more stable materials than MOFs, made of coordination bonds, between the nodes and the linkers, more likely to be hydrolyzed.

Porous Organic

COFs are crystalline porous polymers, synthesized in two steps: first, the condensation reactions between linkers enable to form sheets, stacking afterwards to generate a framework. Linkers' geometry (trigonal planar, tetragonal, etc.) determines the pore type (hexagonal, tetragonal, etc.) of the final COF. However, despite the robustness of their covalent bonds, they can undergo reversible reactions, added to the possibility of sheets stack splitting due to solvent infiltration.

Unlike COFS, POP solids are amorphous, a feature linked to the variety of synthesis pathway: radical polymerization, alkyne trimerization, nitrile trimerization, Sonogashira coupling, Friedel-Crafts reactions, and miscellaneous reactions. [224] These syntheses are led by using monomers with specific binding sites. The connection of these binding sites, through the aforementioned reactions, enables to build porous organic networks.

A distinction can be made between the metal-catalyzed polymerization reactions (alkyne and nitrile trimerization, Sonogashira coupling, Friedel-Crafts reactions) and the others (radical polymerization and miscellaneous reactions). This distinction enables to highlight the fact that metal traces can be found in the final POP and for catalytic purposes, it is required either to ensure the non-activity of the pristine POP for the considered reaction, or either purify thoroughly the POP (by an acid treatment for example) before infiltrating a metal. Furthermore, uncontrolled traces of metal can also hamper POP synthesis (and afterwards catalytic results) reproducibility. [226,152] An alternative would be to resort to noncatalyzed polymerization reactions.

Despite this drawback, POPs are microporous materials with high surface areas (like MOFs) and enable to achieve high amounts of catalytic active sites per mass of material. [222] Furthermore, these catalytic active sites, borne by coordination sites monomers (bipyridine, phosphine, porphyrin, etc.), can be isolated within the network with, in most of the cases,