Hétérogénéisation de catalyseurs moléculaires à base de nickel au sein de matériaux poreux pour l'oligomérisation de l'éthylène

Ethylene α-oligomers are 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 highly economically viable to produce selectively α-oligomers from this gas. However, despite a spread 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. Therefore, not only heterogeneous catalysts enable to separate products from the catalyst more easily, it also allows to control the shape of the catalyst, while obtaining isolated active sites preventing them from interaction between them leading to deactivation. Macroligands enable 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 macroligands 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 coordinated with nickel(II) chloride complexes in order to obtain isolated active sites. Given the fact that ill-defined active sites could be obtained with UiO-67-bpy-based catalysts, a series of catalyst have been synthesized with Bpy-MP-1 and Bpy-MP-2 macroligands. These series were characterized and it can be assessed, for the Bpy-MP-1-based catalysts, that the bipyridyl sites within the structure are coordinated with nickel(II) chloride complexes. However, traces of Pd originating from their C-C coupling 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 radical polymerization, Bpy-MP-3, enabled to prepare a series of catalyst with different loadings of nickel. These series were fully characterized and it can be also assessed that the bipyridyl sites within their structure are coordinated with nickel(II) chloride complexes. These four series of catalysts were tested for ethylene oligomerization and for given conditions, the catalyst series obtained with Bpy-MP-3 enabled to obtain TOFs (above 10 000 mmololigomers.mmolnickel-1.h-1) than its homogeneous counterpart Ni(bpy)Cl2 and its heterogeneous counterparts UiO-67-bpy, Bpy-MP-1 et Bpy-MP-2. However, despite being highly active for ethylene oligomerization and selective in butene, Bpy-MP-3-based catalysts are also highly active for ethylene polymerization, decreasing the global selectivity in oligomers and causing the deactivation of the catalyst. Different possible causes were elucidated concerning the origin of the uncontrolled polymerization reaction during this thesis work. It was also proved that the same type of active sites within the catalyst was capable of both oligomerizing and polymerizing ethylene at the same time. However, a result proved in homogeneous catalysis was successfully adapted in heterogeneous catalysis: the addition of PPh3 during the reaction enabled to stop ethylene polymerization and promote ethylene oligomerization. Based on that result, a MOF-808-DPPB and a Phos-MP-3 POP, both phosphine-based and not bipyridyl-based anymore, were synthesized and characterized to evaluate the ability of the macroligands to oligomerize ethylene and not polymerize it. This present work enables to present promising perspectives for the selective ethylene oligomerization with UiO-67-bpy and MOF-808-DPPB MOFs and with Bpy-MP-1, Bpy-MP-2, Bpy-MP-3 et Phos-MP-3 POPs. Their structure versatility offer large perspectives regarding the modulation of their activity and their selectivity towards ethylene oligomerization.Les α-oligomères de l’éthylène sont utilisés en copolymérisation avec l’éthylène afin de moduler les propriétés du polyéthylène. Avec une disponibilité accrue en gaz de schiste, il est intéressant de produire sélectivement des α-oléfines à partir de l'éthylène. Malgré une utilisation répandue en industrie, la catalyse homogène de cette réaction peut présenter certaines limites comme la présence de résidus métalliques ou un manque de stabilité des catalyseurs. Ainsi, la catalyse hétérogène présente cette facilité de séparation du catalyseur et du milieu réactionnel mais permet aussi de contrôler la forme des catalyseurs, tout en obtenant des sites actifs ben définis évitant la désactivation du catalyseur par interaction des sites actifs entre eux. Les macroligands permettent d’établir une passerelle entre catalyse homogène et hétérogène afin de conserver les activités catalytiques et les sélectivités obtenues en homogène tout en obtenant des sites actifs isolés. Durant ce travail de thèse, deux types de macroligands, 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 été coordinnés avec différents taux de chlorure de nickel(II) afin d’obtenir des sites actifs isolés. Des sites actifs non-contrôlés sont obtenus avec le MOF UiO-67-bpy et une série de catalyseurs a été synthétisée à partir de Bpy-MP-1 et Bpy-MP-2. Ces séries ont été caractérisées et pour les catalyseurs obtenus à partir de Bpy-MP-1, il a été montré que les sites bipyridyls au sein de la structure sont coordinnés par des complexes de chlorure de nickel(II). Cependant, les traces de Pd retrouvées dans les matériaux Bpy-MP-1 et Bpy-MP-2, lié à leur méthode de synthèse catalysée au Pd peut entraîner des réactions secondaires, des interactions entre sites actifs de Pd et de Ni et causer la désactivation du catalyseur. Ainsi, un nouveau POP a été synthétisé par polymérisation radicalaire, le Bpy-MP-3. Une série de catalyseurs infiltrées avec différents taux de nickel a été synthétisée à partir de ce matériau et caractérisée. Comme pour les catalyseurs obtenus à partir de Bpy-MP-1, les sites bipyridyls du Bpy-MP-3 sont coordinnés par des complexes de chlorure de nickel(II). Ces quatre séries de catalyseurs ont été testées en oligomérisation de l’éthylène et pour des conditions données, la série obtenue avec le Bpy-MP-3 présente une activité plus importante (supérieure à 10 000 mmololigomères.mmolnickel-1.h-1) que son homologue homogène Ni(bpy)Cl2 et ses homologues hétérogènes UiO-67-bpy, Bpy-MP-1 et Bpy-MP-2. Cependant, 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 et réduisant la sélectivité globale en oligomères. Différentes voies d’investigation ont été élucidées durant ce travail de thèse sur l’origine possible de cette polymérisation non-contrôlée. Il a été prouvé qu’un même site actif au sein des catalyseurs à base de Bpy-MP-3 était responsable d’oligomériser et de polymériser l’éthylène. Plus tard, il a été prouvé qu’en ajoutant des équivalents de PPh3 durant la réaction, cette polymérisation peut être stoppée et l’oligomérisation favorisée. À partir de ce dernier résultat, le MOF-808-DPPB et un POP, le Phos-MP-3, tous deux avec des sites de phosphine, ont synthétisés et caractérisés afin d’évaluer la capacité de ces macroligands à oligomériser sélectivement l’éthylène. Ces travaux permettent de montrer que les matériaux poreux infiltrés au nickel, tels que les MOFs UiO-67-bpy et MOF-808-DPPB et les POPs Bpy-MP-1, Bpy-MP-2, Bpy-MP-3 et Phos-MP-3 sont des matériaux prometteurs pour l’oligomérisation de l’éthylène et offrent de larges perspectives de travail pour moduler leur activité et leur sélectivité

Molecular Rhodium Complex within N‐Rich Porous Polymer Macroligand as Heterogeneous Catalyst for the Visible‐Light Driven CO2 Photoreduction

The heterogenization of molecular catalysts within a porous solid acting as macroligand can advantageously open access to enhanced stability and productivity, and thus to more sustainable catalytic process. Herein, a porous organic polymer (POP) made through metal‐free polymerization using bipyridine repeating units is reported. This N‐rich POP is an efficient macroligand for the heterogenization of molecular rhodium complexes. The intrinsic catalytic activity of the heterogenized catalyst is slightly higher than that of its homogeneous molecular counterpart for formic acid production as a unique carbon‐containing product. The heterogenization of the rhodium catalysts enables recycling for a total productivity of up to 8.3 g of formic acid per gram of catalyst after 7 reuses using visible light as the sole energy source

Rhodium-based metal–organic polyhedra assemblies for selective CO2 photoreduction

Heterogenization of molecular catalysts via their immobilization within extended structures often results in a lowering of their catalytic properties due to a change in their coordination sphere. Metal–organic polyhedra (MOP) are an emerging class of well-defined hybrid compounds with a high number of accessible metal sites organized around an inner cavity, making them appealing candidates for catalytic applications. Here, we demonstrate a design strategy that enhances the catalytic properties of dirhodium paddlewheels heterogenized within MOP (Rh-MOP) and their three-dimensional assembled supramolecular structures, which proved to be very efficient catalysts for the selective photochemical reduction of carbon dioxide to formic acid. Surprisingly, the catalytic activity per Rh atom is higher in the supramolecular structures than in its molecular sub-unit Rh-MOP or in the Rh-metal–organic framework (Rh-MOF) and yields turnover frequencies of up to 60 h–1 and production rates of approx. 76 mmole formic acid per gram of the catalyst per hour, unprecedented in heterogeneous photocatalysis. The enhanced catalytic activity is investigated by X-ray photoelectron spectroscopy and electrochemical characterization, showing that self-assembly into supramolecular polymers increases the electron density on the active site, making the overall reaction thermodynamically more favorable. The catalyst can be recycled without loss of activity and with no change of its molecular structure as shown by pair distribution function analysis. These results demonstrate the high potential of MOP as catalysts for the photoreduction of CO2 and open a new perspective for the electronic design of discrete molecular architectures with accessible metal sites for the production of solar fuels

Heterogenization of a Molecular Ni Catalyst within a Porous Macroligand for the Direct C-H Arylation of Heteroarenes

International audienceDirect C–H functionalization catalyzed by a robust and recyclable heterogeneous catalyst is highly desirable for sustainable fine chemical synthesis. Bipyridine units covalently incorporated into the backbone of a porous organic polymer were used as a porous macroligand for the heterogenization of a molecular nickel catalyst. A controlled nickel loading within the porous macroligand is achieved, and the nickel coordination to the bipyridine (bpy) sites is assessed at the molecular level using IR and solid-state NMR spectroscopy. The heterogenized Ni-bpy catalyst was successfully applied to the direct and fully selective C2 arylation of benzothiophenes, thiophene, and selenophene, as well as for the arylation of free NH-indole. Recyclability of the catalyst was achieved by employing hydride activators to reach a cumulative turnover number of more than 300 after seven cycles of catalysis, which corresponds to a total productivity of 12 g of 2-phenylbenzothiophene, chosen as model target biaryl, per gram of catalyst