N-heterocyclic carbenes (NHCs) can be used as ligands for organometallics complexes, which can then facilitate numerous catalytic applications, such as, C-H activation, small molecule activation and numerous materials applications. The use of anionically-tethered NHCs for usage with electropositive metals has been pioneered by the Arnold group within the last decade. This thesis describes the synthesis of both aryloxide- and amide-tethered NHC organometallic complexes of s-, p-, d- and f-block metals to provide a platform for small molecule activation. Once synthesised, the reactivity of some of these complexes were tested by reaction with CO2 with the aim of turning a molecule considered a harmful (environmentally), waste product into value added products, potentially providing an alternative fuel source. Chapter One introduces the use of anionically-tethered NHCs for use in a number of organometallic complexes as well as their current potential as catalysts for a number of important small molecules. This chapter focuses upon the differences between complexes tethered with anionic O, N, P, S elements, f-element NHC complexes and the use of d-block NHC complexes for catalysis. Chapter Two contains the synthesis and characterisation of a number of aryloxy-tethered NHC p-, d- and f-block organometallic complexes using the ligand H2(LArO R)2. The synthesis of SnII complexes including the synthesis of new ‘normal’ ‘abnormal’ complexes given enough steric bulk around the Sn centre due to the lone pair present in Sn complexes, preventing one of the ligands binding through the classical carbene position and therefore binding through the backbone C4 carbon. The synthesis of MII (Zn, Co and Fe) complexes to compare the solid-state structure and binding mode of the carbenes. The synthesis and characterisation of MIII (Ce and Eu) complexes to assess the solid-state structure and binding modes within f-bock complexes. Chapter Three investigates the reactivity of the MII complexes (Sn, Zn, and Fe) with CO2. Successful reactions were characterised using NMR and further treated with alkynes to target catalytic reactions. Chapter Four contains reactions to target a number of amide-tethered bis (NHC) s-, p-, d- and f-block organometallic complexes using the proligand, H4(LN Mes)Cl3. Deprotonation studies undertaken with a number of bases to give the MI (Li and K) salts and MII (Mg) salts and proved to be unsuccessful upon isolation. Reactions to synthesise the p-, d- and f-block complexes were then undertaken using in situ free carbene production as well as the attempted isolation of the free carbene, both of which also proved unsuccessful. Chapter Five provides an overall conclusion to the work presented in Chapters Two, Three and Four within this thesis. Chapter Six gives the experimental and characterising data for the complexes and reactions.

N-Heterocyclic carbenes (NHCs) are good ligands to most transition metals forming stable complexes. Many of the NHC-metal complexes are now widely used catalysts. However, the usage of these catalysts encounters the general problems associated with homogeneous catalysis: the purification of the catalysis reaction products is often time-consuming and generates large amounts of waste. Moreover, the toxic or expensive catalysts are difficult to be separated, recycled, and reused. Chapters II and III of this dissertation focus on addressing these problems through the development of an easier and “greener” process to improve the usage of some NHC-metal complexes. Polymer-supported catalysts and polymer-supported sequestrants were prepared and used to facilitate the separation/recycling of catalysts and the purification of products. These polymer-supported ligands, catalysts, and sequestrants showed comparable reactivity to their low molecular weight counterparts and had different solubility properties due to the nature of polymers. Using these materials with the corresponding operations provides simple methods to separate deeply colored, metal-containing by-products from the reaction mixtures. Chapter IV of this dissertation aims at solving a fundamental question about the nature of NHC-silver(I) complexes. The NHC-silver(I) complex is an important synthetic intermediate as it can be used to prepare other NHC-metal complexes through transmetallation. The carbene carbon of an NHC-silver(I) complex in 13C NMR spectra was usually reported as a doublet of doublets or as a singlet in different cases. This phenomenon was explained with a ligand exchange mechanism proposed twelve years ago. However, few reports are available in the literature about the mechanism of the NHC ligand exchange processes at silver. In order to facilitate the study of the solution behaviors of NHC-silver(I) complexes, 13C-labeled NHC-silver(I) complexes were prepared and studied using variable temperature 13C NMR spectroscopy. This study could be useful for future applications of ligand transferring from silver to other metals for the preparation of NHC-metal complexes.

The goal of this PhD was to elaborate supported Ru-NHC catalytic materials based on hybrid organic-inorganic materials having imidazolium units perfectly distributed within a silica matrix. Passivation of these imidazolium materials followed by formation of NHC-carbene and reaction with [RuCl2(p-cymene)]2 provided these well-defined surface sites of general structures RuCl2(NHC)(L), where L was para-cymene (p-cymene) or THF depending on the reaction conditions, which could be further replaced by PMe3. These systems were then tested in the hydrogenation of CO2 in presence of amine to give formamides. The mono-NHC systems were highly active only in the presence of PMe3 ligands, but suffered from Ru leaching, evidencing the low stability of the NHC-Ru bond under the reaction conditions. On the other hand, dinuclear bis-NHC Ru systems were also developed, and they displayed much improved activity and stability in the hydrogenation of CO2 in the presence of PMe3 compared to the mono-NHC systems. This allowed the use of much higher reaction temperatures (200 °C) and provided heterogeneous catalysts with performances close to those obtained with the best homogeneous catalysts, Cl2Ru(dppe)2.

Les travaux de recherche fondamentale présentés ici sont ancrés au cœur de la chimie organique de synthèse moderne, et plus particulièrement dans le domaine de la multi-organocatalyse énantiosélective. Dans ce manuscrit, nous avons identifié deux organocascades originales et démontré la pertinence synthétique de l'une d'elle par des applications en synthèse totale de produits naturels. L’originalité de ce travail repose sur l’utilisation d’un NHC de la classe des 1,3-imidazol-2-ylidenes comme base de Brønsted ou base de Lewis organocatalytique / The basic research work presented herein is anchored at the core of modern synthetic organic chemistry, and more specifically in the field of enantioselective multi-organocatalysis. In this manuscript, we have identified two original organocascades and demonstrated the synthetic relevance of one of these through applications in total synthesis. The originality of the work lies on the use of a 1,3-imidazol-2-ylidene NHC as an organocatalytic Brønsted or Lewis base.

En synthèse organique, la recherche de nouveaux catalyseurs est un point crucial pour améliorer les conditions réactionnelles et découvrir de nouvelles réactions, particulièrement en chimie de l’or. Pour contribuer à ce développement, nous nous sommes intéressés à la nature du contre-ion, dont dépend la réactivité du catalyseur d’or, avec les polyoxométallates. Ces polyanions, de par leur nature intrinsèque, ont permis d’obtenir de nouveaux catalyseurs efficaces, polyvalents, multi-fonctionnels et hétérogènes, et applicables à un grand nombre de réactions catalysées à l’or.Nous avons aussi étudié un autre paramètre essentiel de la composition d’un catalyseur d’or : le ligand. Notre intérêt s’est porté sur les ligands carbènes N-hétérocycliques (NHC), dont la modularité de leurs propriétés électronique et stérique confère à l’or d’importantes activités. Nous avons ainsi développé différents types de NHC, en les fonctionnalisant pour les rendre acteurs de la réactivité, ou encore en leur attribuant de nouveaux groupements très encombrant pour influencer la réactivité et la sélectivité. / In organic synthesis, the research of new catalysts is an essential issue to improve reactional conditions and to discover new reactions, especially in gold chemistry. To contribute to this development, we were interested in the nature of the counter-ion, which impact the reactivity of the gold catalyst, with the polyoxometalates. These polyanions, thanks to their nature, allowed to obtain new efficient, polyvalent, multi-functional and heterogeneous catalysts, which could be applied to a wide scope of gold catalyzed reactions.We also studied another essential parameter of the composition of gold catalysts: the ligand. We focused our attention on the N-heterocyclic carbenes (NHC), whose modularity of their electronic and steric properties confer important activities to gold catalysts. Thus we developed different kind of NHC, by functionalizing them so they can be involved in the reactivity, or by attributing them very bulky groups to influence the reactivity and selectivity.

La photopolymérisation est un procédé en plein essor qui permet d’accéder à des matériaux polymères, notamment sous la forme de films ou de revêtements. Néanmoins, celle-ci est majoritairement basée sur un mécanisme de polymérisation radicalaire qui proscrit l’obtention de matériaux totalement biodégradables. Aussi, au cours de cette thèse, nous nous sommes intéressés à la photopolymérisation par ouverture de cycle (photoROP) d’esters et de carbonates cycliques à l’aide de deux grandes familles de photogénérateurs de bases (PBGs). Tout d’abord, des PBGs, pouvant libérer des superbases de type amidine et guanidine cycliques ont été employées pour mener efficacement la photoROP du L-LA et du TMC en solution. Puis, nous nous sommes attachés à développer, sur le modèle des photobases précédentes, de nouveaux PBGs qui libèrent sous irradiation UV des carbènes N-hétérocycliques (NHCs). La libération des NHCs à partir de ces « NHCs photolatents » a été prouvée par RMN 1H et par la formation d’adduits NHC.CS2. De même, ces PBGs se sont révélés actifs pour la photoROP du L-LA et du TMC en solution, mais avec une plus faible efficacité que les PBGs précédents. En effet, les cinétiques de polymérisation sont lentes du fait de la présence de CO2 dans le milieu (libéré lors de l’irradiation UV) qui conduit à la formation d’adduit NHC.CO2 inactif en ROP. Ainsi, la photobase la plus performante, libérant du TBD, a été employée afin d’effectuer la photoROP en masse d’esters cycliques liquides (ε-CL, δ-VL et un mélange innovant L-LA/TMC). Finalement, des réseaux ont été formés par incorporation dans le milieu réactionnel d’un monomère bifonctionnel, permettant d’obtenir sur demande (contrôle temporel) des matériaux réticulés potentiellement entièrement biodégradables. / Photopolymerization is a growing process allowing preparing polymer materials, notably in the form of films or coatings. Nevertheless, it is mostly based on a radical polymerization mechanism that prevents obtaining fully biodegradable materials. The goal of this PhD work was thus to develop the photopolymerization of cyclic esters and carbonates by using two families of photobase generators (PBGs). First, already described PBGs, releasing cyclic amidine and guanidine-type superbases, were effectively employed to carry out the photopolymerization of L-LA and TMC in solution. Then, taking previous PBGs as models, we developed new PBGs able to release N-heterocyclic carbenes (NHCs) under UV irradiation. The release of NHCs from these “photolatent NHCs” was proven both by 1H NMR and by the formation of NHC.CS2 adducts. These PBGs also proved to be active for the ROP of L-LA and TMC in solution, but to a lesser extent than previous photobases. Indeed, slower kinetics of polymerization were observed, which was attributed to the presence of CO2 in the reaction medium (CO2 released by photodegradation of the PBG) that leads to the formation of NHC.CO2 adduct (inactive for ROP). Thus, the most efficient photobase (releasing TBD) was employed to carry out the bulk photopolymerizations of liquid cyclic esters (ε-CL, δ-VL and even an innovative L-LA / TMC mixture). Finally, polymer networks have been formed by incorporating a bifunctional monomer into the reaction medium, allowing the preparation “on demand” (temporal control) of potentially fully biodegradable materials in a one-pot process.

No description available.

Various ways of preparing enantiomerically pure 2-amino[6]helicene derivatives were explored. Ni(0) mediated cyclotrimerization of enantiopure triynes provided (M)- and (P)-7,8-bis(p-tolyl)hexahelicene-2-amine in >99% ee as well as its benzoderivative in >99% ee. The stereocontrol was found to be inefficient for a 2- aminobenzo[6]helicene congener with an embedded five-membered ring. Helically chiral imidazolium salts bearing one or two helicene moieties have been synthesized and applied in enantioselective [2+2+2] cyclotrimerization catalyzed by an in situ formed Ni(0)-NHC complex. The synthesis of the first helically chiral Pd- and Ru- NHC complexes and their application in enantioselective catalysis was demonstrated. The latter shows promising results in enantioselective olefin metathesis reactions. A mechanistic proposal for asymmetric ring closing metathesis is provided.

No description available.

The use of Au-NHC complexes in homogenous gold catalysis has become very popular during the last 10 years. The work described in this thesis represents a modest contribution towards a better understanding of the reactivity of these fascinating complexes and the intermediate species involved during gold-catalysed transformations. There are two main themes that permeate the following chapters: a) synthesis and reactivity studies of monoaurated species and b) synthesis and reactivity studies of diaurated species. The main motivation for the work presented herein was to develop more efficient synthetic routes towards a series of gold complexes, such as [Au(NHC)Cl], [Au(NHC)(OH)] and [{Au(IPr)}₂(μ-OH)][X], in order to be able to further explore their reactivity. Chapter 2 constitutes the first approach that I had with the chemistry of Au-NHC complexes, and describes our efforts to evaluate how the use of a highly sterically demanding NHC ligand affects gold-catalysed transformations. Chapters 3 and 4 explore alternative, more efficient synthetic routes towards known Au- NHC complexes. For example, a new, highly robust protocol has been developed for the synthesis of [Au(NHC)X] (X = Cl, Br, I) complexes, which are the starting materials to prepare a wide range of Au-NHC based species. Moreover, as a result of our investigations it has been possible to isolate a series of [Au(NHC)(OH)] species and to gain some insight into the stability of these complexes. Chapters 5 and 6 describe the synthesis and applications of digold hydroxide species [{Au(IPr)}₂(μ-OH)][X] in a series of catalytic and stoichiometric transformations. For example, they have been used as silver-free catalysts for water-inclusive gold-catalysed transformations or to access key intermediates in gold catalysis, such as gem-diaurated and σ,π-digold-acetylide species. Finally, Chapter 7 combines what we learned about the reactivity of [{Au(IPr)}₂(μ- OH)][X] in order to develop for the first time a gold-catalysed transformation where two gold centres independently react with two substrate molecules to catalyse the hydrophenoxylation of alkynes.