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.

This thesis describes the development and rationalization of processes involved in a new methodology developed in our group, minor enantiomer recycling. The first part of the thesis addresses mechanistic studies of one of the reactions involved in minor enantiomer recycling, dual Lewis acid-Lewis base catalyzed acetylcyanation of aldehydes. The methodology uses a combination of a chiral titanium-salen  complex with a tertiary amine as a catalytic  system  in  the enantioselective  synthesis  of  O-acylated  cyanohydrins from aldehydes and ketonitriles. Mechanistic investigations revealed that the rate-determining step in the reaction changes, depending on the nature of the aldehyde that was used. It was also concluded that cyanohydrin is coordinated to the Lewis acid in the acylation step. The second part of the thesis deals with minor enantiomer recycling, a highly selective one-pot recycling system. In a first step the product is formed as a minor and a major enantiomer by asymmetric catalysis. Recycling of the minor enantiomer, by selective kinetic resolution, regenerates the starting material. Continuous addition of a second reagent, also involved in a coupled exergonic process, leads to an increase of both yield and enantiomeric excess. Recycling procedures for the synthesis of O-acylated and O-formylated cyanohydrins have been developed with high yield and high enantiomeric excess of the products. The study includes development of the systems, comparison to other methodologies in asymmetric catalysis, and attempts to understand the processes involved. / <p>QC 20141202</p>

This thesis deals with method development in asymmetric catalysis and specifically syntheses of enantioenriched O-functionalized cyanohydrins. The first part describes the development of a method for the synthesis of O‑alkoxycarbonylated and O-acylated cyanohydrins. Ethyl cyanoformate and acyl cyanides were added to aldehydes in a reaction catalyzed by a chiral dimeric Ti-salen complex together with a tertiary amine. High yields and enantioselectivities were in most cases obtained. Mechanistic studies were performed and a reaction mechanism was proposed. ­ The second part describes a method in which the undesired minor enantiomer in a Lewis acid–Lewis base-catalyzed acylcyanation is continuously recycled into prochiral starting material. Close to enantiopure O‑acylated cyanohydrins were obtained in high yields. The third part deals with asymmetric acylcyanations of ketones. Acetyl cyanide was found to add to α‑ketoesters in a reaction catalyzed by a chiral Lewis base. Yields up to 77% and 82% ee were obtained. The final part describes an enzymatic method for high-throughput analysis of O‑acylated cyanohydrins. The enantiomeric excess and conversion were determined for products obtained from a number of aromatic and aliphatic aldehydes. / QC 20100818

Dans ce travail de thèse, plusieurs approches ont été développées pour permettre une utilisation plus variée des carbènes N-hétérocycliques (NHCs) et des phosphines en tant que catalyseurs/activateurs organiques.Les précurseurs de NHCs étudiés dans un premier temps, c'est-à-dire les hydrogénocarbonates d’azolium, peuvent être synthétisés en une seule étape, à l’inverse des NHCs dont la synthèse et l’isolation sont souvent compliquées. Nous avons démontré que ces espèces sont stables à l’air et sont à l’équilibre en solution avec leurs homologues carboxylates d’azolium (adduits NHC-CO2). Leur utilisation permet donc de faciliter la manipulation des NHCs tout en conservant une activité catalytique satisfaisante tant en synthèse moléculaire qu’en chimie des polymères.Des paires de Lewis silane ou borane/NHC ont ensuite été employées afin d’augmenter le potentiel des NHCs pour des réactions “modèles” de chimie (macro)moléculaire par un effet de double assistance (acide/base de Lewis).Enfin, une phosphine commerciale a été utilisée pour catalyser la polymérisation par transfert de groupe des (méth)acrylates d’alkyle de façon “vivante/contrôlée”. / In this thesis work, some points are adressed in order to broaden the scope of the application of N-heterocyclic carbenes (NHCs) as organic catalysts/activators.The novel NHC precursors studied first, i.e. azolium hydrogen carbonates, are synthesized in a one-step undemanding process, in contrast to NHCs whose synthesis and isolation is often a tedious procedure. We then showed that these species are air-stable and are at the equilibrium, in solution, with their azolium-2-carboxylates homologues (NHC-CO2 adducts). The use of such precatalysts thus allows facilitating the manipulation of NHCs, while maintaining an efficient catalytic activity in molecular chemistry as well as in polymer synthesis.We then proposed to use NHCs in conjunction with organic Lewis acids (silanes or boranes) as a possible means to induce a cooperative dual activation mechanism (Lewis acid/base) in order to increase the potential of NHCs for “model” (macro)molecular reactions.Finally, a commercial phosphine was used to trigger the group transfer polymerization of alkyl (meth)acrylates in a “controlled/living” fashion.

Deux carbènes N-hétérocycliques (NHCs) de type imidazol-2-ylidène ont été étudiés en tant qu’amorceurs organiques pour la polymérisation directe de monomères vinyliques de type (méth)acrylates d’alkyle, principalement le méthacrylate de méthyle(MMA), en l’absence tout autre activateur. Une différence de réactivité a été mise en évidence en fonction des substituants du carbène et de la nature du substrat. Des études théoriques ont permis de rationaliser les résultats expérimentaux par l’influence des effets électroniques et stériques intervenant au cours des réactions mises en jeu. Un NHC en particulier a été ensuite utilisé comme véritable catalyseur de la polymérisation du MMA en présence d’alcools comme amorceurs. En utilisant des macroamorceurs hydroxylés de type poly(oxyde d’éthylène), des copolymères amphiphiles ontété ainsi synthétisés. Des études théoriques ont encore une fois permis d’identifier les mécanismes réactionnels de cette polymérisation. Enfin, des paires de Lewis composées d’un acide à base de silicium et d’une base de typeNHC ou phosphine trialkyle(aryle) ont été ensuite utilisées comme système d’activation de polymérisation du MMA. Ce type de polymérisation est basé sur une activation duale du monomère par effet coopératif de la base et de l’acide. / The reactivity of imidazol-ylidene N-heterocyclic carbenes (NHCs) as direct initiators for the polymerization of miscellaneous (meth)acrylic monomers, mainly methylmethacrylate (MMA), has been screened in the absence of any other co-activator.Different reactivities have been observed according to the structure of the NHC and thenature of the substrate. Computational studies allowed rationalizing steric and electroniceffects involved in these reactions.The use of a peculiar NHCs as catalyst for the polymerization of MMA using alcohols as initiators has then been investigated. This simple and efficient method also allows achieving amphiphilic block copolymers by using hydroxylated poly(ethylene oxide)s asmacro-initiators. Combined computational and experimental investigations have provided insights into the mechanism of polymerization.Various Lewis pairs including a silicon-based compound as acid and NHC or a trialkyl(aryl)phosphine as base, have been investigated to trigger an efficient polymerization of MMA.In this case, the polymerization is expected to proceed via a cooperative/dual activation mechanism.