The functionalisation of silsesquioxanes results in materials with novel physical properties. A series of compounds has been coupled with silsesquioxanes [HSiO_3/2]₈ and [SiO_3/2]₈ [OSi(CH₃)₂H]₈ and the properties of the products investigated. Typically, coupling reactions involved hydrosilylation with H₂PtCl₆ or [Pt{(η-ViMe₂Si)₂O}(P^tBu₃)]. Mesogenic compounds have been shown to undergo a change in the liquid crystalline phase produced, once attached to the silsesquioxane core. A more ordered phase was observed due to the tethering of the mesogen to the cage. The silsesquioxanes core was considered to have been deformed in the production of this phase. Silsesquioxanes capable of complexing metal atoms have also been studied. Polyether derivatised cages were prepared and preliminary studies indicate potential for potassium complexation. Vinyl functionalised silsesquioxanes have also been shown to complex platinum, in an exchange reaction with [Pt{(η-ViMe₂Si)₂O}(P^tBu₃)]. Investigations into the hydrosilylation reaction have involved coupling triethylsilane, triethoxysilane and the silsesquioxanes with a variety of vinyl, allyl and alkenic compounds. The proportions of α and β adducts were considered. Particular substituents were found to encourage α addition, with species having an oxygen or phenyl group at the allylic position producing the α-regioisomer as well as the typical β product. It is suggested that such substitution affects the mode of cis ligand insertion in the Chalk Harrod mechanism. A preference for the α-regioisomer was also observed for the hydrosilylations of vinyl silsesquioxane compounds.

The aim of the work carried out in this thesis is to develop new efficient catalytic systems for the synthesis of enantioenriched secondary alcohols. The access to this class of important synthetic intermediates is possible either by nucleophilic addition of organometallic reagents to aldehydes or by reduction of prochiral ketones catalysed with chiral complexes. We have thus developed two new catalytic systems for the asymmetric hydrosilylation of ketones using polymethylhydrosiloxane (PMHS) as an inexpensive reducing agent. A first approach is based on the synthesis of new N, S ligands and zinc complexes bearing a ferrocenyl backbone with planar chirality. Those compounds were prepared and evaluated first in the addition of diethyl zinc to aldehydes, reaching enantiomeric excesses up to 74%. The precatalysts were also evaluated in the reduction of prochiral ketones with PMHS. In that case, a good reactivity was observed and enantioselectivities up to 61% could be reached. It is assumed that a zinc hydride complex formed by thermal ß-elimination of the corresponding ethyl complex is the active species. This catalytic system also allows the hydrosilylation of dialkyl ketones, a challenging goal in asymmetric catalysis. In a second part of this work, we have developed a new catalytic system for hydrosilylation of ketones based on the hypothetical formation of a chiral cobalt hydride catalyst. This intermediate is supposed to be formed by reaction of the corresponding neutral cobalt (II) complex with tetrabutyl ammonium triphenyldifluorosilicate (TBAT) as activator and a silane. Following a preliminary screening, salen type ligands were found to be the most efficient when activated with TBAT in presence of PMHS. Modifications on this structure by replacing the phenol group of the ligand by various sulfonamide groups led, after optimisation of the reaction parameters, to a highly efficient catalytic system with enantioselectivities reaching 84 % for the reduction of tetralone. This work should thus open new perspective for the design of highly enantioselective and low cost catalytic systems for the hydrosilylation of prochiral ketones.

Iron-catalysed carbonyl reduction, nitro reduction, formal hydroamination, and the radical alkenylation of alkyl halides have been developed. A Simple, easy-to-make, air- and moisture-stable iron(III) amine-bis(phenolate) complex catalysed the hydrosilylation of carbonyl compounds efficiently using triethoxysilane as the reducing agent. The reaction tolerated a wide range of substrates to give the corresponding alcohol products in good to excellent yields after hydrolysis of the hydrosilylated products (Scheme A1). Scheme A1. Iron-Catalysed Hydrosilylation of Carbonyl Compounds. The same catalyst was also an active catalyst for the chemoselective reduction of nitro arenes into corresponding amines using triethoxysilane as reducing agent. The method exhibited excellent chemoselectivity as other reducible functional groups such as halogen, ester, nitrile all kept unchanged during the reaction. This catalytic system was then successfully applied to the formal hydroamination of alkene to give substituted amine in synthetic useful yields under mild condition. The reaction is hypothesised to proceed through a radical intermediate (Scheme A2). Scheme A2. Iron-Catalysed Nitro Reduction and Alkene Formal Hydroamination. Finally, FeCl2-catalysed formal Heck cross-coupling has been developed between alkyl halides and styrenes. The reaction tolerated both electron-rich and electron-neutral substrates to give the products in moderate to excellent yields. Initial studies revealed that the reaction also proceeds through a radical intermediate (Scheme A3). Scheme A3. Iron-Catalysed Formal Heck Cross-Coupling of Functionalised Alkyl Halides.

Thèse doctorat : Chimie : Strasbourg 1 : 2006. / Titre provenant de l'écran-titre. Notes bibliogr.

Thesis (Ph. D.)--Open University. BLDSC no. DXN043595.

No description available.

Les ressources carbonées fossiles (pétrole, charbon, gaz) couvrent 85 % des besoins énergétiques mondiaux et servent de matières premières pour 95 % des consommables chimiques organiques (plastiques, engrais, pesticides…). L’amenuisement des ressources pétrolières et l’accumulation du CO2 résultant de leur utilisation posent donc un problème écologique, énergétique et de disponibilité en matières premières pour l’industrie chimique. Dans ce contexte, il convient de proposer de nouvelles voies de synthèse de consommables chimiques, de manière à construire une industrie durable basée sur l’utilisation de ressources carbonées renouvelables. Contourner la pétrochimie et valoriser au maximum son déchet carboné, le CO2, pour construire des édifices moléculaires sans vocation énergétique (polymères, engrais, textiles synthétiques…) représente donc un enjeu scientifique de premier plan. Dans cet optique, de nouveaux procédés de synthèse de molécules azotées ont été mis au point à partir de CO2 comme source de carbone, d’amines comme source d’azote et de réducteurs doux de type hydrosilanes et hydroboranes comme source d’hydrogène. Ces procédés sont accélérés par l’utilisation de catalyseurs sans métaux et permettent de produire des formamides, des formamidines, des aminals et des méthylamines, qui constituent des molécules de bases de l’industrie chimique. / The fossil carbon resources (oil, coal, gas) cover 85% of world energy portfolio and serve as raw materials for 95% of organic chemicals consumables (plastics, fertilizers, pesticides...). The decrease of oil resources and the accumulation of CO2 arising from their use thus pose environmental, energetic and availability of raw materials problems for the chemical industry. In this context, it is appropriate to propose new methods of chemical synthesis to build a sustainable industry based on the use of renewable carbon resources. Bypassing petrochemicals and valorize its carbon waste, CO2, to build molecular structures without energy purposes (polymers, fertilizers, synthetic textiles ...) represents a leading scientific challenge. From this perspective, new nitrogen molecules synthetic processes have been developed from CO2 as a carbon source, amines as nitrogen source and mild reductant such as hydrosilanes and hydroboranes as a hydrogen source. These processes are accelerated by the use of metal-free catalysts and enable the production of formamides, formamidines, aminals and methylamines, which are basic molecules of the chemical industry.

De nos jours, les limites du réacteur batch, outil conventionnel de l'industrie de la chimie fine, en termes de transfert thermique et de transfert de matière, conduisent à envisager le passage en continu de réactions dont les problématiques d'exothermie et de rapidité rendent leur industrialisation difficile. Les réacteurs-échangeurs compacts sont un exemple de technologies intensifiées continues alliant les performances d'un échangeur de chaleur couplées à un bon mélange ainsi qu'à un comportement de type piston offert par le design spécifique de leurs canaux. L'objectif de ces travaux est de démontrer la faisabilité de la transposition en continu d'une réaction fondamentale de la chimie des silicones, recensée comme l'une des plus exothermiques, dans un réacteur-échangeur intensifié conçu dans un matériau innovant : le Carbure de Silicium. La démarche a consisté à étudier les différentes phases de la réaction à plusieurs échelles afin de construire un modèle cinétique. L'exploitation de ce modèle a permis de définir les conditions optimales de la réaction permettant de répondre aux contraintes industrielles en termes de conversion, de consommation de catalyseur et de production industrielle. Enfin, une démarche d'optimisation et d'extrapolation du réacteur a été mise en place pour le pilotage industriel de la réaction étudiée. / Nowadays in the field of fine chemistry, limitations of conventional batch reactors in term of heat and mass transfer lead to increase the interest in the transposition of reactions from batch to continuous mode. It is particularly the case of fast and highly exothermic reactions as they raise safety issues in batch reactor. Compact heat-exchanger reactors (HEX reactor) are an example of continuous intensified technologies as they offer the heat transfer performances of heat exchangers coupled with high mixing and plug-flow behaviour, thanks to specific designs of channels. The aim of this work is to demonstrate the feasibility of the transposition of a fast and highly exothermic hydrosilylation reaction, a fundamental method for the industrial synthesis of organosilicon compounds, into a continuous heat-exchanger reactor made of a very innovative material: the silicone carbide. The methodology adopted consists in investigating hydrosilylation kinetics studies at different residence time scales. Then kinetics modelling and optimisation allow defining the features for process industrialization. Industrials objectives in terms of conversion and catalyst reduction are reached with a shorter time. Moreover the outstanding heat transfer performances of the HEX reactor, which entirely absorb the high exothermicity, successfully demonstrate the feasibility of the transposition into continuous

L'hydrosilylation des alcènes est une méthode cruciale de formation de liaisons carbone-silicium. Elle est utilisée industriellement pour la production de fluides silicones fonctionnels et d'élastomères silicones. Les procédés actuels d'hydrosilylation des alcènes utilisent des complexes de platine comme catalyseurs. Bien que ces complexes soient extrêmement efficients, ils ne sont d'habitude pas récupérés en fin de réaction, ce qui rend leur utilisation coûteuse et peu durable, étant donnée la rareté du platine. Dans ce projet, nous avons synthétisé et testé plusieurs types de nanoparticules métalliques comme catalyseurs pour l'hydrosilylation des alcènes, dans un effort vers des catalyseurs durables. D'abord, nous avons synthétisé des nanoparticules de platine de 2 nm de diamètre et les avons comparées avec le complexe de Karstedt, le catalyseur de référence en hydrosilylation des alcènes. Nous avons montré que les nanoparticules de platine étaient aussi efficientes que le complexe de Karstedt dans des conditions proches des conditions industrielles, malgré leur dispersion métallique plus faible. Ces observations ont réactivé le débat sur la nature réellement homogène ou colloïdale du complexe de Karstedt pendant la catalyse. Ensuite, un catalyseur hétérogène à base de platine, résistant à la lixiviation, a été développé, basé sur l'encapsulation de nanoparticules de platine dans la matrice d'une silice mésostructurée, la SBA-15. Enfin, d'autres catalyseurs alternatifs ont été développés, basés sur d'autres métaux / Alkene hydrosilylation is a crucial method of forming carbon-silicon bonds. It is used industrially for the production of functional silicone fluids and silicone elastomers. The current industrial alkene hydrosilylation processes use platinum complexes as catalysts. Although these complexes are extremely efficient, they are usually not recovered at the end of the synthesis, making their use expensive and unsustainable, given the scarcity of platinum. In this work, we have synthesized and evaluated several kinds of metal nanoparticles as catalysts for alkene hydrosilylation, in a quest towards sustainable catalyts. First, we have synthesized platinum nanoparticles of 2 nm diameter and compared them with Karstedt's complex, the benchmark catatalyst in alkene hydrosilylation. It was shown that platinum nanoparticles were as efficient as Karstedt's complex in industrially relevant hydrosilylation conditions, despite their lower metal dispersion. These findings reactivated the debate on whether's Karstedt's complex was truly homogeneous or colloidal during catalysis. Then, a leaching-resistant heterogeneous platinum catalyst was developed, based on the embedding of platinum nanoparticles in the matrix of a mesostructured silica, SBA-15. Finally, other alternative catalytic systems were developed, based on other metals

La première partie de ce travail recense les différentes technologies permettant de générer des mousses silicone. Des généralités sur les émulsions, sur la génération de matériaux poreux à base d’émulsions inverses concentrées, ainsi que sur le principe d’inversion de phase d’une émulsion par élévation de température sont discutées. La production de mousses silicone à partir d’émulsions a été retenue pour sa polyvalence. Des mousses ont donc été synthétisées à partir d’émulsions inverses concentrées dans un premier temps. La variation de la formulation et des paramètres de procédé ont permis de mieux appréhender les phénomènes qui gouvernent les morphologies finales des mousses. Les limites rencontrées avec les émulsions inverses (viscosité élevée, « pot life » court etc.) ont orienté notre choix sur la technologie d’inversion de phases d’émulsions directes. Nous nous sommes attardés sur la compréhension du phénomène d’inversion de phase ainsi que sur la température de point de troubles des tensioactifs afin de comprendre son influence sur les morphologies des mousses générées. Enfin les enductions ont permis de générer des films de mousse légers, fins, homogènes et à porosité ouverte après avoir réglé des problèmes de stabilité en adaptant notamment le protocole d’émulsification. / The first part of this work lists the various technologies that make possible the formation of silicone foams. Global knowledge on emulsions, on the generation of porous materials emulsion templated, as well as on the principle of emulsion phase inversion temperature (PIT) are discussed. The production of silicone foams from emulsions has been retained for its versatility. Foams were synthesized from concentrated inverse emulsions at first. The variation of the formulation and the process parameters made it possible to better understand the phenomena which govern the final morphologies of the foams. The limits encountered with inverse emulsions (high viscosity, short pot life, etc.) have led us to move our approach to phase inversion temperature technology of oil-in-water emulsions. We then focused on the comprehension of the phase inversion phenomenon, as well as on the surfactant cloud point temperature, in order to understand their influence on the morphologies of the generated foams. Finally, the coating process allowed the production of thin, light, homogeneous and open-porous foams after having solved stability issues, in particular by adapting the emulsification protocol.