Exploration de nouvelles réactivités et sélectivités dans la réduction catalytique utilisant des hydrures de silicium et leurs substituts

Dependence on fossil resources has fuelled global growth, but their overexploitation and depletion, together with population growth, make it necessary to switch to renewable energies and sustainable carbon raw materials to reduce carbon footprints and promote environmental-friendly chemical processes. This growing demand for sustainable, environmental-friendly chemical processes has led to increased interest in renewable energy sources, reagents and catalysts. The reduction of carbon-oxygen (C=O) bonds is at the heart of many synthetic transformations. It is a key step in the production of a wide range of chemicals, pharmaceuticals and materials. Although conventional reducing agents (lithium aluminum hydride, sodium borohydride, etc.) are highly efficient, they are produced from non-renewable sources by energy-intensive processes and often generate toxic by-products. This dependence on non-renewable sources poses a major challenge as far as sustainability in chemical synthesis is concerned. In this scenario, renewable hydrides, derived from bio-based materials or CO₂, offer an attractive alternative for the reduction of C–O bonds. Renewable hydrides can replace fossil-based reductants, thereby lowering the carbon footprint while performing chemical transformations. This thesis deals with the utilization of silyl formate as a renewable hydride in performing the transfer hydrosilylation reactions of imine and ester functionalities. The challenges and the pitfalls associated with the conventional reducing agents are discussed in the respective chapters. In the case of imines, a novel reactivity for silylformates was observed. Specifically, they can facilitate a new hydrocarboxysilylation reaction through the formal insertion of the C=N linkage into the C–H bond of silylformates, without loss of CO₂. Furthermore, with the aim of developing better catalytic systems for the transformation of naturally abundant oxygenated functional groups into high-value chemicals, a scandium triflate-based catalytic system was developed for reductive deoxygenation reactions. Using hydrosilane as the reductant, reductive deoxygenation of alcohols and ketones was achieved using a relatively more robust, water-tolerant and cost-effective Lewis acid catalyst: scandium triflate (Sc(OTf)₃). Furthermore, the (Sc(OTf)₃/hydrosilane) system exhibited excellent chemoselectivity, preferentially reducing σ-bonds (alcohols) over π-bonds (ketones) using only one equivalent of hydrosilane, an advantageous feature not observed with previously reported systems, underscoring the superior performance and broad applicability of the Sc(OTf)₃-catalyzed approach. Furthermore, the applicability of this system is extended to hydrodehalogenation reactions.