UC Santa Barbara

Catalytic hydrosilylation is an efficient method for making organosilicon compounds and one of the most widely used reactions in silicon chemistry. Metal-catalyzed hydrosilylation of carbonyl compounds is an atom-economical methodology to access synthetically useful silyl ethers. Considering the heightened interest in hydrosilylation catalyzed by high-valent pincer oxo-rhenium complexes and the current lack of detailed mechanistic understanding, catalytic hydrosilylation of various carbonyl compounds, including biomass-derived carbonyl molecules, using oxo rhenium(V) pincer complex [Re(O)2(PNN)][OTf] (OTf = CF3SO3⎻) with organosilanes is described in this work. Direct reductive deoxygenation can be accomplished at moderate temperature (80 ℃). Both the isolation of the potential intermediate metal hydride and stoichiometric deuterium scrambling experiment reveal that the rhenium hydride is not the active catalyst, hydride transfer results from additional silane in the system. An alternative nonhydride Lewis acid catalysis pathway is proposed with the formation of frustrated Lewis pair between metal center and silane. In-situ 1H NMR experiments were conducted to address the kinetics of benzaldehyde hydrosilylation in a rhenium pincer system. The rate of reaction is determined to be independent of substrate concentration but first-order with respect to silane and catalyst, suggesting silane activation is the rate-determining step.