Highly chemoselective catalytic transfer hydrosilylation of aldehydes

International audienceCatalytic hydrosilylation has found widespread applications in the silicon industry and in synthetic organic chemistry owing to its ability to induce both reduction ($hydro$) and functionalization ($silylation$) of unsaturated bonds such as C=C or c=o bonds in an atom-economical manner. Nevertheless, the preparation of hydrasilanes (R$_3$SiH) relies on energy-intensive processes based either on costly redox-manipulation of Si or on the reduction of chlorasilanes with highly reactive metal hydrides such as LiAIH$_4$. To circumvent these limitations, we have developed a conceptual alternative consisting in the utilization of silyl formates (R$_3$SiOC(O)H), readily prepared from formic acid and chlorasilanes, as surragates of hydrasilanes in hydrasilylation reactions. The key feature of this endeavor stems fram the renewability of the hydridic counterpart in the silyl formates since formic acid can be obtained by 2$^{e-}$ electroreduction of CO$_2$. The viability of the aforementioned concept has been demonstrated with the catalytic transfer hydrasilylation of aldehydes. In the presence of a well-defined ruthenium catalyst, various aldehydes are efficiently and chemoselectively reduced to silyl ethers with the concomitant release of CO$_2$. Mechanistic insights were gained by both experimental observations and DFT calculations and they highlight the pivotal role of a transmetallation step to rationalize the outstanding chemoselectivity of the process