Computational study on the reaction mechanism of hydrosilylation of carbonyls catalyzed by high-valent rhenium(V)-di-oxo complexes

Density functional theory (DFT) calculations have been performed to elucidate the reaction mechanism of hydrosilylation of carbonyl compounds catalyzed by high-valent rhenium(V)-di-oxo complexes ReO2I(PR3)(2) (R = Me, Ph). The calculations suggest that the most favorable mechanism involves the rate-determining dissociative [2 + 2] addition of the Si-H bond across a Re=O bond to form a Re(V) hydrido siloxy intermediate; this is followed by carbonyl coordination, reduction of the carbonyl, rearrangement, and final intramolecular nucleophilic attack from the alkoxy group to the silyl center (dissociative retro[2 + 2] addition). It was also found that the additional oxo ligand in the ReO2I(PR3)(2) complexes promotes the [2 + 2] addition across the rhenium-oxo bond both kinetically and thermodynamically, as compared to the neutral rhenium(V)-mono-oxo complex ReOCl3(PMe3)(2). The effect of different silanes on the [2 + 2] addition barriers is also studied.