Analysis of an Unprecedented Mechanism for the Catalytic Hydrosilylation of Carbonyl Compounds

This work details an in-depth evaluation of an unprecedented mechanism for the hydrosilylation
of carbonyl compounds catalyzed by (PPh3)2Re(O)2I. The proposed mechanism involves addition of a silane
Si−H bond across one of the rhenium−oxo bonds to form siloxyrhenium hydride intermediate 2 that reacts
with a carbonyl substrate to generate siloxyrhenium alkoxide 4, which, in turn, affords the silyl ether product.
Compelling evidence for the operation of this pathway includes the following:  (a) isolation and structural
characterization by X-ray diffraction of siloxyrhenium hydride intermediate 2, (b) demonstration of the catalytic
competence of intermediate 2 in the hydrosilylation reaction, (c) 1H and 31P{1H} NMR and ESI-MS evidence
for single-turnover conversion of 2 into 1, (d) observation of intermediate 2 in the working catalyst system,
and (e) kinetic analysis of the catalytic hydrosilylation of carbonyl compounds by 1.