Hydrosilylation with biscarbene Rh(I) complexes: experimental evidence for a silylene-based mechanism.

A detailed study investigating the mechanism of the hydrosilylation of 4-F-acetophenone by N-heterocyclic biscarbene rhodium(I) complexes was performed, delivering substantial experimental evidence for a recently proposed catalytic cycle and explaining the observed side-product formation. Labeling experiments, silylene trapping reactions, and specific catalytic reactions were employed to substantiate each step of the catalytic cycle and explain the differences observed for different types of chiral catalysts. It is further shown that hydrosilylation and dehydrocoupling reactions with dihydrosilanes are mechanistically related.