Asymmetric catalysis. Mechanism of asymmetric catalytic intramolecular hydrosilylation

The mechanism of asymmetric catalytic intramolecular hydrosilation using [Rh(diphosphine)] + catalysts has been investigated by the use of specifically labeled deuterated substrates. It is concluded that oxidative addition of the silicon hydride bonds to the catalysts is rapid and reversible for most systems. Both 5-membered and 6-membered metallacycles are inferred to form rapidly and reversibly. These species are unproductive catalytic intermediates. It was inferred that β-hydride elimination is very rapid and is faster than chelate ring conformational interconversion