Highly Regio- and Stereoselective Hydrosilylation of Internal Thioalkynes under Mild Conditions.

A general and mild hydrosilylation of thioalkynes is described. With the cationic catalyst Cp*Ru(MeCN)3 and the bulky silane (TMSO)3 SiH, a range of thioalkynes underwent smooth hydrosilylation at room temperature with excellent α regioselectivity and syn stereoselectivity. DFT calculations provided important insight into the mechanism, particularly the unusual syn selectivity with the Cp*Ru(MeCN)3 catalyst. The sulfenyl group in the substrates was found to provide important chelation stabilization to direct the reaction through a new mechanistic pathway.