Experimental and computational studies of the ruthenium-catalyzed hydrosilylation of alkynes: Mechanistic insights into the regio- and stereoselective formation of vinylsilanes

The ruthenium hydride complex (PCy₃)₂(CO)RuHCl was found to be a highly effective catalyst for the regio- and stereoselective hydrosilylation of alkynes to form vinylsilane products. (Z)-Vinylsilane products were selectively formed for sterically nondemanding terminal alkynes, while (E)-vinylsilane products resulted from sterically demanding terminal alkynes. Kinetic data were obtained from the hydrosilylation of phenylacetylene. The phosphine inhibition study showed an uncompetitive Michaelis-Menten type of inhibition kinetics. The empirical rate law rate = k_obs[1]¹[alkyne]⁰[silane]⁰ was established from the reaction rate as a function of both [alkyne] and [silane]. DFT calculations were performed and found that Z/E isomerization is facile via a metallacyclopropene transition state and that the isomerization occurs prior to the silane substrate binding. A detailed mechanistic scheme on the hydrosilylation reaction has been delineated on the basis of both experimental and computational data.