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 = kobs[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.