Relative Rates of Hydrosilylation of Representative Alkenes and Alkynes by Cp(2)YMe.THF and [Cp(TMS)(2)YMe](2)

Reactivity in the hydrosilylation of alkenes and alkynes catalyzed by the organoyttrium catalysts Cp(2)YMe.THF and [Cp(TMS)(2)YMe](2) is generally determined by the steric environment of the substrate. Alkynes and conjugated alkenes show an increased reaction rate because of electronic effects; the magnitude of this increase is highly substrate dependent. The electron rich pyrrole system is particularly reactive, especially with the sterically open [Cp(TMS)(2)YMe](2) precatalyst. For nonconjugated substrates, Cp(2)YMe.THF is generally a more selective catalyst than [Cp(TMS)(2)YMe](2).