Magnesium-catalyzed hydrosilylation of α,β-unsaturated esters.

ToMgHB(CF) (, To = tris(4,4-dimethyl-2-oxazolinyl)phenylborate) catalyzes the 1,4-hydrosilylation of α,β-unsaturated esters. This magnesium hydridoborate compound is synthesized by the reaction of ToMgMe, PhSiH, and B(CF). Unlike the transient ToMgH formed from the reaction of ToMgMe and PhSiH, the borate adduct persists in solution and in the solid state. Crystallographic characterization reveals tripodal coordination of the HB(CF) moiety to the six-coordinate magnesium center with a ∠Mg-H-B of 141(3)°. The pathway for formation of is proposed to involve the reaction of ToMgMe and a PhSiH/B(CF) adduct because the other possible intermediates, ToMgH and ToMgMeB(CF), react to give an intractable black solid and ToMgCF, respectively. Under catalytic conditions, silyl ketene acetals are isolated in high yield from the addition of hydrosilanes to α,β-unsaturated esters with as the catalyst.