Metal-Catalyzed Hydrosilylation of Alkenes and Alkynes Using Dimethyl(pyridyl)silane

Metal-catalyzed hydrosilylation of alkenes and alkynes using dimethyl(pyridyl)silane is described. The hydrosilylation of alkenes using dimethyl(2-pyridyl)silane (2-PyMe2SiH) proceeded well in the presence of a catalytic amount of RhCl(PPh3)3 with virtually complete regioselectivity. By taking advantage of the phase tag property of the 2-PyMe2Si group, hydrosilylation products were isolated in greater than 95% purity by simple acid−base extraction. Strategic catalyst recovery was also demonstrated. The hydrosilylation of alkynes using 2-PyMe2SiH proceeded with a Pt(CH2CHSiMe2)2O/P(t-Bu)3 catalyst to give alkenyldimethyl(2-pyridyl)silanes in good yield with high regioselectivity. A reactivity comparison of 2-PyMe2SiH with other related hydrosilanes (3-PyMe2SiH, 4-PyMe2SiH, and PhMe2SiH) was also performed. In the rhodium-catalyzed reaction, the reactivity order of hydrosilane was 2-PyMe2SiH ≫ 3-PyMe2SiH, 4-PyMe2SiH, PhMe2SiH, indicating a huge rate acceleration with 2-PyMe2SiH. In the platinum-catalyzed reaction, the reactivity order of hydrosilane was PhMe2SiH, 3-PyMe2SiH ≫ 4-PyMe2SiH > 2-PyMe2SiH, indicating a rate deceleration with 2-PyMe2SiH and 4-PyMe2SiH. It seems that these reactivity differences stem primarily from the governance of two different mechanisms (Chalk−Harrod and modified Chalk−Harrod mechanisms). From the observed reactivity order, coordination and electronic effects of dimethyl(pyridyl)silanes have been implicated.