MECHANISTIC STUDY OF RUTHENIUM-CATALYZED HYDROSILATION OF 1-(TRIMETHYLSILYL)-1-BUTEN-3-YNE

Catalytic hydrosilation of 1-(trimethylsilyl)-1-buten-3-yne (1) with three kinds of hydrosilanes (HSiMePh2, HSiMe2Ph, and HSiEt3) in CDCl3 at 30 °C in the presence of a catalytic amount of RuHCl(CO)(PPh3)3 (2) gave five types of reaction products:  (1E,3E)-CH(SiR3)CHCHCHSiMe3 (3), R3SiCH2CHCHCH2SiMe3 (4), R3SiCHCCHCH2SiMe3 (5), (1Z,3E)-CH(SiR3)CHCHCHSiMe3 (6), and R3SiC⋮CCHCHSiMe3 (7). Detailed investigations on the stoichiometric reactions of intermediate ruthenium species provided definitive evidence for the catalytic mechanism comprised of two catalytic cycles, the Chalk−Harrod cycle A and the modified Chalk−Harrod cycle C, and their interconnecting processes B and D. Product 3 is formed by the insertion of 1 into the Ru−H bond of 2 followed by the reaction of the resulting terminal dienyl complex Ru(CHCHCHCHSiMe3)Cl(CO)(PPh3)2 (8) with hydrosilane. The latter process regenerates 2 and the sequence of reactions proceeds catalytically (cycle A). The reaction of 8 with hydrosilane is accompanied by a sid...