Reactions of hydrido(hydrosilylene)tungsten complexes with α,β-unsaturated carbonyl compounds:: Selective formation of (η3-siloxyallyl)tungsten complexes

Hydrido(hydrosilylene)tungsten complexes (C5Me4R1)(CO)(2)(H)W=Si(H)[C(SiMe3)(3)] [R-1 = Me (1a), R-1 = Et (1b)] reacted with (alpha,beta-Punsaturated carbonyl compounds (RC)-C-2(O)CH=CHR3 (R-2 = Me, R-3 = H or Ph; R-2 = OMe, R-3 = H) at room temperature to give exo-anti (3]-siloxyallyl)tungsten complexes (C5Me4R1)(CO)(2)W[(eta 3)-(RHCCHCROSiH2)-H-3-O-2{C(SiMe3)(3))] almost quantitatively and regioselectively. Possible reaction mechanisms involving a [2+4] cycloaddition process are proposed.