The reactions of hydrosilanes with the methoxycarbonyl complexes Cp(L) (CO) MCO2Me (M = Fe, Ru; L = CO, PPh3) and (L)(CO) xMCO2Me (M = Co, Mn; L = CO, PPh3; x = 3,4, with and without catalysis

Article abstract of DOI:10.1016/S0022-328X(97)00274-X

The reactivity of selected organotransition metal methoxycarbonyl complexes towards hydrosilanes differs significantly from their acetyl analogs in that hydrosilation does not occur across the methoxycarbonyl ligand. Only hydrosilane/manganese carbonyl precatalyst systems that had proved to be more active towards the acetyl ligand on Cp(L)(CO)MC(O)CH₃ (M = Fe, Ru; L = CO, PPh₃, PPh₃) reacted with the methoxycarbonyl complexes Cp(CO)₂MCO₂CH₃ (1, M = Fe; 2, M = Ru). These reactions involving PhSiH₃/2-3% (PPh₃)(CO)₄MnC(O)CH₃ for 1 and 2, or PhMe₂SiH/2-3% (CO)₅MnCH₃ for 1 afforded their η⁴-cyclopentadiene compounds (η⁴-C₅H₆)M(CO)₃ (M = Fe, Ru) plus methoxysilanes. Results with PhMe₂SiD/3% (CO)₅MnCH₃ support exo deutende transfer to the Cp ligand; a mechanism is proposed. The low reactivity of methoxycarbonyl complexes under hydrosilation catalysis conditions also is consistent with the inactivity of PhSiH₃ or Ph₂SiH₂/Rh(PPh₃)₃Cl towards 1 or 2 and with the inertness of Cp(PPh₃)(CO)FeCO₂CH₃ and Cp*(CO)₂FeCO₂CH₃ under all attempted hydrosilation conditions. This diminution of hydrosilane reactivity extends to cobalt and manganese carbonyl methoxycarbonyl complexes (L)(CO)_xMCO₂CH₃ (3, M = Mn, x = 4, L = CO; 4, M = Co, x = 3, L = PPh₃; 5, M = Co, x = 3, L = CO). Although their acetyl analogs (L)(CO)_xMC(O)CH₃ are sensitive to hydrosilanes, both 3 and 4 are inert towards PhMe₂SiH or Ph₂SiH₂. Treatment of 5 with PhMe₂SiH released methyl formate and left the silyl complex (CO)₄CoSiMe₂Ph, a result that resembles the hydrogenation chemistry of 5.