Mechanism of ketone hydrosilylation by Cu(I) catalysts: A theoretical study

The plausibility of the catalytic cycle suggested for the hydrosilylation of ketones by Cu(I) hydrides has been investigated by a theoretical DFT study. A model system made up of a CuH(PH3)(2) catalyst, acetone and SiH4 gives us the necessary insight into the intrinsic reactivity of the system. This reactivity is confirmed, by introducing the more rigid CuH[C4H4(PH2)(2)] catalyst, as well as tetra-coordinated, CuH(PH3)(3) and CuH(PH3)[C4H4(PH2)(2)] compounds. Computations show the activation of the copper fluoride pre-catalyst, as well as both steps of the catalytic cycle to involve a 4 center metathesis transition state as suggested in literature. These results show the reaction to be favored by the formation of a Van der Waals complex resembling the transition states. The formation of these latter is induced by stabilizing electrostatic interactions between those atoms involved in the bond breaking and bond forming. Both steps of the actual catalytic cycle show a free energy barrier of about 10 kcal/mol with respect to the isolated reactants, hereby confirming the plausibility of the suggested cycle. We have found a substantial overall exothermicity of the catalytic cycle of about 35 kcal/mol. (C) 2009 Elsevier B.V. All rights reserved.