Mechanism of Alkane C−H Bond Activation by Copper and Silver Homoscorpionate Complexes

Abstract

DFT Becke3LYP calculations are applied to the computational study of the activation of alkane C−H bonds by metallocarbene homoscorpionate complexes. A total of 16 different combinations of metallocarbene complex and alkane are explored, defined by the use of TpAgC(H)(CO2CH3), TpBr3AgC(H)(CO2CH3), TpCuC(H)(CO2CH3), and TpBr3CuC(H)(CO2CH3) species as metallocarbene and methane, ethane, propane, and butane as alkane. The reaction is found to be under kinetic control, and the selectivity is decided in a step with a low-barrier transition state where the key bond-breaking and bond-forming processes take place in a concerted way. This transition state has several possible conformations, which are systematically explored to find the one with lowest energy for each reaction. Variations of the energy barrier as a function of the nature of metal, ligand, and alkane are analyzed and discussed.