Mechanism of alkane C-H bond activation by copper and silver homoscorpionate complexes

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 TpAg=C(H)(CO2CH3), Tp(Br3)Ag= C(H)(CO2CH3), TpCu=C(H)(CO2CH3), and Tp(Br3)Cu=C(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.