The mechanism of Cu-catalyzed C–N cyclization from N-phenylbenzamidine to 2-phenylbenzimidazole: A DFT study

Possible mechanisms of copper-catalyzed N–H/C–H activation from N-phenylbenzamidine to 2-phenylbenzimidazole have been investigated using density functional theory (DFT) calculations. In comparison with the C–H activation mechanism, the N–H/C–H activation with a Cu-assisted concerted metalation–deprotonation (CMD) mechanism is found to be more kinetically favorable. Facile occurrence of the studied reactions is supported by the low activation energies of their respective rate-determining steps. A possible alternative mechanism involving a Cu–H agostic transition state is presented, but it is unfavored by the relatively higher activation barriers.