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-phenyl-benzimidazole 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. (C) 2014 Elsevier B.V. All rights reserved.