Mechanistic details of the cobalt-mediated dehydrogenative dimerization of aminoquinoline-directed benzamides.

Key mechanistic features of the cobalt-mediated and aminoquinoline-directed dehydrogenative aryl-aryl coupling were investigated computationally and experimentally. A series of Co and Co complexes relevant to the proposed reaction cycle have been synthesized and characterized. Stoichiometric reactions and electrochemical studies were used to probe the role of different additives in the reaction pathway. Computationally, three different mechanisms, such as , , and were explored. It is shown that the mono-metallic and mechanisms are the most favorable ones, among which the former mechanism is slightly more encouraging and proceeds the: (a) concerted-metalation-deprotonation (CMD) of the first benzamide C-H bond, (b) PivOH-to-PivO rearrangement, (c) CMD of the second benzamide C-H bond, (d) C-C coupling, (e) product formation facilitated by the amide nitrogen re-protonation, and (f) catalyst regeneration. The rate-determining step of this multi-step process is the C-C coupling step. The computational studies suggest that the electronics of both the aryl-benzamide and pyridine fragments of the aminoquinoline-benzamide ligand control the efficiency of the reaction.