Understanding Formation and Roles of Ni^II Aryl Amido and Ni^III Aryl Amido Intermediates in Ni-Catalyzed Electrochemical Aryl Amination Reactions

Ni-catalyzed electrochemical aryl amination (e-amination)is anattractive, emerging approach to building C-N bonds. Here,we report in-depth experimental and computational studies that examinedthe mechanism of Ni-catalyzed e-amination reactions. Key Ni-II-amine dibromide and Ni-II aryl amido intermediates werechemically synthesized and characterized. The combination of experimentsand DFT calculations suggest (1) there is coordination of an amineto the Ni-II catalyst before the cathodic reduction andoxidative addition steps, (2) a stable Ni-II aryl amidointermediate is produced from the cathodic half-reaction, a criticalstep in controlling the selectivity between cross-coupling and undesiredhomo-coupling reaction pathways, (3) the diazabicycloundecene additiveshifts the aryl halide oxidative addition mechanism from a Ni-I-based pathway to a Ni-0-based pathway, and (4)redox-active bromide in the supporting electrolyte functions as aredox mediator to promote the oxidation of the stable Ni-II aryl amido intermediate to a Ni-III aryl amido intermediate.Subsequently, the Ni-III aryl amido intermediate undergoesfacile reductive elimination to provide a C-N cross-couplingproduct at room temperature. Overall, our results provide new fundamentalunderstandings about this e-amination reaction and guidance for furtherdevelopment of other Ni-catalyzed electrosynthetic reactions suchas C-C and C-O cross-couplings.