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 an attractive, emerging approach to forging C−N bonds as it uses air-stable Ni catalysts and efficiently proceeds at room temperature. However, in-depth mechanistic understandings of this new C−N cross-coupling methodology remain underexplored. Herein, extensive experimental and computational studies were conducted to examine the mechanism of Ni-catalyzed electrochemical aryl amination reactions. The results suggest coordination of an amine to the Ni(II) catalyst occurs before the cathodic reduction and oxidative addition steps. A stable Ni(II) aryl amido intermediate is produced from the cathodic half-reaction, a critical step in controlling the selectivity between cross-coupling and undesired homo-coupling reaction pathways. In addition, redox-active bromide in the supporting electrolyte functions as a redox 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 undergoes facile reductive elimination to provide a C−N cross-coupling product at room temperature. These mechanistic insights about the Ni-catalyzed aryl e-amination are valuable for understanding and developing new Ni-catalyzed aryl e-amination reactions and also other Ni-catalyzed electrosynthetic reactions such as C−C and C−O cross-couplings.