Theoretical investigation of mechanism on nickel-catalyzed electrochemical cross-coupling of aryl bromides and arylamines

Based on our previous experimental studies on the reductive neutral cross-coupling reaction of aryl bromides and arylamines over various nickel catalysts and ligands, a broad substrate scope has been developed under mild conditions. The catalytic activity varied widely in the substituents on the bipyridine or tridentate ligands of the catalyst. The formation of carbon radicals and the regeneration of low-valent nickel species under electrolysis have also been experimentally proposed, but the detailed mechanism is still unclear. At present, a theoretical electrochemical study of original organic systems is rare due to the lack of a well-defined DFT computational method for the electrochemical process. In this work, the electrochemical neutral cross-coupling reaction involving the steps of oxidative addition, cathodic reduction, radical addition, and reductive elimination was explored using density functional theory (DFT) calculations. The catalytic cycle likely starts with Ni(i), oxidative addition is the rate-determining step, and the radical addition forms C-C bonds through the inner-sphere mechanism. The analysis of the steric effect of the ligand shows a non-negligible effect on the activity. The ADCH (atomic dipole moment corrected Hirshfeld population) charge and frontier molecular orbital (FMO) analysis suggest that the central nickel atom has higher electron density and the highest occupied molecular orbital (HOMO) is unstable when the bipyridine ring has an electron-donating group, which is beneficial to enhancing the catalytic activity.