Theoretical Study of Ni-Catalyzed C-N Radical-Radical Cross-Coupling.

A computational study was carried out to investigate the mechanism and the origin of chemoselectivity in nickel-catalyzed C-N radical-radical cross-coupling reaction. The global electrophilicity index ω° and global nucleophilicity index N° were used to quantitatively describe the electrophilic or nucleophilic character of the carbon radical, nitrogen radical, and Ni(II) complex. The calculated ω° and N° values indicate that introduction of nickel makes C-N cross-coupling to be a facile process. Detailed theoretical results show that the cross-coupling occurs through the combination of Ni(I) complex with a nitrogen-centered radical, a minimum energy crossing point to form the singlet Ni(II) complex, and radical addition of the nucleophilic carbon-centered radical lead to C-N bond formation. On the basis of the theoretical results, a generalized scheme is provided to clarify the origin of the chemoselectivity in nickel-catalyzed C-N radical-radical cross-coupling.