Theoretical Insight on the High Reactivity of Reductive Elimination of Ni III Based on Energy- and Electron-Transfer Mechanisms.

Iridium/nickel (Ir/Ni) metallaphotoredox dual catalysis overcomes the challenging reductive elimination (RE) of Ni(II) species and has made a breakthrough progress to construct a wide range of C-X (X = C, N, S, and P) bonds. However, the corresponding reaction mechanisms are still ambiguous and controversial because the systematic research on the nature of this synergistic catalysis is not sufficient. Herein, Ir III /Ni II and Ir III /Ni 0 metallaphotoredox catalysis have been theoretically explored taking the aryl esterification reaction of benzoic acid and aryl bromide as an example by a combination of density functional theory (DFT), molecular dynamics, and time-dependent DFT computations. It is found that an electron-transfer mechanism is applicable to Ir III /Ni II metallaphotoredox catalysis, but an energy-transfer mechanism is applicable to Ir III /Ni 0 combination. The Ir III /Ni II metallaphotoredox catalysis succeeds to construct a Ni I -Ni III catalytic cycle to avoid the challenging RE of Ni(II) species, while the RE occurs from triplet excited-state Ni(II) species in the Ir III /Ni 0 metallaphotoredox catalysis. In addition, the lower lowest unoccupied molecular orbital energy level of Ni(III) species than that of Ni(II) species accelerates RE from Ni(III) one. The triplet excited-state Ni(II) species can resemble a Ni(III) center, considering the metal-to-ligand charge transfer character to promote the RE.