Mechanistic insights into aryl nickel-catalyzed benzylic dehydrogenation of electron-deficient heteroarenes by using DFT calculations

Abstract

We recently investigated the mechanism of aryl nickel-catalyzed benzylic dehydrogenation of electron-deficient heteroarenes by using DFT calculations, which is an elegant protocol for accessing important precursor compounds such as 2-alkenyl heteroarenes. In this work, we proposed a novel γ-hydride elimination mechanism. Theoretical calculations supported our inference and ruled out the β-hydride elimination route proposed by the experimental group. Moreover, we found that the coordination of heterocyclic nitrogen to nickel metal is an important factor preventing the β-hydride elimination. Consistent with the experimental findings, the calculation conclusion confirmed that benzylic deprotonation is a reversible process. Additionally, we also found that a zinc salt plays an important role in affording the precursor of the transmetalation process, and the benzylic deprotonation is most likely to be a rate-determining step for this transformation. Finally, based on our calculations, we proposed an amended catalytic conversion mechanism.