Mechanism of Nickel(II)-Catalyzed Oxidative C(sp²)-H/C(sp³)-H Coupling of Benzamides and Toluene Derivatives

Abstract

The Ni-catalyzed C(sp(2))-H/C(sp(3))-H coupling of benzamides with toluene derivatives was recently successfully achieved with mild oxidant iC3F7I. Herein, we employ density functional theory (DFT) methods to resolve the mechanistic controversies. Two previously proposed mechanisms are excluded, and our proposed mechanism involving iodine-atom transfer (IAT) between iC3F7I and the Ni(II) intermediate was found to be more feasible. With this mechanism, the presence of a carbon radical is consistent with the experimental observation that (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) completely quenches the reaction. Meanwhile, the hydrogen-atom abstraction of toluene is irreversible and the activation of the C(sp(2))-H bond of benzamides is reversible. Both of these conclusions are in good agreement with Chatani's deuterium-labeling experiments.

Keywords: C−H activation; cross-coupling; density functional calculations; nickel; reaction mechanisms.