Mechanisms of Nickel-Catalyzed Cross-Coupling Reactions

Advances in nickel-catalyzed cross-coupling reactions have expanded the chemical space of accessible structures and enabled newsynthetic disconnections. The unique properties of Ni catalysts facilitate the activation of traditionally inert substrates, tolerate alkyl coupling partners that undergo decomposition via b-hydride (b-H) elimination with Pd, and enable stereoconvergent cross-couplings. The radical pathways accessed by Ni catalysts have been merged with photoredox and electrochemical catalysis to achieve new reactivity. The growing utility of Ni catalysis is, in no small part, due to advances in our fundamental understanding of the properties of Ni catalysts and the mechanisms by which the reactions occur. This review highlights recent important contributions to the field with an emphasis on studies that have afforded mechanistic insight.