Emerging N-Heterocyclic Carbene–Nickel Catalysis: Bond Activations, Cross-Coupling Reactions, and Beyond

Abstract N-Heterocyclic carbenes (NHCs) are widely recognized as versatile ligands in catalysis owing to their high stability and adjustable electronic and steric features. These attributes make them highly useful for the efficient synthesis of pharmaceuticals, functional materials, and structurally complex organic molecules. The NHC ligand enables more streamlined and effective catalyst design, as its reactivity can be tuned more readily than the traditional phosphine ligands. Advantageously, a combination of NHC ligands with base metals such as nickel often exceeds expectations in reactivity and selectivity. Nickel–NHC complexes are emerging as powerful catalysts and exhibit diverse mechanistic pathways, including cationic, two-electron, and one-electron pathways, thereby broadening the scope of their ample reactivities. From both synthetic and sustainability perspectives, nickel catalysis supported by NHC ligands provides an attractive alternative to precious metal systems, offering economical and versatile solutions. A wide range of NHCs, from classical to abnormal, has been developed and employed with nickel catalysts for C–F, C–C, C–N, C–H, and C–O bond activations, as well as for several cross-coupling reactions. This review highlights advances over the past decade in NHC–nickel catalysis, emphasizing their reactivity, mechanistic insights, and broad synthetic applications, while also discussing current challenges and future directions in this rapidly evolving field, including chiral, abnormal, redox-neutral, non-classical, and synergistic NHC catalysis.