Rational Ligand Design of Air‐Stable Ni–NHC Precatalysts for Challenging C─N Bond Formation: Balancing Steric Demand and Reactivity

ABSTRACT

A series of air‐stable Ni(II)–NHC precatalysts (NHC = N ‐heterocyclic carbene) was developed for metal‐catalyzed amination through systematic steric and electronic ligand evaluation. Chlorination of the NHC backbone, together with varying N ‐aryl bulk flanking the Ni center, enabled precise control over catalyst reactivity and selectivity, revealing the importance of a balanced steric approach in optimizing nickel catalysts for this purpose. Increased steric demand within this tailored ligand framework enhanced catalytic performance by facilitating reductive elimination and suppressing competing β‐hydride elimination pathways, while maintaining sufficient accessibility for substrate coordination. This structure–reactivity relationship revealed a rational pairing of NHC sterics and substrate structure. This illustrates a divergence of reactivity patterns with Pd–NHC catalysts where increasing ligand bulk invariably yielded better cross‐coupling outcomes, regardless of substrate size.