Air-stable, well-defined palladium–BIAN–NHC chloro dimer: Highly efficient N-Heterocyclic carbene (NHC) catalyst platform for Buchwald–Hartwig C–N cross-coupling reactions

Abstract

Buchwald-Hartwig amination has become the fundamental method for constructing molecular architectures throughout chemical research, including the synthesis of pharmaceutical agents, natural products, fine chemicals, and advanced materials. Herein, we report air-stable, well-defined palladium–BIAN–NHC chloro dimer, [Pd(BIAN–NHC)(μ-Cl)Cl]₂, for Buchwald-Hartwig C–N cross-coupling reactions of aryl halides. This rapidly activating catalyst framework merges the reactive properties of palladium chloro dimers, [Pd(NHC)(μ-Cl)Cl]₂, with the structural features of acenaphthoimidazol-2-ylidenes. [Pd(BIAN–NHC)(μ-Cl)Cl]₂ is the most reactive Pd(II)–NHC precatalyst to date, undergoing fast activation under both inert atmosphere and aerobic conditions. The catalyst shows an excellent reactivity in Buchwald-Hartwig amination of aryl halides (59 examples), including challenging substrates, diamination and direct functionalization of pharmaceuticals. The steric protection enables high reactivity under both inert atmosphere and aerobic conditions. [Pd(BIAN–IPr)(μ-Cl)Cl]₂ should be routinely utilized for the synthesis of C–N bonds to make valuable amines, where it replaces the most commonly deployed at present IPr (IPr = 1,3-bis(2,6-isopropyl)imidazol-2-ylidene).