An air-stable, well-defined palladium-BIAN-NHC chloro dimer: a fast-activating, highly efficient catalyst for cross-coupling.

We report the synthesis, characterization and reactivity of an air-stable, well-defined acenaphthoimidazolylidene palladium-BIAN-NHC chloro dimer complex, [Pd(BIAN-IPr)(μ-Cl)Cl]. This rapidly activating catalyst merges the reactive properties of palladium chloro dimers, [Pd(NHC)(μ-Cl)Cl], with the attractive structural features of the BIAN framework. [Pd(BIAN-IPr)(μ-Cl)Cl] is the most reactive Pd(II)-NHC precatalyst discovered to date undergoing fast activation under both an inert atmosphere and aerobic conditions. The catalyst features bulky-yet-flexible sterics that render the C-H substituents closer to the metal center in combination with rapid dissociation to monomers and strong σ-donor properties. [Pd(BIAN-IPr)(μ-Cl)Cl] should be considered as a catalyst for reactions using well-defined Pd(II)-NHCs.