Benzimidazolyl Palladium Complexes as Highly Active and General Bifunctional Catalysts in Sustainable Cross-Coupling Reactions

A family
of air- and moisture-stable dinuclear palladium complexes
bearing 2-benzimidazolyl ligands is reported and shown to be a highly
effective and general catalytic platform in diverse cross-coupling
reactions. The rigidity and conformation of the ligand scaffold was
readily modified via tethering of the 2-benzimidazolyl moiety to diamine
ligands, resulting in significant changes in catalytic activity. Under
optimal conditions, Suzuki, Heck, and Sonogashira-type couplings of
aryl bromides can all be performed efficiently with good functional
group compatibility using only 0.1 mol % of catalyst, in aqueous
or alcohol solvents. Experimental evidence highlights the importance
of the bifunctional character of the ligand for catalytic activity,
where the basic N-functionality in the ligand framework
is proposed to accelerate (trans)­metalation steps via intramolecular
assistance.