Metal-Ligand Cooperativity via Π-Π Interactions Supporting Outer-Sphere Hydride Transfer.

A set of phosphine-free Ru(II)-CNC pincer complexes with benzimidazolylidene-based CNC-ligands has been synthesized and characterized, which show excellent catalytic activity toward α-alkylation of ketones using primary alcohols. DFT investigations revealed that these seemingly nonbifunctional complexes can operate via inner- and outer-sphere mechanisms for the alcohol dehydrogenation step; however, the outer-sphere path is favored for the subsequent steps. The outer-sphere path is found to be supported by π-π interaction between the extended aromatic ring system of the benzimidazolylidene-based CNC-ligand and aromatic rings of the substrates in a new, unprecedented case of metal-ligand cooperativity.