Bis-chelate N-heterocyclic tetracarbene Ru(II) complexes: Synthesis, structure, and catalytic activity toward transfer hydrogenation of ketones

Abstract Ru(II) complexes with two chelating di- N -heterocyclic carbenes (NHC) and two acetonitrile ligands (NHC = 1,1′-dialkyl-3,3′-methylene-diimidazol-2,2′-diylidene, and alkyl = methyl and n -butyl) were synthesized and structurally characterized. The crystal structures of the complexes determined by X-ray diffraction analyses show that the Ru(II) center is bound to two bidentate carbene ligands and two acetonitrile molecules, forming a distorted octahedron. The complexes prove to be an efficient catalyst having exceedingly high turnover frequencies and good reusability in transfer hydrogenation of ketones.