Synthesis and structures of ruthenium–NHC complexes and their catalysis in hydrogen transfer reaction

Ruthenium complexes [Ru(L1)(2)(CH(3)CN)(2)](PF(6))(2) (1), [RuL1(CH(3)CN)(4)](PF(6))(2) (2) and [RuL2(CH(3)CN)(3)](PF(6))(2) (3) (L1= 3-methyl-1-(pyrimidine-2-yl)imidazolylidene, L2 = 1,3-bis(pyridin-2-ylmethyl)benzimidazolylidene) were obtained through a transmetallation reaction of the corresponding nickel–NHC complexes with [Ru(p-cymene)(2)Cl(2)](2) in refluxing acetonitrile solution. The crystal structures of three complexes determined by X-ray analyses show that the central Ru(II) atoms are coordinated by pyrimidine- or pyridine-functionalized N-heterocyclic carbene and acetonitrile ligands displaying the typical octahedral geometry. The reaction of [RuL1(CH(3)CN)(4)](PF(6))(2) with triphenylphosphine and 1,10-phenanthroline resulted in the substitution of one and two coordinated acetonitrile ligands and afforded [RuL1(PPh(3))(CH(3)CN)(3)](PF(6))(2) (4) and [RuL1(phen)(CH(3)CN)(2)](PF(6))(2) (5), respectively. The molecular structures of the complexes 4 and 5 were also studied by X-ray diffraction analysis. These ruthenium complexes have proven to be efficient catalysts for transfer hydrogenation of various ketones.