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

Summary

Ruthenium complexes [Ru(L1) ₂(CH ₃CN) ₂](PF ₆) ₂ ( 1), [RuL1(CH ₃CN) ₄](PF ₆) ₂ ( 2) and [RuL2(CH ₃CN) 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) ₂Cl 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 ₃CN) 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 ₃CN) ₃](PF ₆) ₂ ( 4) and [RuL1(phen)(CH ₃CN) 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.

Abstract