Neutral and cationic ruthenium carbonyl complexes [Ru(CO)(2,2′-dipyridylamine)(PR3)Cl2] and [Ru(CO)(N–N)(PPh3)2(H)]Cl: synthesis, structural characterization and transfer-hydrogenation

Abstract

The neutral complexes [Ru(CO)(dpa)(PR3)Cl2] (R = Ph (1) or p-tol (2); dpa = 2,2′-dipyridylamine) were synthesized by the reaction of [Ru(CO)(dmf)(PR3)2Cl2] (dmf = N,N-dimethylformamide) and the dpa ligand, while the cationic carbonyl hydride complexes [Ru(CO)(N–N)(PPh3)2(H)]Cl were synthesized by reaction of [Ru(CO)(PPh3)3Cl(H)] and the appropriate N–N ligand [N–N = 2,2′-bipyridine = bipy (3), 2,2′-4,4′dimethyl-bipyridine = dmb (4) and 2,2′-dipyridylamine = dpa (5)]. The complexes were characterized by NMR (31P, 1H and HMBC 1H-31P), FTIR, elemental analysis and X-ray diffraction. The molecular structure of [Ru(CO)(dpa)(PPh3)Cl2] (1) was determined by X-ray crystallography. The crystal packing is stabilized by strong (CH3)O–H···Cl and N–H···OH(CH3) hydrogen bonds between symmetry-related molecules leading to the formation of dimers. Complexes 1–6 were evaluated as pre-catalysts for the reduction of acetophenone under transfer-hydrogenation conditions using isopropanol as hydrogen source, and conversions up to 86 % in 4 h were achieved.