Ruthenium(II) diphosphine(phosphine)/imine/amine/CO complexes as efficient catalysts in transfer hydrogenation of ketones

Abstract

Abstract Treatment of [RuCl2(CO)2]n with different phosphine ligands, four Ru(II) complexes of cis-, cis-, trans- RuCl2(CO)2L2 (L\u202f=\u202fPH(C6H11)2 (1), PPh3 (2), PPh2(C6F5) (3) and PMe3 (4)), in which 1 and 3 are novel complexes, have been generated in methylene chloride and isolated as pure compound in solid. In CH2Cl2 mixed 1:1 molar ratio of RuCl2(PPh3)3 and 1,1′-bis(diphenylphosphine)ferrocene (DPPF), and further reacted with quantitative 2-aminopyridine (ampy), 2-picolylamine (picam) and pyridine ligands, the complexes of RuCl2(DPPF)(ampy) (5), RuCl2(DPPF)(picam) (6) and RuCl2(DPPF)(Py)2 (7) were generated in situ and isolated in solid. All complexes are fully characterized by multinuclear NMR (1H, 13C, 31P and 19F), element analysis and FTIR spectroscopies. Meanwhile, the single crystal structures of 1 and 8 complexes were determined by X-ray crystallography. The observed IR and crystal data of 1 ∼ 4 clearly indicate that different phosphine donor ligands occupying trans axis position of Ru(II)Cl2(CO)2 skeleton can affect the coordination carbonyl C-O bond distance (1.143(3) A (1), 1.135(3) A (4) and 1.131(5) A (2)), and this interaction can be quantitatively detected by its FTIR vibration frequencies. The homogeneous hydrogenation transfer catalytic reactivity of so-synthesized complexes has been tested in a basic 2-propanol solution and they indeed perform the catalytic activities in different behavior, e.g. complexes 1 and 6 are the most active catalysts and represent maximum conversion yield (1: 90.4% and 6: 90.0%) and turnover frequency (TOF) (1 18.84 h−1 and 6 37.5 h−1) at our tested experimental condition of these two types of structural complexes, which are discussed in the details.