Chiral and Nonchiral [OsX2(diphosphane)(diamine)] (X: Cl, OCH2CF3) Complexes for Fast Hydrogenation of Carbonyl Compounds

The osmium complexes trans-[OsCl2(dppf)(diamine)] (dppf: 1,1′-bis(diphenylphosphino)ferrocene; diamine: ethylenediamine in 3, propylenediamine in 4) were prepared by the reaction of [OsCl2(PPh3)3] (1) with the ferrocenyl diphosphane, dppf and the corresponding diamine in dichloromethane. The reaction of derivative 3 with NaOCH2CF3 in toluene afforded the alkoxide cis-[Os(OCH2CF3)2(dppf)(ethylenediamine)] (5). The novel precursor [Os2Cl4(P(m-tolyl)3)5] (2) allows the synthesis of the chiral complexes trans-[OsCl2(diphosphane)(1,2-diamine)] (6–9; diphosphane: (R)-[6,6′-dimethoxy(1,1′-biphenyl)-2,2′-diyl]bis[1,1-bis(3,5-dimethylphenyl)phosphane] (xylMeObiphep) or (R)-(1,1′-binaphthalene)-2,2′-diylbis[1,1-bis(3,5-dimethylphenyl)phosphane] (xylbinap); diamine=(R,R)-1,2-diphenylethylenediamine (dpen) or (R,R)-1,2-diaminocyclohexane (dach)), obtained by the treatment of 2 with the diphosphane and the 1,2-diamine in toluene at reflux temperature. Compounds 3–5 in ethanol and in the presence of NaOEt catalyze the reduction of methyl aryl, dialkyl, and diaryl ketones and aldehydes with H2 at low pressure (5 atm), with substrate/catalyst (S/C) ratios of 10 000–200 000 and achieving turnover frequencies (TOFs) of up to 3.0×105 h−1 at 70 °C. By employment of the chiral compounds 6–9, different ketones, including alkyl aryl, bulky tert-butyl, and cyclic ketones, have successfully been hydrogenated with enantioselectivities up to 99 % and with S/C ratios of 5000–100 000 and TOFs of up to 4.1×104 h−1 at 60 °C.