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. The wizard of Os: A novel class of highly modular diphosphane/diamine–osmium complexes (see structures) are found to be extremely active catalysts in the hydrogenation of ketones and aldehydes (substrate/catalyst ratios and turnover frequencies of up to 2×105 and 3×105 h−1, respectively). High enantioselectivity is achieved with the osmium complexes obtained from the new precursor [Os2Cl4{P(m‐tolyl)3}5] and the correctly matched chiral ligands.