Asymmetric hydrogenation of aromatic ketones catalyzed by achiral monophosphine TPPTS-stabilized Ru in ionic liquids

Achiral monophosphine TPPTS [TPPTS: P(m-C6H4SO3Na)3]-stabilized Ru was synthesized by reduction of RuCl3·3H2O with hydrogen in ethanol using TPPTS as the stabilizer. The catalytic asymmetric hydrogenation of aromatic ketones using TPPTS-stabilized Ru modified by a chiral diamine (1R,2R)-DPENDS [disodium salt of sulfonated (1R,2R)-1,2-diphenyl-1,2-ethylene-diamine] was investigated in hydrophilic ionic liquid [RMIM]Ts (1-alkyl-3-methylimidazolium p-methylphenylsulfonates, R = ethyl, butyl, octyl, dodecyl, hexadecyl). Hundred percent conversion and 85.1% ee were obtained for acetophenone under optimized conditions. The resulting products can be easily separated from the catalyst immobilized in ionic liquid by simple extraction with n-hexane, and the catalyst can be reused several times without a significant loss of ee value or conversion. In particular, the addition of water can improve the catalyst performance.

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(S)-(−)-1-PhenylethanolC8H10OEe = 80.3%[α]D28=-23.2 (c 1.08, CH2Cl2)Source of chirality:asymmetric hydrogenationAbsolute configuration:(S)

(S)-(−)-1-PhenylpropanolC9H12OEe = 80.0%[α]D28=-39.5 (c 1.52, C2H5OH)Source of chirality:asymmetric hydrogenationAbsolute configuration:(S)

(S)-(−)-1-(2′-Fluorophenyl)ethanolC8H9OFEe = 54.3%[α]D28=-35.7 (c 1.26, CHCl3)Source of chirality:asymmetric hydrogenationAbsolute configuration:(S)

(S)-(−)-1-(2′-Chlorophenyl)ethanolC8H9OClEe = 77.3%[α]D28=-29.5 (c 1.76, CHCl3)Source of chirality:asymmetric hydrogenationAbsolute configuration:(S)

(S)-(−)-1-(2′-Bromophenyl)ethanolC8H9OBrEe = 82.7%[α]D28=-31.3 (c 1.60, CHCl3)Source of chirality:asymmetric hydrogenationAbsolute configuration:(S)

(R)-(+)-1-(2′-Methoxyphenyl)ethanolC9H12O2Ee = 45.4%[α]D28=+33.3 (c 1.05, CHCl3)Source of chirality:asymmetric hydrogenationAbsolute configuration:(R)

(S)-(−)-1-(4′-Methoxyphenyl)ethanolC9H12O2Ee = 76.5%[α]D28=-29.1 (c 1.03, CHCl3)Source of chirality: asymmetric hydrogenationAbsolute configuration: (S)

(S)-(−)-1-(4′-Trifluoromethylphenyl)ethanolC9H9OF3Ee = 58.7%[α]D28=-39.0 (c 1.41, CH3OH)Source of chirality: asymmetric hydrogenationAbsolute configuration: (S)