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 RuCl(3 center dot)3H(2)O 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. (c) 2007 Elsevier Ltd. All rights reserved.