Cationic rhodium complexes with chiral tetradentate ligands as catalysts for enantioselective reduction of simple ketones

The interaction of [Rh(COD)Cl](2) with two equivalents of (S)-N,N'-bis[o-(d iphenylphosphino)benzylidene]propane-1,2-diamine [(S)-1] or (S)-N,N'-bis[o- (diphenylphosphino)benzyl]propane-1,2-diamine [(S)-2] in benzene/methanol m ixture and then precipitation by the addition of a solution of NH,PF, in wa ter afforded cationic rhodium(I) complexes [Rh(S)-MeP2N2][PF6] and [Rh(S)-M eP2(NH)(2)][PF6] in good yield, respectively. Complexes [Rh(R,R)-C6P2N2][PF 6] and [Rh(R,R)-C6P2(NH)(2)][PF6] were also prepared by an analogous manner . All these rhodium complexes have been characterized by analytical and spe ctroscopic methods and their asymmetric catalytic properties for enantiosel ective transfer hydrogenation of acetophenone have been tested. [Rh(R,R)-C6 P2(NH)(2)][PF6] was used as an excellent catalyst precursor for enantiosele ctive transfer reduction of acetophenone in 2-propanol, leading to 2-phenyl athanol in 97% yield and in 91% ee after 7 h at 83 degrees C. (C) 2000 Else vier Science B.V. All rights reserved.