Ruthenium complexes of chiral diphosphinite ligands with cyclohexane or chiro-inositol backbones as catalysts for asymmetric hydrogenation reactions

Abstract

Treatment of [RuCl2(COD)]n with the chiral diphosphinite ligand (1S,2S)-1,2-trans-bis-(O-diphenylphosphino)cyclohexane [(1S,2S)-14] and triethylamine gives the bis(diphosphinite) complex RuHCl[(1S,2S)-14]2 (15) in good yield. If (rac)-1,2-trans-bis-(O-diphenylphosphino)cyclohexane [(rac)-14] is used in place of (1S,2S)-14 in this reaction, a racemic mixture of RuHCl[(1S,2S)-14]2 and RuHCl[(1R,2R)-14]2 [(rac)-16] is formed. The X-ray crystal structure of (rac)-16 center dot(2.5CH2Cl2) has been determined. Treatment of (rac)-16 with hydrogen in iso-propanol leads to the formation of a racemic mixture of RuH2[(1S,2S)-14]2 and RuH2[(1R,2R)-14]2 [(rac)-17]. The structure of (rac)-17 was confirmed by the X-ray analysis of a racemic crystal. Ruthenium mono(diphosphinite), diamine complexes of the general formula RuCl2(NN)(PP) are formed by the treatment of RuCl2(PPh3)3 with the appropriate diphosphinite (PP) and diamine (NN) ligands. In this way, the following complexes have been synthesized: RuCl2[(+)-DPEN][(1S,2S)-14] (18), RuCl2[(-)-DPEN][(1S,2S)-14] (19), RuCl2[(+)-DPEN][(1R,2R)-14] (20), RuCl2[(-)-DPEN][(1R,2R)-14] (21), RuCl2[(+)-DPEN][(rac)-14] (22), RuCl2[(-)-DPEN][(rac)-14] (23), RuCl2(D-NN2)[(1S,2S)-14] (24), RuCl2(EDA)[(1S,2S)-14] (25), RuCl2(D-NN2)(D-10) (26), RuCl2(EDA)(D-10) (27), RuCl2[(+)-DPEN](D-10Et) (28), RuCl2(D-NN2)(D-10Et) (29), [where DPEN = 1,2-diphenylethylenediamine, D-NN2 = 1D-1,2-dideoxy-1,2-diamino-3,4,5,6-tetra-O-benzyl-myo-inositol, EDA = 1,2-diaminoethane, D-10 = 1D-3,4-bis(O-diphenylphosphino)-1,2,5,6-tetra-O-methyl-chiro-inositol, D-10Et = 1D-3,4-bis(O-diphenylphosphino)-1,2,5,6-tetra-O-ethyl-chiro-inositol]. These ruthenium complexes catalyze the hydrogenation of the ketones acetophenone and 3-quinuclidinone to give the corresponding alcohols in high yields, but with moderate to low enantiomeric excesses.