The condensation of (S)-propane-1, 2-diamine with two equivalents of o- (diphenylphosphino) benzaldehyde gives (S)-N, N'-bis[o-(diphenylphosphino) benzylidenexpropane-1, 2-diaminew [(S)-1] ligand. The reduction of (S)-1 with excess NaBH4 is carried out in refluxing ethanol to afford corresponding (S)-N, N'-bis [o-(diphenylphosphino) benzylxpropane-1, 2-diamine [(S)-2]. The interaction of trans-RuCl2(DMSO)4 with one equivalent of (S)-1 or (S)-2 in refluxing toluene gives (S)-3 or (S)-4 in good yield, respectively. (S)-1, (S)-2, (S)-3 and (S)-4 have been fully characterized by analytical and spectroscopic methods. The structure of (R)-3 has been also established by an X-ray diffraction study. Catalytic studies showed that (S)-4 as an excellent catalyst precursor for the asymmetric transfer hydrogenation of acetophenone with 90% yield and up to 91% enantiomeric excess.

The interaction of [Rh(COD)Cl]2 with two equivalents of (S)-N,NX-biswo-( diphenylphosphino) benzylidenexpropane-1, 2-diamine [(S)-1] or (S)-N, N'-bis [o-(diphenylphosphino) benzylxpropane-1, 2-diamine [(S)-2] in benzene/methanol mixture and then precipitation by the addition of a solution of NH4PF6 in water afforded cationic rhodium (I) complexes [Rh(S)-MeP2N2] [PF6] and [Rh(S)-MeP2 (NH)2] [PF6] in good yield, respectively. Complexes [Rh(R,R)-C6P2N2] [PF6] 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 spectroscopic methods and their asymmetric catalytic properties for enantioselective transfer hydrogenation of acetophenone have been tested. [Rh(R,R)-C6P2(NH)2] [PF6] was used as an excellent catalyst precursor for enantioselective transfer reduction of acetophenone in 2-propanol, leading to 2-phenylathanol in 97% yield and in 91% ee after 7 h at 83℃.

The interaction of [Ir(COD)Cl]2 with chiral tetradentate diaminodiphosphine ligands gave chiral diaminodiphosphine-Ir(I) complexes, which were characterized by IR, NMR and CD. The new chiral iridium(I) complex catalysts were applied to asymmetric transfer hydrogenation of various aromatic ketones using 2-propanol as a source of hydrogen. The results showed that the corresponding chiral alcohols could be obtained with high activity (up to 99.4% yield) and excellent enantioselectivities (up to 99.0% ee) under mild conditions. Propiophenone was a preferred substrate with respect to catalytic activity and enantioselectivity in the presence of base. The catalytic turnover reached 4780mol product/mol iridium and the turnover frequency was as high as 1593h−1 at 55℃.

The condensation of o-(diphenylphosphino)benzaldehyde and various chiral diamine gives a series of diimino-diphosphine tetradentate ligands, which are reduced with excess NaBH4 in refluxing ethanol to afford the corresponding diaminodiphosphine ligands in good yield. The reactivity of these ligands toward trans-RuCl2(DMSO)4 and [Rh(COD)Cl]2 had been investigated and a number of chiral Ru(II) and Rh(I) complexes with the PNNP-type ligands were synthesized and characterized by microanalysis and IR, NMR spectroscopic methods. The chiral Ru(II) and Rh(I) complexes have proved to be excellent catalyst precursors for the asymmetric transfer hydrogenation of aromatic ketones, leading to optically active alcohols in up to 97% ee. Chirality 12: 383-388, 2000.

Summary: The trans-RuIICl2 complexes with structurally similar N,N¢-bis[o-(diphenylphosphino)benzylidene]cyclohexane-1,2-diamine and N,N¢-bis[o-(diphenylphosphino)-benzyl]cyclohexane-1,2-diamine ligands have been synthesized, and their molecular structures have been determined. The C2-symmetric diphosphine/diaminebased Ru complex acts as an excellent catalyst precursor in asymmetric transfer hydrogenation of acetophenone in a 0.1 M 2-propanol solution, leading to 2-phenylethanol in 97% ee and in 93% yield after 7h at 45℃. This transfer hydrogenation is characterized by low reversibility under these conditions.