Preparation and use of polymer‐supported chiral ruthenium complex catalyst

The chiral diiminodiphosphine ligand, [( R,R )‐P 2 N 2 ],has been prepared by the condensation of o ‐(diphenylphosphino)benzaldehyde and 1,2‐diaminocyclohexane. [( R,R )‐P 2 N 2 ] was reduced with excess NaBH 4 in refluxing ethanol to afford the corresponding diaminodiphosphine ligand [( R,R )‐P 2 (NH) 2 ]. The interaction of [( R,R )‐P 2 (NH) 2 ] with trans ‐RuCl 2 (DMSO) 4 gave the chiral ruthenium complex [( R,R )‐RuP 2 (NH) 2 ] in 84% yield. The reaction of [( R,R )‐RuP 2 (NH) 2 ] with poly‐(acrylic acid) using dicyclohexylcarbodiimine as the coupling agent, gave water soluble poly(acrylic acid salt)‐supported chiral ruthenium complex [PAA‐( R,R )‐RuP 2 (NH) 2 ]. These chiral ligands and ruthenium complexes have been fully characterized by microanalysis and IR, NMR spectroscopic methods. The polymer‐bound ruthenium complex [PAA‐( R,R )‐RuP 2 (NH) 2 ] as catalyst was used in asymmetric transfer hydrogenation of acetophenone in 2‐propanol, producing the 1‐phenylethanol in 95% yield and 96% ee. The catalyst was reused twice with some loss of activity and enantioselectivity. Copyright © 2001 John Wiley & Sons, Ltd.