Asymmetric transfer hydrogenation of prochiral ketones catalyzed by chiralruthenium complexes with aminophosphine ligands

The condensation of (S)-propane-1,2-diamine with two equivalents of o-(diph enylphosphino)benzaldehyde gives (S)-N,N'-bis[o-(diphenylphosphino)benzylid ene]propane-1,2-diamine [(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)benzyl]propane-1,2-diamine [(S)-2]. The interacti on of trans-RuCl2(DMSO)(4) with one equivalent of (S)-1 or (S)-2 in refluxi ng 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 spectroscop ic methods. The structure of (R)-3 has been also established by an X-ray di ffraction study. Catalytic studies showed that (S)-4 as an excellent cataly st precursor for the asymmetric transfer hydrogenation of acetophenone with 90% yield and up to 91% enantiomeric excess. (C) 1999 Elsevier Science B.V . All rights reserved.