Synthesis and Characterization of Ruthenium(II) Complexes Containing Chiral Bis(ferrocenyl)−P3or −P2S Ligands. Asymmetric Transfer Hydrogenation of Acetophenone

Abstract

A number of new chiral bis(ferrocenyl)−triphosphine ligands have been synthesized by the reaction of cyclohexylphosphine with different chiral ferrocenyl aminophosphines in hot acetic acid. The thioether ligand bis{(S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl} sulfide has been similarly prepared by the reaction of (S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl acetate with either (S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl mercaptan or (S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl mercaptan sodium salt. All the above reactions proceed with retention of configuration on the side-chain stereocenters of the starting materials. Monomeric Ru(II) complexes containing either chloride or acetonitrile coligands have been prepared with all the chiral tridentate ligands. Both the new ligands and the ruthenium complexes have been characterized by multinuclear NMR spectroscopy. The structure of [(S)-(R)-Pigiphos]RuCl2·2CH2Cl2 ((S)-(R)-Pigiphos = bis{(S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl}cyclohexylphosphine) has been determined by X-ray diffraction. The asymmetric transfer hydrogenation of acetophenone catalyzed by various Ru(II) bis(ferrocenyl) tridentate complexes in propan-2-ol is also reported.