Asymmetric hydrogenation of aromatic ketones with MeO-PEG-supported BIPHEP/DPEN ruthenium catalysts

A soluble polymer (MeO-PEG) supported biphenylbisphosphine (BIPHEP)-Ru/chiral diamine (1,2-diphenylethylenediamine) complex, in which the polymer is attached to the two phenyl rings of BIPHEP ligand, has been prepared, and shown to be highly active with good enantioselectivity for the catalyzed asymmetric hydrogenation of unfunctionalized aromatic ketones. The derived chiral ruthenium complex 5 proved to be stable in air allowing facile catalyst recycling. Especially for 4′-tert-butyl-acetophenone and 1-acetonaphthone, excellent ee values up to 96.5% and 95.9% have been obtained which are comparable to or even higher than the enantioselectivity achieved with 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl-Ru-DPEN catalyst under similar conditions.

The soluble MeO-PEG-supported BIPHEP-Ru/chiral diamine (DPEN) complex 5 was prepared, and employed as catalyst for asymmetric hydrogenation of various aromatic ketones, providing comparable or even higher enantioselectivity than that achieved with BINAP-Ru-DPEN catalyst under similar conditions. The catalyst showed good recoverability, and could be used for five consecutive runs without a significant drop in enantioselectivity.Figure optionsDownload as PowerPoint slide