Screening of C2-symmetric chiral phosphinites as ligands for ruthenium(II)-catalyzed asymmetric transfer hydrogenation of prochiral aromatic ketones

Metal-catalyzed transfer hydrogenation processes provide a widely-used alternative to direct hydrogenation processes of ketones. As part of an ongoing program, we report enantioselective C-2-symmetric bis(phosphinite)-ruthenium(II) catalytic systems for the transfer hydrogenation of prochiral aromatic ketones. The new catalytic systems can readily be formed under in situ conditions from C-2-symmetric chiral bis(phosphinite) ligands and [Ru(eta(6)-p-cymene)(mu-Cl)Cl](2) in transfer hydrogenation reaction media. These chiral ruthenium catalytic systems serve as catalyst precursors for the asymmetric transfer hydrogenation of acetophenone derivatives in iso-PrOH and giving the corresponding optical active secondary alcohols up to 94% ee. (C) 2013 Elsevier B.V. All rights reserved.