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

Abstract

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 C2-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 C2-symmetric chiral bis(phosphinite) ligands and [Ru(η6-p-cymene)(μ-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.