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 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.

Graphical abstractWe report enantioselective C2-symmetric bis(phosphinite)–ruthenium(II) catalytic systems for the transfer hydrogenation of prochiral aromatic ketones. The 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.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Novel C2-symmetric chiral bis(phosphinite) ligands were synthesized. ► Ru(II) systems were used as catalysts in the transfer hydrogenation of ketones. ► Optically active secondary alcohols were obtained in 99% yield and up to 94% ee.