Asymmetric Transfer Hydrogenation of Arylketones Catalyzed by Enantiopure Ruthenium(II)/Pybox Complexes Containing Achiral Phosphonite and Phosphinite Ligands.

A family of complexes of the formula -[RuCl(L)(R-pybox)] (R-pybox = (,)-Pr-pybox, (,)-Ph-pybox, L = monodentate phosphonite, PPh(OR), and phosphinite, L = PPh(OR), ligands) were screened in the catalytic asymmetric transfer hydrogenation of acetophenone, observing a strong influence of the nature of both the R-pybox substituents and the L ligand in the process. The best results were obtained with complex -[RuCl{PPh(OEt)}{(,)-Ph-pybox}] (), which provided high conversion and enantioselectivity (up to 96% enantiomeric excess, ) for the reduction of a variety of aromatic ketones, affording the ()-benzylalcohols.