Mechanism of Asymmetric Hydrogenation of Aromatic Ketones Catalyzed by a Combined System of Ru(π-CH2C(CH3)CH2)2(cod) and the Chiral sp(2)N/sp(3)NH Hybrid Linear N4 Ligand Ph-BINAN-H-Py.

The combination of a Goodwin-Lions-type chiral N4 ligand, (R)-Ph-BINAN-H-Py ((R)-3,3'-diphenyl-N(2),N(2')-bis((pyridin-2-yl)methyl)-1,1'-binaphthyl-2,2'-diamine; L), with Ru(π-CH2C(CH3)CH2)2(cod) (A) (cod = 1,5-cyclooctadiene) catalyzes the hydrogenation of acetophenone (AP) to (R)-1-phenylethanol (PE) with a high enantiomer ratio (er). Almost no Ru complex forms, with A and L remaining intact throughout the reaction while generating PE quantitatively according to [PE] = k(obs)t(2). An infinitesimal amount of reactive and unstable RuH2L (B) with C2-Λ-cis-α stereochemistry is very slowly and irreversibly generated from A by the action of H2 and L, which rapidly catalyzes the hydrogenation of AP via Noyori's donor-acceptor bifunctional mechanism.