Development of Asymmetric Reactions Catalyzed by Ruthenium Complexes with Two Kinds of Ligands

Two types of chiral Ru(II) complexes, each with two kinds of ligands, have been designed and utilized as catalysts for several asymmetric reactions under appropriate conditions. The first type, the diphosphine/diamine-Ru(II)-type complexes, were found to catalyze the hydrogenation of a variety of simple and functionalized ketones as well as imino compounds with high activity and enantioselectivity. The double asymmetric hydrogenation of alpha,beta-unsaturated ketones into the chiral saturated alcohols was achieved by using the dual catalyst system, which reversibly forms two catalytic species. The asymmetric isomerization of primary allylic alcohols into the optically active aldehydes with almost perfect enantioselectivity was realized with this type of catalyst. The second type, the amino acid/diphosphine-Ru(II)-type complexes combined with Li compounds, exhibited excellent catalyst performance in the asymmetric cyanosilylation of aldehydes as well as simple and functionalized ketones. The isolated Ru.Li bimetallic complexes were suitable for the asymmetric hydrocyanation of aldehydes. This combined system was applicable to the asymmetric conjugate hydrocyanation of alpha,beta-unsaturated ketones and carboxylic acid derivatives, and the Strecker-type reaction of the pi-isoelectronic N-alkoxycarbonyl aldimines. This account describes the concept underlying the design of these catalysts, and the catalyst performance in the asymmetric reactions.