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Until the early 1970s, chemical access to enantiomerically pure substances from prochiral precursors remained extremely difficult. Recent dramatic advances in man-made catalysts, however, are converting the chemists' dream into reality. Particularly, homogeneous asymmetric catalysis using chiral metal complexes provides an ideal way to multiply chirality, beginning a new era where production of large amounts of chiral compounds of either absolute configuration is possible with a very small quantity of chiral source. This methodology based on accumulated chemical knowledge is highly rational and flexible, and the opportunities it affords are practically unlimited. Reported examples of the highly enantioselective catalyses include hydrogenation, hydrosilylation, and hydroboration of unsaturated compounds, epoxidation of allylic alcohols, vicinal hydroxylation, hydrovinylation, hydroformylation, cyclopropanation, and isomerization of olefins, propylene polymerization, organometallic addition to aldehydes, allylic alkylation, organic halide-organo-

The ternary system consisting of [RuCl 2 (η 6 -benzene)] 2 , N-tosylethylenediamine or ethanolamine, and KOH (Ru:amine:KOH ) 1:1:2 molar ratio) catalyzes reversible hydrogen transfer between alcohols and carbonyl compounds. The use of chiral amine auxiliaries effects asymmetric transformation. The theoretical calculations using methanol/formaldehyde transformation as the model indicates the operation of a novel metalligand bifunctional catalysis, which is contrary to currently accepted putative pathways. The results reveal that: (1) KOH is necessary for the generation of a formal 16-electron Ru complex, Ru(NHCH 2 CH 2 Y)(η 6benzene) (Y ) O or NH) (catalyst), from an 18-electron Ru chloride, RuCl(NH 2 CH 2 CH 2 Y)(η 6 -benzene) (precatalyst), by a Dcb elimination of HCl, and not for increasing alkoxide concentration; (2) Ru alkoxides do not intervene in transfer hydrogenation; (3) the Ru alkoxide, even if formed, serves merely as a reservoir of the 16-electron catalyst; (4) the key 18-electron Ru hydride, RuH(NH 2 CH 2 CH 2 Y)(η 6 -benzene) (reducing intermediate), is generated by dehydrogenation of methanol with coordinatively unsaturated Ru(NHCH 2 CH 2 Y)-(η 6 -benzene); (5) this process and reverse hydrogen delivery from RuH(NH 2 CH 2 CH 2 Y)(η 6 -benzene) to formaldehyde take place by a pericyclic mechanism via a six-membered transition structure; (6) neither carbonyl oxygen nor alcoholic oxygen interacts with Ru throughout the hydrogen transfer; (7) the carbonyl oxygen atom interacts with NH on Ru and the hydroxy function with the amido nitrogen via hydrogen bonding; (8) the Ru center and nitrogen ligand simultaneously participate in both forward and reverse steps of the hydrogenation transfer. The ethanolamine-and ethylenediamine-based complexes behave similarly. In the asymmetric transformation catalyzed by chiral Ru complexes, the stereochemical bias originates primarily from the chirality of the heteroatom-based five-membered chelate rings in the transition structure. The calculated mechanism explains a range of experimental observations including the ligand acceleration effect, the structural characteristics of the isolated Ru(II) complexes, the role of the NH or NH 2 end of auxiliaries, the effect of a strong base cocatalyst, the kinetic profile, the reactivities of hydrogen donors and acceptors, the CdO vs CdC chemoselectivity, and the origin of enantioselection. This metal-ligand bifunctional catalysis is in sharp contrast to many other metal-centered catalyses.