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.

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The /3-dialkylamino alcohol-promoted reaction of dialkylzincs and aldehydes has been studied by ab initio molecular orbital calculations using a model system consisting of 2-aminoethanol, dimethylzinc, and formaldehyde.In the organometallic addition reaction, methylzinc alkoxide 1 formed from dimethylzinc and 2-aminoethanol by elimination of methane acts as an actual catalyst, which exists in equilibration with stereoisomeric dimers 2. Sterically less congested anti-2 is more stable than syn-2 by 3.1 kcal/mol. The tricoordinate Zn compound 1, acting as a bifunctional catalyst, assembles dimethylzinc and formaldehyde via 3 or 4 to form the product-forming complex 5. The frontier MOs and structure of 5 indicate that the formation of the mixed-ligand Zn complexes considerably increases the nucleophilic character of the Zn-CH3 group and electrophilic property of the aldehyde. As a consequence, 5 undergoes intramolecular alkyl migration to produce zinc ethoxide 6 which has a bridged structure. This turnover-limiting reaction occurs via the 4/4-bicyclic transition structure, antior syn-10, where the methyl group migrates with retention of configuration. The six-membered cyclic transition state that causes the alkyl migration with inversion of configuration is of higher energy. The final product 6 which is viewed as a complex of 1 and Zn alkoxide 7, upon interaction with dimethylzinc or formaldehyde, collapses into 3 or 4, respectively, and 9 (a tetramer of 7). The structural characteristics of the intermediates, products, and transition states are described. This calculation also clarifies the origin of the ligand acceleration; why the reaction is effected only when a few mol %, but not 0% or 100%, of an amino alcohol is employed. The high stability of the final tetrameric Zn alkoxide 9 prevents the undesired product inhibition of the catalytic reaction. The relative stability of the catalyst dimers, syn-and anti-2, is consistent with the chiral amplification phenomena experimentally observed with (25)-3-exo-(dimethylamino)bomeol. The presence of the amino moiety plays a significant role in the dissociation of the dimers.

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