title: 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.
abstract: 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. A CH-π-stabilized Si-face selective transition state, CSi, gives (R)-PE together with an intermediary Ru amide, D, which is inhibited predominantly by formation of the Ru enolate of AP. The rate-determining hydrogenolysis of D completes the cycle. The time-squared term relates both to the preliminary step before the cycle and to the cycle itself, with a highly unusual eight-order difference in the generation and turnover frequency of B. This mechanism is fully supported by a series of experiments including a detailed kinetic study, rate law analysis, simulation of t/[PE] curves with fitting to the experimental observations at the initial reaction stage, X-ray crystallographic analyses of B-related octahedral metal complexes, and Hammett plot analyses of electronically different substrates and ligands in their enantioselectivities.
authors.affiliation: †Graduate School of Pharmaceutical Sciences, Graduate School of Science, and Research Center for Materials Science, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakatsuka
authors.affiliation: †Graduate School of Pharmaceutical Sciences, Graduate School of Science, and Research Center for Materials Science, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
authors.forename: Tomoya
authors.initials: T
authors.lastname: Yamamura
authors.affiliation: †Graduate School of Pharmaceutical Sciences, Graduate School of Science, and Research Center for Materials Science, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Shuto
authors.affiliation: †Graduate School of Pharmaceutical Sciences, Graduate School of Science, and Research Center for Materials Science, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Tanaka
authors.affiliation: ‡Division of Liberal Arts and Sciences, Aichi Gakuin University, Iwasaki, Nisshin 470-0195, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Yoshimura
authors.affiliation: †Graduate School of Pharmaceutical Sciences, Graduate School of Science, and Research Center for Materials Science, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Kitamura
mesh_terms: D000098:Acetophenones / Q000737:chemistry*; D000466:Alkadienes / Q000737:chemistry; D001592:Benzyl Alcohols / Q000737:chemistry; D002384:Catalysis; D018360:Crystallography, X-Ray; D003959:Diamines / Q000737:chemistry; D006841:Hydrocarbons, Aromatic / Q000737:chemistry*; D006865:Hydrogenation; D007659:Ketones / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D009281:Naphthalenes / Q000737:chemistry; D012428:Ruthenium / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: C500338:1,1'-binaphthyl-2,2'-diamine; D000098:Acetophenones; D000466:Alkadienes; D001592:Benzyl Alcohols; D003959:Diamines; D006841:Hydrocarbons, Aromatic; D007659:Ketones; D008024:Ligands; D009281:Naphthalenes; C439868:1,5-cyclooctadiene; D012428:Ruthenium; C002017:methylphenyl carbinol; C038699:acetophenone