title: Aerobic catechol oxidation catalyzed by a bis(mu-oxo)dimanganese(III,III) complex via a manganese(II)-semiquinonate complex.
abstract: A 3,5-di-tert-butyl-1,2-semiquinonato (DTBSQ) adduct of Mn(II) was prepared by a reaction between Mn(II)(TPA)Cl(2) (TPA = tris(pyridin-2-ylmethyl)amine) and DTBSQ anion and was isolated as a tetraphenylborate salt. The X-ray crystal structure revealed that the complex is formulated as a manganese(II)-semiquinonate complex [Mn(II)(TPA)(DTBSQ)](+) (1). The electronic spectra in solution also indicated the semiquinonate coordination to Mn. The exposure of 1 in acetonitrile to dioxygen afforded 3,5-di-tert-butyl-1,2-benzoquione and a bis(mu-oxo)dimanganese(III,III) complex [Mn(III)(2)(mu-oxo)(2)(TPA)(2)](2+) (2). The reaction of 2 with 3,5-di-tert-butylcatechol (DTBCH(2)) quantitatively afforded two equivalents of 1 under anaerobic conditions. The highly efficient catalytic oxidation of DTBCH(2) with dioxygen was achieved by combining the above two reactions, that is, by constructing a catalytic cycle involving both manganese complexes 1 and 2. It was revealed that dioxygen is reduced to water but not to hydrogen peroxide in the catalytic cycle.
authors.affiliation: Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Japan. hitomi@moleng@.kyoto-u.ac.jp
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Hitomi
authors.forename: Akira
authors.initials: A
authors.lastname: Ando
authors.forename: Hajime
authors.initials: H
authors.lastname: Matsui
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Ito
authors.forename: Tsunehiro
authors.initials: T
authors.lastname: Tanaka
authors.forename: Seiji
authors.initials: S
authors.lastname: Ogo
authors.forename: Takuzo
authors.initials: T
authors.lastname: Funabiki