title: Enhanced electron-transfer reactivity of nonheme manganese(IV)-oxo complexes by binding scandium ions.
abstract: One and two scandium ions (Sc(3+)) are bound strongly to nonheme manganese(IV)-oxo complexes, [(N4Py)Mn(IV)(O)](2+) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) and [(Bn-TPEN)Mn(IV)(O)](2+) (Bn-TPEN = N-benzyl-N,N',N'-tris(2-pyridylmethyl)-1,2-diaminoethane), to form Mn(IV)(O)-(Sc(3+))1 and Mn(IV)(O)-(Sc(3+))2 complexes, respectively. The binding of Sc(3+) ions to the Mn(IV)(O) complexes was examined by spectroscopic methods as well as by DFT calculations. The one-electron reduction potentials of the Mn(IV)(O) complexes were markedly shifted to a positive direction by binding of Sc(3+) ions. Accordingly, rates of the electron transfer reactions of the Mn(IV)(O) complexes were enhanced as much as 10(7)-fold by binding of two Sc(3+) ions. The driving force dependence of electron transfer from various electron donors to the Mn(IV)(O) and Mn(IV)(O)-(Sc(3+))2 complexes was examined and analyzed in light of the Marcus theory of electron transfer to determine the reorganization energies of electron transfer. The smaller reorganization energies and much more positive reduction potentials of the Mn(IV)(O)-(Sc(3+))2 complexes resulted in remarkable enhancement of the electron-transfer reactivity of the Mn(IV)(O) complexes. Such a dramatic enhancement of the electron-transfer reactivity of the Mn(IV)(O) complexes by binding of Sc(3+) ions resulted in the change of mechanism in the sulfoxidation of thioanisoles by Mn(IV)(O) complexes from a direct oxygen atom transfer pathway without metal ion binding to an electron-transfer pathway with binding of Sc(3+) ions.
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, ALCA, Japan Science and Technology Agency, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Heejung
authors.initials: H
authors.lastname: Yoon
authors.forename: Yong-Min
authors.initials: YM
authors.lastname: Lee
authors.forename: Xiujuan
authors.initials: X
authors.lastname: Wu
authors.forename: Kyung-Bin
authors.initials: KB
authors.lastname: Cho
authors.forename: Ritimukta
authors.initials: R
authors.lastname: Sarangi
authors.forename: Wonwoo
authors.initials: W
authors.lastname: Nam
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fuhkuzumi
mesh_terms: D001665:Binding Sites; D002412:Cations / Q000737:chemistry; D056831:Coordination Complexes / Q000737:chemistry*; D004579:Electron Transport; D005029:Ethylenediamines / Q000737:chemistry; D008345:Manganese / Q000737:chemistry*; D008744:Methylamines / Q000737:chemistry; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry; D012538:Scandium / Q000737:chemistry*
chemical_list: D002412:Cations; D056831:Coordination Complexes; D005029:Ethylenediamines; D008744:Methylamines; D011725:Pyridines; C121054:bis(2-pyridyl)methylamine; D008345:Manganese; C031234:ethylenediamine; D010100:Oxygen; D012538:Scandium