title: Mechanistic borderline of one-step hydrogen atom transfer versus stepwise Sc(3+)-coupled electron transfer from benzyl alcohol derivatives to a non-heme iron(IV)-oxo complex.
abstract: The rate of oxidation of 2,5-dimethoxybenzyl alcohol (2,5-(MeO)(2)C(6)H(3)CH(2)OH) by [Fe(IV)(O)(N4Py)](2+) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) was enhanced significantly in the presence of Sc(OTf)(3) (OTf(-) = trifluoromethanesulfonate) in acetonitrile (e.g., 120-fold acceleration in the presence of Sc(3+)). Such a remarkable enhancement of the reactivity of [Fe(IV)(O)(N4Py)](2+) in the presence of Sc(3+) was accompanied by the disappearance of a kinetic deuterium isotope effect. The radical cation of 2,5-(MeO)(2)C(6)H(3)CH(2)OH was detected in the course of the reaction in the presence of Sc(3+). The dimerized alcohol and aldehyde were also produced in addition to the monomer aldehyde in the presence of Sc(3+). These results indicate that the reaction mechanism is changed from one-step hydrogen atom transfer (HAT) from 2,5-(MeO)(2)C(6)H(3)CH(2)OH to [Fe(IV)(O)(N4Py)](2+) in the absence of Sc(3+) to stepwise Sc(3+)-coupled electron transfer, followed by proton transfer in the presence of Sc(3+). In contrast, neither acceleration of the rate nor the disappearance of the kinetic deuterium isotope effect was observed in the oxidation of benzyl alcohol (C(6)H(5)CH(2)OH) by [Fe(IV)(O)(N4Py)](2+) in the presence of Sc(OTf)(3). Moreover, the rate constants determined in the oxidation of various benzyl alcohol derivatives by [Fe(IV)(O)(N4Py)](2+) in the presence of Sc(OTf)(3) (10 mM) were compared with those of Sc(3+)-coupled electron transfer from one-electron reductants to [Fe(IV)(O)(N4Py)](2+) at the same driving force of electron transfer. This comparison revealed that the borderline of the change in the mechanism from HAT to stepwise Sc(3+)-coupled electron transfer and proton transfer is dependent on the one-electron oxidation potential of benzyl alcohol derivatives (ca. 1.7 V vs SCE).
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering,  Osaka University , ALCA, Japan Science and Technology Agency (JST), Suita, Osaka 565-0871, Japan.
authors.forename: Yuma
authors.initials: Y
authors.lastname: Morimoto
authors.forename: Jiyun
authors.initials: J
authors.lastname: Park
authors.forename: Tomoyoshi
authors.initials: T
authors.lastname: Suenobu
authors.forename: Yong-Min
authors.initials: YM
authors.lastname: Lee
authors.forename: Wonwoo
authors.initials: W
authors.lastname: Nam
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
mesh_terms: D019905:Benzyl Alcohol / Q000737:chemistry*; D004579:Electron Transport; D006859:Hydrogen / Q000737:chemistry*; D058085:Iron Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D012538:Scandium / Q000737:chemistry*
chemical_list: D058085:Iron Compounds; D006859:Hydrogen; D019905:Benzyl Alcohol; D010100:Oxygen; D012538:Scandium