title: Tuning the Reactivity of Mononuclear Nonheme Manganese(IV)-Oxo Complexes by Triflic Acid.
abstract: Triflic acid (HOTf)-bound nonheme Mn(IV)-oxo complexes, [(L)MnIV(O)]2+-(HOTf)2(L = N4Py and Bn-TPEN; N4Py =N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) and Bn-TPEN =N-benzyl-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine), were synthesized by adding HOTf to the solutions of the [(L)MnIV(O)]2+complexes and were characterized by various spectroscopies. The one-electron reduction potentials of the MnIV(O) complexes exhibited a significant positive shift upon binding of HOTf. The driving force dependence of electron transfer (ET) from electron donors to the MnIV(O) and MnIV(O)-(HOTf)2complexes were examined and evaluated in light of the Marcus theory of ET to determine the reorganization energies of ET. The smaller reorganization energies and much more positive reduction potentials of the [(L)MnIV(O)]2+-(HOTf)2complexes resulted in much enhanced oxidation capacity towards one-electron reductants andpara-X-substituted-thioanisoles. The reactivities of the Mn(IV)-oxo complexes were markedly enhanced by binding of HOTf, such as a 6.4 × 105-fold increase in the oxygen atom transfer (OAT) reaction (i.e., sulfoxidation). Such a remarkable acceleration in the OAT reaction results from the enhancement of ET frompara-X-substituted-thioanisoles to the MnIV(O) complexes as revealed by the unified ET driving force dependence of the rate constants of OAT and ET reactions of [(L)MnIV(O)]2+-(HOTf)2. In contrast, deceleration was observed in the rate of H-atom transfer (HAT) reaction of [(L)MnIV(O)]2+-(HOTf)2complexes with 1,4-cyclohexadiene as compared with those of the [(L)MnIV(O)]2+complexes. Thus, the binding of two HOTf molecules to the MnIV(O) moiety resulted in remarkable acceleration of the ET rate when the ET is thermodynamically feasible. When the ET reaction is highly endergonic, the rate of the HAT reaction is decelerated due to the steric effect of the counter anion of HOTf.
authors.affiliation: Department of Chemistry and Nano Science, Department of Bioinspired Science, Center for Biomimetic System, Ewha Womans University, Seoul 120-750, Korea.
authors.forename: Junying
authors.initials: J
authors.lastname: Chen
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, ALCA, JST, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Heejung
authors.initials: H
authors.lastname: Yoon
authors.affiliation: Department of Chemistry and Nano Science, Department of Bioinspired Science, Center for Biomimetic System, Ewha Womans University, Seoul 120-750, Korea.
authors.forename: Yong-Min
authors.initials: YM
authors.lastname: Lee
authors.affiliation: Department of Chemistry and Nano Science, Department of Bioinspired Science, Center for Biomimetic System, Ewha Womans University, Seoul 120-750, Korea.
authors.forename: Mi Sook
authors.initials: MS
authors.lastname: Seo
authors.affiliation: Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States.
authors.forename: Ritimukta
authors.initials: R
authors.lastname: Sarangi
authors.affiliation: Department of Chemistry and Nano Science, Department of Bioinspired Science, Center for Biomimetic System, Ewha Womans University, Seoul 120-750, Korea ; Department of Material and Life Science, Graduate School of Engineering, ALCA, JST, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
authors.affiliation: Department of Chemistry and Nano Science, Department of Bioinspired Science, Center for Biomimetic System, Ewha Womans University, Seoul 120-750, Korea.
authors.forename: Wonwoo
authors.initials: W
authors.lastname: Nam