title: Switchover of the Mechanism between Electron Transfer and Hydrogen-Atom Transfer for a Protonated Manganese(IV)-Oxo Complex by Changing Only the Reaction Temperature.
abstract: Hydroxylation of mesitylene by a nonheme manganese(IV)-oxo complex, [(N4Py)Mn(IV) (O)](2+) (1), proceeds via one-step hydrogen-atom transfer (HAT) with a large deuterium kinetic isotope effect (KIE) of 3.2(3) at 293 K. In contrast, the same reaction with a triflic acid-bound manganese(IV)-oxo complex, [(N4Py)Mn(IV) (O)](2+) -(HOTf)2 (2), proceeds via electron transfer (ET) with no KIE at 293 K. Interestingly, when the reaction temperature is lowered to less than 263 K in the reaction of 2, however, the mechanism changes again from ET to HAT with a large KIE of 2.9(3). Such a switchover of the reaction mechanism from ET to HAT is shown to occur by changing only temperature in the boundary region between ET and HAT pathways when the driving force of ET from toluene derivatives to 2 is around -0.5 eV. The present results provide a valuable and general guide to predict a switchover of the reaction mechanism from ET to the others, including HAT.
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 03760, Korea.
authors.forename: Jieun
authors.initials: J
authors.lastname: Jung
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 03760, Korea.
authors.forename: Surin
authors.initials: S
authors.lastname: Kim
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 03760, Korea.
authors.forename: Yong-Min
authors.initials: YM
authors.lastname: Lee
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 03760, Korea. wwnam@ewha.ac.kr.
authors.forename: Wonwoo
authors.initials: W
authors.lastname: Nam
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 03760, Korea. fukuzumi@chem.eng.osaka-u.ac.jp.|Faculty of Science and Engineering, ALCA, SENTAN Japan Science and Technology Agency (JST), Meijo University, Nagoya, Aichi, 468-0073, Japan. fukuzumi@chem.eng.osaka-u.ac.jp.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
keywords: bioinorganic chemistry; electron transfer; hydrogen atom transfer; manganese(IV)-oxo complex; mechanism switchover