Electron-Transfer and Redox Reactivity of High-Valent Iron Imido and Oxo Complexes with the Formal Oxidation States of Five and Six

Xiaoyan Lu, Xiao Xi Li, Yong Min Lee, Yuri Jang, Mi Sook Seo, Seungwoo Hong, Kyung Bin Cho, Shunichi Fukuzumi, Wonwoo Nam

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Abstract

We report for the first time electron-transfer (ET) properties of mononuclear nonheme iron-oxo and-imido complexes with the formal oxidation states of five and six, such as an iron(V)-imido TAML cation radical complex, which is formally an iron(VI)-imido complex [FeV(NTs)(TAML+â¢)] (1; NTs = tosylimido), an iron(V)-imido complex [FeV(NTs)(TAML)]- (2), and an iron(V)-oxo complex [FeV(O)(TAML)]- (3). The one-electron reduction potential (Ered vs SCE) of 1 was determined to be 0.86 V, which is much more positive than that of 2 (0.30 V), but the Ered of 3 is the most positive (1.04 V). The rate constants of ET of 1-3 were analyzed in light of the Marcus theory of adiabatic outer-sphere ET to determine the reorganization energies (λ) of ET reactions with 1-3; the λ of 1 (1.00 eV) is significantly smaller than those of 2 (1.98 eV) and 3 (2.25 eV) because of the ligand-centered ET reduction of 1 as compared to the metal-centered ET reduction of 2 and 3. In oxidation reactions, reactivities of 1-3 toward the nitrene transfer (NT) and oxygen atom transfer (OAT) to thioanisole and its derivatives and the C-H bond activation reactions, such as the hydrogen atom transfer (HAT) of 1,4-cyclohexadiene, were compared experimentally. The differences in the redox reactivity of 1-3 depending on the reaction types, such as NT and OAT versus HAT, were interpreted by performing density functional theory calculations, showing that the ligand-centered reduction seen on ET reactions can switch to metal-centered reduction in NT and HAT.

Original languageEnglish
Pages (from-to)3891-3904
Number of pages14
JournalJournal of the American Chemical Society
Volume142
Issue number8
DOIs
StatePublished - 26 Feb 2020

Bibliographical note

Funding Information:
The authors acknowledge the NRF of Korea through CRI (NRF-2012R1A3A2048842 to W.N.), GRL (NRF-2010-00353 to W.N.), Basic Science Research Program (2017R1D1A1B03029982 to Y.M.L., 2017R1D1A1B03032615 to S.F., and 2019R1I1A1A01055822 to M.S.S.), and MSIP (NRF-2017R1C1B2002037 to S.H.), Sookmyung Women’s University Grants (1-1703-2039 to S.H.), and Grants-in-Aid (no. 16H02268 to S.F.) from MEXT, Japan.

Publisher Copyright:
© 2020 American Chemical Society.

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