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.
Bibliographical noteFunding 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.
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