Tuning the Redox Properties of a Nonheme Iron(III)-Peroxo Complex Binding Redox-Inactive Zinc Ions by Water Molecules

Redox-inactive metal ions play important roles in tuning chemical properties of metal-oxygen intermediates. Herein we report the effect of water molecules on the redox properties of a nonheme iron(III)-peroxo complex binding redox-inactive metal ions. The coordination of two water molecules to a Zn²⁺ ion in (TMC)Fe^III-(O₂)-Zn(CF₃SO₃)₂ (1-Zn²⁺) decreases the Lewis acidity of the Zn²⁺ ion, resulting in the decrease of the one-electron oxidation and reduction potentials of 1-Zn²⁺. This further changes the reactivities of 1-Zn²⁺ in oxidation and reduction reactions; no reaction occurred upon addition of an oxidant (e.g., cerium(IV) ammonium nitrate (CAN)) to 1-Zn²⁺, whereas 1-Zn²⁺ coordinating two water molecules, (TMC)Fe^III-(O₂)-Zn(CF₃SO₃)₂-(OH₂)₂ [1-Zn²⁺-(OH₂)₂], releases the O₂ unit in the oxidation reaction. In the reduction reactions, 1-Zn²⁺ was converted to its corresponding iron(IV)-oxo species upon addition of a reductant (e.g., a ferrocene derivative), whereas such a reaction occurred at a much slower rate in the case of 1-Zn²⁺-(OH₂)₂. The present results provide the first biomimetic example showing that water molecules at the active sites of metalloenzymes may participate in tuning the redox properties of metal-oxygen intermediates.