Ligand Topology Effect on the Reactivity of a Mononuclear Nonheme Iron(IV)-Oxo Complex in Oxygenation Reactions

Mononuclear nonheme iron(IV)-oxo complexes with two different topologies, cis-α-[Fe^IV(O)(BQCN)]²⁺ and cis-β-[Fe^IV(O)(BQCN)]²⁺, were synthesized and characterized with various spectroscopic methods. The effect of ligand topology on the reactivities of nonheme iron(IV)-oxo complexes was investigated in C–H bond activation and oxygen atom-transfer reactions; cis-α-[Fe^IV(O)(BQCN)]²⁺ was more reactive than cis-β-[Fe^IV(O)(BQCN)]²⁺ in the oxidation reactions. The reactivity difference between the cis-α and cis-β isomers of [Fe^IV(O)(BQCN)]²⁺ was rationalized with the Fe^IV/III redox potentials of the iron(IV)-oxo complexes: the Fe^IV/III redox potential of the cis-α isomer was 0.11 V higher than that of the cis-β isomer.