Characterization of a paramagnetic mononuclear nonheme iron-superoxo complex

Abstract

O2 bubbling into a THF solution of FeII(BDPP) (1) at -80 °C generates a reversible bright yellow adduct 2. Characterization by resonance Raman and Mössbauer spectroscopy provides complementary insights into the nature of 2. The former shows a resonance-enhanced vibration at 1125 cm-1, which can be assigned to the ν(O-O) of a bound superoxide, while the latter reveals the presence of a high-spin iron(III) center that is exchange-coupled to the superoxo ligand, like the FeIII-O 2- pair found for the O2 adduct of 4-nitrocatechol-bound homoprotocatechuate 2,3-dioxygenase. Lastly, 2 oxidizes dihydroanthracene to anthracene, supporting the notion that Fe III-O2- species can carry out H atom abstraction from a C-H bond to initiate the 4-electron oxidation of substrates proposed for some nonheme iron enzymes. © 2014 American Chemical Society.