A Nonheme Iron(III) Superoxide Complex Leads to Sulfur Oxygenation

Abstract

A new alkylthiolate-ligated nonheme iron complex, Fe^II(BNPA^Me2S)Br (1), is reported. Reaction of 1 with O₂ at -40 °C, or reaction of the ferric form with O₂^•- at -80 °C, gives a rare iron(III)-superoxide intermediate, [Fe^III(O₂)(BNPA^Me2S)]⁺ (2), characterized by UV-vis, ⁵⁷Fe Mössbauer, ATR-FTIR, EPR, and CSIMS. Metastable 2 then converts to an S-oxygenated Fe^II(sulfinate) product via a sequential O atom transfer mechanism involving an iron-sulfenate intermediate. These results provide evidence for the feasibility of proposed intermediates in thiol dioxygenases.