Evidence for the formation of a mononuclear ferric-hydroperoxo complex via the reaction of dioxygen with an (N4S(thiolate))iron(II) complex.

Addition of O(2)(g) at low-temperature to a mononuclear, nonheme iron(ii) complex comprising a tetraazamacrocyclic N(4) donor and an arylthiolate S donor leads to the generation of a deep red complex assigned as a low-spin Fe(III)?OOH complex, formed via metal- and ligand-assisted oxidation.