Activation of dioxygen by a mononuclear non-heme iron complex: characterization of a FeIII(OOH) intermediate

The reaction of the iron(II) complex supported by the ligand L(5)(2)aH (2,2-dimethyl-N-[6-({[2-(methyl-pyridin-2- ylmethyl-amino)-ethyl]-pyridin-2-ylmethyl-amino}-methyl)-pyridin-2-yl]-propionamide) with dioxygen, in the presence of HClO4 and NaBPh4 yields the corresponding low spin (S = 1/2) Fe-III(OOH) complex. This reaction, where the anion BPh4- acts as an electron donor, is reminiscent of the reductive activation of O-2 by enzymatic systems. Under these specific experimental conditions, the hydroperoxoiron(III) complex evolves in an unexpected way to yield a high spin (S = 5/2) green species. This transformation is shown to arise from the reaction between the hydroperoxoiron(III) intermediate and BPh3, a side product of BPh4-.