Kinetic Analysis of H2O2 Activation by an Iron(III) Complex in Water Reveals a Nonhomolytic Generation Pathway to an Iron(IV)oxo Complex

[Fe III (OH)(tpena)] + (tpena – = N, N, N ′-tris(2-pyridylmethyl)ethylenediamine- N ′-acetate) catalytically activates H 2 O 2 with the concomitant formation of the active oxidants [Fe IV (O)(tpena)] + and HO • in aqueous solutions at pH 8. A kinetic model is used to demonstrate that the activation of [Fe III (OH)(tpena)] + by H 2 O 2 proceeds by the formation of [Fe III (OOH)(tpena)] + . Two previously unreported reactions of [Fe III (OOH)(tpena)] +, the first with another H 2 O 2 molecule to afford [Fe III (OH)(tpena)] +, O 2 •–, and HO • and the second, and dominant, with [Fe III (OH)(tpena)] + to yield 2 equiv of [Fe IV (O)(tpena)] + and H 2 O, are found to be the major pathways for the formation of HO • and [Fe IV (O)(tpena)] +, respectively. The production of HO • was quantified by a chemiluminescence method showing that [Fe IV (O)(tpena)] + is produced in much larger yields than HO • . The generation of HO • compromises the stability of [Fe III (OH)(tpena)] + unless an external substrate is present that can outcompete [Fe III (OH)(tpena)] + for HO • . Significantly, we demonstrate that the reaction commonly assumed to occur in the decay of nonheme iron(III)hydroperoxides, homolytic O–O bond cleavage, is of minor significance for the generation of HO • and the iron(IV)oxo complex. The production of both a reactive high-valent iron–oxo species and HO • under mild, aqueous ambient conditions represents a significant contribution to the current state of the art for biomimetic nonheme chemistry in water.