Kinetic Analysis of H₂O₂Activation by an Iron(III) Complex in Water Reveals a Nonhomolytic Generation Pathway to an Iron(IV)oxo Complex

[FeIII(OH)(tpena)]+ (tpena- = N,N,N′-tris(2-pyridylmethyl)ethylenediamine-N′-acetate) catalytically activates H2O2 with the concomitant formation of the active oxidants [FeIV(O)(tpena)]+ and HO• in aqueous solutions at pH 8. A kinetic model is used to demonstrate that the activation of [FeIII(OH)(tpena)]+ by H2O2 proceeds by the formation of [FeIII(OOH)(tpena)]+. Two previously unreported reactions of [FeIII(OOH)(tpena)]+, the first with another H2O2 molecule to afford [FeIII(OH)(tpena)]+, O2•-, and HO• and the second, and dominant, with [FeIII(OH)(tpena)]+ to yield 2 equiv of [FeIV(O)(tpena)]+ and H2O, are found to be the major pathways for the formation of HO• and [FeIV(O)(tpena)]+, respectively. The production of HO• was quantified by a chemiluminescence method showing that [FeIV(O)(tpena)]+ is produced in much larger yields than HO•. The generation of HO• compromises the stability of [FeIII(OH)(tpena)]+ unless an external substrate is present that can outcompete [FeIII(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.