H2O2 Oxidation by Fe-III-OOH Intermediates and Its Effect on Catalytic Efficiency

Juan Chen, Apparao Draksharapu, Davide Angelone, Duenpen Unjaroen, Sandeep K. Padamati, Ronald Hage, Marcel Swart, Carole Duboc, Wesley R. Browne*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Abstract

The oxidation of the C-H and C=C bonds of hydrocarbons with H2O2 catalyzed by non-heme iron complexes with pentadentate ligands is widely accepted as involving a reactive Fe-IV=O species such as [(N4Py)Fe-IV=O](2+) formed by homolytic cleavage of the O-O bond of an Fe-III-OOH intermediate (where N4Py is 1,1-bis(pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine). We show here that at low H2O2 concentrations the Fe-IV=O species formed is detectable in methanol. Furthermore, we show that the decomposition of H2O2 to water and O-2 is an important competing pathway that limits efficiency in the terminal oxidant and indeed dominates reactivity except where only sub-/near-stoichiometric amounts of H2O2 are present. Although independently prepared [(N4Py)Fe-IV=O](2+) oxidizes stoichiometric H2O2 rapidly, the rate of formation of Fe-IV=O from the Fe-III-OOH intermediate is too low to account for the rate of H2O2 decomposition observed under catalytic conditions. Indeed, with excess H2O2, disproportionation to O-2 and H2O is due to reaction with the Fe-III-OOH intermediate and thereby prevents formation of the Fe-IV=O species. These data rationalize that the activity of these catalysts with respect to hydrocarbon/alkene oxidation is maximized by maintaining sub-/near-stoichiometric steady-state concentrations of H2O2, which ensure that the rate of the H2O2 oxidation by the Fe-III-OOH intermediate is less than the rate of the O-O bond homolysis and the subsequent reaction of the Fe-IV=O species with a substrate.

Original languageEnglish
Pages (from-to)9665-9674
Number of pages19
JournalACS Catalysis
Volume8
Issue number10
DOIs
Publication statusPublished - 5-Oct-2018

Keywords

  • iron
  • oxidation
  • peroxide
  • catalase
  • Raman spectroscopy
  • EPR spectroscopy
  • NONHEME IRON(IV)-OXO COMPLEXES
  • H BOND-CLEAVAGE
  • ACTIVATED BLEOMYCIN
  • HYDROGEN-PEROXIDE
  • ELECTRON-TRANSFER
  • HIGH-SPIN
  • SPECTROSCOPIC CHARACTERIZATION
  • OXOIRON(IV) FORMATION
  • (FEO)-O-IV COMPLEXES
  • ROOM-TEMPERATURE

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