H2O2 Oxidation by FeIII-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

Research output: Contribution to journalArticlepeer-review

20 Scopus citations

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 FeIV=O species such as [(N4Py)FeIV=O]2+ formed by homolytic cleavage of the O-O bond of an FeIII-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 FeIV=O species formed is detectable in methanol. Furthermore, we show that the decomposition of H2O2 to water and O2 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)FeIV=O]2+ oxidizes stoichiometric H2O2 rapidly, the rate of formation of FeIV=O from the FeIII-OOH intermediate is too low to account for the rate of H2O2 decomposition observed under catalytic conditions. Indeed, with excess H2O2, disproportionation to O2 and H2O is due to reaction with the FeIII-OOH intermediate and thereby prevents formation of the FeIV=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 FeIII-OOH intermediate is less than the rate of the O-O bond homolysis and the subsequent reaction of the FeIV=O species with a substrate.

Original languageEnglish (US)
Pages (from-to)9665-9674
Number of pages10
JournalACS Catalysis
Volume8
Issue number10
DOIs
StatePublished - Oct 5 2018

Bibliographical note

Funding Information:
The COST association action CM1305 ECOSTBio (STSM grant 34080), the European Research Council (ERC 279549 W.R.B.), the labex arcane (ANR-11-LABX-003), MINECO (CTQ2014-59212-P and CTQ2015-70851-ERC, M.S.), GenCat (2014SGR1202, MS), FEDER (UNGI10-4E-801, M.S.), and the Chinese Scholarship Council (CSC) are acknowledged for financial support.

Funding Information:
The COST association action CM1305 ECOSTBio (STSM grant 34080), the European Research Council (ERC 279549, W.R.B.), the labex arcane (ANR-11-LABX-003), MINECO (CTQ2014-59212-P and CTQ2015-70851-ERC, M.S.), Gen-Cat (2014SGR1202, MS), FEDER (UNGI10-4E-801, M.S.), and the Chinese Scholarship Council (CSC) are acknowledged for financial support.

Publisher Copyright:
© 2018 American Chemical Society.

Copyright:
Copyright 2018 Elsevier B.V., All rights reserved.

Keywords

  • EPR spectroscopy
  • Raman spectroscopy
  • catalase
  • iron
  • oxidation
  • peroxide

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