Intermediates in the oxygenation of a nonheme diiron(II) complex, including the first evidence for a bound superoxo species

Xiaopeng Shan, Lawrence Que

Research output: Contribution to journalArticlepeer-review

78 Scopus citations

Abstract

The reaction of [Fe2(μ-OH)2(6-Me 3-TPA)2]2+ (1) [6-Me3-TPA, Tris(6-methyl-2-pyridylmethyl)amine] with O2 in CH2Cl 2 at -80°C gives rise to two new intermediates, 2 and 3, before the formation of previously characterized [Fe2(O)(O 2)(6-Me3-TPA)2]2+ (4) that allow the oxygenation reaction to be monitored one electron-transfer step at a time. Raman evidence assigns 2 and 3 as a diiron-superoxo species and a diiron-peroxo species, respectively. Intermediate 2 exhibits its ν(O-O) at 1,310 cm -1 with a -71-cm-1 18O isotope shift. A doublet peak pattern for the 16O18O isotopomer of 2 in mixed-isotope Raman experiments strongly suggests that the superoxide ligand of 2 is bound end-on. This first example of a nonheme iron-superoxo intermediate exhibits the highest frequency ν(O-O) yet observed for a biomimetic metal-dioxygen adduct. The bound superoxide of 2, unlike the bound peroxide of 4, is readily reduced by 2,4-di-tert-butylphenol via a proton-coupled electron-transfer mechanism, emphasizing that metal-superoxo species may serve as oxidants in oxygen activation mechanisms of metalloenzymes. The discovery of intermediates 2 and 3 allows us to dissect the initial steps of dioxygen binding at a diiron center leading to its activation for substrate oxidation.

Original languageEnglish (US)
Pages (from-to)5340-5345
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume102
Issue number15
DOIs
StatePublished - Apr 12 2005

Keywords

  • Nonheme diiron enzymes
  • Oxygen activation
  • Superoxo intermediate

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