page_title: High-valent iron
section_title: Fe(IV)O
hierarchical_section_title: High-valent iron / Oxoiron compounds / Fe(IV)O
caption_attribution_description: English: png version of Fe4TMCSOPF6.svg
context_page_description: High-valent iron commonly denotes compounds and intermediates in which iron is found in a formal oxidation state > 3 that show a number of bonds > 6 with a coordination number ≤ 6. The term is rather uncommon for hepta-coordinate compounds of iron. It has to be distinguished from the terms hypervalent and hypercoordinate, as high-valent iron compounds neither necessarily violate the 18-electron rule nor necessarily show coordination numbers > 6. The ferrate(VI) ion [FeO₄]²⁻ was the first structure in this class synthesized. The synthetic compounds discussed below contain highly oxidized iron in general, as the concepts are closely related.
context_section_description: Several syntheses of oxoiron(IV) species have been reported. These compounds model biological complexes such as cytochrome P450, NO synthase, and isopenicillin N synthase. Two such reported compounds are thiolate-ligated oxoiron(IV) and cyclam-acetate oxoiron(IV).
  Thiolate-ligated oxoiron(IV) is formed by the oxidation of a precursor, [Feᴵᴵ(TMCS)](PF₆) (TMCS = 1-mercaptoethyl-4,8,11-trimethyl-1,4,8,11-tetraza cyclotetradecane), and 3-5 equivalents of H₂O₂ at -60 ˚C in methanol. The iron(IV) compound is deep blue in color and shows intense absorption features at 460 nm, 570 nm, 850 nm, and 1050 nm. This species Feᴵⱽ(=O)(TMCS)+ is stable at -60 ˚C, but decomposition is reported as temperature increases. Compound 2 was identified by Mössbauer spectroscopy, high resolution electrospray ionization mass spectrometry (ESI-MS), X-ray absorption spectroscopy, extended X-ray absorption fine structure (EXAFS), ultraviolet–visible spectroscopy (UV-vis), Fourier-transform infrared spectroscopy (FT-IR), and results were compared to density functional theory (DFT) calculations.
  Tetramethylcyclam oxoiron(IV) is formed by the reaction of Feᴵᴵ(TMC)(OTf)₂, TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane; OTf = CF₃SO₃, with iodosylbenzene (PhIO) in CH₃CN at -40 ˚C. A second method for formation of cyclam oxoiron(IV) is reported as the reaction of Feᴵᴵ(TMC)(OTf)₂ with 3 equivalents of H₂O₂ for 3 hours. This species is pale green in color and has an absorption maximum at 820 nm. It is reported to be stable for at least 1 month at -40 ˚C. It has been characterized by Mössbauer spectroscopy, ESI-MS, EXAFS, UV-vis, Raman spectroscopy, and FT-IR.
  High-valent iron bispidine complexes can oxidize cyclohexane to cyclohexanol and cyclohexanone in 35% yield with an alcohol to ketone ratio up to 4.
caption: thiolate-ligated oxoiron(IV)
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