Reactivities of Fe(IV) complexes with oxo, hydroxo, and alkylperoxo ligands: An experimental and computational study

Adam T. Fiedler, Lawrence Que

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In a previous paper [Jensen et al. J. Am. Chem. Soc. 2005, 127, 10512], we reported the synthesis of the turquoisecolored intermediate [Fe IV(βBPMCN)(OOtBU)(OH)]2+ (Tq; BPMCN = N,N'-bis(2-pyridylmethyl)-N,N'-dimethyltrans-1,2-diaminocyclohexane). The structure of Tq is unprecedented, as it represents the only synthetic example to date of a nonheme FeIV complex with both alkylperoxo and hydroxide ligands. Given the significance of similar highvalent Fe intermediates in the mechanisms of oxygenase enzymes, we have explored the reactivity of Tq at -70°C, a temperature at which it is stable, and found that it is capable of activating weak X-H bonds (X = C, O) with bond dissociation energies ≤∼80 kcal/mol. The FeIV-OH unit of Tq, and not the alkylperoxo moiety, performs the initial H-atom abstraction. However at -45°C, Tq decays at a rate that is independent of substrate identity and concentration, forming a species capable of oxidizing substrates with stronger C-H bonds. Parallel reactivity studies were also conducted with the related oxoiron(IV) complexes [FeIV(β-BPMCN)(O)(X)]2+ (3-X; X = pyridine or nitrile), thereby permitting a direct comparison of the reactivity of Fe IV centers with oxo and hydroxide ligands. We found that the H-atom abstracting ability of the FeIV-O species greatly exceeds that of the FeIV-OH species, generally by greater than 100-fold. Examination of the electronic structures of Tq and 3-X with density functional theory (DFT) provides a rationale for their differing reactivities.

Original languageEnglish (US)
Pages (from-to)11038-11047
Number of pages10
JournalInorganic chemistry
Issue number23
StatePublished - 2009


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