Browsing by Subject "oxoiron(IV)"

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    Characterization and Reactivity of Synthetic Nonheme Oxoiron(IV) Complexes
    (2015-05) Bigelow, Jennifer
    Nonheme iron enzymes are prevalent throughout nature and utilize oxygen as the oxidant. While some intermediates are proposed, such as iron(IV)-oxo and iron(III)-peroxo species, the nature of the reactivity of these species has not yet been fully explored. Nonheme synthetic iron model complexes allow for easy modification to probe the reactivity of such species, and allow for characterization for later comparison with enzymes. This dissertation explores the reactivity of iron(IV)-oxo species supported by a tetramethycyclam framework. Interesting, in contrast to what had been reported previously, the electron-donating properties of the axial ligand do not correspond to the hydrogen atom transfer (HAT) reactivity, while a consistent trend for oxygen atom transfer (OAT) is observed. Ligand tethering is found to have a large impact on the enthalpy of activation. It is proposed that the iron(IV)-oxo moiety rises out of the plane to react, which forces tethered ligands to weaken the axial bond. The activation of oxygen by synthetic iron complexes, in the presence of either a hydrogen atom donor or an acid and a proton source, has been proposed to mimic enzymatic activity. However, the reexamination of mechanisms previously reported to follow an enzyme-mimicking pathway are instead due to peroxyl radicals. This highlights the importance of testing such mechanisms, as autooxidation is a common problem with many compounds in the presence of dioxygen. Finally, species such as iron(IV)-oxo and iron(III)-peroxo complexes, as well as related complexes, are characterized by resonance Raman spectroscopy. Many of these complexes have a ligand with a carboxylate moiety, as seen in nonheme enzymes. Characterization of these complexes show similarities between iron(IV)-oxo and iron(III)-peroxo and chromium(IV)-peroxo species reported previously, having similar vibration values, while major differences exist in vibrations between previously reported iodosylarene-iron(III) complexes and new iodosylarene-iron(III) complexes.
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    Structural- and Spectroscopic-Reactivity Relationships of Nonheme Oxoiron(IV) Complexes
    (2019-05) Rasheed, Waqas
    Non-heme oxoiron(IV) motifs have been identified as key intermediates that activate strong C—H bonds. Unlike the enzymatic intermediates however, most oxoiron(IV) complexes in synthetic chemistry have a triplet ground spin state and thus differ in their functional and electronic properties from the S = 2 units characterized in the enzymes. One striking exception is the complex [FeIV(O)(TQA)(L)]2+, where TQA = tris(2-quinolylmethyl)amine, which has Mössbauer parameters that closely resemble those of TauD-J, an enzymatic intermediate that has been relatively well-characterized. This oxoiron(IV) complex contains quinoline donors, and its thermal instability precludes its structural characterization (half-life = 15 minutes at 233 K). In this dissertation, several oxoiron(IV) complexes supported by pentadentate and tetradentate ligands are characterized, and examined for their reactivity and spectroscopic features. Crystallographic characterization of a few of these molecules is also reported. The structurally characterized oxoiron(IV) complexes along with some previously reported oxoiron(IV) complexes are used to set up structure-reactivity and spectroscopic-reactivity relationships, and show linear correlations with increasing isomer shifts, λmax values as well as metal-ligand distances. In addition, this thesis also uses 1H-NMR spectroscopy as an effective tool to identify solution-state structure as well the spin state of oxoiron(IV) complexes. We also characterize the first example of a spin crossover oxoiron(IV) complex, examples of which are only seen in iron(II) and iron(III) complexes.