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Scharf, Austin

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Scharf

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Austin

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Scharf, Austin

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2011 - 20132

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Author's Publications: search.filters.isAuthorOfPublication.647df8ac-9b0d-4f12-bbe8-453ddffaa825

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    First-Row Transition Metal Complexes of Dipyrrinato Ligands: Synthesis and Characterization
    (2013-10-15) Scharf, Austin; Betley, Theodore A; Jacobsen, Eric; Friend, Cynthia
    A library of variously-substituted dipyrrins and their first-row transition metal (Mn, Fe, Cu, Zn) complexes have been synthesized, and the effects of peripheral substituents on the spectroscopic, electrochemical, and structural properties of both the free-base dipyrrins and their metal complexes has been explored. The optical and electrochemical properties of the free dipyrrins follow systematic trends; with the introduction of electron-withdrawing substituents in the 2-, 3-, 5-, 7-, and 8-positions of the dipyrrin, bathochromic shifts in the absorption spectra are observed, oxidation becomes more difficult, and reduction becomes more facile. Similar effects are seen for iron(II) dipyrrinato complexes, where peripheral substitution of the dipyrrinato ligand induces red-shifts in the absorption spectra and increases the oxidation potential of the bound iron. Steric interactions between the peripheral halogens and the 5-substituent of the dipyrrinato ligand can induce distortion of the ligand from planarity, resulting in widely varying 57Fe Mössbauer quadrupole splitting (|ΔEQ|) parameters.
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    Electronic Perturbations of Iron Dipyrrinato Complexes via Ligand β-Halogenation and meso -Fluoroarylation
    (American Chemical Society (ACS), 2011) Scharf, Austin; Betley, Theodore
    Systematic electronic variations were introduced into the monoanionic dipyrrinato ligand scaffold via halogenation of the pyrrolic β-positions and/or via the use of fluorinated aryl substituents in the ligand bridgehead position in order to synthesize proligands of the type 1,9-dimesityl-β-R4-5-Ar-dipyrrin [R = H, Cl, Br, I; Ar = mesityl, 3,5-(F3C)2C6H3, C6F5 in ligand 5-position; β = 2,3,7,8 ligand substitution; abbreviated (β,ArL)H]. The electronic perturbations were probed using standard electronic absorption and electrochemical techniques on the different ligand variations and their divalent iron complexes. The free-ligand variations cause modest shifts in the electronic absorption maxima (λmax: 464–499 nm) and more pronounced shifts in the electrochemical redox potentials for one-electron proligand reductions (E1/2: −1.25 to −1.99 V) and oxidations (E1/2: +0.52 to +1.14 V vs [Cp2Fe]+/0). Installation of iron into the dipyrrinato scaffolds was effected via deprotonation of the proligands followed by treatment with FeCl2 and excess pyridine in tetrahydrofuran to afford complexes of the type (β,ArL)FeCl(py) (py = pyridine). The electrochemical and spectroscopic behavior of these complexes varies significantly across the series: the redox potential of the fully reversible FeIII/II couple spans more than 400 mV (E1/2: −0.34 to +0.50 V vs [Cp2Fe]+/0); λmax spans more than 40 nm (506–548 nm); and the 57Fe Mössbauer quadrupole splitting (|ΔEQ|) spans nearly 2.0 mm/s while the isomer shift (δ) remains essentially constant (0.86–0.89 mm/s) across the series. These effects demonstrate how peripheral variation of the dipyrrinato ligand scaffold can allow systematic variation of the chemical and physical properties of iron dipyrrinato complexes.