916148-28-2Relevant academic research and scientific papers
X-ray absorption spectroscopy and reactivity of thiolate-ligated Fe III-OOR complexes
Stasser, Jay,Namuswe, Frances,Kasper, Gary D.,Jiang, Yunbo,Krest, Courtney M.,Green, Michael T.,Penner-Hahn, James,Goldberg, David P.
, p. 9178 - 9190 (2011/01/12)
The reaction of a series of thiolate-ligated iron(II) complexes [FeII([15]aneN4)(SC6H5)]BF4 (1), [Fe II([15]aneN4)-(SC6H4-p-Cl)]BF 4 (2), and [FeII([15]aneN4)(SC 6H4-p-NO2)]BF4 (3) with alkylhydroperoxides at low temperature (-78 °C or-40 °C) leads to the metastable alkylperoxo-iron(III) species [FeIII ([15]aneN 4)(SC6H5)(OOtBu)]BF4 (1a), [Fe III ([15]aneN4)(SC6H4-p-Cl)(OOtBu)]BF 4 (2a), and [FeIII ([15]aneN4)(SC 6H4-p-NO2)(OOtBu)]BF4 (3a), respectively. X-ray absorption spectroscopy (XAS) studies were conducted on the FeIII-OOR complexes and their iron(II) precursors. The edge energy for the iron(II) complexes (～7118 eV) shifts to higher energy upon oxidation by ROOH, and the resulting edge energies for the FeIII-OOR species range from 7121-7125 eV and correlate with the nature of the thiolate donor. Extended X-ray absorption fine structure (EXAFS) analysis of the iron(II) complexes 1-3 in CH2Cl2show that their solid state structures remain intact in solution. The EXAFS data on 1a-3a confirm their proposed structures as mononuclear, 6-coordinate FeIII-OOR complexes with 4N and 1S donors completing the coordination sphere. The Fe-O bond distances obtained from EXAFS for 1a-3a are 1.82-1.85 a, significantly longer than other low-spin FeIII-OOR complexes. The Fe-O distances correlate with the nature of the thiolate donor, in agreement with the previous trends observed for v(Fe-O) from resonance Raman (RR) spectroscopy, and supported by optimized geometries obtained from density functional theory (DFT) calculations. Reactivity and kinetic studies on 1a-3a show an important influence of the thiolate donor.
A low-spin alkylperoxo-iron(III) complex with weak Fe-O and O-O bonds: Implications for the mechanism of superoxide reductase
Krishnamurthy, Divya,Kasper, Gary D.,Namuswe, Frances,Kerber, William D.,Sarjeant, Amy A. Narducci,Moenne-Loccoz, Pierre,Goldberg, David P.
, p. 14222 - 14223 (2008/02/09)
The synthesis of a mononuclear, five-coordinate ferrous complex [([15]aneN4)FeII(SPh)](BF4) (1) is reported. This complex is a new model of the reduced active site of the enzyme superoxide reductase (SOR), which is comprised of a [(NHis)4(Scys)FeII] center. Complex 1 reacts with alkylhydroperoxides (tBuOOH, cumenylOOH) at low temperature to give a metastable, dark red intermediate (2a: R = tBu; 2b: R = cumenyl) that has been characterized by UV-vis, EPR, and resonance Raman spectroscopy. The UV-vis spectrum (-80 °C) reveals a 526 nm absorbance (ε = 2150 M-1 cm-1) for 2a and a 527 nm absorbance (ε = 1650 M-1 cm-1) for 2b, indicative of alkylperoxo-to-iron(III) LMCT transitions, and the EPR data (77 K) show that both intermediates are low-spin iron(III) complexes (g = 2.20 and 1.97). Definitive identification of the Fe(III)-OOR species comes from RR spectra, which give ν(Fe-O) = 612 (2a) and 615 (2b) cm-1, and ν(O-O) = 803 (2a) and 795 (2b) cm-1. The assignments for 2a were confirmed by 18O substitution (tBu18O18OH), resulting in a 28 cm-1 downshift for ν(Fe-18O), and a 46 cm-1 downshift for ν(18O-18O). These data show that 2a and 2b are low-spin FeIII-OOR species with weak Fe-O bonds and suggest that a low-spin intermediate may occur in SOR, as opposed to previous proposals invoking high-spin intermediates. Copyright
