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Rohde, Jan-Uwe
Transition Metal Chemistry
Research Interests
  • Inorganic chemistry, coordination chemistry, organometallic chemistry, chemical synthesis, catalysis, green chemistry, inorganic reaction mechanisms.

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Spectroscopic and quantum chemical studies on low-spin Fe-IV=O complexes: Fe-O bonding and its contributions to reactivity

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Title
Spectroscopic and quantum chemical studies on low-spin Fe-IV=O complexes: Fe-O bonding and its contributions to reactivity
Author
Decker, AndreaRohde, Jan-UweKlinker, Eric J.Wong, Shaun D.Que, Lawrence, Jr.Solomon, Edward I.
Issue Date
2007-12
Publisher
AMER CHEMICAL SOC
Citation
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, v.129, no.51, pp.15983 - 15996
Abstract
High-valent Fe-IV=O species are key intermediates in the catalytic cycles of many mononuclear non-heme iron enzymes and have been structurally defined in model systems. Variable-temperature magnetic circular dichroism (VT-MCD) spectroscopy has been used to evaluate the electronic structures and in particular the Fe-O bonds of three Fe-IV=O (S = 1) model complexes, [Fe-IV(O)(TMC)(NCMe)](2+), [Fe-IV(O)(TMC)(OC(O)CF3)](+), and [Fe-IV(O)(N4py)](2+). These complexes are characterized by their strong and covalent Fe-O pi-bonds. The MCD spectra show a vibronic progression in the nonbonding -> pi(*) excited state, providing the Fe-O stretching frequency and the Fe-O bond length in this excited state and quantifying the pi-contribution to the total Fe-O bond. Correlation of these experimental data to reactivity shows that the [Fe-IV(O)(N4py)](2+) complex, with the highest reactivity toward hydrogen-atom abstraction among the three, has the strongest Fe-O pi-bond. Density functional calculations were correlated to the data and support the experimental analysis. The strength and covalency of the Fe-O pi-bond result in high oxygen character in the important frontier molecular orbitals (FMOs) for this reaction, the unoccupied beta-spin d(xz/yz) orbitals, that activates these for electrophilic attack. An extension to biologically relevant Fe-IV=O (S = 2) enzyme intermediates shows that these can perform electrophilic attack reactions along the same mechanistic pathway (pi-FMO pathway) with similar reactivity but also have an additional reaction channel involving the unoccupied alpha-spin d(z(2)) orbital (sigma-FMO pathway). These studies experimentally probe the FMOs involved in the reactivity of Fe-IV=O (S = 1) model complexes resulting in a detailed understanding of the Fe-O bond and its contributions to reactivity
URI
https://scholarworks.unist.ac.kr/handle/201301/11974
URL
http://pubs.acs.org/doi/abs/10.1021/ja074900s
DOI
10.1021/ja074900s
ISSN
0002-7863
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CHM_Journal Papers
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