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Combined experimental and theoretical study on aromatic hydroxylation by mononuclear nonheme iron(IV)-oxo complexes

Title
Combined experimental and theoretical study on aromatic hydroxylation by mononuclear nonheme iron(IV)-oxo complexes
Authors
De Visser S.P.Oh K.Han A.-R.Nam W.
Ewha Authors
남원우
SCOPUS Author ID
남원우scopus
Issue Date
2007
Journal Title
Inorganic Chemistry
ISSN
0020-1669JCR Link
Citation
vol. 46, no. 11, pp. 4632 - 4641
Indexed
SCI; SCIE; SCOPUS WOS scopus
Abstract
The hydroxylation of aromatic compounds by mononuclear nonheme iron(IV)-oxo complexes, [FeIV(Bn-tpen)(O)]2+ (Bn-tpen = N-benzyl-N,N′,N′-tris(2-pyridylmethyl)ethane-1,2-diamine) and [FeIV(N4Py)(O)]2+ (N4Py = N,N-bis(2-pyridylmethyl)-N- bis(2-pyridyl)methylamine), has been investigated by a combined experimental and theoretical approach. In the experimental work, we have performed kinetic studies of the oxidation of anthracene with nonheme iron(IV)-oxo complexes generated in situ, thereby determining kinetic and thermodynamic parameters, a Hammett ρ value, and a kinetic isotope effect (KIE) value. A large negative Hammett ρ value of -3.9 and an inverse KIE value of 0.9 indicate that the iron-oxo group attacks the aromatic ring via an electrophilic pathway. By carrying out isotope labeling experiments, the oxygen in oxygenated products was found to derive from the nonheme iron(IV)-oxo species. In the theoretical work, we have conducted density functional theory (DFT) calculations on the hydroxylation of benzene by [FeIV(N4Py)(O)]2+. The calculations show that the reaction proceeds via two-state reactivity patterns on competing triplet and quintet spin states via an initial rate determining electrophilic substitution step. In analogy to heme iron(IV)-oxo catalysts, the ligand is noninnocent and actively participates in the reaction mechanism by reshuttling a proton from the ipso position to the oxo group. Calculated kinetic isotope effects of C6H6 versus C6D6 confirm an inverse isotope effect for the electrophilic substitution pathway. Based on the experimental and theoretical results, we have concluded that the aromatic ring oxidation by mononuclear nonheme iron(IV)-oxo complexes does not occur via a hydrogen atom abstraction mechanism but involves an initial electrophilic attack on the π-system of the aromatic ring to produce a tetrahedral radical or cationic σ-complex. © 2007 American Chemical Society.
DOI
10.1021/ic700462h
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자연과학대학 > 화학·나노과학전공 > Journal papers
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