Regioselective Arene Hydroxylation Mediated by a (<i>μ</i>-Peroxo)diiron(III) Complex:  A Functional Model for Toluene Monooxygenase

Yamashita, Masakazu; Furutachi, Hideki; Tosha, Takehiko; Fujinami, Shuhei; Saito, Wataru; Maeda, Yonezo; Takahashi, Kenji; Tanaka, Koji; Kitagawa, Teizo; Suzuki, Masatatsu

doi:10.1021/ja063987z

Cited by 46 publications

(45 citation statements)

References 19 publications

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“…Similar Mössbauer parameters have been assigned to a synthetic, structurally characterized model (μ-1,2-peroxo)diiron(III) model complex supported by a tris(pyrazolyl)borate ligand scaffold (57) as well as the peroxodiiron(III) intermediate generated in the W48A/D84E variant of RNR-R2 that are assigned μ-peroxide binding geometries (12, 58). The absorbance of P ∗ around 720 nm (ε = 1250 M −1 cm −1 ) is similar to those of well-characterized peroxodiiron(III) species in enzymes (10, 15, 42, 59, 60) and model systems (57, 61) assigned as peroxo-to-Fe(III) charge transfer transitions. Because of its spectroscopic similarities to those of known enzyme intermediates and model complexes, P ∗ is likely to contain a peroxodiiron(III) unit.…”

Section: Discussionsupporting

confidence: 69%

Revisiting the Mechanism of Dioxygen Activation in Soluble Methane Monooxygenase from M. capsulatus (Bath): Evidence for a Multi-Step, Proton-Dependent Reaction Pathway

2009

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Stopped-flow kinetic investigations of soluble methane monooxygenase (sMMO) from M. capsulatus (Bath) have clarified several discrepancies that exist in the literature regarding aspects of catalysis by this enzyme. The development of thorough kinetic analytical techniques has led to the discovery of two novel oxygenated iron species that accumulate in addition to the well-established intermediates Hperoxo and Q. The first intermediate, P∗, is a precursor to Hperoxo and was identified when the reaction of reduced MMOH and MMOB with O2 was carried out in the presence of ≥578 μM methane to suppress the dominating absorbance signal due to Q. The optical properties of P∗ are similar to those of Hperoxo, with ε420 = 3500 M−1 cm−1 and ε720 = 1250 M−1 cm−1. These values are suggestive of a peroxo-to-iron(III) charge-transfer transition and resemble those of peroxodiiron(III) intermediates characterized in other carboxylate-bridged diiron proteins and synthetic model complexes. The identified second intermediate, Q∗, forms on the pathway of Q decay when reactions are performed in the absence of hydrocarbon substrate. Q∗ does not react with methane and is independent of buffer content. Its optical spectrum displays a unique shoulder at 455 nm. Studies conducted at different pH values reveal that rate constants corresponding to P∗ decay/Hperoxo formation and Hperoxo decay/Q formation are both are significantly retarded at high pH and indicate that both events require proton transfer. The processes exhibit normal kinetic solvent isotope effects (KSIEs) of 2.0 and 1.8, respectively, when the reactions are performed in D2O. Mechanisms are proposed to account for the observations of these novel intermediates and the observed proton transfer dependencies of P∗ decay/Hperoxo formation and Hperoxo decay/Q formation.

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Section: Discussionsupporting

confidence: 69%

Revisiting the Mechanism of Dioxygen Activation in Soluble Methane Monooxygenase from M. capsulatus (Bath): Evidence for a Multi-Step, Proton-Dependent Reaction Pathway

2009

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“…In light of this fact, rR spectra of 2 •O 2 AsMe 2 , 2 •O 2 PPh 2 and 3 •O 2 PPh 2 were collected, analyzed and compared with spectra presented in earlier reports21,26,40,42–46 in an attempt to gain insight into their individual molecular structures.…”

Section: Resultsmentioning

confidence: 99%

Characterization of Two Distinct Adducts in the Reaction of a Nonheme Diiron(II) Complex with O₂

Frisch

Martinho

et al. 2009

Inorg. Chem.

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“…Complexes 1 and 2 exhibit similar reactivity patterns, but 1 generates a more powerful oxidant than 2. Recently, efficient and selective intramolecular aromatic hydroxylations were reported with mononuclear [28,29] or dinuclear [30][31][32][33][34] iron complexes in which the aromatic ring is forced into close proximity of the iron center by a covalent linkage to the supporting polydentate ligand. The need to independently prepare the compounds containing both reactive iron center and the aromatic substrate, however, limits the applicability of these systems.…”

Section: Introductionmentioning

confidence: 99%

Iron‐Promoted ortho‐ and/or ipso‐Hydroxylation of Benzoic Acids with H₂O₂

Makhlynets

Das

Taktak

et al. 2009

Chemistry A European J

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Regioselective hydroxylation of aromatic acids with hydrogen peroxide proceeds readily in the presence of iron(II) complexes with tetradentate aminopyridine ligands [Fe(II)(BPMEN)(CH(3)CN)(2)](ClO(4))(2) (1) and [Fe(II)(TPA)(CH(3)CN)(2)](OTf)(2) (2), where BPMEN=N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)-1,2-ethylenediamine, TPA=tris-(2-pyridylmethyl)amine. Two cis-sites, which are occupied by labile acetonitrile molecules in 1 and 2, are available for coordination of H(2)O(2) and substituted benzoic acids. The hydroxylation of the aromatic ring occurs exclusively in the vicinity of the anchoring carboxylate functional group: ortho-hydroxylation affords salicylates, whereas ipso-hydroxylation with concomitant decarboxylation yields phenolates. The outcome of the substituent-directed hydroxylation depends on the electronic properties and the position of substituents in the molecules of substrates: 3-substituted benzoic acids are preferentially ortho-hydroxylated, whereas 2- and, to a lesser extent, 4-substituted substrates tend to undergo ipso-hydroxylation/decarboxylation. These two pathways are not mutually exclusive and likely proceed via a common intermediate. Electron-withdrawing substituents on the aromatic ring of the carboxylic acids disfavor hydroxylation, indicating an electrophilic nature for the active oxidant. Complexes 1 and 2 exhibit similar reactivity patterns, but 1 generates a more powerful oxidant than 2. Spectroscopic and labeling studies exclude acylperoxoiron(III) and Fe(IV)=O species as potential reaction intermediates, but strongly indicate the involvement of an Fe(III)--OOH intermediate that undergoes intramolecular acid-promoted heterolytic O-O bond cleavage, producing a transient iron(V) oxidant.

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Regioselective Arene Hydroxylation Mediated by a (μ-Peroxo)diiron(III) Complex: A Functional Model for Toluene Monooxygenase

Cited by 46 publications

References 19 publications

Revisiting the Mechanism of Dioxygen Activation in Soluble Methane Monooxygenase from M. capsulatus (Bath): Evidence for a Multi-Step, Proton-Dependent Reaction Pathway

Revisiting the Mechanism of Dioxygen Activation in Soluble Methane Monooxygenase from M. capsulatus (Bath): Evidence for a Multi-Step, Proton-Dependent Reaction Pathway

Characterization of Two Distinct Adducts in the Reaction of a Nonheme Diiron(II) Complex with O₂

Iron‐Promoted ortho‐ and/or ipso‐Hydroxylation of Benzoic Acids with H₂O₂

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Regioselective Arene Hydroxylation Mediated by a (μ-Peroxo)diiron(III) Complex: A Functional Model for Toluene Monooxygenase

Cited by 46 publications

References 19 publications

Revisiting the Mechanism of Dioxygen Activation in Soluble Methane Monooxygenase from M. capsulatus (Bath): Evidence for a Multi-Step, Proton-Dependent Reaction Pathway

Revisiting the Mechanism of Dioxygen Activation in Soluble Methane Monooxygenase from M. capsulatus (Bath): Evidence for a Multi-Step, Proton-Dependent Reaction Pathway

Characterization of Two Distinct Adducts in the Reaction of a Nonheme Diiron(II) Complex with O2

Iron‐Promoted ortho‐ and/or ipso‐Hydroxylation of Benzoic Acids with H2O2

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Characterization of Two Distinct Adducts in the Reaction of a Nonheme Diiron(II) Complex with O₂

Iron‐Promoted ortho‐ and/or ipso‐Hydroxylation of Benzoic Acids with H₂O₂