Evidence for a Nonheme Fe(IV)O Species in the Intramolecular Hydroxylation of a Phenyl Moiety

Lange, Steven J.; Que, Lawrence

doi:10.1021/ja990233u

Cited by 90 publications

(79 citation statements)

References 21 publications

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“…Recently, the intramolecular hydroxylation of an aromatic ring has been observed for a non-heme Fe IV O moiety also. [44] 2 and Fe ± BLM reveals marked differences, which appear to be related to the number of coordinating N atoms in the ligand. The systems (1 and Fe ± BLM) with pentadentate ligands show similar reactivity to a number of substrates.…”

Section: Mechanistic Probes Of Alkane Hydroxylationmentioning

confidence: 94%

Catalytic Oxidation with a Non-Heme Iron Complex That Generates a Low-Spin FeIIIOOH Intermediate

et al. 2000

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The antitumor drug bleomycin (BLM) is proposed to act via a low-spin iron(III) hydroperoxide intermediate called "activated bleomycin". To gain more insight into the mechanistic aspects of catalytic oxidation by these intermediates we have studied the reactivity of [(N4Py)Fe(CH3CN)](ClO4)2 (1) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) with excess H2O2. Under these conditions a transient purple species is generated, [(N4Py)FeOOH]2- (2), which has spectroscopic features and reactivity strongly reminiscent of activated bleomycin. The catalytic oxidation of alkanes such as cyclohexane, cyclooctane, and adamantane by 1 with H2O2 gave the corresponding alcohols and ketones in up to 31% yield. It was concluded, from the O2 sensitivity of the oxidation reactions, the formation of brominated products in the presence of methylene bromide, and the nonstereospecificity of the oxidation of cis- or trans-dimethylcyclohexane, that long-lived alkyl radicals were formed during the oxidations. Oxidation of alkenes did not afford the corresponding epoxides in good yields but resulted instead in allylic oxidation products in the case of cyclohexene, and cleavage of the double bond in the case of styrene. Addition of hydroxyl radical traps, such as benzene and acetone, led to only partial quenching of the reactivity. The kinetic isotope effects for cyclohexanol formation, ranging from 1.5 in acetonitrile to 2.7 in acetone with slow addition of H2O2, suggested the involvement of a more selective oxidizing species in addition to hydroxyl radicals. Monitoring the UV/Vis absorption of 2 during the catalytic reaction showed that 2 was the precursor for the active species. On the basis of these results it is proposed that 2 reacts through homolysis of the O-O bond to afford two reactive radical species: [(N4Py)Fe(IV)O]2+ and *OH. The comparable reactivity of 1 and Fe-BLM raises the possibility that they react through similar mechanistic pathways.

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Section: Mechanistic Probes Of Alkane Hydroxylationmentioning

confidence: 94%

Catalytic Oxidation with a Non-Heme Iron Complex That Generates a Low-Spin FeIIIOOH Intermediate

et al. 2000

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“…In general, m-oxo dinuclear complexes are obtained upon reaction of dichloroiron(ii) species with molecular dioxygen or organic peroxides. [21,38] The present situation, however, is different: because of the presence of protons and radicals, the oxygenation conditions are more drastic and lead to some ligand decomposition. As a consequence, free ironA C H T U N G T R E N N U N G (iii) is generated and is trapped by the catechol substituents.…”

Section: Full Papermentioning

confidence: 99%

The Coordination Chemistry of FeCl₃ and FeCl₂ to Bis[2‐(2,3‐dihydroxyphenyl)‐6‐pyridylmethyl](2‐pyridylmethyl)amine: Access to a Diiron(III) Compound with an Unusual Pentagonal‐Bipyramidal/Square‐Pyramidal Environment

Machkour

Thallaj

Benhamou

et al. 2006

Chemistry A European J

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Coordination of FeCl3 to the title ligand yields a mononuclear iron(III) complex 1, which was characterized by spectroscopic techniques and X-ray diffraction. The ligand is (kappa3-N) tridentate and the metal, which lies in a pseudo-octahedral environment, is bound to a phenolate group from the catechol substituent. The dichloroiron(II) complex 2 was easily obtained by metalation of the ligand with FeCl2 and characterized by various spectroscopic techniques. In their cyclic voltammograms both 1 and 2 display the same reversible FeII/FeIII wave at E1/2=10 mV (vs. SCE). Reduction of compound 1 with Zn/Hg yields 2', which displays identical properties to 2. Taken together, these findings indicate that in spite of the different oxidation state of the metal in 2, no major geometrical/structural change is observed at the metal center with respect to 1. The reaction of 2 with dioxygen in the absence of organic substrates proceeds extremely rapidly and yields compound 3, which is a diiron(III) derivative whose X-ray crystal structure is also reported. The possibility of a radical-based mechanism is discussed. Compound 3 displays an unusual geometry: one iron(III) center is seven-coordinate, whereas the other lies in a square-pyramidal environment. The two iron atoms are bridged by the catecholato substituents. To the best of our knowledge, 3 is the first example of a seven-coordinate iron(III) derivative with tris(2-pyridylmethyl)amine ligands.

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“…[18][19][20][21] In addition, a Fe IV =O intermediate is proposed to be the hydroxylating species in the heme enzymes cytochrome P450, [22] in methane monooxygenase, and in isopenicillin N synthase. [23] One mechanistic issue that has not been clarified is the question of the number of water molecules coordinated to iron at the various stages of the catalytic reaction. The Xray crystal structures of the catalytic domain of active human (h) PAH (hPAH-Fe II -BH 4 ) [24] and inactive hTPH (hTPH-Fe III -BH 2 ), [25] and the catalytic and tetramerization domain of inactive rat (r) TH (rTH-Fe III -BH 2 ), [26] all in a binary complex with the cofactor (BH 4 ) or a cofactor analogue (BH 2 ), possess three [24,25] or two [26] water molecules coordinated to the iron center.…”

Section: Introductionmentioning

confidence: 99%

Formation of the Iron–Oxo Hydroxylating Species in the Catalytic Cycle of Aromatic Amino Acid Hydroxylases

Olsson

Martı́nez

Teigen

et al. 2011

Chemistry A European J

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The first part of the catalytic cycle of the pterin-dependent, dioxygen-using nonheme-iron aromatic amino acid hydroxylases, leading to the Fe(IV)=O hydroxylating intermediate, has been investigated by means of density functional theory. The starting structure in the present investigation is the water-free Fe-O(2) complex cluster model that represents the catalytically competent form of the enzymes. A model for this structure was obtained in a previous study of water-ligand dissociation from the hexacoordinate model complex of the X-ray crystal structure of the catalytic domain of phenylalanine hydroxylase in complex with the cofactor (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin (BH(4)) (PAH-Fe(II)-BH(4)). The O-O bond rupture and two-electron oxidation of the cofactor are found to take place via a Fe-O-O-BH(4) bridge structure that is formed in consecutive radical reactions involving a superoxide ion, O(2)(-). The overall effective free-energy barrier to formation of the Fe(IV)=O species is calculated to be 13.9 kcal mol(-1), less than 2 kcal mol(-1) lower than that derived from experiment. The rate-limiting step is associated with a one-electron transfer from the cofactor to dioxygen, whereas the spin inversion needed to arrive at the quintet state in which the O-O bond cleavage is finalized, essentially proceeds without activation.

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Evidence for a Nonheme Fe(IV)O Species in the Intramolecular Hydroxylation of a Phenyl Moiety

Cited by 90 publications

References 21 publications

Catalytic Oxidation with a Non-Heme Iron Complex That Generates a Low-Spin FeIIIOOH Intermediate

Catalytic Oxidation with a Non-Heme Iron Complex That Generates a Low-Spin FeIIIOOH Intermediate

The Coordination Chemistry of FeCl₃ and FeCl₂ to Bis[2‐(2,3‐dihydroxyphenyl)‐6‐pyridylmethyl](2‐pyridylmethyl)amine: Access to a Diiron(III) Compound with an Unusual Pentagonal‐Bipyramidal/Square‐Pyramidal Environment

Formation of the Iron–Oxo Hydroxylating Species in the Catalytic Cycle of Aromatic Amino Acid Hydroxylases

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Evidence for a Nonheme Fe(IV)O Species in the Intramolecular Hydroxylation of a Phenyl Moiety

Cited by 90 publications

References 21 publications

Catalytic Oxidation with a Non-Heme Iron Complex That Generates a Low-Spin FeIIIOOH Intermediate

Catalytic Oxidation with a Non-Heme Iron Complex That Generates a Low-Spin FeIIIOOH Intermediate

The Coordination Chemistry of FeCl3 and FeCl2 to Bis[2‐(2,3‐dihydroxyphenyl)‐6‐pyridylmethyl](2‐pyridylmethyl)amine: Access to a Diiron(III) Compound with an Unusual Pentagonal‐Bipyramidal/Square‐Pyramidal Environment

Formation of the Iron–Oxo Hydroxylating Species in the Catalytic Cycle of Aromatic Amino Acid Hydroxylases

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The Coordination Chemistry of FeCl₃ and FeCl₂ to Bis[2‐(2,3‐dihydroxyphenyl)‐6‐pyridylmethyl](2‐pyridylmethyl)amine: Access to a Diiron(III) Compound with an Unusual Pentagonal‐Bipyramidal/Square‐Pyramidal Environment