Understanding the dioxygen reaction chemistry of diiron proteins through synthetic modeling studies

Bois, J. Du; Mizoguchi, Tadashi; Lippard, Stephen J.

doi:10.1016/s0010-8545(00)00336-2

Cited by 200 publications

(161 citation statements)

References 149 publications

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“…[9][10][11] Nonheme iron-containing enzymes that activate dioxygen are a more recently studied class of metalloproteins in which the metal center at the active site can be either mono-or dinuclear. [12][13][14] With the exception of enzymes for which non innocent substates such as catechol may modify the electronic structure of the iron center on coordination, [15,16] a generally accepted common mechanism involves coordination of dioxygen to a iron(II) center as initial step. [12] An alternative and convenient way to generate potentially reactive ironbased species is the so-called shunt reaction involving reaction of metal sites and peroxides, that is, an already reduced form of oxygen, whereas Nature uses molecular dioxygen.…”

Section: Introductionmentioning

confidence: 99%

Reactivity of Molecular Dioxygen towards a Series of Isostructural Dichloroiron(III) Complexes with Tripodal Tetraamine Ligands: General Access to μ‐Oxodiiron(III) Complexes and Effect of α‐Fluorination on the Reaction Kinetics

Thallaj

Rotthaus

Benhamou

et al. 2008

Chemistry A European J

101

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We have synthesized the mono, di-, and tri-alpha-fluoro ligands in the tris(2-pyridylmethyl)amine (TPA) series, namely, FTPA, F(2)TPA and F(3)TPA, respectively. Fluorination at the alpha-position of these nitrogen-containing tripods shifts the oxidation potential of the ligand by 45-70 mV per added fluorine atom. The crystal structures of the dichloroiron(II) complexes with FTPA and F(2)TPA reveal that the iron center lies in a distorted octahedral geometry comparable to that already found in TPAFeCl(2). All spectroscopic data indicate that the geometry is retained in solution. These three isostructural complexes all react with molecular dioxygen to yield stable mu-oxodiiron(III) complexes. Crystal structure analyses are reported for each of these three mu-oxo compounds. With TPA, a symmetrical structure is obtained for a dicationic compound with the tripod coordinated in the kappa(4)N coordination mode. With FTPA, the compound is a neutral mu-oxodiiron(III) complex with a kappa(3)N coordination mode of the ligand. Oxygenation of the F(2)TPA complex gave a neutral unsymmetrical compound, the structure of which is reminiscent of that already found with the trifluorinated ligand. On reduction, all mu-oxodiiron(III) complexes revert to the starting iron(II) species. The oxygenation reaction parallels the well-known formation of mu-oxo derivatives from dioxygen in the chemistry of porphyrins reported almost three decades ago. The striking feature of the series of iron(II) precursors is the effect of the ligand on the kinetics of oxygenation of the complexes. Whereas the parent complex undergoes 90 % conversion over 40 h, the monofluorinated ligand provides a complex that has fully reacted after 30 h, whereas the reaction time for the complex with the difluorinated ligand is only 10 h. Analysis of the spectroscopic data reveals that formation of the mu-oxo complexes proceeds in two distinct reversible kinetic steps with k(1) approximately 10 k(2). For TPAFeCl(2) and FTPAFeCl(2) only small variations in the k(1) and k(2) values are observed. By contrast, F(2)TPAFeCl(2) exhibits k(1) and k(2) values that are ten times higher. These differences in kinetics are interpreted in the light of structural and electronic effects, especially the Lewis acidity at the metal center. Our results suggest coordination of dioxygen as an initial step in the process leading to formation of mu-oxodiiron(III) compounds, by contrast with an unlikely outer-sphere reduction of dioxygen, which generally occurs at negative potentials.

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Section: Introductionmentioning

confidence: 99%

Reactivity of Molecular Dioxygen towards a Series of Isostructural Dichloroiron(III) Complexes with Tripodal Tetraamine Ligands: General Access to μ‐Oxodiiron(III) Complexes and Effect of α‐Fluorination on the Reaction Kinetics

Thallaj

Rotthaus

Benhamou

et al. 2008

Chemistry A European J

101

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“…[3] Evidence has been obtained for the existence of hydroperoxo species, which are the precursors of the fleeting high valent entities, in natural systems such as MMO(dinuclear) [4] and bleomycin (mononuclear), [5] and several synthetic models have also been prepared. [6] To date, no evidence for conversion of a hydroperoxo species to a high valent iron-oxo species in synthetic models has been obtained spectroscopically.…”

Section: Introductionmentioning

confidence: 99%

Iron Complexes Containing the Ligand N,N′‐Bis(6‐methyl‐2‐pyridylmethyl)‐N,N′‐bis(2‐pyridylmethyl)ethane‐1,2‐diamine: Structural, Spectroscopic, and Electrochemical Studies, Reactivity with Hydrogen Peroxide and the Formation of a Low‐Spin Fe−OOH Complex

et al. 2003

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The ligand N,N′‐bis(6‐methyl‐2‐pyridylmethyl)‐N,N′‐bis(2‐pyridylmethyl)ethane‐1,2‐diamine (L622M) has allowed to prepare the new FeII complex [(L622M)FeCl2] (1), and to compare its structural and spectroscopic characteristics with [(L622M)FeCl]PF6 (2). The molecular structure of 1, resolved by X‐ray diffraction, exhibits the ligand tetracoordinated with the two non‐methylated pyridine rings coordinated. As shown by UV/Vis spectroscopy and cyclic voltammetry, upon dissolution in methanol or acetonitrile, one chloride ion is released and replaced by a pyridine group. Therefore, complexes 1 and 2 adopt identical structures in solution, i.e. [(L622M)FeCl+. However, upon oxidation complex 1 gives several ferric complexes with the ligand L622M pentacoordinated, or tetracoordinated with two chloride ions. This peculiar behaviour is due to the presence of chloride ions in solution in the case of 1. Upon reaction with H2O2 in methanol, complex 2 leads to the formation of low‐spin [(L622M)FeIII(OOH)2+, whereas it is not observed in the case of 1. Based on the presence or not of chloride ions in solution, a mechanism is proposed for the reactivity of complexes 1 and 2 toward H2O2. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

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“…These are the synthetic model compounds. 32,33 Model compounds mimic an active center within a large molecule, while being structurally simple enough to be readily synthesized.…”

mentioning

confidence: 99%

High‐spin versus broken symmetry—Effect of DFT spin density representation on the geometries of three diiron (III) model compounds

Binning¹,

Bacelo²

2007

J Comput Chem

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Unrestricted density functional theory calculations have been conducted on three diiron(III) synthetic model compounds containing antiferromagnetically coupled high-spin (HS) irons for which crystallographic structures and Raman spectral data are available. Three density functionals have been employed: BPW91, PWC, and BOP. The study compares the effects on optimized geometries and harmonic vibrational frequencies of spin-paired (SP) low-spin, HS, and broken symmetry antiferromagnetically coupled singlet representations of the spin density distribution. The geometries around the diiron centers in the HS and broken symmetry (BS) representations are found to be similar, both markedly different from those arising from the SP representation. Small differences between the HS and BS results are seen in bond lengths, angles, Raman frequencies, and spin densities associated with oxo and peroxo bridges between the irons.

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Understanding the dioxygen reaction chemistry of diiron proteins through synthetic modeling studies

Cited by 200 publications

References 149 publications

Reactivity of Molecular Dioxygen towards a Series of Isostructural Dichloroiron(III) Complexes with Tripodal Tetraamine Ligands: General Access to μ‐Oxodiiron(III) Complexes and Effect of α‐Fluorination on the Reaction Kinetics

Reactivity of Molecular Dioxygen towards a Series of Isostructural Dichloroiron(III) Complexes with Tripodal Tetraamine Ligands: General Access to μ‐Oxodiiron(III) Complexes and Effect of α‐Fluorination on the Reaction Kinetics

Iron Complexes Containing the Ligand N,N′‐Bis(6‐methyl‐2‐pyridylmethyl)‐N,N′‐bis(2‐pyridylmethyl)ethane‐1,2‐diamine: Structural, Spectroscopic, and Electrochemical Studies, Reactivity with Hydrogen Peroxide and the Formation of a Low‐Spin Fe−OOH Complex

High‐spin versus broken symmetry—Effect of DFT spin density representation on the geometries of three diiron (III) model compounds

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