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A high-spin alkylperoxo-iron(iii) complex with cis-anionic ligands: implications for the superoxide reductase mechanism.

ABSTRACT: The N₃O macrocycle of the 12-TMCO ligand stabilizes a high spin (S = 5/2) [Fe^III(12-TMCO)(OO^tBu)Cl]⁺ (3-Cl) species in the reaction of [Fe^II(12-TMCO)(OTf)₂] (1-(OTf)₂) with tert-butylhydroperoxide (^tBuOOH) in the presence of tetraethylammonium chloride (NEt₄Cl) in acetonitrile at -20 °C. In the absence of NEt₄Cl the oxo-iron(iv) complex 2 [Fe^IV(12-TMCO)(O)(CH₃CN)]²⁺ is formed, which can be further converted to 3-Cl by adding NEt₄Cl and ^tBuOOH. The role of the cis-chloride ligand in the stabilization of the Fe^III-OO^tBu moiety can be extended to other anions including the thiolate ligand relevant to the enzyme superoxide reductase (SOR). The present study underlines the importance of subtle electronic changes and secondary interactions in the stability of the biologically relevant metal-dioxygen intermediates. It also provides some rationale for the dramatically different outcomes of the chemistry of iron(iii)peroxy intermediates formed in the catalytic cycles of SOR (Fe-O cleavage) and cytochrome P450 (O-O bond lysis) in similar N₄S coordination environments.

SUBMITTER: Devi T

PROVIDER: S-EPMC10762717 | biostudies-literature | 2024 Jan

REPOSITORIES: biostudies-literature

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A high-spin alkylperoxo-iron(iii) complex with cis-anionic ligands: implications for the superoxide reductase mechanism.

Devi Tarali T Dutta Kuheli K Deutscher Jennifer J Mebs Stefan S Kuhlmann Uwe U Haumann Michael M Cula Beatrice B Dau Holger H Hildebrandt Peter P Ray Kallol K

Chemical science 20231206 2

The N3O macrocycle of the 12-TMCO ligand stabilizes a high spin (S = 5/2) [FeIII(12-TMCO)(OOtBu)Cl]+ (3-Cl) species in the reaction of [FeII(12-TMCO)(OTf)2] (1-(OTf)2) with tert-butylhydroperoxide (tBuOOH) in the presence of tetraethylammonium chloride (NEt4Cl) in acetonitrile at -20 °C. In the absence of NEt4Cl the oxo-iron(iv) complex 2 [FeIV(12-T ...[more]

PMID: 38179538

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Project description:We have synthesized and characterized, using X-ray crystallographic, spectroscopic, and computational techniques, a six-coordinate diazide Fe (3+) complex, LFe(N 3) 2 (where L is the tetradentate ligand 7-diisopropyl-1,4,7-triazacyclononane-1-acetic acid), that serves as a model of the azide adducts of Fe (3+) superoxide dismutase (Fe (3+)SOD). While previous spectroscopic studies revealed that two distinct azide-bound Fe (3+)SOD species can be obtained at cryogenic temperatures depending on protein and azide concentrations, the number of azide ligands coordinated to the Fe (3+) ion in each species has been the subject of some controversy. In the case of LFe(N 3) 2, the electronic absorption and magnetic circular dichroism spectra are dominated by two broad features centered at 21 500 cm (-1) (approximately 4000 M (-1) cm (-1)) and approximately 30 300 cm (-1) (approximately 7400 M (-1) cm (-1)) attributed to N3 (-) --> Fe (3+) charge transfer (CT) transitions. A normal coordinate analysis of resonance Raman (RR) data obtained for LFe(N 3) 2 indicates that the vibrational features at 363 and 403 cm (-1) correspond to the Fe-N 3 stretching modes (nu Fe-N3) associated with the two different azide ligands and yields Fe-N 3 force constants of 1.170 and 1.275 mdyne/A, respectively. RR excitation profile data obtained with laser excitation between 16,000 and 22,000 cm (-1) reveal that the nu Fe-N3 modes at 363 and 403 cm (-1) are preferentially enhanced upon excitation in resonance with the N 3 (-) --> Fe (3+) CT transitions at lower and higher energies, respectively. Consistent with this result, density functional theory electronic structure calculations predict a larger stabilization of the molecular orbitals of the more strongly bound azide due to increased sigma-symmetry orbital overlap with the Fe 3d orbitals, thus yielding higher N 3 (-) --> Fe (3+) CT transition energies. Comparison of our data obtained for LFe(N 3) 2 with those reported previously for the two azide adducts of Fe (3+)SOD provides compelling evidence that a single azide is coordinated to the Fe (3+) center in each protein species.

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A high-spin alkylperoxo-iron(iii) complex with cis-anionic ligands: implications for the superoxide reductase mechanism.

Publications

A high-spin alkylperoxo-iron(iii) complex with <i>cis</i>-anionic ligands: implications for the superoxide reductase mechanism.

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