biostudies-literatureChing WMDivision of ChemistryMinistry of Science and Technology, TaiwanAlexander von Humboldt-StiftungNational Institute of General Medical SciencesNIGMS NIH HHS11129-11140https://www.ebi.ac.uk/biostudies/studies/S-EPMC8991986biostudies-literatureUnknown56(18)Nonheme mononuclear hydroxoiron(III) species are important intermediates in biological oxidations, but well-characterized examples of synthetic complexes are scarce due to their instability or tendency to form μ-oxodiiron(III) complexes, which are the thermodynamic sink for such chemistry. Herein, we report the successful stabilization and characterization of a mononuclear hydroxoiron(III) complex, [Fe^III(OH)(TMC-py)]²⁺ (3; TMC-py = 1-(pyridyl-2'-methyl)-4,8,11-trimethyl-1,4,8,11-tetrazacyclotetradecane), which is directly generated from the reaction of [Fe^IV(O)(TMC-py)]²⁺ (2) with 1,4-cyclohexadiene at -40 °C by H-atom abstraction. Complex 3 exhibits a UV spectrum with a λ_max at 335 nm (ε ≈ 3500 M^-1 cm^-1) and a molecular ion in its electrospray ionization mass spectrum at m/z 555 with an isotope distribution pattern consistent with its formulation. Electron paramagnetic resonance and Mössbauer spectroscopy show 3 to be a high-spin Fe(III) center that is formed in 85% yield. Extended X-ray absorption fine structure analysis reveals an Fe-OH bond distance of 1.84 Å, which is also found in [(TMC-py)Fe^III-O-Cr^III(OTf)₃]⁺ (4) obtained from the reaction of 2 with Cr(OTf)₂. The S = 5/2 spin ground state and the 1.84 Å Fe-OH bond distance are supported computationally. Complex 3 reacts with 1-hydroxy-2,2,6,6-tetramethylpiperidine (TEMPOH) at -40 °C with a second-order rate constant of 7.1 M^-1 s^-1 and an OH/OD kinetic isotope effect value of 6. On the basis of density functional theory calculations, the reaction between 3 and TEMPOH is classified as a proton-coupled electron transfer as opposed to a hydrogen-atom transfer.Inorganic chemistryCharacterization of the Fleeting Hydroxoiron(III) Complex of the Pentadentate TMC-py Ligand.PMC8991986P41 GM103393GM38767CHE-1361595CHE-1361773CHE-1654060R01 GM038767Cramer CJKlein JEMNQue LZhou AGuo YChing WMKnizia GFan RfalseCharacterization of the Fleeting Hydroxoiron(III) Complex of the Pentadentate TMC-py Ligand.Nonheme mononuclear hydroxoiron(III) species are important intermediates in biological oxidations, but well-characterized examples of synthetic complexes are scarce due to their instability or tendency to form μ-oxodiiron(III) complexes, which are the thermodynamic sink for such chemistry. Herein, we report the successful stabilization and characterization of a mononuclear hydroxoiron(III) complex, [Fe^III(OH)(TMC-py)]²⁺ (3; TMC-py = 1-(pyridyl-2'-methyl)-4,8,11-trimethyl-1,4,8,11-tetrazacyclotetradecane), which is directly generated from the reaction of [Fe^IV(O)(TMC-py)]²⁺ (2) with 1,4-cyclohexadiene at -40 °C by H-atom abstraction. Complex 3 exhibits a UV spectrum with a λ_max at 335 nm (ε ≈ 3500 M^-1 cm^-1) and a molecular ion in its electrospray ionization mass spectrum at m/z 555 with an isotope distribution pattern consistent with its formulation. Electron paramagnetic resonance and Mössbauer spectroscopy show 3 to be a high-spin Fe(III) center that is formed in 85% yield. Extended X-ray absorption fine structure analysis reveals an Fe-OH bond distance of 1.84 Å, which is also found in [(TMC-py)Fe^III-O-Cr^III(OTf)₃]⁺ (4) obtained from the reaction of 2 with Cr(OTf)₂. The S = 5/2 spin ground state and the 1.84 Å Fe-OH bond distance are supported computationally. Complex 3 reacts with 1-hydroxy-2,2,6,6-tetramethylpiperidine (TEMPOH) at -40 °C with a second-order rate constant of 7.1 M^-1 s^-1 and an OH/OD kinetic isotope effect value of 6. On the basis of density functional theory calculations, the reaction between 3 and TEMPOH is classified as a proton-coupled electron transfer as opposed to a hydrogen-atom transfer.2017-01-01T00:00:00Z2017 Sep2025-06-01T12:09:51.427Z2025-06-01T12:09:51.427ZS-EPMC89919862885849610.1021/acs.inorgchem.7b01459