93862-22-7Relevant academic research and scientific papers
Redox potentials of oxoiron(IV) porphyrin π-cation radical complexes: Participation of electron transfer process in oxygenation reactions
Takahashi, Akihiro,Kurahashi, Takuya,Fujii, Hiroshi
, p. 6922 - 6928 (2011/09/20)
The oxoiron(IV) porphyrin π-cation radical complex (compound I) has been identified as the key reactive intermediate of several heme enzymes and synthetic heme complexes. The redox properties of this reactive species are not yet well understood. Here, we report the results of a systematic study of the electrochemistry of oxoiron(IV) porphyrin π-cation radical complexes with various porphyrin structures and axial ligands in organic solvents at low temperatures. The cyclic voltammogram of (TMP)FeIVO, (TMP = 5,10,15,20-tetramesitylporphyrinate), exhibits two quasi-reversible redox waves at E1/2 = 0.88 and 1.18 V vs SCE in dichloromethane at -60 °C. Absorption spectral measurements for electrochemical oxidation at controlled potential clearly indicated that the first redox wave results from the (TMP)FeIVO/[(TMP+?)FeIVO]+ couple. The redox potential for the (TMP)FeIVO/[(TMP +?)FeIVO]+ couple undergoes a positive shift upon coordination of an anionic axial ligand but a negative shift upon coordination of a neutral axial ligand (imidazole). The negative shifts of the redox potential for the imidazole complexes are contrary to their high oxygenation activity. On the other hand, the electron-withdrawing effect of the meso-substituent shifts the redox potential in a positive direction. Comparison of the measured redox potentials and reaction rate constants for epoxidation of cyclooctene and demethylation of N,N-dimethylanilines enable us to discuss the details of the electron transfer process from substrates to the oxoiron(IV) porphyrin π-cation radical complex in the oxygenation mechanisms.
One-electron oxidized product of difluoroiron(iii) porphyrin: Is it iron(iv) porphyrin or iron(iii) porphyrin π-cation radical?
Ikezaki, Akira,Takahashi, Masashi,Nakamura, Mikio
experimental part, p. 9163 - 9168 (2011/10/17)
The electronic structure of [Fe(TMP)F2], which is formally a one-electron oxidation equivalent above [FeIII(TMP)F 2]-, has been examined in solution by 1H NMR, UV-Vis, and Moessbauer spectroscopy. In CD2Cl2-CD 3OD solution at 193 K, the pyrrole-H and m-H signals appeared at 128.2 and 116.7 ppm, respectively. The UV-Vis spectrum showed broad absorption bands at 560-680 nm. The Moessbauer spectrum taken in frozen toluene-methanol solution exhibited a very broad single line from which the IS and QS values were determined by computer simulation to be 0.50 and 0.14 mm s-1, respectively. On the basis of these results, it was concluded that the one-electron oxidized product of [Fe(TMP)F2]- should be formulated as the iron(iii) radical cation [FeIII(TMP) F2], not as iron(iv) porphyrin [FeIV(TMP)F2] as previously suggested.
Effect of imidazole and phenolate axial ligands on the electronic structure and reactivity of oxoiron(IV) porphyrin π-cation radical complexes: Drastic increase in oxo-transfer and hydrogen abstraction reactivities
Takahashi, Akihiro,Kurahashi, Takuya,Fujii, Hiroshi
, p. 2614 - 2625 (2009/07/30)
To study the effect of axial ligands on the electronic structure and reactivity of compound I of peroxidases and catalases, oxoiron(IV) porphyrin π-cation radical complexes with imidazole, 2-methylimidazole, 4(5)-methylimidazole, and 3-fluoro-4-nitropheno
Preparation and Characterization of a Dialkoxyiron(IV) Porphyrin
Groves, John T.,Quinn, Robert,McMurry, Thomas J.,Nakamura, Mikio,Lang, George,Boso, Brian
, p. 354 - 360 (2007/10/02)
(Perchlorato)(tetramesitylporphyrinato)iron(III) was oxidized with ferric perchlorate to generate the corresponding iron(III) porphyrin cation radical, Fe(TMP)(ClO4)2 (1).The 1H NMR and visible spectra of 1 were similar to those of other bis(perchlorato)iron(III) porphyrin cation radicals.The reaction of 1 with 1 equiv of potassium iodide regenerated Fe(TMP)(ClO4).The treatment of 1 with 2 equiv of sodium methoxide in methanol produced a new species, 2, which was shown to be an iron(IV) complex.The β-pyrrole protons of 2 were found at very high field, -37.5 ppm relative to TMS at -78 deg C in CD2Cl2.All other resonances were observed near the expected diamagnetic positions.The temperature dependence of the β-pyrrole resonance displayed the characteristic Curie behaviour of an isolated paramagnet.The sharp singlet observed for the meta hydrogens of 2 suggested a structure with D4h symmetry.The coordination of methoxide in 2 was inferred from the requirement of 2 equiv of alkoxide to form them and the broadened 1H-methyl resonances, respectively.The oxidation of (TMP)FeIII(OCH3) with 1.2 equiv of iodosylmesitylene in methanol produced 2 and 0.7 equiv of free iodomesitylene.The Moessbauer spectra of 2 under conditions of variable temperature and variable magnetic field indicated a non-Kramers system with an isomer shift (δ) of -0.025 and a quadrupole splitting (ΔEQ) of 2.10.Magnetic susceptibility measurements on 2 gave a value of μβ=2.9, close to the spin-only value for two unpaired electrons.No EPR signals were detected for 2.Taken together the data support an S=1 iron(IV) porphyrin dimethoxide structure IV(TMP)(OCH3)2> for 2.
