Generation of oxoiron (IV) tetramesitylporphyrin pi-cation radical complexes by m-CPBA oxidation of ferric tetramesitylporphyrin derivatives in butyronitrile at - 78 degrees C. Evidence for the formation of six-coordinate oxoiron (IV) tetramesitylporphyrin pi-cation radical complexes FeIV = O(tmp*)X (X = Cl-, Br-), by Mössbauer and X-ray absorption spectroscopy.
The generation of six-coordinate oxoiron (IV) tetramesitylporphyrin pi-caption radical complexes by m-CPBA (meta-chloroperbenzoic acid) oxidation of ferric tetramesitylporphyrin derivatives in butyronitrile at - 78 degrees C was investigated. UV-Vis and EPR spectroscopies indicate that the axial ligand present in the ferric starting derivatives is retained in the high-valent iron complexes. Indirect evidence for the formation of six-coordinate oxoiron (IV) tetramesitylporphyrin complexes FeIV = O(tmp*)X (X=Cl-, Br-) by m-CPBA oxidation of FeX(tmp) (X=Cl-, Br-) in butyronitrile at - 78 degrees C was also obtained by Mössbauer spectroscopy. Direct confirmation of the presence of a halide ion as second axial ligand of iron in these high-valent iron species was obtained by X-ray absorption spectroscopy. The EXAFS spectra of the samples obtained by m-CPBA oxidation of FeX(tmp) (X=Cl-, Br-) were refined using two different coordination models including both four porphyrinato-nitrogens and the axial oxo group. The two models include (model I) or exclude (model II) the axial halogen. The statistical tests indicate the presence of a halide ion as second axial ligand of iron in both derivatives. The refinements led to the following bond distances: FeIV=O(tmp*)Cl(3):Fe-O=1.66(1),Fe-Cl=2.39(2) and Fe-Np=1.99(1) A;FeIV=O(tmp*)Br(4):Fe-O=1.65(1),Fe-Br=2.93(2), Fe-Np=2.02(1) A. The lengthening of the Fe-X(X=Cl-, Br-) distances relative to those occurring in the ferric precursor porphyrins is, most probably, related to the strong trans influence of the oxoiron(IV) fragment present in 3 or 4.
Wolter
T
T
Laboratoire de Cristallochimie et de Chimie Structurale (UMR 7513), Institut Le Bel, Université Pasteur, 4 rue B. Pascal, 67070 Strasbourg, France.
Meyer-Klaucke
W
W
Müther
M
M
Mandon
D
D
Winkler
H
H
Trautwein
A X
AX
Weiss
R
R
D002723:Chlorobenzoates; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000737:chemistry*; D008665:Metalloporphyrins / Q000737:chemistry*; D009570:Nitriles; D010084:Oxidation-Reduction; D015204:Spectroscopy, Mossbauer; D013057:Spectrum Analysis; D013696:Temperature; D014965:X-Rays
D002723:Chlorobenzoates; D005290:Ferric Compounds; D008665:Metalloporphyrins; D009570:Nitriles; C000433:3-chloroperbenzoic acid; C032723:N-butyronitrile