Preparation and Characterization of a Dialkoxyiron(IV) Porphyrin

Article abstract of DOI:10.1021/ja00288a014

(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 D_4h 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)Fe^III(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 (ΔE_Q) of 2.10.Magnetic susceptibility measurements on 2 gave a value of μ_β=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.