Preparation and Characterization of a Dialkoxyiron(IV) Porphyrin

(Perchlorato)(tetramesitylporphyrinato)iron(III) [Fe(TMP)(C1O₄)] was oxidized with ferric perchlorate to generate the corresponding iron(III) porphyrin cation radical, Fe(TMP)(C1O₄)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)(C10₄). 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 0-pyrrole protons of 2 were found at very high field, -37.5 ppm relative to TMS at -78 °C in CD₂C1₂. All other resonances were observed near the expected diamagnetic positions. The temperature dependence of the 0-pyrrole resonance displayed the characteristic Curie behavior 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 Mossbauer 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 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 [Fe^IV(TMP)(OCH₃)₂] for 2.