Formation and ¹H NMR spectra of low spin ferric porphyrin radical cations with orientationally fixed imidazole ligands

Chemical oxidation of tetradurylporphyrinatoiron(III) chloride followed by the addition of 2-methylimidazole at -78 °C gave the first example of the low spin ferric porphyrin radical cation with orienta ionally fixed imidazole ligands, [Fe(TDP^̇)(2-MeIm)₂]²⁺. The degree of asymmetric spin distribution on the pyrrole β carbons in the radical cation was estimated to be close to that in the starting low spin complex, [Fe(TDP)(2-MeIm)₂]⁺, which was ascribed to the orthogonality of porphyrin a_2u with imidazole π orbitals.