Abstract
Addition of aryl Grignard reagents to an iron(III) tetraphenylporphyrin π cation radical, [(TPP⋅)Fe^III^Cl] (SbCl~6~), in dichloromethane solution at 202 K yields a mixture of σ‐phenyl iron(IV) tetraphenylporphyrin, [(TPP)Fe^IV^(Ph)] (SbCl~6~), and σ‐phenyl iron(III) tetraphenylporphyrin, (TPP)Fe^III^Cl. A σ‐phenyliron(III) complex is also formed by nucleophilic addition to the tetraphenylporphyrin macrocycle accompanied by σ‐phenyl axial coordination. The complexes formed were identified by ^1^H NMR spectroscopy. A new route for generating σ‐aryl iron(IV) porphyrin species from the iron(III) porphyrin π cation radical was established. The characteristic ^1^H NMR pattern of the low‐spin iron(III) porphyrin ring modified species reflects its C~s~ symmetry and includes four upfield‐shifted pyrrole resonances (2.31, −10.40, 20.39 and −20.87 ppm, 202 K) accompanied by a set of σ‐phenyl resonances (ortho, −188.4; p‐H, −102.5; p‐CH~3~ for σ‐p‐tolyl, 162.3 ppm). Analysis of the paramagnetic shifts of the σ‐phenyl (σ‐p‐tolyl) ligand of the new species indicates a high π spin density consistent with the electronic structure of low‐spin iron(III) and the contribution of a σ‐delocalization mechanism via donation from a filled σ‐phenyl orbital to an empty d~z2~; orbital. The formation of a low‐spin σ‐phenyliron(III) isoporphyrin or low‐spin σ‐phenyl N‐arylporphyrin is considered. The meso substitution can be accounted for by a mechanism which emphasizes the radical nature of the reaction substrate and involves the formation of σ‐transient forms.