Wydział Chemii

Piotr J. Chmielewski

Lechosław Latos-Grażyński

Krystyna Rachlewicz

1993

Magnetic Resonance in Chemistry

31

47-52

10.1002/MRC.1260311311

Naukowa

Angielski

Artykuł

Addition of aryl Grignard reagents to an iron(III) tetraphenylporphyrin π cation radical, [(TPP⋅)Fe^IIICl] (SbCl₆), in dichloromethane solution at 202 K yields a mixture of σ-phenyl iron(IV) tetraphenylporphyrin, [(TPP)Fe^IV(Ph)] (SbCl₆), and σ-phenyl iron(III) tetraphenylporphyrin, (TPP)Fe^IIICl. 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 ¹H 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 ¹H 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-CH₃ 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.

https://doi.org/10.1002/MRC.1260311311

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