Ferric isoporphyrins from hydroperoxide oxidation of (tetraphenylporphinato)iron(III) complexes

Abstract

Reaction of chloro[tetrakis(4-methoxyphenyl)porphinato]iron(III) with Zert-butyl hydroperoxide yields an isoporphyrin, hydroxo-or 10,15,-5/f,21/f-porphinato]iron(III), isolated as a microcrystalline solid. This compound is of interest as an example of an isoporphyrin generated by chemical rather than electrochemical oxidation and because it represents an alternative to the oxoiron species currently presumed to be involved in biomimetric oxidations utilizing peroxy acids and hydroperoxides mediated by (meso-tetraphenylporphinato)iron(III) complexes. The structure of the isoporphyrin has been established by its distinctive electronic spectrum with strong bands in the near-IR region, by high-field *H NMR, and by fast atom bombardment mass spectrometry. The presence of the peroxo linkage has been confirmed by redox titration, IR spectroscopy, and determination of elemental composition by high-resolution mass spectrometry. ZerZ-Butylperoxy substitution of the porphyrin ring has been confirmed by demonstrating that the peroxy functionality remains after treatment of the isoporphyrin with hydrogen chloride.

Metalloisoporphyrins: from synthesis to applications

“…Gold and co-workers first reported the synthesis of an iron isoporphyrin, [5-(tert-butylperoxy)-5,10,15,20-tetrakis(4-methoxyphenyl)-5H,21Hporphinato]iron(III), (6) by the reaction of [Fe(4-OCH 3 -TPP)Cl] with tert-butyl hydroperoxide. 23 Observing the formation of isoporphyrin as the reaction product of iron porphyrin, [Fe(4-OMe-TPP)Cl] with excess tert-butyl hydroperoxide oxidant, author suggested that biomimetic oxidations of heme proteins may proceed via a peroxy-isoporphyrin intermediate rather than the high-valent iron(IV)-oxo species. They characterized the iron-isoporphyrin using electronic, 1 H NMR and mass spectrometry.…”

“…Paramagnetic isoporphyrins like iron isoporphyrin show a similar upfield shifting of pyrrole β-H peaks in the 1 H NMR spectrum. 23 Infra-red spectroscopy can be used as a tool for the formation of some isoporphyrin complexes, since a free molecule or a nucleophile has a different vibrational frequency from the same nucleophile that has been covalently bound. There is a report on characterization of the zinc nitrato-isoporphyrin, which showed a strong peak at 1659 cm −1 due to the covalently bound nitrite anion to the meso carbon atom which is different from the free nitrate anion stretching frequency.…”

“…26 The synthesis of a number of metalloisopor-phyrins is conducted by a similar method i.e., oxidation followed by nucleophilic attack at a meso-carbon of the dication. 23,27 Complex zinc 5′ benzoyloxy-5,10,15,20-tetraphenylisoporphyrin benzoate (2) is reported to synthesize from the reaction between ZnTPP and dibenzoyl peroxide which follows a similar mechanism i.e., oxidation followed by a nucleophilic attack at a meso-carbon. 27 Smith and co-workers first reported the synthesis of stable metallo-isoporphyrin by the condensation of 5,5-disubstituteddipyrromethanes with a 1,9-diformyl-pyrromethane under MacDonald's conditions in the presence of a metal salt (Scheme 2).…”

Quest for Zinc Methoxyisoporphyrin Molecules: Experimental and Theoretical Studies

“…synthesized Zn methoxy‐isoporphyrin from ZnTPP by electrochemical oxidation and followed by the addition of methanol [5] . In the following years, researchers tried to synthesize and isolate stable isoporphyrin complexes but not succeeded due to reconversion into the corresponding porphyrins [6–8] . In 1992, Xie et al.…”

Syntheses, properties and cellular studies of metallo-isoporphyrins

“…The existence of this type of compound was first suggested by Woodward [1] in 1961, whose prediction was confirmed about a decade later when Dolphin et al [2] reported the first synthesis of a metalloisoporphyrin ( 4 ) from zinc 5,10,15,20-tetraphenylporphyrin by way of electrochemical oxidation. Other methods for directly generating metallo-isoporphyrins since then include peroxide oxidation [3, 4] and photooxidation [5–8]. …”