Oxoiron(IV) porphyrins derived from charged iron(III) tetraarylporphyrins and chemical oxidants in aqueous and methanolic solutions

Abstract

The oxidation of six charged iron( 111) tetraarylporphyrins with chemical oxidants has been investigated. In aqueous solution each can be converted by tert-butyl hydroperoxide or monopersulphate into its corresponding oxoiron( iv) porphyrin, whereas in methanol only the iron (111) tetra (N-methylpyridyl) porphyrins form detectable ferryl porphyrins at ambient temperatures.On standing, the iron species revert to the parent porphyrin with a small loss due t o non-reversible oxidative destruction. That the oxidised porphyrin intermediates are oxoiron (iv) species has been determined using UV-VIS, resonance Raman, 'H NMR and EPR spectroscopy.The mechanism of formation of the ferryl porphyrins and the factors that influence their stability are examined and discussed. I n particular steric effects and to a lesser extent electron-withdrawing substituents are shown to be important in stabilising the iron(iv) species. These effects are explained in terms of their influence on the disproportionation of two ferryl species into an iron(iii) porphyrin and an iron(iv) porphyrin K radical cation.Paper 0/04944A

Transition Metal Complexes and the Activation of Dioxygen

“…The Fe-O bonding has been characterized by EXAFS and rR, which have shown the Fe-O bond distance to be approximately 1.6 Å with values of ν(Fe-O) in the range of 800-850 cm À1 [69,70]. These latter values are also sensitive to axial coordination as well as electron-withdrawing aryl substituents, which tend to result in negative shifts of ν(Fe-O) [63,[71][72][73][74].…”

Bioinspired Dismutation of Chlorite to Dioxygen and Chloride Catalyzed by a Water‐Soluble Iron Porphyrin

“…Absorption spectroscopy (acquired on a stopped-flow analyzer) shows a red shift in the Soret band from 405 to 410 nm with a 12 % increase in absorptivity, a spectrum consistent with the oxoferryl species [O=Fe IV (TF 4 TMAP)] (compound II). [11] This spectrum reverts back to the Fe III form over the course of 30 min (Figure 1).…”

Ab initio simulations of the intercalation of iron(III) porphyrinates in Zn 2 Al-LDH: Structural analysis and evaluation of their basic and acid sites

“…The mechanistic features of these oxidation reactions are also of great interest since the oxygen donor seems to affect the catalytic activity (Bell et al, 1991;In et al, 2003;Guedes et al, 2005). For example, in the case of the use of hydrogen peroxide, the oxygen radical released by the oxygen donor is captured by the iron(III) center and a homolytic or heterolytic path may occur (Goh and Nam, 1999;Nam et al, 2000;Nam, 2007;Stephenson and Bell, 2007b).…”