A view on the mechanism of metalloporphyrin degradation in hydrogen peroxide epoxidation reactions

Abstract

The stability of biomimetic catalysts is an essential characteristic for them to be of some practical use. The study of the reaction of metalloporphyrin catalysts in hydrogen peroxide oxidations in the presence of benzoic acid allowed to understand whether an intramolecular or intermolecular mechanism is operative in catalyst degradation. Under certain reaction conditions, the presence of a radical inhibitor minimises the catalyst degradation, and therefore, improves the catalytic process.

Computational and experimental insights into the oxidative stability of iron porphyrins: A mono‐ortho‐substituted iron porphyrin with unusually high oxidative stability

“…Over the last three decades, synthetic metalloporphyrins as models of the cytochrome P‐450 enzymes have been used as catalyst in various oxidation reactions . However, the majority of metalloporphyrins suffer from oxidative degradation of the catalyst at the meso, α and β positions of the aromatic macrocycle by intermolecular and intramolecular mechanisms . In this regard, the Zn(II) and Fe(III) complexes of meso‐tetraphenylporphyrin were found to be sensitive to hydroxylation at the meso positions by NO 2 .…”

Towards robust alkane oxidation catalysts: electronic variations in non-heme iron(ii) complexes and their effect in catalytic alkane oxidation

“…[45][46][47] Porphyrin-based iron catalysts have long been known to degrade during oxidation catalysis and, together with increased rates of H 2 O 2 decomposition, this has been attributed to higher concentrations of hydroxyl radicals. [48][49][50][51] In fact, the problem also exists in living organisms, where heme and non-heme oxidases have a limited lifetime, but nature has developed a sophisticated catalyst regeneration system to overcome this problem. 52 Here we report our investigations into electronic effects on the catalytic activity of non-heme iron catalysts containing linear and tripodal tetradentate ligands.…”

Unraveling the origins of catalyst degradation in non-heme iron-based alkane oxidation

“…In hemebased oxidation catalysts, one mode of deactivation has been shown to involve oxidation of the porphyrin ligand. [4][5][6][7][8] While the exact deactivation pathway in the large variety of non-heme metal catalysts is not known at this stage, oxidative degradation of the ligand is probably one of the main causes for catalyst deactivation. Another possible deactivation pathway that has been invoked in a number of non-heme catalyst systems is the formation of inactive dinuclear μ-oxo iron(III) complexes.…”

“…Replacing vulnerable C-H bonds with C-Me bonds has previously been used to improve the catalyst stability in other non-heme catalysts, 56 and a recent report on a related iron(II) catalyst with C(Ph)H linkages has shown promising results in asymmetric epoxidations. 57 In a third series, we have explored the application of linear pentadentate ligands in oxidation catalysis (5)(6)(7)(8). An additional donor could result in greater catalyst stability and within this series we have examined the effect of N-H (5) versus N-Me substitution (6), the removal of CH 2 linkages ( 7) and an alternative donor set (8) on the catalytic behaviour in cyclohexane oxidation.…”