The axial ligand effect of oxo-iron porphyrin catalysts. How does chloride compare to thiolate?

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    We have performed density functional theory calculations on an oxo-iron porphyrin catalyst with chloride as an axial ligand and tested its reactivity toward propene. The reactions proceed via multistate reactivity on competing doublet and quartet spin surfaces. Close-lying epoxidation and hydroxylation mechanisms are identified, whereby in the gas phase the epoxidation reaction is dominant, while in environments with a large dielectric constant the hydroxylation pathways become competitive. By contrast to reactions with thiolate as an axial ligand all low-lying pathways have small ring-closure and rebound barriers, so it is expected that side products and rearrangements will be unlikely with Fe = O(porphyrin)Cl, whereas with Fe = O(porphyrin)SH some side products were predicted. The major differences in the electronic configurations of Fe = O(porphyrin)Cl and Fe = O(porphyrin)SH are due to strong mixing of thiolate orbitals with iron 3d orbitals, a mixing which is much less with chloride as an axial ligand. Predictions of the reactivity of ethylbenzene-h12 versus ethylbenzene-d12 are made. © SBIC 2005.
    Original languageEnglish
    Pages (from-to)168-178
    Number of pages10
    JournalJournal of Biological Inorganic Chemistry
    Issue number2
    Publication statusPublished - Mar 2006


    • Cytochrome P450
    • Density functional theory
    • Enzyme models
    • Epoxidation
    • Hydroxylation


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