Mechanistic insights into the reversible formation of iodosylarene-iron porphyrin complexes in the reactions of oxoiron(IV) porphyrin π-cation radicals and iodoarenes: Equilibrium, epoxidizing intermediate, and oxygen exchange

Woon Ju Song, Ying Ji Sun, Sun Kyung Choi, Wonwoo Nam

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Abstract

We have shown previously that iodosylbenzene-iron(III) porphyrin intermediates (2) are generated in the reactions of oxoiron(IV) porphyrin π-cation radicals (1) and iodobenzene (PhI), that 1 and 2 are at equilibrium in the presence of PhI, and that the epoxidation of olefins by 2 affords high yields of epoxide products. In the present work, we report detailed mechanistic studies on the nature of the equilibrium between 1 and 2 in the presence of iodoarenes (ArI), the determination of reactive species responsible for olefin epoxidation when two intermediates (i.e., 1 and 2) are present in a reaction solution, and the fast oxygen exchange between 1 and H218O in the presence of ArI. In the first part, we have provided strong evidence that 1 and 2 are indeed at equilibrium and that the equilibrium is controlled by factors such as the electronic nature of iron porphyrins, the electron richness of ArI, and the concentration of ArI. Secondly, we have demonstrated that 1 is the sole active oxidant in olefin epoxidation when 1 and 2 are present concurrently in a reaction solution. Finally, we have shown that the presence of ArI in a reaction solution containing 1 and H218O facilitates the oxygen exchange between the oxo group of 1 and H 218O and that the oxygen exchange is markedly influenced by factors such as ArI incubation time, the amounts of ArI and H 218O used, and the electronic nature of ArI. The latter results are rationalized by the formation of an undetectable amount of 2 from the reaction of 1 and ArI through equilibrium that leads to a fast oxygen exchange between 2 and H218O.

Original languageEnglish
Pages (from-to)130-137
Number of pages8
JournalChemistry - A European Journal
Volume12
Issue number1
DOIs
StatePublished - 16 Dec 2005

Keywords

  • Enzyme models
  • Epoxidation
  • Equilibrium
  • Oxygen
  • Reaction mechanisms

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