Reactivity of Mono-Meso-Substituted Iron(II) Octaethylporphyrin Complexes with Hydrogen Peroxide in the Absence of Dioxygen. Evidence for Nucleophilic Attack on the Heme

Heather Kalish, Jason E. Camp, Marcin Stepien, Lechoslaw Latos-Grazynski, Alan L. Balch

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Abstract

Treatment of the mono-meso-substituted iron(II) octaethylporphyrin complexes, (py)2FeII(meso-NO2-OEP), (py)2FeII(meso-CN-OEP), (py)2FeII(meso-HC(O)-OEP), (py)2FeII(meso-Cl-OEP), (py)2FeII(meso-OMe-OEP), (py)2FeII(meso-Ph-OEP), and (py)2FeII(meso-Bu-OEP), with hydrogen peroxide in pyridine-d5 at -30° in the strict absence of dioxygen was monitored by 1H NMR spectroscopy. The product oxophlorin complexes are stable as long as the samples are protected from exposure to dioxygen. Hydrogen peroxide reacts cleanly with mono-meso-substituted iron(II) porphyrins in pyridine soln. under an inert atm. to form mixts. of three possible oxygenation products, (py)2Fe(cis-meso-R-OEPO), (py)2Fe(trans-meso-R-OEPO), and (py)2Fe(OEPO). The yields of (py)2Fe(OEPO), which results from replacement of the unique meso substituent, as a function of the identity of the meso substituent decrease in the order NO2 > HC(O) ∼ CN ∼ Cl > OMe > Ph, Bu, which suggests that the species responsible for attack on the porphyrin periphery is nucleophilic in nature. A mechanism involving isoporphyrin formation through attack of hydroxide ion on a cationic iron porphyrin with an oxidized porphyrin ring is suggested. The identity of the unique meso functionality also affects the regiospecificity of substitution when the unique meso group is retained. Although random attack at the two different meso sites is expected to yield a cis/trans product ratio of 2, the obsd. ratios vary in the following order: cyano, 5.0; Bu, 4.9; chloro, 3.2; formyl, 2.6; methoxy, 1.9; Ph 1.4. 
Original languageEnglish
Pages (from-to)11719-11727
Number of pages9
JournalJournal of the American Chemical Society
Volume123
Issue number47
DOIs
Publication statusPublished - 1 Nov 2001

Keywords

  • iron mono substituted porphyrinate reaction hydrogen peroxide
  • oxophlorinate iron isomer complex prepn

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