Nonheme Iron Centers in Oxygen Activation: Characterization of an Iron(in) Hydroperoxide Intermediate

摘要

Peroxoiron(III) complexes are increasingly being considered as potential intermediates in oxidations catalyzed by nonheme iron centers in biology, because of anticipated difficulties in stabilizing high-vaient iron-oxo species in the absence of por-phyrins. For example, spectroscopic studies of "activated bleoraycin" (BLM), an antitumor drug that effects the oxida-tive cleavage of DNA and the oxidation of hydrocarbons, cumulatively support its formulation as a low-spin hydroperox-idoiron(m) species.)A model for "activated BLM" has been synthesized that mimics its reactivity and gives rise to the same optical and EPR spectra; however, more detailed spectroscopic data is not yet available. In a related area, alkylperox-oiron(III) complexes have beenimplicated in hydrocarbon oxidations; several have been stabilized at low temperature and spectroscopically characterized. To date, however, "activated BLM" remains the only characterized iron hydroperoxide complex in a nonheme environment. Our own efforts have been directed at generating analogous species in different but related nonheme iigand environments We thus present here the synthesis and X-ray structure of 1, an iron(II) complex of a new penta-dentate Iigand ("N4Py"). Complex 1 reacts with H_2O_2 to generate a transient purple species 2 which is characterized as a low-spin hydroperoxoiron(III) complex, (The compound numbers 1 and 2 are used both for the Fe~(II) and Fe~(III) cations, respectively, and also for their perchlorate salts.)