REACTIONS OF ARYL IRON(III) PORPHYRINS WITH DIOXYGEN - FORMATION OF ARYLOXY IRON(III) AND ARYL IRON(IV) COMPLEXES

The reaction of dioxygen with low-spin, five-coordinate complexes, PFeIIIAr (P, porphyrin dianion; Ar, aryl group) has been examined for comparison with previous work (Arasasingham, R. D. et al. J. Am. Chem. Soc. 1989, 111, 4357) on the corresponding alkyl complexes which showed that peroxo complexes PFeIIIOOR formed initially and then decomposed to form PFeOH and an aldehyde or ketone when R was a primary or secondary alkyl group. Dioxygen addition to TTPFeln(C6H4CH3-p) at 25 ° C in toluene yields the phenoxide complex, TTPFe(OC6H4CH3-p), as the principle product, while addition to TTPFeIIIC6H5 at-30 ° yields TTPFeIIIOC6H5 and small amounts of TTPFeIII(OC6H4OH-p) and TTPFeIIIOC6H4OFeIIITTP. These reactions have been monitored by both 1H NMR and ESR spectroscopies. No intermediates have been detected in the formation of these products. Mechanisms for the formation of these products have been formulated in terms of the initial insertion of dioxygen into the Fe-C bond followed by rapid homolysis to form PFeIv=O and ·OAr, with subsequent reactions yielding the final products. Addition of dioxygen to a solution of TTPFeIII(C6H4CH3-p) in chloroform at-60 ° yields a mixture of [TTPFeIv(C6H4CH3-p)]+ and TTPFeIIICl with no evidence for the formation of the phenoxide complexes. In this case electron transfer to yield the oxidized iron porphyrin and superoxide ion is driven by the solvent polarity and the ability of the solvent to destroy superoxide ion as it is formed. © 1990, American Chemical Society. All rights reserved.