The mechanism of oxidation of tetramesityliron(III) porphyrins [FeIIITMP(X)] with peroxyacids has been examined. The reaction of FemTMP(Cl) (1) with peroxyacids in methylene chloride at -46 °C afforded the corresponding oxoiron(IV) porphyrin cation radical [FeIVTMP.+(O)] (3). The kinetics of this process were complicated by an induction period that depended on the acidity of the peroxyacid used. By contrast, similar oxidation of FeIIITMP(OH) gave evidence for rapid ligand metathesis to afford an acylperoxoiron(III) complex, FeIIITMP(OOC(O)Ar) (2). The decomposition of 2 to form 3 was found to be first order in 2 and catalyzed by acid. Electron-withdrawing substituents on the aryl portion of the peroxyacid facilitated this reaction (ρ = +0.5). The temperature dependence between -32 and -48 °C indicated Ea= 4 ± 0.4 kcal/mol, ΔH* = 3.6 ± 0.4 kcal/mol, and ΔS* > -25 eu. The oxidation of l-(m-chiorobenzoate) in toluene with peroxyacids afforded an iron (III)porphyrin N-oxide (5). The reaction required 2 equiv of peroxyacid and afforded 1 mol of a diacylperoxide. The presence of acid discouraged the formation of 5. Substituent effects in the peroxyacid were the opposite for the formation of 5 (ρ= -0.4) than for the formation of 3. The results indicated that there are competing homolytic and heterolytic O–O bond cleavage reactions for 2 mediated by iron(III).
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry