Evidence for the Participation of Two Distinct Reactive Intermediates in Iron(III) Porphyrin Complex-Catalyzed Epoxidation Reactions

Abstract

We have studied the competitive epoxidations of olefins with cis- and trans-stilbenes and with cyclooctene and trans-stilbene in iron porphyrin complex-catalyzed epoxidation reactions by H2O2, tert-butyl hydroperoxide (t-BuOOH), and m-chloroperoxybenzoic acid (m-CPBA) in protic solvent (i.e., a solvent mixture of CH3OH and CH2Cl2) and aprotic solvent (i.e., a solvent mixture of CH3CN and CH2Cl2) at room temperature under catalytic reaction conditions. The competitive epoxidations were also carried out with in situ generated high-valent iron(IV) oxo porphyrin cation radical complexes in aprotic solvent under stoichiometric reaction conditions. By determining the ratios of epoxide products formed in the competitive epoxidations, we were able to conclude unambiguously that the reactive species generated in protic solvent are high-valent iron(IV) oxo porphyrin cation radical complexes 3 and the intermediates formed in aprotic solvent are oxidant−iron porphyrin intermediates 2. A protic solvent such as methano...