Nature of the epoxidizing species generated by reaction of alkyl hydroperoxides with iron(III) porphyrins. Oxidations of cis-stilbene and (Z)-1,2-bis(trans-2, trans-3-diphenylcyclopropyl)ethene by tert-BuOOH in the presence of [meso-tetrakis(2,4,6-trimethylphenyl)porphinato]-, [meso-tetrakis(2,6-dichlorophenyl)porphinato]-, and [meso-tetrakis(2,6-dibromophenyl)porphinato]iron(III) chloride