Kinetics of the iron porphyrin catalysed oxidation of cyclohexene with substituted iodosylbenzenes

Abstract

A quantitative kinetic study has been carried out on the iron porphyrin catalysed oxidation of cyclohexene with iodosylbenzenes bearing increasingly electronegative aryl substituents. The effect of increasingly electronegative substituents placed on the porphyrin aryl periphery has also been studied. A mixed solvent system (CH₂Cl₂–CH₃OH–H₂O, 80:18:2) ensured homogeneous conditions for determinations of the observed rate constants at 25 °C. Of the halogenated iron(III) porphyrin catalysts used, 5,10,15,20-tetra(pentafluorophenyl)porphyrinatoiron(III) chloride exhibited sufficient stability to obtain comparative values for oxidant uptake from iodosylbenzene through to pentafluoroiodosylbenzene. Increasingly electronegative iodosylbenzene substituents are seen to increase dramatically the rate of porphyrin activation, demonstrated as the rate determining step of the cyclohexene oxidation process. The effects of the iodosylbenzene substituents on a proposed iron porphyrin–iodosylbenzene transition state are discussed.