Iron porphyrin catalyzed hydroxylation of ethylbenzene by ozone

The hydroxylation of ethylbenzene by ozone under catalysis of tetramesitylporphyrinato iron(III) complexes with various axial ligands was studied in order to elucidate the principles which determine the efficiency of this biomimetic system. Reaction conditions were carefully chosen to ensure that oxygen-atom transfer from oxidized catalyst to hydrocarbon is rate limiting. The catalyst's proximal ligand was found to affect both the stability and the reactivity of the high-valent iron porphyrin intermediate l-X, the reactivity pattern being distinctively different from the related epoxidation reactions. The most pronounced and intriguing effect was of methanol, which stabilized the I-X complex as to completely inhibit its reactivity toward the alkane. Preliminary results for two halogenated-porphyrin iron(III) complexes are presented too, to demonstrate the potential of the present system for practical purposes.