OXIDATION OF POLYCYCLIC AROMATIC-HYDROCARBONS BY AN OXOFERRYL PORPHYRIN PI-CATION RADICAL

Pre-formed oxoferryl tetrakis (2,6-dichlorophenyl)porphinatoiron pi-ca tian radical at -80 degrees C in methylene chloride:methanol-d(4) is u sed as a low-turnover oxidant to elucidate oxidation pathways of pyren e and benzanthracene. Quantitative incorporation of the oxo oxygen in pyrene quinones and benzanthracene phenols, determined by O-18-labelin g experiments, indicates that a substantial proportion of the products arise via a tight complex in which the oxoferryl unit is accessible t o the periphery of the polycyclic aromatic hydrocarbon. Methoxylated p roducts indicate that one-electron transfers by an outer-sphere oxidat ion mechanism also occur. Thus dual reaction pathways are demonstrated . Modeling cytochrome P450-mediated oxidations by reactions of pre-for med oxoferryl porphyrin rr-cation radicals under single-or low-turnove r conditions appears to be a straightforward strategy for investigatio n of cytochrome P450 mechanisms. Nevertheless, it has rarely been expl oited and, to date, reports concern only oxoferryl tetramesitylporphyr in pi-cation radical epoxidation of olefins. The catalyst employed her e is more active, and thus closer in behavior to cytochrome P450. (C) 1997 Elsevier Science B.V.