OXOPORPHINATOIRON(V) OXIDATION OF POLYCYCLIC AROMATICS

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The long-term goal of this project is to provide insight into the mechanisms of monooxygenation by the family of isozymes, cytochromes P450. A premise underlying the strategy for achieving this objective is that the catalytically competent intermediates are oxoferryl prophyrin cation radicals (cpd I analogues). The approach to be followed will be to characterize a series of synthetic oxoferryl porphyrin cation radicals in order to determine parameters of molecular and electronic structure and to correlate parameters with chemistry by using the oxoferryl porphyrin cation radicals as oxidants with selected polycyclic aromatic hydrocarbon (PAH) substrates as probes. Of particular interest will be the implications of the ferryl-porphyrin radical spin coupling for chemical reactivity in the synthetic model systems. Although model cpd I analogues exhibit strong parallel (ferromagnetic) coupling, coupling in all known enzymic species is either weak or anti-parallel (antiferromagnetic). While synthetic models do not approach the complexity of the enzymes, much will be learned concerning the chemistry of oxoferryl porphyrin cation radicals and the oxidation of PAH by this species. The oxoferryl porphyrin cation radicals to be studied are derived from tetraaryl porphinatoiron complexes with the following aryl substituents: 2,4,6-trimethylphenyl (mesityl); 2,4,6-trimethoxyphenyl; 2,6- dichlorophenyl. In addition, cpd I analogues from 2,4,6-trimethlyphenyl complexes substituted on the pyrrole B-positions with bromine and fluorene will be characterized. Two tetraaryl chlorin (7,8-dihydro tetraphenylporphyrin) complexes: 2,6-dichlorophenyl-and 2,6- bistrifluoromethyl chlorin, will be investigated in light of indications that the high-valent complexes have unusual physico-chemical properties. PAH substrates are rubrene, which is expected to undergo facile one- electron oxidation to a stable cation radical, benzanthracene and benz[k] acephenanthrylene. The latter two PAH should give 7,12-quinones by one- electron oxidation and dihydrodiols and/or phenols by an electrophilic addition-rearrangement mechanism.