SOLUTION SPECTROSCOPIC STUDIES OF ELECTROLYTICALLY GENERATED IRON(III) AND IRON(IV) TETRAKIS(2,6-DIFLUOROPHENYL)PORPHYRIN PI CATION RADICALS

Electrochemical oxidation of tetrakis(2,6-difluorophenylporphinato)haloiron(III) ([(F8-TPP)Fe(III)X], where X = Cl- or F-) at high potentials in dichloromethane or nitromethane solution results in the generation of iron porphyrin radicals sufficiently stable for spectral characterization at ambient temperature. Proton, deuterium, and fluorine-19 NMR spectroscopic characterization has permitted evaluation of the oxidation state of the metal. Bulk electrolysis at a potential slightly anodic of the first oxidation wave (+1.45 V vs SCE) yields high-spin iron(III) (fluorophenyl)prophyrin radicals that exhibit unique NMR spectral properties in comparison with the nonfluorinated derivatives. Large alternate downfield and upfield phenyl proton and fluorine-19 NMR shifts point to formation of the porphyrin pi-cation radical with large unpaired spin density at the phenyl ortho fluorine position. Bulk electrolysis of [(F8-TPP)Fe(III)X] at higher potentials (+1.60 V) results in the generation of an additional product presumably due to the removal of the second electron from the metal center. The NMR spectra of this unstable oxidized product are consistent with an iron(IV) porphyrin pi-cation-radical species. Phenyl proton and fluorine signals are drastically shifted in directions opposite to those of the singly oxidized species. Evidence is thus presented for generation of the first iron(IV) porphyrin pi-cation-radical species without an axial oxo ligand. Electrochemical oxidation of the dinuclear (mu-oxo)iron(III) porphyrin, [((pyrr-d8)-F8-TPP)Fe]2O at potentials of +1.20 and +1.50 V yields respective monocation and dication iron(III) porphyrin radical complexes.