PHOTOCHEMICAL REDUCTION OF CERIUM(IV) PORPHYRIN SANDWICH COMPLEXES

Irradiation of cerium(iv) complexes of 5,10,15,20-tetraphenyl- and 2,3,7,8,12,13,17,18-octaethylporphyrin (H-2tpp and H-2oep, respectively) with visible light, in the presence of triethylamine as an electron donor, leads to their photoreduction. The process was followed using electron absorption and ESR spectroscopies. Photoirradiation of [Ce(IV){tpp(-2)}2] resulted in the formation of [Ce(III){tpp(-2)}{tpp(-2)}]-. The reverse oxidation of this compound with chloroform as an electron acceptor was also observed. The photoreduction of [Ce(IV){oep(-2)}{oep(-2)}] was more complicated, giving rise to the photoreduced neutral complex [Ce(III){oep(-1)}{oep(-2)}] which exhibits an ESR spectrum typical of lanthanoid(III) bis(porphyrinates).