Photochemical reduction of cerium(IV) porphyrin sandwich complexes

Abstract

Irradiation of cerium(IV) complexes of 5,10,15,20-tetraphenyl- and 2,3,7,8,12,13,17,18-octaethyl-porphyrin (H₂tpp and H₂oep, 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 spectros-copies. 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).