Photoinitiated catalysis in Nafion membranes containing palladium (II) meso-tetrakis(N-methyl-4-pyridyl)porphyrin and iron(III) meso-tetrakis(2,6-dichlorophenyl)porphyrin for O2-mediated oxidations of alkenes

Immobilisation of both palladium(II) meso-tetrakis(N-methyl-4-pyridyl)porphyrin (PdTMPyP4+) and iron-(III) meso-tetrakis(2,6-dichlorophenyl)-porphyrin (FeTDCPP+) in the same membrane of Nafion creates a new composite system, in which the photo-excited palladium complex induces the O2-mediated oxidation of cyclohexene to the corresponding allylic hydroperoxide and the iron porphyrin works as a catalyst for specific oxygenations of cyclohexene and cyclooctene. The role of PdTMPyP4+ is to induce the photoactivation of O2 with visible light (λ > 500 nm) to generate singlet oxygen (1O2) by means of energy transfer from the excited triplet state. Consequently, the 1O2-mediated oxidation of cyclohexene to cyclohexenyl hydroperoxide can be realised with a selectivity greater than 90%. Spectroscopic and photophysical investigations show that the tetracationic palladium porphyrin is mainly fixed to the external part of the Nafion membrane, it is characterised by a triplet-state lifetime signific...