Kinetics of electron transfer from cobalt(II) porphyrins to various metalloporphyrin pi-radical cations in irradiated carbon tetrachloride solutions

One-electron oxidation of a series of metallotetraphenylporphyrins (M-TPP) was studied by pulse radiolysis in CCl4 solutions. The resultant pi-radical cations were found to oxidize Co/sup II/TPP to Co/sup III/TPP with rate constants of the order of 105 M-1 s-1, much slower than the diffusion-controlled rates despite the high free energies of these reactions. In the presence of pyridine these electron-transfer reactions were much faster (107-108 M-1 s-1), suggesting that pyridine, as an axial ligand, facilitates the electron transfer between metalloporphyrins. 20 references, 1 table