One- and two-electron oxidation of lead(II) tetrakis (N-methylpyridyl)porphyrins in aqueous solution

Abstract

In aqueous solution at pH 9, lead(II) tetrakis(N-methylpyridyl)porphyrins are oxidised rapidly to the metalloporphyrin π-radical cations by Br^˙–₂, under pulse radiolytic conditions. The π-radical cations disproportionate at a rate close to the diffusion-controlled limit. The doubly oxidised metalloporphyrin so formed can be assigned to the lead(IV) porphyrin, on the basis of absorption spectroscopy. These highly oxidised metalloporphyrins decay via first-order kinetics (k= 0.93 ± 0.05 s^–1) at pH 9. Even in the presence of colloidal RuO₂·2H₂O, this decay process does not oxidise water to O₂.