Integrated photocatalysts for hydrocarbon oxidation: Polyoxotungstates/ iron porphyrins systems in the reductive activation of molecular oxygen

The photochemical and photocatalytic properties of (nBu4N) 3PW12O40 (PW12O403-), (nBu4N)4W10O32 and (Et4N)4W10O32 (W10O324) were investigated in the presence of several Fe(III) meso-tetraarylporphyrins (Fe(III)Por). Laser flash photolysis experiments show that in the (nBu4N)3PW12O40/Fe(III)Por integrated systems the electron transfer from the photoreduced polyoxotungstate to the Fe(III) Por is the first step for the subsequent reductive activation of O2 by the ferrous complex. In contrast, the direct reduction of O2 by the photoreduced polyoxotungstate is the kinetically favored process in the (nBu4N)4W10O32/Fe(III) Por systems. A comparison between the results obtained using (nBu4N)4W10O32 and (Et4N)4W10O32 shows that the decrease in the steric hindrance of the counterion. surrounding the photochemically active polyoxoanion, increases the rate of electron transfer between W10O325 and Fe(III)Por. thus enabling the decatungstate to contribute to the activation of dioxygen through the re...