Fe(III)-porphyrin heterogenized on MCM-41: matrix effects on the oxidation of 1,4-pentanediol

The metal complex iron meso-tetrakis(2,6-dichlorophenyl)porphyrin (FeIIIP) has been covalently linked on the surface of the mesoporous material MCM-41 and of amorphous SiO2 to give the photocatalysts FeIIIP/MCM-41 and FeIIIP/SiO2 respectively. The effect of porphyrin addition on specific surface area and porosity of these materials has been evaluated by means of BET and BJH model applied to N2 adsorption/desorption isotherms. It is seen that the MCM-41 sample presents the largest modification due to the presence of porphyrin: the pore size changes in average value and distribution, the pores formed in the presence of porphyrin being smaller and presenting a larger distribution. The photochemical characterization of FeIIIP/MCM-41 reveals that this is a robust photocatalyst able to induce the O2-assisted oxidation of 1,4-pentanediol. In particular, photoexcitation of FeIIIP/MCM-41 causes the conversion of 1,4-pentanediol to the aldehyde derivative compound with good regioselectivity. It is noteworthy that this product can be accumulated with no formation of further oxidized compounds. Due to its high specific surface area, which guarantees a good dispersion of the active centres, FeIIIP/MCM-41 is about four times more efficient than FeIIIP/SiO2. Moreover, the nature of the support controls the regioselectivity of the photocatalytic process: this is due to both adsorption phenomena and steric effects, which can control the approach of the diol to the photoactive iron porphyrin.