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

Abstract

The metal complex iron meso-tetrakis (2,6-dichlorophenyl)porphyrin (Fe IIIP) has been covalently linked on the surface of the mesoporous material MCM-41 and of amorphous SiO 2 to give the photocatalysts Fe IIIP/MCM-41 and Fe IIIP/SiO 2 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 N 2 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 Fe IIIP/MCM-41 reveals that this is a robust photocatalyst able to induce the O 2-assisted oxidation of 1,4-pentanediol. In particular, photoexcitation of Fe IIIP/MCM-41 causes the conversion of 1,4-pentanediol to the aldehyde derivative compound with 70% 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, Fe IIIP/MCM-41 is about four times more efficient than Fe IIIP/SiO 2. Moreover, the nature of the support controls the regioselectivity of the photocatalytic process: this is due to both uptake phenomena and steric effects, which can control the approach of the diol to the photoactive iron porphyrin.