Metalloporphyrin-functionalized hexagonal mesoporous silica: Synthesis, structural properties and catalytic activity as cytochrome P450 model

Abstract

The manganese(III) and iron(III)-5,10,15,20-tetrakis(pentafluorophenyl)porphyrin chlorides were successfully immobilized inside the mesopores of HMS and characterized by a variety of physical techniques. The assembly of the catalysts FeP-HMS C12, FeP-HMS C16, MnP-HMS C12, and MnP-HMS C16 was achieved by using two different surfactants, n-dodecylamine and n-hexadecylamine, so as to compare the framework structure and the catalytic behavior of the different solids. The mesoporous structure of the HMS materials was confirmed by XRD and N2 adsorption–desorption isotherm. The MnP-HMS systems have larger pore sizes (5.05–5.72nm) compared with the FeP-HMS systems (2.38–4.09nm). The SEM images revealed an organized structure for all the catalysts. The high catalytic yields and the short reaction time obtained for the MeP/PhIO systems during the oxidation of (Z)-cyclooctene indicated the easy access of the reactants to the reactive sites of the catalysts. The stabilities of the materials MnP-HMS C12, MnP-HMS C16, FeP-HMS C12 and FeP-HMS C16 were tested, and MnP-HMS C16 maintained its catalytic activity during 10 reaction cycles. The effect of the support on the catalytic performance of FeP-HMS C12, FeP-HMS C16, MnP-HMS C12, and MnP-HMS C16 was studied during the oxidation of cyclohexane. The higher selectivity toward cyclohexanol suggested that the oxygen rebound mechanism was favored inside the mesopores, thus preventing solvent cage escape and radical processes. The catalytic results indicated that the encapsulation of MePs into mesopores confered some hydrophobicity to the reaction site microenvironment, thereby enhancing the biomimetic behavior of these materials.