Characterization and Catalytic Activity of Mn(salen) Supported on a Silica/Clay-Mineral Composite: Influence of the Complex/Support Interaction on the Catalytic Efficiency

Abstract

We investigated different strategies to prepare Mn(salen) complexes supported on a silica/clay-mineral composite. The silica/clay-mineral surfaces were modified by grafting aminosilane groups, then Mn(salen) complexes were either grafted through a cross-linker, or deposited on the surface through interactions between amino group and manganese center. Two additional strategies, based on hydrogen bonds and electrostatic interactions, were also considered for comparison. The resulting materials were characterized using IR in diffuse reflectance mode, thermogravimetric analysis and elemental analysis in order to determine the manganese content and to establish the nature of the interaction between Mn(salen) complexes and silica/clay-mineral material surface for the different preparation protocols. These catalysts, were used for cyclohexene oxidation by tert-Butyl hydroperoxide with the objective of correlating the nature of the interaction between the metallic complex and the support to the catalytic activity. They were also compared to similar systems prepared using fumed silica as support, evidencing the input of this silica/clay-mineral composite in the catalytic performances. The obtained materials exhibited differences in both reactivity and selectivity that can be related to the nature of the interaction between the metallic center and the oxide support. The highest conversions were observed when the Mn complexes were immobilized with rigidness on the support. Interestingly, the resulting materials exhibited a remarkable stability, as evidenced by the absence of leaching of Mn(salen) in the reaction batch, and hence an excellent reusability.