Mesoporous MCM-41 Materials Modified with Oxodiperoxo Molybdenum Complexes: Efficient Catalysts for the Epoxidation of Cyclooctene

Abstract

An organic−inorganic hybrid heterogeneous catalyst system was synthesized by covalently anchoring oxodiperoxo molybdenum complexes [(L−L)MoO(O2)2] (L−L = (3-triethoxysilylpropyl)[3-(2-pyridyl)-1-pyrazolyl]acetamide) onto the mesoporous silica MCM-41 (Si−MCM-41) and aluminosilicate MCM-41 (Al−MCM-41) materials. Characterization of the functionalized materials by powder X-ray diffraction (XRD), N2 adsorption, and solid-state CP-MAS NMR spectroscopy (13C and 29Si) demonstrates that the oxodiperoxo molybdenum complexes are grafted successfully into the mesoporous MCM-41 materials. The structures of both the mesoporous materials and the molybdenum complex are preserved during the grafting process. All the hybrid materials are active and truly heterogeneous catalysts for the liquid-phase epoxidation of cyclooctene with tBuOOH as the oxygen source. The catalytic properties (activity and recyclability) of the supported materials can be improved by their further silylation using Me3SiCl, which can be explained by the increase of hydrophobicity of the mesoporous surface due to removal of residual Si−OH groups. The modified aluminosilicate MCM-41 materials show higher activities than the corresponding siliceous materials, which might be due to the incorporation of Lewis acidic centers.