Design Of Hybrid Catalysts Based On Mesoporous Propylthiol And Schiff-base Group-functionalized Complexes And Their Oxidation Catalytic Behaviors

Salen transition metal complexes have become a matter of current interest because oftheir wide applications as catalysts in epoxidation, cyclopropanation. Among all kinds of theepoxidation catalysts, Schiff base complexes, especially metal-salen complexes, have beenproved efficient towards the target reactions. Metal-salen complex-catalyzed reactionsgenerally proceed in homogeneous systems, and the major drawback of homogeneouscatalysis is the need for separation and recovery of the metal-salen complexes from thereaction mixture at the end of the process. Heterogeneous metal-salen complexes, which arerecyclable and readily separable from the reaction system, offer the opportunity to reduce theimpact on environment and increase industrial interest for the liquid phase oxidation catalyticprocess. Moreover, the porosity of the heterogeneous metal-salen complexes plays animportant role to enhance the catalytic activity. Accordingly, mesoporous silica materialshave been widely used as the supports in the immobilization of metal-salen complexes.1. Mesoporous propylthiol group-functionalized silica supported manganese（III）-salencomplexes with2D hexagonal p6mm and3D interconnected sponge-like structures wereprepared by a multistep grafting method by using tetraethyl orthosilicate （TEOS） or1,2-bis（trimethoxysilyl）ethane （BTMSE） as a silica source and3-mercaptopropyltriethoxysilane（MPTES） as a linker reagent. The structure, morphology, and porosity of the resulting hybridmaterials were well-characterized by spectroscopy method, X-ray diffraction analysis,transmission electron microscopy, and nitrogen physisorption measurement. Subsequently,their oxidation catalytic activity and stability were evaluated through the epoxidation ofstyrene by using aqueous NaClO as the oxygen source, and the influences of sulphur atom inthe hybrid materials, textural properties and pore morphologies of the materials, and the kindsof the substituents in the diimine bridges of the manganese（III）-salen complexes on thecatalytic activity of the hybrid materials were discussed.2. A series of manganese-salen-based hybrid catalysts, Mn（salen）/C₃N₂Schiff SBA15and Mn（salen）/C₄N₂Schiff SBA15, were demonstrated for the first time by a multistepgrafting method. As-prepared hybrid catalysts exhibited well-defined mesostructure includinghighly ordered2D hexagonal p6mm pore geometry, large BET surface area (268293m²g⁹（-1）,uniform pore size （5.26.4nm） as well as high pore volume (0.350.41cm³g^-1); meanwhile,the structural integrity of the starting manganese-salen complexes and other functionalities（Schiff ligand and C₃N₂or C₄N₂unit） remained intact in the hybrid catalysts. These hybridcatalysts were subsequently utilized as efficient, selective and reusable catalysts in epoxidation of alkenes including styrene, cyclohexene and1-phenylcyclohexene by usingNaClO as the oxidant, and the contribution of imidazole or piperazine and Schiff base to theoverall catalytic activity of the hybrid catalysts were evaluated and explained.