| As the development of technology, single material could not meet the requirements of man. There is a current tendency to synthesize more hybrid materials which are composed of several elements.. Complementarity and optimization of these elements could make hybrid materials excellent feature. Methodology of covalent immobilization could convert a homogeneous catalyst into a heterogeneous catalyst. The aim is to utilize the organic moiety as the activity site and the solid to provide avenues to recovery and possibly recyclability of the organic active site. These organic-inorganic hybrid materials could solve the problem of limitation in the nature of active sites of traditional heterogeneous catalysts and inability to be recycled of soluble catalysts.3-(2-pyridyl)-1-pyrazolyl could coordinate with a range of transition metal complexs. Thus, catalytic applications in liquid reaction of ligand-supported materials are extended. Previously, we synthesized supported heterogeneous catalysts by covalently anchoring oxodiperoxo molybdenum complexes [(L-L)MoO(O2)2] (L-L) (3-triethoxysilyl- propyl)[3-(2-pyridyl)-1-pyrazolyl]acetamide) onto the mesoporous silica MCM-41 materials and found these materials showed high activity for the liquid-phase epoxidation of cyclooctene with tBuOOH and stability against leaching of active molybdenum species.In the present work, three different mesoporous materialsAlPO4, Si-MCM-41 and SBA-15 were used to anchor (2-pyridyl)-1- pyrazolyl]. Further heterogeneous catalysts were synthesized from different transition metal, such as Mo, Pd,Os..,and catalytic properties were investigated separately.In addition, we also use ligand- supported materials as catalysts of the transesterification of dimethyl oxalate with phenol.1. The epoxidation of transition . The covalent attachment of the chelate ligand (3-trimethoxy- silylpropyl)[3-(2-pyridyl)-1-pyrazolyl]acetamide was abtained by the reaction of condensation between triethoxy-organo-silanes and the surface–OH groups of amorphous AlPO4 support. Solid epoxidation catalysts can be obtained by introducing oxodiperoxomolybdenum species MoO(O2)2 (DMF) into the hybrid materials via a ligand exchange reaction. All molybdenum-containing catalysts showed high activity for the liquid-phase epoxidation of transition with tBuOOH and stability against leaching of active molybdenum species. The same result was obtained in the absence of solvent.2. The oxidation of benzyl alcohol The catalysts containing Pd(Ⅱ) (Pd-SiMCM-41) were synthesized and were applied in oxidation of benzyl alcohol. A variety of inorganic bases, such as pyridine NaOAc, K2CO3 and NaOH, were tried for aerobic oxidations of alcohols. However, inorganic bases, ranging from weak to strong, appeared unsuitable.No product was formed except NaOH was added. However, with the NaOH as additive base, Pd(0) precipitated and oxidation was not continued. The deactivation of active centers may be due to strong interaction between ligand and metal complex and the introduction of NaOH might break this interaction. We also applied catalysts in this reaction with tBuOOH as oxidation and they showed good catalytic activity. However, they suffered from the disadvantage of a significant reduction in reactivity when they were cycled.3. The dihydroxylation of styrene The catalysts containing Os(Ⅵ) Os-SiMCM-41 were applied in reaction of dihydroxylation of styrene. Althoug the catalysts displayed an excellent activity, the selectivity is poor4. The transesterification of dimethyl oxalate with phenol. we discovered hybrid materials containing 3-(2-pyridyl) -1-pyrazolyl ligands with MCM-41 as support were active catalysts for the transesterification of dimethyl oxalate with phenol. In addition, these heterogeneous catalysts showed a better DPC yield than homogeneous system for the same amount of ligand. In the supported catalysts, the surface characteristics of the supports and the ligand dispersion appeared to be critical to the yield of DPC. |
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