| Homogeneous catalyst shows high activity and selectivity. But most traditional homogeneous catalyst has several shortcomings, such as recycling problem, the difficult separation and recovery of homogeneous catalyst. Heterogeneous catalyst exhibits excellent catalytic activity and stability, and can be recovered easily. Recently, the immobilization of homogeneous catalysts to facilitate easy catalyst recovery and recycling, as well as product separation has received much attention.A mesoporous silica MCM-41supported Pd-Schiff base catalyst was prepared. The catalyst and its intermediates were characterized by1H NMR,13C NMR, MS, IR, XRD, TGA TEM, elemental analysis, ICP-AES. It was found that the Schiff base was successfully supported on the mesoporous silica (MCM-41) by covalent bonds. The loading of organic ligand, determined by elemental analysis, was0.25mmol·g-1, and the loading of Pd, determined by ICP, was0.18mmol·g-1.The as-prepared catalyst Pd/MCM-41was found to be an efficient catalyst for Suzuki coupling reactions in aqueous medium. The reactions of various aryl bromides with arylboronic acids could be carried out Various aryl bromides could couple with aryl boronic acids in high yields (86～98%) under a very low loading of palladium (0.1mol%Pd). The Pd/MCM-41could be reused for5times without significant loss of activity in Suzuki coupling reaction. It could be easily recovered by simple filtration.The Pd/MCM-41also had high catalytic activity in Heck coupling reaction. Different substrates proceeded well at100℃under nitrogen and gave high yields for the corresponding produets (81～98%) in Heck reaction in the presence of0.5mol%Pd. Pd/MCM-41recycled in different systems indicated that inorganic bases had greater damage for the silica structure, so that resulting in the loss of catalytic activity. In addition, the catalyst could get a higher activity while using the mesoporous silica as a carrier. The catalyst can be reused for5times with almost consistent efficiency. |
PDF Full Text Request