Preparation And Characterization Of Some Inorganic Supported Catalysts And Their Applications In Organic Reactions

The development of supported catalysts is an elegant way to solve the problem of the separation, recovery and reuse of homogeneous catalysts. Inorganic matrixes have many advantages, such as abundant source, low cost, and excellent stability, so the inorganic supported catalysts have attracted wide attention. Among them, the silicon-based materials and silica coated ferric oxide magnetic nanoparticles are often chosen as supports, because there are a lot of hydroxyl groups on their surfaces or pores, some silane functionalized organic molecules can be easily immobilized via condensation reactions with the hydroxyl groups of supports. Moreover, due to the attractive magnetic property, the magnetic nanoparticles supported molecules can be rapidly and efficiently separated from the mixture. Considering the great value of ionic liquids (ILs) and noble metal palladium in the field of organic catalysis, and the disadvantage of high dosage and difficult recovery, it’s very significant to develop some novel supported ionic liquid and palladium catalysts.Herein, some new inorganic supported catalysts were prepared, including amorphous silica and magnetic nanoparticles supported IL catalyst, mesoporous silica supported Pd complex, and magnetic nanoparticles supported nano-Pd catalyst. In addition, their applications in the organic reactions were investigated.An amorphous silica supported acid ionic liquid was prepared via condensation reaction with silane functionalized IL and silica hydroxyl group. It could effectively catalyze the esterification, acetalation, and one-pot synthesis of amidoalkyl naphthols and benzopyrans by multicomponent reactions under mild conditions. The catalyst was simply recovered by filtration, and it could be used several times without significant loss of activity.The silica coated Fe3O4was chosen as the support, and another two supported IL catalyst were then prepared by the similar method. The as-prepared supported acid ionic liquid was found to be an efficient catalyst for the one-pot synthesis of benzoxanthenes by a three-component condensation of dimedone with aldehyde and2-naphthol under solvent-free conditions. The reaction could be well carried out within30-60min at90℃under a low catalyst loading (1.5mol%), and good to excellent yields (80-94%) were obtained. The supported basic IL catalyst prepared in a similar way, could effectively catalyze unsymmetrical Hantzsch reaction of aryl aldehyde, ethyl acetoacetate, dimedone and ammonium acetate at room temperature. The reaction proceeded within1.5-3.5h under3.6mol%catalyst loading to afford the corresponding products in high yields (76-88%). The catalyst could be easily recovered by an external magnet and reused five times without remarkable loss of efficiency.A new mesoporous silica supported palladium imino-pyridine complex was successfully prepared by attaching palladium acetate to a novel imino-pyridine ligand functionalized MCM-41. It was found to be an efficient catalyst for Suzuki reactions under mild conditions, and the reactions of various aryl bromides with arylboronic acids could proceed well within1.0-4.5h at50℃to give excellent yields of coupling products (86-98%). The catalyst was simply recovered by filtration, and it could be used five times without significant loss of activity.A magnetic nanoparticle-supported palladium imino-pyridine complex was prepared by a similar process and was applied for Heck reactions. Aryl iodides and aryl bromides with electron-withdrawing groups could undergo smooth transformation during1-4h at100-120℃to give excellent yields of products (80-98%). The catalyst could be simply recovered by magnetic separation, and its reusability was affected by the base used in the reactions. When triethylamine was used as the base, the yield was still as high as92%after the sixth run. However, the catalytic activity was obviously reduced after three times, when potassium carbonate was chosen as the base.A novel magnetic nanoparticle-supported nano-palladium catalyst was successfully prepared via a "click" route and evaluated in Suzuki reactions. It was found to be highly efficient for the reactions of various aryl halides with arylboronic acids. The reactions proceeded well within3-8h at60℃to give high yields of products (80-99%). The catalyst could be simply recovered by magnetic separation, and its reusability was affected by the water in the solvent. It could be reused six times without significant loss of activity when95%EtOH was used as the solvent.