Preparation Of Silica Supported Palladium Catalysts And Their Catalytic Performance

Heck coupling and Suzuki coupling reactions which lead to form new C-C bonds are of importance in synthetic organic chemistry.These reactions offer a convenient method to join small molecules to large compounds.Despite the high activity and selectivity of homogeneous catalysts,there are some shortcomings,including separation from products and reusability of the catalysts.However,heterogeneous catalysts have the practical advantages with similar reactivity.Hence,the development of new heterogeneous catalysts still considered to be important work for material scientists.The bulky support is the main part of the catalyst,which is employed to load the active component and maintain the perfect shape.In this paper,fumed silica and silicon nanosheet were served as support for palladium nanoparticles.Fumed silica is one cheap commercial product with high specific surface area and tunable surface properties.At first,the fumed silica was modified with 3-aminopropyltriethoxysilane,followed by treatment with palladium chloride,and then the reduction with N₂H₄·H₂O in ethanol.After vacuum drying,the functionalized silica-supported palladium catalysts?Pd/AS-Si O₂?were obtained.Silicon nanosheet is the graphene-like honeycomb lattice structure or buckled sheet with Si-H and Si-OH on the surface,which could be readily functionalized using appropriate functional groups.Silicon nanosheet supported palladium catalysts?Pd/AS-SNS?were synthesized in a process similar to Pd/AS-Si O₂.These products were confirmed by infrared radiation?IR?,transmission electron microscopy?TEM?,inductively coupled plasma mass spectrometry?ICP-MS?and x-ray diffraction?XRD?.The catalytic properties of the materials?Pd/AS-SiO₂?were tested for the Heck and Suzuki reactions.After optimized the reaction conditions,the Pd catalyst supported on the surface modified fumed silica exhibits very high activity,recoverability and stability with a wide range of aryl iodides and bromides with electron donating and electron-withdrawing groups or without.Similarly,high efficiency and stability of Pd/AS-SNS was also shown for Suzuki coupling reactions with a number of aryl halides under the optimized reaction condition.Besides,the recovery and reusability of the catalysts were tested in the Suzuki reaction of bromotoluene and phenylboronic acid under the optimized reaction condition.The recovered catalyst could maintain its original activity even in the eighth cycle under optimized conditions.