Synthesis Of Magnetic Fe₃O₄-supported Catalysts And Their Applications In Organic Transformations

As an ideal support, magnetic Fe₃O₄ is non-toxic, easy to prepare, active for modification and functionalization. Magnetic Fe₃O₄-supported catalysts can be easily recovered and recycled from the reaction mixture by applying an external magnet, therefore they have been widely used in many organic reactions. The magnetic Fe₃O₄-supported catalysts are of great interest for researchers and now have become one of the research contents of green chemistry.In chapter 2 a trifunctional magnetic Fe₃O₄ nanocatalyst Fe₃O₄@SiO₂-NH2 was designed and synthesized. Firstly, the Fe₃O₄ magnetic nanoparticles?Fe₃O₄ MNPs? were prepared using a reported chemical coprecipitation method with a slight modification. Secondly, the surface of Fe₃O₄ was coated with a silica shell by the hydrolysis and condensation of tetraethyl orthosilicate?TEOS? in ethanol/ammonia mixture to yield Fe₃O₄@SiO₂. Then treatment of Fe₃O₄@SiO₂ with chloropropyl triethoxysilane obtained chloropropyl modified Fe₃O₄@SiO₂?Fe₃O₄@SiO₂-Cl?. Finally, Fe₃O₄@SiO₂-NH2 was synthesized via the substitution of Fe₃O₄@SiO₂-Cl with excess of ethylenediamine. The catalytic activity of Fe₃O₄@SiO₂-NH₂ was evaluated for cooperatively catalytic synthesis of nitroalkenes. Under the optimized conditions, various representative substrates were extended. Combined with the experimental data and literatures, possible reaction mechanism for synthesis of nitroalkenes through a trifunctional cooperative catalysis was proposed. In the recycling experiments, the significant decrease of catalytic activity might be due to the formation of aminals causing chemical poisoning deactivation.In chapter 3 N-methylimidazole was grafted to the surface of Fe₃O₄@SiO₂ by covalent bond, then coordinated with palladium acetate to prepare N-methylimidazole functionalized magnetic Fe₃O₄ supported palladium catalyst Fe₃O₄@SiO₂-NMIM-Pd. The catalytic activity in Suzuki coupling reaction was explored in air. Under the optimized conditions, various representative substrates were extended to obtain the corresponding product in a moderate or excellent yield. After third recycling experiments, the yield decreased even in prolonged reaction time. Combined with the experimental data and ICP-AES test results, the significantly decrease of catalytic activity might be due to the aggregation or leaching of palladium nanoparticles coordinated with hydroxyl or adsorpted directly on the surface of Fe₃O₄@SiO₂-NMIM. In addition, the adsorption of K2CO3 and boronic salts on the surface of Fe₃O₄@SiO₂-NMIM-Pd was possible reason.