The Preparation And Research On Catalytic Properties Of Fe₃O₄@SiO₂-Cu（Ⅱ）

Alkenyl nitriles and tetrazoles are both classical compounds in organic synthesis because of their wide range of practical applications in major areas of sciences. Various routes have been reported for the synthesis of alkenyl nitriles and tetrazoles, general methods were carried out by using numerous homogenous catalysts such as Lewis acid, non-metallic inorganic salts and metal salts. These synthesis methods could get the target products efficiently, while the acid, alkali and metal salts which unable to recycle in the synthesis reaction caused the environmental pollution and resource wastes. Consequently, the exploration of an innovative catalytic system is a crucial task for us to overcome these shortcomings and achieve the criteria of a mild, efficient, and environmentally friendly solution for the synthesis of alkenyl nitriles and tetrazoles. Two kinds of magnetic heterogeneous copper catalysts were prepared and used in the synthesis of alkenyl nitriles and tetrazoles, respectively. Specific research work in this paper was carried out as follows:（1） A new copper catalyst based on Fe₃O₄@SiO₂ nanoparticles was systhesized in this paper, and the leaching of the copper minimized by cross-linking. The whole process is as follows: firstly, the SiO2 nanoparticles were prepared using hydrothermal method with a slight modification. Then SiO2 nanoparticles were functional with aminopropyltrimethoxysilane（APTS） and oxalyl dichloride to form some cyclic structures. Subsequently, CuCl2 was entangled over SiO2 nanoparticles and stabilized by cyclic structures. Finally, the Fe₃O₄ nanoparticles were entangled in the materials. The compositions, morphology, size and magnetic properties of the catalyst were characterized by FT-IR, XRD, SEM, TEM and VSM. The weight percentage of Cu in the catalyst, as determined by Inductively Coupled Plasma-Optical Emission Spectrometry（ICP-OES） analysis, was 3.38 wt%. The methods to synthesize alkenyl nitriles were improved using homemade heterogenous copper catalysts in order to better implement the requirements of sustainable development. Meanwhile, the factors influencing the yield, such as the species and dosage of catalyst, the type and dosage of alkali, reaction time, reaction temperature and atmosphere were investigated, and the catalytic effects of catalyst after recycling were studied. The optimal reaction conditions were considered to included aromatic aldehydes（1 equiv）, CH3CN（10 equiv）, KOH（3 equiv）, and DMA as the solvent at room temperature for 6 h, and the isolated yield of alkenyl nitrile was 86%. The catalyst could be easily recovered through by an external magnet, washed thoroughly with EtOH, and drying in an oven at 50 °C overnight, then new substrates were added for the next cycle and the results indicated no significant decreases in yields after 4 cycles.（2） A simple and efficient protocol for preparing 5-substituted 1H-tetrazole derivatives has been reported by one-pot three-component reaction using Fe₃O₄@SiO₂-Cu（Sal-Asn）-NH₂ as a highly efficient and reusable heterogeneous catalyst. In this paper, all calculations about the four kinds of copper complexes were carried out using Gaussian 03 package. The Density Functional Theory（DFT） and Linear Combination of Atomic Orbitals（LCAO） were performed for the balance geometry structures, net charges of atom, energy of frontier molecule orbit, and frequency calculation. The calculation results show that the catalytic activity of the four kinds of complexes is Cu（Sal-Asn） > Ligand/Cu（II） > Cu-Salen > SB-Cu（II）. Then the Cu（Sal-Asn） complex was covalently linked to SiO2 nanoparticles using APTS as cross-linker. Finally, the Fe₃O₄ nanoparticles were entangled in the materials. The compositions, morphology, size and magnetic properties of the catalyst were characterized by FT-IR, UV-Vis, XRD, SEM, TEM and VSM. The weight percentage of Cu in the catalyst, as determined by ICP-OES analysis, was 3.75 wt%. In this paper, a protocol for preparing 5-substituted 1H-tetrazole derivatives was reported by one-pot three-component reaction of various aldehydes, hydroxylamine and sodium azide using Fe₃O₄@SiO₂-Cu（Sal-Asn）-NH₂ as the catalyst. The major role of Fe₃O₄@SiO₂-Cu（Sal-Asn）-NH₂ as a catalyst in the cycloaddition was ascertained, and in order to investigate the optimized conditions, the reaction was studied by applying different molar ratios of reactants as well as solvents at different temperatures. The optimal reaction conditions were considered to included n（aromatic aldehydes）: n（hydroxylamine）: n（sodium azide） = 1: 1: 1.5, and DMF as the solvent at 80 oC for 5 h, and the isolated yield of tetrazole was 92%. The catalyst could be conveniently recovered from the reaction system through the use of an external magnet and reused in five cycles without significant loss in catalytic activity.