Azide-Assisted Growth of Copper Nanostructures and Their Application as a Carbon Supported Catalyst in Two-Step Three-Component Azide–Alkyne Cycloadditions

Copper nanostructures were obtained from the reduction of Cu(I) under mild conditions in ethanol/water using sodium-l-ascorbate and sodium azide while performing an amination reaction. When the halobenzene substrate was reacted in the presence of a bulk carbon black (CB) support, clustered copper sub-micrometer particles (SMPs) and microparticles (MPs) form. The growth conditions of the MPs were optimized, and the supported nanostructures were isolated and characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetry, and inductively-coupled plasma mass spectrometry. The particles are mobile and supported within the CB matrix and proved to be active catalysts in the azide–alkyne cycloaddition (CuAAC). The catalytic competency of the particles was assessed in a two-step three-component azide–alkyne cycloaddition of benzyl bromide, sodium azide, and phenylacetylene as a model reaction. The reaction conditions were optimized, and the optimized conditions were applied for the synthesis of triazole compounds with varying levels of functionalization. The recyclability of the catalysts was investigated, depletion modes were discussed, and the conditions were fine-tuned to reach good recyclability. This demonstrates the broader applicability of the SMPs/MPs as CuAAC-catalyst and its limitations.

本研究在乙醇/水混合溶剂的温和条件下，以L-抗坏血酸钠与叠氮化钠为还原剂，通过一价铜还原并同步进行胺化反应，制备得到铜纳米结构。当卤代苯底物在本体炭黑（CB）载体存在下进行反应时，会生成团聚状铜亚微米颗粒（SMPs）与微米颗粒（MPs）。研究人员对微米颗粒的生长条件进行了优化，并通过扫描电子显微镜（scanning electron microscopy）、能量色散X射线能谱（energy dispersive X-ray spectroscopy）、热重分析（thermogravimetry）以及电感耦合等离子体质谱法（inductively-coupled plasma mass spectrometry）对负载型纳米结构进行了分离与表征。该颗粒可在炭黑载体基质中移动，且在叠氮-炔环加成（CuAAC）反应中表现出优异的催化活性。以溴化苄、叠氮化钠与苯乙炔的两步法三组分叠氮-炔环加成为模型反应，评估了该颗粒的催化性能。对反应条件进行优化后，将最优条件应用于不同官能化程度的三唑类化合物的合成。研究考察了该催化剂的循环使用性能，探讨了其损耗模式，并通过微调反应条件实现了良好的循环稳定性。上述结果证明了铜亚微米/微米颗粒作为CuAAC反应催化剂的更广泛应用潜力，同时也揭示了其局限性。