氮杂环有机催化CO_(2)环加成反应:咪唑环的弱协同效应

N-Heterocyclic organocatalyst for carbon dioxide cycloaddition:weak synergistic effect of imidazolium

稳定的CO_(2)需要高能分子的活化,如环氧化物。而亲核试剂有助于诱发三元氧环的开环,进而实现CO_(2)的插入活化。针对聚苯乙烯负载的有机催化剂,考察不同含氮杂环材料在催化CO_(2)环加成中的活性差异,发现五元氮杂环显示出了高于六元氮杂环的催化活性,五元氮杂环对底物间弱的协同效应是诱发环氧丙烷开环和活化CO_(2)插入的关键。进而与引入ZnCl2、烷基胺的聚苯乙烯负载型催化剂作对比,虽然后两者反应速率得以提高,但也造成了选择性的下降。在无金属、无卤素、无添加剂、无溶剂下,PS-Im这种简单、廉价、稳定且可回收利用的聚苯乙烯负载氮杂环材料适合于工业推广。

Stable CO_(2) has to be activated by high-energy chemicals,such as epoxide.Nucleophilic reagents are acted as the trigger for the ring-opening of epoxides and CO_(2) insertion.In this work,a series of polystyrene supported N-heterocycles were tested for their difference on CO_(2) cycloaddition.It is found that five-membered heterocyclic compounds exhibited higher activity than six-membered ones.A weak interaction between five membered heterocycles and substrates is the key point to promote the ring-opening of epoxide and the activation of CO_(2) insertion.By comparison,the introduction of ZnCl2 andalkyl amine boosted the reaction rate,but decreased the selectivity.As a simple,cost-effective,stable and reusable material,polystyrene-supported imidazole without metal,halide,co-catalyst and solvent,is considered as a suitable catalyst for industrial application.