基于氮杂环卡宾的金属-有机框架的合成与催化性能研究

N-heterocyclic carbene (NHC) complexes are widely used in the organic transformations due to their high thermal stabilities and excellent catalytic performance. Metal–organic frameworks (MOFs) are tunable porous coordination polymers which are prepared by joining organic links and inorganic building units, and their high stability and designability enable them to be the potential excellent supporting materials for immobilized catalysts. Immobilizing NHC compounds in the MOFs would overcome the difficulty in separation of the product and recycling of the catalyst for the homogenous catalysis. And meanwhile, both the selective accessibility for organic substrates of MOFs and high catalytic performance of homogeneous catalysts can be integrated in the resulting immobilized materials, which make them very good candidates for heterogeneous catalysts. This project principally aims to develop effective methods for the construction of MOFs with NHC compounds by using tetrazolyl functionalized imidazolium salts as synthetic precursors. After a variety of NHCs-based MOFs were obtained, their catalytic performance in organic transformations will be thoroughly explored. By taking advantage of comprehensive characterization of the immobilized materials and evaluation of their catalytic performance in comparison to the homogeneous analogues, we provide complete evidence for the mechanisms involved immobilization as well as catalytic reactions. These studies can provide important basis for developing efficient immobilized catalysts based on MOFs.

氮杂环卡宾化合物由于其高度的稳定性以及优异的催化活性而广泛应用于各种有机转化中。由有机配体连接无机构筑单元形成的金属-有机框架（MOFs）是一类结构可调的多孔配位聚合物，其框架的相对稳定性和可设计性为其作为负载型催化剂载体提供了基础。将氮杂环卡宾化合物通过负载的方式引入到MOFs中不仅可以解决均相催化剂循环使用和产物不易分离的难题，产生的负载型材料还可以有效结合MOFs框架对有机底物的选择性以及氮杂环卡宾化合物的催化高效性，是一类潜在的优良多相催化剂。本课题拟以四氮唑基官能化的咪唑盐为合成前驱体，系统探索基于氮杂环卡宾的MOFs的合成方法。在拓展结构多样化的基础上，开发它们在催化有机转化中的应用。通过对负载型材料的系统表征以及催化性能评估，为深入理解负载过程和催化机理的研究提供充分的证据。该研究将为开发基于MOFs的高效负载型催化剂提供重要依据。

二氧化碳（CO2）的吸附与转化研究对于解决目前日益加剧的温室效应具有十分重要的意义。金属-有机框架（MOFs）易于调节的孔结构、易于修饰的金属节点和有机配体等性质赋予其在CO2吸附与催化转化应用方面独特的优势。申请人通过本项目的支持开展了这方面的研究，并取得了系列进展：（一）将高密度的银簇作为节点用于构筑稳定的二维MOFs，获得了迄今最为高效的催化炔丙基胺与CO2环化的多相催化剂；（二）通过对MOF节点进行金属掺杂的方式有效提高其CO2吸附能力。这些研究结果揭示并验证了提高MOFs在CO2固定以及转化性能的有效策略，为设计与合成基于MOFs的功能材料提供了新的启示。