具有双功能活性位点的稀土簇MOFs的设计合成及催化串联反应研究

Metal organic framework (MOFs) are porous crystalline materials the structure of which is comprised of nodes of metal ions or small clusters of metal ions connected through metal coordination interactions with organic linkers. MOFs are widely used in the field of catalysis. Cascade reaction is to combine two or more independent reactions into a cascade process, which possesses the advantages of atomic economy, and environment friendly characteristics. It requires bi-/multifunctional catalysts comprised of more than one type of active site. A large versatility in composition and structures and High surface area offered by MOFs are very adequate to develop bi- and multifunctional catalysts suitable for cascade reactions. This project plan to construct the polynuclear rare-earth cluster-based MOFs, which possess the Lewis acid sites and the Brønsted base sites in their structure simultaneously, from the preliminary synthesized pentanuclear and hexanuclear rare earth metal ion cluster-based MOFs. Meanwhile, the target materials and polyoxometalate composite materials can be obtained via the post-synthesized methods. The in-situ Py-IR and CO-IR enable to detect the type and strength of active sites within the materials. According to the features of target multifunctional catalysts, cascade reactions were designed as the follows: (1) Deacetalization to give aldehyde and Knoevenagel condensation reaction of nitrile compounds and aldehydes. (2) Oxidation of the olefins to epoxides, which further participation in the ring-opening reaction of epoxides and trimethylsilylazide. (3) Oxidation of the olefins into the epoxides, which further reacted with CO2 resulting in the formation of cyclic carbonates. The reaction mechanism will be explored. The above reactions exhibit many advantages, such as the easily available of reactants, their characteristic of environmentally friendly and the extensive applications of products.

金属有机骨架材料（MOFs）是由金属离子或簇与有机桥联配体形成的多孔晶态材料。串联反应指的是两步或两步以上的反应连续发生，具有原子经济、环境友好的优点。MOFs的可设计性及可调控性可用作串联反应的双功能催化剂。本项目拟从前期合成的稀土簇MOFs出发，构建同时具有Lewis酸、Brønsted碱位点的稀土簇MOFs。并通过后合成修饰合成具有Lewis酸、Brønsted酸稀土簇MOFs/杂多酸复合材料。用原位红外光谱研究催化活性位点的类型及强度。并把所合成的双功能催化剂应用于有机串联反应中，主要包括以下几个方面：1.缩醛脱甲醇生成醛，醛与腈类化合物的诺林格尔缩合反应。2.烯烃氧化生成环氧乙烷，叠氮基三甲基硅烷做亲核试剂的环氧乙烷开环反应。3.烯烃氧化生成环氧乙烷，环氧乙烷与二氧化碳环加成生成碳酸丙烯酯。并研究其反应机理。上述拟开展反应具有原料易得、环境友好、产物用途广泛等优点。

金属有机骨架材料(MOFs)作为一种新兴的多孔材料，不但具有极高的表面积、可调节的孔尺寸、可循环性和大量的活性位点，而且还可以通过预功能化和后合成修饰的方法向金属有机骨架材料中引入多种活性位点，所以近年来在催化领域发展迅速，被广泛的应用于非均相催化方面。串联反应和多组分反应，都可以减少化学品的使用，减少污染物的产生和缩短反应时间，是经济，有效和环境友好型的化学方法，吸引了越来越多研究者的兴趣。我们采用12连接的六核稀土簇次级结构单元[Ln6(OH)8(COO-)12]和配体H2BDC-NH2通过溶剂热的方法合成一系列六核稀土簇基的MOFs，[(CH3)2NH2]2[Ln6(OH)8(BDC-NH2)6(H2O)6](solv)x (Ln =Yb, Dy, Sm)。在溶剂热的条件下制备了一种新型的双功能核壳MOFs@POPs复合材料。提出了一个新颖的策略，通过 π-π 堆积的相互作用力构筑了一种多级孔的MOF@COF复合材料。制备的材料具有极好的化学稳定性、热稳定性、可回收性和持久的催化活性。可作为一锅串联反应的高效双功能催化剂，可以有效地催化deacetalization-Knoevenagel缩合串联反应。. 在聚丙烯腈(PAN)纳米纤维上接枝γ-氨基丁酸(GABA)，然后再在纤维表面原位生长Eu-MOF晶体制备稀土MOF膜复合材料。采用2,6-奈二酸合成了稀土簇MOF材料[(CH3)2NH2][RE3(OH)(NDC)3(HCOO)3] (RE = Y, Tb, Er)；采用功能性线性二羧酸配体构筑的合成了系列六核簇MOFs。并研究该材料催化CO2环加成反应的性能。