酸性纳米沸石组装Fe(Cu）金属氧化物簇双功能催化剂的构建及其对烯烃双官能化反应的高效催化

Alkene difunctionalization reactions are important approaches for simultaneous construction of C-N, C-O or C-S bonds in one organic molecule, which was realized mainly through activation of the C=C bond of alkenes. However, these kinds of transformations are commonly studied using homogeneous transition-metal-salts as catalysts, simultaneously, various indispensable additives, such as ligands, oxidants, and organic or inorganic alkali salts are required. This not only complicates the reaction, but also results in process uneconomic, limiting their potential applications. In this study, we utilize the chemisorption and activation of C=C bond on the zeolite acidic sites, the confinement effect of the micropore mouth on metal clusters and the electronic modification of the metal on zeolite framework to embed the metal oxide clusters (MxOy, M=Fe or Cu) at the surface openings of the acidic zeolite crystals for preparation of functionalized and high-efficient metal catalysts in the alkene difunctionalization. The following issues are illuminated through combination of the catalytic activity results and the results from characterization, adsorption experiment and DFT calculation: ① the activation mechanism of the C=C bond in alkenes on the acidic sites and the influence of the activation mechanism on the reaction activity; ② the catalytic action of the MxOy clusters structure on the reactive substrate; ③ the effect of zeolite framework on the modification of MxOy clusters and on the catalytic performance of MxOy clusters. It is expected that these studies would open new perspectives and enlighten widow for the preparation of functionalized metal-zeolite catalysts in synthetic and industrial chemistry.

烯烃的双官能化是通过C=C键活化，在一个分子中同时构建C-N、C-O、C-S键制备生物活性化合物的重要途径。但该类反应不但需要使用金属盐催化剂，还需要有机配体、氧化剂、有机或无机碱等导致反应体系复杂，失去了其潜在的工业应用价值。本项目利用沸石酸中心对烯烃C=C键的吸附活化作用、沸石微孔孔口对金属簇的空间限制作用、沸石骨架对金属的电子修饰作用，将金属氧化物簇(MxOy, M=Fe or Cu)嵌于酸性纳米沸石表面开放的孔口，制备功能化催化剂实现烯烃双官能化反应的高效催化。通过催化剂表征、反应底物吸附、DFT计算等，重点阐明：烯烃分子C=C键在酸中心上的活化机制及对反应性能的影响；嵌于沸石表面孔口的金属氧化物簇的物相结构对另一反应底物的催化作用；沸石骨架原子对金属氧化物簇的修饰作用及对催化性能的影响。期望这些研究能够为开发功能性催化剂在现代有机合成中的应用开启一扇扩大视野、启迪思路的窗口。

现代有机合成反应在制备各种新型生物活性化合物中发挥着越来越重要的作用，但是，大多数反应，如烯烃双官能化，不但需要使用金属盐催化剂，而且还需要有机配体、氧化剂、碱等添加剂，这不仅导致反应体系变得复杂，而且产物分离提纯变得繁琐和困难，限制其在工业中的应用。本项目中，利用酸性沸石表面特殊的羟基性质、微孔孔口对金属簇的空间限制作用，制备了嵌于沸石晶粒表面微孔孔口的Cu和Pd簇催化剂，研究发现：酸性沸石上的Brönsted酸不仅可以诱导吸附活化苯乙烯分子中的C=C键，而且也能够与芳烃醇类分子中的羟基发生作用，促进其吸附活化转化为对应的碳正离子；酸性沸石的阴离子骨架对组装的金属具有电子修饰作用，促进了金属位点在反应条件下发生电子转移；另外，酸性沸石上四配位骨架铝结构中的氧原子通过配位键与金属位点相互作用，形成稳定的空间配位结构，进一步提高了金属的活性。相关研究结果发表在ACS Catal., Appl. Catal. B, Appl.Catal. A国际期刊上。与此同时，也合成了高比表面积的纳米ETS-10沸石，制备了嵌于沸石微孔孔口、高活性的Cu、Ni和Co催化剂，研究发现：沸石上的Lewis碱不仅可以吸附并活化底物分子，而且利于底物分子变为相应的自由基，因此，金属基的纳米ETS-10催化剂在自由基反应中表现出优异的活性和目的产物选择性，相关研究结果发表在Ind. Eng. Chem. Res., Catal. Commun., RSC Adv.期刊上。期望这些研究对设计、开发功能化的沸石基催化剂应用到清洁、高效的有机合成反应中提供一般性的理论认识。