原子精确的Pd基金属团簇及催化Suzuki-Miyaura反应的研究

Due to the size polydispersity and structural heterogeneity of conventional Pd nanocatalysts, it is difficult to understand of the origin of palladium nanocatalysis. Focusing on these key issues, in this project, the main research objects are a class of Pd-based nanoclusters. This project consists of three parts. The facile solution-based strategies are explored to synthesize Pd-based nanoclusters. Synthetic routes and reaction conditions (ligands, solvents, reluctants, etc.) are systematically investigated to fine-tune the sizes, compositions and specific atoms of Pd nanoclusters. .Specially, a specific number of foreign atoms (e.g. Au，Ag，Cu，Ni) can be doped to produce heteroatom-substituted Pd-based bimetallic clusters. Subsequently, their crystal structures are obtained through slow evaporation and liquid/liquid diffusion. Total structure determination of atomically precise Pd-based clusters is further characterized by single crystal X-ray diffraction analysis and electrospray ionization mass spectrum. .And on this basis, these well-defined Pd-based nanoclusters are expected to represent a promising class of model catalysts, will provide new opportunities for achieving a precise correlation between structure (electronic and atomic structure) and catalytic activities. The catalysis of monodisperse palladium-based nanoclusters with atomically precise structure could be used as a bridge between homogeneous and heterogeneous Pd catalysis. Herein, Suzuki-Miyaura reaction is chosen a target in the hope of understanding the catalytic behavior of Pd-based clusters at the atomic or molecular level. The research will contribute to the design of high efficient Pd catalysts.

本项目以Pd团簇及Pd系双金属团簇为研究对象。针对当前Pd纳米催化剂合成中存在尺寸和结构无法绝对单一、可控的基本问题，拟开展：(1) 探索简易的Pd团簇及Pd系双金属团簇的液相合成方法，从反应路线和反应条件（表面配体、溶剂、还原剂等）出发，调控Pd团簇及Pd系双金属团簇的尺寸、组成和原子数，制备原子数确定的Pd团簇或部分异金属（Au、Ag、Cu、Ni）替代的Pd系双金属团簇；(2) 通过液-液扩散和溶剂挥发等方法培养Pd基金属团簇的单晶，并通过X-射线单晶衍射和电喷雾离子化质谱等手段对其确切晶体结构进行解析；(3) 以具有确定结构的Pd基金属团簇为模型催化剂，有望揭示其结构（电子结构、原子结构等）与催化性能之间清晰的构效关系，从而为研究均相和异相Pd催化过程构架桥梁。拟以Suzuki-Miyaura反应为模型反应，从原子、分子水平理解其催化本质，为设计新型高效Pd催化剂奠定基础。

原子精确的金属纳米团簇为从分子水平上理解催化过程提供了可能。本项目中，在合成钯等金属团簇的基础上，考察了所制备团簇催化剂在Suzuki-Miyaura等催化反应中的催化性能，并对其反应机理进行了合理的推测。主要结果如下：.1. 发展了钯等精确原子团簇的合成策略。设计合成并精确表征了[Pd3Cl(PPh2)2(PPh3)3]+团簇(缩写为Pd3Cl)。团簇中三中心，两个电子的Pd-Pd-Pd键和桥接配体保证了三角形Pd3簇骨架的完整性。此外，合成了（4-氯苯基）膦和氯配体保护的Au11纳米团簇。值得注意的是，团簇表面配体的调控对其结构也是至关重要的。采用一种多配体方法制备了两个手性银纳米团簇；利用两相配体交换策略合成了水溶性金银纳米团簇。.2. 利用高稳定性的Pd3Cl团簇作为模型催化剂，研究了Pd3Cl团簇催化Suzuki-Miyaura偶联反应的催化过程。研究表明，Pd3Cl催化的反应机理与经典的均相钯催化剂的催化机理显著不同。在反应过程中，转移金属化是Pd3Cl催化Suzuki-Miyaura反应的第一步。Pd3Cl首先与苯硼酸反应生成中间体Pd3Ar。底物Ar-Br进攻中间体Pd3Ar形成最终产物。值得注意的是，Br-可以取代中间体Pd3Ar中的Ar-生成Pd3Br，Pd3Br在随后的反应中继续充当催化剂的角色。.3. 基于Pd3Cl团簇的异相催化剂的设计与催化应用。利用金属-载体相互作用策略构建了可回收的Pd3Cl/钛酸盐纳米管多相催化剂，其在催化苯甲醇有氧氧化反应中显示优异的性能。此外，通过静电吸引策略，将带正电荷的Pd3Cl团簇与带负电荷的SBA-15棒复合，理性设计了Pd3Cl/SBA-15催化剂，该催化剂在Sonogashira C-C偶联反应显示出良好的催化活性和可回收性。