催化活性点分离的双功能负载型催化剂的构建和串联不对称反应研究

Realization of recycling of expensive transit-metal-based catalysts and development of atom economical tandem reactions are two important research directions in the field of green chemistry. In this research, taking advantage of yolk-shell-structured mesoporous silica, we construct catalytically active site-isolated bifunctional heterogeneous catalysts by using a site-isolated strategy to immobilize chiral and achiral organometallic complexes in yolk and shell part, and apply them in enantioselective tandem reactions that is difficult in a homogeneous catalysis system arising from incompatibility of bimetallic complexes. Meanwhile, it is expected to avoid the loss of expensive metals and to realize the recycling of bifunctional heterogeneous catalysts..In this proposal, by screening two types of chiral/achiral ligand-based silica resources, utilizing step-by-step assembly strategy and the coordinated optimization between metals and ligands, we assemble three series of yolk-shell-structured catalytically active site-isolated bifunctional heterogeneous catalysts. Their applications in four enantioselective tandem reactions are explorted. By adjusting the property of hydrophobicity/hydrophilicity for their silicate networks, highly reaction rate are obtained in the enantioselective tandem reactions. Based on the investigations of their confinement effect and synergistic effect, their roles in heterogeneous asymmetric catalysis reactions are expatiated and the enantioselectivities are improved. Furthermore, by taking advantage of the supported catalysts, it offers a possibility to disclose the nature of their catalytic mechanisms in the enantioselective tandem reactions from a view of heterogeneous catalysis. Thus, it is highly expected that series of heterogeneous catalysts with excellent catalytic activity, excellent enantioselectivity and high recyclability could be developed from this research.

实现昂贵金属催化剂的回收再利用和发展原子经济的串联反应是绿色化学的两个重要研究方向。本研究拟利用蛋壳结构的介孔硅，采用活性点分离的策略分别在蛋核和壳上负载手性和非手性两类有机金属配合物，构筑催化活性点分离的双功能负载型催化剂，试图发展在均相条件下因两类金属配合物不兼容而导致难以完成的串联不对称反应；同时利用负载型催化剂的优势解决昂贵金属流失实现双功能催化剂的回收再利用。.本项目选用含有手性配体和非手性配体的两系列硅源，采用分步组装，及配体与金属的配位优化方法制备三个系列具有蛋核结构的活性点分离的双功能负载型催化剂，发展四类串联不对称反应；通过调控催化剂材料的亲疏水性能提升串联反应的反应速度；利用催化剂材料的协同效应和限域效应提高串联反应的催化活性和対映选择活性；发挥负载型催化剂材料的优势探索双功能催化剂在串联反应中的反应历程。以期发展系列高效、高对映选择性和可重复使用的双功能负载型催化剂。

实现昂贵金属催化剂的回收再利用和发展原子经济的串联反应是绿色化学研究领域的两个重要研究方向。本项目以设计具有活性点分离特色的双功能催化剂为出发点，通过解决了两类双活性中心的不兼容性来探讨均相共催化难以完成的串联不对称反应。该类双功能催化不仅能有效实现贵催化剂回收再利用而且可完成原子经济的连续不对称反应。. 针对催化活性点分离的双功能催化剂的构建，采用不同类型的介孔硅（蛋壳、空壳、核壳、聚合物包裹硅球）为载体，利用硅材料的不同位置或者壳/核的分离特性，通过组合策略（键链/离子对吸附/包埋），实现了不兼容的催的两个活性物种的分离负载，建立了系列具备活性点分离特色的双功能催化剂的构筑方法。在串联反应中发现了一些重要的作用规律，对多相双功能催化剂设计具有借鉴意义。1）蛋壳和空壳结构的介孔硅的空腔尺寸或孔道尺寸所导致的限域效应对串联反应的反应速度和协同效应有显著的影响。如项目报道的卡宾金/手性钌催化剂在合适的空腔和孔道尺寸能促进偶联/还原的不对称串联反应的催化效率和对映选择性能；2）负载的硅材料的亲疏水性能/两亲性能的调节有利于催化反应的高效完成，如项目报道的两亲性的膦钯配合物/手性钌的双功能催化剂能高效进行两相的串联反应。3）双载体具有明显的优势，如本项目的聚合物包裹硅的双功能催化剂，可方便在外部的聚合物和内部的硅进行分离负载，能简化负载流程减少对手性活性中心的影响；更为重要的是，通过对聚合物改性，可构建具有刺激相应功能的智能型双功能催化剂，这些催化剂不仅能控制反应次序，而且可以调节反应进程，在高对映选择性手性产物的合成，特别是远程的双或多手性骨架中心的制备具有明显优势。如报道的方酰胺/手性钌催化剂能高效地用于双手性中心的制备。