Endohedrally Functionalized Metal–Organic Cage-Cross-Linked Polymer Gels as Modular Heterogeneous Catalysts

The immobilization of homogeneous catalysts onto supports to improve recyclability while maintaining catalytic efficiency is often a trial-and-error process limited by poor control of the local catalyst environment and few strategies to append catalysts to support materials. Here, we introduce a modular heterogenous catalysis platform that addresses these challenges. Our approach leverages the well-defined interiors of self-assembled Pd12L24 metal–organic cages/polyhedra (MOCs): simple mixing of a catalyst-ligand of choice with a polymeric ligand, spacer ligands, and a Pd salt induces self-assembly of Pd12L24-cross-linked polymer gels featuring endohedrally catalyst-functionalized junctions. Semi-empirical calculations show that catalyst incorporation into the MOC junctions of these materials has minimal affect on the MOC geometry, giving rise to well-defined nanoconfined catalyst domains as confirmed experimentally using several techniques. Given the unique network topology of these freestanding gels, they are mechanically robust regardless of their endohedral catalyst composition, allowing them to be physically manipulated and transferred from one reaction to another to achieve multiple rounds of catalysis. Moreover, by decoupling the catalyst environment (interior of MOC junctions) from the physical properties of the support (the polymer matrix), this strategy enables catalysis in environments where homogeneous catalyst analogues are not viable, as demonstrated for the Au­(I)-catalyzed cyclization of 4-pentynoic acid in aqueous media.将均相催化剂固定于载体以提升回收效率同时维持催化性能，通常需依赖试错法完成，且受限于两大瓶颈：一是难以精准调控局部催化剂环境，二是可用于将催化剂接枝至载体材料的成熟策略匮乏。于此，我们提出一种模块化多相催化平台，以解决上述挑战。该策略依托自组装Pd₁₂L₂₄金属有机笼/多面体（metal–organic cages/polyhedra, MOCs）的规整内部空腔：将目标催化剂配体、聚合物配体、间隔配体与钯盐简单混合，即可诱导形成Pd₁₂L₂₄交联的聚合物凝胶，其内部包含端锚定催化剂功能化的连接位点。半经验计算结果表明，将催化剂引入此类材料的MOC连接位点，对MOC的几何结构仅产生极小影响，由此可形成定义明确的纳米限域催化区域，该结论已通过多种实验技术得到验证。鉴于此类自立式凝胶独特的网络拓扑结构，无论其笼内催化剂组成如何，均具备优异的机械稳定性，可通过物理操作从一个反应体系转移至另一反应体系，从而实现多轮催化循环。此外，通过将催化剂环境（MOC连接位点内部）与载体的物理性质（聚合物基质）解耦，该策略可在均相催化剂无法适用的环境中实现催化，例如在水介质中进行的Au(I)催化4-戊炔酸环化反应，便验证了这一特性。