Synthesis of Chiral Dendrimer-Encapsulated Nanoparticle (DEN) Catalysts
Synthesis of Chiral Dendrimer-Encapsulated Nanoparticle (DEN) Catalysts
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DOI：
10.1007/s11244-018-0955-9
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发表时间：
2018-05
影响因子：
3.6
通讯作者：
Zhihuan Weng;F. Zaera
中科院分区：
文献类型：
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作者：
Zhihuan Weng;F. Zaera
开发了几种用于制备手性树枝状聚合物包裹的Pt纳米颗粒（Pt DEN）催化剂的合成策略。在一种方法中，首先使用“点击”化学和癸二酸作为接头用辛可尼定衍生化常规OH封端的聚酰胺胺（PAMAM）树枝状聚合物。第四代PAMAM树状聚合物中多达一半的64个末端OH基团可以以这种方式修饰，并且可以通过在合成期间控制CD：PAMAM比率来调节总体辛可尼定含量。然后将铂纳米颗粒加入到这些辛可尼定修饰的树枝状聚合物中。在另一种途径中，首先使用PAMAM制备常规Pt DEN，然后用辛可尼丁衍生化所得材料。这两种合成路线被证明是成功的，但导致材料具有不同的光谱和催化性能，大概是因为第一种情况下的金属纳米颗粒是在辛可尼定官能团附近制成的，在树枝状聚合物结构的外部而不是在其内部，正如第二种方法所认为的那样。在第二个方案中还确定了与合成过程中Pt纳米颗粒表面中毒相关的潜在并发症。这些催化剂用于α-酮酯氢化的催化性能在所有情况下都被证明是差的，推测是因为与树枝状聚合物结构内部的质量传递限制和外部手性分支的受限柔性相关的许多问题，这些外部手性分支可能不能与催化表面相互作用。然而，有趣的综合经验教训，从我们的工作与其他应用程序的潜在价值。
Several synthetic strategies were developed for the preparation of chiral dendrimer-encapsulated Pt nanoparticle (Pt DEN) catalysts. In one approach, regular OH-terminated polyamidoamine (PAMAM) dendrimers were first derivatized with cinchonidine using “click” chemistry and sebacic acid as a linker. As many as half of the 64 terminal OH groups in a 4th generation PAMAM dendrimer could be modified this way, and the overall cinchonidine content could be tuned by controlling the CD:PAMAM ratio during synthesis. Platinum nanoparticles were then added to these cinchonidine-modified dendrimers. In an alternative route, regular Pt DENs were made first using PAMAM, and the resulting material was then derivatized with cinchonidine. The two synthetic routes proved successful, but led to materials with different spectroscopic and catalytic properties, presumably because the metal nanoparticles in the first case are made near the cinchonidine functionality, in the outside of the dendrimer structure rather than in its inside, as believed to be the case with the second procedure. A potential complication related to the poisoning of the Pt nanoparticle surface during synthesis was also identified in the second protocol. The catalytic performance of these catalysts for the hydrogenation of α-ketoesters proved to be poor in all cases, presumably because of a number of problems associated with mass transport limitations inside the dendrimer structures and restricted flexibility of the outer chiral branches, which may not be able to interact with the catalytic surfaces. Nevertheless, interesting synthetic lessons were derived from our work with potential value for other applications.