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首页> 外文期刊>Chemistry: A European journal >“Catalysis in a Tea Bag”: Synthesis, Catalytic Performance and Recycling of Dendrimer-Immobilised Bis- and Trisoxazoline Copper Catalysts
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“Catalysis in a Tea Bag”: Synthesis, Catalytic Performance and Recycling of Dendrimer-Immobilised Bis- and Trisoxazoline Copper Catalysts

机译：“茶袋中的催化”：固定化的树枝状大分子双-和三恶唑啉铜催化剂的合成，催化性能和回收利用

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Bis- and trisoxazolines (BOX and trisox), containing a linker unit in the ligand backbone that allows their covalent attachment to carbosilane dendrimers, have been employed as polyfunctional ligands for recyclable CuII Lewis acid catalysts that were immobilised in a membrane bag. The oxazolines contained an alkynyl unit attached to their backbone that was deprotonated with LDA or BuLi and then reacted with the chlorosilyl termini of zeroth-, first- and second-generation carbosilane dendrimers in the presence of TlPF6. The functionalised dendritic systems were subsequently separated from excess ligand by way of dialysis. The general catalytic potential of these systems was assessed by studying two benchmark reactions, the a-hydrazination of a b-keto ester as well as the Henry reaction of 2-nitrobenzaldehyde with nitromethane. For both reactions the bisoxazoline-based catalysts displayed superior selectivity and, in particular, catalyst activity. The latter was interpreted as being due to the hindered decoordination of the third oxazoline unit, the key step in the generation of the active catalyst, in the immobilised trisox–copper complexes. Solutions of the second-generation dendrimer catalysts were placed in membrane bags, fabricated from commercially available dialysis membranes, with the purpose of catalyst recycling based on dialysis. Overall, the supported BOX catalyst gave good and highly reproducible results throughout the study, whereas the performance of the trisox dendrimer system decreased monotonically. The reason for the different behaviour is the markedly lower activity of trisox-based catalysts relative to those based on the BOX ligand. This necessitated an increased reaction time for each cycle of the trisox derivatives, resulting in higher levels of catalyst leaching, which was attributed to a modification of the structure of the membrane by its exposure to the solvent trifluoroethanol at 40 8C.
机译：双和三恶唑啉（BOX和trisox）在配体主链中包含一个连接单元，允许它们与碳硅烷树状大分子共价连接，已被用作固定在膜袋中的可回收CuII Lewis酸催化剂的多官能团配体。恶唑啉含有连接至其骨架的炔基单元，该炔基单元用LDA或BuLi去质子化，然后在TlPF6存在下与零代，第一代和第二代碳硅烷树状大分子的氯甲硅烷基末端反应。随后通过透析将功能化的树突系统与过量配体分离。通过研究两个基准反应，即β-酮酸酯的α-酰肼化以及2-硝基苯甲醛与硝基甲烷的亨利反应，评估了这些系统的总体催化潜力。对于这两个反应，基于双恶唑啉的催化剂显示出优异的选择性，特别是催化剂活性。后者被认为是由于固定的三羟甲基铜化合物中第三个恶唑啉单元的阻碍配位，这是活性催化剂生成的关键步骤。将第二代树状聚合物催化剂的溶液放置在由可商购的透析膜制成的膜袋中，目的是基于透析回收催化剂。总体而言，负载的BOX催化剂在整个研究过程中均提供了良好且高度可重复的结果，而trisox树枝状聚合物系统的性能却单调下降。行为不同的原因是相对于基于BOX配体的三s基催化剂，其活性明显较低。这就需要增加三环氧化物衍生物每个循环的反应时间，导致催化剂浸出水平更高，这归因于膜在40 8 C下暴露于溶剂三氟乙醇中而改变了膜的结构。

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