Catalysis of an Aldol Condensation Using a Coordination Cage
Catalysis of an Aldol Condensation Using a Coordination Cage
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DOI：
10.3390/chemistry2010004
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发表时间：
2020-01
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影响因子：
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通讯作者：
Cristina Mozaceanu;Christopher G. P. Taylor;Jerico R. Piper;S. Argent;M. Ward
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文献类型：
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作者：
Cristina Mozaceanu;Christopher G. P. Taylor;Jerico R. Piper;S. Argent;M. Ward
用M8L12立方配位笼（Hw）催化吲哚-1,3-二酮（ID）在水中缩合生成“苯酮”。在弱酸性条件下（pH 3-4）反应的绝对速率很慢，但在没有催化剂的情况下是检测不到的。在水中，ID在Hw空腔中的结合常数约为2.4（±1.2）× 103 M−1，结合的∆G为- 19.3（±1.2）kJ mol−1。该配合物的晶体结构显示，有两个客体ID分子堆叠在腔内，填充系数为74%，另一个分子与笼的外表面形成氢键。我们认为，催化作用的发生是由于笼形结构的16+表面稳定了ID的烯醇阴离子，由于笼形结构的疏水性，它也吸引了中性ID分子到笼形结构表面。因此，笼通过两种不同的相互作用将中性ID及其烯化阴离子聚集在一起来催化反应，正如对照实验所显示的那样，反应发生在笼的外表面而不是笼腔内。
The aldol condensation of indane-1,3-dione (ID) to give ‘bindone’ in water is catalysed by an M8L12 cubic coordination cage (Hw). The absolute rate of reaction is slow under weakly acidic conditions (pH 3–4), but in the absence of a catalyst it is undetectable. In water, the binding constant of ID in the cavity of Hw is ca. 2.4 (±1.2) × 103 M−1, giving a ∆G for the binding of −19.3 (±1.2) kJ mol−1. The crystal structure of the complex revealed the presence of two molecules of the guest ID stacked inside the cavity, giving a packing coefficient of 74% as well as another molecule hydrogen-bonded to the cage’s exterior surface. We suggest that the catalysis occurs due to the stabilisation of the enolate anion of ID by the 16+ surface of the cage, which also attracts molecules of neutral ID to the surface because of its hydrophobicity. The cage, therefore, brings together neutral ID and its enolate anion via two different interactions to catalyse the reaction, which—as the control experiments show—occurs at the exterior surface of the cage and not inside the cage cavity.