Halide recognition by tetraoxacalix[2]arene[2]triazine receptors: concurrent noncovalent halide-pi and lone-pair-pi interactions in host-halide-water ternary complexes.
Halide recognition by tetraoxacalix[2]arene[2]triazine receptors: concurrent noncovalent halide-pi and lone-pair-pi interactions in host-halide-water ternary complexes.
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DOI：
10.1002/anie.200801705
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发表时间：
2008-09
影响因子：
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通讯作者：
De‐Xian Wang;Qi-Yu Zheng;Qi‐Qiang Wang;Mei-Xiang Wang
中科院分区：
文献类型：
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作者：
De‐Xian Wang;Qi-Yu Zheng;Qi‐Qiang Wang;Mei-Xiang Wang
阴离子识别由于其在生物和环境科学中的重要性而受到广泛关注。已经合成了大量的合成主体分子用于阴离子络合的目的。值得注意的是，几乎所有合成的阴离子受体都是为了利用氢键、静电相互作用、疏水效应和与金属离子的配位而设计的。然而，近年来，人们对阴离子-p相互作用，即阴离子与缺电子对芳烃物种之间的相互作用越来越感兴趣。例如，许多理论研究已经报道了阴离子与芳香族化合物如全氟、硝基和氰基取代的苯、吡啶、吡嗪和三嗪衍生物的非共价相互作用。然而，支持阴离子-p与电荷中性芳烃的纯粹非共价相互作用的实验证据非常罕见。最近的一项研究表明，确实非共价阴离子-p相互作用的贡献小于氢键形成的复杂的氯化物-p-C6FnH6n（n = 0 - 5）。杂原子桥连杂芳杯芳烃是一类新型的大环化合物。由于它们的电子性质，一些杂原子（例如氮）可以采用不同的构型以与相邻的杂芳环形成不同程度的共辄，从而产生大环杂原子连接的杂芳族杯芳烃，其具有与常规杯芳烃不同的构象和尺寸。它们最近被用作超分子化学中的多功能主体分子。作为杂原子桥连的杂芳族杯芳烃的典型实例，四氧杂杯[2]芳烃[2]三嗪1（方案1）已被报道采用预组织的1，3-交替构象，产生由两个p-缺电子三嗪环形成的裂缝。我们设想，这个缺p电子的空腔将作为一个受体，通过p-阴离子相互作用与阴离子相互作用。在此，我们报告了四氧杂杯[2]芳烃[2]三嗪主体分子的卤化物识别，以及三嗪对卤化物-p相互作用的相当大的取代基效应。最令人惊讶的是，X射线晶体学揭示了水、氯或溴与二氯取代的四氧杂杯[2]芳烃[2]三嗪主体之间的非共价p-卤化物和p-孤对电子相互作用的同时形成。通过分光光度法，研究了卤代物与二氯取代四氧杂杯[2]芳烃[2]三嗪1（一种大环化合物）的相互作用。如图1（上图）所示，用四丁基氟化铵滴定后，1的UV/维斯光谱中在302 nm处形成了新的吸收带。1与四丁基氟化铵的相互作用还导致主体分子在304 nm处的发射信号淬灭，伴随着在452 nm处出现新的荧光发射（图1（底部））。这些光谱变化不是由样品中的阳离子或水分引起的，因为使用高氯酸四丁基铵或水作为滴定剂的对照实验显示对1的吸收或发射光谱没有影响。然后研究了四丁基氯化铵和四丁基溴化铵对1的光度滴定。在相同条件下，用氯离子和溴离子滴定的结果与用氟离子滴定的结果有很大的不同。例如，氯化物或溴化物的添加不影响主体方案1的UV/维斯光谱。二氯取代的四氧杂杯[2]芳烃[2]三嗪1及其转化为2和3。a）H2，Pd/C，Na0Ac/HOAc，50 ° C，12小时，82%。B）Me2NH·HCl，K2CO3，THF，70 ° C，9小时，65%。
Anion recognition has attracted much attention because of its importance in biological and environmental sciences. A large number of synthetic host molecules have been synthesized for the purpose of anion complexation. Noticeably, almost all synthetic anion receptors were designed to exploit hydrogen bonding, electrostatic interactions, hydrophobic effects, and coordination to metal ions. In recent years, however, there has been a growing interest in anion–p interactions, the interaction between an anion and an electron-deficient p-arene species. A number of theoretical studies, for example, have reported the noncovalent interactions of anions with aromatic compounds such as perfluoro-, nitro-, and cyano-substituted benzene, pyridine, pyrazine, and triazine derivatives. Experimental evidence to support the purely noncovalent anion–p interaction with charge-neutral arenes, however, is very rare. A recent study indicated indeed that the noncovalent anion–p interaction contributed less significantly than hydrogen bonding to the formation of the complex chloride–p-C6FnH6 n (n= 0– 5). Heteroatom-bridged heteroaromatic calixarenes are an emerging type of novel macrocyclic molecules. Because of their electronic nature, some heteroatoms, such as nitrogen, can adopt different configurations to form varying degrees of conjugation with adjacent heteroaromatic rings, resulting in macrocyclic heteroatom-linked heteroaromatic calixarenes with conformations and sizes different to those of conventional calixarenes. They have recently been utilized as versatile host molecules in supramolecular chemistry. As a typical example of heteroatom-bridged heteroaromatic calixarenes, tetraoxacalix[2]arene[2]triazine 1 (Scheme 1) has been reported to adopt a pre-organized 1,3-alternate conformation, yielding a cleft formed by two p-electron deficient triazine rings. We envisioned that this pelectron-deficient cavity would act as a receptor to interact with anions through p–anion interactions. Herein, we report halide recognition by tetraoxacalix[2]arene[2]triazine host molecules, and considerable substituent effects of the triazine on the halide–p interaction. Most astonishingly, X-ray crystallography revealed the concurrent formation of noncovalent p–halide and p–lone-pair electron interactions between water, chloride, or bromide, and the dichlorosubstituted tetraoxacalix[2]arene[2]triazine host. By means of spectrophotometric measurements, we examined the interaction of halides with dichloro-substituted tetraoxacalix[2]arene[2]triazine 1, a macrocycle readily accessible in large scale and good yield from the coupling of resorcinol and cyanuric acid chloride, under very mild conditions. As illustrated in Figure 1 (top), a new absorption band formed at 302 nm in the UV/Vis spectrum of 1 upon titration with tetrabutylammonium fluoride. Interaction of 1 with tetrabutylammonium fluoride also led to quenching of the host molecule emission signal at 304 nm with the concomitant emergence of a new fluorescence emission at 452 nm (Figure 1 (bottom)). These spectral changes were not caused by the cation or by moisture in the sample, as the control experiments using tetrabutylammonium perchlorate or water as a titrant showed no influence on either the absorption or the emission spectrum of 1. We then investigated the spectrophotometric titration of 1 with tetrabutylammonium chloride and tetrabutylammonium bromide. Under identical conditions, the outcomes of titration with chloride and bromide were very different to that for the titration with fluoride. For example, addition of chloride or bromide did not affect the UV/Vis spectrum of the host Scheme 1. Dichloro-substituted tetraoxacalix[2]arene[2]triazine 1 and its transformations into 2 and 3. a) H2, Pd/C, NaOAc/HOAc, 50 8C, 12 h, 82%. b) Me2NH·HCl, K2CO3, THF, 70 8C, 9 h, 65%.