Ion-π interactions in ligand design for anions and main group cations.
Ion-π interactions in ligand design for anions and main group cations.
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DOI：
10.1021/ar300100g
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发表时间：
2013-04-16
影响因子：
18.3
通讯作者：
Johnson, Darren W.
中科院分区：
文献类型：
--
作者：
Watt, Michelle M.;Collins, Mary S.;Johnson, Darren W.
离子与芳香环之间的相互作用是超分子化学领域的一个重要研究方向。最初在气相中表征的原型阳离子-π相互作用现在被认为是蛋白质结构、酶功能的重要贡献者，并且是在许多合成系统中发现的非共价力。互补的“阴离子-π相互作用”-定义为位于芳环质心上的阴离子之间的静电吸引-最近出现为超分子体系中的另一种可逆离子-π相互作用。这种类型的相互作用可以提供新的选择性结合弱碱性，强溶剂化的阴离子，也可能影响结构，生物功能和阴离子转运。这个帐户描述了我们小组在两个领域的离子-π相互作用的努力。我们首先描述了一系列自组装的第15族（磷属元素）-硫醇盐配合物，所有具有突出的三价磷属元素和配体的芳环之间的阳离子-π相互作用。这种结构特征似乎稳定了各种自组装的双核大环化合物，双核M2 L3穴醚类似物，和四核As 4L 2 dyclophane。这些配合物都是非常稳健的，并具有分子内阳离子-π相互作用，这表明这些相互作用可能是第15族元素配体设计的重要特征。我们还强调我们的努力，以表征阴离子和缺电子的芳香环在溶液中的相互作用。补充晶体学和计算研究表明，偏心弱-σ相互作用在稳定阴离子-芳烃加合物中起主导作用，除非存在酸性CH键参与有利的CH···阴离子氢键。在溶液中，弱-σ配合物的核磁共振谱中质子共振出现低场位移。对于更易极化的阴离子，如溴离子和碘离子，我们还通过UV/维斯光谱观察到阴离子结合。初始溶液研究表明，这些可逆的相互作用在有机溶剂中是弱的，但在阴离子结合的霍夫迈斯特偏差可以减轻，如果不是逆转，在卤化物中使用这些阴离子-π型相互作用。
Interactions between ions and aromatic rings are now a mainstay in the field of supramolecular chemistry. The prototypical cation-π interaction, first characterized in the gas phase, is now well known as an important contributor to protein structure, enzyme function, and as a noncovalent force found in many synthetic systems. The complementary “anion-π interaction” – defined as an electrostatic attraction between an anion positioned over the centroid of an aromatic ring – has recently emerged as another reversible ion-π interaction in supramolecular systems. This type of interaction could offer new selectivity in binding poorly basic, strongly solvated anions and may also affect structure, biological function, and anion transport. This Account describes our group’s efforts in ion-π interactions in two areas. We first describe a series of self-assembled Group 15 (pnictogen)-thiolate complexes, all featuring prominent cation-π interactions between the trivalent pnictogen and an aromatic ring of the ligand. This structural feature appears to stabilize a variety of self-assembled dinuclear macrocycles, dinuclear M2L3 cryptand-analogs, and a tetranuclear As4L2 metallocyclophane. These complexes are all remarkably robust and feature intramolecular cation-π interactions, which suggest that these interactions could be an important feature in ligand design for the Group 15 elements. We also highlight our efforts to characterize the interaction between anions and electron-deficient aromatic rings in solution. Complementary crystallographic and computational studies suggest that off-center weak-σ interactions play the dominant role in stabilizing the anion-arene adducts unless an acidic CH bond is present to participate in favorable CH···anion hydrogen bonds. In solution the weak-σ complexes show downfield shifts of the proton resonances in their NMR spectra. With more polarizable anions such as bromide and iodide, we also observe anion binding by UV/Vis spectroscopy. Initial solution studies suggest these reversible interactions are weak in organic solvents, but the Hofmeister bias in anion binding could be mitigated, if not reversed, in the halides using these anion-π type interactions.
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