A cyclic [4]rotaxane that behaves as a switchable molecular receptor: formation of a rigid scaffold from a collapsed structure by complexation with copper(I) ions.
A cyclic [4]rotaxane that behaves as a switchable molecular receptor: formation of a rigid scaffold from a collapsed structure by complexation with copper(I) ions.
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一种充当可切换分子受体的环状[4]轮烷：通过与铜(I)离子络合从塌陷结构形成刚性支架。
DOI：
10.1002/anie.201004008
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发表时间：
2010
影响因子：
--
通讯作者：
Y. Trolez
中科院分区：
文献类型：
--
作者：
J. Collin;F. Durola;V. Heitz;F. Reviriego;J. Sauvage;Y. Trolez
最有效的分子受体通常是具有中空部分的刚性建筑物，该中空部分能够通过基质与主体的络合部分之间的电子和几何互补性来容纳络合物质。通过与诱导适应相关的生物过程进行类比，其他主客体过程是基于能够使其几何形状适应待识别物种的柔性宿主。在索烃、轮烷和分子机器的非常活跃的领域中，很少有系统被认为是分子客体的感兴趣的受体。对这一研究领域的主要贡献之一是各种互锁化合物对阴离子的识别。我们的研究小组最近也描述了一种[3]轮烷，它能够作为一种可调节的受体。该系统由两个环组成，两个环通过一个轴螺纹连接，环可以在轴上自由移动。络合单元是锌卟啉，其牢固地附着于轮烷环，并且能够与由带有4-吡啶基的双末端官能化化合物组成的给定底物相互作用。结果表明，主机在其无金属形式的显着的几何适应性允许与客人的非常不同的大小的相互作用。本文报道了一种相关化合物，即环状双卟啉[4]轮烷的性质，它的行为与以前研究的线性[3]轮烷的行为完全不同。与后一种化合物相反，不含金属的[4]轮烷完全塌陷，不显示任何络合特性，而铜（I）络合化合物是二胺和联吡啶底物的良好和选择性受体，因为四个金属中心的支架效应（图1）。因此，识别过程可以通过将游离配体与四个Cu离子络合或使金属络合物脱金属来分别打开和关闭。轮烷1 [7]及其相关的[4]假轮烷的合成已经报道。1是脱金属使用大量过量的KCN（约。50当量）。将反应混合物搅拌2.5小时，然后通过硅胶色谱法纯化粗产物，得到脱金属的轮烷2，产率为88%（方案1）。轮烷2通过1H NMR谱（COSY、ROESY、DOSY）、电喷雾质谱和UV/维斯光谱进行表征。非常令人惊讶的是，轮烷2的1H NMR谱显示出与金属化体系1相比相当大的对称性损失，在金属化体系1中所有Cu中心以及四个终止剂是化学等价的。因此，仅需考虑四分之一的轮烷1用于完整的NMR归属。相比之下，与轮烷1的1H NMR信号相比，2的1H NMR信号加倍。可以鉴定出具有显著不同的1H NMR信号的两种不同的终止剂，因此可以鉴定出显著不同的环境。NOE之间的相互作用2的一些部分被清楚地检测到，而这些片段太远，彼此在1显示任何相互作用。例如，一种类型的终止剂的tBu基团的一些质子（H-re '; r=“棒”）与2中的1，10-菲咯啉单元的质子H-b4'和Hb 7 '（B=双大环）相关，因此表明该终止剂和给定的1，10-菲咯啉单元彼此非常接近。由于双大环和轴都是刚性的，两个这样的片段之间的接近倾向于表明2的地形与1的地形明显不同，并且2具有完全塌陷的结构。这一假设得到了额外观察的证实。例如，（CH 2）3接头（H-r9）的一个质子在解络合时被强烈屏蔽;相应的信号从图1移动。识别过程的原理，通过金属化或去金属化来开启和关闭。小灰点：铜离子;灰色方块：卟啉;黑色双箭头：客体化合物。1和2的化学结构示于方案1中。
The most efficient molecular receptors are usually rigid edifices with a hollow part that is able to accommodate the complexed species through an electronic and geometrical complementarity between the substrate and the complexing parts of the host. By analogy with biological processes related to induced fit, other host–guest processes are based on flexible hosts that are able to adapt their geometry to that of the species to be recognized. In the very active field of catenanes, rotaxanes, and molecular machines, very few systems have been considered as interesting receptors for molecular guests. One of the main contributions to this subfield of research is that of anion recognition by various interlocking compounds. Our research group has also recently described a [3]rotaxane that is able to act as an adjustable receptor. The system consists of two rings threaded by an axis on which the rings can move freely. The complexing units are zinc porphyrins that are firmly attached to the rotaxane rings and are able to interact with given substrates that consist of doubly end functionalized compounds bearing 4-pyridyl groups. It was shown that the marked geometrical adaptability of the host in its metal-free form allows interaction with guests of very different sizes. Herein we report the properties of a related compound, namely a cyclic bisporphyrin [4]rotaxane, the behavior of which is totally different from that of a previously studied linear [3]rotaxane. Contrary to the latter compound, the metal-free [4]rotaxane collapses completely and does not show any complexation properties, whereas the copper(I)complexed compound is a good and selective receptor for diamine and dipyridyl substrates because of the scaffolding effect of the four metal centers (Figure 1). The recognition process can thus be switched on and off by complexing the free ligand to four Cu ions or demetalating the metalcomplexed species, respectively. The synthesis of rotaxane 1 [7] as well as that of its related [4]pseudorotaxane have already been reported. 1 was demetalated using a large excess of KCN (ca. 50 equivalents) at room temperature. The reaction mixture was stirred for 2.5 hours, and the crude product was then purified by chromatography on silica gel to afford the demetalated rotaxane 2 in 88% yield (Scheme 1). Rotaxane 2 was characterized by H NMR spectroscopy (COSY, ROESY, DOSY), electrospray mass spectrometry and UV/Vis spectroscopy. Very surprisingly, the H NMR spectrum of rotaxane 2 shows considerable loss of symmetry compared to the metalated system 1, in which all the Cu centers as well as the four stoppers were chemically equivalent. A quarter of the rotaxane 1 only had thus to be considered for complete NMR assignment. By contrast, the H NMR signals of 2 were doubled compared to those of rotaxane 1. Two distinct stoppers with significantly different H NMR signals and thus markedly different environments can be identified. NOE interactions between some parts of 2 were clearly detected, whereas these fragments were too far away from one another in 1 to show any interaction. For instance, some protons of the tBu groups of one type of stopper (H-re’; r= “rod”) correlate to protons H-b4’ and Hb7’ (b=bismacrocycle) of the 1,10-phenanthroline unit in 2, thus indicating that this stopper and a given 1,10-phenanthroline unit are located very close to one another. As the bismacrocycles and the axles are both rigid, the proximity between two such fragments tends to indicate that the topography of 2 is markedly different from that of 1, and that 2 has a totally collapsed structure. This hypothesis was confirmed by additional observations. For instance, one proton of the (CH2)3 linker (H-r9) is strongly shielded upon decomplexation; the corresponding signal moves from Figure 1. Principle of the recognition process that is switched on and off by metalation or demetalation. Small gray dots: Cu ions; gray squares: porphyrins; black double arrow: guest compound. The chemical structures of 1 and 2 are shown in Scheme 1.