Au36 crown: a macrocyclization directed by metal-metal bonding interactions.
Au36 crown: a macrocyclization directed by metal-metal bonding interactions.
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DOI：
10.1002/anie.200801001
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发表时间：
2008-06
影响因子：
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通讯作者：
Shu‐Yan Yu;Qingfu Sun;Terence K.-M. Lee;E. Cheng;Yi-zhi Li;V. Yam
中科院分区：
文献类型：
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作者：
Shu‐Yan Yu;Qingfu Sun;Terence K.-M. Lee;E. Cheng;Yi-zhi Li;V. Yam
自从1967年发现冠醚以来，40多年来，大环分子一直令化学家们兴奋不已。[1]诺贝尔奖获得者Pedersen，[1]Lehn，[2]和Cram[3]在冠醚、密码和球体方面的开创性工作导致了超分子化学领域的发展，其中大环体系在寻找新的功能材料和装置方面发挥了重要作用。[4-7]由于构建大环分子的挑战，自组装已被认为是传统有机合成的一种有前途的替代方案。特别是，金属定向自组装方法已经导致了许多功能性的含金属环的合成，例如金属-有机(配位键合)大环[8-11]和带有通过小基团(X)桥连的金属(M±X型键)的大环聚集体[16]。然而，构建包含连续金属-金属键(M±M型)[15]或键相互作用(M·M型)[16]的大环聚集体仍然是一个挑战。AUI····AUI键相互作用具有与氢键相似的强度，已成为具有特殊性质的超分子聚集体设计中的结构主题。[17]虽然有许多小环具有连续的AUI····AUI键相互作用，例如AU3(三角形)、AU4(正方形)、AU5(五角形)和AU6(六边形)，但在金环家族中，手性AU16环的自组装是最近才报道的，它是由非手性分子单元中独特的金属-金属键相互作用构成的。我们报道了一个冠状Au36环的自发分级异手性自组装，它是迄今为止金环家族中最大的成员，由非手性组分强烈的AuI···Aui键相互作用引导。[20]在二氯甲烷中加入[Au(Tht)Cl](tht=四氢噻吩环)到室温下0.5摩尔当量1的乙醇溶液中(图式1)，导致红色沉淀物的形成。从反应混合物中挥发溶剂，然后以氯仿为洗脱液对残留物进行闪蒸层析，得到淡黄色的溶液。将二乙醚蒸气缓慢扩散到这种稀溶液中几天，得到黄色立方结晶产物，其结构被X射线结晶学进一步证实为AU6簇(单体I)(见支持信息表S1)。稀溶液浓缩后，颜色从淡黄色急剧变化为深红色。通过将甲醇分层到这个红色溶液上结晶，以75%的产率得到了标题化合物，即暗红色晶体(六角体I6)。~1H核磁共振谱表明，I_6在稀溶液中(在氯化镉中)是单体(I)，在d=6.3和4.4ppm(PhCH2)和d=5.6和4.6ppm(FcCH2)处，亚甲基的质子共振分裂成两对双峰。1H-1H余弦谱的相关信号表明，两个不同亚甲基中的两个质子处于不同的环境中。这两个发现都表明产物是高度不对称的结构，这与单体I的晶体结构一致。对I6的暗红色晶体的X-射线晶体分析表明，它包含一个由六个AU6单体通过强烈的AUI···AUI相互作用连接的超分子Au36环(见支持信息中的表S2)。用MALDI-TOF质谱仪进一步证实了六聚体结构，显示了单体(I+1，m/z 3227.6)、二聚体(I2+1，m/z 6460.8)和三聚体(i3+1，m/z 9697.5)的信号。AU36环的形成涉及AUI···AUI和…
Large-ring molecules have excited chemists for over 40 years since the discovery of crown ethers in 1967.[1] The pioneering work of Nobel laureates Pedersen,[1] Lehn,[2] and Cram [3] on crown ethers, cryptands, and spherands has led to the development of the field of supramolecular chemistry, in which large-ring systems play a fundamental role in the search for novel functional materials and devices.[4–7] With the challenge of constructing large ring molecules, self-assembly has been recognized as a promising alternative to conventional organic synthesis. In particular, metal-directed selfassembly approaches have led to the synthesis of numerous functional metal-containing rings, for example, metal–organic (coordination bonding) macrocycles [8–11] and large cyclic aggregates bearing cluster units with metals bridged by small groups (X)(MÀXÀM type bonding).[12–14] However, the construction of large-ring aggregates containing continuous metal–metal bonds (MÀM type)[15] or bonding interactions (M··· M type)[16] remains a challenge. AuI··· AuI bonding interactions, which have similar strengths to hydrogen bonds, have emerged as structural motifs in the design of supramolecular aggregates with unusual properties.[17] Although there are numerous small rings with continuous AuI··· AuI bonding interactions, for example Au3 (triangle), Au4 (square), Au5 (pentagon), and Au6 (hexagon), in the gold ring family,[18] only very recently was the self-assembly of a chiral Au16 ring, constructed by unique metal–metal bonding interactions from achiral molecular units, reported by us.[19] Herein, we present the spontaneous hierarchical hetero-chiral self-assembly of a crown-like Au36 ring, the largest member of the gold ring family to date, directed by strong AuI··· AuI bonding interactions from achiral components.[20]Addition of [Au (tht) Cl](tht= tetrahydrothiophene) in dichloromethane to a solution of 0.5 molar equivalents of 1 in ethanol at room temperature (Scheme1) resulted in the formation of a red precipitate. Evaporation of the solvent from the reaction mixture, followed by flash chromatography of the residue with chloroform as eluent, gave a pale-yellow solution. Slow diffusion of diethyl ether vapor into this dilute solution over several days gave a yellow cubic crystalline product whose structure was subseqently confirmed to be that of an Au6 cluster (monomer I) by X-ray crystallography (see Table S1 in the Supporting Information). A dramatic color change from pale yellow to dark red occurred upon concentration of the dilute solution. Crystallization by layering methanol onto this red solution gave the title compound as dark-red crystals (the hexamer I6) in 75% yield. The 1H NMR spectrum of I6 reveals it to be monomeric (I) in dilute solution (in CDCl3) as the proton resonances of the methylene groups split into two pairs of doublets at d= 6.3 and 4.4 ppm (PhCH2), and d= 5.6 and 4.6 ppm (FcCH2), respectively. Correlation signals from the 1H-1H COSY spectrum indicate that the two protons in each of the two different methylene groups are in different environments. Both these findings suggest a highly asymmetric structure of the product, which is consistent with the crystal structure of the monomer I. X-ray crystallography of a dark-red crystal of I6 showed it to contain a supramolecular Au36 ring consisting of six Au6 monomers joined by strong AuI··· AuI interactions (see Table S2 in the Supporting Information). The hexameric structure was further confirmed by MALDI-TOF mass spectrometry, which showed signals for the monomer (I+ 1, m/z 3227.6), dimer (I2+ 1, m/z 6460.8), and trimer (I3+ 1, m/z 9697.5). The formation of the Au36 ring involves an AuI··· AuI …