Supramolecular dynamics of cyclic [6]paraphenyeneacetylene complexes with [60]- and [70]fullerene derivatives: Electronic and structural effects on complexation
Supramolecular dynamics of cyclic [6]paraphenyeneacetylene complexes with [60]- and [70]fullerene derivatives: Electronic and structural effects on complexation
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DOI：
10.1002/anie.200460630
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发表时间：
2004-01-01
影响因子：
16.6
通讯作者：
Akasaka, T
中科院分区：
文献类型：
--
作者：
Kawase, T;Fujiwara, N;Akasaka, T
虽然各种各样的主体分子已被广泛研究，以阐明巴克敏斯特富勒烯C60的包容现象，其他富勒烯，包括富勒烯衍生物的超分子性质，尚未得到很好的理解。[1-3]与Ih-对称C60相反，这些其他富勒烯在结构和电子上受到扰动。众所周知，[60]富勒烯衍生物的电子性质与附着原子的电负性密切相关。[4]例如，电子正性硅原子的附着大大增加了[60]富勒烯衍生物的π系统的电子密度。[4，5]最近，我们发现碳纳米环1（环状[6]对苯乙炔）与富勒烯C60，C70和C61（COOEt）2 2在溶液和固态中形成稳定的包合物。[2b动态1H NMR谱揭示了这些配合物的有趣特征：1）解离的吉布斯活化能（ΔGdis）为评估富勒烯复合物的稳定性提供了可靠的量度，以及2）每个富勒烯的中心不与1的中心对齐，C70分子在空腔中心附近振动的活化能高于络合物解离的活化能，而C60分子的活化能低于络合物解离的活化能。这些结果可以归因于C60和C70之间的结构差异。C70的包合现象已经从富勒烯纯化的角度进行了研究;[2]然而，迄今为止还没有详细研究C60和C70的超分子性质的差异。为了探索弯曲共轭体系的性质，并基于富勒烯衍生物构建新的超分子结构，[7]我们研究了1与几种富勒烯衍生物（3-10）（包括甲硅烷基化富勒烯6和7）的复合物的动力学行为。[5]通过在Camps和Hirsch使用的条件下用富勒烯处理相应的丙二酸酯，以中等产率制备了新的亚甲基富勒烯衍生物3-5、9和10 [8]。[9]这些新化合物的形成和区域化学通过酯交换成已知的衍生物2和8来证实。[10-12]富勒烯衍生物3-10在CD 2Cl 2溶液中与1形成稳定的包合物。[13]图1显示了作为典型示例的1· 7和1· 9的光谱变化。类似于1· 2的1H NMR光谱，[6 b] 1的光谱在1008 C下在等量3-7的存在下显示出两个强度相等的单峰，但在308 C下只有一个单峰。然而，在308 ℃下，在等量的8-10存在下出现为单线态的1的芳香族信号中的一个在约208 ℃开始加宽，并且在约508 ℃下首次出现两个相对较小的等强度单线态。主信号最终在10808 C处分裂成两个强度相等的单峰（图1b）。光谱变化表明亚甲基[70]富勒烯复合物应该存在于两种非对映异构体（A和B）的平衡混合物中，如方案1所示。异构体的比例随取代基和温度而变化（对于1· 8=约A：B）。9：1，1· 9=约。3：1和1· 10= ca。9：1 at 808C）。1· 9的NOE实验表明，主要成分为异构体A，次要成分为B。由于C70相对平坦的中段的各向异性效应，两种异构体的内部质子（Ha和Hc）的化学位移在比外部质子（Hb和Hd）高约0.4 ppm的场处共振。NMR光谱分析提供了1· 3-7的一个Δ G值和1· 8-10的两个Δ G值（表1）。C_（60）衍生物的Δ G_（dis）值的顺序为1> 2-5> 6> 7; C_（60）衍生物的Δ G_（dis）值的顺序为2 -5> 6> 7。
Although a variety of host molecules have been studied extensively to elucidate the inclusion phenomena of buckminsterfullerene C60, the supramolecular properties of other fullerenes, including fullerene derivatives, are not yet well understood.[1–3] In contrast to Ih-symmetrical C60, these other fullerenes are perturbed structurally and electronically. It has been known that the electronic properties of [60] fullerene derivatives correlate well with the electronegativity of the attached atoms.[4] For example, the attachment of electronpositive silicon atoms considerably increase the electron density of the π systems of [60] fullerene derivatives.[4, 5] Recently we found that the carbon nanoring 1 (cyclic [6] paraphenyleneacetylene) forms stable inclusion complexes with the fullerenes C60, C70, and C61 (COOEt) 2 2 in solution as well as in the solid state.[2b, 6] Dynamic 1H NMR spectra have revealed the interesting features of these complexes: 1) the Gibbs activation energies for dissociation (ΔGdis) provide a reliable measure for evaluating the stability of the fullerene complexes and 2) the center of each fullerene is not aligned with the center of 1, and the activation energy for vibration of a C70 molecule around the center of the cavity is higher than the value for dissociation of the complex, while that of C60 is lower. These results can be attributed to the structural difference between C60 and C70. The inclusion phenomena of C70 have been studied from the viewpoint of purification of fullerenes;[2] however, the difference in the supramolecular properties of C60 and C70 has not been studied in detail so far. To explore the nature of the curved conjugated systems, and to construct new supramolecular structures based on fullerene derivatives,[7] we have studied the dynamic behavior of the complexes of 1 with several fullerene derivatives (3–10) including the silylated fullerenes 6 and 7.[5] New methanofullerene derivatives 3–5, 9, and 10 [8] were prepared in moderate yields by treating the corresponding malonic esters with fullerenes under the conditions used by Camps and Hirsch.[9] The formation and regiochemistry of these new compounds were confirmed by transesterification into the known derivatives 2 and 8.[10–12] Fullerene derivatives 3–10 form stable inclusion complexes with 1 in CD2Cl2 solutions.[13] Figure1 shows the spectral changes of 1· 7 and 1· 9 as typical examples. Similar to the 1H NMR spectra of 1· 2,[6b] the spectrum of 1 shows two singlets of equal intensity at À1008C in the presence of an equal amount of 3–7, but only one singlet at 308C. However, one of the aromatic signals of 1 that appears as a singlet in the presence of an equal amount of 8–10 at 308C begins to broaden at about À208C, and two relatively small singlets of equal intensity first appear at about À508C. The major signal finally splits into two singlets of equal intensity at À808C (Figure 1b). The spectral changes indicate that the methano [70] fullerene complexes should exist in an equilibrium mixture of two diastereomers (A and B) as shown in Scheme 1. The ratio of the isomers varies with the substituents and temperatures (A: B for 1· 8= ca. 9: 1, 1· 9= ca. 3: 1 and 1· 10= ca. 9: 1 at À808C). The NOE experiments of 1· 9 reveal that the major component is isomer A and the minor one is B. The chemical shifts of the inner protons (Ha and Hc) of both isomers resonate at about 0.4 ppm higher field than those of the outer protons (Hb and Hd) because of the anisotropy effect of the relatively flat midsection of C70. Analysis of the NMR spectra provide one ΔGvalue for 1· 3–7 and two ΔGvalues for 1· 8–10 (Table 1). The ΔGdis values of C60 derivatives are in the order 1> 2–5> 6> 7; the …