Servalli Marco, Trapp Nils, Wörle Michael, Klärner Frank-Gerrit
Laboratory of Polymer Chemistry, Department of Materials, ETH Zurich , Vladimir-Prelog-Weg 5, 8093 Zurich, Switzerland.
Laboratory of Inorganic Chemistry, Small Molecule Crystallography Center, Department of Chemistry and Applied Biosciences, ETH Zurich , Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland.
J Org Chem. 2016 Mar 18;81(6):2572-80. doi: 10.1021/acs.joc.6b00209. Epub 2016 Mar 4.
The novel hydrocarbon propeller-shaped D3h-symmetric cyclophane (3), "anthraphane", was prepared through a revisited and optimized gram-scale synthesis of the key building block anthracene-1,8-ditriflate 7. Anthraphane has a high tendency to crystallize and single crystals in size ranges of 100-200 μm are easily obtained from different solvents. The crystallization behavior of 3 was extensively studied to unravel packing motifs and determine whether the packing can be steered into a desired direction, so to allow topochemical photopolymerization. SC-XRD shows that anthraphane packs in layers irrespective of the solvent used for crystallization. However, within the layers, intermolecular arrangements and π-π interactions of the anthracene units vary strongly. Four interaction motifs for the anthracene moieties are observed and discussed in detail: two types of exclusively edge-to-face (etf), a mixture of edge-to-face and face-to-face (ftf), and no anthracene-anthracene interaction at all. To elucidate why an exclusive ftf stacking was not observed, electrostatic potential surface (EPS) calculations with the semiempirical PM3 method were performed. They show qualitatively that the anthracene faces bear a strong negative surface potential, which may be the cause for this cyclophane to avoid ftf interactions. This combined crystallographic and computational study provides valuable insights on how to create all-ftf packings.
新型碳氢化合物螺旋桨状的D3h对称环芳（3），即“蒽环芳”，是通过对关键构建单元蒽-1,8-二磺酸酯7进行重新审视和优化后的克级合成制备而成。蒽环芳具有很高的结晶倾向，从不同溶剂中很容易获得尺寸范围为100 - 200μm的单晶。对3的结晶行为进行了广泛研究，以揭示堆积模式，并确定堆积是否可以引导到期望的方向，从而实现拓扑化学光聚合。单晶X射线衍射（SC-XRD）表明，无论用于结晶的溶剂如何，蒽环芳都以层状堆积。然而，在层内，蒽单元的分子间排列和π-π相互作用差异很大。观察并详细讨论了蒽部分的四种相互作用模式：两种完全是边对面（etf）类型、边对面和面对面（ftf）的混合类型，以及根本没有蒽-蒽相互作用的类型。为了阐明为什么没有观察到完全的面对面堆积，使用半经验PM3方法进行了静电势表面（EPS）计算。计算结果定性地表明，蒽面带有很强的负表面电势，这可能是这种环芳避免面对面相互作用的原因。这项结合晶体学和计算的研究为如何创建全面对面堆积提供了有价值的见解。
