Institute for Molecular Science , Myodaiji, Okazaki 444-8787, Japan.
J Am Chem Soc. 2013 Sep 25;135(38):14074-7. doi: 10.1021/ja407842z. Epub 2013 Sep 12.
An aromatic saddle was designed from the hypothetical three-dimensional graphene with the negative Gaussian curvature (Schwarzite P192). Two aromatic saddles, tetrabenzo[8]circulene (TB8C) and its octamethyl derivative OM-TB8C, were synthesized by the Scholl reaction of cyclic octaphenylene precursors. The structure of TB8C greatly deviates from planarity, and the deep saddle shape was confirmed by single-crystal X-ray crystallography. There are two conformers with the S4 symmetry, which are twisted compared to the DFT structure (D2d). The theoretical studies propose that the interconversion of TB8C via the planar transition state (125 kcal mol(-1)) is not possible. However, the pseudorotation leads to a low-energy tub-to-tub inversion via the nonplanar transition state (7.3 kcal mol(-1)). The ground-state structure of TB8C in solution is quite different from the X-ray structure because of the crystal-packing force and low-energy pseudorotation. OM-TB8C is a good electron donor and works as the p-type semiconductor.
设计了具有负高斯曲率（Schwarzite P192）的假设三维石墨烯的芳香鞍座。通过环状八苯烯前体的 Scholl 反应合成了两个芳香鞍座，四苯并[8]环轮烯（TB8C）及其八甲基衍生物 OM-TB8C。TB8C 的结构严重偏离平面，通过单晶 X 射线晶体学证实了深鞍形。存在两个具有 S4 对称性的构象异构体，与 DFT 结构（D2d）相比是扭曲的。理论研究表明，TB8C 通过平面过渡态（125 kcal mol(-1))的互变是不可能的。然而，通过非平面过渡态（7.3 kcal mol(-1))，准旋转导致 tub-to-tub 反转的低能。由于晶体堆积力和低能准旋转，TB8C 在溶液中的基态结构与 X 射线结构有很大的不同。OM-TB8C 是一种良好的电子给体，是 p 型半导体。
