Pentagon-Fused Hollow Fullerene in C₇₈ Family Retrieved by Chlorination

C78 is one of the most widely investigated higher fullerenes. Among its huge isomer family, only one non-IPR (IPR = isolated pentagon ring) cage, the C2-symmetric #22010C78, was previously stabilized by endohedral derivatization. Here we report a new C1-symmetric non-IPR hollow isomer, #23863C78, which was captured as #23863C78Cl8 and then subjected to a regioselective substitution reaction with benzyl hydroperoxide to form #23863C78(OOCH2C6H5)Cl7. The structural connectivity of #23863C78, which contains a pair of fused pentagons, was confirmed by single-crystal X-ray diffraction analysis of the #23863C78(OOCH2C6H5)Cl7 molecule, which shares the same fullerene core with #23863C78Cl8; support for the structure is provided by comparable IR measurements and computation. Theoretical studies suggest that the differences in C−Cl bond length, intermediate stability, and steric effects of the involved molecules account for the chemical regioselectivity of the substitution reaction.C₇₈是当前研究最为广泛的高富勒烯之一。在其庞大的异构体家族中，此前仅有一种非IPR（IPR=孤立五边形环，isolated pentagon ring）笼状结构——具有C₂对称性的#22010C₇₈，通过内嵌衍生化手段得以稳定。本研究报道了一种全新的C₁对称性非IPR空心异构体#23863C₇₈：该异构体以#23863C₇₈Cl₈的形式被分离捕获，随后与苄基过氧化氢发生区域选择性取代反应，生成产物#23863C₇₈(OOCH₂C₆H₅)Cl₇。通过对#23863C₇₈(OOCH₂C₆H₅)Cl₇分子的单晶X射线衍射分析，证实了该异构体（含有一对稠合五边形）的结构连接方式，该衍生物与#23863C₇₈Cl₈拥有完全一致的富勒烯骨架；红外光谱比对与理论计算结果亦为该结构提供了有力佐证。理论研究表明，相关分子的C−Cl键长差异、中间体稳定性以及位阻效应，共同决定了该取代反应的化学区域选择性。