State Key Laboratory of Materials Processing and Die & Mold Technology, School of Materials Science and Engineering, Huazhong University of Science and Technology (HUST), Wuhan 430074, China.
J Am Chem Soc. 2013 Aug 28;135(34):12730-5. doi: 10.1021/ja405223t. Epub 2013 Aug 15.
Endohedral metallofullerenes (EMFs) encapsulating divalent metal ions have received limited attention because of their low production yields. Here, we report the results of structural determination and chemical functionalization of a typical divalent metallofullerene, Yb@C84(II). Single-crystal X-ray crystallographic studies of Yb@C84/Ni(II)(OEP) cocrystals (OEP is the dianion of octaethylporphyrin) unambiguously established the chiral C2(13)-C84 cage structure and revealed multiple sites for Yb(2+), indicating a moving metal ion inside the cage. The chemical property of Yb@C2(13)-C84 was probed with the electrophillic adamantylidene carbene (1). Three monoadduct isomers were isolated and characterized. Crystallographic results of the major isomer (2b) revealed that, although the cycloaddition breaks a [5,6]-bond on the cage, Yb(2+) is localized under a hexagonal ring distant from the sites of addition. Thus, it is proved that the dynamic motion of the divalent metal ion in Yb@C84 has been effectively halted by exohedral functionalization. Spectroscopic results show that the electronic property of Yb@C2(13)-C84 is pertained in the derivatives, although the addend exerts a mild reduction effect on the electrochemical behavior of the EMF. Computational works demonstrated that addition of 1 to Yb@C2(13)-C84 is mainly driven by releasing the local strains of cage carbons rather than charge recombination, which is always prominent to the affinity of typical trivalent EMFs such as M@C2v(9)-C82 (M = Sc, Y, La, Ce, Gd) toward 1. Accordingly, it is speculated that the chemical behaviors of divalent EMFs more likely resemble those of empty fullerenes because both are closed-shell compounds, but they differ from those of trivalent EMFs, which have open-shell electronic configurations instead.
金属富勒烯（EMFs）笼内包金属离子由于其低产率而受到的关注有限。在这里，我们报告了一种典型二价金属富勒烯，Yb@C84（II）的结构测定和化学功能化的结果。Yb@C84/Ni（II）（OEP）共晶体的单晶 X 射线晶体学研究明确建立了手性 C2（13）-C84 笼状结构，并揭示了 Yb（2+）的多个位置，表明笼内有一个移动的金属离子。用亲电金刚烷亚基卡宾（1）探测了 Yb@C2（13）-C84 的化学性质。分离并表征了三种单加成异构体。主要异构体（2b）的晶体学结果表明，尽管环加成破坏了笼上的[5,6]-键，但 Yb（2+）定位在远离加成位置的六边形环下。因此，证明了二价金属离子在 Yb@C84 中的动态运动已通过外笼功能化有效停止。光谱结果表明，尽管添加物对 EMF 的电化学行为具有轻微的还原作用，但 Yb@C2（13）-C84 的衍生物保留了其电子性质。计算工作表明，1 加成到 Yb@C2（13）-C84 主要是由释放笼碳原子的局部应变驱动的，而不是电荷重组，这对于典型的三价 EMFs（如 M@C2v（9）-C82（M = Sc、Y、La、Ce、Gd）与 1 的亲和力总是很明显。因此，推测二价 EMF 的化学行为更可能类似于空富勒烯，因为两者都是闭壳化合物，但与具有开壳电子构型的三价 EMF 不同。
