Development of the Organic Method for the Synthesis of Endohedral Fullerenes

(1)采用所谓的“分子外科入路”合成了第一个包封分子氢的内嵌富勒烯H2@C60。因此，在富勒烯C60表面通过1,2,4-三嗪衍生物的环加成形成一个8元环孔，然后在单线态氧氧化下扩大成一个12元环。通过在孔口边缘插入硫，进一步将孔口扩大为13元环，然后施加高压氢气，形成100%包封H2的开笼富勒烯。采用同步辐射MEM x射线分析直接观察笼内的氢分子。然后关闭孔板，同时保留被封装的氢，通过四步合成，从起始的C60中获得H2@C60约9%的总收率。(2) C70的类似处理产生H2@C70和少量（H2）2@C70。通过变温1H NMR测量，观察了开笼[70]富勒烯中两个氢分子的运动。(3)通过电子测量和13C核磁共振谱分析，发现包裹氢与富勒烯笼外pi体系的电子相互作用很小。(4)氢同位素H2、HD和D2也被包裹在开笼富勒烯衍生物中。合成了D2@C60，并澄清了H2@C60的区别。5)发现氦比氢更容易被封装到开笼富勒烯中。封闭笼富勒烯He@C60的合成方法与H2@C60相同。

(1)The first endohedral fullerene encapsulating molecular hydrogen, H2@C60, was synthesized by so-called "molecular surgical approach". Thus, an 8-membered-ring orifice was formed on the surface of fullerene C60, via cycloaddition of a 1,2,4-triazine derivative to C60, followed by its enlargement into a 12-membered ring by oxidation with singlet oxygen. The opening was further enlarged into a 13-membered ring by insertion of sulfur into the rim of the orifice, and then high-pressure hydrogen was applied to afford an open-cage fullerene encapsulating H2 in 100%. The molecular hydrogen inside the cage was directly observed by means of MEM X-ray analysis using synchrotron radiation. Then the orifice was closed, while retaining the encapsulated hydrogen, by a four-step synthesis to afford H2@C60 in about 9% overall yield from the starting C60.(2)The similar treatment of C70 afforded H2@C70 and also a small amount, of (H2)2@C70. The motion of the two hydrogen molecules in the open-cage [70]fullerene was observed by variable temperature 1H NMR measurement.(3)The electronic interaction between the encapsulated hydrogen and the outer pi-system of fullerene cage was shown to be rather small by electronic measurement and also by 13C NMR spectroscopy.(4)Hydrogen isotopes, i.e., H2, HD, and D2, were also encapsulated into the derivatives of open-cage fullerene. D2@C60 was synthesized and the difference between H2@C60 was clarified.5) Helium was found to be encapsulated into the open-cage fullerene much more readily than hydrogen. [4] The closed-cage fullerene He@C60 was synthesized in the same way as that for H2@C60.