An Open-Cage Fullerene That Mimics the C H (5,5)-Carbon Nanotube Endcap to Host Acetylene and Hydrogen Cyanide Molecules.

Treatment of the open-cage fullerene C H NO (Ph) (Py)(N C H ) (1) with methanol at 150 °C results in an orifice-enlargement reaction to give C H NO(CO Me)(Ph)(Py)(N C H ) (2). The overall yield from C to isolated 2 is 6.1 % (four steps). Compound 2 contains a 24-membered elliptic orifice that spans 8.45 Å along the major axis and 6.37 Å along the minor axis. The skeleton of 2 resembles the hypothetic C H (5,5)-carbon nanotube endcap. The cup-shaped structure of 2 is able to include water, hydrogen cyanide, and acetylene, forming H O@2, HCN@2, and C H @2, respectively. The molecular structures of H O@2 and HCN@2 have been determined by X-ray crystallography. The H NMR spectra reveal substantial upfield shifts for the endohedral species, such as δ=-10.30 (for H O), -2.74 and -14.26 (for C H ), and -1.22 ppm (for HCN), owing to the strong shielding effects of the fullerene cage.