Studies of endohedral fullerenes.

摘要

Noble gas atoms and molecule gas molecules were placed inside pristine C60 as well as its open-cage derivates. Small, NMR-active 'guests' inside C60 act as chemical probes during addition reactions. These gas-containing fullerenes were prepared using either high-pressure/high-temperature (HPHT) labeling or chemical synthesis to insert the guest gas. The equivalence of 3He C60 and H2 C60 in the Diels-Alder monoaddition of 9,10--dimethylanthracene (DMA) was determined via NMR competition experiment. The reactivity of the fullerene was unaffected by these small guests. Next, proton NMR was used to measure the kinetics of the addition of DMA to H2 C60. Using a T-Jump experiment and modified rate law, the kinetics parameters of the addition were determined.;The competition experiment was repeated using 3He C 60 and 129Xe C60. In this case, the guest perturbed the equilibrium constant of the fullerene reaction, showing the 129Xe C60 to be two times less reactive at room temperature. The extent of this effect changed with temperature, and above 35° C the 3He C60 became less reactive. Apparently, both DeltaH and DeltaS had been changed by the encapsulation of xenon. To explain this effect, ab initio quantum calculations of Xe C60 were attempted at the MP2 level. These showed that the electron density outside the fullerene cage had significantly increased, presumably from xenon repelling fullerene electrons normally inside the cage. Finally, the perturbations to the vibrations of C60 caused by the xenon atom were experimentally measured with FTIR and Raman spectroscopy.;A small amount of 15N2 C60 was created with HPHT labeling. Its HPLC retention time was determined and the sample was enriched to about 10% filled fullerene. The 13C NMR resonance for the filled carbon cage was found for this molecule and the internal dynamics of the nitrogen were computationally modeled, as was the effect of the fullerene on the N-N bond length. Finally, an NH3 molecule trapped in a permanently opened fullerene with a twenty-member oriface was examined. The NMR signal of the NH3 protons was found to be broadened by 14N- 1H coupling. The nitrogen was successfully decoupled, yielding the N-14 resonance.