Synthesis and Properties of Endohedral Aza[60]fullerenes: H2O@C59N and H2@C59N as Their Dimers and Monomers

The macroscopic-scale syntheses of the first endohedral aza:[60]fullerenes X@C59N (X = H2O, H-2) were achieved in two different ways: (1) synthesis from endohedral fullerene H2O@C-60, as a starting material and (2) molecular surgical synthesis from a C59N precursor having a considerably small opening. In the neutral state of H2O@C59N, we expected the H-bonding, interaction or repulsive N-O interaction between entrapped-H2O and a nitrogen atom on the C59N cage. However, an attractive electrostatic N-O interaction was suggested from the results of variable temperature NMR, nuclear magnetic relaxation times (T-1, T-2), and density functional theory (DFT) calculations. Upon the reaction with acetone via cationic intermediate C59N+, we found a difference in reaction rates between H2O@C59N and H-2@C59N dimers (observed reaction rates: k'(H2O)/k'(H-2) = 1.74 +/- 0.16). The DFT calculations showed thermal stabilization of C59N+ by -entrapped H2O through the electrostatic interaction.