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, H2) were achieved in two different ways: (1) synthesis from endohedral fullerene H2O@C60 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 (T1, T2), 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 H2@C59N dimers (observed reaction rates: k'(H2O)/k'(H2) = 1.74 ± 0.16). The DFT calculations showed thermal stabilization of C59N(+) by entrapped H2O through the electrostatic interaction.