Synthesis and Properties of Endohedral Aza[60]fullerenes: H_2O@C_(59)N and H_2@C_(59)N as Their Dimers and Monomers

摘要

The macroscopic-scale syntheses of the first endohedral aza[60]fullerenes X@C_(59)N (X = H_2O, H_2) were achieved in two different ways: (1) synthesis from endohedral fullerene H_2O@C_(60) as a starting material and (2) molecular surgical synthesis from a C_(59)N precursor having a considerably small opening. In the neutral state of H_2O@C_(59)N, we expected the H-bonding interaction or repulsive N-O interaction between entrapped H_2O and a nitrogen atom on the C_(59)N 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 C_(59)N~+, we found a difference in reaction rates between H_2O@C_(59)N and H_2@C_(59)N dimers (observed reaction rates: k'(H_2O)/k'(H_2) = 1.74 ± 0.16). The DFT calculations showed thermal stabilization of C_(59)N~+ by entrapped H_2O through the electrostatic interaction.