Direct Through-Space Substituent-π Interactions in Noncovalent Arene-Fullerene Assemblies.

The arene-arene interactions between electron-rich and deficient aromatics have been less understood. Herein, we focus on a [60]fullerene π-surface as an electron-deficient aromatics. Using a 1H signal of H2O@C60 as a magnetic probe, the presence of benzene-fullerene interactions was confirmed. To investigate substituent effects on the noncovalent arene-fullerene interactions, NMR titration experiments were carried out using an open-[60]fullerene and a series of substituted benzenes, i. e., PhX (X=NO2, CN, Cl, OMe, H, CH3, and NH2), demonstrating a 1 : 2 stoichiometry with a positive correlation between stabilization energies upon the first association (ΔG1) and Hammet constants (σm). The destabilization of the self-assembled structure for X=OMe with a σ-withdrawing nature clearly showed direct through-space substituent-π interactions describable by the Wheeler-Houk model while the second association was suggested to be considerably perturbed by the secondary effects.