Direct Through‐Space Substituent‐π Interactions in Noncovalent Arene–Fullerene Assemblies

The substituents effects in arene-fullerene interactions were examined by NMR titration experiments using an open-[60]fullerene as a host, revealing self-assembling behavior with substituted benzenes by a 1 : 2 stoichiometry. The destabilization of the OMe-substitution clearly indicates the presence of direct through-space substituent-π interactions describable by the Wheeler-Houk model.

Abstract

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 (ΔG ₁) and Hammet constants (σ _m). 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.

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