Through-space interactions between face-to-face, center-to-edge oriented arenes: importance of polar–π effects

Abstract

Two series of conformationally restricted polycyclic compounds (1–3 and 4–7) have been synthesized as model systems for studying the through-space interactions between face-to-face, center-to-edge (parallel-offset) oriented arenes. These compounds feature different X substituents on one of the interacting rings. By monitoring the variation of the ΔG^≠ for the rotation around the aryl–aryl bond in 1–7 as a function of X by 2D [¹H,¹H] EXSY NMR spectroscopy, it was found that the barriers increase on passing from electron-donating to electron-withdrawing substituted derivatives. Quantum mechanical calculations [MP2/DVZ (2d,p)//B3LYP/DVZ(2d,p)] gave barrier values and variations in agreement with the experimental data. The results are consistent with a repulsive arene–arene interaction dominated by electrostatic effects.