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(2nd.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.