Inhibition of C(2)-H/D exchange of a bis(imidazolium) dication upon complexation with cucubit[7]uril

Abstract

Inclusion of the α,α′-bis(3-(1-methylimidazolium))-p-xylene dication in cucurbit[7]uril (CB[7], K_CB[7] = (4.3 × 10⁹ M⁻¹), with C–H⋯OC hydrogen bonding between the guest C(2)-protons and the carbonyl oxygens of the host portals, inhibits the H/D exchange for the C(2)-proton with k_OD (25 °C, D₂O) decreasing from 1.2 × 10³ M⁻¹ s⁻¹ (pK_a = 22.3) in the absence of CB[7] to 0.9 M⁻¹ s⁻¹ (pK_a = 25.4) in the presence of 1.1 equiv. CB[7].