Selective Anion Encapsulation by a Metalated Cryptophane with a π-Acidic Interior

Metalation of the exterior arene faces of the molecular capsule (±)-cryptophane-E with [Cp*Ru]+ moieties results in a π-acidic cavity capable of encapsulating anions. The [CF3SO3]- and [SbF6]- salts have been crystallographically characterized and demonstrate the encapsulation of these anions by the metalated cryptophane. 1H and 19F NMR spectroscopy establish the binding of anions in NO2CD3 solution and reveal the relative affinity of the cavity for different anions (KX−/KOTf−):  [BF4]- ≈ 0, [PF6]- = 1.18, [CF3SO3]- ≡ 1, [SbF6]- = 0.30. Variable temperature rate studies reveal the activation barrier for triflate encapsulation to be ΔG⧧298K = 18.0(8) kcal·mol-1 (ΔH⧧ = 17.5(4) kcal·mol-1 and ΔS⧧ = 2(1) cal·mol-1·K-1).