A High-Affinity and Removable Iminium Dication Guest for Recycling of Cucurbit[7]uril Materials

An iminium dication 1 was designed as a high-affinity and easily removable guest for cucurbit[7]uril (CB[7]). X-ray crystallographic analysis shows that maximized N+···O═C ion-dipole interactions and perfect packing coefficient are responsible for the high affinity of 1 for CB[7] (Ka > 1011 M-1). Under alkaline conditions, included 1 in CB[7]·1 is hydrolyzed into 2,6-adamantanedione and pyrrolidine that can be fully removed by further extraction, enabling the recycling of CB[7] materials.