Synthesis of a Pillar[5]arene-Based Heteroditopic Host and Its Complexation with n-Octyltriethylammonium Salts

A new pillar[5]arene-based heteroditopic receptor containing a urea anion recognition site was designed and made. It was demonstrated that the introduction of the urea group remarkably promoted the binding affinity to n-octyltriethylammonium salts with different counterions in chloroform, as the corresponding monotopic host, 1,4-dimethoxypillar-[5]arene, showed weak complexation with these guests. The important role of the urea unit was investigated and it was shown that the urea group and the macrocyclic unit not only provided positioned binding sites for the guests but also acted cooperatively in binding these guests.