The influence of the framework: an anion-binding study using fused [n]polynorbornanes

A series of bis-thiourea-functionalized [n]polynorbornane hosts (1-6) with increasing size were synthesized and their anion-binding properties were evaluated by using ¹H NMR spectroscopic titration and Job’s plot analysis. The larger bis-thiourea-[3]polynorbornane scaffolds 4 and 5 bound acetate in a 1:1 (cooperative) arrangement, whereas the corresponding smaller norbornane host 2, identical in preorganization, bound acetate in a 1:2 (independent) arrangement. In contrast, the size of the framework had no influence on the binding of dihydrogenphosphate. These results clearly highlight the subtle influence that the framework itself can have on host-guest interactions.