Inclusion of [60]Fullerene in a Self-assembled Homooxacalix[3]arene-based Dimeric Capsule Constructed by a PdII–pyridine Interaction. The Li+-binding to the Lower Rims can Improve the Inclusion Ability

A capsule-like cage molecule was constructed by dimerization of pyridine-containing homooxacalix[3]aryl esters utilizing a PdII–pyridine interaction. Interestingly, it was found that this molecule can include [60]fullerene in the inner cavity and the exchange rate is slower than the 1H and 13C NMR time-scales, giving rise to new separate NMR peaks assignable to the capsule[60]fullerene complex. From the integral intensity ratio the association constant (Kass) was estimated to be 39 dm3 mol−1 (at 30°C). The ΔδH between Hax and Heq in the ArCH2O methylene protons gave a sign that when Li+ cations are bound to the ionophoric lower rims, the capsule molecule is changed to a more flattened conformation which is more suitable to [60]fullerene inclusion. This Li+-induced preorganization enhanced the Kass up to 2100 dm3 mol−1(at 30°C). Thus, the present study is the first example that [60]fullerene is included in a capsule-like cage molecule and the exchange rate appears to be the slower than the NMR time-scales.