Inclusion of [60]fullerene in a self-assembled homooxacalix[3]arene- based dimeric capsule constructed by a Pd(II)-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 Pd(II)-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 (K(ass)) was estimated to be 39 dm³ mol^-1 (at 30°C). The Δδ(H) between H(ax) and H(eq) 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 K(ass) 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.