A Highly C70 Selective Shape-Persistent Rectangular Prism Constructed through One-Step Alkyne Metathesis

Dynamic covalent chemistry (DCC) provides an intriguing and highly efficient approach for building molecules that are usually thermodynamically favored. However, the DCC methods that are efficient enough to construct large, complex molecules, particularly those with three-dimensional (3-D) architectures, are still very limited. Here, for the first time, we have successfully utilized alkyne metathesis, a highly efficient DCC approach, to construct the novel 3-D rectangular prismatic molecular cage COP-5 in one step from a readily accessible porphyrin-based precursor. COP-5 consists of rigid, aromatic porphyrin and carbazole moieties as well as linear ethynylene linkers, rendering its shape-persistent nature. Interestingly, COP-5 serves as an excellent receptor for fullerenes. It forms 1:1 complexes with C ₆₀ and C ₇₀ with association constants of 1.4 × 10 ⁵ M ^-1 (C ₆₀) and 1.5 × 10 ⁸ M ^-1 (C ₇₀) in toluene. This represents one of the highest binding affinities reported so far for purely organic fullerene receptors. COP-5 shows an unprecedented high selectivity in binding C ₇₀ over C ₆₀ (K _C70/K _C60 > 1000). Moreover, the binding between the cage and fullerene is fully reversible under the acid-base stimuli, thus allowing successful separation of C ₇₀ from a C ₆₀-enriched fullerene mixture (C ₆₀/C ₇₀, 10/1 mol/mol) through the "selective complexation-decomplexation" strategy.