Catenated cages mediated by enthalpic reaction intermediates

Abstract

Catenated cages are generally considered thermodynamically more stable than their constituent monomeric cages. However, the catenation mechanism is yet to be elucidated; it would require systematic investigation into the structural effects of the building blocks, their enthalpic and entropic contributions, and the effect of solvents. By inspecting these factors, we rationalized some design principles for the efficient construction of catenated cages. Our study revealed that a steric hindrance linker and a rigid panel led to the formation of an enthalpy-favored encapsulated intermediate before catenation occurred. The stability of this enthalpic intermediate was crucial for cage catenation, as the reactions were otherwise outcompeted by an entropy-favored intermediate. The formation of the latter was facilitated significantly by a flexible panel and solvent molecules that stably resided within the monomeric cage. This study provides a guideline for the elaboration of catenated cages with more sophisticated topologies, which could be extended to other complex supramolecular assemblies.