Synthesis of covalently linked knotted cage frameworks

Abstract

Interwoven molecular structures underpin the functions of many biomolecules, yet synthesizing artificial topologically complex structures in high yield remains challenging. Here we describe a streamlined, high-yield one-pot synthesis of knotted cage frameworks by using a subcomponent designed to bridge over the faces of a predesigned cage framework. A ZnII4L3 (where L corresponds to a tritopic pyridyl-imine ligand that coordinates to the metal vertices) open-faced cage framework was employed as the basis for a topologically chiral perplexane, and a ZnII4L4 tetrahedron was built into a topologically chiral trefoil tetrahedron. Both interwoven architectures can be prepared through one-pot subcomponent self-assembly from a trialdehyde, the bridging triamine and a zinc(II) salt. The trefoil tetrahedron was observed to mechanically lock guests inside the cavity, resulting in a guest exchange half-life 17,000 times longer than that of the original tetrahedral cage. Both cage frameworks were reduced and demetallated to yield metal-free interwoven structures, with the perplexane producing an achiral product and the trefoil tetrahedron maintaining its topological chirality. Our strategy may enable the knotting of many existing cage frameworks produced using subcomponent self assembly, enhancing their robustness and ability to lock guests inside.