Stereoselective Self-Assembly of a Topologically Chiral [6]Catenane with 18 Crossings

Abstract

Mechanically interlocked molecules (MIMs) exhibit unique properties and functions arising from their structural entanglement, features of which are absent in their individual components. However, synthesizing topologically complex architectures, particularly those with topological chirality, remains a significant challenge due to the lack of general methods for controlled entanglement. Herein, we report the stereoselective synthesis of a 24-metal-center topologically chiral [6]catenane featuring 18 crossings ($$ link), representing one of the most intricate MIMs constructed to date. This complex architecture was achieved in high yield (71%) via one-step coordination-driven self-assembly of 12 chiral semirigid bidentate ligands and 12 conjugated binuclear half-sandwich organometallic clips. Critically, chirality transfer from enantiopure ligands enabled exclusive formation of topological enantiomer pairs (Rh-1S/Rh-1R), each containing four topologically chiral stereogenic units—three cyclic [3]catenane components and one closed three-link chain component. The self-assembly is synergistically directed by integrated noncovalent interactions (sevenfold π–π stacking, hydrogen bonding, and solvophobic effects), as unambiguously confirmed by single-crystal X-ray diffraction and nuclear magnetic resonance spectroscopy. This design strategy, incorporating tailored noncovalent interaction sites in building blocks, provides a viable approach for synthesizing other structurally complex topologically chiral MIMs.