Molecular [2]catenanes consist of two or more interlocked macrocycles and are fascinating synthetic targets in supramolecular chemistry. They are usually constructed by a template-based approach. Coordination-driven self-assembly can also be a useful method, particularly for the syntheses of more complex molecules.

Guo-Xin Jin, Fudan University, Shanghai, China, F. Ekkehardt Hahn, Unversity of Münster, Germany, and colleagues have synthesized a series of molecular metalla[2]catenanes (example pictured) from 1,5-bis[2-(4-pyridyl)ethynyl]anthracenes and dinuclear half-sandwich iridium complexes. The components are pre-orientated for the catenane formation by π⋅⋅⋅π stacking in a highly selective fashion. The interlocked structures were, thus, obtained by template-free, coordination-driven self-assembly.

Single-crystal X-ray diffraction analysis indicated that the [2]catenanes adopt two different configurations depending on the halogen atoms at the dinuclear iridium complex bridge (either no halogen, Cl, or Br). The developed simple approach for the preparation of metalla[2]catenane architectures through π–π stacking and control of the topology by halogen atoms could be applied to the design of new supramolecular assemblies and molecular machines.

• Highly Selective Synthesis of Iridium(III) Metalla[2]catenanes through Component Pre-Orientation by π⋅⋅⋅π Stacking,
  Wei-Long Shan, Yue-Jian Lin, F. Ekkehardt Hahn, Guo-Xin Jin,
  Angew. Chem. Int. Ed. 2019.
  https://doi.org/10.1002/anie.201900556