Stereoselective Self-Assembly of Chiral Metalla[2]Catenanes and Lemniscular Macrocycles

Designing and stereoselectively constructing chiral mechanically interlocked molecules (MIMs) is a goal that many chemists are pursuing due to their potential in the development of functional molecular machines involved in catalysis, sensing, and chiroptical switching. However, the synthesis of enantio-pure supramolecular entities with crystallographic structures remains challenging. Herein, the stereoselective self-assembly of chiral metalla[2]catenanes interlocked by two D-shaped macrocycles was realized by combining long binuclear half-sandwich organometallic Cp*RhIII (Cp* = eta 5-pentamethylcyclo-pentadienyl) clip and ditopic monodentate ligand incorporating L-leucine residues. The resulting metalla[2]catenane displayed unique co-conformational mechanical helical chirality characteristics arising from the chirality transfer of the chiral ligand. Furthermore, decreasing the length of the binuclear Cp*RhIII clip and adjusting the steric hindrance of the amino-acid side chains (L-alanine and L-phenylala-nine) in the ligands resulted in two lemniscular macrocycles with left-handed (M)-twisted conformational chirality. To the best of our knowledge, the synthesized macrocycles are the first family of homochiral abnormal lemniscate-shaped organometallic macrocycles featuring figure-eight geometries. Metalla[2]catenanes and macrocycles with opposite chirality were also generated by employing corresponding D-amino acid ligands, as evidenced by single-crystal X-ray diffraction, nuclear magnetic resonance, mass, and circular dichroism spectroscopies. Our present study demonstrates that homochiral MIMs can be accessed readily using amino acid-containing ligands through rational molecular design.