Solvent-Directed Social Chiral Self-Sorting in Pd₂L₄ Coordination Cages

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Organic Synthesis

Background:

• Axially chiral diamino-[1,1'-biazulene] ligands serve as azulene-based surrogates for BINOL.
• Coordination cages offer tunable cavities for molecular recognition and catalysis.

Purpose of the Study:

• To investigate the formation of Pd2L4 cages using novel biazulene-based ligands.
• To explore the phenomenon of "social" chiral self-sorting in coordination cage assembly.
• To understand the role of solvents in directing the stereochemical outcome of cage formation.

Main Methods:

• Synthesis of axially chiral diamino-[1,1'-biazulene] ligands with pyridine and isoquinoline donors.
• Preparation of Pd2L4 coordination cages via self-assembly.
• Characterization using NMR spectroscopy and single-crystal X-ray diffraction.
• Computational analysis including explicit solvation models.

Main Results:

• A shorter biazulene ligand derivative undergoes solvent-dependent "social" chiral self-sorting from its racemate, exclusively forming the meso-trans Pd2L4 cage.
• Solvent molecules act as hydrogen-bonding tethers, locking the cage into a single isomeric form.
• A larger biazulene ligand derivative does not exhibit social self-sorting but forms homochiral cages capable of binding metal complexes and discriminating enantiomers.

Conclusions:

• Solvent-mediated hydrogen bonding is crucial for achieving selective chiral self-sorting in the assembly of specific coordination cages.
• The size and donor groups of chiral ligands significantly influence their self-sorting behavior.
• The developed biazulene-based cages demonstrate potential for host-guest chemistry and enantioselective recognition.