Diastereoselective Polypseudorotaxane Formation with Planar Chiral Pillar[5]arenes via Co-crystallization Processes

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Organic Synthesis

Background:

• Chiral polyrotaxanes present numerous stereoisomers, complicating selective synthesis.
• Developing efficient methods for stereoisomer control in complex molecular architectures is crucial.

Purpose of the Study:

• To investigate a novel co-crystallization strategy for the diastereoselective synthesis of polypseudorotaxanes.
• To enhance stereochemical control in the assembly of chiral ring molecules on polymer chains.

Main Methods:

• Solid-state co-crystallization of poly(ethylene glycol) with diastereomeric pillar[5]arene molecules.
• Analysis of diastereomeric excess (de) in solution, evaporation, and co-crystallization systems.
• Computational analysis of stabilization energies to understand selectivity.

Main Results:

• Co-crystallization yielded polypseudorotaxanes with high diastereomeric excess (approximately 88% de).
• Solution and evaporation methods showed significantly lower selectivity (approximately 10% de).
• High selectivity was maintained with higher molecular weight poly(ethylene glycol)s.

Conclusions:

• Solid-state co-crystallization effectively promotes dense assembly of chiral ring molecules, enabling diastereoselective synthesis.
• The packing effect in co-crystals is key to achieving high stereochemical control.
• Cooperative effects among ring molecules on the polymer chain, supported by computational data, drive the observed selectivities.