Pillararene-Catalyzed Kemp Elimination: High Efficiency through Orthogonal Self-Sorting Binding and Ion Modulation

Area of Science:

• Supramolecular chemistry
• Catalysis
• Organic chemistry

Background:

• Supramolecular catalysis is key for efficient chemical transformations.
• Developing water-soluble catalysts enhances sustainability and reaction scope.
• Macrocyclic catalysts often face limitations in efficiency and product inhibition.

Purpose of the Study:

• To develop highly efficient and versatile water-soluble supramolecular catalysts.
• To investigate the catalytic mechanism of Kemp elimination using pillar[6]arenes.
• To address product inhibition challenges in macrocyclic catalysis.

Main Methods:

• Synthesis of water-soluble pillar[6]arenes with quaternary ammonium groups.
• Aqueous-phase Kemp elimination reaction of 1,2-benzisoxazole.
• Kinetic studies to determine catalytic efficiency (kcat/kuncat) and analyze reaction mechanisms.
• Investigation of substrate-binding and product-release mechanisms using self-sorting principles.

Main Results:

• Pillar[6]arenes achieved a kcat/kuncat ratio up to 1.5 × 10^5 at pH 8 for Kemp elimination.
• Catalytic efficiency rivals that of coordination cages and surpasses previously reported macrocycles.
• Orthogonal self-sorting binding facilitates substrate preorganization and ion-mediated product release.
• Effective catalysis observed at pH 6-7, demonstrating robustness and reduced product inhibition.

Conclusions:

• Water-soluble pillar[6]arenes represent a powerful new class of supramolecular catalysts for aqueous-phase reactions.
• The catalyst design effectively overcomes product inhibition, leading to enhanced turnover.
• This enzyme-mimetic strategy provides a sustainable and recyclable approach to catalysis.