Size- and Shape-Selective Catalysis with a Functionalized Self-Assembled Cage Host

Area of Science:

• Supramolecular Chemistry
• Catalysis
• Organic Synthesis

Background:

• Self-assembled cages offer unique environments for chemical transformations.
• Carboxylic acid functionalized cages can act as acid catalysts.
• Understanding substrate-specific reactivity is crucial for catalyst design.

Purpose of the Study:

• To investigate the catalytic activity of a self-assembled Fe4L6 cage.
• To compare the cage's catalytic performance with small acid catalysts.
• To elucidate the factors governing substrate selectivity in cage-catalyzed reactions.

Main Methods:

• Synthesis of a self-assembled Fe4L6 cage with internal carboxylic acid groups.
• Assaying dissociative nucleophilic substitution reactions catalyzed by the cage.
• Comparing reaction rates and selectivities with free acid catalysts and varying substrates.

Main Results:

• The Fe4L6 cage demonstrated significant rate accelerations for thioetherification and thioacetal formation.
• Reactivity varied substantially with substrate structure, with up to 1000-fold acceleration observed.
• Factors like substrate inhibition, binding affinity, and accessibility influenced catalytic efficiency.
• The cage exhibited selectivity for substrate shape, favoring or disfavoring certain guest molecules.

Conclusions:

• The Fe4L6 cage functions as a promiscuous yet shape-selective catalyst.
• Catalytic activity is modulated by intricate host-guest interactions, not just charge or concentration.
• The cage's behavior mimics enzymatic selectivity, offering a platform for designing artificial enzymes.