Cation-triggered switchable asymmetric catalysis with chiral Aza-CrownPhos

Area of Science:

• Organic Chemistry
• Catalysis
• Supramolecular Chemistry

Background:

• Asymmetric hydrogenation is crucial for synthesizing chiral molecules.
• Controlling catalyst activity with external stimuli remains a challenge.
• Host-guest interactions offer a pathway for modulating catalytic systems.

Purpose of the Study:

• To design and synthesize a novel aza-crown ether-modified phosphoramidite ligand.
• To investigate the reversible ON/OFF switching of its rhodium catalyst activity.
• To explore the modulation of catalytic activity via host-guest interactions in asymmetric hydrogenation.

Main Methods:

• Synthesis of a custom aza-crown ether-phosphoramidite ligand.
• Preparation of the corresponding rhodium catalyst complex.
• Investigation of catalytic activity in asymmetric hydrogenation of dehydroamino acid esters.
• Analysis of catalyst behavior under varying conditions, including the presence of alkali metal cations.

Main Results:

• The designed catalyst exhibits an ON/OFF reversible switchable activity.
• In the OFF state, intermolecular complex formation renders the catalyst inactive (<1% conversion).
• Addition of alkali metal cations triggers the ON state, leading to full conversion and high enantioselectivity (up to 98% ee).

Conclusions:

• A novel switchable catalytic system based on host-guest interactions has been developed.
• This system allows for precise control over catalytic activity in asymmetric hydrogenation.
• The findings open avenues for designing responsive catalysts for complex organic synthesis.