Supramolecular chirality transfer in a stereodynamic catalysts

Area of Science:

• Organometallic Chemistry
• Asymmetric Catalysis
• Supramolecular Chemistry

Background:

• Development of stereoselective catalysts is crucial for synthesizing enantiomerically pure compounds.
• Axially chiral ligands offer unique opportunities for controlling stereochemistry in catalysis.
• Non-covalent interactions can be harnessed to influence catalyst behavior and enantioselectivity.

Purpose of the Study:

• To design and synthesize novel rhodium catalysts featuring stereodynamic axially chiral phosphinite ligands.
• To investigate the role of non-stereoselective amide modifications in inducing chirality transfer.
• To explore the mechanism of supramolecular complex formation and its impact on enantioselective hydrogenation.

Main Methods:

• Synthesis of rhodium catalysts incorporating biphenol-derived phosphinite ligands functionalized with amides.
• Chirality transfer studies using (R)- or (S)-acetylphenylalanine methyl amide as chiral auxiliaries.
• Nuclear Magnetic Resonance (NMR) spectroscopy to elucidate interaction mechanisms and supramolecular complex formation.
• Asymmetric hydrogenation of (Z)-methyl-α-acetamidocinnamate.

Main Results:

• Successful demonstration of chirality transfer from the amide auxiliary to the catalyst's axial chirality.
• Formation of supramolecular complexes driven by non-covalent interactions at the amide sites.
• Enrichment of specific (R_ax)- or (S_ax)-enantiomers of the tropos catalysts.
• High enantioselectivity in the hydrogenation of (Z)-methyl-α-acetamidocinnamate, yielding (R)- or (S)-acetylphenylalanine methyl ester.

Conclusions:

• Stereodynamic axially chiral phosphinite ligands modified with non-stereoselective amides are effective in rhodium-catalyzed asymmetric hydrogenation.
• Non-covalent interactions play a key role in directing catalyst enantiomer enrichment and achieving high stereoselectivity.
• This approach provides a novel strategy for controlling enantioselectivity through supramolecular assembly in catalysis.