Ion aggregation and its impact on asymmetric catalysis

Charged intermediates and reagents are omnipresent in asymmetric synthesis. Ion pairing- or ion aggregation of intermediate species with chiral ionic small molecules offers a novel strategy for chirality transfer. In contrast to extensive studies on mono-, bi- and tridentate ligand design with well-defined, covalently modified structure, this idea of counter ion catalysis has only recently emerged and provides a powerful strategy for catalytic enantioselective synthesis.

This project focuses on the design of ion-tagged chiral ligands and utilizes the aggregation and organization in charged intermediates for chirality transfer towards the development of ion-paired ligands for asymmetric catalysis. Catalysis will relies on organo- and transition metal catalysed industrially relevant reactions for fine chemical production, with the overall goal of improved catalyst selectivity and high atom efficiency.

Representing publications:
Pálvölgyi et al., Counterion Enhanced Pd/Enamine-Catalysis: Direct Asymmetric α-Allylation of Aldehydes with Allylic Alcohols by Chiral Amines and Achiral or Racemic Phosphoric Acids, J. Org. Chem. 2020, in press;
Scharinger et al. Counterion Enhanced Organocatalysis: A Novel Approach for the Asymmetric Transfer Hydrogenation of Enones, Chem Cat. Chem. 2020, 12, 3776.

Fast reactions in water

In terms of modern synthetic chemistry, water has been much under-investigated as a solvent because of poor solubility of organic molecules, although it adds to the over-all energy and cost balance of a process and directly influences reactions via the formation of nanoreactors. The effective concentration of reagents within a micelle can be quite high, and hence, reaction rates are increased relative to those normally observed in organic media. Considering the known enhancements of targeted surfactants in chemical reactivity or catalytic performance, we investigate micellar solutions as reaction media for multiple applications ranging from organic synthesis, transition metal catalysis or photocatalytic water splitting for clean energy production.

Representing publications:
Pálvölgyi et al. Ion-tagged chiral ligands for asymmetric transfer hydrogenations in aqueous medium ACS Sus. Chem. Eng. 2019, 7, 3414;
Cognigni et al. Surface-active ionic liquids in micellar catalysis: Impact of anion selection on reaction rates in nucleophilic substitutions, Phys. Chem. Chem. Phys. 2016, 18, 13375.

Cooperations: Prof. M. Bester Rogac, University of Ljubljana, Slovenia
R. Buchner, University of Regensburg, Germany

Multiphase & thermoswitchable catalysis

Microemulsions have been well studied in a wide range of catalytic reactions, particularly for the application in multiphase catalysis. Ionic liquid-based microemulsions can be applied as reaction medium, e.g. for Palladium catalyzed cross coupling and for asymmetric transfer hydrogenations, resulting in high reactivity even at low catalyst loadings. To address the problem of catalyst recovery and reuse, we rely on thermo-responsive three-phase systems of ionic liquid, water and heptane that enable facile product separation and optional catalyst recovery while maintaining high catalytic activity.

Representing publications:

Hejazifar et al. Asymmetric Transfer Hydrogenation in Thermomorphic Microemulsions Based on Ionic Liquids, Org. Proc. Res. Dev. 2019, 23, 1841;
Hejazifar et al. Ionic Liquid-Based Microemulsions in Catalysis, J. Org. Chem. 2016, 81, 12332.

Cooperations: Prof. Ken R. Seddon, QUILL, The Queen’s University Belfast, UK