Chiral Functionalised Ionic Liquids as Reaction Media
Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
Final Report Abstract
Within the ChirIL Fun project chiral functionalised ionic liquids have been developed and interactions with transition metal complexes at different levels investigated. Asymmetric transition metal catalysis was used as a sensitive "molecular probe" for detecting interplay between metal complexes and cIL, and the transfer of chiral information as an indisputable evidence for synergistic interactions. Multinuclear NMR-spectroscopy allowed the characterisation of these interactions giving valuable information for understanding the mechanism responsible for the chiral induction. We reported how a counter-ion may affect the outcome of a catalytic process. Carefully designed IL with chiral-anion gives rise to n-n interactions with the ligand backbone and, presumably, with the entering substrate, which resulted in catalyst activation. A significant improvement of enantioselectivity of the process could be achieved too. We described the multistep synthesis of tropos BIPHEP ligands functionalized with amino and amidino groups in the 5,5'-position enlarging the portfolio of ligands with this structure. These basic groups can be protonated and allowing for electrostatic interaction as well as for associations through hydrogen bonding. In preliminary investigations, no measurable interaction could be evidenced between the BIPHEP ligands with cationic tags and an IL with chiral borate anion. In contrast, these ligands interact with the chiral cationic (S)-prolinmethylester-bis(trifluoromethyl)sulfonylamid through hydrogen bonding, as evidenced by NMR-spectroscopy. Moreover, significant level of enantioselectivity of up to 54 % ee could be achieved in the Rh-catalysed asymmetric hydrogenation of methyl-2-acetamidoacrylate. Association of the deprotonated cIL in the first coordination sphere of metal center was found to be responsible for the transfer of the chiral information in the first place and the pathways leading to the preferential formation of the opposite enantiomers fully elucidated.
Publications
- Enantioselective catalysis with tropos ligands in chiral Ionic liquids, Chem. Commun., 2007,4012-4014
M. Schmitkamp, D. Chen, W. Leitner, J. Klankermayer, G. Francio
- Enantioselective Hydrogenation with Racemic and Enantiopure BINAP in the Presence of a Chiral Ionic Liquid, Angew. Chem 2008, 120, 7449-7451
M. Schmitkamp, D. Chen, J. Klankermayer, G. Francio, W. Leitner
- Asymmetric Induction by Chiral Borate Anions in Enantioselective Hydrogenation using a Racemic Rh-Binap Catalyst, ChemCatChem 2010, 2, 55-57
D. Chen, B. Sundararaju, R. Krause, J. Klankermayer, P. H. Dixneuf, W. Leitner
- Continuous flow organometalllc catalysis: new wind in old sails, Chem. Commun. 2011, 47, 3691-3701
U. Hintermair, G. Francio, W. Leitner
