David J. Watson
Heterogeneously Catalyzed Asymmetric Hydrogenation of C=C Bonds Directed by Surface-Tethered Chiral Modifiers
Watson, David J.; Jesudason, R.J. Bennie Ram John; Beaumont, Simon K.; Kyriakou, Gergios; Burton, Jonathan W.; Lambert, Richard M.
Authors
R.J. Bennie Ram John Jesudason
Dr Simon Beaumont simon.beaumont@durham.ac.uk
Associate Professor
Gergios Kyriakou
Jonathan W. Burton
Richard M. Lambert
Abstract
Asymmetric hydrogenation of C═C bonds is of the highest importance in organic synthesis, and such reactions are currently carried out with organometallic homogeneous catalysts. Achieving heterogeneous metal-catalyzed hydrogenation, a highly desirable goal, necessitates forcing the crucial enantiodifferentiating step to take place at the metal surface. By synthesis and application of six chiral sulfide ligands that anchor robustly to Pd nanoparticles and resist displacement, we have for the first time accomplished heterogeneous enantioselective catalytic hydrogenation of isophorone. High resolution XPS data established that ligand adsorption from solution occurred exclusively on the Pd nanoparticles and not on the carbon support. All ligands contained a pyrrolidine nitrogen to enable their interaction with the isophorone substrate while the sulfide functionality provided the required interaction with the Pd surface. Enantioselective turnover numbers of up to 100 product molecules per ligand molecule were found with a very large variation in asymmetric induction between ligands: observed enantiomeric excesses increased with increasing size of the alkyl group in the sulfide. This likely reflects varying degrees of ligand dispersion on the surface: bulky substituent groups hinder close approach of ligand molecules to each other, inhibiting close-packed island formation, favoring dispersion as separate molecules, and leading to effective asymmetric induction. Conversely, small substituents favor island formation leading to very low asymmetric induction. Enantioselective reaction most likely involves initial formation of an enamine or iminium species, confirmed by use of an analogous tertiary amine, which leads to racemic product. Ligand rigidity and resistance to self-assembled monolayer formation are important attributes that should be designed into improved chiral modifiers.
Citation
Watson, D. J., Jesudason, R. B. R. J., Beaumont, S. K., Kyriakou, G., Burton, J. W., & Lambert, R. M. (2009). Heterogeneously Catalyzed Asymmetric Hydrogenation of C=C Bonds Directed by Surface-Tethered Chiral Modifiers. Journal of the American Chemical Society, 131(40), 14584-14589. https://doi.org/10.1021/ja906356g
Journal Article Type | Article |
---|---|
Publication Date | Sep 15, 2009 |
Deposit Date | Nov 27, 2012 |
Publicly Available Date | Apr 15, 2014 |
Journal | Journal of the American Chemical Society |
Print ISSN | 0002-7863 |
Electronic ISSN | 1520-5126 |
Publisher | American Chemical Society |
Peer Reviewed | Peer Reviewed |
Volume | 131 |
Issue | 40 |
Pages | 14584-14589 |
DOI | https://doi.org/10.1021/ja906356g |
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Copyright Statement
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of the American Chemical Society, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/ja906356g.
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