Cinchona Alkaloids as Chirality Transmitters in Metal‐Catalyzed Asymmetric Reductions

Blaser, Hans‐Ulrich

doi:10.1002/9783527628179.ch2

Cited by 1 publication

(1 citation statement)

References 72 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This approach is particularly promising in chiral systems, as enantioselectivity requires changes in the transition state of the relevant steps that are too subtle to be accomplished by designing solid catalysts with specific adsorption sites. Instead, the molecular-level modification is attained by the addition of discrete molecules. − Unfortunately, this idea has so far proven viable only for a limited number of systems and reactions, mainly associated with the hydrogenation of ketoesters promoted either by Ni-based surfaces modified with tartaric acid − or by Pt catalysts modified with cinchona alkaloids. − …”

Section: Introductionmentioning

confidence: 99%

Adsorption of Chiral Modifiers from Solution onto Supported Platinum Catalysts: The Effect of the Solvent, Other Coadsorbates, and the Support

Wang

Lee

et al. 2020

J. Phys. Chem. C

View full text Add to dashboard Cite

The adsorption from a solution of s-1-(1-naphthyl)ethylamine (s-NEA), cinchonidine, and cinchonine on Pt/SiO2, Pt/Al2O3, and a Pt disk was probed in situ by infrared absorption spectroscopy. Adsorption on the supported catalysts shows similar behavior to that seen on flat polycrystalline Pt surfaces, with the adsorption geometry transitioning from the aromatic ring lying close to parallel to the metal surface at low coverages to a more tilted geometry at monolayer saturation. The extent of the adsorption of the chiral modifiers and its degree of irreversibility both vary with the nature of the liquid (CCl4, toluene, ethanol), tracking solubility. Carbon monoxide can be coadsorbed with s-NEA, a coadsorption that leads to a compression and an increase in ordering of the s-NEA layer (aided by exposing the surface to H2). In contrast, s-NEA adsorption dominates when competing with quinoline. Finally, a few small differences were seen in the IR spectra of the chiral modifiers adsorbed on Pt/SiO2 (compared to the other solids) because of the smaller size of the Pt nanoparticles associated with that catalyst. In general, it is crucial to characterize the adsorption of chiral modifiers in situ in the presence of the liquid phase, but the contribution from the catalyst support appears to be minor.

show abstract