Heterogeneous Enantioselective Hydrogenation over Cinchona Alkaloid Modified Platinum:  Mechanistic Insights into a Complex Reaction

Bürgi, Thomas; Baiker, Alfons

doi:10.1021/ar040072l

Cited by 251 publications

(171 citation statements)

References 52 publications

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“…The molecular adsorption footprint is of central importance in dictating the supramolecular assembly of molecules at surfaces and the orientation of their functional groups, which in turn dictate the response of the interface to the environment, to guest molecules and the alignment of reactants in 'modifier-directed' heterogeneous enantioselective catalysis. 4,30,31 The 'chiral footprint model' is also implicated in the origin of optical activity in metalbased electronic transitions. 7,32 Our work shows the importance of considering the dynamical response of the molecular adsorption footprint to the local adsorption environment, leading to more nuanced behaviour than hitherto anticipated, which could, ultimately, be tailored to create environment and stimuliresponsive chiral surfaces.…”

Section: Introductionmentioning

confidence: 99%

Chiral segregation driven by a dynamical response of the adsorption footprint to the local adsorption environment: bitartrate on Cu(110)

Darling

Forster

Lin

et al. 2017

Phys. Chem. Chem. Phys.

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Local or global ordering of chiral molecules at a surface is a key step in both chiral separation and heterogeneous enantioselective catalysis. Using density functional theory and scanning probe microscopy results, we find that the accepted structural model for the well known bitartrate on Cu(110) chiral system cannot account for the chiral segregation observed. Instead, we show that this strongly bound, chiral adsorbate changes its adsorption footprint in response to the local environment. The flexible adsorption geometry allows bitartrate to form stable homochiral trimer chains in which the central molecule restructures from a rectangular to an oblique footprint, breaking its internal hydrogen bonds in order to form strong intermolecular hydrogen bonds to neighbouring adsorbates. Racemic structures containing mixed enantiomers do not form strong hydrogen bonds, providing the thermodynamic driving force for the chiral separation that is observed experimentally. This result shows the importance of considering the dynamical response of molecular adsorption footprints at the surface in directing chiral assembly and segregation. The ability of strongly-chemisorbed enantiomers to change footprint depending on the local adsorption environment indicates that supramolecular assemblies at surfaces may exhibit more complex dynamical behaviour than hitherto suspected, which, ultimately, could be tailored to lead to environment and stimuli-responsive chiral surfaces.

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Section: Introductionmentioning

confidence: 99%

Chiral segregation driven by a dynamical response of the adsorption footprint to the local adsorption environment: bitartrate on Cu(110)

Darling

Forster

Lin

et al. 2017

Phys. Chem. Chem. Phys.

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“…19 An increasingly important class of metal surfaces are those modified with a chiral molecule, [20][21] which have for example been used for heterogeneous enantioselective catalysis 22 and chiral discrimination. [23][24] The discrimination between and separation of enantiomers or the selective production of one enantiomer is of great importance, as chirality is a fundamental aspect of molecular biology.…”

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confidence: 99%

Vibrational circular dichroism of N-acetyl-l-cysteine protected gold nanoparticles

Gautier

Bürgi

2005

Chem. Commun.

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Vibrational circular dichroism is used to determine the conformation of a thiol adsorbed on gold nanoparticles.Monolayer protected metal nanoparticles are of considerable interest due to their potential application in various fields such as bio-sensing, catalysis, electronics and nanotechnology.1 Whereas the physical properties of monolayer protected nanoparticles (MPNs) are largely associated with the metal core, their chemical behaviour such as solubility, molecular recognition and organization, is determined by the protection layer. The engineering of the latter is currently making tremendous progress. 2 The conformation of the molecules adsorbed on the metal particles directly affects the chemical properties. Structure determination would therefore greatly help the rational design of functionalized particles. Vibrational circular dichroism (VCD) spectroscopy, i.e. the differential absorption of left and right circular polarized infrared light, yields detailed information on the conformation of a chiral molecule in solution.3 VCD is more sensitive towards conformation than infrared (IR) spectroscopy and its power for structure determination of dissolved molecules, by the comparison between experimental and theoretical spectra, has impressively been demonstrated in the past. 4-7In this contribution we show that very small (,2 nm) gold nanoparticles chirally modified with N-acetyl-L-cysteine (Scheme 1) exhibit VCD activity associated with the molecules in the protection layer. Comparison with calculated VCD spectra of N-acetyl-L-cysteine adsorbed on small gold clusters allows getting rather detailed structural information. Whereas optical activity in the UV-vis of MPNs has been reported before, 8 to the best of our knowledge this is the first report on the VCD activity associated with MPNs.

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“…Theoretical calculations have predicted that a flat active site ensemble of approximately 20～25 atoms is necessary to accommodate this large complex. [39] Small particles (≤2 nm) which have large fraction of edge and corner sites could not provide sufficient space to accommodate the bulky cinchonidine-substrate intermediates, leading to the formation of racemic products. [40] For the current Pd/Al 2 O 3 catalysts, even the small Pd nanoparticles (2 nm) were large enough to supply a stable adsorption of the CD-substrate intermediate as the large particles (8～14 nm), resulting in almost constant enantioselectivities.…”

Section: Pd Particle Size Effectmentioning

confidence: 99%

Enantioselective Hydrogenation of α,β-Unsaturated Carboxylic Acids：Effects of Palladium Particle Size and Support Acidic Property

陈春辉¹,

展恩胜²,

李勇³

et al. 2013

Acta Chim. Sinica

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Effects of Pd particle size and support acidity on enantioselective hydrogenation of α,β-unsaturated carboxylic acids were systematically studied using Pd nanoparticles with different size immobilized on various oxides. Small Pd particles showed higher activity in the hydrogenation of (E)-2-methyl-2-pentenoic acid due to the larger fraction of edge sites which were more active in olefin hydrogenation; but they did not change the reaction mechanism and/or the adsorption mode of reaction intermediates. Similar correlations in the hydrogenation of (E)-2-methyl-2-butenoic acid and 2-acetamidoacrylic acid further confirmed that the size of Pd particles only mediated the activity but did not alter the enantioselectivity. On the other hand, the activity and the enantioselectivity were strongly dependent on the acidity of the support. The TOF and the ee value followed the order TiO 2 ＞γ-Al 2 O 3 ＞SiO 2 ＞CeO 2 , suggesting that the acidic support favored the adsorption of the reaction intermediates.

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Heterogeneous Enantioselective Hydrogenation over Cinchona Alkaloid Modified Platinum: Mechanistic Insights into a Complex Reaction

Cited by 251 publications

References 52 publications

Chiral segregation driven by a dynamical response of the adsorption footprint to the local adsorption environment: bitartrate on Cu(110)

Chiral segregation driven by a dynamical response of the adsorption footprint to the local adsorption environment: bitartrate on Cu(110)

Vibrational circular dichroism of N-acetyl-l-cysteine protected gold nanoparticles

Enantioselective Hydrogenation of α,β-Unsaturated Carboxylic Acids：Effects of Palladium Particle Size and Support Acidic Property

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