Adsorption of 1‐(1‐Naphthyl)ethylamine from Solution onto Platinum Surfaces: Implications for the Chiral Modification of Heterogeneous Catalysts

Gordon, Alexander D.; Zaera, Francisco

doi:10.1002/ange.201209815

Cited by 6 publications

(3 citation statements)

References 36 publications

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“…This model provides a rationale for the catalytic observations in which enhanced hydrogenation rates are found for chirally modified surfaces. However, care must be taken in directly transferring observations made for model systems in ultrahigh vacuum to supported catalysts operating in more severe solution environments, where, for example, different modifier adsorption geometries may occur 59 .…”

Section: Discussionmentioning

confidence: 99%

Enhanced hydrogenation activity and diastereomeric interactions of methyl pyruvate co-adsorbed with R-1-(1-naphthyl)ethylamine on Pd(111)

et al. 2016

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Unmodified racemic sites on heterogeneous chiral catalysts reduce their overall enantioselectivity, but this effect is mitigated in the Orito reaction (methyl pyruvate (MP) hydrogenation to methyl lactate) by an increased hydrogenation reactivity. Here, this effect is explored on a R-1-(1-naphthyl)ethylamine (NEA)-modified Pd(111) model catalyst where temperature-programmed desorption experiments reveal that NEA accelerates the rates of both MP hydrogenation and H/D exchange. NEA+MP docking complexes are imaged using scanning tunnelling microscopy supplemented by density functional theory calculations to allow the most stable docking complexes to be identified. The results show that diastereomeric interactions between NEA and MP occur predominantly by binding of the C=C of the enol tautomer of MP to the surface, while simultaneously optimizing C=O····H2N hydrogen-bonding interactions. The combination of chiral-NEA driven diastereomeric docking with a tautomeric preference enhances the hydrogenation activity since C=C bonds hydrogenate more easily than C=O bonds thus providing a rationale for the catalytic observations.

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Section: Discussionmentioning

confidence: 99%

Enhanced hydrogenation activity and diastereomeric interactions of methyl pyruvate co-adsorbed with R-1-(1-naphthyl)ethylamine on Pd(111)

et al. 2016

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“…In order to test the mass transport through the shells of our nanostructures under more realistic conditions, the uptake of a number of aromatic and cinchona–alkaloid based molecules was studied in situ in liquid solutions. The general cinchona motive used here stems from our particular interest in using those structures as chiral modifiers for enantioselective catalysis, − but the results from this work are expected to be more general and to provide a semiquantitative picture of the mass transport limitations associated with core–shell and yolk–shell nanostructures as a function of the size and shape of the molecules involved. The structures of the specific molecules used here are provided in Figure , and some of their relevant physical properties are given in Table .…”

Section: Resultsmentioning

confidence: 99%

Mass Transport across the Porous Oxide Shells of Core–Shell and Yolk–Shell Nanostructures in Liquid Phase

Liang

Joo

et al. 2013

J. Phys. Chem. C

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The mass transport of a number of molecules dissolved in a liquid solvent through the shells of Pt@SiO2 core–shell and Pt@Void@TiO2 yolk–shell nanostructures was characterized in situ by infrared absorption spectroscopy. Our samples, which were used here to represent the core–shell and yolk–shell nanostructures that have become so popular in recent times, were determined to exhibit a dual distribution of pore sizes, with a majority of micropores with diameters of less than 1 nm and a second group of mesopores with windows approximately 4 nm in diameter. The uptake of carbon monoxide from CCl4 or ethanol solutions onto the surface of the metal of these nanostructures was characterized first. It was determined that adsorption is possible with both samples, and that saturation on the metal surface precedes saturation on the oxide shell. This latter observation suggests that the access of the CO molecules (and all other molecules studied here) to the inside of the yolk–shell structures may be controlled by the mass transport of the liquid through the porous network of the shells, not by the diffusion of the dissolved gas alone. Additional studies were carried out with a family of cinchona alkaloid derivatives and with a porphyrin, covering a range of molecular sizes of approximately 5–20 Å in diameter. Adsorption of all those molecules on the Pt surfaces of both nanoarchitectures was deemed possible by a combination of tests, including the detection of changes in peak frequencies or peak intensities and measurements of the reversibility of the adsorption. Our results indicate that although the sol–gel synthetic method used to prepare the shells usually produces solids with microporous structures, a secondary mesoporous network that also develops in these nanostructures can provide a direct path to the metal nanocores, affording the mass transport of large molecules in liquid solutions in and out of the inside volumes. We also show that the attoliter-size volumes encased by typical shells in yolk–shell nanostructures are sufficient to afford adsorption displacement processes.

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“…29 On the other hand, 1-naphthylethylamine, which is chemically similar to cinchonidine, does not self-assemble on palladium, suggesting that it acts as a one-to-one modifier. [30][31][32][33][34] While such studies provide detailed information on the local and extended chiral structures on the surface, with the exception of studies of co-adsorbed tartaric acid and methylacetoacetate on nickel, 15 they provide little information on the interactions that lead to enantioselectivity. Such interactions can be explored using chiral probe molecules (here, R-and S-propylene oxide (PO) or glycidol) on chirally modified surfaces.…”

Section: Introductionmentioning

confidence: 99%

Chemisorptive enantioselectivity of chiral epoxides on tartaric-acid modified Pd(111): three-point bonding

Mahapatra

2015

Phys. Chem. Chem. Phys.

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The chemisorption of two chiral molecules, propylene oxide and glycidol, is studied on tartaric-acid modified Pd(111) surfaces by using temperature-programmed desorption to measure adsorbate coverage. It is found that R-glycidol shows preferential enantioselective chemisorption on (S,S)-tartaric acid modified Pd(111) surfaces, while propylene oxide does not adsorb enantioselectively. The enantioselectivity of glycidol depends on the tartaric acid coverage, and is exhibited for low tartaric acid coverages indicating that the bitartrate phase is responsible for the chiral recognition. The lack of enantioselectivity when using propylene oxide as a chiral probe implies that the enantiospecific interaction between glycidol and bitartate species is due to hydrogen-bonding interactions of the -OH group of glycidol. Scanning tunneling microscopy images were collected for tartaric acid adsorbed on Pd(111) under the same experimental conditions as used for enantioselective experiments. When tartaric acid is dosed at room temperature and immediately cooled to 100 K for imaging, individual bitartrate molecules were found. Density functional theory (DFT) calculations show that bitartrate binds to Pd(111) through its carboxylate groups and the -OH groups are oriented along the long axis of the bitartrate molecule. An enantiospecific interaction is found between glycidol and bitartate species where R-glycidol binds more strongly than S-glycidol to (S,S)-bitartate species by simultaneously forming hydrogen bonds with both the hydroxyl and carboxylate groups, thereby providing three-point bonding.

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Adsorption of 1‐(1‐Naphthyl)ethylamine from Solution onto Platinum Surfaces: Implications for the Chiral Modification of Heterogeneous Catalysts

Cited by 6 publications

References 36 publications

Enhanced hydrogenation activity and diastereomeric interactions of methyl pyruvate co-adsorbed with R-1-(1-naphthyl)ethylamine on Pd(111)

Enhanced hydrogenation activity and diastereomeric interactions of methyl pyruvate co-adsorbed with R-1-(1-naphthyl)ethylamine on Pd(111)

Mass Transport across the Porous Oxide Shells of Core–Shell and Yolk–Shell Nanostructures in Liquid Phase

Chemisorptive enantioselectivity of chiral epoxides on tartaric-acid modified Pd(111): three-point bonding

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