The most stable adsorption geometries of two chiral modifiers on Pt(111)

Zeng, Yang; Masini, Federico; Rasmussen, Anton M. H.; Groves, Michael N.; Albert, Vincent; Boukouvalas, John; McBreen, Peter H.

doi:10.1016/j.susc.2018.02.008

Cited by 9 publications

(14 citation statements)

References 42 publications

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“…The broad feature at 1320–1230 cm –1 is composed of three peaks: an ester group vibration at ∼1297 cm –1 and two lower-frequency bands due to ρ(O–CH 3 ) and ν sym (CF 3 ) vibrations. Chemisorption of the chiral modifier is detected by a δ sym (CH 3 ) band at 1377 cm –1 (Figure b) . As reported elsewhere, the selective RAIRS activity of this peak in the midfrequency region is fully consistent with the predicted ( R )-NEA adsorption geometry (insert to Figure b) where the naphthyl group is π-bonded to the surface and the amine group forms an additional on-top bond to a platinum atom …”

Section: Resultssupporting

confidence: 85%

Ligand-Assisted Carbonyl Bond Activation in Single Diastereomeric Complexes on Platinum

et al. 2022

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It is a significant challenge to relate ligand-assisted bond activation on metal surfaces to specific adsorption and intermolecular binding structures. To address this objective, we studied carbonyl bond activation in single chirality transfer complexes formed by methyl 3,3,3-trifluoropyruvate (i.e., MTFP) and (R)-1-(1-naphthyl)ethylamine (i.e., (R)-NEA) on a Pt(111) surface. The experiments combined reflectance absorbance infrared spectroscopy (RAIRS), scanning tunneling microscopy (STM), and density functional theory (DFT) methods. While STM measurements, in combination with DFT calculations, permit the study of single surface complexes, RAIRS is an ensemble technique that yields a composite spectrum resulting from an often heterogeneous distribution of molecular structures on the sampled surface. We show that the intrinsic thermal behavior of the MTFP/(R)-NEA/Pt(111) system facilitates meaningful comparison between single complex measurements by STM and ensemble measurements by RAIRS in that the vibrational signal can be attributed to a small number of complexation configurations, one of which has a high relative abundance. We take advantage of mode mixing in a ν(CF3) + ν(CO)keto vibration to detect a spectroscopic signature for complexation-induced carbonyl bond activation. A red-shift of the band correlates with DFT-predicted lengthening of the bridge-bonded carbonyl group. While the intensity of the shifted band is in the majority due to the most abundant complexation configuration, minority states produce line broadening. In addition to providing insight on rate-enhancement in enantioselective reactions on catalysts bearing chiral auxiliaries, the study contributes to the development of ligand control of reactivity and selectivity in heterogeneous catalysis.

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Section: Resultssupporting

confidence: 85%

Ligand-Assisted Carbonyl Bond Activation in Single Diastereomeric Complexes on Platinum

et al. 2022

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“…Simpler models have been used to better be able to address the fundamental chemistry involved, following a so-called modern surface science approach. Well-defined surfaces, single crystal or polycrystalline disks of the main metal in this case, are placed in well-controlled environments, namely, ultrahigh vacuum (UHV) conditions, to be able to use a battery of surface-sensitive techniques such as X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), − scanning tunneling microscopy (STM), ,,, temperature-programmed desorption (TPD), ,,, and reflection–absorption infrared absorption spectroscopy (RAIRS), ,,− to extract molecular details on the adsorption and reactivity of the reactants and modifiers. ,, This approach has provided much insight into the surface chiral chemistry involved, but is limited by the simplicity of the systems used, which do not include the solvent present under catalytic conditions (a fact referred to as the “pressure gap”), − and ignores the characteristics of realistic catalysts, where the metal is present as small nanoparticles (NPs) dispersed on a high-surface-area support, typically an oxide such as silica or alumina (the “materials gap”). ,− …”

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

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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.

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“…In contrast, it can be seen from the comparison of structures g and i that the amine–Pt interaction has a similar on-top geometry for both ( R )-8Me-NEA-1 and ( R )-NEA-1. The possibility that ( R )-8Me-NEA undergoes partial dehydrogenation on Pt(111) is considered because Papp and co-workers reported that the conversion of toluene (Ph–CH 3 ) to benzyl (Ph–CH 2 ) on Pt(111) occurs upon heating above 270 K. However, as described elsewhere, detailed reflectance absorbance infrared spectroscopy measurements provide no clear evidence for dehydrogenation to ( R )-8CH 2 -NEA on Pt(111) . The thermal stability of the modifier may differ from that of toluene because of adsorption site constraints imposed by combined naphthyl–Pt and amine–Pt bonding.…”

Section: Results and Discussionmentioning

confidence: 99%

“…This is in keeping with the strong chemisorption interaction, combining πchemisorption of the naphthyl ring and an additional N−Pt bond (Figure 1g−j). 29,37 Hence, for both chiral modifiers, the relative populations of the two conformers are determined by adsorption dynamics: once a naphthyl face finds its optimal interaction with the surface it cannot then convert under vacuum to a state with the opposite naphthyl face toward the surface. We attribute the lower calculated adsorption energy of (R)-8Me-NEA-2 relative to (R)-8Me-NEA-1 to intramolecular steric repulsion that forces the N−Pt bonding interaction out of its optimal on-top geometry.…”

Section: ■ Introductionmentioning

confidence: 99%

Relative Abundances of Surface Diastereomeric Complexes Formed by Two Chiral Modifiers That Differ by a Methyl Group

et al. 2020

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Enantioselectivity in heterogeneous catalysis can be induced through the adsorption of optically active compounds known as chiral modifiers. The modifiers typically stereodirect prochiral reactants on the metal surface through the formation of diastereomeric complexes. Surface science measurements on model systems show several examples where such complexes display multiple abundant binding configurations. Insights into the factors determining the relative populations of complexation states can be potentially gained from comparing slightly variant chiral modifiers. Here, we compare scanning tunneling microscopy (STM) data for chirality transfer complexes formed by (R)-1-(1-naphthyl)ethylamine and (R)-1-(8-methyl-1-naphthyl)ethylamine coadsorbed with the prochiral substrate 2,2,2-trifluoroacetophenone in order to probe for changes induced by the methyl substituent. The comparison shows changes in relative abundances beyond those predicted by only direct steric interaction. Density functional theory (DFT) methods are used to calculate complexation energies. A number of rationalizations are proposed for the experimentally determined differences in relative abundances and also for differences between DFT-predicted and STM-measured populations.

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The most stable adsorption geometries of two chiral modifiers on Pt(111)

Cited by 9 publications

References 42 publications

Ligand-Assisted Carbonyl Bond Activation in Single Diastereomeric Complexes on Platinum

Ligand-Assisted Carbonyl Bond Activation in Single Diastereomeric Complexes on Platinum

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

Relative Abundances of Surface Diastereomeric Complexes Formed by Two Chiral Modifiers That Differ by a Methyl Group

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