Orientation of 10,11-dihydrocinchonidine on Pt(111)

Evans, T.; Woodhead, A.P.; Gutiérrez-Sosa, A.; Thornton, G.; Hall, T.J.; Davis, A.A.; Young, Nigel A.; Wells, Peter B.; Oldman, R. J.; Plashkevych, Oleksandr; Vahtras, Olav; Ågren, H.; Carravetta, Vincenzo

doi:10.1016/s0039-6028(99)00694-9

Cited by 77 publications

(63 citation statements)

References 16 publications

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“…The same is suggested by the different effects of increasing concentrations of the two modifiers on ee: it is well-known that the geometry of CD adsorption changes with increasing surface coverage. At lower CD concentrations, parallel adsorption via the quinoline ring was observed, whereas at higher concentrations the tilted species was also observed [27,29,36].…”

Section: Interpretation Of the Results And Conclusionmentioning

confidence: 92%

Enantioselective hydrogenation of ethyl pyruvate catalysed by cinchonine-modified Pt/Al2O3: tilted adsorption geometry of cinchonine

et al. 2005

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The enantioselective hydrogenation of ethyl pyruvate (EtPy) was studied on Pt-alumina catalyst modified by cinchonine (CN) and for comparison by cinchonidine (CD) in toluene and in AcOH. The effects of the modifiers concentration on the reaction rate and the enantioselectivity were examined. Using the Engelhard 4759 catalyst under mild experimental conditions (room temperature, hydrogen pressure 1 bar) in the case of CN (S)-ethyl lactate (EtLt) formed in excess (ee) (in AcOH ee max $ 88%; in toluene ee max $ 72%). In the case of CD (R)-EtLt formed in excess (in AcOH ee max $93%; in toluene ee max $ 84%). The results of H-D exchange measurements and results of modifier mixtures suggest that the compounds responsible for chiral induction are different intermediates, which structure depends mostly on the acidic or non-acidic nature of the hydrogenation medium. The proposed structure of intermediate responsible for enantioselection is an 1:1 CN-or CD-EtPy surface complex in which the quinoline skeleton of CD approximately parallel on the Pt surface while the quinoline plane of CN being tilted relative to the Pt surface under identical experimental conditions.

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Section: Interpretation Of the Results And Conclusionmentioning

confidence: 92%

Enantioselective hydrogenation of ethyl pyruvate catalysed by cinchonine-modified Pt/Al2O3: tilted adsorption geometry of cinchonine

et al. 2005

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“…The adsorption of 10,11-dihydrocinchonidine on Pt(111) under ultrahigh vacuum conditions was investigated by near-edge X-ray absorption fine structure spectroscopy (NEXAFS). 26 At room temperature, a mean angle of about zero was found between the quinoline plane and the surface, whereas at 323 K, the quinoline ring was more tilted away from the surface, forming a mean angle of about 60°. Quinoline itself was investigated by the group of Lambert and was also found to adsorb preferentially flat on Pt(111) at room temperature.…”

Section: Validation Of Model Assumptionsmentioning

confidence: 97%

“…Furthermore, the loss in enantioselectivity when blocking the quinuclidine N of the modifier would indicate that the quinuclidine N is involved in the formation of the "chiral footprint". However, in situ infrared 23,24 and Raman spectroscopies 25 of cinchonidine adsorption, as well as near edge X-ray absorption fine structure spectroscopy (NEXAFS), of 10,11-dihydrocinchonidine on Pt-(111) in ultrahigh vacuum 26 indicate that the modifier is anchored via the quinoline ring. Thus in the light of currently available experimental findings a "chiral footprint" mechanism seems improbable for the Pt-cinchona alkaloid system.…”

Section: Chiral Recognition On a Metal Surfacementioning

confidence: 99%

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

Buergi¹,

Baiker²

2005

ChemInform

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Modification of a metal surface by a strongly adsorbed chiral organic molecule has proven to be an interesting strategy for heterogeneous chiral catalysis. Platinum chirally modified by cinchona alkaloids, successfully applied for the enantioselective hydrogenation of R-ketoesters, is probably the most prominent catalyst based on this concept. Despite considerable research efforts toward understanding of this complex catalytic system, the proposed mechanistic models are still debated. Here we discuss how enantiodifferentiation can be induced on a catalytically active surface and validate the models proposed for the platinumcinchona system in the light of the existing molecular knowledge.

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“…In fact, the D type catalyst was prepared at room temperature in THF while the B type was prepared at $95°C in aqueous solutions. Since it is known that cinchonidine adsorbs predominantly in the flat mode at lower temperatures [21,22], it is possible that this is one of the differences between the B and D type systems.…”

Section: Comparison Of D B ''Quasi-homogeneous''mentioning

confidence: 99%

Examination of catalytic behavior and origin of the initial transient period for Pt nanoclusters modified with cinchonidine

2006

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Nanoclusters prepared by a novel water-free method are compared directly with nanoclusters prepared by the known aqueous preparation as well as conventional Pt/Al 2 O 3 for the enantioselective hydrogenation of ethyl pyruvate. The catalytic behavior of cinchonidine on colloidal Pt was investigated during ethyl pyruvate hydrogenation in acetic acid under 10 bar of hydrogen at 22°C with (1 mmol L )1 ) and without addition of free cinchonidine. The effect of hydrogen pressure, cinchonidine concentration, ethyl pyruvate and catalyst loading on the enantiomeric excess (EE) with time were also studied. Through these studies, we propose that the nature of the observed initial transient period (ITP) for these ''quasi-homogeneous'' systems may be explained by desorption of the weakly adsorbed tilted ''N lone pair bonded'' cinchonidine species from the Pt surface due to interaction with hydrogen.

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Orientation of 10,11-dihydrocinchonidine on Pt(111)

Cited by 77 publications

References 16 publications

Enantioselective hydrogenation of ethyl pyruvate catalysed by cinchonine-modified Pt/Al2O3: tilted adsorption geometry of cinchonine

Enantioselective hydrogenation of ethyl pyruvate catalysed by cinchonine-modified Pt/Al2O3: tilted adsorption geometry of cinchonine

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

Examination of catalytic behavior and origin of the initial transient period for Pt nanoclusters modified with cinchonidine

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