Chiral Modification of Catalytic Surfaces

Ma, Zhen; Zaera, Francisco

doi:10.1002/9783527625321.ch5

Cited by 17 publications

(9 citation statements)

References 138 publications

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“…For the case of cinchonidine tethered via a mercapto linker attached to the peripheral vinyl moiety in the quinuclidine ring (Scheme ), 29 Si CP-MAS NMR data strongly suggest that a direct bond is formed between the surface and the OH group of the cinchona alkaloid (Figure ). The latter problem could be avoided by tethering the cinchonidine using a carbamate linker instead, since that attaches directly to the alcohol moiety (Scheme ), but, either way, the chiral pocket in cinchonidine, believed to be responsible for much of its enantioselective catalysis, ,, may be compromised. Alternatively, the cinchonidine–surface interaction may be avoided or broken by changing the solvent: it does not appear to survive after washing the catalyst with ethanol.…”

Section: Discussionmentioning

confidence: 99%

Interference of the Surface of the Solid on the Performance of Tethered Molecular Catalysts

Hong

Zaera

2012

J. Am. Chem. Soc.

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The catalytic performance of cinchonidine in the promotion of thiol additions to conjugated ketones was used as a probe to assess the tethering of molecular functionality onto solid surfaces using well-known "click" chemistry involving easy-to-react linkers. It has been assumed in many applications that the tethered molecules retain their chemical properties and dominate the chemistry of the resulting solid systems, but it is shown here that this is not always the case. Indeed, a loss of enantioselectivity was observed upon tethering, which could be accounted for by a combination of at least three effects: (1) the nonselective catalytic activity of the surface of the solid itself; (2) the activity of the OH species generated by hydrolysis of some of the Si-alkoxy groups in the trialkoxy moieties used to bind many linkers to oxide surfaces; and (3) the bonding of the molecule to be tethered directly to the surface. Several ideas were also tested to minimize these problems, including the silylation of the active OH groups within the surface of the oxide support, the selection of solvents to optimize silane polymerization and minimize their breaking up via hydrolysis or alcoholysis reactions, and the linking at defined positions in the molecule to be tethered in order to minimize its ability to interact with the surface.

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Section: Discussionmentioning

confidence: 99%

Interference of the Surface of the Solid on the Performance of Tethered Molecular Catalysts

Hong

Zaera

2012

J. Am. Chem. Soc.

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“…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

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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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“…This idea has been central in some recent attempts to make known hydrogenation catalysts enantioselective for the manufacture of chiral compounds. , Unfortunately, because of the present lack of understanding of the molecular details that drive this type of catalytic promotion, only a handful of examples are yet known where chiral modification is operative, notably those involving cinchona alkaloids (Figure ) . Molecular modifiers can also be used to stabilize specific structures in nanoparticles, even chiral ones …”

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The New Materials Science of Catalysis: Toward Controlling Selectivity by Designing the Structure of the Active Site

Zaera

2010

J. Phys. Chem. Lett.

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New self-assembly and nanotechnology synthetic methodology is finding its way into the preparation of heterogeneous catalysts. The new approaches afford better design of active sites to fine-tune the selectivity of specific catalytic processes. Examples are provided here for the preparation of supports for catalysts with well-defined structures, for the use of nanostructures with well-defined sizes and shapes as active phases, for the grafting of molecular functionality to solid surfaces, and for the assembly of complex nanostructures to illustrate the recent advances in this area of research. It is argued that by combining these new synthetic tools with mechanistic studies via surface science and theoretical studies, it should be finally possible to design highly selective catalysts from first principles, the holy grail of the field of catalysis.

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Chiral Modification of Catalytic Surfaces

Cited by 17 publications

References 138 publications

Interference of the Surface of the Solid on the Performance of Tethered Molecular Catalysts

Interference of the Surface of the Solid on the Performance of Tethered Molecular Catalysts

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

The New Materials Science of Catalysis: Toward Controlling Selectivity by Designing the Structure of the Active Site

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