Supramolecular Complex of 2-Hydroxypropyl-β-cyclodextrin with <scp>d</scp>- and <scp>l</scp>-tryptophan

An efficient, selective and recoverable catalytic system for ligand-free aqueous Heck reactions using hydroxypropylated cyclodextrins (HPCDs) and palladium on calcium carbonate (Pd/CaCO 3 ) is highlighted. Remarkably, stereo-and chemoselectivities could be tuned by the cavity size of cyclodextrins, exploiting the relevance of host-guest interactions. UVVis experiments have led to strong evidence concerning an interplay between Pd(II) and a-HPCD, possibly ascribed to a reduction/stabilization effect of CDs. Unexpectedly, hydroarylation was the favored pathway with acrylonitrile which provided access to 3-phenylpropionitrile derivatives without usual hydride donors. Finally, determination of soluble PdA C H T U N G T R E N N U N G (0/II) via AAS enabled the definition of a predominant homogeneous mechanism in which TONs over 5000 were observed.

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Palladium on Calcium Carbonate Combined to 2‐Hydroxypropyl‐α/β‐cyclodextrins: A Selective Catalytic System for Aqueous Heck Coupling and Hydroarylation

Senra

Malta

Souza

et al. 2008

Adv Synth Catal

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Hydroxypropyl‐α‐Cyclodextrin‐Capped Palladium Nanoparticles: Active Scaffolds for Efficient Carbon‐Carbon Bond Forming Cross‐Couplings in Water

et al. 2009

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A new approach for the preparation of palladium nanoparticles in water from a renewable source, 2-hydroxypropyl-a-cyclodextrin (a-HPCD), which acts both as a reductant and capping agent, is presented. The palladium nanoparticles were characterized by using dynamic light scattering (DLS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), which revealed the formation of spherical particles in the size range of 2-7 nm. Further analysis by Fourier-transform infrared spectroscopy (FT-IR) and 1 H NMR did not show covalent bonds between cyclodextrins and palladium nanoparticles, suggesting that a-HPCD is only physically adsorbed on the nanoparticle surface, presumably through hydrophobic interactions which limit the mutual coalescence of nanoclusters. The catalytic activity was tested in Suzuki, Heck and Sonogashira reactions in neat water, providing good yields and selectivities of coupling products under very low Pd loadings (0.5-0.01 mol%). Remarkably, the nanocatalyst showed significant stability hence the aqueous phase remained active for four subsequent runs. The combination of a binding site for substrates (the HPCD cavity) and a reactive centre (Pd core) provides a potential to explore functional catalysis in aqueous medium.

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Cyclodextrin ‐ Stabilized Palladium Nanoparticles on Ceria: Investigation of Support Interactions and Pivotal Promotion in the Suzuki‐Miyaura Reaction

et al. 2020

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The present work is focused on the understanding of the CeO2 support interactions with cyclodextrin‐stabilized palladium nanoparticles (PdNPs) and the effect in the Suzuki‐Miyaura reaction outcome. Mostly, it is evidenced the strong influence of the cyclodextrin torus on the reactivity of PdNPs towards the ceria matrix. Structural characterization by X‐rays photoelectron spectroscopy (XPS) Raman spectroscopy, diffuse reflectance spectroscopy (DRS) and powder X‐rays diffraction (XRD, via Rietveld refinement) afforded to infer that palladium is being partially brought into the CeO2 structure. Transmission electron microscopies (TEM and STEM) visualizations allowed to evidence a bimodal size distribution of PdNPs (1–5 nm and 20–100 nm) over the catalysts even though particles up to 5 nm are probably the most responsible for the catalytic results reported herein.

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Supramolecular Complex of 2-Hydroxypropyl-β-cyclodextrin with d- and l-tryptophan

Cited by 11 publications

References 16 publications

Palladium on Calcium Carbonate Combined to 2‐Hydroxypropyl‐α/β‐cyclodextrins: A Selective Catalytic System for Aqueous Heck Coupling and Hydroarylation

Palladium on Calcium Carbonate Combined to 2‐Hydroxypropyl‐α/β‐cyclodextrins: A Selective Catalytic System for Aqueous Heck Coupling and Hydroarylation

Hydroxypropyl‐α‐Cyclodextrin‐Capped Palladium Nanoparticles: Active Scaffolds for Efficient Carbon‐Carbon Bond Forming Cross‐Couplings in Water

Cyclodextrin ‐ Stabilized Palladium Nanoparticles on Ceria: Investigation of Support Interactions and Pivotal Promotion in the Suzuki‐Miyaura Reaction

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