β-Cyclodextrins grafted with chiral amino acids: A promising supramolecular stabilizer of nanoparticles for asymmetric hydrogenation?

• Ruthenium suspensions were efficiently prepared and characterized in water.
• Stabilization of nanoparticles by randomly methylated β-cyclodextrins grafted with chiral amino-acid moieties was investigated.
• Ruthenium suspensions were evaluated in biphasic hydrogenation.
• Promising results in terms of activity and selectivity were obtained.

Water-soluble ruthenium nanoparticles stabilized by randomly methylated β-cyclodextrins (RaMeCDs) grafted with chiral amino-acid moieties like l-alanine (Ala) and l-leucine (Leu) were prepared in aqueous solution by two approaches: (i) a one-step hydrogen reduction of ruthenium trichloride as metal source in the presence of appropriate cyclodextrins (one-pot method) or (ii) a NaBH4 reduction of the metal salts, followed by the stabilization of ruthenium hydrosol by the addition of chirally modified RaMeCDs (cascade method). The influence of the ligand's nature and the synthesis methodologies on the size, dispersion and surface properties of the obtained ruthenium colloids were studied by TEM and NMR analyses. The spherical ruthenium suspensions contain very small particles (0.82–1.00 nm) with narrow size distributions. Their catalytic properties were evaluated in biphasic hydrogenation of various prochiral compounds (olefins, ketones and disubstituted arenes) showing promising results in terms of activity and selectivity. Nevertheless, no significant enantiomeric excesses were observed.

Figure optionsDownload high-quality image (154 K)Download as PowerPoint slide