251
The synthesized nanoparticles (diphosphine alone and phosphine-cyclodextrin
mixture) were fully characterized by several techniques (transmission electron
microscopy, high-resolution transmission electron microscopy, wide-angle X-ray
scattering, dynamic light scattering, liquid and solid NMR spectroscopy). Whatever
the stabilizer (without or with cyclodextrin as co-additive), transmission electron
microscopy images showed small and well-dispersed particles with an average
diameter between 1.2 nm and 1.5 nm. The nanoparticle environment in solution was
studied by dynamic light scattering. The results showed that the hydrodynamic
radius depended on the amount of cyclodextrin present during the nanoparticle synthesis which was a strong indication that the cyclodextrins surround the metal
nanoparticle surface. Resonance shifts in
1
H and
31
P NMR in D 2 O confirmed the
presence of a weak interaction between the dppbs and RaMe-β-cyclodextrin (aromatic protons and protons which are in the cyclodextrin cavity). However, the addition of RaMe-β-cyclodextrin on a preformed dppbs-stabilized Ru nanoparticle
solution did not change the NMR spectra, thus evidencing that the dppbs/cyclodextrin complex was formed only if the diphosphine and cyclodextrin were both present at the beginning of the synthesis.
In order to investigate the influence of the cyclodextrin on the catalytic performances of the diphosphine-stabilized nanoparticles, the hydrogenation of model
compounds such as styrene, acetophenone, and m-methylanisole was carried out.
Based on turnover frequency values, whatever the substrate, an activity improvement was observed with increasing the initial amount of cyclodextrin. More interestingly, in the case of m-methylanisole, it was observed that the quantity of
cyclodextrin dramatically influenced the stereoselectivity toward the preferential
Fig. 5.18 Synthesis of dppbs: RaMe-β-cyclodextrin Ru nanoparticle system. (Adapted from
Guerrero et al. 2013)
5 Metal Nanoparticles and Cyclodextrins for Catalytic Applications
The synthesized nanoparticles (diphosphine alone and phosphine-cyclodextrin
mixture) were fully characterized by several techniques (transmission electron
microscopy, high-resolution transmission electron microscopy, wide-angle X-ray
scattering, dynamic light scattering, liquid and solid NMR spectroscopy). Whatever
the stabilizer (without or with cyclodextrin as co-additive), transmission electron
microscopy images showed small and well-dispersed particles with an average
diameter between 1.2 nm and 1.5 nm. The nanoparticle environment in solution was
studied by dynamic light scattering. The results showed that the hydrodynamic
radius depended on the amount of cyclodextrin present during the nanoparticle synthesis which was a strong indication that the cyclodextrins surround the metal
nanoparticle surface. Resonance shifts in
1
H and
31
P NMR in D 2 O confirmed the
presence of a weak interaction between the dppbs and RaMe-β-cyclodextrin (aromatic protons and protons which are in the cyclodextrin cavity). However, the addition of RaMe-β-cyclodextrin on a preformed dppbs-stabilized Ru nanoparticle
solution did not change the NMR spectra, thus evidencing that the dppbs/cyclodextrin complex was formed only if the diphosphine and cyclodextrin were both present at the beginning of the synthesis.
In order to investigate the influence of the cyclodextrin on the catalytic performances of the diphosphine-stabilized nanoparticles, the hydrogenation of model
compounds such as styrene, acetophenone, and m-methylanisole was carried out.
Based on turnover frequency values, whatever the substrate, an activity improvement was observed with increasing the initial amount of cyclodextrin. More interestingly, in the case of m-methylanisole, it was observed that the quantity of
cyclodextrin dramatically influenced the stereoselectivity toward the preferential
Fig. 5.18 Synthesis of dppbs: RaMe-β-cyclodextrin Ru nanoparticle system. (Adapted from
Guerrero et al. 2013)
5 Metal Nanoparticles and Cyclodextrins for Catalytic Applications