247
cavities of cyclodextrin but may interact with other functional groups such as carbonyls and nitrogenated groups. The catalytic activity of Au n clusters for reduction
of 4-nitrophenol in the presence of NaBH 4 was also studied. It was found that
Langmuir-Hinshelwood kinetic model fitted the reaction and the reaction proceeded
with no induction time.
Subnanometer size noble metal colloids were synthesized using a cyclodextrin
polymer-based network (from azido-β-cyclodextrin and diethynylbenzene using
click chemistry) as stabilizing agent. Transmission electron microscopy images
showed ultra-small Pd nanoparticles which were well-dispersed in the polymeric
matrix. The catalytic activity of these colloids was evaluated in the reduction of
4-nitrophenol and in a C–C coupling reaction. In the case of the 4-nitrophenol
reduction, the authors emphasize the role of the cavity of the cyclodextrin. The
cyclodextrin, whose secondary face is free, formed inclusion complex and allowed
the guest molecule to be close to the metal surface.
5.2.4 Nanoparticles Stabilized by Cyclodextrin-Based
Inclusion Complex
The combination of cyclodextrins with other stabilizing agents, i.e., alkyl ammonium salts, phosphanes, and dendrimers, was also reported for the synthesis of
metallic nanoparticles dispersed into the aqueous phase. Another strategy consisted
into the combination of cyclodextrins with polymers likely to form supramolecular
complexes leading to the development of a new reaction medium named hydrogel.
Whatever the strategy, the catalytic activity of these colloidal suspensions was also
evaluated for different kinds of reactions.
Nanoparticles Stabilized by Quaternary Ammonium-Based Salts/
Cyclodextrin Inclusion Complexes
Ionic surfactants such as alkyl ammonium salts are known to be good candidates to
stabilize active metallic nanoparticles. Moreover, this family of surfactants is well
known to strongly interact with β-cyclodextrin derivatives. Randomly methylated
cyclodextrins combined with ammonium salts bearing a lipophilic chain was used
for the synthesis of aqueous Ru nanoparticles (Hubert et al. 2009) (Fig. 5.16).
NMR spectroscopic studies were performed to prove the formation of an inclusion complex between RaMe-β-cyclodextrin and the chloride salt of N, N-dimethyl,
N-hexadecyl, N-(2-hydroxyethyl)ammonium (HEA16Cl) in water. The continuous
variation technique, named Job’s method, and transverse rotating-frame Overhauser
effect spectroscopy experiments emphasized the existence of such a complex. The
resulting nanoparticles were characterized by transmission electron microscopy and
showed a homogeneous distribution with an average size of about 4 nm. The
5 Metal Nanoparticles and Cyclodextrins for Catalytic Applications
cavities of cyclodextrin but may interact with other functional groups such as carbonyls and nitrogenated groups. The catalytic activity of Au n clusters for reduction
of 4-nitrophenol in the presence of NaBH 4 was also studied. It was found that
Langmuir-Hinshelwood kinetic model fitted the reaction and the reaction proceeded
with no induction time.
Subnanometer size noble metal colloids were synthesized using a cyclodextrin
polymer-based network (from azido-β-cyclodextrin and diethynylbenzene using
click chemistry) as stabilizing agent. Transmission electron microscopy images
showed ultra-small Pd nanoparticles which were well-dispersed in the polymeric
matrix. The catalytic activity of these colloids was evaluated in the reduction of
4-nitrophenol and in a C–C coupling reaction. In the case of the 4-nitrophenol
reduction, the authors emphasize the role of the cavity of the cyclodextrin. The
cyclodextrin, whose secondary face is free, formed inclusion complex and allowed
the guest molecule to be close to the metal surface.
5.2.4 Nanoparticles Stabilized by Cyclodextrin-Based
Inclusion Complex
The combination of cyclodextrins with other stabilizing agents, i.e., alkyl ammonium salts, phosphanes, and dendrimers, was also reported for the synthesis of
metallic nanoparticles dispersed into the aqueous phase. Another strategy consisted
into the combination of cyclodextrins with polymers likely to form supramolecular
complexes leading to the development of a new reaction medium named hydrogel.
Whatever the strategy, the catalytic activity of these colloidal suspensions was also
evaluated for different kinds of reactions.
Nanoparticles Stabilized by Quaternary Ammonium-Based Salts/
Cyclodextrin Inclusion Complexes
Ionic surfactants such as alkyl ammonium salts are known to be good candidates to
stabilize active metallic nanoparticles. Moreover, this family of surfactants is well
known to strongly interact with β-cyclodextrin derivatives. Randomly methylated
cyclodextrins combined with ammonium salts bearing a lipophilic chain was used
for the synthesis of aqueous Ru nanoparticles (Hubert et al. 2009) (Fig. 5.16).
NMR spectroscopic studies were performed to prove the formation of an inclusion complex between RaMe-β-cyclodextrin and the chloride salt of N, N-dimethyl,
N-hexadecyl, N-(2-hydroxyethyl)ammonium (HEA16Cl) in water. The continuous
variation technique, named Job’s method, and transverse rotating-frame Overhauser
effect spectroscopy experiments emphasized the existence of such a complex. The
resulting nanoparticles were characterized by transmission electron microscopy and
showed a homogeneous distribution with an average size of about 4 nm. The
5 Metal Nanoparticles and Cyclodextrins for Catalytic Applications