encapsulated metal clusters (DEMCs) [103]. L-Amino acid-derived chiral NHCs
with a hydroxyl group were chosen as a modifier. The hydroxy group was expected
to strengthen interactions of the NHC-ligated Au nanoparticle with SBA-15 and to
facilitate proto-deauration that had been postulated to be turnover-limiting step
[104]. Au nanoparticles were prepared from a chiral NHC-Au complex in the
presence of a dendrimer (G4OH) that enhances the stability of the nanoparticles to
aggregation, and they were further loaded on SBA-15 (Scheme 39). XPS, XANES,
and time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis revealed
that the Au nanoparticles prepared from the NHC complex were coated with monolayers of Au(I) species, presumably NHC-Au(I) complexes.
Scheme 37 Preparation of a molecular catalyst and a Pd nanoparticle catalyst from Fe 3 O 4 -
supported chiral NHC 26
Scheme 38 Chiral NHC-Pd nanoparticle catalyzed asymmetric allylation of 4-nitrobenzaldehyde
with allyltributyltin
Scheme 39 Preparation of supported Au nanoparticles with NHC ligand 29
Chiral Metal Nanoparticles for Asymmetric Catalysis
301