Graphene Film-Supported Oriented 1.1.1 Gold(0) Versus 2.0.0 Copper(I) Nanoplatelets as Very Efficient Catalysts for Coupling Reactions

Few-layered graphene-supported 1.1.1 and 2.0.0 oriented Au and Cu₂O nanoplatelets were prepared by one-step pyrolysis of the corresponding metal salts embedded in chitosan at 900 °C under inert atmosphere. These nanometric films containing oriented nanoplatelets were investigated in a series of reactions as Ullmann-type homocoupling, C–N cross-coupling and Michael addition. The catalysts exhibited turnover numbers (TONs) three to six orders of magnitude higher than those of analogous graphene-supported unoriented metal nanoparticles. In addition it has been found that oriented Cu₂O and Au nanoplatelets grafted on defective graphene also exhibit activity to promote the Michael addition of compounds with active methylene and methine hydrogens to α,β-conjugated ketone. An exhaustive characterization of these materials using spectroscopic and electron microscopy analyses has been carried out. CO₂ thermoprogrammed desorption measurements show that films of these two graphene supported catalysts exhibit some basicity that can explain their activity to promote Michael addition.