Ligand effects in the stabilization of gold nanoparticles anchored on the surface of graphene: Implications in catalysis

Abstract

Gold nanoparticles (Au NPs) functionalized with N-heterocyclic carbene (NHC) ligands immobilized ontographene are obtained via spontaneous decomposition of well-defined gold-NHC complexes by reducedgraphene oxide (rGO) without reducing agents. NHC ligands are responsible for the formation of air-stable, crystalline and small (3.0–4-0 nm) Au NPs homogeneously distributed on the surface of graphene.The catalytic properties of three Au NPs functionalized with different ligands were tested in two bench-mark reactions (hydration of alkynes and intramolecular hydroamination of alkynes). The results reveal apronounced ligand effect on the stability of Au NPs on graphene, by acting as a bridge between them. TheAu NPs functionalized with a NHC ligand lacking a polyaromatic group or having a naphthyl tag displayedlimited stability and fast deactivation in the first run. On the contrary, the Au NPs functionalized with aNHC ligand containing a pyrenyl handle showed superior catalytic activity and can be recycled at leastten times. The particle size of the Au NPs is preserved after the recycling process indicating a high stabil-ity. These results illustrate the use of purposely designed ligands having affinity for both Au NPs and gra-phene to increase the stability of the hybrid catalyst.