A New Heterogeneous Catalyst Obtained via Supramolecular Decoration of Graphene with a Pd²⁺ Azamacrocyclic Complex

A new G-(H₂L)-Pd heterogeneous catalyst has been prepared via a self-assembly process consisting in the spontaneous adsorption, in water at room temperature, of a macrocyclic H₂L ligand on graphene (G) (G + H₂L = G-(H₂L)), followed by decoration of the macrocycle with Pd²⁺ ions (G-(H₂L) + Pd²⁺ = G-(H₂L)-Pd) under the same mild conditions. This supramolecular approach is a sustainable (green) procedure that preserves the special characteristics of graphene and furnishes an efficient catalyst for the Cu-free Sonogashira cross coupling reaction between iodobenzene and phenylacetylene. Indeed, G-(H₂L)-Pd shows an excellent conversion (90%) of reactants into diphenylacetylene under mild conditions (50 °C, water, aerobic atmosphere, 14 h). The catalyst proved to be reusable for at least four cycles, although decreasing yields down to 50% were observed.