Gold nanoparticles stabilized by PEG-tagged imidazolium salts as recyclable catalysts for the synthesis of propargylamines and the cycloisomerization of γ-alkynoic acids†
We report the synthesis of PEGylated imidazolium (bromide and tetrafluoroborate) and tris-imidazolium (bromide) salts containing triazole linkers, and their use as stabilizers for the preparation of water-soluble gold nanoparticles by reduction of tetrachloroauric acid with sodium borohydride. The nanomaterials have been characterized. The X-Ray Photoelectron Spectroscopy (XPS) indicated the presence of Au(I) and Au(0) species, the oxidized form being more abundant in the nanomaterial derived from the tris-imidazolium bromide. The catalytic activity of these gold nanoparticles has been proved in the A3 coupling between carbonyl compounds, terminal alkynes and amines to afford propargylamines, and in the cycloisomerization of γ-alkynoic acids to enol lactones. The nanomaterial derived from the PEG-tagged tris-imidazolium bromide provided the best performance and it has been recycled in both reactions (up to four and six runs) taking advantage of its solubility properties.