Gold nanoparticles stabilized by PEG-tagged imidazolium salts as recyclable catalysts for the synthesis of propargylamines and the cycloisomerization of γ-alkynoic acids

Abstract

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.