Efficient one-pot synthesis of propargylamines catalysed by gold nanocrystals stabilized on montmorillonite

Abstract

Size selective Au⁰-nanoparticles were generated in situ in the nanopores of modified montmorillonite. The modification of montmorillonite was carried out with HCl under controlled conditions for generating nanopores (less than 8 nm) in the matrix and these nanopores acted as “hosts” for the in situ generation of Au⁰-nanoparticles. The synthesis consisted of impregnation of the acid-activated montmorillonite with HAuCl₄ aqueous solution followed by reduction with NaBH₄. The synthesised Au⁰-nanoparticles crystallized in the face centred cubic lattice were single crystals with a preferential growth direction along the (111) plane. A N₂ adsorption–desorption study revealed specific surface areas of 327–579 m² g⁻¹, large specific pore volumes ~0.7 cm³ g⁻¹, and pore diameters of 0–10 nm of the support. TEM, FESEM and X-ray studies indicate that Au⁰-nanoparticles of 0–10 nm were evenly distributed on the support which then serves as an efficient green catalyst for the one-pot, three-component coupling of an aldehyde, an amine and an alkyne via C–H alkyne-activation to synthesize propargylamines with 82–94% yield and 100% selectivity under mild reaction conditions. The nanocatalysts can be recycled and reused several times without significant loss of their catalytic activity.