Efficient three-component coupling reactions catalyzed by Cu0-nanoparticles stabilized on modified montmorillonite

Abstract

The in situ generation of Cu⁰-nanoparticles into the nanopores of modified montmorillonite and their catalytic performance in the three component (A³) coupling reactions of aldehyde, amine and alkyne to synthesize propargylamines have been described here. The modification of montmorillonite was carried out with HCl under controlled conditions for generating nanopores into the matrix and these pores act as a “host” for the in situ generation of Cu⁰-nanoparticles. The Cu⁰-nanoparticles were generated in the nanopores of the acid activated clay mineral matrix by the successful loading of a Cu(CH₃COO)₂ metal precursor using an incipient wetness impregnation technique followed by reduction with NaBH₄. The TEM study reveals that Cu⁰-nanoparticles of below 10 nm in size are evenly distributed on the support. The synthesized Cu⁰-nanoparticles exhibit a face centered cubic (fcc) lattice. The Cu⁰-nanoparticles serve as an efficient green and heterogeneous catalyst for three-component coupling via C–H alkyne-activation to synthesize propargylamines with excellent yields (82–94%) and 100% selectivity under mild reaction conditions without requiring any additives or an inert atmosphere. The nanocatalysts can be recycled and reused several times without significant loss of their catalytic activity.