One-Pot Multicomponent Synthesis of Allyl and Alkylamines Using a Catalytic System Composed of Ruthenium Nanoparticles on Copper N-Heterocyclic Carbene-Modified Silica

The integrated one-pot synthesis of valuable allylamines and alkylamines from amines, formaldehyde, and terminal alkynes is achieved using a single catalyst material. This multifunctional catalytic system is composed of a silica support on which are jointly assembled ruthenium nanoparticles and covalently functionalized copper N-heterocyclic carbene (NHC) complexes, introducing a new generation of nanoparticles immobilized on molecularly modified surfaces. The textural, structural, morphological, and electronic properties of the resulting Ru@SiO2-[Cu-NHC] material were studied by a variety of techniques including N2 adsorption, solid-state NMR, electron microscopy, and X-ray photoelectron spectroscopy. Ru@SiO2-[Cu-NHC] was found active and selective for the one-pot synthesis of a wide range of allylamines and alkylamines, products of great importance in the fine chemical and pharmaceutical industry. Detailed investigations evidenced that the immobilized molecular Cu(I)-NHC complex is responsible for the atom-efficient A3 coupling of amines, formaldehyde, and terminal alkynes, while the selective hydrogenation of the resulting propargyl amines is catalyzed by Ru(0) nanoparticles. The design strategy and the preparation method to combine molecular and nanoparticle sites on a single support are flexible, opening the way to the development of multifunctional catalytic systems capable of performing complex reaction sequences in one pot.