Copper-based magnetic catalysts for alkyne oxidative homocoupling reactions

We successfully prepared copper-based magnetic catalysts combining copper oxide and magnetite nanoparticles. These systems are active and selective in the oxidative homocoupling reaction of phenylacetylene in the absence of an external base. These systems are particularly interesting since the addition of an external base induces copper leaching by production of soluble molecular copper-base complexes. Some of these systems were also supported on oxidized few layer graphene to investigate a potential role of this support. We discover that this supported system is three times more active than the other ones. We propose that the role of graphene support is to improve catalyst dispersion, but also to provide a favorable micro-environment around the active phase via a pre-adsorption of the substrate on the support, which affords a substrate rich micro-environment around the active particles. Recycling experiments show that the graphene-supported systems cannot be recycled, while the other ones can. This result could be explained by a competitive pre-adsorption between the substrate and the product of the reaction on the surface of the support. (C) 2017 Elsevier B.V. All rights reserved.