Copper(i) oxide nanoparticle-mediated C–C couplings for synthesis of polyphenylenediethynylenes: evidence for a homogeneous catalytic pathway

Abstract

During the last few decades, substantial attention has been devoted to copper and copper oxide nanocatalysts, due to copper's natural abundance, low cost and lower toxicity in comparison to precious metal-based nanoparticles. Cuprous oxide (Cu₂O) nanoparticles show versatility in catalyzing and mediating carbon–carbon (C–C) and carbon–heteroatom (e.g., C–N, C–O, C–S and C–Se) bond-forming reactions. Here, we demonstrate Cu₂O nanoparticle-mediated oxidative C–C homocoupling reactions for the synthesis of polyphenylenediethynylenes under ligandless conditions, mild base and atmospheric air as the oxidant, with reasonable yields and moderate number-average molecular weights. Also, we demonstrate that, during the reaction, Cu₂O nanoparticles undergo substrate-induced leaching to form homogeneous copper catalytic species. The leaching of catalytic species and in situ formation of copper complexes are characterized by electrospray ionization mass spectrometry, ultraviolet-visible extinction spectroscopy, transmission electron microscopy and reactor study. The results confirm the contribution of a homogeneous catalytic pathway for the oxidative C–C homocoupling reactions under the reaction conditions used.