Cu Catalyst Supported on Nitrogen and Phosphorus Co-Doped Carbon Nanosheets for Homocoupling of Terminal Alkynes Using CO₂ as a Soft Oxidant

A bifunctional role of carbon dioxide (CO2) was developed in this research as a medium for catalyst preparation and as a soft oxidant for the subsequent coupling reaction. A highly dispersed and low-content Cu catalyst (Cu/NPC) was obtained by homogeneously loading copper oxide (CuO) on porous nitrogen–phosphorus co-doped carbon (NPC) under supercritical-CO2 (sc-CO2) conditions. Cu/NPC shows an irregular and highly cross-linked three-dimensional (3D) morphology which is assembled by ultrathin and lamellar-like nitrogen–phosphorus co-doped carbon nanosheets. The resulting Cu/NPC catalyst can efficiently promote dehydrogenative homocoupling of terminal alkynes by using CO2 as a soft oxidant for 1,3-diyne syntheses. Quantitative 1,3-diyne yields up to 99% were achieved with a broad terminal alkyne scope by using Cu/NPC. Additionally, Cu/NPC can be readily reused in the coupling reaction. This research thus demonstrates dehydrogenative homocoupling of terminal alkynes with CO2 as a renewable, green, readily available, and soft oxidant by using a Cu-based catalyst.