Membrane‐Free Selective Semi‐Hydrogenation of Alkynes Over an In Situ Formed Copper Nanoparticle Electrode

Selective semi‐hydrogenation of alkynes is a significant reaction for preparing functionalized alkenes. Electrochemical semi‐hydrogenation presents a sustainable alternative to the traditional thermal process. In this research, affordable copper acetylacetonate is employed as a catalyst precursor for the electrocatalytic hydrogenation of alkynes, using MeOH as the hydrogen source in an undivided cell. Good to excellent yields for both aromatic and aliphatic internal/terminal alkynes are obtained under constant current conditions. Notably, up to 99% Z selectivity is achieved for various internal alkynes. Mechanistic investigations revealed the formation of copper nanoparticles (NPs) at the cathode during electrolysis, acting as the catalyst for the selective semireduction of alkynes. The copper NPs deposited cathode demonstrated reusable for further hydrogenation. A practical semi‐hydrogenation method is documented for alkynes in an undivided cell using Cu(acac)2 as a cost‐effective precatalyst, showcasing a remarkable substrate scope, including both aromatic and aliphatic internal/terminal alkynes. This method demonstrates exceptional selectivity in producing Z‐alkenes from internal alkynes. Mechanistic insights indicates the generation of copper nanoparticles during electrolysis served as the catalyst.