Heteroleptic Dicopper Molecular Design Unlocks Distinct Dual Synergies in Electrocatalytic Hydrodimerization of Dilute Acetylene to 1,3-Butadiene.

Electrocatalytic hydrodimerization of acetylene to 1,3-butadiene is an attractive sustainable route, yet reconciling the disparate kinetic demands of acetylene dimerization and hydrogenation remains challenging, especially in catholyte-free membrane electrode assembly (MEA) systems with dilute acetylene feeds. Herein, we report a heteroleptic dicopper molecular catalyst featuring piperonylate and acetate ligands that effectively addresses this incompatibility-a distinctive advantage over homoleptic catalysts. Mechanistic studies reveal that the heteroleptic design provides distinct dual synergies: (i) heteroleptic coordination minimizes steric hindrance and optimizes the Cu d-band center of dicopper sites, promoting efficient acetylene activation and dimerization; (ii) heteroleptic-induced localized electric fields reorganize interfacial water structure and enrich free water molecules, critically enhancing hydrogen availability for hydrogenation. The heteroleptic catalyst substantially surpasses homoleptic analogues across a broad range of acetylene concentrations (15%-100%), delivering 91% Faradaic efficiency toward 1,3-butadiene at just 15% acetylene in a flow cell. In a MEA setup, the catalyst continuously operates at -500 mA for 31 h, converting 15% acetylene to 1,3-butadiene and accumulating 224 mmol of product despite restricted hydrogen availability. This work demonstrates heteroleptic molecular design as a powerful and versatile strategy for selectively controlling competing pathways in complex multi-carbon electrosynthesis.