Electrocatalytic Semi-Hydrogenation of Pyridine Derivatives over an In Situ Assembled Cu Cathode.

Selective electrochemical hydrogenation of pyridine derivatives to piperidines, two of the most prevalent nitrogen heterocycles in pharmaceuticals, is essential for accessing structurally diverse and isotopically labeled analogs in drug discovery. Here, we present a rare example of selective electrochemical semihydrogenation of pyridine derivatives using an in situ-assembled copper cathode, obviating the need for prefabricated precious-metal electrodes. Mechanistic studies reveal that the copper surface governs selectivity by promoting stronger adsorption of the pyridinium intermediate than of the semihydrogenated product, thereby disfavoring over-reduction. Oxalate-assisted surface modulation is essential for reactivity, as it confines active hydrogen at the interface and suppresses competing hydrogen evolution. Moreover, the direct use of copper-containing industrial wastewater as both the metal precursor and reaction medium enables concurrent electrode fabrication and effluent purification, establishing an environmentally responsible and scalable approach to sustainable electrocatalysis and waste valorization.