In situ selective deuterated (hydrogenated) aryl alkynes to alkenes on Pd/Ni(OH)2-nickel foam

Abstract

The preparation of deuterated alkenes via electrochemistry from a readily available deuterated source has the advantages of mild reaction conditions, sustainability, and cost-effectiveness. Hydrogen isotopic exchange is a simple method to introduce deuterium atoms into molecules without prior functionalization. However, this process typically requires complex ligand catalysts, costly sources of deuterium, and strong bases and acids to activate the robust C-H bonds. The deuterated incorporation sites and their corresponding numbers are difficult to control. In this study, an in-situ electrochemical deuteration system is reported that is based on a Pd/Ni(OH)2 nanoflake catalyst grown on a commercial nickel foam conductive substrate was used as the cathodic working electrode. A room-temperature, one-pot, two-step transformation of 4-ethynylaniline to deuterated 4-vinylanilin was achieved with a conversion rate of up to 96%, selectivity of 98%, and a deuterium ratio of 99% using D2O as the deuterium source. The interaction between Pd and Ni(OH)2-NF promoted the rapid cleavage of D2O during the semi-deuteration of aryl alkynes. The key deuterium and carbon radical intermediates were confirmed using electron paramagnetic resonance spectroscopy. A wide range of substrates and easy access to hydrogenated alkenes highlight the promising applications.