Selective electrochemical reductive amination of benzaldehyde at heterogeneous metal surfaces

Ammonia is one of the largest-volume commodity chemicals, and electrochemical routes to ammonia utilization are appealing due to increasingly available renewable electricity. In this work, we demonstrate an electrochemical analog to reductive amination for the synthesis of benzylamine from benzaldehyde and ammonia. Previous works on electrochemical reductive amination have generally focused on proof-of-concept outer-sphere routes. In our system, imine hydrogenation proceeds via an inner-sphere route on an Ag electrocatalyst at ambient conditions with an initial Faradaic efficiency toward the primary amine product of ∼80% and partial current greater than 4 mA/cm2 at −1.96 V versus Fc/Fc+ (−1.36 V versus the normal hydrogen electrode). Ag was selected after evaluating diverse transition metal electrocatalysts, and the rate-determining step was the initial electron transfer to the imine. Overall, this work represents a step toward inner-sphere electrochemical reductive amination systems, opening a large phase space of heterogeneous electrocatalysts for reactions that currently rely on thermochemical routes.