Thermochemical Polarization-Driven Heterolytic Hydrogenation in an Electrochemical Palladium-Membrane Reactor.

Heterolytic hydrogenation via hydride species transfer represents a fundamental transformation in industry for chemical synthesis, but H2 or organic hydride donors are often utilized as the hydrogen source. An electrochemical palladium (Pd) membrane reactor shows the ability to catalyze heterolytic reactions by using water as the hydrogen source, but quantitative descriptions of this reactivity remain absent, and the reaction often relies on external polarization of the chemical compartment. Herein, we report thermochemical polarization-driven heterolytic hydrogenation in an electrochemical Pd-membrane reactor. By employing Hantzsch ester (HEH) regeneration as a model reaction, we first established a quantitative thermodynamic framework by showing basicity-dependent activity, and then provided experimental evidence supporting the kinetics by observing an interfacial charge transfer process, together demonstrating a heterolytic hydrogenation mechanism. Moreover, the origin of the electrons that generate hydride species was supported by experimental evidence using mixed potential theory (MPT)─a theory widely applied in metal corrosion and thermal catalysis but rarely applied to electrochemical systems. As a proof of concept, by employing the regenerated HEH as a mediator, we achieved asymmetric hydrogenation of imines with high yield (up to 99.1%) and enantioselectivity (up to 98.1% e.e.), thus demonstrating the integration of electrochemical hydrogen generation with homogeneous asymmetric catalysis. This work provides a mechanistic foundation for heterolytic hydrogenation in a Pd-membrane reactor and inspires the rational design of catalyst modifications.