Samarium as a Catalytic Electron-Transfer Mediator in Electrocatalytic Nitrogen Reduction to Ammonia.

Samarium diiodide (SmI) exhibits high selectivity for NR catalyzed by molybdenum complexes; however, it has so far been employed only as a stoichiometric reagent (0.3 equiv of NH per Sm) combined with coordinating proton sources (e.g., HO, ROH). The latter inhibit catalytic turnover of Sm owing to buildup of stable hydroxide/alkoxide sinks. Here, we report a tandem Sm/Mo-catalyzed NR system that achieves the lowest overpotential and highest Faradaic efficiency (82%) reported to date for nonaqueous NR at ambient pressure. Up to 8.4 equiv of NH is produced per Sm, representing a 25-fold increase over NR with stoichiometric SmI. A noncoordinating proton source enables electrochemical SmI/SmI cycling at the applied potential of -1.45 V vs Fc.