Electrocatalytic Nitrogen Reduction on a Molybdenum Complex Bearing a PNP Pincer Ligand

Electrocatalytic nitrogen reduction (N2R) mediated by welldefined molecular catalysts is poorly developed by comparison with other reductive electrocatalytic transformations. Herein, we explore the viability of electrocatalytic N2R mediated by a molecular Mo-PNP complex. A careful choice of acid, electrode material, and electrolyte mitigates electrode-mediated HER under direct electrolysis and affords up to 11.7 equiv of NH3 (Faradaic efficiency < 43%) at -1.89 V versus Fc(+)/Fc. The addition of a proton-coupled electron transfer (PCET) mediator has no effect. The data presented are rationalized by an initial electron transfer (ET) that sets the applied bias needed and further reveal an important impact of [Mo] concentration, thereby pointing to potential bimolecular steps (e.g., N-2 splitting) as previously proposed during chemically driven N2R catalysis. Finally, facile reductive protonation of [Mo(N)Br(HPNP)] with pyridinium acids is demonstrated.

Automated summary

Electrocatalytic nitrogen reduction (N2R) mediated by a molecular Mo-PNP complex has been investigated. By carefully choosing the acid, electrode material, and electrolyte, the electrode-mediated hydrogen evolution reaction (HER) was mitigated, and up to 11.7 equiv of NH3 was obtained at -1.89 V (Faradaic efficiency < 43%) relative to Fc(+)/Fc. The addition of a proton-coupled electron transfer (PCET) mediator did not affect the results. The data suggest an initial electron transfer (ET) that determines the applied bias needed and highlight the importance of [Mo] concentration, indicating potential bimolecular steps (e.g., N-2 splitting) during chemically driven N2R catalysis as proposed previously.