Electrocatalytic Nitrogen Reduction on a Molybdenum Complex Bearing a PNP Pincer Ligand
Electrocatalytic nitrogen reduction (N2R) mediated by well-defined 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., N₂ splitting) as previously proposed during chemically driven N₂R catalysis. Finally, facile reductive protonation of [Mo(N)Br(ᴴPNP)] with pyridinium acids is demonstrated.
© 2022 American Chemical Society. We thank the Dow Next Generation Educator Funds and Instrumentation Grants for their support of the NMR facility at Caltech. We also thank the Resnick Water and Environment Laboratory and the Molecular Materials Resource Center at Caltech for the use of their instrumentation. The authors thank Dr. Michael Takase for assistance with X-ray crystallography. We thank the following funding agencies: Department of Energy, Office of Basic Energy Sciences (DOE-0235032), Catalysis Science Program (for the development and applications of PCET mediators) and National Institutes of Health (R01 GM-075757) (for fundamental studies of N₂R catalysis). P.G.B. thanks the Ramón Areces Foundation for a postdoctoral fellowship.