Evaluating Molecular Cobalt Complexes for the Conversion of N₂ to NH₃

Well-defined molecular catalysts for the reduction of N₂ to NH₃ with protons and electrons remain very rare despite decades of interest and are currently limited to systems featuring molybdenum or iron. This report details the synthesis of a molecular cobalt complex that generates superstoichiometric yields of NH₃ (>200% NH₃ per Co-N₂ precursor) via the direct reduction of N₂ with protons and electrons. While the NH₃ yields reported herein are modest by comparison to those of previously described iron and molybdenum systems, they intimate that other metals are likely to be viable as molecular N₂ reduction catalysts. Additionally, a comparison of the featured tris(phosphine)borane Co-N₂ complex with structurally related Co-N₂ and Fe-N₂ species shows how remarkably sensitive the N₂ reduction performance of potential precatalysts is. These studies enable consideration of the structural and electronic effects that are likely relevant to N₂ conversion activity, including the π basicity, charge state, and geometric flexibility.