Exploring the role of pendant amines in transition metal complexes for the reduction of N₂ to hydrazine and ammonia

This review examines the synthesis, properties, and acid reactivity of transition metal dinitrogen complexes bearing phosphine ligands containing pendant amine groups in the second coordination sphere. We have synthesized non-precious metal dinitrogen complexes containing bidentate, tridentate, and tetradentate phosphine ligands, some of which generate N₂ derived ammonia and/or hydrazine in the presence of excess acid. The metal identity, metal oxidation state, ligand denticity, and functional groups on phosphorus/nitrogen all play a role in controlling the site of protonation (at the metal, pendant amine, or coordinated dinitrogen) with the addition of exogenous acid.