Catalytic Reduction of Dinitrogen to Ammonia and Hydrazine Using Iron- Dinitrogen Complexes Bearing Anionic Benzene-Based PCP-Type Pincer Ligands

Among synthetic models of nitrogenases, iron-dinitrogen complexes with an Fe-C bond have attracted increasing attention in recent years. Here we report the synthesis of square-planar iron(I)-dinitrogen complexes supported by anionic benzene-based PCP- and POCOP-type pincer ligands as carbon donors. These complexes catalyze the formation of ammonia and hydrazine from the reaction of dinitrogen (1 atm) with a reductant and a proton source at -78 degrees C, producing up to 252 equiv of ammonia and 68 equiv of hydrazine (388 equiv of fixed N atom) based on the iron atom of the catalyst. Anionic iron(0)-dinitrogen complexes, considered an essential reactive species in the catalytic reaction, are newly isolated from the reduction of the corresponding iron(I)-dinitrogen complexes. This study examines their reactivity using experiments and DFT calculations.