N 2 Reduction and Hydrogenation to Ammonia by a Molecular Iron-Potassium Complex

A molecular iron complex offers insights into the industrial iron catalyst used to split nitrogen to make ammonia. The most common catalyst in the Haber-Bosch process for the hydrogenation of dinitrogen (N 2 ) to ammonia (NH 3 ) is an iron surface promoted with potassium cations (K + ), but soluble iron complexes have neither reduced the N-N bond of N 2 to nitride (N 3– ) nor produced large amounts of NH 3 from N 2 . We report a molecular iron complex that reacts with N 2 and a potassium reductant to give a complex with two nitrides, which are bound to iron and potassium cations. The product has a Fe 3 N 2 core, implying that three iron atoms cooperate to break the N-N triple bond through a six-electron reduction. The nitride complex reacts with acid and with H 2 to give substantial yields of N 2 -derived ammonia. These reactions, although not yet catalytic, give structural and spectroscopic insight into N 2 cleavage and N-H bond-forming reactions of iron.