Catalytic Nitrogen Fixation Using Well-Defined Molecular Catalysts under Ambient or Mild Reaction Conditions.

Ammonia (NH) is industrially produced from dinitrogen (N) and dihydrogen (H) by the Haber-Bosch process, although H is prepared from fossil fuels, and the reaction requires harsh conditions. On the other hand, microorganisms have fixed nitrogen under ambient reaction conditions. Recently, well-defined molecular transition metal complexes have been found to work as catalyst to convert N into NH by reactions with chemical reductants and proton sources under ambient reaction conditions. Among them, involvement of both N-splitting pathway and proton-coupled electron transfer is found to be very effective for high catalytic activity. Furthermore, direct electrocatalytic and photocatalytic conversions of N into NH have been recently achieved. In addition to catalytic formation of NH, selective catalytic conversion of N into hydrazine (NHNH) and catalytic silylation of N into silylamines have been reported. Catalytic C-N bond formation has been more recently established to afford cyanate anion (NCO) under ambient reaction conditions. Further development of direct conversion of N into nitrogen-containing compounds as well as green ammonia synthesis leading to the use of ammonia as an energy carrier is expected.