Reactivity of Dinitrogen Bound to Mid- and Late-Transition-Metal Centers

This review presents a comprehensive overview of the reactions of N-2 within the coordination sphere of transition metals of groups 6 to 9. Many of these metals mediate the reaction of N-2 with protons under reductive conditions, which can lead to the (catalytic) formation of ammonia or hydrazine, and the mechanisms of these reactions somewhat resemble the mode of action of nitrogenase enzymes. Alternatively, coordinated N-2 can react with carbon and silicon electrophiles and radicals to allow, for example, the catalytic formation of silylamines. Another approach in N-2 activation involves the homolytic splitting of dinitrogen to form intermediate nitrides in analogy to the Haber-Bosch process. Thus formed nitrides can undergo follow-up reactions with protons or carbon electrophiles. Molybdenum, tungsten, and iron reveal the richest chemistry of coordinated N-2; however, chromium, manganese, rhenium, osmium, and cobalt systems provide alternative pathways in the making and breaking of bonds on the dinitrogen molecule.