Dinitrogen-Transition Metal Complexes: Synthesis,Properties, and Significance

Compared to the large number of CO complexes, N₂ complexes are still rare. In certain cases they may be formed from N₂ gas and metal compounds under physiological conditions, and are therefore frequently considered as possible intermediates in N₂ assimilation. However, despite numerous attempts it has not yet been possible to reduce the N₂ ligand of a fully characterized N₂ complex to NH₃. This negative evidence recently prompted the discoverers of the first dinitrogen complex, the [Ru(NH₃)₅N₂]^2⊕ ion isolated in 1965, to express doubt whether such complexes really do play a part in the enzymatic reduction of N₂. The latest findings nevertheless incline toward a somewhat more optimistic view. Thus, the mild partial reduction of the N₂ ligand in metal complexes with inert gas configuration, hitherto considered nonreducible, justifies the hope that a suitable system permitting the catalytic reduction of molecular nitrogen under normal conditions will one day be found. Even apart from any technical potential, the N₂ complexes constitute an interesting chapter of modern inorganic chemistry.