Ammonia Synthesis – Homogeneous

Abstract

Transformations of molecular nitrogen into ammonia promoted by transition‐metal complexes are summarized. Treatment of transition‐metal salts, mostly those of Groups 4, 5, and 6 metals, with strong reducing agents under N 2 in aprotic media gives ammonia after hydrolysis of the reaction mixtures, while amorphous V(II) and Mo(III) hydroxides as well as V(II) catecholate complexes react with N 2 in protic media to afford ammonia and/or hydrazine. The coordinated N 2 in numerous mononuclear and multinuclear N 2 complexes can be converted into ammonia and/or hydrazine by treatment with protic acids. Among these complexes, N 2 complexes of Mo and W with tertiary phosphine coligands are outstanding because the coordinated N 2 is transformed into ammonia and/or hydrazine in high yields by protonation and the detailed mechanism is revealed by isolation of several intermediates. Furthermore, a tungsten N 2 complex reacts with a ruthenium H 2 complex at 55°C to form ammonia, although the reaction is stoichiometric.

Enhanced Activation of Coordinated Dinitrogen with p‐Block Lewis Acids

“…At the same time, these investigations paved the way for the development of catalysts for ammonia synthesis that could potentially operate under ordinary pressure and temperature conditions . The synthesis of organonitrogen compounds also fueled interest in the coordination chemistry community . Having an estimate of the Brønsted or Lewis basicity of the N 2 ligand appeared to be important for the conception of the above‐mentioned reactions.…”