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Reactivity
Hypothesized cycle for M-catalysed nitrogen fixation according to Chatt et al.

Primarily, the major theme of transition metal dinitrogen complexes have been in regards to nitrogen fixation well known in biology. A vast majority of chemists who are interested in this topic, more specifically, aimed to leverage the existing knowledge of MoFe nitrogenase enzyme responsible for reduction of dinitrogen in biological context. Thus, the chemistry of transition metals together with dinitrogen stemmed from mostly Mo- or Fe-containing compounds in order to perform the desired abiological nitrogen fixation. Nevertheless, recent studies have broadened the scope of this field to include transition metal complexes with other metals besides Mo and Fe as well.

Dinitrogen Reduction
Since in the 1970s, J. Chatt had proposed the renowned dinitrogen reduction pathway, which is now commonly known as the "Chatt Cycle". The catalytic cycle entails multiple protonation and one-electron reduction steps applied to a generic metal-dinitrogen complex to ultimately produce ammonia and regenerate an N2-free metal for another dinitrogen reduction cycle. While this schematic catalytic cycle has never been realized in practice, electrochemical evidence has been done to prove the reductive cycle. Besides the two Mo systems capable of reducing dinitrogen (J. Chatt's [LP4Mo(N2)] and Richard R. Schrock's [(RN3N)Mo(N2)] ), the study of dinitrogen reduction mediated by biomimetic transition metal complexes have also extended into Fe, W , and more.

(Fig.)

Cleavage to Nitrides
Although the strong N-N bond of dinitrogen (BDE = 226 kcal/mol) had set a challenge for chemists to leverage the ubiquitous N2 for a long time, the Cummins group elegantly reported a cleavage of a N-N triple bond via their Mo(III) complexes. As a result, metal nitrido complexes were formed, and the reaction was proposed to go through a structurally characterized N2-bridged Mo dimer as shown in the scheme:


 * 2 Mo(NR2)3 + N2 → (R2N)3Mo-N2-Mo(NR2)3
 * (R2N)3Mo-N2-Mo(NR2)3 → 2 N≡Mo(NR2)3

Formation of Nitriles
Once a new gateway into dinitrogen chemistry was opened by the report of the N-N triple bond cleavage, chemists have reported many conversion of dinitrogen into N-containing organic molecules facilitated by transition metal complexes. One the targeted molecules are the nitrile products, such as acetonitrile and benzonitrile.