Dinitrogen protonation chemistry

Figure 9-4 A summary of the protonation chemistry of dinitrogen complexes of molybdenum and tungsten based on a wide range of chemical, electrochemical, and kinetic researches. Species characteristic of all these stages except MVI have been isolated and characterized. In a typical case M = M(Ph2PCH2CH2PPh2)2, X = Q, and M = Mo or W (redrawn from R. R. Eady and G. J. Leigh, J. Chem. Soc., Dalton Trans. 1994, 2739).

Species not mentioned in this chapter include the coordination chemistry of dinitrogen, and of hydrazines, hydroxylamine and hydroxylaminato anions. The chemistry of coordinated dinitrogen has been extensively reviewed, and its protonation has been discussed in detail.1... 

During the early stages of the turnover of the enzyme, nitrogenase, an intermediate stage of protonation of dinitrogen was detected by quenched-flow experiments (328). Analysis of presteady state kinetics (314), and comparison with the chemistry outlined above, indicates that this is a hydrazido(2 -) stage. 

Following the discovery of rrans-Mo(N2)2(dppe)2, 15, by Hidai in 1969, " a series of four landmark reactions in the area of the chemistry of coordinated dinitrogen were reported by Chatt and co-workers over a period of three years. These are (i) the reaction of 33 with acyl halides to form nitrogen-carbon bonds (Equation (ii) protonation of 15 and... 

A detailed discussion of the distribution of electrons over the Fe-S and Mo centres of Kpl under various conditions is beyond the scope of this short article and the reader should consult Lowe, Eady and Thorneley (1978) for the most recent data and a literature review. However, at some stage in the catalytic cycle, electrons and protons are accepted by N2 to give NH3. The chemistry of certain Mo-complexes suggests an enzymic mechanism involving the stepwise addition of electrons and protons to N2 coordinated to Mo to yield NH3 via partially-reduced dinitrogen-hydride species (Thorneley et al. 1979). 

This process is an indirect ammonia synthesis. There are three steps including formation of dinitrogen complex, protonation and eduction of ammonia. This method requires complete destruction of complex, otherwise, the N-N bond cannot be disbanded and an effective synthetic cycle for ammonia cannot be realized. The effective way to solve this problem is to supply extra electron by chemistry or electrochemistry in order to realize controllable break of N-N bond and a synthetic recycle from nitrogen to ammonia. ... 

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