Ammonia, coordinated dinitrogen reduction

There are two types of interesting and important reactions involving the coordinated dinitrogen, its reduction to hydrazine and ammonia, and the reactions leading to carbon-nitrogen bond formation. 

Zero-valent iron complexes can activate small molecules. For example, reduction of FeCl2(diphos)2 under nitrogen atmosphere resulted in formation of Fe(N2)(diphos)2 [diphos = dmpe or depe] (Scheme 10.13). Interestingly protonolysis of Fe(N2)(dmpe)2 was reported to give ammonia under ambient conditions [75]. In addition, the coordinated dinitrogen in Fe(N2)(depe)2 [76-77] can be readily replaced with CO or CO2. 

Top row the three components of the Yandulov-Schrock cycle for catalytic dinitrogen reduction. Left the catalyst with the substrate Nj coordinated to Mo (Ar refers to the aryl substituent drawn in detail for one of the nitrogens). Centre the reductant bis(pentamethylcyclopentadienyl)chromium, CpjCr. Right the proton source 2,6-lutidinium borate. Bottom row vanadium complexes with intermediates of nitrogen reduction activated dinitrogen or diazenido(2—) (46a), imide (46b) and ammonia (46c). 

Khan, M. and Rao, N.N. Stepwise reduction of coordinated dinitrogen to ammonia via diazinido and hydrazido intermediates on a visible-light irradiated Pt/CdS/Ag2S/Ru02 particulate system suspended in an aqueous-solution of K[Ru(EDTA-H)C1]2H20. j. Photochem. Photobiol. A Chem. 1991, 56, 101. 

More recently, electrochemical methods have been used to bring about a controlled reduction of the dialkylhydrazide compounds formulated above, and the whole system has been cyclized, as shown in Scheme 4/ This ppens the way for the production of amines directly from coordinated dinitrogen, without the intermediacy of ammonia. It suggests a possible electrochemical cycle for the production of ammonia, too, but until recently this has not been a feasible route, because reduction of the hydrazine derivative ( NNHj stage) always led to the evolution of hydrogen rather than to the reduction of the compound and loss of the bromide, as occurs in the alkylated-nitrogen cycle. 

Dinitrogen usually coordinates in an end-on fashion, (89) or (90), and sometimes in a side-on rc-bonded mode (91). Hoffmann and coworkers consider that side-on coordination to two metal centres such as (92) is possible,407 and Yamabe and coworkers have also considered theoretical aspects in relation to possible reduction to hydrazine or ammonia.408... 

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