Complexes and Nitrogen Fixation

Dinitrogen Complexes and Nitrogen Fixation.—Nitrogenase from Azotobacter vinelandii has been purified and the molybdoferrodoxin protein crystallized as needles.A molybdenum-containing peptide of mol. wt. ca. 1000 has been isolated from this system and shown to contain at least ten naturally occurring amino-acids, with leucine and isoleucine being most prominent molybdenum is present as both Mo and Tungsten has been incorporated into 

A nitrogenase model reaction has been accomplished in which significant amounts of NH3 (0.013-0.044 mol NH3/M0) are produced when trans-[Mo(N2)2(Ph2PCH2CH2PPh2)2] is added to[FeS(SCHPhCHPhS)]4 reduced to the 4 — or lower level. The molybdenum complex is also reducible by an excess of Na (naphthalene) to afford NH3 (0.100—0.300 mol NH3/M0). No N2H4 was observed in either reduction. The iron-dithiolen system alone is capable of fixing N2 at the 4— level under an N2 atmosphere NH3 up to 

137 mol NHj/Fe is produced. Addition of an excess of Na (naphthalene) to this mixture increases the quantity of NH3 produced to ca. 0.265 mol NH3/Fe4- It is considered that the nitrogenase model reaction involves the loss of co-ordinated dinitrogen as the first step, followed by its reduction by 

Several new dinitrogen complexes of the type cis- and trans-[Mo(N2)2L4] (M = Mo or W, L = tertiary phosphine) have been isolated and the reaction of [Mo(N2)2(Ph2PCH2CH2PPh2)2] with [FeH4(PEtPh2)3] in 1 1 or 1 2 proportions shown to form [MoH2(Ph2PCH2CH2PPh2)2] and 

The reactions of molybdocene and tungstocene with N2 have been further investigated and the conclusion reached that, whilst molybdocene is a reactive species which co-ordinates N2, it does not provide an easy route to the reduction of this molecule.  

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The only reactions of molecular nitrogen at ambient temperature are the formation of lithium nitride Li3N, reactions with certain transition metal complexes, and nitrogen fixation with nitrogenase in the bacteria of the root nodules of legumes and in blue algae (Sections 14.1.1 and 14.1.2). Above 500 °C nitrogen reacts with some elements, especially with metals (nitride formation). 

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