Nitrogen complexes diazenes

Lemal and McGregor (1966) have provided data and a correlation diagram for the decomposition of cis- and (raras-diazenes (Fig. 18). The novel feature of Fig. 18 is the use of a p orbital of nitrogen in the reactants and and irNl orbital of nitrogen in the product. (Alternative bookkeeping schemes of orbitals and their symmetries, e.g. inclusion of lone pairs, are unnecessarily complex.) On the basis of the level diagram, the prediction is that thermolysis of pyrroline will produce a diene by the... 

Dieter Otto Sellmann Iron-diazene complex as model for enzymatic nitrogen fixation... 

The likelihood that alkyl radicals, like their aryl counterparts, bind to the iron before shifting to the nitrogen is supported by the observation that the type II complexes formed between alkyldiazenes and P450 in the absence of oxygen are converted, in the presence of limited amounts of oxygen, to complexes with an absorption maximum at 480 nm characteristic of iron-carbon o-bonded complexes Furthermore, alkyl diazene-iron tetraphenylporphyrin complexes can be prepared under anaerobic conditions. However, the alkyl-iron complexes are much less stable and less well characterized than the aryl-iron complexes and their involvement in heme iV-alkylation reactions remains to be demonstrated. 

From our knowledge on structure and reactivity of the dinitrogen molecule, e. g., the very high dissociation energy of the triple bond (940 kJ mol ), it is obvious that the major problem is not the formation of the diazenido complex (1), but the consecutive steps (2)-(4). In particular, it is unlikely that diazene (HN=NH) is an intermediate, as it is thermodynamically very unfavorable. Chemical research on nitrogen fixation concentrated, therefore, in recent years on reduction mechanisms of dinitrogen complexes (see review of Shilov, 1992). 

In contrast to their Fe(ii) congeners, Fe(i) or Fe(0) do activate N2 toward protonation. A first example was the so-called Leigh cycle, which involves the conversion of N2 to NH3 mediated by iron(O) phosphine complexes. In this context, Tyler and coworkers synthesized the complex [Fe(N2) (DMeO-PrPE)2] supported by the DMeOPrPE = l,2-bis[bis(methoxypropyl)phos-phinojethane ligand, which renders the iron-N2 complex water soluble. Based on this work, the reduction and protonation of N2 coordinated to the simpler Fe(dmpe)2 complex has been treated by DFT. In this work, three plausible mechanistic pathways were evaluated (1) symmetric protonation, where protons are added to each nitrogen in an alternating sequence proceeding through diazene and hydrazine intermediates (2) asymmetric... 

No phosphorus analogues of multiply bonded nitrogen species such as diazene, HN=NH, tetra-zene, H2N-N=N-NH2, and hydrazoic acid, HN3 have been isolated. Diphosphene, HP=PH, appears to have been detected spectroscopically [9,10], and some metal complexes have been made (8.262). Various organic derivatives RP=PR have been synthesised (Chapter 6.19), however, and the PH molecule has been studied spectroscopically [11]. Metallo derivatives of H2P-P=P-PH2 are known (Chapter 8). 

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