The Diazenido Ligand

It can be envisaged that, depending upon the electronic requirements of the metal, the diazenido ligand can adopt one of the following geometries. 

As a point of interest, a recent ab initio calculation (145) indicates that the sideways bonded form of LiN2H is the most stable configuration. 

1 This form has now been dectected in Ti(C5H6)Cl i(N.,iPh)], Dilworth et al. (unpublished observations). 

Of the two possible modes of bonding for bridging diazenido ligands, form 10 has been authenticated in [ Mn(N2Ph)(CO)4 2] (1) and 

There are six principal routes available to prepare diazenido complexes and these have been reviewed before (143, 154, 275, 317), although for convenience the relevant routes will be outlined here. Other routes such as the reaction of nitrosyl complexes with an aniline (41), or the reactions of 1,3-diaryltriazenes in acid (ready cleavage to yield diazonium ions in situ) with transition metal complexes (317), are of much less general utility. 

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The presence of three lone pairs of electrons in the diazenido ligand (R-N = ISO allows it to bind in a bridging fashion to several metals at once. Three bridging modes of binding for diazenido ligands have been observed (25-27). 

The kinetics of the reaction between Irons- Ml N2Me)Br(dppe)21 and methyl iodide in tetrahydrofuran exhibit a first-order dependence in the concentration of complex and first-order in the concentration of methyl iodide. When M = W, the reaction with methyl iodide is 38 times faster than the reaction with ethyl iodide, which is typical ofSN2 reactions. Therefore, it is concluded that the secondary alkylation is a bimolecular nucleophilic substitution (Scheme 10) in which nucleophilic attack of the diazenido ligand on the carbon atom of the alkyl halide is the rate-limiting step (93). 

The diazenido ligand can be regarded as RN2, RN2, or RN2 and when coordinated, there is a considerable range in the observedN=N stretch (2100-1440 cm ). Obviously, there is a close analogy between NO and RN2 as ligands. Diazines can be formed from diazenido complexes by electrophilic... 

X-Ray photoelectron spectroscopy has been used to study diazenido com-plexes. " " Sample decomposition, problems with sample charing, and poor spectral resolution (range of chemically induced shifts vj. spectral line widths) limit the general utility of XPES. The diazenido ligand shows a large positive ligand shifts (RN = 1.6 eV, RNj = 0.6 eV)... 

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