Nitrogen diimide

The accessibility of the +4 and +6 oxidation states for sulfur and, to a lesser extent, selenium gives rise to both acyclic and cyclic molecules that have no parallels in N-O chemistry. Thus there is an extensive chemistry of chalcogen diimides RN=E=NR (E = S, Se, Te) (Section 10.4). In the case of Te these unsaturated molecules form dimeric structures reflecting the increasing reluctance for the heavier chalcogens to form multiple bonds to nitrogen. The acyclic molecule N=Sp3,... 

In general, it was found that this process is strongly endothermic for sulfur diimides, approximately thermoneutral for selenium diimides and strongly exothermic for tellurium diimides, consistent with experimental observations. These differences can be attributed to the expected trend to lower r-bond energies for chalcogen-nitrogen (np-2p) r-bonds along the series S (n = 3), Se (n = 4) and Te (n = 5). 

The simplest chain compounds of the type RS NyR are the sulfur diimides RNSNR (Section 10.4) The other known thiazyl chains are summarized in Table 14.1. They can be conveniently classified as sulfur-rich, nitrogen-rich or even-chain species. 

Repeat your analysis for pyridazine. Do any of the resonanee eontributors provide an adequate deseription of its geometry Does pyridazine incorporate a nitrogen-nitrogen double bond (Refer to hydrazine and to diimide as examples of moleeules ineorporating NN single and double bonds, respeetively.)... 

Diimide can act as both a hydrogen acceptor and donor, undergoing disproportionation as a side-reaction which produces a considerable amount of nitrogen gas. From a practical point of view the occurrence of this disproportionation reaction requires the use of an excess of the diimide precursor. 

Diimide diimine, diazene), N2H2 or HN=NH, is an ephemeral species which results from decomposition with acids of potassium azodicarboxylate [264, 265] from thermal decomposition of anthracene-9,10-diimine [266, 267], and of hydrazine [268,269] and its derivatives [270]. Although this species has not been isolated, its transient existence has been proven by mass spectroscopy and by its reactions in which it hydrogenates organic compounds with concomitant evolution of nitrogen [271]. 

Alkyl-5-alkyliminothiatriazolines (50) decompose slowly around 40-60 "C and rapidly at 125°C with formation of sulfur, nitrogen, and carbodiimide (51) (Equation (4)). However, the carbo-diimides (51) formed react with undecomposed thiatriazoline (50), which in part explains the low yields of isolable carbodiimide. It has not been possible by trapping experiments to decide whether the decomposition involves an intermediate as addition of electron-rich alkenes or heterocumulenes induces immediate nitrogen evolution in a bimolecular reaction (see Section 4.19.5.2) <78JCS(P1)1440>. 

Davis and Goddard calculated that the heat of formation (298 K) of singlet H2NN is 90.1 kcal/mol. This value is only 14 kcal/mol below that of molecular nitrogen and two hydrogen atoms, and is 54 kcal/mol above A//f(298 K) for frani-diimide determined experimentally by Willis et al. The relative energies of 1,1- and frani-1,2-diazene have been calculated by several methods these studies have been reviewed by Parsons and Dykstra. It was found using the... 

The ESR spectra of radical anions of the trimethylsilyl derivatives of diimine (95), 1,4-benzoquinone diimide (65), and N-trimethylsilyl derivatives of aniline and p-phenylenediamine (62) have been obtained, and the data are summarized in Table IX. The results for all the systems illustrate the ability of the trimethylsilyl group to withdraw electron density from nitrogen. Its ability to delocalize 7r-spin population lies intermediate between alkyl groups and the phenyl ring (93, 63). The N-trimethylsilyl aniline and p-phenylenediamine radical anions represent the only known cases of aniline radical anions in which the odd electron occupies the antisymmetric 7r -orbital (62). Other systems in which this orbital might be anticipated to be lower in energy than the symmetric 77 -orbital have not been successfully reduced (83). 

The behavior and reactivity of diimide can be understood best by considering the thermochemistry of hydrogenation of nitrogen ... 

The first step is strongly endothermic and is the main hurdle to overcome in the hydrogenation of nitrogen to ammonia. Conversely, the reverse reaction, which is the dehydrogenation of diimide, is strongly exothermic. Therefore we may expect that diimide will have a pronounced tendency to revert to molecular nitrogen. This is in fact so and, at normal temperatures, diimide exists only as a transient intermediate that cannot be isolated. It is extremely reactive and readily transfers hydrogen to carbon-carbon multiple bonds ... 

The other well-known type of group transfer reaction is represented by the concerted syn delivery of two hydrogen atoms from the reactive intermediate diimide 1.25 to an alkene or alkyne, driven by the formation of the stable molecule nitrogen. 

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