Nitrogen diimine

The 1.4-dihydro-l,4-diazocines prepared from iyn-benzene diimines (Section 1.4.1.2.) can be transformed to other derivatives by exchange of the substituents at nitrogen. For this purpose, the dipotassium salt of 1,4-diazocine is generated and then reacted with appropriate electrophiles. For example, reduction of the bistosyl derivative 3 gives a relatively stable dianion, a lOrr-electron system analogous to cyclooctatetraene dianion, which on protonation clearly gives the parent l,4-dihydro-l,4-diazocine (4, E = H) as the only product. 

Chiral nitrogen chelates derived from sugars were prepared by Ruffo [48], introducing diimines and diamines functionalities on inexpensive monoses, a-D-glucose and a-D-mannose. 

Nitrogen heterocycles have a strong affinity for platinum(II), and complexes of these ligands, particularly pyridine and related diimines such as bipy, are ubiquitous.189,190 The favorable electronic (strong cr-donor/weak 7r-acceptor) and steric properties of such ligands lead to the... 

The cubic NLO properties of Ru11 tris-(a-diimine) complexes have been investigated only relatively recently by Ji and co-workers using 540 nm Z-scan all of the complexes studied exhibit both NLO absorption and SDF behavior.135-138 The large and 7 values of complexes such as (73) depend on the position of the -N02 group in the order 4- > 2- > 3-.135 Also, the NLO responses decrease on deprotonation of the imidazolyl nitrogens (although this effect is only... 

Another compound of nitrogen and hydrogen is diimine, N2H2, which has the structure HN=NH. The compound decomposes to give N2 and H2, but it is believed to be a transient species in some reactions. The reactions that lead to formation of diimine can be summarized as follows ... 

Numerous modifications to the bis(aryl)-a-diimine ligand motif have been reported, especially in the patent literature. The review by Ittel includes an index of diimine and related ligands in proprietary publications up to the year 2000 [26]. Instead, this discussion will focus on academic reports of Ni(II) and Pd(II) polymerization catalysts bearing a-diimine or other closely related chelating neutral nitrogen ligands. 

Fig. 5 a-Diimine and related neutral nitrogen ligands (and complexes) utilized in ethylene and a-olefin polymerizations... 

The [Fe(diimine)2X2] system has been modified by replacing the diimines by unidentate nitrogen donors. [Fe(diimine)(py)2(NCS)2] is a crossover system when the diimine is 2,2 -bipyrimidine or phen [99] but [Fe(py)4(NCS)2] is purely high spin [100]. However, [Fe(py)4(NCS)2] systems containing substituted pyridine derivatives have been shown to exhibit thermal SCO [101], while 4,4 -bipyridine derivatives are able to bridge Fe(II) centres and form polynuclear structures containing SCO [Fe(py)4(NCS)2] centres [102]. SCO is maintained in certain instances when the diimines are replaced by an N4 quadridentate [103,104]. 

One very fast and reliable method for the reduction of double bonds is that of transfer hydrogenation with diimine (Scheme 20.30). Under the influence of traces of copper ion and oxygen from air, hydrazine is rapidly transformed into diimine. This compound is able to hydrogenate double bonds with great success under the formation of nitrogen [120],... 

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]. 

Synthetic routes to the nitrogen analogues of thiophene-1-oxides and thiophene-1,1-dioxides have been developed. Treatment of thiophene-1-oxide 48 with TsN=IPh gave sulfoximide 49 <99TL3785>, while a similar reaction involving thiophene 50 provided a mixture of thiophene-1-imine 51 and thiophene-1,1-diimine 52 amongst several products <99TL5549>. 

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 reaction is generally applicable to further extension for making macrobicyclic diamines4 with bridgehead nitrogen atoms by using monocyclic diimines and an appropriate acid chloride. The main... 

A number of observations show the profound effect of chelation on the stability of Schiff bases and similar unsaturated nitrogen-containing ligands. Eichhorn and coworkers found that the Schiff base of bis(thiaphenal)ethylene-diimine is hydrolyzed in the presence of Cu+2, with the formation of the ethylene-diamine complex (Equation 18) (26, 28). 

The suggested literature mechanisms for the first step of the diimine ligand oxidation in basic solution include (1) simple electron transfer, (2) dissociation of a ligand proton, (3) adduct formation at a ligand carbon atom, and (4) dissociation of a metal-nitrogen bond. These four mechanistic possibilities are shown in Scheme 1 and are discussed below. 

The mechanism depicted in Scheme 2 involves two main steps. Rupture of the first metal-nitrogen bond accompanied by coordination of a water ligand at the metal center is followed by reversible deprotonation and intramolecular reduction of the metal center. Under the experimental conditions wherein the concentration of base is much larger than the concentration of tris(diimine) complex, and, applying the steady-state approximation to the concentration of the intermediate species with the monodentate diimine ligand, Eq. (6) can be derived as... 

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