Triazenes complexes

The coordination of catenated nitrogen ligands to transition metals also dates back to the early work of Griess 89, 90), which included references to copper and silver derivatives of 1,3-diphenyltriazene. Around the turn of the century Meldola and Streatfeild 146-148), Meunier 150-152), Niemen-towski and Roszkowski 159), Cuisa and Pestalozza 55,56), and others reported extensively on triazene complexes of copper, silver, and mercury, and in the late 1930s and early 1940s Dwyer and colleagues 69-74) extended this work to include derivatives of nickel and palladium. However, most work on the coordination chemistry of triazenes and other catenated... 

Most triazene complexes are thermally stable and, where mass spectra have been recorded, molecular ions are usually observed. Fragmentation initially involves loss of ancillary ligands, notably CO cleavage of the diaryltriazenide ligands generates aryl, aryldiazo, and arylazo ions together with nitrene species [L M=NAr] (/, 42, 174, 179). 

The reaction of l-azido-3-chloropropane with Grignard reagents, followed by breakup of the Mg-triazene complex on Dowex resin, affords l-alkyl-3-(3-chloropropyl)triazenes which on concentration undergo cyclization to l-alkyl-1,4,5,6-tetrahydro-l,2,3-triazines 30a-d isopropylamine is added to neuttalize any HCl (Equation 104) <1997JOC8660>. 

The N-N distances are typically 1.26 to 1.35 A and the N-N-N angles are typically 99.1 to 111.9° in the 54 triazene complexes reported in the Cambridge Crystallographic Database (version 5.29, February 2(X)8) in which one metal is coordinated to two nitrogen atoms of the triazene ligand. 

The coupling reaction of 3-methylindole (Scheme 12-21) is complex, as it involves an initial ipso-addition at the 3-position followed by rearrangement of the arylazo group to the 2-position (Jackson and Lynch, 1987 Jackson et al., 1987). However, under slightly different conditions Spande and Glenner (1973) isolated the unusual triazene 12.41. Based on the change in the UV spectrum of the reaction mixture with time, Sarma and Barooah (1977) proposed a mechanism involving initial formation... 

Primary aromatic amines (e.g., aniline) and secondary aliphatic-aromatic amines (e. g., 7V-methylaniline) usually form triazenes in coupling reactions with benzenedi-azonium salts. If the nucleophilicity of the aryl residue is increased by addition of substituents or fused rings, as in 3-methylaniline and 1- and 2-naphthylamine, aminoazo formation takes place (C-coupling). However, the possibility has also been noted that in aminoazo formation the initial attack of the diazonium ion may still be at the amine N-atom, but the aN-complex might rearrange too rapidly to allow its identification (Beranek and Vecera, 1970). 

An intramolecular rearrangement of the conjugate acid of the triazene compound to form the oc-complex without an additional molecule of amine would correspond to a thermal [l,3]-sigmatropic rearrangement. However, such a mechanism can be ruled out on the grounds of the antarafacial pathway required from orbital symmetry considerations (Woodward-Hoffmann rules). 

However, an evaluation of the observed (overall) rate constants as a function of the water concentration (5 to 25 % in acetonitrile) does not yield constant values for ki and k2/k i. This result can be tentatively explained as due to changes in the water structure. Arnett et al. (1977) have found that bulk water has an H-bond acceptor capacity towards pyridinium ions about twice that of monomeric water and twice as strong an H-bond donor property towards pyridines. In the present case this should lead to an increase in the N — H stretching frequency in the o-complex (H-acceptor effect) and possibly to increased stabilization of the incipient triazene compound (H-donor effect). Water reduces the ion pairing of the diazonium salt and therefore increases its reactivity (Penton and Zollinger, 1971 Hashida et al., 1974 Juri and Bartsch, 1980), resulting in an increase in the rate of formation of the o-complex (ik ). 

I think that this problem can be answered satisfactorily only by direct evidence for a (Z)-a-complex 13.24. This may take some time, but I hope not as long as the 78 years between the discoveries of the first (Z)/(is)-stereoisomerism and that of the triazenes (See Wiberg and Pracht, 1972b Fanghanel et al., 1975a, 1975b see also Sec. 13.1.)... 

A hexadentate N202S2 ligand (116) has been synthesized as a dithiaalkyl-substituted triazene-1-oxide and forms an unusual hexacoordinated zinc complex with thioether donors. Both the phenyl and the methyl derivatives form structurally characterized octahedral complexes.896... 

A combination of the SNAr feature and the coordination ability of a copper complex has led to the development of a new O-arylation method that makes use of a triazene as an activating and directing group (Equation (2)).32,33 This protocol, though necessitating a three-step removal sequence of the triazene moiety, has been successfully applied to the total synthesis of vancomycin1 6 and extended to a solid-phase synthesis in which the triazene unit serves as an anchor to the resin.37... 

This procedure represents the most convenient synthesis of l-methyl-3-/>-tolyltriazene. Triazenes with more complex alkyl groups may be prepared from the corresponding amine2 or Grignard reagent.3... 

Figure 33 shows the octahedral geometry of the Mn(II) complex with the ligand dithio-methyl-triazene-1 -oxide, [MeN(0)N-NHC6H4S]2 (CH2)2. Because of the presence of different N202S2 chelating atoms the complex is considerably distorted.48... 

Triazene 1-oxides (17) in methanol react with TiCl4 to give dinuclear complexes which are suggested to have the oxygen-bridged structure (18) on the basis of i.r. and n.m.r. studies. ... 

Aryltriazenes can also be decomposed by hydrogen fluoride in organic solution after extraction from their aqueous mother phase. In this case, hydrogen fluoride can be used in small excess but the nature of the solvent is crucial for example, tetrahydrofuran gives complex mixtures, dichloromethane promotes radical reactions (dimerizations, reductions) and acetic acid favors triazene decomposition before fluorination. Aromatic and haloaromatic compounds seem to be the best solvents.283 Such a technique, especially suited for the rapid introduction of an 18F atom, has been employed to produce [ 8F]haloperidol (3), the specific receptors of which have been localized in the brain by positron emission transaxial tomography.298... 

Triazenes and related compounds. A complex of thorium tetranitrate with 2,4,6-tris(dimethylamino)triazene (C9H18N6, hexamethylmelamine), Th(N03)4-C9Hi8N6, and the probably polymeric derivatives of purine and adenine, Th(CsH3N4)2Cl2, have been recorded,43 but little is known about them. 

However, the production of the />-phenylenediamine [106-50-3] intermediate is more complex, because it involves the diazotization and coupling of aniline [65-53-3]. Aniline reacts with nitrogen oxides, produced via the oxidation of ammonia, to form 1,3-diphenyltriazene [136-35-6] in the process used by Du Pont (208,209) (see Amines, aromatic-aniline and its derivatives). In the Akzo process a metal nitrite salt and acid in water is used (210). The triazene rearranges in the presence of acid and an excess of aniline to form predominately the p-aminoazobenzene [60-09-3] and a small amount of the ortho isomer, 0-aminoazobenzene [2835-58-7]. The mixture of isomers is catalytically reduced to the respective diamines, and they are then separated from the aniline, which is recycled (208,209). The 0-phenylenedi amine [95-54-5] is used in the manufacture of herbicides (see Amines, aromatic-phenylenediamines). 

This review, which complements an earlier one (Part I) dealing with transition metal complexes of triazenes, tetrazenes, tetraazadienes, and pentaazadienes, examines the coordination chemistry of related cyclic catenated nitrogen ligands. Six-membered rings containing three, four, or five adjacent nitrogen atoms — 1,2,3-triazines, 1,2,3,4-tetrazines, and pentazines, respectively — are either unknown or are relatively unstable species whose coordination chemistry has yet to be explored. 

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