Diazenes formation

Mahy JP, Gaspard S, Delaforge M et al (1994) Reactions of prostaglandin-H synthase with monosubstituted hydrazines and diazenes - formation of iron(II)-diazene and iron(III)-sigma-alkyl or iron(III)-sigma-aryl complexes. Eur J Biochem 226 445 157... 

Little is known about the mode of action of hydra-zinecarboxamide-derived fungicides. Since diazene formation is involved in the fungitoxic action of phenyl-thiosemicarbazide (2 2) and is implicated in a glutathione-oxidation mechanism to account for fungi-toxicity of similarly structured compounds (2 1 ), it is conceivable that diazenes described in this study may well play a critical role in the action of fluorine-substituted hydrazinecarboxamide fungicides and perhaps larvicides as well. 

The production of nitrosobenzaldehydes is a third possible drawback associated with the use of nitrobenzyl linkers. The reactive aldehyde can react with an amine in the released product, thereby substantially decreasing the yield of photolysis. Additionally, the nitroso group can engage in a second photoreaction through intermolecular diazene formation (Scheme 17.6). The produced diazene is not only an internal filter (/Wx=325nm) [19], but also cross-links the resin, which slows down photocleavage and eventually blocks product release from the resin. 

RESULTS AND DISCUSSION I. Kinetic study of the diazene formation... 

Reductive Transposition of Allylic Alcohols. Similar to the synthesis of allenes from propargylic alcohols, the Mitsunobu displacement of allylic alcohols with IPNBSH followed by hydrolysis, diazene formation, and sigmatropic loss of dinitrogen provides reductively transposed alkenes. This methodology has proven effective for the reductive transposition of a variety of allylic alcohols (eq 2). The overall transformation provides the desired olefin with high selectivity in the formation of the irans-alkene (eq 3). ... 

Reductive Transposition of Allylic Halides. Displacement of allylic leaving groups with the sodium sulfonamide of IPNBSH followed by in situ hydrolysis, allylic monoalkyl diazene formation, and sigmatropic loss of dinitrogen affords the reductively transposed product (eq 6). 

Alkene Reduction. 2,4,6-Triisopropylbenzenesulfonyl hydrazide (TPSH) undergoes solvent-dependent thermal degradation into diazene (diimide) between 35 and 65 °C, resulting in the in situ reduction of alkenes and other double bonds in good to excellent yields. TPSH remains one of the best sources of diazene, and addition of amine bases increases the rate of both diazene formation and hydrogenation. It is the most reactive of the common arenesulfonylhydrazides, being 380 and 24 times more reactive than /j-toluenesulfonylhydrazide and mesitylenesulfonylhy-drazide, respectively, under base-catalyzed conditions. ... 

Acyclic ADC compounds, which are more correctly named as derivatives of diazene, are generally prepared from hydrazine derivatives. For example, diethyl azodicarboxylate (Chemical Abstracts name diethyl diazene-1,2-dicarboxylate)5 is prepared from hydrazine by treatment with ethyl chloro-formate followed by oxidation with chlorine in benzene-water.6 Other oxidants which have been used include JV-bromosuccinimide,7 nitric acid,8 inorganic nitrates,9 potassium dichromate,10 silver carbonate on celite,11 and phenyl iodosotrifluoroacetate.12 The hydrazine derivative may also be... 

Following a similar approach, the first bis(triorganosilyl) diazene 402 that is stable at room temperature could be obtained.410 Thus, the reaction of (/-Bu2MeSi)HNNH(SiMe/-Bu2) 403, an analog of 399, with 2 equiv. of BuLi has provided (/-Bu2MeSi)LiNNLi(SiMe/-Bu2) 404, whose oxidation with bromine has led to the formation of the diazene /-Bu2MeSiNNSiMe/-Bu2 402 (Scheme 58). Recently, the stepwise synthesis of cyclic and open-chain silyl hydro-xylamines has been reported by Klingebiel < / /.411 14 For hypervalent silyl hydroxylamines, see Section 6.8. 

In the case of tetra(A-oxide) of the initial bis(diazene), one-electron oxidation in Scheme 3.32 leads to the formation of a novel, O-stabilized, 3e/4N cation-radical with 3-D delocalization of the unpaired electron (Exner et al. 1999). 

Insertion of mono- or bis(aryldiazonium) cations into the Re—bonds of the hydride complexes [ReH(CO)5 (PR3)J (PR3 = P(OEt)3, PPh(OEt)2, PPh2(OEt) =1 ) results in the formation of cationic aryldiazene complexes of the compositions [Re(HNNAr)(CO)5 (PR3) ]" or [ Re(CO)5 (PR3) 2(/r-HNNArNNH)] +. " Bifunctional diazene/diazonium derivatives which can be prepared in this way are excellent building blocks for heterobinuclear and heterotrinuclear compounds with bis(aryldiazene) bridging ligands as has been demonstrated for Re-Ru, Re-Os,... 

Azoadamantane exposed to 2 mol equivalents of T CIO4 at room temperature rapidly and quantitatively evolved nitrogen, and thianthrene and products derived from the adamantyl cation were obtained. Equations (38)-(40) (AA, azo-adamantane Ad, adamantane) make clear why 2 mol equivalents of the radical oxidant are required (85JA2561). The comparable interaction of T with phenylazotriphenylmethane and di-ter/-butyl diazene, using a 2 1 ratio of radical cation to substrate, also leads to the formation of thianthrene and nitrogen (85PS111). 

Hydrazone formation of pyridazine-3-hydrazines with aldoses, dialdofuranoses, and dialdopyranoses was studied by Stanovnik and co-workers. The respective hydrazones could be cyclized with Bt2 in MeOH or Pb(OAc)4 to j-triazolo[4,3-3]pyridazin-3-yl substituted polyols <1997JHC1115, 1998JHC513>. Similarly, 4-[(dimethylamino)-methylene]-l,8,8-trimethyl-2-oxabicyclo[3.2.1]octan-3-one was reacted with pyridazine-3-hydrazines and the resulting mixtures were subsequently treated with Pb(OAc)4. Besides j-triazolo[4,3-3]pyridazine formation also diazenes were obtained. This can be rationalized by the enehydrazine-hydrazone mixtures observed in the first reaction. For phthalazin-l-hydrazines only diazenes were obtained after oxidation <2005TA2927>. Also cyclizations of... 

Reaction of the malononitrile-derived diazene 275 with active methylene compounds proceeds via addition to a cyano group followed by intramolecular hydrazide or thiohydrazide formation, pyridazin-3(2//)-ones and thio analogs 276 are respectively produced (Equation 70) <1999JCM8>. 

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 redox reactions of hydrazine toward main-group and transition metal oxidants have been reviewed (73). Different stoichiometries have been found, with N2 appearing as the N-containing oxidized product, sometimes accompanied by the formation of NH3 and/or HN3. The mechanisms have been analyzed in terms of the one- or two-electron nature of the oxidants, and imply both outer-and inner-sphere routes, depending on the oxidant. The very reactive, key intermediate, diazene (diimide), N2H2, has been proposed in most of these reactions. 

The high lability of bound N2 in [FeII(CN)5N2]3 regenerates the active site, namely the [FeII(CN)5H20]3 ion, which is able to further bind and process hydrazine. A more detailed kinetic study could be warranted for this interesting set of reactions. Some uncertainties still remain as to the nature of the intramolecular electron-transfer rate processes (91). At the employed concentration levels of the complex, the participation of mixtures of mononuclear and dinuclear complexes complicate the spectral evolution. Even the nature of the dinuclear intermediates (cyano- or hydrazino-bridged) could be put into question (probably both are involved, due to the labile interconversion equilibria). The participation of Fe(III) species, either in the mononuclear or dinuclear species, as reactive intermediate precursors of the formation of diazene and N2... 

Fig. 19. Catalytic cycle promoted by the [Fe(CN)eH20]3 ion, for the reaction of hydrazine with 02, giving N2, with the intermediate formation of bound diazene as mononuclear and dinuclear complexes.

The 3,4-dimethylenethiophene (333) has been generated from diazene (332) by either thermolysis or photolysis (310-380 nm). The purple-colored biradical (333) undergoes intramolecular dimerization to (334) at - 78°C (the formation of intermolecular dimers is possible at higher temperatures). However, (333) is quiet stable up to 160 K at frozen glassy solution in 2-methyltetrahydrofuran. 

Normally, the dehydrofluorination process is a 1,2-elimination, but an unusual 1,4-elimination of hydrogen fluoride is also observed in the formation of 15.38 However, the elimination is not concerted, but proceeds via an enolate in a multistep reaction. A second example involves the preparation of polyfluoroalkene(phenyl)diazenes 16a and b.39-40 Interestingly, for the derivative with Rf = C3F7, a 1,2-climination to the perfluoroalkene(phcnyl)hydrazone 16c is observed with phenylhydrazine as base rather than the 1,4-elimination to 16a and b found with triethylaminc.39... 

A,TV-Dimethyl-A -phenylthiourea has been shown to coordinate to Rh111 as an N—S bidentate involving four-membered chelate ring formation.154 N-Substituted thioamides also may bond in this manner.155 156 l-Amidino-2-thioureas (44) may behave either as N—S or as N—N bidentates, with this donor choice being dependent mainly on pH and the nature of the metal ion.157 As N—S donors they are known to stabilize lower oxidation states.158 As part of a study on Mo—S-containing complexes as models for redox-active molybdoenzymes, Dilworth et al. have shown that some p-(substituted)phenylhydrazines may coordinate as N—S bidentates in three different ways to one metal atom.159 The three diazenido, diazene and hydrazonido forms vary in their degree of deprotonation and therefore their anionic nature. 

Full papers have appeared on the formation and reactivity of the compounds ML(CNR)2 (M = Ni, Pd, Pt L = Oz, azobenzene, olefin, diazo-fluorene, acetylene) (231-237) (see also Sections IV,D,2 and V,D). Complexes of the type Ni(olefin)(CNBu )2 have been prepared for a large range of olefins (234, 237). The isocyanide stretching frequencies have been measured and related to the electron-withdrawing properties of the olefin. Other unsaturated molecules such as imines, diazenes, ketones, nitroso compounds, and acetylenes have been similarly studied. The effect of substituent change has been found to be cumulative and an empirical relationship has been developed to predict v(NC) (237). 

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