Diazenium cations

Anodically electrogenerated species can undergo cycloaddition reactions with other reagents. For example, in Scheme 5 a diazenium cation reacts with styrene [8, 9]. 

The electrochemical oxidation of Af,Af-diarylhydrazines affords diazenium cations that undergo cycloadditions with olefins vide supra Scheme 5) [8, 9, 68-70]. Acetonitrile can participate in the formation of cycloadducts. 

In the medium pH range where both the diazenium cation and the diazene exist in solution, these two species react rapidly to afford a substituted tetrazene [141], The second oxidation wave, observed for disubstituted hydrazenes in acetonitrile with a pyridine base present, is due to the further oxidation of the tetrazene to a dicationic species. 

Oxidation of a 1,1-disubstituted hydrazine in MeCN containing HCIO4 [132-134] or anhydrous HBF4 [135] forms a diazenium cation that may react with alkenes in a cycloaddition reaction to a tetrahydrocinnoline. If both substituents on nitrogen are aryl, an oxidative coupling between them may compete with the dipolar reaction [135]. 

The proton affinity of HN3 has been reported at 179 kcalmol and 176.6 kcalmol-i The QCISD(T)//MP2 level PA value in Table 3 to form H2NNN+ is 188.7 kcalmoP, from which is subtracted the ZPE difference with the neutral parent (Table 3 5) of 7.9 kcalmokk This gives an adjusted PA of 180.8 kcalmoP which is in good agreement with both reported measured values. It has recently been claimed that the true experimental PA of HN3 is somewhat (<9 kcalmol" ) higher than reported experimentally from proton transfer equilibria. The diazenium cations is QCISD(T) calculated to be 24.5 kcal mol less stable than the diazonium ion (Table 3). 

An interesting example of internal spin trapping by a nitro group has been reported by Snyder during a study of the diazenium cation 240, hydrazyl radical 241, and nitroxide radical 242 equilibrium (Scheme 100). Analogous spin trapping of alkyl radicals by the nitro group has been reported in the Cy5/Cy6 and Cy4/Cy5 cases. ... 

Early Intermediates in Hydrazine Oxidations Hydrazine Cation Radicals, Hydrazyls, and Diazenium Cations... 

We have put considerable effort over the past several years into study of the early intermediates expected in hydrazine (I) oxidation. As indicated in Scheme 1, electron and proton loss should alternate in the presence of a one electron oxidant, giving hydrazine radical cations (II), hydrazyl radicals (III), and trisubstituted diazenium cations (IV). Other types... 

To enable measurement of kESR for bis(diazenium) radical cations, it was necessary to decrease Fn, so we synthesized the 6-bond-bridged systems 14 and 15, which required first making the 6-bond-bridged bis(azo) compound. They indeed have slow enough... 

Table 4 Eyring activation parameters and extrapolated ESR rate constants for 6-cr-bond-bridged bis(diazenium) IV radical cations...

The energy of the barrier-crossing frequency, cov, is employed in the pre-exponential term.8 We used cdv = 800 cm-1 for bis(hydrazines), which is both close to the value estimated using semiempirical dynamics calculations on 11+ 33 and obtained in as yet unpublished resonance Raman data for 20 +. 87 We used cov = 1100 cm-1 for bis(diazenium) radical cations. This value is smaller than the 1403 cm-1 obtained from dynamics calculations on sB4T+ (7+)33 but close to the 1053 cm-1 obtained from resonance Raman work in collaboration with Williams and Hupp.88... 

Analogues to the five-electron bonded 2a/27t/l7t disulfide radical cations in nitrogen-based systems, namely, hydrazine radical cations could be generated by one-electron reduction of trialkyl diazenium salts (eq. 49) and subsequent equilibration of the neutral product radical with its protonated form. The pK of the R=t-butyl substituted species, incidentally, is 7.0, 2.6 units below that of the parent hydrazine compound. The results emphasize the importance of structural parameters, in particular those which control orbital orientation and overlap. >46,147 Jhe alternative possibility to generate such... 

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