Aminonitrenes 1,1-Diazenes

The aminonitrenes have much in common with the five-membered aromatic nitrenes, but are a class apart due to strong resonance stabilization of the 1,1-diazene form. General reviews on aminonitrenes are available.390-392 

The first heterocyclic 1,1-diazene (355) has been isolated at — 78°C and characterized by IR and UV spectroscopy.393 A considerable degree of 

Gilchrist and C. W. Rees, Carbenes, Nitrenes, and Arynes. Nelson, London, 1969. 

N=N double bond character is indicated, as also supported by generalized valence bond calculations on the simple H2NN.394 Compound 335 dimerizes to the corresponding tetrazene on warming, concomitant with fragmentation via the diradical 356 (Eq. 105).395 Related five-membered 1,1-diazenes fragment to 1,4-diradicals in the gas phase.396 

Kinetic evidence for the existence of a discrete heteroaromatic amino-nitrene (or diazene) (357) comes from an examination of the ratio of fragmentation to trapping products using various oxidants (Eq. 106).397 

Gilchrist and C. W. Rees, Carbenes, Nitrenes, and Arynes. Nelson, London, 1969. D. M. Lemal, in Nitrenes (W. Lwowski, ed.). Chapter 10, p. 345. Wiley (Interscience), New York, 1970. 

The lead tetraacetate oxidation of 1-aminobenzotriazole leads to benzyne (Eq. 107), whereas 2-aminobenzotriazole ring opens to Z,Z-mucononitrile (Eq. 108).  

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Schultz, Dervan, and co-workers " subsequently reported the synthesis and characterization of the five-membered ring analogue 65. As before, the oxidation of the appropriate hydrazine at 78 °C gave a clear, colored solution of the aminonitrene. This 1,1-diazene absorbs at 497 nm (in CH2CI2) and 487 nm (in 2-propanol). The IR spectrum shows a strong absorption at 1638 cm that disappears on warming to 25 °C. The isotopomer has a vibration at 1612 cm a shift of 26 cm. ... 

The oxidation of 1,1-disubstituted hydrazines can be achieved by a wide range of oxidants. The oxidative removal of hydrogen formally leads to the production of aminonitrene, or 1,1-diazene, intermediates and many products of such reactions have been interpreted as being derived from aminonitrene intermediates. Indeed, several of these species, derived from sterically hindered hydrazines by oxidation with nickel peroxide or r-butyl hypochlorite, have been detected and characterized in solution at low temperature. Examples include the diazenes (14) and (15). The diazene (16) is stable enough to persist in solution at room temperature for several days. ... 

It should be noted that -aminotetrachlorophenylnitrene is a phenylene analogue of the diazene (aminonitrene) NHj—N- <-> NH2=N . Furthermore, 1,1 -diazenes are known to protonate to give relatively stable cations (R N—NH- ) (Lemal, 1970). 

To favour the formation of the endocyclic hydrazone, it is necessary to know the kinetics of aminonitrene-hydrazone rearrangement. The difficulty of this study results from impossibility to follow the diazene content according to time. The kinetic parameters are thus determined by degeneration of the precursor process (1). 

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