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| Names | |||
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| IUPAC name Diazene | |||
| Other names Diimide Diimine Dihydridodinitrogen Azodihydrogen | |||
| Identifiers | |||
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3D model (JSmol) | |||
| ChEBI | |||
| ChemSpider |
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| KEGG |
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| MeSH | Diazene | ||
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| Properties | |||
| H2N2 | |||
| Molar mass | 30.030 g·mol−1 | ||
| Appearance | Yellow gas | ||
| Melting point | −80 °C (−112 °F; 193 K) | ||
| Related compounds | |||
Otheranions | diphosphene dinitrogen difluoride | ||
Othercations | azo compounds | ||
Related Binaryazanes | |||
Related compounds | |||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Diimide, also calleddiazene ordiimine, is a compound having the formula HN=NH. It exists as twogeometric isomers,E (trans) andZ (cis). The term diazene is more common for organic derivatives of diimide. Thus,azobenzene is an example of an organic diazene.
A traditional route to diimide involves oxidation ofhydrazine with hydrogen peroxide or air.[1]
Alternatively the hydrolysis ofdiethyl azodicarboxylate orazodicarbonamide affords diimide:[2]
Nowadays, diimide is generated by thermal decomposition of 2,4,6‐triisopropylbenzenesulfonylhydrazide.[3]
Because of its instability, diimide is generated and usedin-situ. A mixture of both thecis (Z-) andtrans (E-) isomers is produced. Both isomers are unstable, and they undergo a slow interconversion. Thetrans isomer is more stable, but thecis isomer is the one that reacts with unsaturated substrates, therefore the equilibrium between them shifts towards thecis isomer due toLe Chatelier's principle. Some procedures call for the addition of carboxylic acids, which catalyse the cis–trans isomerization.[4] Diimide decomposes readily. Even at low temperatures, the more stabletrans isomer rapidly undergoes various disproportionation reactions, primarily forminghydrazine andnitrogen gas:[5]
Because of this competing decomposition reaction, reductions with diimide typically require a large excess of the precursor reagent.
Diimide is occasionally useful as a reagent inorganic synthesis.[4] It hydrogenates alkenes and alkynes with selective delivery of hydrogen from one face of the substrate resulting in the same stereoselectivity as metal-catalysedsyn addition ofH2. The only coproduct released is nitrogen gas. Although the method is cumbersome, the use of diimide avoids the need for high pressures or hydrogen gas and metal catalysts, which can be expensive.[6] The hydrogenation mechanism involves a six-memberedC2H2N2 transition state:
Diimide is advantageous because it selectively reduces alkenes and alkynes and is unreactive toward manyfunctional groups that would interfere with normalcatalytic hydrogenation. Thus,peroxides,alkyl halides, andthiols are tolerated by diimide, but these same groups would typically be degraded by metal catalysts. The reagent preferentially reduces alkynes and unhindered or strained alkenes[1] to the corresponding alkenes and alkanes.[4]
Thedicationic form,H−N+≡N+−H (diazynediium, diprotonated dinitrogen), is calculated to have the strongest known chemical bond. This ion can be thought of as a doubly protonated nitrogen molecule. Therelative bond strength order (RBSO) is 3.38.[7]F−N+≡N+−H (fluorodiazynediium ion) andF−N+≡N+−F (difluorodiazynediium ion) have slightly lower strength bonds.[7]
In the presence of strong bases, diimide deprotonates to form thepernitride anion,N−=N−.
