Diazene

Not to be confused with Diazine.

Diazene

Names
IUPAC name Diazene
Other names Diimide Diimine
Identifiers
CAS Number	3618-05-1 Y 15626-43-4 (E)-diazene Y 15626-42-3 (Z)-diazene Y
ChEBI	CHEBI:30096 Y
ChemSpider	10612167 Y
Jmol 3D model	Interactive image
KEGG	C05360 Y
MeSH	Diazene
PubChem	123195
InChI InChI=1S/H2N2/c1-2/h1-2H Y Key: RAABOESOVLLHRU-UHFFFAOYSA-N Y InChI=1/H2N2/c1-2/h1-2H Key: RAABOESOVLLHRU-UHFFFAOYAG
SMILES N=N
Properties
Chemical formula	H2N2
Molar mass	30.03 g·mol−1
Appearance	Yellow gas
Melting point	−80 °C (−112 °F; 193 K)
Related compounds
Other anions	diphosphene dinitrogen difluoride
Other cations	azo compounds
Related Binary azanes	ammonia diazane triazane
Related compounds	triazene tetrazene
Y verify (what is YN ?)
Infobox references

Diazene, also called diimine or diimide, is a compound having the formula (NH)₂. It exists as two geometric isomers, E and Z. Diazene is also the parent member of the entire class of azo compounds with the formula (NR)₂, where R is an organyl group. Thus, azobenzene is an example of an organic diazene.

Synthesis

The traditional route to diazene involves oxidation of hydrazine with hydrogen peroxide or air. Alternatively the decarboxylation of azodicarboxylic acid affords diazene:

(NCO₂H)₂ → (NH)₂ + 2 CO₂

Diazene can also be efficiently generated by elimination of sulfonohydrazides using a suitable base. For example, 2,4,6-triisopropylbenzenesulfonohydrazide eliminates diazene upon treatment with sodium bicarbonate, a very mild base.

Because of its instability, diazene is generated and used in-situ. A mixture of both the cis (Z-) and trans (E-) isomers is produced. Both isomers are unstable, and they undergo a slow interconversion. The trans isomer is more stable, but the cis isomer is the one that reacts with unsaturated substrates, therefore the equilibrium between them shifts towards the cis isomer due to Le Chatelier's principle. Some procedures call for the addition of carboxylic acids, which catalyse the cis–trans isomerization. Diazene decomposes readily. Even at low temperatures, the more stable trans isomer rapidly undergoes various disproportionation reactions, primarily forming hydrazine and nitrogen gas:

2 HN=NH → H₂N–NH₂ + N₂

Because of this competing decomposition reaction, reductions with diazene typically require a large excess of the precursor reagent.

Applications to organic synthesis

Main article: Reductions with diimide

cis-Diazene is occasionally useful as a reagent in organic synthesis. It hydrogenates alkenes and alkynes with selective delivery of hydrogen from one face of the substrate resulting in the same stereoselectivty as metal-catalysed syn addition of H₂. The only coproduct released is nitrogen gas. Although the method is cumbersome, the use of diazene avoids the need for high pressures or hydrogen gas and metal catalysts, which can be expensive. The hydrogenation mechanism involves a six-membered C₂H₂N₂ transition state:

Mechanism of hydrogenation using diazene

Selectivity

Diazene is advantageous because of it selectively reduces alkenes and alkynes and is nonreactive toward many functional groups that would interfere with normal catalytic hydrogenation. Thus, peroxides, alkyl halides, and thiols are tolerated by diazene, but these same groups would typically be degraded by metal catalysts. The reagent preferentially reduces alkynes and unhindered or strained alkenes to the corresponding alkenes and alkanes.

Related

The dication diazene HNNH²⁺ is calculated to have the strongest known chemical bond. This ion can be thought of as doubly protonated nitrogen. The relative bond strength order (RBSO) is 3.38. FNNH²⁺ and FNNF²⁺ have slightly lower strength bonds.