Diimide
Diimide, also called diazene or diimine, is a compound having the formula (NH). It exists as two geometric isomers, "E" ("trans") and "Z" ("cis"). The term diazene is more common for organic derivatives of diimide. Thus, azobenzene is an example of an organic diazene. Synthesis. A traditional route to diimide involves oxidation of hydrazine with hydrogen peroxide or air. Alternatively the hydrolysis of diethyl azodicarboxylate or azodicarbonamide affords diimide: Nowadays, diimide is generated by thermal decomposition of 2,4,6‐triisopropylbenzenesulfonylhydrazide. Because of its instability, diimide 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. Diimide decomposes readily. Even at low temperatures, the more stable "trans" isomer rapidly undergoes various disproportionation reactions, primarily forming hydrazine and nitrogen gas: Because of this competing decomposition reaction, reductions with diimide typically require a large excess of  the precursor reagent. Applications to organic synthesis. Diimide 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 H. 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. The hydrogenation mechanism involves a six-membered CHN transition state: Selectivity. Diimide is advantageous because it selectively reduces alkenes and alkynes and is  unreactive toward many functional groups that would interfere with normal catalytic hydrogenation. Thus, peroxides, alkyl halides, and thiols 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 to the corresponding alkenes and alkanes. Related. The dicationic form, HNNH (diprotonated dinitrogen), is calculated to have the strongest known chemical bond. This ion can be thought of as a doubly protonated nitrogen molecule. The relative bond strength order (RBSO) is 3.38. FNNH and FNNF have slightly lower strength bonds.