Diimide

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

Applications to organic synthesis

Main article: Reductions with diimide

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 stereoselectivity as metal-catalysed syn addition of . 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 transition state:

:[[File:DiimineReduction.png|500px|Mechanism of hydrogenation using diimide.]]

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, (diazynediium, 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. (fluorodiazynediium ion) and (difluorodiazynediium ion) have slightly lower strength bonds.

In the presence of strong bases, diimide deprotonates to form the diazenide anion, .

References

References

1. (1973). "cis-Cyclododecene".
2. (2001). "Inorganic Chemistry". [[Elsevier]].
3. (2008). "Encyclopedia of Reagents for Organic Synthesis".
4. (2001). "Inorganic Chemistry". Academic Press.
5. Pasto, D. J.. (2001). "Diimide". John Wiley & Sons.
6. Miller, C. E.. (1965). "Hydrogenation with Diimide". Journal of Chemical Education.
7. (12 September 2013). "Identification of the Strongest Bonds in Chemistry". The Journal of Physical Chemistry A.