Diimide, also called diazene or diimine, is a compound having the formula (NH)₂. It exists as two

geometric isomer Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is c ...

s, ''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 Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...

with hydrogen peroxide or air. Alternatively the hydrolysis of

diethyl azodicarboxylate Diethyl azodicarboxylate, conventionally abbreviated as DEAD and sometimes as DEADCAT, is an organic compound with the structural formula CH3CH2O2CN=NCO2CH2CH3. Its molecular structure consists of a central azo functional group, RN=NR, flanke ...

or azodicarbonamide affords diimide: :(NCOOH)₂ → (NH)₂ + 2 CO₂ 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 Le Chatelier's principle (pronounced or ), also called Chatelier's principle (or the Equilibrium Law), is a principle of chemistry used to predict the effect of a change in conditions on chemical equilibria. The principle is named after French ...

. 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

and nitrogen gas: :2 HN=NH → H₂N–NH₂ + N₂ 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 Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

. 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 diimide 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: : DiimineReduction

Selectivity

Diimide is advantageous because it selectively reduces alkenes and alkynes and is unreactive toward many

functional group In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the r ...

s that would interfere with normal

catalytic hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic ...

. Thus,

peroxide In chemistry, peroxides are a group of compounds with the structure , where R = any element. The group in a peroxide is called the peroxide group or peroxo group. The nomenclature is somewhat variable. The most common peroxide is hydrogen p ...

alkyl halide The haloalkanes (also known as halogenoalkanes or alkyl halides) are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely us ...

s, and

thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...

s 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.

The dicationic form, HNNH²⁺ (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. FNNH²⁺ and FNNF²⁺ have slightly lower strength bonds.

References

{{Hydrides by group Azo compounds Nitrogen hydrides Reducing agents Gases with color

Synthesis

Applications to organic synthesis

Selectivity

Related

References