Diimide

Diimide, commonly known as diazene, is the simplest member of the diimide family with the formula N2H2. In its neutral form it exists as the diazene molecule, HN=NH, featuring a nitrogen–nitrogen double bond with one hydrogen attached to each nitrogen. The molecule is planar and highly reactive, and diimide is typically generated and used in situ because it is unstable at room temperature, tending to decompose to nitrogen and hydrogen gas.

Preparation and handling

Diimide is not usually isolated as a pure compound. In the laboratory it is generated in situ from hydrazine derivatives under mild oxidative conditions or other decomposition routes, and it is consumed in the same reaction mixture. Due to its instability and potential hazards, diimide is handled only under controlled conditions with appropriate safety precautions.

Reactions and applications

Diimide is a mild, neutral reducing agent that transfers two hydrogen atoms to unsaturated substrates in a syn fashion. Its most notable application is the selective hydrogenation of alkenes to alkanes, with nitrogen gas produced as a benign byproduct. The reaction generally proceeds without affecting many other functional groups and can be advantageous for the hydrogenation of sensitive substrates that are difficult to reduce with catalytic hydrogenation. Limitations include the need for in situ generation, variable stability, and the potential for exothermic decomposition.

Safety

Diimide is hazardous due to its instability and potential to decompose violently, releasing nitrogen and hydrogen. It should be prepared and used only in properly equipped laboratories with appropriate protective equipment and procedures for handling reactive nitrogen hydrides.