How are diazo compounds used to produce carbenes?

Diazo compounds—organic substances containing a group of two nitrogen atoms bonded to a carbon atom—are the most frequently used precursors for generating carbenes.

Because carbenes are high-energy, highly reactive molecules, their formation requires the input of external energy. Diazo compounds are converted into carbenes through two primary methods:

• Photolysis: Treatment with light, where the energy absorbed by the diazo compound facilitates the cleavage of the molecule.
• Pyrolysis: Treatment with heat, which similarly triggers the decomposition of the precursor.

During these processes, the diazo compound cleaves to yield the corresponding carbene and a free molecule of nitrogen gas. When performed at very low temperatures in an unreactive solid medium—a technique known as matrix isolation—the resulting carbene can be stabilized and prevented from undergoing further, immediate reactions, allowing it to be studied in its transient state.1