Nitrene

A nitrene is a reactive nitrogen-containing species with the formula RN:. It is a neutral, divalent nitrogen atom possessing six electrons in its valence shell and is isoelectronic with a carbene. In organic chemistry, nitrenes exist in two spin states: singlet nitrenes, with paired electrons, and triplet nitrenes, with two unpaired electrons. Singlet nitrenes are typically more electrophilic and engage in two-electron insertions, while triplet nitrenes behave more like biradicals and follow radical-type pathways.

Nitrenes are usually generated in situ from precursors such as organic azides (RN3) by photolysis or thermolysis, which releases N2 and forms RN:. They can also arise from sulfonyl azides, hydroxylamine derivatives, or iminoiodinane reagents that transfer the nitrene to substrates. Stabilized nitrenes, such as sulfonyl nitrenes, can be intercepted or trapped to affect selectivity in synthetic sequences.

Reactivity patterns include aziridination of alkenes to give aziridines, and insertion into C–H or O–H bonds. Triplet nitrenes may abstract hydrogen atoms or participate in radical-type additions, while singlet nitrenes tend to undergo concerted insertions. A common decomposition pathway for aryl or alkyl nitrenes is rearrangement to isocyanates under heating, a process related to Curtius-type rearrangements of acyl azides.

Applications in synthesis focus on installing nitrogen selectively, enabling C–H amination, aziridination, and the formation of amines and related products. The high reactivity of nitrenes requires controlled generation and often catalytic approaches to improve selectivity and safety.