nitrenes

Nitrenes are highly reactive nitrogen-centered intermediates characterized by a divalent nitrogen atom bearing a lone pair and two substituents, R-N:. They are neutral species and are isoelectronic with carbenes. In many cases, nitrenes exist in two spin states: singlet and triplet; the singlet is typically more electrophilic, while the triplet is a diradical and often less selective.

Nitrenes are generated from various precursors. The most common source is organic azides (R-N3), which upon photolysis or thermal decomposition expel nitrogen gas to furnish nitrenes. Other routes include iminoiodinane reagents that transfer a nitrene fragment to substrates and sulfonyl azides that form sulfonyl nitrenes. Some nitrenes can also be prepared from hydroxylamine-derived precursors under suitable conditions.

Reactivity patterns depend on the spin state. Singlet nitrenes tend to insert into C–H bonds and form new C–N bonds in concerted steps, whereas triplet nitrenes often undergo stepwise radical additions to double bonds and related rearrangements. Common transformations include aziridination of alkenes, direct amination of C–H bonds, and various insertion and rearrangement processes that build nitrogen-containing rings and frameworks.

Applications and limitations: Nitrenes are valuable tools in synthetic organic chemistry for constructing amine and heterocyclic motifs. Their extreme reactivity requires careful control of reaction conditions and often specialized precursors or catalysts to improve selectivity. Due to their transient nature, nitrene chemistry typically proceeds under low temperatures or in the presence of stabilizing substituents or transfer reagents to manage reactivity.