Shengfa Ye, Gengwen Tan, and colleagues, Sun Yat-sen University, Guangzhou, China, and Chinese Academy of Sciences, Dalian, China, have successfully isolated and characterized a thermally stable triplet nitrene (M^sFluid*-N, pictured above). Triplet nitrenes are highly reactive and have short lifetimes, therefore, their isolation in the condensed phase under ambient conditions is challenging. However, nitrene-involved reactions are one of the most practical approaches for synthesizing nitrogen-
containing molecules. The researchers attribute the high stability of their triplet nitrene to the steric hindrance and effective electron delocalization provided by the supporting bulky hydrindacene ligand.

First, the team synthesized the azide precursor, M^sFluid*-N₃ by reacting a lithium salt of the hydrindacene ligand with tosyl azide (TsN₃). The precursor was subjected to photolysis in benzene solution at 0°C using an UV lamp (313 nm). After five hours of irradiation, the triplet nitrene M^sFluid*-N formed.

The C–N bond length in the triplet nitrene was measured as 1.320(3) Å, which is shorter than the C–N bond in the corresponding amine (1.404(5) Å). A shorter C–N bond typically suggests greater double bond character.

The researchers also explored the reactivity of the triplet: When photolyzed in THF or n-hexane, it decomposed rapidly to form an amine, likely through hydrogen abstraction from the solvent. Reacting M^sFluid*-N with trimethylphosphine produced a phosphinimide. In aziridination reactions, M^sFluid*-N reacted with styrene to form an aziridine via a [1 + 2] cycloaddition.

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• Isolation and characterization of a triplet nitrene,
  Dongmin Wang, Wang Chen, Haonan Chen, Yizhen Chen, Shengfa Ye, Gengwen Tan
  Nature Chemistry 2024.
  https://doi.org/10.1038/s41557-024-01669-9

 

Correction (December 2, 2024)

In the text it was incorrectly stated that this is the first time that a stable triplet nitrene has been isolated and characterized. Janssen et al. have previously reported a stable triplet nitrene:
Marvin Janssen, Thomas Frederichs, Marian Olaru, Enno Lork, Emanuel Hupf, Jens Beckmann, Synthesis of a stable crystalline nitrene, Science 2024, 385(6706), 318-321. https://doi.org/10.1126/science.adp4963