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 for the first time (MsFluid*-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, MsFluid*-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 MsFluid*-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 MsFluid*-N with trimethylphosphine produced a phosphinimide. In aziridination reactions, MsFluid*-N reacted with styrene to form an aziridine via a [1 + 2] cycloaddition.
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