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A Crystalline Singlet Phosphinonitrene: A Nitrogen Atom–Transfer Agent

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Science  21 Sep 2012:
Vol. 337, Issue 6101, pp. 1526-1528
DOI: 10.1126/science.1226022

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N on P

Nitrogen atoms form strong, relatively unreactive triple bonds with themselves (in N2) and with carbon (in cyanide and nitriles). In contrast, binding to transition metals often leaves an otherwise naked nitrogen center more prone to reactivity. Dielmann et al. (p. 1526) prepared a compound with nitrogen bound to divalent phosphorus, which acted more like a metal than a light element. Although the compound, formally a nitrene, was sufficiently stable to isolate at room temperature and characterize by x-ray diffraction, it transferred the nitrogen efficiently to unsaturated carbon compounds.

Abstract

A variety of transition metal–nitrido complexes (metallonitrenes) have been isolated and studied in the context of modeling intermediates in biological nitrogen fixation by the nitrogenase enzymes and the industrial Haber-Bosch hydrogenation of nitrogen gas into ammonia. In contrast, nonmetallic nitrenes have so far only been spectroscopically observed at low temperatures, despite their intermediacy in a range of organic reactions. Here, we report the synthesis of a bis(imidazolidin-2-iminato)phosphinonitrene, which is stable at room temperature in solution and can even be isolated in the solid state. The bonding between phosphorus and nitrogen is analogous to that observed for metallonitrenes. We also show that this nitrido phosphorus derivative can be used to transfer a nitrogen atom to organic fragments, a difficult task for transition metal–nitrido complexes.

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