In organic chemistry, isodiazomethane, also known as isocyanamide, aminoisonitrile, or systematically as isocyanoamine,[1] is the parent compound of a class of derivatives of general formula R2N–NC. It has the condensed formula H2N–N+≡C–, making it an isomer of diazomethane. It is prepared by protonating an ethereal solution of lithiodiazomethane, LiCHN2, with aqueous NaH2PO4 or NH4Cl.[2] The parent compound is only marginally stable at room temperature and is isolated by removal of solvent at –50 °C.[3] Derivatives are generally prepared by dehydration of the corresponding substituted formylhydrazine with COCl2 and Et3N.[4]
Earlier, the compound was misidentified as the isomeric nitrilimine, HN––N+≡CH. However, this structure was disproven by 1H NMR studies, which show a compound with a single signal at δ 6.40 ppm in (CD3CD2)2O instead of two signals expected for nitrilimine. Moreover, an infrared band at 2140 cm−1 was assigned to the isocyano group. Transition metal complexes of isodiazomethane have been prepared.[5] In bulk form isodiazomethane is a liquid which decomposes when the temperature exceeds 15 °C. If it is heated to 40 °C, the substance explodes.[6] A solution of isodiazomethane in diethyl ether at –30 °C gradually isomerizes to diazomethane upon exposure to sodium hydroxide for 20 min.
Microwave spectroscopy indicates that unlike diazomethane, isodiazomethane is not completely planar, with the amino nitrogen undergoing inversion.[7] An ab initio study indicated that there is some N–N double bond character in H2N–N≡C, although less so than in the N–C bond of H2N–C≡N.[8] Like other isocyanide derivatives and carbon monoxide, its primary resonance form carries a negative charge and lone pair on carbon, a comparatively rare situation for neutral molecules. A resonance form with zero formal charge on all atoms also has some importance; however, the carbon atom only has a sextet of electrons and is formally a carbene.