Attempted isolation and characterization of diazirinone (N2CO)

Stimulated and intrigued by the report of the synthesis of diazirinone (1), a metastable adduct of N(2) and CO, we carried out further experimental and theoretical studies aimed at the detailed spectroscopic characterization of this species. Our attempts to generate and detect diazirinone (1) in either the condensed phase (using matrix isolation spectroscopy) or in the gas phase (using millimeter-wave rotational spectroscopy), however, have been unsuccessful. Trapping the volatile products produced from the reaction of 3-chloro-3-(p-nitrophenoxy)diazirine (5) with tetrabutylammonium fluoride (TBAF) under matrix-isolation conditions affords chlorofluorodiazirine (8) and carbon monoxide but fails to provide evidence for diazirinone (1). Moreover, sophisticated ab initio calculations of the structure and fundamental vibrational frequencies of diazirinone (1) produce an estimate for the fundamental band origin of the C=O stretch (2046 cm(-1)) that is ca. 100 cm(-1) lower in frequency than the experimental value previously attributed to this band. This discrepancy lies well outside any expected solvent shift or calculation error at this level of theory. In an effort to reconcile our findings with the earlier reports concerning diazirinone (1), we reconsidered the infrared spectral evidence upon which the original claim of diazirinone synthesis was based. New experiments demonstrate that these spectra may be explained and reproduced with a combination of solution-phase and gas-phase absorptions of CO, without recourse to invoke diazirinone (1).