Attempted Isolation and Characterization of Diazirinone (N₂CO)

Abstract

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).

Das schwer fassbare Diazirinon, N2CO

“…[6] Über die Synthese von 1 durch Reaktionen von p-Nitrophenoxychlordiazirin mit Halogenidsalzen wurde kürzlich in der Literatur berichtet. [7][8][9][10] In einer nachfolgenden Arbeit [11] wurde allerdings festgestellt, dass die IR-Bande in der früheren Studie [7] nicht dem cyclischen N 2 CO, sondern nur CO in kondensierter Phase zugeordnet werden kann. Somit blieb Diazirinon bis jetzt eine noch nicht entdeckte Spezies.…”

Matrix Isolation of Two Isomers of N4CO

“…Further loss of N 2 by near-UV irradiation yielded CO and N 2 . No other intermediates, for example, the long-sought diazirinone, N 2 CO, [12] or its isomers, [13] were observed under our experimental conditions. The novel carbonyl nitrene was proved to adopt a triplet ground state by its characteristic IR and UV spectra.…”

Fascinating Diazirinone: A Violet Gas

“…0.8 μs. [9] More recently, V has been identified in solid noble gas matrices as an unanticipated pyrolysis product of OC(N 3 ) 2 . A significant barrier of 108 kJ mol -1 , resulting from aromatic stabilization, was predicted for its exothermic (400 kJ mol -1 ) dissociation into N 2 and CO. A straightforward synthetic approach to this cyclic isomer is still missing.…”