Thermally persistent carbonyl nitrene: FC(O)N.

Area of Science:

• Organic Chemistry
• Physical Chemistry
• Reaction Mechanisms

Background:

• Carbonyl nitrenes (RC(O)N) are typically transient intermediates.
• They are usually formed from carbonyl azides (RC(O)N3) via thermal or photochemical decomposition.
• These intermediates readily undergo the Curtius rearrangement to form isocyanates (RNCO).

Purpose of the Study:

• To investigate the stability and formation pathways of carbonyl nitrenes.
• To challenge the common belief regarding the high lability of carbonyl nitrenes.
• To explore the potential for isolating or observing persistent carbonyl nitrene species.

Main Methods:

• Flash pyrolysis of fluoroformyl azide (FC(O)N3).
• Computational chemistry using CBS-QB3 method to calculate activation barriers.
• Spectroscopic analysis to characterize reaction intermediates and products.

Main Results:

• A persistent triplet carbonyl nitrene, fluoroformyl nitrene (FC(O)N), was successfully generated.
• Flash pyrolysis of FC(O)N3 yielded FC(O)N in 49% yield.
• Computational analysis revealed a significantly lower activation barrier (29 kJ mol(-1)) for the decomposition of FC(O)N3 to FC(O)N compared to a concerted pathway producing fluoro isocyanate (FNCO).

Conclusions:

• The study demonstrates the existence of a thermally persistent carbonyl nitrene, contrary to prevailing chemical understanding.
• The findings suggest that specific structural features can stabilize these otherwise highly reactive intermediates.
• This discovery has implications for synthetic strategies involving carbonyl nitrenes and related compounds.