Numerous radical chains comprising several nitrogen atoms have been effectively synthesized, demonstrating impressive stability at room temperature for extended periods. Scientists are hopeful that this stability may allow these chains to function as a viable storable source of nitrenes. Nitrenes are often challenging to manage due to their significant reactivity but hold considerable value for the creation of nitrogen-based pharmaceuticals and other compounds, including the facilitation of C–H activation.
In the Earth’s ionosphere, powerful solar radiation can disassociate the strong dinitrogen triple bonds, merging nitrogen molecules into chains. Nevertheless, these entities are generally unstable under normal conditions, quickly decomposing into dinitrogen gas. They typically necessitate extreme pressures of around 10GPa for stability.
Investigators from the University of Manchester and Oxford have accomplished the synthesis of linear nitrogen radical chains featuring four nitrogen atoms at normal room temperature, without depending on metal cations for their stability. This was achieved by reducing para-substituted phenyl azides with potassium graphite, testing various substituents including fluorine, chlorine, bromine, methyl, and hydrogen.
The brominated version exhibited remarkable stability, lasting for several weeks under sealed conditions, which facilitated an in-depth analysis of the delocalized electronic structure of the nitrogen chain through spectroscopic and fluorescence methods. Traditionally, this sort of analysis has been problematic due to the rapid decomposition or reaction tendencies of these compounds.
Additionally, the researchers successfully activated the C–H bond in 4-iodobenzaldehyde utilizing the brominated nitrogen chain, leading to the creation of a molecule containing an amide bond. The enhanced stability implies that these nitrogen chains could potentially serve as a storable source of nitrene radical anions, paving the way for new opportunities in chemical synthesis and material science.