Stable
organic radicals have been of great academic interest not
only in the context of fundamental understanding of reactive intermediates
but also because of their numerous applications as functional materials.
Apart from the early examples of triphenylmethyl and TEMPO derivatives,
reports on air- and water-stable organic radicals are scarce, and
their development remains a challenge. Herein, we present the design
and synthesis of a novel organic radical based on a 1,2-dicarbonyl
scaffold supported by N-heterocyclic carbenes (NHCs).
The presented radical cations exhibit remarkable stability toward
various harsh conditions, such as the presence of reactive chemicals
(reductants, oxidants, strong acids, and bases) or high temperatures,
by far exceeding the stability of triphenylmethyl and TEMPO radicals.
In addition, physiological conditions including aqueous buffer and
blood serum are tolerated. The steric and electronic stabilization
provided by the two NHC moieties enabled the successful design of
the highly stable radical.
Non-aqueous all organic redox flow batteries (NORFBs) are one of the promising options for large-scale renewable energy storage systems owing to their scalability with energy and power along with the affordability. The discovery of new redox-active organic molecules (ROMs) for the anolyte/catholyte would bring them one step closer to the practical application, thus it is highly demanded. Here, we report a new class of ROMs based on cationic triazenyl systems supported by Nheterocyclic carbenes (NHCs) and demonstrate, for the first time, that the triazenyl can serve as a new redox motif for ROMs and could be significantly stabilized for the use in NORFBs by the coupling with NHCs even at radical states. A series of NHC− triazenyl ROM families were successfully synthesized via the reaction of a synthon, N-heterocyclic carbene azido cation, with various Lewis bases including NHCs. Remarkably, it is revealed that NHCs substituted on the triazenyl fragments can serve as a versatile platform for tailoring the electrochemical activity and stability of triazenyl-based compounds, introducing various ROMs exploiting triazenyl redox motif, as demonstrated in the full cell of NORFBs for an anolyte.
<div>The present manuscript describes the design, synthesis, and characterization of the most stable organic radical reported up to date.</div><div><br></div><div>Here we report:</div><div>▪ Synthesis and full characterization including X-ray structure of stable 1,2-dicarbonyl radicals</div><div>▪ Proposed mechanism for the formation of the presented radicals</div><div>▪ Redox reactivity of the radicals</div><div>▪ Stability of the radicals under various organic and inorganic conditions</div><div><u></u></div>
<div>The present manuscript describes the design, synthesis, and characterization of the most stable organic radical reported up to date.</div><div><br></div><div>Here we report:</div><div>▪ Synthesis and full characterization including X-ray structure of stable 1,2-dicarbonyl radicals</div><div>▪ Proposed mechanism for the formation of the presented radicals</div><div>▪ Redox reactivity of the radicals</div><div>▪ Stability of the radicals under various organic and inorganic conditions</div><div>▪ Demonstration of the radicals as potential organic radical contrast agent candidate</div><div><u></u></div>
<div>The present manuscript describes the design, synthesis, and characterization of the most stable organic radical reported up to date.</div><div><br></div><div>Here we report:</div><div>▪ Synthesis and full characterization including X-ray structure of stable 1,2-dicarbonyl radicals</div><div>▪ Proposed mechanism for the formation of the presented radicals</div><div>▪ Redox reactivity of the radicals</div><div>▪ Stability of the radicals under various organic and inorganic conditions</div><div>▪ Demonstration of the radicals as potential organic radical contrast agent candidate</div><div><u></u></div>
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