Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea.
J Am Chem Soc. 2021 Jun 16;143(23):8527-8532. doi: 10.1021/jacs.1c00707. Epub 2021 May 11.
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 -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.
稳定的有机自由基不仅在反应中间体的基础理解方面具有重要的学术意义，而且因为其作为功能材料的众多应用而受到广泛关注。除了三苯甲基和 TEMPO 衍生物的早期例子外，关于空气和水稳定的有机自由基的报道很少，它们的发展仍然是一个挑战。在此，我们提出了一种基于 1,2-二羰基支架的新型有机自由基的设计和合成，该支架由 -杂环卡宾 (NHCs) 支撑。所提出的自由基阳离子对各种苛刻条件表现出显著的稳定性，例如存在反应性化学物质（还原剂、氧化剂、强酸和强碱）或高温，远远超过三苯甲基和 TEMPO 自由基的稳定性。此外，还可以耐受生理条件，包括水缓冲液和血清。两个 NHC 部分提供的空间和电子稳定性使得成功设计出高度稳定的自由基成为可能。
