美国加利福尼亚大学圣迭戈分校Bertrand, Guy团队报道了一种结晶的双氧化碳烯。相关研究成果发表在2023年9月20日出版的《自然》。

碳的化学性质受八隅体规则的控制，八隅体法则指的是碳的价壳层中有八个电子的倾向。然而，确实存在一些例外，例如，分别具有7价电子和6价电子的三苯甲基自由基（Ph₃C）和碳正离子（Ph₃C⁺），以及碳烯（R₂C:）——具有形式上6价电子的两个配位八隅体违抗物种。碳烯现在是化学中强有力的工具，甚至在材料和医学科学中也有应用。人们可以通过去除碳烯的非键电子来进一步剥离碳烯吗？

该文中，研究人员描述了通过从富含电子的碳烯中提取两个电子的氧化/氧化物离子序列来合成结晶双氧化碳烯（R₂C₂⁺）。尽管具有累积结构和强的正电荷离域，二坐标碳中心仍保持着显著的亲电性，并拥有两个可接近的空位轨道。双电子还原/去质子化序列再生母体碳烯，完全符合其作为双氧化碳烯的描述。

该项工作表明，使用体积庞大的强电子供体取代基可以同时赋予中心碳原子上的两个空位轨道电子稳定和空间保护，为分离各种双氧化碳烯铺平道路。

附：英文原文

Title: A crystalline doubly oxidized carbene

Author: Loh, Ying Kai, Melaimi, Mohand, Gembicky, Milan, Munz, Dominik, Bertrand, Guy

Issue&Volume: 2023-09-20

Abstract: The chemistry of carbon is governed by the octet rule, which refers to its tendency to have eight electrons in its valence shell. However, a few exceptions do exist, for example, the trityl radical (Ph3C) (ref.1) and carbocation (Ph3C+) (ref.2) with seven and six valence electrons, respectively, and carbenes (R2C:)—two-coordinate octet-defying species with formally six valence electrons3. Carbenes are now powerful tools in chemistry, and have even found applications in material and medicinal sciences4. Can we undress the carbene further by removing its non-bonding electrons Here we describe the synthesis of a crystalline doubly oxidized carbene (R2C2+), through a two-electron oxidation/oxide-ion abstraction sequence from an electron-rich carbene5. Despite a cumulenic structure and strong delocalization of the positive charges, the dicoordinate carbon centre maintains significant electrophilicity, and possesses two accessible vacant orbitals. A two-electron reduction/deprotonation sequence regenerates the parent carbene, fully consistent with its description as a doubly oxidized carbene. This work demonstrates that the use of bulky strong electron-donor substituents can simultaneously impart electronic stabilization and steric protection to both vacant orbitals on the central carbon atom, paving the way for the isolation of a variety of doubly oxidized carbenes.

DOI: 10.1038/s41586-023-06539-x

Source: https://www.nature.com/articles/s41586-023-06539-x