Liu Shihua, Zheng Shunlin, Lin Jieli, Grützmacher Hansjörg, Su Cheng-Yong, Li Zhongshu
LIFM, IGCME, School of Chemistry, Sun Yat-Sen University Guangzhou 510006 China
Key Laboratory of Guangdong Higher Education Institutions of Northeast Guangdong New Functional Materials, School of Chemistry and Environment, Jiaying University Meizhou 514015 Guangdong China.
Chem Sci. 2025 Sep 9. doi: 10.1039/d5sc06158j.
The Büchner reaction enables the construction of functionalized cycloheptatrienes and aromatic tropylium cations, and has recently been extended to the ring expansion of arenes with low-valent main-group systems. Although stable 6π-aromatic biradicaloids typically exhibit characteristic biradical reactivity, we leverage the aromaticity of dicarbondiphosphides (1) to achieve an unprecedented Büchner-type ring expansion, yielding air-stable aromatic 1,3-diphospholium cations (3). Multimodal characterization (NMR, UV-vis, SC-XRD, computational studies) confirms the 6π-aromaticity of 3. Reduction of 3 yields stable 7π-electron neutral radicals (4), which contrast with conventional five-membered neutral radicals possessing 5π-electron systems. These radicals (4a: = 1113.2 nm; 4b: = 1330.7 nm) exhibit strong second near-infrared biowindow (NIR-II, 1000-1350 nm) absorptions, and shown promising application potential as the first phosphorus radical-derived organic NIR-II photothermal materials.
布赫纳反应可用于构建官能化的环庚三烯和芳族环庚三烯阳离子，并且最近已扩展到使用低价主族体系对芳烃进行扩环反应。尽管稳定的6π芳族双自由基通常表现出特征性的双自由基反应性，但我们利用二碳二磷化物（1）的芳香性实现了前所未有的布赫纳型扩环反应，生成了空气稳定的芳族1,3-二磷鎓阳离子（3）。多模态表征（核磁共振、紫外可见光谱、单晶X射线衍射、计算研究）证实了3的6π芳香性。3的还原产生了稳定的7π电子中性自由基（4），这与具有5π电子体系的传统五元中性自由基形成对比。这些自由基（4a：λ = 1113.2 nm；4b：λ = 1330.7 nm）表现出强烈的第二近红外生物窗口（NIR-II，1000 - 1350 nm）吸收，并且作为首批磷自由基衍生的有机NIR-II光热材料显示出有前景的应用潜力。
