Ruhr-Universität Bochum, Lehrstuhl für Physikalische Chemie I, Universitätsstr. 150, Bochum D-44801, Germany.
Technische Universität Dortmund, Lehrstuhl für Computational Bioengineering, Dortmund 44227, Germany.
J Am Chem Soc. 2023 May 31;145(21):11544-11552. doi: 10.1021/jacs.2c12274. Epub 2023 May 19.
A novel surface-confined C-C coupling reaction involving two carbene molecules and a water molecule was studied by scanning tunneling microscopy in real space. Carbene fluorenylidene was generated from diazofluorene in the presence of water on a silver surface. While in the absence of water, fluorenylidene covalently binds to the surface to form a surface metal carbene, and water can effectively compete with the silver surface in reacting with the carbene. Water molecules in direct contact with fluorenylidene protonate the carbene to form the fluorenyl cation before the carbene can bind to the surface. In contrast, the surface metal carbene does not react with water. The fluorenyl cation is highly electrophilic and draws electrons from the metal surface to generate the fluorenyl radical which is mobile on the surface at cryogenic temperatures. The final step in this reaction sequence is the reaction of the radical with a remaining fluorenylidene molecule or with diazofluorene to produce the C-C coupling product. Both a water molecule and the metal surface are essential for the consecutive proton and electron transfer followed by C-C coupling. This C-C coupling reaction is unprecedented in solution chemistry.
研究人员在真空间进行扫描隧道显微镜研究，发现了一种涉及两个卡宾分子和一个水分子的新型表面限制 C-C 偶联反应。在银表面上存在水的情况下，二氮杂芴生成芴亚基卡宾。而在没有水的情况下，芴亚基与表面通过共价键结合形成表面金属卡宾，水可以有效地与卡宾竞争与银表面反应。与芴亚基直接接触的水分子将卡宾质子化，在卡宾与表面结合之前形成芴阳离子。相比之下，表面金属卡宾不会与水反应。芴阳离子具有高亲电性，从金属表面吸取电子，生成在低温下可在表面上移动的芴自由基。此反应序列的最后一步是自由基与剩余的芴亚基分子或二氮杂芴反应，生成 C-C 偶联产物。连续的质子和电子转移以及随后的 C-C 偶联都需要水分子和金属表面。这种 C-C 偶联反应在溶液化学中是前所未有的。
