Mendez-Vega Enrique, Portela-González Adrián, Karir Ginny, Hemberger Patrick, Sander Wolfram
Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, Universitätsstraße 150, 44801, Bochum, Germany.
Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute (PSI), Villigen, CH-5232, Switzerland.
Angew Chem Int Ed Engl. 2025 Sep 22;64(39):e202512761. doi: 10.1002/anie.202512761. Epub 2025 Aug 11.
We report the first direct observation of the pentafluorophenyl cation in the gas phase via vacuum ultraviolet (VUV) photoionization (PI) of the thermally generated pentafluorophenyl radical. The reactive intermediates and stable reaction products were characterized utilizing photoelectron photoion coincidence (PEPICO) spectroscopy with synchrotron radiation. Electron removal from the pentafluorophenyl radical yields the cation with an adiabatic ionization energy (AIE) of 9.84 ± 0.02 eV. Threshold photoelectron spectra combined with high-level ab-initio calculations show that the cation is described as a πσ diradical with an open-shell singlet (A) ground state, while the triplet (A) state lies only 1.5 ± 0.4 kcal mol higher in energy. The closed-shell singlet (A) state is highly distorted and lies >4 kcal mol above the ground state. This unique aryl carbenium ion exhibits a ∼40 kcal mol higher hydride affinity (HA) as compared to the parent phenyl cation, explaining its high reactivity and elusive character. In addition, the radical's reactivity was investigated upon hydrogen abstraction and unimolecular decomposition, forming tetrafluoro ortho-benzyne as well as smaller fluorinated species.
我们报道了通过热生成的五氟苯基自由基的真空紫外（VUV）光电离（PI）在气相中首次直接观测到五氟苯基阳离子。利用同步辐射光电子光离子符合（PEPICO）光谱对反应中间体和稳定反应产物进行了表征。从五氟苯基自由基中去除电子产生的阳离子的绝热电离能（AIE）为9.84±0.02 eV。阈值光电子能谱结合高水平的从头算计算表明，该阳离子被描述为具有开壳单重态（A）基态的πσ双自由基，而三重态（A）态的能量仅高1.5±0.4 kcal/mol。闭壳单重态（A）态高度扭曲，比基态高出>4 kcal/mol。与母体苯基阳离子相比，这种独特的芳基碳正离子表现出约40 kcal/mol更高的氢化物亲和力（HA），这解释了其高反应活性和难以捉摸的特性。此外，还研究了该自由基在氢提取和单分子分解时的反应活性，形成了四氟邻苯炔以及较小的氟化物种。
