Department of Chemistry, Graduate School of Science, Osaka University , Toyonaka, Osaka 560-0043, Japan.
J Am Chem Soc. 2014 Sep 10;136(36):12784-93. doi: 10.1021/ja507005c. Epub 2014 Aug 25.
Organic neutral radicals have long fascinated chemists with a fundamental understanding of structure-reactivity relationships in organic reactions and with applications as new functional materials. However, the elusive nature of these radicals makes the synthesis, isolation, and characterization very challenging. In this work, the synthesis of three long-lived, fluorenyl-based radicals are reported. The geometry and electronic structures of these radicals were systematically investigated with a combination of various experimental methods, besides density functional theory (DFT) calculations, which include X-ray crystallographic analysis, electron spin resonance (ESR), electron nuclear double resonance (ENDOR), cyclic voltammetry, and UV-vis-NIR measurements. Their half-life periods (τ(1/2)) in air-saturated solution under ambient conditions were also determined. Surprisingly, all three radicals showed remarkable stabilities: τ(1/2) = 7, 3.5, and 43 days.
有机中性自由基长期以来一直吸引着化学家，使他们对有机反应中的结构-反应性关系有了基本的了解，并为新型功能材料的应用提供了帮助。然而，这些自由基难以捉摸的性质使得它们的合成、分离和表征极具挑战性。在这项工作中，报道了三种长寿命的芴基自由基的合成。通过各种实验方法（包括 X 射线晶体学分析、电子自旋共振（ESR）、电子核双共振（ENDOR）、循环伏安法和紫外可见近红外测量）与密度泛函理论（DFT）计算相结合，系统地研究了这些自由基的几何和电子结构。还确定了它们在室温下空气中饱和溶液中的半衰期（τ(1/2)）。令人惊讶的是，所有三种自由基都表现出显著的稳定性：τ(1/2) = 7、3.5 和 43 天。
