Wang Zhe, Yadav Pinky, Abe Manabu
Department of Chemistry, Graduate School of Advanced Science and Engineering, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
Chem Commun (Camb). 2021 Oct 28;57(86):11301-11309. doi: 10.1039/d1cc04581d.
Localised singlet cyclopentane-1,3-diyl diradicaloids have been considered promising candidates for constructing carbon-carbon π-single bonds (C-π-C). However, the high reactivity during formation of the σ-bond has limited a deeper investigation of its unique chemical properties. In this feature article, recent progress in kinetic stabilisation based on the "stretch effect" and the "solvent dynamic effect" induced by the macrocyclic system is summarised. Singlet diradicaloids S-DR4a/b and S-DR4d containing macrocyclic rings showed much longer lifetimes at 293 K (14 μs for S-DR4a and 156 μs for S-DR4b in benzene) compared to the parent singlet diradicaloid S-DR2 having no macrocyclic ring (209 ns in benzene). Furthermore, the dynamic solvent effect in viscous solvents was observed for the first time in intramolecular σ-bond formation, the lifetime of S-DR4d increased to 400 μs in the viscous solvent glycerin triacetin at 293 K. The experimental results proved the validity of the "stretch effect" and the "solvent dynamic effect" on the kinetic stabilisation of singlet cyclopentane-1,3-diyl diradicaloids, and provided a strategy for isolating the carbon-carbon π-single bonded species (C-π-C), and towards a deeper understanding of the nature of chemical bonding.
局域化单线态环戊烷 - 1,3 - 二基双自由基类化合物被认为是构建碳 - 碳π单键（C - π - C）的有前景的候选物。然而，σ键形成过程中的高反应活性限制了对其独特化学性质的深入研究。在这篇专题文章中，总结了基于大环体系诱导的“拉伸效应”和“溶剂动力学效应”在动力学稳定方面的最新进展。与没有大环的母体单线态双自由基S - DR2（在苯中为209纳秒）相比，含大环的单线态双自由基S - DR4a / b和S - DR4d在293 K时显示出长得多的寿命（在苯中，S - DR4a为14微秒，S - DR4b为156微秒）。此外，在分子内σ键形成中首次观察到粘性溶剂中的动态溶剂效应，在293 K时，S - DR4d在粘性溶剂甘油三乙酸酯中的寿命增加到400微秒。实验结果证明了“拉伸效应”和“溶剂动力学效应”对单线态环戊烷 - 1,3 - 二基双自由基类化合物动力学稳定的有效性，并为分离碳 - 碳π单键物种（C - π - C）以及更深入理解化学键的本质提供了一种策略。
