Nakakuki Yusuke, Hirose Takashi, Matsuda Kenji
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering , Kyoto University , Katsura, Nishikyo-ku , Kyoto 615-8510 , Japan.
J Am Chem Soc. 2018 Nov 14;140(45):15461-15469. doi: 10.1021/jacs.8b09825. Epub 2018 Nov 2.
A π-expanded helicene that is the helically twisted analogue of kekulene was synthesized using a 6-fold ring-closing olefin metathesis (RCM) reaction as a key step. The π-expanded geometry with large helical diameter ( d = 10.2 Å), consisting only of carbon and hydrogen atoms (CH), was unambiguously determined by single-crystal X-ray analysis. We found that the π-expanded helicene with large helical diameter will act as a soft molecular spring with a small spring constant. Interestingly, the mechanical properties of the molecular springs roughly satisfied a physical formula for macroscopic spring materials; i.e., the force constant of the elongation of a molecular spring ( k) is inversely proportional to the third power of the helical diameter ( k ∝ d).
一种作为凯库勒烯螺旋扭曲类似物的π-扩展螺旋烯，通过六重闭环烯烃复分解（RCM）反应作为关键步骤合成。仅由碳原子和氢原子（CH）组成的具有大螺旋直径（d = 10.2 Å）的π-扩展几何结构，通过单晶X射线分析得到明确确定。我们发现，具有大螺旋直径的π-扩展螺旋烯将作为具有小弹簧常数的软分子弹簧。有趣的是，分子弹簧的力学性能大致满足宏观弹簧材料的物理公式；即，分子弹簧伸长的力常数（k）与螺旋直径的三次方成反比（k ∝ d⁻³）。
