Ding Shihao, Wang Wenkai, Germann Anne, Wei Yiting, Du Tianyi, Meisner Jan, Zhu Rong, Liu Yun
Beijing National Laboratory for Molecular Sciences, Center for Soft Matter Science and Engineering, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, and College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, China.
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, and College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, China.
J Am Chem Soc. 2024 Mar 6;146(9):6104-6113. doi: 10.1021/jacs.3c13589. Epub 2024 Feb 20.
Polymer mechanochemistry has been established as an enabling tool in accessing chemical reactivity and reaction pathways that are distinctive from their thermal counterparts. However, eliciting diversified reaction pathways by activating different constituent chemical bonds from the same mechanophore structure remains challenging. Here, we report the design of a bicyclo[2.2.0]hexene (BCH) mechanophore to leverage its structural simplicity and relatively low molecular symmetry to demonstrate this idea of multimodal activation. Upon changing the attachment points of pendant polymer chains, three different C-C bonds in bicyclo[2.2.0]hexene are specifically activated via externally applied force by sonication. Experimental characterization confirms that in different scenarios of polymer attachment, the regioisomers of BCH undergo different activation reactions, entailing retro-[2+2] cycloreversion, 1,3-allylic migration, and retro-4π ring-opening reactions, respectively. Control experiments with small-molecule analogues reveal that the observed diversified reactivity of BCH regioisomers is possible only with mechanical force. Theoretical studies further elucidate that the differences in the positions of substitution between regioisomers have a minimal impact on the potential energy surface of the parent BCH scaffold. The mechanochemical selectivity between different C-C bonds in each constitutional isomer is a result of selective and effective coupling of force to the aligned C-C bond in each case.
聚合物机械化学已成为一种有力工具，可用于探索与热反应截然不同的化学反应性和反应途径。然而，通过激活同一机械基团结构中的不同组成化学键来引发多样化的反应途径仍然具有挑战性。在此，我们报告了一种双环[2.2.0]己烯（BCH）机械基团的设计，利用其结构简单性和相对较低的分子对称性来证明这种多模态激活的概念。通过改变侧链聚合物链的连接点，双环[2.2.0]己烯中的三个不同碳 - 碳键通过超声处理施加的外力被特异性激活。实验表征证实，在聚合物连接的不同情况下，BCH的区域异构体分别经历不同的激活反应，即逆[2 + 2]环化逆转、1,3 - 烯丙基迁移和逆4π开环反应。小分子类似物的对照实验表明，只有通过机械力才能观察到BCH区域异构体多样化的反应性。理论研究进一步阐明，区域异构体之间取代位置的差异对母体BCH支架的势能面影响最小。每种构造异构体中不同碳 - 碳键之间的机械化学选择性是在每种情况下力与排列的碳 - 碳键选择性有效耦合的结果。
