Department of Chemistry & IRIS Adlershof, Humboldt-Universität zu Berlin, Berlin, Germany.
Nat Chem. 2018 Oct;10(10):1031-1036. doi: 10.1038/s41557-018-0106-8. Epub 2018 Aug 13.
Bond formation between two molecular entities in a closed system strictly obeys the principle of microscopic reversibility and occurs in favour of the thermodynamically more stable product. Here, we demonstrate how light can bypass this fundamental limitation by driving and controlling the reversible bimolecular reaction between an N-nucleophile and a photoswitchable carbonyl electrophile. Light-driven tautomerization cycles reverse the reactivity of the C=O/C=N-electrophiles ('umpolung') to activate substrates and remove products, respectively, solely depending on the illumination wavelength. By applying either red or blue light, selective and nearly quantitative intermolecular bond formation/scission can be achieved, even if the underlying condensation/hydrolysis equilibrium is thermodynamically disfavoured. Exploiting light-driven in situ C=N exchange, our approach can be used to externally regulate a closed dynamic covalent system by actively and reversibly removing specific components, resembling a molecular and bidirectional version of a macroscopic Dean-Stark trap.
在封闭体系中，两个分子实体之间的成键严格遵循微观可逆性原则，并且有利于热力学上更稳定的产物。在这里，我们展示了光如何通过驱动和控制 N-亲核试剂和光致可切换羰基亲电试剂之间的可逆双分子反应来绕过这一基本限制。光驱动的互变异构循环将 C=O/C=N-亲电试剂的反应性“反转”（umpolung），分别激活底物和去除产物，这完全取决于照明波长。通过应用红光或蓝光，可以选择性地实现近乎定量的分子间键形成/断裂，即使潜在的缩合/水解平衡在热力学上是不利的。利用光驱动的原位 C=N 交换，我们的方法可用于通过主动和可逆地去除特定组件来外部调节封闭的动态共价体系，类似于宏观 Dean-Stark 阱的分子和双向版本。
