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Author Spotlight: Experimental Approaches for the Synthesis of Low-Valent Metal-Organic Frameworks from Multitopic Phosphine Linkers
Published on: May 12, 2023
Pyridine-Functionalized Covalent Organic Frameworks as Metal-Free Photocatalysts for Chlorotrifluoromethylation of
Shibing Wu1, Xilong Yan1,2,3, Yang Li1,2,3
1School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300350, P. R. China.
Abstract:
The photocatalytic chlorotrifluoromethylation of alkenes using trifluoromethanesulfonyl chloride represents an important difunctionalization method. However, the recyclable and stable heterogeneous catalysts have been rarely reported. Herein, two pyridine-functionalized isomeric covalent organic frameworks (denoted as COF-25Th and COF-36Th) with distinct conjugation modes are synthesized and serve as metal-free photocatalysts to achieve chlorotrifluoromethylation of alkenes via an inner-sphere mechanism. The linearly conjugated COF-25Th exhibits enhanced planarity compared to the cross-conjugated COF-36Th, endowing COF-25Th with superior optoelectronic properties. Therefore, COF-25Th displays exceptional photocatalytic chlorotrifluoromethylation activity, achieving a maximum 99% conversion rate for various substrates, along with excellent recyclability. Experimental results and theoretical calculations reveal that the pyridine nitrogen in COF-25Th acts as a binding site for trifluoromethanesulfonyl chloride, mediating the formation of the electron-deficient pyridinium salt that establishes an inner-sphere electron transfer pathway. This work develops a metal-free heterogeneous COF catalyst for efficient chlorotrifluoromethylation of alkenes based on an inner-sphere mechanism.
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