Pyridine‐Functionalized Covalent Organic Frameworks as Metal‐Free Photocatalysts for Chlorotrifluoromethylation of Alkenes via Inner‐Sphere Mechanism

Why It Matters

The work provides a scalable, recyclable heterogeneous catalyst for installing valuable CF3Cl groups, reducing reliance on metal catalysts and advancing sustainable fluorination chemistry.

Key Takeaways

• Linear COF-25Th achieves 99% alkene conversion
• Pyridine sites bind trifluoromethanesulfonyl chloride forming pyridinium
• Inner‑sphere electron transfer drives metal‑free photocatalysis
• Catalyst recyclable with minimal activity loss over cycles

Pulse Analysis

The emergence of pyridine‑functionalized covalent organic frameworks marks a significant shift in photocatalytic fluorination. By embedding basic nitrogen sites directly into the COF backbone, researchers create a built‑in binding pocket for trifluoromethanesulfonyl chloride. This interaction forms a transient pyridinium species that acts as an electron‑deficient hub, channeling light‑generated electrons straight to the reactive center. The result is a highly efficient inner‑sphere electron‑transfer mechanism that bypasses the need for transition‑metal mediators, addressing both cost and environmental concerns.

COF‑25Th’s linear conjugation enhances planarity and delocalization, yielding superior optoelectronic properties compared with the cross‑conjugated COF‑36Th. The extended π‑system lowers the band gap, facilitating stronger absorption of visible light and faster charge mobility. Computational studies corroborate these findings, showing lower excitation energies and more favorable frontier orbital alignment for COF‑25Th. Consequently, the material achieves near‑quantitative conversion of alkenes to chlorotrifluoromethylated products, a transformation valuable for pharmaceuticals and agrochemicals where the CF3Cl motif imparts metabolic stability and lipophilicity.

Beyond performance, the heterogeneous nature of COF‑25Th offers practical advantages. The catalyst can be filtered, washed, and reused with negligible loss of activity after several cycles, aligning with green chemistry principles. Its metal‑free composition eliminates contamination risks in downstream processing, a critical factor for high‑purity drug synthesis. As the industry seeks more sustainable pathways for fluorine‑rich building blocks, these pyridine‑functionalized COFs provide a compelling platform that combines tunable chemistry, robust recyclability, and scalable production potential.