A Strongly Reducing sp2 Carbon-Conjugated Covalent Organic Framework Formed by N-Heterocyclic Carbene Dimerization

• Published in: Angewandte Chemie International Edition p. e202416480
• Main Authors: Pitt, Tristan A, Azbell, Tyler J, Kim, Jaehwan, Shi, Zixiao, Muller, David A, Addicoat, Matthew A, Milner, Phillip
• Format: Journal Article
• Language: English
• Published: Germany 15.09.2024
• Subjects: N-heterocyclic carbene; Covalent organic framework; tetracyanoethylene; radical; magnet
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.202416480

Covalent organic frameworks linked by carbon-carbon double bonds (C=C COFs) are an emerging class of crystalline, porous, and conjugated polymeric materials with potential applications in organic electronics, photocatalysis, and energy storage. Despite the rapidly growing interest in sp2 carbon-conjugated COFs, only a small number of closely related condensation reactions have been successfully employed for their synthesis to date. Herein, we report the first example of a C=C COF, CORN-COF-1 (CORN = Cornell University), prepared by N-heterocyclic carbene (NHC) dimerization. In-depth characterization reveals that CORN-COF-1 possesses a two-dimensional layered structure and hexagonal guest-accessible pores decorated with a high density of strongly reducing tetraazafulvalene linkages. Exposure of CORN-COF-1 to tetracyanoethylene (TCNE, E1/2 = 0.13 V and -0.87 V vs. SCE) oxidizes the COF and encapsulates the radical anion TCNE•- and the dianion TCNE2- as guest molecules, as confirmed by spectroscopic and magnetic analysis. Notably, the reactive TCNE•- radical anion, which generally dimerizes in the solid state, is uniquely stabilized within the pores of CORN-COF-1. Overall, our findings broaden the toolbox of reactions available for the synthesis of redox-active C=C COFs, paving the way for the design of novel materials.