Cycloadditions and Cyclization Reactions via Post-Synthetic Modification and/or One-Pot Methodologies for the Stabilization of Imine-Based Covalent Organic Frameworks: History
Please note this is an old version of this entry, which may differ significantly from the current revision.

Interest in covalent organic frameworks as high-value materials has grown steadily since their development in the 2000s. However, the great advantage that allows us to obtain these crystalline materials—the reversibility of the bonds that form the network—supposes a drawback in terms of thermal and chemical stability. Among the different strategies employed for the stabilization of imine-based Covalent Organic Frameworks (COFs), cycloaddition and other related cyclization reactions are especially significant to obtain highly stable networks with extended π-delocalization and new functionalities, expanding even further the potential application of these materials. Therefore, this entry gathered the most recent research strategies for obtaining stable COFs by means of cyclization reactions, including the Povarov reaction and intramolecular oxidative cyclization reactions as well as some other recent innovative approaches.

  • covalent organic frameworks
  • post-synthetic modification
  • one-pot synthesis
  • stabilization
  • imine-based-COFs
  • cycloaddition reaction
  • Povarov reaction
  • aza-Diels–Alder
  • oxidative cyclization
Since the first reported synthesis of covalent organic frameworks (COFs) in 2005 by Yaghi and collaborators [1], these porous and crystalline materials have gained attention, importance, and applicability in different scientific and technological areas such as catalysis [2] (including photo- [3][4] and electrocatalysis [5][6][7]), CO2 capturing [8], electronics [9], medicine [10][11], and food security [12], among others [13][14][15]. The great relevance acquired by these materials is mainly due to the possibility of tuning different chemical or physical properties such as porosity, functionalities, and stability according to the specific needs, with imine-based COFs being of special interest [16][17]. In this regard, stability is often one of the limiting factors for the applicability of COFs because the characteristic reversibility of the bonds formed in the polymerization reactions makes these materials more prone to chemical or thermal degradation. Therefore, the development of new COFs nowadays involves a thorough design toward stabilization to prevent degradation processes as much as possible.
The prevention of the degradation of imine-based COFs has been addressed by employing different strategies, such as the design and construction of materials with specific interlayer interactions that help maintain the integrity of the network. Other efforts have focused on preventing hydrolysis of the imine group, either by blocking it from nucleophiles or by creating intramolecular hydrogen bonding or hydrophobic environments around the imine group [18]. However, the blocking of the -C=N- bond that seems to be gaining attention during the last few years is its irreversible transformation into another functional group. The conversion of the reversible imine linkages into irreversible moieties has also been used to simultaneously incorporate new functionalities into the network. Thus, this strategy has allowed the conversion of the imine linkages into amines using different methods such as the Leuckart–Wallach reduction [19], the thiol-ene click reaction [20], or the Strecker reaction [21]. Other efforts have been focused on embedding the imine linkages into new heterocyclic rings, amplifying the π-electron delocalization of the lattices and, in many cases, adding new functionalities. These blocking bond steps initially were performed by the post-synthetic modification (PSM) of the COFs. However, one-pot (OP) syntheses, in which COF and its transformation are carried out in a cascade process, are gaining importance due to the savings in efforts and recurses that it entails.
The great interest generated by obtaining ultra-stable crystalline networks from different imine-based COFs by the formation of different cycles is evidenced by the growing number of publications focused on their synthesis and the evaluation of their structural, chemical, and electronic properties for later applications. This entry gathered the synthetic strategies, both by PSM and OP, for the transformation of reversible links of imine-based COFs into stabilized heterocyclic moieties by using cycloaddition or cyclization reactions. Particular attention will be paid to the most recent publications to reflect the state of the art in this field.

This entry is adapted from the peer-reviewed paper 10.3390/encyclopedia3030057

References

  1. Côté, A.P.; Benin, A.I.; Ockwig, N.W.; O’Keeffe, M.; Matzger, A.J.; Yaghi, O.M. Porous, Crystalline, Covalent Organic Frameworks. Science 2005, 310, 1166–1170.
  2. Cheng, H.-Y.; Wang, T. Covalent Organic Frameworks in Catalytic Organic Synthesis. Adv. Synth. Catal. 2021, 363, 144–193.
  3. Chen, H.; Jena, H.S.; Feng, X.; Leus, K.; Van Der Voort, P. Engineering Covalent Organic Frameworks as Heterogeneous Photocatalysts for Organic Transformations. Angew. Chem. Int. Ed. 2022, 61, e202204938.
  4. Alonso-Navarro, M.J.; Barrio, J.; Royuela, S.; Karjule, N.; Ramos, M.M.; Martínez, J.I.; Shalom, M.; Segura, J.L. Photocatalytic Degradation of Organic Pollutants through Conjugated Poly(Azomethine) Networks Based on Terthiophene-Naphthalimide Assemblies. RSC Adv. 2021, 11, 2701–2705.
  5. Royuela, S.; Martínez-Periñán, E.; Arrieta, M.P.; Martínez, J.I.; Ramos, M.M.; Zamora, F.; Lorenzo, E.; Segura, J.L. Oxygen Reduction Using a Metal-Free Naphthalene Diimide-Based Covalent Organic Framework Electrocatalyst. Chem. Commun. 2020, 56, 1267–1270.
  6. Martínez-Fernández, M.; Martínez-Periñán, E.; Royuela, S.; Martínez, J.I.; Zamora, F.; Lorenzo, E.; Segura, J.L. Covalent Organic Frameworks Based on Electroactive Naphthalenediimide as Active Electrocatalysts toward Oxygen Reduction Reaction. Appl. Mater. Today 2022, 26, 101384.
  7. Martínez-Fernández, M.; Martínez-Periñán, E.; Martínez, J.I.; Gordo-Lozano, M.; Zamora, F.; Segura, J.L.; Lorenzo, E. Evaluation of the Oxygen Reduction Reaction Electrocatalytic Activity of Postsynthetically Modified Covalent Organic Frameworks. ACS Sustain. Chem. Eng. 2023, 11, 1763–1773.
  8. Luo, R.; Yang, Y.; Chen, K.; Liu, X.; Chen, M.; Xu, W.; Liu, B.; Ji, H.; Fang, Y. Tailored Covalent Organic Frameworks for Simultaneously Capturing and Converting CO2 into Cyclic Carbonates. J. Mater. Chem. A 2021, 9, 20941–20956.
  9. Bian, G.; Yin, J.; Zhu, J. Recent Advances on Conductive 2D Covalent Organic Frameworks. Small 2021, 17, 2006043.
  10. Bukhari, S.N.A.; Ahmed, N.; Amjad, M.W.; Hussain, M.A.; Elsherif, M.A.; Ejaz, H.; Alotaibi, N.H. Covalent Organic Frameworks (COFs) as Multi-Target Multifunctional Frameworks. Polymers 2023, 15, 267.
  11. Royuela, S.; García-Garrido, E.; Martín Arroyo, M.; Mancheño, M.J.; Ramos, M.M.; González-Rodríguez, D.; Somoza, Á.; Zamora, F.; Segura, J.L. Uracil Grafted Imine-Based Covalent Organic Framework for Nucleobase Recognition. Chem. Commun. 2018, 54, 8729–8732.
  12. Wang, J.; Feng, J.; Lian, Y.; Sun, X.; Wang, M.; Sun, M. Advances of the Functionalized Covalent Organic Frameworks for Sample Preparation in Food Field. Food Chem. 2023, 405, 134818.
  13. Tran, Q.N.; Lee, H.J.; Tran, N. Covalent Organic Frameworks: From Structures to Applications. Polymers 2023, 15, 1279.
  14. Royuela, S.; Almarza, J.; Mancheño, M.J.; Pérez-Flores, J.C.; Michel, E.G.; Ramos, M.M.; Zamora, F.; Ocón, P.; Segura, J.L. Synergistic Effect of Covalent Bonding and Physical Encapsulation of Sulfur in the Pores of a Microporous COF to Improve Cycling Performance in Li-S Batteries. Chem. A Eur. J. 2019, 25, 12394–12404.
  15. Martínez-Fernández, M.; Gavara, R.; Royuela, S.; Fernández-Ecija, L.; Martínez, J.I.; Zamora, F.; Segura, J.L. Following the Light: 3D-Printed (2-hydroxyethyl Methacrylate) Dual Emissive Composite with Response to Polarity and Acidity. J. Mater. Chem. A 2022, 10, 4634–4643.
  16. Segura, J.L.; Mancheño, M.J.; Zamora, F. Covalent Organic Frameworks Based on Schiff-Base Chemistry: Synthesis, Properties and Potential Applications. Chem. Soc. Rev. 2016, 45, 5635–5671.
  17. Qian, C.; Feng, L.; Teo, W.L.; Liu, J.; Zhou, W.; Wang, D.; Zhao, Y. Imine and Imine-Derived Linkages in Two-Dimensional Covalent Organic Frameworks. Nat. Rev. Chem. 2022, 6, 881–898.
  18. Jiang, G.; Zou, W.; Ou, Z.; Zhang, W.; Liang, Z.; Du, L. Stabilization of 2D Imine-linked Covalent Organic Frameworks: From Linkage Chemistry to Interlayer Interaction. Chem. Eur. J. 2022, 29, e202203610.
  19. Grunenberg, L.; Savasci, G.; Terban, M.W.; Duppel, V.; Moudrakovski, I.; Etter, M.; Dinnebier, R.E.; Ochsenfeld, C.; Lotsch, B.V. Amine-Linked Covalent Organic Frameworks as a Platform for Postsynthetic Structure Interconversion and Pore-Wall Modification. J. Am. Chem. Soc. 2021, 143, 3430–3438.
  20. Wang, K.; Zhang, H.; Xiao, Y.; Ren, S.; Wang, Y.; Li, L. Efficient Exfoliation of Covalent Organic Frameworks by a Facile Thiol-Ene Reaction. Chem. Eng. J. 2023, 454, 140283.
  21. Li, X.-T.; Zou, J.; Wang, T.-H.; Ma, H.-C.; Chen, G.-J.; Dong, Y.-B. Construction of Covalent Organic Frameworks via Three-Component One-Pot Strecker and Povarov Reactions. J. Am. Chem. Soc. 2020, 142, 6521–6526.
More
This entry is offline, you can click here to edit this entry!