Catalyst-Enabled In Situ Linkage Reduction in Imine Covalent Organic Frameworks

Abstract

New linkages for covalent organic frameworks (COFs) have been continuously pursued by chemists as they serve as the structure and property foundation for the materials. Developing new reaction types or modifying known linkages have been the only two methods to create new COF linkages. Herein, we report a novel strategy that uses H3PO3 as a bifunctional catalyst to achieve amine-linked COFs from readily available amine and aldehyde linkers. The acidic proton of H3PO3 catalyzes the imine framework formation, which is then in situ reduced to the amine COF by the reductive P–H moiety. The amine-linked COF outperforms its imine analogue in promoting Knoevenagel condensation because of the more basic sites and higher stability.

Metal Oxide Catalysts for the Synthesis of Covalent Organic Frameworks and One-Step Preparation of Covalent Organic Framework-Based Composites

“…There is also a critical need for robust and low-cost catalysts for synthesizing high-quality COFs under mild reaction conditions. , For example, imine COFs are typically synthesized via reversible Schiff-base reactions under solvothermal conditions with acetic acid as the catalyst . However, producing high-quality crystalline COFs requires tedious optimization of the reaction conditions for each set of monomers selected and commonly requires a reaction time of several days and elevated temperatures .…”

Tailoring NH3 Sensing Responsiveness through Amine Modification of Imine-Based Nanoporous Covalent Organic Polymer

“…The FT-IR spectra of 3,4-diaminobenzhydrazide exhibit significant peaks at 3393, 1623, and 1575 cm –1 , corresponding to NH 2 , CO (amide I), and C–N (amide II), respectively. , In TP3F, the peak observed at 1680 cm –1 is attributed to CO. , In nCOPI, the appearance of a peak at 1601 cm –1 and the disappearance of the peak at 1680 cm –1 confirm the formation of a CN functional group . Additionally, the appearance of peaks at 3345 (stretching frequency of NH), 1595 (bending stretch of C–N–H bond), 1355 (stretching frequency of C–N), and 1212 cm –1 (vibration stretching of C–N bond in the secondary amine linkage) in the nCOPA spectra confirms the presence of C–N bonds. , Furthermore, a powder X-ray diffraction (PXRD) experiment was performed to analyze the amorphous and crystalline properties of TP3F, nCOPI, and nCOPA (Figure b). The PXRD spectra of 3,4-diaminobenzhydrazide and TP3F show sharp peaks, indicating its crystalline behavior, while nCOPI and nCOPA exhibit sharp peaks with a slightly broad hump, indicating their lower degree of crystallinity. ,, Furthermore, the formation of nCOPA was confirmed using 13 C CP-MAS NMR.…”

Fe(III)-Anchored Porphyrin-Based Nanoporous Covalent Organic Frameworks for Green Synthesis of Cyclic Carbonates from Olefins and CO2 under Atmospheric Pressure Conditions

“…The preparation of porphyrin-based COFs has been achieved by employing various synthetic routes. , Particularly, the solvothermal approach is generally followed to obtain COFs with high crystallinity. ,, The porphyrin-COF (P-COF) was prepared by adopting the reported solvothermal procedure with minor modifications (Scheme and the Supporting Information) and characterized by different techniques. The FT-IR spectra of P-COF depicted the disappearance of characteristic stretching frequencies due to the −NH 2 group of tetra­( p -amino-phenyl)­porphyrin (TAPP) and also the carbonyl group (CO) of 1,4-benzenedicarboxaldehyde (BDA), indicating complete consumption of the precursors during the COF synthesis.…”