Rapid, Ambient Temperature Synthesis of Imine Covalent Organic Frameworks Catalyzed by Transition Metal Nitrates
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Covalent Organic Frameworks (COFs) are crystalline, porous organic materials with promise for applications including catalysis, energy storage, electronics, gas storage, water treatment, and drug delivery. Conventional solvothermal synthesis approaches to COFs require elevated temperatures, inert reaction environments, and long reaction times. Here, we report that transition metal nitrates can catalyze the rapid synthesis of imine COFs. We tested a series of transition metal nitrates as catalysts for the synthesis of a model COF and found that all transition metal nitrates produced crystalline COF products for reactions conducted at ambient temperatures. The reactions were insensitive to the presence of oxygen. Fe(NO3)3·9H2O was found to produce the most crystalline product, and by optimizing the catalyst loading we found that crystalline COF could be produced within 10 minutes. We further tested Fe(NO3)3·9H2O as a catalyst for 6 different COF targets varying in linker lengths, substituents, and stabilities, and found that Fe(NO3)3·9H2O effectively catalyzed the synthesis of all imine COFs tested. This work demonstrates a simple, low-cost approach for the synthesis of imine COFs and will significantly lower the barrier for the development of imine COFs for various applications.