Mechanochemical Cyclotrimerization: A Versatile Tool to Covalent Organic Frameworks with Tunable Stacking Mode

We introduce the first mechanochemical cyclotrimerization of nitriles, a facile strategy for synthesizing triazine-containing molecules and materials, overcoming challenges related to carbonization and solubility. Conducting this solid-state approach in a mixer ball mill with 4-Methylbenzonitrile, we synthesize Tris(4-methylphenyl)-1,3,5-triazine quantitatively in as little as 90 minutes. Just as fast, this mechanochemical method facilitates the synthesis of the covalent triazine framework CTF-1 using 1,4 Dicyanobenzene. Material characterization confirms its porous (650 m2 g-1) and crystalline nature. Adjusting the induced mechanical energy allows control over the obtained stacking conformation of the resulting CTFs - from a staggered AB arrangement to an eclipsed AA stacking conformation. Finally, a substrate scope demonstrates the versatility of this approach, successfully yielding various CTFs. This work presents, for the first time, the mechanochemical cyclotrimerization of nitriles. Utilizing Trifluoromethanesulfonic acid and a ball mill, both small molecules and large organic frameworks could be obtained. Screening the reaction of 1,4-Dicyanobenzene by various parameters, such as reaction time, frequency, or temperature, significant impacts on the porosity of the polymer and its crystallinity were revealed. image