Gram-Scale Synthesis of Imine-Linked Covalent Organic Frameworks at Ambient Conditions Using Metal Triflimides

Abstract

Imine-linked covalent organic frameworks (COFs) are crystalline and permanently porous networks with significant prospects for addressing current challenges pertinent to energy and environmental sustainabilities, including gas adsorption, energy storage, catalysis, optoelectronics, and many more. These crystalline networks are conventionally prepared by condensing a polyfunctional aldehyde and amine building blocks of different symmetricities and point groups for multiple days at an elevated temperature. Here, we demonstrate the catalytic role of metal triflimides in accelerating the synthesis of robust and fragile imine-linked COFs under ambient conditions. We first tested a range of metal triflimides, Zn(NTf₂)₂, Co(NTf₂)₂, Mg(NTf₂)₂, and Sc(NTf₂)₃, for the synthesis of a model TAPB-PDA COF and found that all metal triflimides afforded crystalline frameworks in quantitative yields under ambient temperatures and in the presence of air. Zn(NTf₂)₂ was found to produce the most crystalline framework in less than 15 min under optimized catalyst loading. Zn(NTf₂)₂ was further tested as a catalyst for over 15 different COFs of varying building blocks, substituents, and topologies, and it effectively catalyzed the rapid fabrication of all imine frameworks targeted, including previously unreported TAPB-DMTPDA COFs. Notably, this catalyst was also successful in the gram-scale fabrication of both robust and fragile COFs underlining a simple, scalable, low-cost, rapid, and benchtop approach for the synthesis of imine-linked COFs that can potentially eliminate barriers to the commercialization of imine COFs for a variety of applications.