Rapid, Low Temperature Formation of Imine-linked COFs Catalyzed by Metal Triflates.

Imine-linked two-dimensional covalent organic frameworks (2D COFs) are crystalline polymer networks with enhanced stability and broader monomer scope compared to boronate ester-linked systems. They are traditionally prepared by condensing polyfunctional aldehydes and amines at elevated temperature in a mixture of organic solvents and aqueous CH3CO2H, which catalyzes imine formation and exchange. Under these conditions, an amorphous imine-linked polymer network precipitates quickly and then crystallizes after extended reaction times (hours to days). Here we employ metal triflates, which are water-tolerant Lewis acids, to vastly accelerate 2D imine-linked COF synthesis and improve their materials quality. Low catalyst loadings provide crystalline polymer networks in nearly quantitative yields. The generality of these conditions is demonstrated for several monomer combinations, including heteroatom-containing aromatic systems of interest for optoelectronic applications.