Flexible porous organic polymers constructed using C(sp3)–C(sp3) coupling reactions and their high methane-storage capacity

Abstract

Carbon–carbon coupling is a basic design principle for the synthesis of porous organic polymers, which are widely used in gas adsorption/separation, photocatalysis, energy storage, etc. However, the C(sp³)–C(sp³) coupling reaction to construct porous organic polymers remains an important yet elusive objective due to its low reactivity and unknown side reactions. Herein, we report that nickel bis(1,5-cyclooctadiene) (Ni(COD)₂), which was a famous catalyst for C(sp²)–C(sp²) coupling reactions, enables highly efficient C(sp³)–C(sp³) homo-coupling reactions to construct porous linear crystalline polymers and flexible three-dimensional porous aromatic frameworks (PAFs) under mild reaction conditions. The resulting linear polymers generated with dibromomethyl arenes have good crystallinity and high melting points (T_m = 286 °C) due to controllability of reaction sites. Furthermore, the PAFs (PAF-64, PAF-65 and PAF-66) stemmed from tri-/tetra-bromomethyl arenes show high surface area (S_BET = 390 m² g⁻¹) and high methane-storage capacity (up to 313 cm³ cm⁻³) because of their flexible frameworks. This work sheds new light on the construction of novel porous polymers through C(sp³)–C(sp³) coupling reactions and the development of methane-storage materials.