Transition metal complex directed synthesis of porous cationic polymers for efficient CO₂ capture and conversion

The advent of porous polymers capable of both CO₂ capture and conversion is an emerging research area to tackle ever-increasing CO₂ emissions into the atmosphere and also to use CO₂ as a sustainable C1 source. Porous cationic polymers, which are analogous to zeolites, with exchangeable counteranions offer ideal platform for the simultaneous capture and conversion of CO₂. Here, we report on the porous cationic polymers (Ru-PCPs) with increased number of charges synthesized through condensation reaction between tris(1,10-phenanthroline-5,6-dione)Ru(II) dichloride and ortho-aromatic amines in AlCl₃ at 400 °C. Ru-PCPs exhibited surface areas up to 526 m² g⁻¹ and CO₂ uptake capacities as high as 3.76 mmol g⁻¹, which is among the highest reported to date for porous cationic polymers. The high CO₂-philicity of Ru-PCPs originating from the presence of multiple charges and nitrogen sites coupled with the nucleophilic Cl⁻ anions rendered Ru-PCPs as highly efficient heterogeneous catalysts for the conversion of CO₂ and propylene oxide to propylene carbonate through atom economy reaction. Notably, unlike previously reported porous cationic organocatalysts which require CO₂ pressures of 10–30 bar, Ru-PCPs were shown to operate efficiently even under atmospheric pressure of CO₂ mainly arising from the increased number of charges and counteranions.