Phosphonium Ionic Imine Cage with an Uncommon Tri 2 4 Di 6 Topology for Selective Capture of Propyne in Propyne/Propylene Separation

The incorporation of phosphine units into porous organic cages (POCs) imparts the rich chemistry of phosphorus atoms to the POC system and enables a range of relevant applications. However, phosphine-containing POCs remain underexplored. In this work, quaternary phosphonium ionic cages were successfully constructed via the integration of phosphine groups, where premethylation and anion exchange of the triphenylphosphine (PPh 3 )-aldehyde precursor were employed before the imine condensation reaction. The counterions of the PPh 3 -aldehyde precursor were found to play a crucial role in dictating the topology of the resulting cage product. While the precursor bearing an iodide (I – ) anion yielded a soluble [2 + 3] cage P-cage-I, the bis(trifluoromethane)sulfonimide (NTf 2 – ) and hexafluorophosphate (PF 6 – ) analogues ( P-cage-NTf 2 and P-cage-PF 6 ) formed [4 + 6] assemblies with the rare Tri 2 4 Di 6 (nomenclature for porous organic cage topology classification). Benefiting from the synergistic effects of a favorable topology, flexible windows, and guest-affinitive anions in the Tri 2 4 Di 6 cage structure, P-cage-PF 6 demonstrated excellent propyne/propylene separation performance, as confirmed by breakthrough experiments.