Crosslinked polymeric bis(triphenylphosphine)iminium chloride gels as recyclable catalysts

Abstract

Bis(triphenylphosphine)iminium chloride, PPNCl, is an increasingly important catalyst due to its broad reactivity in both small molecule and polymer synthesis. A recently reported polymeric variant, poly(PPNCl), offers limited recyclability in small molecule synthesis, but its soluble, thermoplastic nature complicates its recovery and reuse. To address this limitation, we developed a crosslinked poly(PPNCl) thermoset that dramatically improves performance and reaction scope. As a catalyst in CO₂/epoxide coupling reactions the crosslinked derivative is faster and more readily recycled. In addition, the reaction scope can be extended to polymer synthesis, with soluble polyesters formed from coupling epoxides with maleic anhydrides isolated by filtration, with activity retained over multiple reaction cycles. Remarkably, the reaction scope can be further extended by anion exchange, with crosslinked poly(PPNCo(CO)₄) used to catalyse the carbonylative ring expansion of epoxides to β-lactones. Together these show that crosslinked poly(PPNCl) is a promising platform for metal-free, robust, recyclable catalysis.