Highly recyclable and magnetic catalyst of a metalloporphyrin-based polymeric composite for cycloaddition of CO2 to epoxide

Abstract

A new core-double-shell microsphere [Fe₃O₄@SiO₂@Zn(Por)OP] was designed and prepared by coating a core–shell composite of Fe₃O₄ magnetic core and SiO₂ shell (Fe₃O₄@SiO₂) with a zinc porphyrin-based organic polymer [Zn(Por)OP]. While, Zn(Por)OP was readily obtained by a convenient condensation of pyrrole and terephthaldehyde in propanoic acid followed by a direct metallation with zinc acetate. Due to the presence of the inner core–shell particles (Fe₃O₄@SiO₂), the cage construction of this composite microsphere Fe₃O₄@SiO₂@Zn(Por)OP was significantly different from that of solid polymeric microsphere Zn(Por)OP, which further infected its physical properties to achieve a controllable morphology regulation easily. Besides, removing the inner core–shell particles of Fe₃O₄@SiO₂ from Fe₃O₄@SiO₂@Zn(Por)OP led to the formation of the Zn(Por)OP hollow microspheres which exhibited outstanding catalytic performance for the cycloaddition of carbon dioxide and propylene oxide to give propylene carbonate (PC) with turnover frequency (TOF) of 13 978 mol_PC mol_Zn⁻¹ h⁻¹. For the Fe₃O₄@SiO₂@Zn(Por)OP composite, the outer organic shell Zn(Por)OP served as the catalytically active layer for the cycloaddition and a PC yield of 97% was obtained. More importantly, the catalyst could be easily recycled from the reaction mixture by magnetic separation and no significant loss of the activity was observed after sixteen cycles. Therefore, this composite microsphere can provide insightful information for further design of magnetic materials with controllable morphology regulation as well as can be extended toward the development of highly efficient, stable and recyclable catalysts in other catalytic reaction systems.