Pillar[5]arene-Based Co(III)-Loaded Covalent Organic Polymer for Efficient CO2 Cycloaddition under Mild Conditions

Abstract

Generating promising materials for the conversion of CO2 to valuable industrial products under mild conditions is important for both ameliorating the greenhouse effect and sustainable development. Pillar[5]arene-incorporated materials have recently emerged as building frameworks to construct versatile functional polymeric materials. Herein, we demonstrate that highly efficient fixation of CO2 to cyclic carbonates can be achieved by employing a novel pillar[5]arene-based Co(III)-loaded covalent organic polymer (COP) as a heterogeneous catalyst (Co(III)-P5COP). The catalyst was created first by condensation of bromo-functionalized pillar[5]arene and a Schiff-base derivative (BHPD-OH) to afford the pillar[5]arene-based COP (P5COP), followed by loading Co(III) to prepare the target material bearing abundant salen-Co(III) sites. Results of catalysis with various substrates reveal excellent catalytic performance for CO2 cycloaddition with the conversion and selectivity of cyclic carbonate reaching up to 96 and 99%, respectively, under mild conditions of 30 °C and 1 atm CO2. Moreover, Co(III)-P5COP exhibits general applicability to other bulky epoxides. The polymeric pillar[5]arene-based catalysts could be easily recovered and reused without marked loss in their activity. Therefore, the marriage of Co(III)-salen and the pillar[5]arene platform constitutes a feasible approach to offering easily accessible and macrocycle-based new materials for the conversion of CO2 to valuable products.