Benzimidazole-containing porous organic polymers as highly active heterogeneous solid-base catalysts

Abstract

To develop efficient heterogeneous catalytic systems for base-catalyzed reactions, two benzimidazole-containing porous organic polymers, BPOP-1 and BPOP-2, were synthesized. As a result of the difference in building units, BPOP-1 exhibits a granular morphology, and BPOP-2 is composed of tiny particles. N2 adsorption measurements show that BPOP-1 is a nonporous framework, whereas BPOP-2 displays good adsorption abilities towards N2, H2, and CO2. Both BPOP-1 and BPOP-2 exhibit a higher catalytic activity in the Knoevenagel condensation reaction than their homogeneous molecular counterpart, and the activity of BPOP-2 is superior to that of BPOP-1. Theoretical calculations show that the Lewis basicity of the N atoms in BPOP-1 is identical to that in BPOP-2. The prominent catalytic performance of BPOP-2 is mainly attributed to its high specific surface area and microporous character. Moreover, the permanent chemical stability of the structural framework endows BPOP-2 with an outstanding recyclability. All about that base: Two benzimidazole-containing porous organic polymers (BPOP-2 and BPOP-2) are presented. They exhibit a higher catalytic activity in the Knoevenagel condensation reaction than their homogeneous molecular counterpart. The specific surface area and pore character, not Lewis basicity, are responsible for the difference of catalytic activity in the two polymers.