Benzimidazole-Containing Porous Organic Polymers as Highly Active Heterogeneous Solid-Base Catalysts

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. N-2 adsorption measurements show that BPOP-1 is a nonporous framework, whereas BPOP-2 displays good adsorption abilities towards N-2, H-2, 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.