Tröger’s Base Network Polymers of Intrinsic Microporosity (TB-PIMs) with Tunable Pore Size for Heterogeneous Catalysis

Abstract

Heterogeneous catalysis plays a pivotal role in the preparation of value-added chemicals, and it works more efficiently when combined with porous materials and supports. Because of that, a detailed assessment of porosity and pore size is essential when evaluating the performance of new heterogeneous catalysts. Herein, we report the synthesis and characterization of a series of novel microporous Tröger’s base polymers and copolymers (TB-PIMs) with tunable pore size. The basicity of TB sites is exploited to catalyze the Knoevenagel condensation of benzaldehydes and malononitrile, and the dimension of the pores can be systematically adjusted with an appropriate selection of monomers and comonomers. The tunability of the pore size provides the enhanced accessibility of the catalytic sites for substrates, which leads to a great improvement in conversions, with the best results achieving completion in only 20 min. In addition, it enables the use of large benzaldehydes, which is prevented when using polymers with very small pores, typical of conventional PIMs. The catalytic reaction is more efficient than the corresponding homogeneous counterpart and is ultimately optimized with the addition of a small amount of a solvent, which facilitates the swelling of the pores and leads to a further improvement in the performance and to a better carbon economy. Molecular dynamic modeling of the copolymers’ structures is employed to describe the swellability of flexible chains, helping the understanding of the improved performance and demonstrating the great potential of these novel materials.

CO2-Switchable Hierarchically Porous Zirconium-Based MOF-Stabilized Pickering Emulsions for Recyclable Efficient Interfacial Catalysis

“…The Knoevenagel condensation reaction serves as an imperative and valuable condensation approach in organic chemistry because of the synthesis of important intermediates for fine chemicals such as pharmaceuticals, biologically active compounds, natural products and functional polymers through creating new carbon–carbon bonds between carbonyl compounds and active methylene [ 52 , 53 , 54 ]. Until now, most of Knoevenagel condensation reactions reported have been carried out under homogeneous conditions.…”

Tröger’s Base-Enriched Conjugated Cyclopentannulated Copolymers: Prominent Adsorbents of CO2, H2, and Iodine

“…51 The pronounced hysteresis of copolymers PTB1−PTB3, which can be noticed in Figure 4 and Figure S29 of the Supporting Information, could be explained by the possible swelling of the copolymer pores, where recent studies show that the pore enlargement, which occurs during the adsorption/desorption cycles of condensable probe gases, might be linked to such a noticeable hysteresis. 52,53…”

Catalytic Asymmetric Synthesis of Tröger’s Base Analogues with Nitrogen Stereocenter

“…Among these rigid chiral tertiary amine compounds, one particularly fascinating structure is Tröger’s base. It has two aromatic rings perpendicular to each other which fused to the central bicyclic [3.3.1] framework, enable to form a rigid cleft-like V-shaped scaffold possessing two nitrogen stereocenters. , Hence, Tröger’s base has attracted considerable attention due to its application in self-assembly studies, molecular recognition, DNA-interacting probes, as well as Lewis base catalyst in organic synthesis. − ,− However, enantiopure Tröger’s base has rarely been used excessively, as it is configurationally instable under acidic conditions, − which limits its wide application. To this end, various Tröger’s base analogues with rigid cleft-like skeleton have been developed by modifying the cleft-like scaffold to increase its stability, ,,− most of which involve multiple-step synthesis or late-stage resolution.…”