Porous Polymeric Catalysts Constructed from Vinylated Functionalities

Abstract

ConspectusPorous organic polymers (POPs) have revolutionized the production of advanced catalytic materials with unique features such as a large surface area, tunable pore structure, ease of functionalization with a wide range of functional groups, and the ability to function as hosts for encapsulation of functional species, making them appealing for task-specific applications. Although numerous POP-based catalysts have been developed, they are rarely used as a common tool for preparatory-scale operations in laboratories. The high costs of these materials, because of the expensive reagents and catalysts often used in coupling reactions during their synthesis, primarily hinder their adoption. Since its discovery, free-radical polymerization of vinyl monomers to yield polymers has continuously attracted scientific and industrial attention and has been extensively adopted as an effective reaction for polymer production. Our group has targeted the synthesis of porous polymers via free-radical solvothermal polymerization of vinylated functionalities owing to the high efficiency, cost-effectiveness, and general applicability. More significantly, because of the flexibility of alkyl chains derived from the polymerized vinyl groups, the resulting frameworks are highly flexible, which is beneficial to facilitating the cooperation of catalytic components therein. Given the high catalytic efficiency of enzymes and amenable synthesis of POPs using vinylated functionalities, we have designed efficient heterogeneous catalysts by targeting the following aspects of enzyme mimicry: control over the second sphere of active sites, design of flexible ligand pockets, and construction of hydrophobic reaction microenvironments in POPs. In terms of control over the second sphere of active sites, we proposed the introduction of auxiliary groups or solvation environments via customized synthesis of POPs to perturb reaction pathways, reduce activation energies, and consequently improve catalytic performance. In terms of the design of flexible ligand pockets, we proposed the design concept of “porous ligand sponges” to fabricate quasi-homogeneous organometallic catalysts. The spatial continuity of the ligands on the flexible polymer chains enables their cooperation during catalysis, addressing the long-term challenges posed by the degradation of the catalytic performance after their heterogeneity, thus providing a possible replacement for homogeneous organometallic catalysts. In terms of adjusting the reaction microenvironments, we proposed the creation of hydrophobic environments to concentrate hydrophobic reagents in the vicinity of active sites and repel hydrophilic products to facilitate catalytic transformation.This Account highlights our ongoing research on the construction of POP-based catalysts. We also discuss the design strategies and principles involved with the aim of underscoring the unique features of POPs fabricated via solvothermal free-radical polymerization of vinylated functionalities in designing catalytic materials. This article summarizes our more than a decade of innovation in this field and is anticipated to advance the development of genuinely competitive artificial enzymes.