Polyphenylene-Based Solid Acid as an Efficient Catalyst for Activation and Hydration of Alkynes.

Yiyun Liu,Liqun Kang,Bolun Wang,Feng Ryan Wang,Apostolos Stamatopoulos,Hao Gu

doi:10.1021/acs.chemmater.0c01763

Yiyun Liu, Liqun Kang + Show 4 more

Open Access

https://doi.org/10.1021/acs.chemmater.0c01763

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Abstract

Porous polymer catalysts possess the potential to combine the advantages of heterogeneous and homogeneous catalysis, namely, easy postreaction recycling and high dispersion of active sites. Here, we designed a −SO3H functionalized polyphenylene (PPhen) framework with purely sp2-hybridized carbons, which exhibited high activity in the hydration of alkynes including challenging aliphatic substrates such as 1-octyne. The superiority of the structure lies in its covalent crosslink in the xy-plane with a π–π stacking interaction between the planes, enabling simultaneously high swellability and porosity (653 m2·g–1). High acidic site density (2.12 mmol·g–1) was achieved under a mild sulfonation condition. Similar turnover frequencies (0.015 ± 0.001 min–1) were obtained regardless of acidic density and crosslink content, suggesting high accessibility for all active sites over PPhen. In addition, the substituted benzene groups can activate alkynes through a T-shape CH/π interaction, as indicated by the 8 and 16 cm–1 red shift of the alkyne C–H stretching peak for phenylacetylene and 1-octyne, respectively, in the infrared (IR) spectra. These advantages render PPhen-SO3H a promising candidate as a solid catalyst replacing the highly toxic liquid phase acids such as the mercury salt.

Highlights

Porous organic materials play an important role in gas storage and separation,[1,2] drug release,[3] catalysis, sensing,[4] and membrane separation[5] due to their properties in merging the benefits of porosity, processability, synthesis diversity, and organic nature.[6]
PPhen is synthesized through the palladiumcatalyzed cross-coupling reaction of 1,2,4,5-tetrabromobenzene and benzene-1,4-diboronic acid as reported previously.[34]
Tetrabromobenzene is selectively replaced with 1,4-dibromobenzene. This results in a controlled ratio between phenylene and tetrasubstituted benzene groups in the PPhen framework and determines the crosslink content, which is denoted as

Summary

Introduction

Porous organic materials play an important role in gas storage and separation,[1,2] drug release,[3] catalysis, sensing,[4] and membrane separation[5] due to their properties in merging the benefits of porosity, processability, synthesis diversity, and organic nature.[6] A number of novel polymeric frameworks have been developed in recent years,[6,7] such as polytriazine,[8−10] hyper-cross-link polystyrene (HPS),[11,12] nanoporous polydivinylbenzene (PDVB),[13] dihydroxybenzoic acid-based polymer nanospheres,[14] and porphyrin network polymers.[15,16] The polymeric structures offer a high surface area and well-controlled porosity and provide an organic environment, the advantage of lightweight, and a dynamic structure upon external stimulation They have offered an innovative way to combine the advantages of homogeneous and heterogeneous catalysis.[17] On one hand, a solvent-like reaction environment is established via organic ligands and the geometric structure of the framework, providing well-dispersed high-density active sites. The heterogeneous nature of solid catalysts facilitates postreaction separation, rendering them environment-friendly alternatives for highly toxic homogeneous liquid catalysts

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Conclusion