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

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.