Effective Approach toward Conjugated Porous Organic Frameworks Based on Phenanthrene Building Blocks: Metal-Free Heterogeneous Photocatalysts

This paper reports a simple approach for the preparation of new photo-active conjugated porous polymers (CPPs) based on phenanthrene building blocks with a high Brunauer-Emmett-Teller (BET) surface area. Starting from 2,7-diiodophenanthrene-9,10-dione and its bis-dioxolane derivative with different alkynyl comonomers, we prepared a series of CPPs by C-C Sonogashira-Hagihara coupling activated by microwaves. Moreover, we demonstrated that these functionalized CPPs after hydrolysis to the corresponding diketones show much higher BET surface areas than those obtained directly from the phenanthrene-9,10-dione monomer. Reaction of diketone-hydrolyzed polymers with 2,4-difluoro-6-hydroxybenzaldehyde yields phenantroimidazole derivatives. Indeed, these structurally robust polymers result in efficient, recyclable, heterogeneous photo-organocatalysts for the aza-Henry reaction (C-H functionalization) induced by visible-light irradiation.