Amino-terphenyl covalent triazine polymers as visible-light heterogeneous photocatalysts for aerobic sulfoxidation and cross-dehydrogenative coupling reactions

The synthesis of diamino-p-terphenyl covalent triazine polymers (DAPT-CTPs) is herein described by the direct nucleophilic substitution polymerization between cyanuric chloride (2,4,6-trichloro-1,3,5-triazine, TCT) and 4,4′′-diamino-p-terphenyl (DAPT). DAPT-CTPs were prepared in semi-crystalline and crystalline forms as thermally stable, mesoporous materials with high photocatalytic activity in visible-light-mediated aerobic oxidation processes. The detailed photophysical characterization of DAPT-CTPs indicates that the incorporation of the DAPT unit into the triazine polymers creates an extended π-π and p-π conjugated structure beneficial to expanding the light adsorption range and elevating the excited states of the photocatalyst for the efficient generation of reactive oxygen species (ROS). Dedicated quenching experiments confirmed that photogenerated ROS can initiate sulfide-to-sulfoxide oxidations and cross-dehydrogenative couplings of glycine derivatives through electron and energy transfer mechanisms. By this strategy, a collection of added-value molecules, including non-proteinogenic α-amino acids, was obtained with high efficiency under mild and sustainable conditions. The remarkable stability of recyclable DAPT-CTPs was ultimately exploited for the fabrication of fixed-bed reactors, which were operated in long-term experiments for the continuous-flow production of the pharmacologically active sulfoxide Ricobendazole.