Microporous cobaltporphyrin covalent polymer mediated Co3O4@PNC nanocomposites for efficient catalytic C-H bond activation

Abstract A Cobalt porphyrin conjugated porous polymer (Co/PCP) was obtained by hybrid polymerization of a mixture of Co(II)(5,10,15,20-tetrakis(4-bromophenyl)-21H,23H-porphyrin) (CoTBPP) and 5,10,15,20-tetrakis(4-bromophenyl)-21H,23H-porphyrin (TBPP) (3:7 molar ratio) with the coupling reagent of p-phenyldiboric acid. This Co/PCP was carbonized at 400 °C and the obtained catalyst (denoted as Co3O4@PNC-400) was composed of Co3O4 nanoclusters wrapped in the nitrogen-carbon materials. This catalyst has an extremely high catalytic activity for the aerobic oxidation of C-H bonds. It can efficiently catalyze the oxidation of the C-H bonds in toluene and cyclohexane with high conversion and high selectivity of (alcohol + aldehyde), (alcohol + ketone) compounds, respectively. When heat-treated at 400 °C, the porous framework structure of the porphyrin polymer was partially retained, and the highly active Co3O4 nanoclusters were generated in situ. The reaction of C = N to C-N and connection with the Co3O4 nanoclusters also occurred. Co3O4@PNC-400 has obvious synergistic catalytic effect between Co3O4 and nitrogen-carbon framework during the catalytic reaction. The defective structure caused by the migration of cobalt also greatly improved the catalytic activity. Co/PCPs with different cobalt contents were also synthesized and heat treated at different temperature. These catalysts were a new type of efficient C-H oxidation catalysts with excellent potential application value.