Hybrid of Polyoxometalate-Based Ionic Salt and N-Doped Carbon toward Reductant-Free Aerobic Hydroxylation of Benzene to Phenol

A novel carbon-based hybrid is composed of N-doped ordered mesoporous carbon (NC) and polyoxometalate (POM) based ionic salt (IL-POM), constructing the first efficient non-noble metal heterogeneous catalyst for reductant-free hydroxylation of benzene to phenol with molecular oxygen. Enhanced activity and reusability were achieved and were even better than the previous noble metal involved system. The newly task-specifically designed dicationic ionic liquid tethered with the nitrile group contributed to the high efficiency and heterogeneous property. Systematic structure-activity analysis revealed that the superior activity for this difficult reaction came from the simultaneous activation of benzene by NC and O-2 by V species of IL-POM. This work suggests a new green reaction pathway toward heterogeneous aerobic hydroxylation of the C-sp2-H bond in pi-conjugated aromatic molecules.