Aerobic oxidation of benzene to phenol over polyoxometalate-paired PdII-coordinated hybrid: Reductant-free heterogeneous catalysis

• Reductant-free heterogeneous catalysis for hydroxylation of benzene with O2 is built.
• High phenol yield is obtained from the heterogeneous catalytic system.
• The heterogeneous catalyst is a polyoxometalate-paired PdII-coordinated hybrid.
• The hybrid combines the two catalytic centers of Pd(OAc)2 and PMoV2 together.
• Enhanced synergistic effect between the two active sites leads to the high activity.

Aerobic oxidation of benzene was carried out over the organic–inorganic hybrid catalyst of [(C3CNpy)2Pd(OAc)2]2HPMoV2, a solid catalyst containing the Keggin polyoxometalate PMoV2 and noble metal Pd(OAc)2 in its ionic structure. The features of this heterogeneous reaction system were studied by tuning various reaction parameters including solvent selection, function of buffer agent, and effects of reaction time, reaction temperature and catalyst amount. The results show the high phenol yield of 9.8% without aided by any sacrificial reducing reagents. The conjugation of Pd(OAc)2 and PMoV2 within the ionic structure of [(C3CNpy)2Pd(OAc)2]2HPMoV2 that accounts for its high activity is preliminarily discussed.

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