Selective activation of C–H bonds on the ring of ethylbenzene catalyzed by several diperoxovanadate complexes

The competitive oxidation of the C–H bonds on the aromatic ring and side-chain of ethylbenzene (EB) with hydrogen peroxide is investigated over four diperoxovanadate catalysts, that is, K3[VO(O2)2(ox)] (bpV(ox)), K2[VO(O2)2(pic)] (bpV(pic)), K[VO(O2)2(bpy)] (bpV(bpy)), and K[VO(O2)2(phen)] (bpV(phen)). The selectivity to ring C–H bonds activation is found to be affected by the polarity and acidity of the solvent. The electrophilicity of the diperoxovanadate complexes and their catalytic performance are tuned by different ligands. The high electrophilicity of the vanadium center shows preference for the ring C–H bonds activation. The HOAc molecule was involved not only in the ligand exchange around the vanadium center, but also in the stabilization of the diperoxovanadium species in the media. A polar intermediate mechanism by generating electrophilic catalytic species is proposed. The bpV(bpy)–H2O2–HOAc system is found to be effective for the selective activation of the C–H bonds on aromatic ring of EB (S = 68.3%). It shows promise for the direct one-step synthesis of substituted-phenols from alkylbenzene.

Graphical abstractThe bpV(bpy)–H2O2–HOAc system is found to be effective for the preferential activation of the aromatic ring than the side-chain C–H bonds of ethylbenzene (S = 68.3%).Figure optionsDownload full-size imageDownload high-quality image (28 K)Download as PowerPoint slide