© 2017 The Royal Society of Chemistry. A dual mechanism for direct benzene catalytic hydroxylation is described. Experimental studies and DFT calculations have provided a mechanistic explanation for the acid-free, TpxCu-catalyzed hydroxylation of benzene with hydrogen peroxide (Tpx = hydrotrispyrazolylborate ligand). In contrast with other catalytic systems that promote this transformation through Fenton-like pathways, this system operates through a copper-oxyl intermediate that may interact with the arene ring following two different, competitive routes: (a) electrophilic aromatic substitution, with the copper-oxyl species acting as the formal electrophile, and (b) the so-called rebound mechanism, in which the hydrogen is abstracted by the Cu-O moiety prior to the C-O bond formation. Both pathways contribute to the global transformation albeit to different extents, the electrophilic substitution route seeming to be largely favoured.
Vilella, L., Conde, A., Balcells, D., Mar Díaz-Requejo, M., Lledós, A., & Pérez, P. J. (2017). A competing, dual mechanism for catalytic direct benzene hydroxylation from combined experimental-DFT studies. Chemical Science, 8(12), 8373-8383. https://doi.org/10.1039/c7sc02898a