Mild and Regioselective Hydroxylation of Methyl Group in Neocuproine: Approach to an N,O-Ligated Cu₆ Cage Phenylsilsesquioxane

The self-assembly synthesis of Cu­(II)-silsesquioxane involving 2,9-dimethyl-1,10-phenanthroline (neocuproine) as an additional N ligand at copper atoms was performed. The reaction revealed an unprecedented aerobic hydroxylation of only one of the two methyl groups in neocuproine to afford the corresponding geminal diol. The produced derivative of oxidized neocuproine acts as a two-centered N,O ligand in the assembly of the hexacopper cage product [Cu₆(Ph₅Si₅O₁₀)₂·(C₁₄H₁₁N₂O₂)₂] (1), coordinating two of the six copper centers in the product. Two siloxanolate ligands [PhSi­(O)­O]₅ in the cis configuration coordinate to the rest of the copper­(II) ions. Compound 1 is a highly efficient homogeneous precatalyst in the oxidation of alkanes and alcohols with peroxides.