Hybrid Silsesquioxane/Benzoate Cu 7 -Complexes: Synthesis, Unique Cage Structure, and Catalytic Activity.

A series of phenylsilsesquioxane-benzoate heptacopper complexes - were synthesized and characterized by X-ray crystallography. Two parallel routes of toluene spontaneous oxidation (into benzyl alcohol and benzoate) assisted the formation of the cagelike structure . A unique multi-ligation of copper ions (from () silsesquioxane, () benzoate, () benzyl alcohol, () pyridine, () dimethyl-formamide and () water ligands) was found in . Directed self-assembly using benzoic acid as a reactant afforded complexes - with the same main structural features as for , namely heptanuclear core coordinated by () two distorted pentameric cyclic silsesquioxane and () four benzoate ligands, but featuring other solvate surroundings. Complex was evaluated as a catalyst for the oxidation of alkanes to alkyl hydroperoxides and alcohols to ketones with hydrogen peroxide and tert-butyl hydroperoxide, respectively, at 50 °C in acetonitrile. The maximum yield of cyclohexane oxidation products as high as 32% was attained. The oxidation reaction results in a mixture of cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone. Upon the addition of triphenylphosphine, the cyclohexyl hydroperoxide is completely converted to cyclohexanol. The specific regio- and chemoselectivity in the oxidation of -heptane and methylcyclohexane, respectively, indicate the involvement of of hydroxyl radicals. Complex exhibits a high activity in the oxidation of alcohols.