Combination of Phenylsilsesquioxane and Acetate Ligands as an Approach to a Record High Nuclear Cu₁₃Na₂-Cage. Synthesis, Unique Structure, and Catalytic Activity

Self-assembly synthesis of mixed-ligand (silsesquioxane/acetate) complex allows to isolate record high nuclear copper(II) Cu₁₃-cage (1). In the presence of two additional sodium ions, a unique molecular architecture, with triple combination of ligands (cyclic and acyclic silsesquioxanes as well as acetates), has been formed. The structure was established by single-crystal X-ray diffraction based on the use of synchrotron radiation. Complex 1 was evaluated as precatalyst in the Baeyer–Villiger oxidation of cyclohexanone towards ϵ-caprolactone, employing hydrogen peroxide, tert-butyl hydroperoxide (TBHP) or m-chloroperoxybenzoic acid (mCPBA) as oxidants, in an aqueous acidic acetonitrile medium. The direct formation of the lactone from cyclohexane via a tandem peroxidative oxidation/Baeyer–Villiger oxidation was also studied. For both substrates, the best results (ϵ-caprolactone yields up to 100 % or 26 %, from cyclohexanone or cyclohexane, respectively) were achieved with mCPBA under considerably mild conditions, i. e., conventional heating at 50 °C for 4 h or microwave (MW) irradiation at 80 °C for only 30 minutes.