Cagelike Rb₂-, K₂-, and Na₂-Tetracopper(II) Silsesquioxanes with Quaternary Ammonium Cations: Synthesis, Structures, and Catalytic Activity

Ten copper-based cage silsesquioxanes were prepared via convenient self-assembly synthesis employing halides of different quaternary ammonium cations, namely, Me4NBr, Et4NBr, PhMe3NCl, BzMe3NCl, and BzEt3NCl. This approach led to cages of similar Cu4M2 nuclearity (M = Rb, K, or Na). Sandwich-like structures of all compounds were established by single-crystal X-ray diffraction studies using synchrotron radiation. In all products, anionic cages are based on two cyclic silsesquioxane [Ph6Si6O12] ligands, coordinating to a central hexagonal CuII4M2 motif with a 2M6-1 topology. The complexes include two charge balancers, namely, quaternary N-cations located at the external (crown ether-like) positions to cage fragments. Selected compounds were tested as homogeneous multicopper(II) catalysts in a series of model reactions, such as the mild oxidation and carboxylation of alkanes, including inert gaseous C2–C4 saturated hydrocarbons. This study extends the types of synthetic approaches and family of ionic metallasilsesquioxanes with promising structural features and catalytic properties.