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. © 2023 American Chemical Society.