Cu-6- And Cu-8-Cage Sil- And Germsesquioxanes: Synthetic And Structural Features, Oxidative Rearrangements, And Catalytic Activity

This study reports intriguing features in the self-assembly of cage copper(II) silsesquioxanes in the presence of air. Despite the wide variation of solvates used, a series of prismatic hexanuclear Cu-6 cages (1-5) were assembled under mild conditions. In turn, syntheses at higher temperatures are accompanied by side reactions, leading to the oxidation of solvates (methanol, 1-butanol, and tetrahydrofuran). The oxidized solvent derivatives then specifically participate in the formation of copper silsesquioxane cages, allowing the isolation of several unusual Cu-6-based (6 and 7) and Cu-6-based (8) complexes. When 1,4-dioxane was applied as a reaction medium, deep rearrangements occurred (with a total elimination of silsesquioxane ligands), causing the formation of mononuclear copper(II) compounds bearing oxidized dioxane fragments (9 and 11) or a formate-driven ID coordination polymer (10). Finally, a "directed" self-assembly of sil- and germsesquioxanes from copper acetate (or formate) resulted in the corresponding acetate (or formate) containing Cu-6 cages (12 and 13) that were isolated in high yields. The structures of all of the products 1-13 were established by single-crystal X-ray diffraction, mainly based on the use of synchrotron radiation. Moreover, the catalytic activity of compounds 12 and 13 was evaluated toward the mild homogeneous oxidation of C-s-C-s cycloalkanes with hydrogen peroxide to form a mixture of the corresponding cyclic alcohols and ketones.