Cu6- and Cu8-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.

Automated summary

This study presents the intriguing self-assembly of cage copper(II) silsesquioxanes in the presence of air, showcasing the formation of hexanuclear Cu-6 cages under mild conditions despite varying solvates. Higher temperature syntheses lead to side reactions and oxidation of solvates, while the use of different solvents results in unique copper silsesquioxane cage structures. The structures of the products were confirmed through single-crystal X-ray diffraction, and the catalytic activity of certain compounds in the oxidation of cycloalkanes was evaluated.