Cage-like Cu<sub>5</sub>Cs<sub>4</sub>-Phenylsilsesquioxanes: Synthesis, Supramolecular Structures, and Catalytic Activity
Аlexey N. Bilyachenko, Ivan S. Arteev, Victor N. Khrustalev, Lidia S. Shul’pina, Аlexander А. Korlyukov, Nikolay S. Ikonnikov, Elena S. Shubina, Yuriy N. Kozlov⊗, Nuno Reis Conceição, M. Fátima C. Guedes da Silva, Kamran T. Mahmudov⧫, Armando J. L. Pombeiro
Abstract
A small family of nonanuclear Cu 5 Cs 4 -based phenylsilsesquioxanes 1 – 2 were prepared by a convenient self-assembly approach and characterized by X-ray diffraction studies. The compounds 1 and 2 show some unprecedented structural features such as the presence of a [Ph 14 Si 14 O 28 ] 14– silsesquioxane ligand and a Cu II 5 Cs I 4 nuclearity in which the metal cations occupy unusual positions within the cluster. Copper ions are “wrapped” into a silsesquioxane matrix, while cesium ions are located in external positions. This resulted in cesium-involved aggregation of coordination polymer structures. Both compounds 1 and 2 realize specific metallocene (cesium–phenyl) linkage between neighboring cages. Compound 2 is evaluated as a catalyst in the Baeyer–Villiger (B-V) oxidation of cyclohexanone and tandem cyclohexane oxidation/B-V oxidation of cyclohexanone with m -chloroperoxybenzoic acid (mCPBA) as an oxidant, in an aqueous acetonitrile medium, and HNO 3 as the promoter. A quantitative yield of ε-caprolactone was achieved under conventional heating at 50 °C for 4 h or MW irradiation for 30 min (for cyclohexanone as substrate); 17 and 19% yields of lactone upon MW irradiation at 80 °C for 30 min and heating at 50 °C for 4 h, respectively (for cyclohexane as a substrate), were achieved. Complex 2 was evaluated as a catalyst for the oxidation of alkanes to alkyl hydroperoxides and alcohols to ketones with peroxides at 60 °C in acetonitrile. The maximum yield of cyclohexane oxidation products was 30%. Complex 2 exhibits high activity in the oxidation of alcohols.