Cage-like Cu5Cs4-Phenylsilsesquioxanes: Synthesis, Supramolecular Structures, and Catalytic Activity

Nonanuclear Cu5Cs4-based phenylsilsesquioxanesexhibit unprecedented Si-14-based cyclic silsesquioxaneligand, nontrivial nuclearity, supramolecular organization, and catalyticactivity (i) in the mild oxidative functionalization of alkanes andalcohols, (ii) in the Baeyer-Villiger oxidation of cyclohexanone,and (iii) in the tandem cyclohexane oxidation/B-V oxidation of cyclohexanone. A small family of nonanuclear Cu5Cs4-basedphenylsilsesquioxanes 1-2 were preparedby a convenient self-assembly approach and characterized by X-raydiffraction studies. The compounds 1 and 2 show some unprecedented structural features such as the presenceof a [Ph14Si14O28](14-) silsesquioxane ligand and a Cu-II Cs-5(I) (4) nuclearity in which the metal cations occupy unusualpositions within the cluster. Copper ions are "wrapped"into a silsesquioxane matrix, while cesium ions are located in externalpositions. This resulted in cesium-involved aggregation of coordinationpolymer structures. Both compounds 1 and 2 realize specific metallocene (cesium-phenyl) linkage betweenneighboring cages. Compound 2 is evaluated as a catalystin the Baeyer-Villiger (B-V) oxidation of cyclohexanone andtandem cyclohexane oxidation/B-V oxidation of cyclohexanone with m-chloroperoxybenzoic acid (mCPBA) as an oxidant, in anaqueous acetonitrile medium, and HNO3 as the promoter.A quantitative yield of & epsilon;-caprolactone was achieved under conventionalheating at 50 & DEG;C for 4 h or MW irradiation for 30 min (for cyclohexanoneas substrate); 17 and 19% yields of lactone upon MW irradiation at80 & DEG;C for 30 min and heating at 50 & DEG;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 alkylhydroperoxides and alcohols to ketones with peroxides at 60 & DEG;Cin acetonitrile. The maximum yield of cyclohexane oxidation productswas 30%. Complex 2 exhibits high activity in the oxidationof alcohols.