Encapsulation of Polyoxotungstate into Dendrimers by Ionic Bonding and Their Use As Oxidation Catalyst

Abstract

AbstractA family of 36‐armed dendrimers containing six internal amino groups was synthesized and used to incorporate polyoxometalates (POMs) into their structures by ionic bonding. Allyl‐terminated dendrimer 17 (with oxidizable end groups) and methylphenyl‐terminated dendrimer 18 (with non‐oxidizable end groups) were used for these studies. It was found that the electrostatic incorporation of the tri‐anionic POM [PO4{WO(O2)2}4]3− into the methylphenyl‐terminated dendrimer 18, in an acidic medium, leads to the dendritic POM hybrid 19, bearing two POM units in its structure. In contrast, attempts to encapsulate POMs into allyl‐terminated dendrimer 17 gave unsatisfactory results. Indeed, the epoxidation kinetics of the 36‐olefinic terminated dendrimer 17 was too slow, and the expected 36‐epoxy‐dendritic POM framework 20 was not obtained. Lengthening the reaction up to six hours led to the decomposition of POM species. The solubility in organic solvents of the dendritic POM hybrid 19, combined with its NMR and infrared data, indicate that POM units are clearly connected to the dendritic structure. The catalytic performance of this hybrid material in the oxidation of cyclooctene shows that the properties of POM are retained. The POM‐encapsulated dendrimer 19 was found to be an effective catalyst in the oxidation of cyclooctene.