Hydrolytic Stability and Hydrogen Peroxide Activation of Zirconium-Based Oxoclusters

The hydrolytic stability of [Zr-6(OH)(4)O-4{O(O)CC(CH3)=CH2}(12)] (Zr-6), and [Zr6O4(OH)(4){O(O)CCH2CH=CH2}(12)](2)6[CH2=CHCH2C(O)OH] (Zr-12) oxoclusters in different environments was thoroughly investigated by FTIR, Raman, and X-ray photoelectron spectroscopy (XPS). Specific information about the local structures around the Zr centers during the stability tests was achieved by in situ extended X-ray absorption fine structure (EXAFS) measurements, and the exact compositions were determined by inductively coupled plasma MS (ICP-MS) and elemental analysis. By this multidimensional spectroscopic approach, an overview on the structures formed after different treatments could be gained. The stability of the oxoclusters was then investigated in the presence of hydrogen peroxide, and the formation of peroxo-metal complexes was detected. Thus, a kinetic study was performed in acetonitrile to evaluate the performances of the oxoclusters as oxygen transfer catalysts. The oxidation of methyl p-tolyl sulfide to the corresponding sulfoxide and sulfone was chosen as a model reaction; in some cases, an interesting selectivity towards the formation of the sulfone was found over more than 4700 catalytic cycles.