Tuning the Activity of a Hybrid Polymer–Oxocluster Catalyst: A Composition—Selectivity Correlation

Abstract

Zr-based oxoclusters MxOy(OR)w(OOR’)z are promising catalysts for the activation of hydrogen peroxide. However, they need to be integrated into suitable matrices to increase their hydrolytic stability and allow for their recovery after use. Polymeric materials can be successfully employed for this aim, since they modify the properties of the resulting hybrid materials, in terms of polarity and chemical affinity for the substrates, improving the catalytic activity. Herein, we report the synthesis of different acrylic polymers based on various co-monomers (methyl methacrylate (MMA), 2,2,2-trifluoroethylmethacrylate (TFMA) and 3-methacryloxypropyltrimethoxylsilane (MAPTMS)) covalently cross-linked by a Zr4-based oxocluster, whose composition was tuned to optimise the catalytic oxidation of methyl p-tolyl sulphide. To assess their properties and stability, the materials were characterised via Fourier Transform Infrared (FT-IR) and Raman spectroscopies, Thermogravimetric Analysis (TGA), Solid-State NMR (SS-NMR) and X-Ray Absorption Spectroscopies XAS, before and after catalytic turnover.

Nonaqueous Chemistry of Group 4 Oxo Clusters and Colloidal Metal Oxide Nanocrystals

“…The Zr4 cluster has a more open structure, and one zirconium atom is even only seen-coordinate. Zr4 –methacrylate has two isomers in the solid state, a symmetric and an asymmetric one. , In the Raman spectrum, the Zr–O–Zr modes appear at 190 and 250 cm –1 for Zr6 –methacrylate and at 230 cm –1 for Zr4 –methacrylate. , …”

“…This is a model reaction for the oxidative desulfurization of fuels. Improved performance was achieved using Zr4 –methacrylate clusters and incorporating polymer composites. ,, On the other hand, Hf 18 O 10 (OH) 26 (SO 4 ) 13 ·(H 2 O) 33 clusters were used as heterogeneous catalysts for the selective hydrolysis of proteins . Recently, the discrete Zr12 -acrylate cluster has been used as air and moisture stable molecular catalyst for the formation of amide bonds .…”

“…136,137 In the Raman spectrum, the Zr−O−Zr modes appear at 190 and 250 cm −1 for Zr6−methacrylate and at 230 cm −1 for Zr4−methacrylate. 113,138 While the Zr4 cluster has only been obtained under specific circumstances with methacrylic acid, the Zr6 cluster core appears to be a more universal structural motif. 139 Slight variations were obtained with methacrylic, isobutyric, and benzoic acids, where one bridging ligand (opposite the chelating face) becomes monodentate and a propanol (or water) molecule fills the empty coordination site, e.g, Zr 6 O 4 (OH) 4 (OOCR) 12 (PrOH)•3RCOOH.…”