Structure and properties of tungsten peroxopolyoxo complexes – promising catalysts for organics oxidation. II: Cation type influence on the tungsten peroxocomplex structure

Catalysis via metal complexes has been studied using EXAFS and Raman spectroscopy. EXAFS studies have shown that in tungsten peroxocomplexes containing quaternary ammonium organic cation substitution affects the structure of anion {PO4[WO(O2)2]4}3−. The last complex in series [Bun4N]3{PO4[WO(O2)2]4}, [C5H5NCet]3{PO4[WO(O2)2]4} and [Et2Bn2N]3{PO4[WO(O2)2]4} demonstrates the most evident structure alteration. Vibration spectroscopy proves that structure conversion is related to the strength reduction of end double bond WO. As a result, antibate WO bond strength increases. That effect also changes the strength of tungsten bonding to cations. Synthesized catalytic complexes [Bun4N]3{PO4[WO(O2)2]4} and [C5H5NCet]3{PO4[WO(O2)2]4} were tested in peucedanin oxidation by hydrogen peroxide. Oxidative catalytic transformation of above mentioned coumarin was shown to yield 2-hydorxyoreozelon, which is a bioactive compound used in medicine. Complex with cetylpyridinium cation appears to be the most active in this reaction.

Catalysis via metal complexes has been studied using EXAFS and Raman spectroscopy. EXAFS studies have shown that in tungsten peroxocomplexes containing quaternary ammonium organic cation ([Bun4N]+, [C5H5NCet]+ and [Et2Bn2N]+) substitution affects the structure of anion {PO4[WO(O2)2]4}3−. Synthesized catalytic complexes [Bun4N]3{PO4[WO(O2)2]4} and [C5H5NCet]3{PO4[WO(O2)2]4} were tested in peucedanin oxidation by hydrogen peroxide.Figure optionsDownload high-quality image (127 K)Download as PowerPoint slideHighlights
► EXAFS study shows peroxocomplexes anion structure dependency on organic cation origin.
► Vibration spectroscopy shows relation of structure conversion to WO bond strength changing.
► WO bond strength increases and so does the strength of tungsten bonding to cation.
► [C5H5NCet]3{PO4[WO(O2)2]4} selectively catalyses peucedanin oxidation with 100% conversion.