Effect of the Polyanion Structure on the Mechanism of Alcohol Oxidation with H2O2 Catalyzed by Zr-Substituted Polyoxotungstates

Zr-monosubstituted polyoxometalates (Zr-POMs) of the Lindqvist (Bu4N)6[{W5O18Zr­(μ-OH)}2] (1), Keggin (Bu4N)8[{PW11O39Zr­(μ-OH)}2] (2), and Wells–Dawson (Bu4N)11.3K2.5H0.2[{P2W17O61Zr}2(μ-OH)2] (3) structures catalyze oxidation of alcohols using aqueous hydrogen peroxide as an oxidant. With 1 equiv...

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Veröffentlicht in:Inorganic chemistry 2024-09, Vol.63 (39), p.18043-18057
Hauptverfasser: Maksimchuk, Nataliya V., Marikovskaya, Sofia M., Larionov, Kirill P., Evtushok, Vasilii Yu, Yanshole, Vadim V., Antonov, Artem A., Kholdeeva, Oxana A.
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Sprache:eng
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Zusammenfassung:Zr-monosubstituted polyoxometalates (Zr-POMs) of the Lindqvist (Bu4N)6[{W5O18Zr­(μ-OH)}2] (1), Keggin (Bu4N)8[{PW11O39Zr­(μ-OH)}2] (2), and Wells–Dawson (Bu4N)11.3K2.5H0.2[{P2W17O61Zr}2(μ-OH)2] (3) structures catalyze oxidation of alcohols using aqueous hydrogen peroxide as an oxidant. With 1 equiv of H2O2 and 1 mol % of Zr-POM, selectivity toward aldehydes and ketones varied from good to excellent, depending on the alcohol nature. Catalytic activity and attainable substrate conversions strongly depended on the Zr-POM structure and most often decreased in the order 1 > 2 ≫ 3. The reaction mechanism was probed using a test substrate, cyclobutanol, radical and 1O2 scavengers, and kinetic and spectroscopic (attenuated total reflectance-Fourier transform infrared (ATR-FT-IR), 31P NMR and electrospray ionization-mass spectrometry (ESI-MS)) tools. The results point to heterolytic alcohol oxidation in the presence of 1 and 2 and homolytic alcohol oxidation in the presence of 3. Kinetic and spectroscopic studies implicated an oxidation mechanism that involves both alcohol and peroxide binding to 2 followed by an inner-sphere heterolytic H-abstraction from the α–C-H bond by the Zr-hydroperoxo group, leading to a carbonyl compound. The unique capability of 1 to generate 1O2 upon interaction with H2O2 complicates the reaction kinetics and improves the product yield. Spectroscopic studies coupled with stoichiometric experiments unveiled that dimeric monoperoxo {Zr2(μ-η2:η2-O2)} and monomeric hydroperoxo {Zr­(η2-OOH)} species accomplish the transformation of alcohols to carbonyl compounds.
ISSN:0020-1669
1520-510X
1520-510X
DOI:10.1021/acs.inorgchem.4c02641