Effect of the Polyanion Structure on the Mechanism of Alcohol Oxidation with H2O2 Catalyzed by Zr-Substituted Polyoxotungstates.
Inorg Chem
; 63(39): 18043-18057, 2024 Sep 30.
Article
em En
| MEDLINE
| ID: mdl-39300783
ABSTRACT
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 â« 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-η2η2-O2)} and monomeric hydroperoxo {Zr(η2-OOH)} species accomplish the transformation of alcohols to carbonyl compounds.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Idioma:
En
Revista:
Inorg Chem
/
Inorg. chem
/
Inorganic chemistry
Ano de publicação:
2024
Tipo de documento:
Article
País de afiliação:
Federação Russa
País de publicação:
Estados Unidos