TY - JOUR

T1 - Highly Selective Thioether Oxidation with H2O2 Catalyzed by Zr-Substituted Keggin Phosphotungstate: Mechanistic Insights

AU - Zalomaeva, Olga V.

AU - Maksimchuk, Nataliya V.

AU - Marikovskaya, Sofia M.

AU - Antonov, Artem A.

AU - Kholdeeva, Oxana A.

N1 - This work was supported by the Russian Science Foundation (grant No. 22‐23‐00410, https://rscf.ru/en/project/22‐23‐00410/ ). 1 183

PY - 2024/4/8

Y1 - 2024/4/8

N2 - The Zr-monosubstituted phosphotungstate (Bu4N)8[{PW11O39Zr(μ-OH)(H2O)}2] (1) is a highly active and selective catalyst for thioether sulfoxidation with aqueous H2O2 in acetonitrile or acetonitrile/ethanol. The reaction proceeds unprecedentedly fast and completes within seconds at room temperature. Various sulfides produce corresponding sulfoxides with selectivity of 98–99 % and oxidant utilization efficiency of 92–99 %. The reaction mechanism was investigated using test substrates, kinetic, isotopic labeling, and spectroscopic tools. The oxidation of thianthrene-5-oxide and competitive sulfide-sulfoxide oxidation point to an electrophilic oxidation mechanism, but a V-shaped Hammett plot found for oxidation of p-substituted thioanisoles may suggest a biphilic nature of active species. Kinetic studies revealed that the rate-limiting step of the reaction is the interaction of a peroxo zirconium intermediate with organic substrates. ATR-FT-IR and 31P NMR spectroscopic studies coupled with stoichiometric experiments indicated that peroxo species capable of transferring an oxygen atom to thioethers are dimeric side-on mono- and diperoxo complexes, [Zr2(μ-η2 : η2-O2){PW11O39}2(H2O)x]]8− (I) and [{Zr(μ-η2-O2)}2(PW11O39)2(H2O)y]10− (II), and monomeric Zr-hydroperoxo [Zr(η2-OOH)PW11O39]4− (III) and peroxo [Zr(η2-O2)PW11O39]5− (IV) species, which dominate at high excess of H2O2. While I and III are endowed with electrophilic oxygen, which can be transferred to electron-rich sulfides, more negatively charged II and IV preferably react with thioethers comprising electron-withdrawing substituents.

AB - The Zr-monosubstituted phosphotungstate (Bu4N)8[{PW11O39Zr(μ-OH)(H2O)}2] (1) is a highly active and selective catalyst for thioether sulfoxidation with aqueous H2O2 in acetonitrile or acetonitrile/ethanol. The reaction proceeds unprecedentedly fast and completes within seconds at room temperature. Various sulfides produce corresponding sulfoxides with selectivity of 98–99 % and oxidant utilization efficiency of 92–99 %. The reaction mechanism was investigated using test substrates, kinetic, isotopic labeling, and spectroscopic tools. The oxidation of thianthrene-5-oxide and competitive sulfide-sulfoxide oxidation point to an electrophilic oxidation mechanism, but a V-shaped Hammett plot found for oxidation of p-substituted thioanisoles may suggest a biphilic nature of active species. Kinetic studies revealed that the rate-limiting step of the reaction is the interaction of a peroxo zirconium intermediate with organic substrates. ATR-FT-IR and 31P NMR spectroscopic studies coupled with stoichiometric experiments indicated that peroxo species capable of transferring an oxygen atom to thioethers are dimeric side-on mono- and diperoxo complexes, [Zr2(μ-η2 : η2-O2){PW11O39}2(H2O)x]]8− (I) and [{Zr(μ-η2-O2)}2(PW11O39)2(H2O)y]10− (II), and monomeric Zr-hydroperoxo [Zr(η2-OOH)PW11O39]4− (III) and peroxo [Zr(η2-O2)PW11O39]5− (IV) species, which dominate at high excess of H2O2. While I and III are endowed with electrophilic oxygen, which can be transferred to electron-rich sulfides, more negatively charged II and IV preferably react with thioethers comprising electron-withdrawing substituents.

KW - Keggin phosphotungstate

KW - homogeneous catalysis

KW - hydrogen peroxide

KW - sulfoxidation

KW - zirconium

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-85180180396&origin=inward&txGid=3d2019bba6f76ab2e4ee00e0b71bf67e

UR - https://www.mendeley.com/catalogue/ef3b88bd-4cb8-3d8d-a470-e6dbe28ca73c/

U2 - 10.1002/cctc.202301374

DO - 10.1002/cctc.202301374

M3 - Article

VL - 16

JO - ChemCatChem

JF - ChemCatChem

SN - 1867-3880

IS - 7

M1 - e202301374

ER -