Research output: Contribution to journal › Article › peer-review
Activation of H2O2over Zr(IV). Insights from Model Studies on Zr-Monosubstituted Lindqvist Tungstates. / Maksimchuk, Nataliya V.; Evtushok, Vasilii Yu; Zalomaeva, Olga V. et al.
In: ACS Catalysis, Vol. 11, No. 16, 20.08.2021, p. 10589-10603.Research output: Contribution to journal › Article › peer-review
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TY - JOUR
T1 - Activation of H2O2over Zr(IV). Insights from Model Studies on Zr-Monosubstituted Lindqvist Tungstates
AU - Maksimchuk, Nataliya V.
AU - Evtushok, Vasilii Yu
AU - Zalomaeva, Olga V.
AU - Maksimov, Gennadii M.
AU - Ivanchikova, Irina D.
AU - Chesalov, Yuriy A.
AU - Eltsov, Ilia V.
AU - Abramov, Pavel A.
AU - Glazneva, Tatyana S.
AU - Yanshole, Vadim V.
AU - Kholdeeva, Oxana A.
AU - Errington, R. John
AU - Solé-Daura, Albert
AU - Poblet, Josep M.
AU - Carbó, Jorge J.
N1 - Publisher Copyright: ©
PY - 2021/8/20
Y1 - 2021/8/20
N2 - Zr-monosubstituted Lindqvist-type polyoxometalates (Zr-POMs), (Bu4N)2[W5O18Zr(H2O)3] (1) and (Bu4N)6[{W5O18Zr(μ-OH)}2] (2), have been employed as molecular models to unravel the mechanism of hydrogen peroxide activation over Zr(IV) sites. Compounds 1 and 2 are hydrolytically stable and catalyze the epoxidation of C?C bonds in unfunctionalized alkenes and α,β-unsaturated ketones, as well as sulfoxidation of thioethers. Monomer 1 is more active than dimer 2. Acid additives greatly accelerate the oxygenation reactions and increase oxidant utilization efficiency up to >99%. Product distributions are indicative of a heterolytic oxygen transfer mechanism that involves electrophilic oxidizing species formed upon the interaction of Zr-POM and H2O2. The interaction of 1 and 2 with H2O2 and the resulting peroxo derivatives have been investigated by UV-vis, FTIR, Raman spectroscopy, HR-ESI-MS, and combined HPLC-ICP-atomic emission spectroscopy techniques. The interaction between an 17O-enriched dimer, (Bu4N)6[{W5O18Zr(μ-OCH3)}2] (2′), and H2O2 was also analyzed by 17O NMR spectroscopy. Combining these experimental studies with DFT calculations suggested the existence of dimeric peroxo species [(μ-?2:?2-O2){ZrW5O18}2]6- as well as monomeric Zr-hydroperoxo [W5O18Zr(?2-OOH)]3- and Zr-peroxo [HW5O18Zr(?2-O2)]3- species. Reactivity studies revealed that the dimeric peroxo is inert toward alkenes but is able to transfer oxygen atoms to thioethers, while the monomeric peroxo intermediate is capable of epoxidizing C?C bonds. DFT analysis of the reaction mechanism identifies the monomeric Zr-hydroperoxo intermediate as the real epoxidizing species and the corresponding α-oxygen transfer to the substrate as the rate-determining step. The calculations also showed that protonation of Zr-POM significantly reduces the free-energy barrier of the key oxygen-transfer step because of the greater electrophilicity of the catalyst and that dimeric species hampers the approach of alkene substrates due to steric repulsions reducing its reactivity. The improved performance of the Zr(IV) catalyst relative to Ti(IV) and Nb(V) catalysts is respectively due to a flexible coordination environment and a low tendency to form energy deep-well and low-reactive Zr-peroxo intermediates.
AB - Zr-monosubstituted Lindqvist-type polyoxometalates (Zr-POMs), (Bu4N)2[W5O18Zr(H2O)3] (1) and (Bu4N)6[{W5O18Zr(μ-OH)}2] (2), have been employed as molecular models to unravel the mechanism of hydrogen peroxide activation over Zr(IV) sites. Compounds 1 and 2 are hydrolytically stable and catalyze the epoxidation of C?C bonds in unfunctionalized alkenes and α,β-unsaturated ketones, as well as sulfoxidation of thioethers. Monomer 1 is more active than dimer 2. Acid additives greatly accelerate the oxygenation reactions and increase oxidant utilization efficiency up to >99%. Product distributions are indicative of a heterolytic oxygen transfer mechanism that involves electrophilic oxidizing species formed upon the interaction of Zr-POM and H2O2. The interaction of 1 and 2 with H2O2 and the resulting peroxo derivatives have been investigated by UV-vis, FTIR, Raman spectroscopy, HR-ESI-MS, and combined HPLC-ICP-atomic emission spectroscopy techniques. The interaction between an 17O-enriched dimer, (Bu4N)6[{W5O18Zr(μ-OCH3)}2] (2′), and H2O2 was also analyzed by 17O NMR spectroscopy. Combining these experimental studies with DFT calculations suggested the existence of dimeric peroxo species [(μ-?2:?2-O2){ZrW5O18}2]6- as well as monomeric Zr-hydroperoxo [W5O18Zr(?2-OOH)]3- and Zr-peroxo [HW5O18Zr(?2-O2)]3- species. Reactivity studies revealed that the dimeric peroxo is inert toward alkenes but is able to transfer oxygen atoms to thioethers, while the monomeric peroxo intermediate is capable of epoxidizing C?C bonds. DFT analysis of the reaction mechanism identifies the monomeric Zr-hydroperoxo intermediate as the real epoxidizing species and the corresponding α-oxygen transfer to the substrate as the rate-determining step. The calculations also showed that protonation of Zr-POM significantly reduces the free-energy barrier of the key oxygen-transfer step because of the greater electrophilicity of the catalyst and that dimeric species hampers the approach of alkene substrates due to steric repulsions reducing its reactivity. The improved performance of the Zr(IV) catalyst relative to Ti(IV) and Nb(V) catalysts is respectively due to a flexible coordination environment and a low tendency to form energy deep-well and low-reactive Zr-peroxo intermediates.
KW - DFT
KW - epoxidation
KW - hydrogen peroxide
KW - Lindqvist tungstate
KW - zirconium
UR - http://www.scopus.com/inward/record.url?scp=85113845356&partnerID=8YFLogxK
U2 - 10.1021/acscatal.1c02485
DO - 10.1021/acscatal.1c02485
M3 - Article
AN - SCOPUS:85113845356
VL - 11
SP - 10589
EP - 10603
JO - ACS Catalysis
JF - ACS Catalysis
SN - 2155-5435
IS - 16
ER -
ID: 34107649