Author, as appears in the article.: Maksimchuk, Nataliya V.; Evtushok, Vasilii Yu.; Zalomaeva, Olga V.; Maksimov, Gennadii M.; Ivanchikova, Irina D.; Chesalov, Yuriy A.; Eltsov, Ilia V.; Abramov, Pavel A.; Glazneva, Tatyana S.; Yanshole, Vadim V.; Kholdeeva, Oxana A.; Errington, R. John; Sole-Daura, Albert; Poblet, Josep M.; Carbo, Jorge J.;
Department: Química Física i Inorgànica
URV's Author/s: Carbó Martin, Jorge Juan / Poblet Rius, Josep Maria / Solé Daura, Albert
Keywords: Zirconium compounds Zirconium Utilization efficiency Unsaturated ketones Unsaturated compounds Unfunctionalized alkenes Tungsten compounds Titanium compounds Thioether oxidation Thianthrene 5-oxide Substrates Silanol-functionalized polyoxotungstates Selective epoxidation Reactivity studies Reaction intermediates Rate determining step Product distributions Polyoxometalates Oxygen Oxidation Olefins Nuclear magnetic resonance spectroscopy Niobium compounds Metal-organic framework Mesoporous niobium-silicates Mechanistic probe Lindqvist tungstate Ketones Hydrogen-peroxide Hydrogen peroxide activation Hydrogen peroxide Free energy Fourier transform infrared spectroscopy Epoxidation Dimers Dft Coordination environment Chemical activation Catalytic-properties Catalysts Atomic emission spectroscopy Alkene epoxidation Additives
Abstract: Zr-monosubstituted Lindqvist- type polyoxometalates (Zr-POMs), (Bu4N)(2)[W5O18Zr(H2O)(3)] (1) and (Bu4N)(6)[{W5O18Zr(mu-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 alpha,beta-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 O-17-enriched dimer, (Bu4N)(6)[{W5O18Zr(mu-OCH3)}2] (2'), and H2O2 was also analyzed by O-17 NMR spectroscopy. Combining these experimental studies with DFT calculations suggested the existence of dimeric peroxo species [(mu-eta(2):eta(2)-O-2){ZrW5O18}(2)](6-) as well as monomeric Zr-hydroperoxo [W5O18Zr(eta(2)-OOH)](3-) and Zr-peroxo [HW5O18Zr(eta(2)-O-2)](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 alpha-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.
Thematic Areas: Química Materiais Interdisciplinar General chemistry Engenharias ii Ciências agrárias i Chemistry, physical Chemistry (miscellaneous) Chemistry (all) Catalysis Astronomia / física
licence for use: https://creativecommons.org/licenses/by/3.0/es/
Author's mail: josepmaria.poblet@urv.cat j.carbo@urv.cat
Author identifier: 0000-0002-4533-0623 0000-0002-3945-6721
Record's date: 2024-07-27
Papper version: info:eu-repo/semantics/acceptedVersion
Licence document URL: https://repositori.urv.cat/ca/proteccio-de-dades/
Papper original source: Acs Catalysis. 11 (16): 10589-10603
APA: Maksimchuk, Nataliya V.; Evtushok, Vasilii Yu.; Zalomaeva, Olga V.; Maksimov, Gennadii M.; Ivanchikova, Irina D.; Chesalov, Yuriy A.; Eltsov, Ilia V.; (2021). Activation of H2O2 over Zr(IV). Insights from Model Studies on Zr-Monosubstituted Lindqvist Tungstates. Acs Catalysis, 11(16), 10589-10603. DOI: 10.1021/acscatal.1c02485
Entity: Universitat Rovira i Virgili
Journal publication year: 2021
Publication Type: Journal Publications
Repositori URV