Relevance of Protons in Heterolytic Activation of H2O2 over Nb(V): Insights from Model Studies on Nb-Substituted Polyoxometalates
| Autor: | Oxana A. Kholdeeva, Irina D. Ivanchikova, Jorge J. Carbó, Josep M. Poblet, Nataliya V. Maksimchuk, Albert Solé-Daura, Vasilii Yu. Evtushok, Yuriy A. Chesalov, Raisa I. Maksimovskaya, Gennadii M. Maksimov |
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| Rok vydání: | 2018 |
| Předmět: |
chemistry.chemical_classification
010405 organic chemistry Ligand Alkene Dimer Protonation General Chemistry Nuclear magnetic resonance spectroscopy 010402 general chemistry 01 natural sciences Heterolysis Catalysis 0104 chemical sciences chemistry.chemical_compound Monomer chemistry Polymer chemistry |
| Zdroj: | ACS Catalysis. 8:9722-9737 |
| ISSN: | 2155-5435 |
| DOI: | 10.1021/acscatal.8b02761 |
| Popis: | Nb-monosubstituted Lindqvist-type polyoxometalates (POM), (Bu4N)4[(NbW5O18)2O] (1) and (Bu4N)3[Nb(O)W5O18] (2), catalyze epoxidation of alkenes with hydrogen peroxide and mimic the catalytic performance of heterogeneous Nb-silicate catalysts. Dimer 1 is more active than monomer 2, but the catalytic activity of the latter increases in the presence of acid. Kinetic and spectroscopic studies suggest a mechanism that involves generation of monomer (Bu4N)2[Nb(OH)W5O18] (3), interaction of 3 with H2O2 leading to a protonated peroxo niobium species, (Bu4N)2[HNb(O2)W5O18] (4), followed by oxygen transfer to a C═C bond in alkene. The previously unknown peroxo complex 4 has been isolated and characterized by elemental analysis; UV–vis, FT-IR, Raman, 93Nb, 17O and 183W NMR spectroscopy; cyclic voltammetry; and potentiometric titration. The physicochemical techniques support a monomeric Lindqvist structure of 4 bearing one peroxo ligand attached to Nb(V) in a η2-coordination mode. While the unprotonated peroxo comple... |
| Databáze: | OpenAIRE |
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