Mechanistic Insights into H2O2 Activation over Nb(V) Using Nb-Substituted Lindqvist Tungstates Тезисы доклада
Конференция |
43rd International Conference on Coordination Chemistry 30 июл. - 4 авг. 2018 , Sendai |
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Сборник | 43rd International Conference on Coordination Chemistry (ICCC2018) Сборник, 2018. |
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Вых. Данные | Год: 2018, Номер статьи : S30-2I-A01545-OK, Страниц : 1 | ||||||
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Организации |
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Реферат:
In recent years, Nb-containing single-site catalysts have attracted significant attention. Nb-substituted
tungstates of the Lindqvist structure, (Bu4N)4[(NbW5O18)2O) (1) and (Bu4N)3[NbW5O19] (2), mimic well the catalytic performance of heterogeneous Nb-catalysts in H2O2-based oxidations and have been used as tractable molecular models to gain insights into the structure and reactivity of active Nb(V) species using various
spectroscopic (UV-vis, IR, Raman, 17O, 93Nb and 183W NMR) and computational techniques. While dimer 1 possesses high catalytic activity in alkene epoxidation, monomer 2 reveals a similar catalytic performance only in the presence of acid additives.
The product selectivity and reaction kinetics are consistent with a mechanism that involves hydrolysis of 1 to produce (Bu4N)2[Nb(OH)W5O18] (3), interaction of 3 with H2O2 leading tothe formation of a protonated niobium peroxo complex, (Bu4N)2[HNb(O2)W5O18] (4), followed by oxygen transfer from 4 to a C=C bond in alkene. The protonated peroxo complex 4 has been synthesized via interaction of 1 with an excess of 30% aqueous H2O2
in CH3CN and characterized by using elemental analysis, UV-vis, FT-IR, Raman, 93Nb, 17O and 183W NMR spectroscopy, potentiometric titration, cyclic voltammetry, and DFT calculations. A compilation of all the techniques supports a monomeric Lindqvist type structure of 4 bearing one peroxo ligand attached to Nb(V) in a η2-coordination mode. 4 readily reacts with cyclohexene at 50 °C in CH3CN to give cyclohexene epoxide and 1,2-
trans-cyclohexane diol in a nearly quantitative yield, indicating a heterolytic oxidation mechanism. The IR, Raman, UV-vis, and 17O NMR experiments along with theoretical calculations carried out at the DFT level showed that the activating proton in 4 is presumably localized at a Nb–O–W bridging oxygen rather than at the peroxo group. However, DFT calculations revealed that a hydroperoxo niobium species ‘NbOOH’ has a lower activation barrier of oxygen transfer to alkene relative to the peroxo species ‘HNb(O2)’.
Библиографическая ссылка:
Kholdeeva O.A.
, Maksimchuk N.V.
, Maksimov G.M.
, Evtushok V.Y.
, Ivanchikova I.D.
, Zalomaeva O.V.
, Carbó J.J.
, Pobletc J.M.
Mechanistic Insights into H2O2 Activation over Nb(V) Using Nb-Substituted Lindqvist Tungstates
В сборнике 43rd International Conference on Coordination Chemistry (ICCC2018). 2018.
Mechanistic Insights into H2O2 Activation over Nb(V) Using Nb-Substituted Lindqvist Tungstates
В сборнике 43rd International Conference on Coordination Chemistry (ICCC2018). 2018.
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