The Role of Protons in Cyclohexene Oxidation with H2O2 Catalysed by Ti(IV)-Monosubstituted Keggin Polyoxometalate Научная публикация
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Journal of Molecular Catalysis A: Chemical
ISSN: 1381-1169 |
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| Вых. Данные | Год: 2005, Том: 232, Номер: 1-2, Страницы: 173-178 Страниц : 6 DOI: 10.1016/j.molcata.2005.01.036 | ||
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Реферат:
The effect of the number of protons in the Ti(IV)-monosubstituted Keggin polyoxometalate Na5 − nHnPTiW11O40 (n = 1–5; Ti-POM) on its catalytic behaviour in cyclohexene (CyH) oxidation with aqueous H2O2 in MeCN is reported. It has been found that Ti-POMs with n = 2–5 catalyse efficiently CyH oxidation to yield trans-cyclohexane-1,2-diol as the main reaction product, while Ti-POM containing only one proton shows lower activity in CyH oxidation and produces allylic oxidation products, 2-cyclohexene-1-ol and 2-cyclohexene-1-one, along with comparable amounts of the corresponding epoxide and diol. The obtained results strongly support homolytic oxidation mechanism for CyH oxidation in the presence of the monoprotonated Ti-POM and heterolytic oxygen-transfer mechanism in the presence of Ti-POMs having two and more protons. The 31P and 183W NMR studies revealed that Ti-POMs are stable towards at least 100-fold excess of H2O2 and the high catalytic activity of Ti-POMs with n = 2–5 is not due to the formation of lower nuclearity species. The addition of one equivalent of H+ to the monoprotonated peroxo complex [Bu4N]4[HPTi(O2)W11O39] (I, 31P NMR in MeCN: −12.40 ppm) results in the formation of the diprotonated titanium peroxo species [H2PTi(O2)W11O39]3− (II, 31P NMR in MeCN: −12.14 ppm). This peroxo species can also be obtained by adding an excess of H2O2 to Na5 − nHnPTiW11O40 (n = 2–5) in MeCN. The presence of the second proton in the peroxo species is a crucial factor determining the capability of II to oxidise alkenes via heterolytic oxygen transfer mechanism. Both 31P NMR and GC–MS studies corroborated that II reacts with CyH producing trans-cyclohexane-1,2-diol as the main reaction product, whereas I is not reactive towards CyH under stoichiometric conditions.
Библиографическая ссылка:
Kholdeeva O.A.
, Trubitsina T.A.
, Timofeeva M.N.
, Maksimov G.M.
, Maksimovskaya R.I.
, Rogov V.A.
The Role of Protons in Cyclohexene Oxidation with H2O2 Catalysed by Ti(IV)-Monosubstituted Keggin Polyoxometalate
Journal of Molecular Catalysis A: Chemical. 2005. V.232. N1-2. P.173-178. DOI: 10.1016/j.molcata.2005.01.036 WOS Scopus РИНЦ CAPlusCA OpenAlex Sciact
The Role of Protons in Cyclohexene Oxidation with H2O2 Catalysed by Ti(IV)-Monosubstituted Keggin Polyoxometalate
Journal of Molecular Catalysis A: Chemical. 2005. V.232. N1-2. P.173-178. DOI: 10.1016/j.molcata.2005.01.036 WOS Scopus РИНЦ CAPlusCA OpenAlex Sciact
Даты:
| Поступила в редакцию: | 16 сент. 2004 г. |
| Принята к публикации: | 26 янв. 2005 г. |
| Опубликована online: | 2 мар. 2005 г. |
| Опубликована в печати: | 3 мая 2005 г. |
Идентификаторы БД:
| Web of science: | WOS:000228203100025 |
| Scopus: | 2-s2.0-15344339462 |
| РИНЦ: | 13497081 |
| Chemical Abstracts: | 2005:240079 |
| Chemical Abstracts (print): | 143:285951 |
| OpenAlex: | W1970492630 |
| Sciact: | 7169 |