The Role of Protons in Cyclohexene Oxidation with H2O2 Catalysed by Ti(IV)-Monosubstituted Keggin Polyoxometalate Full article
Journal |
Journal of Molecular Catalysis A: Chemical
ISSN: 1381-1169 |
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Output data | Year: 2005, Volume: 232, Number: 1-2, Pages: 173-178 Pages count : 6 DOI: 10.1016/j.molcata.2005.01.036 | ||
Tags | Cyclohexene, H2O2, Oxidation mechanism, Peroxotitanium species, Ti-substituted polyoxometalate | ||
Authors |
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Affiliations |
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Funding (1)
1 | Russian Foundation for Basic Research | 04-03-32113 |
Abstract:
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.
Cite:
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
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
Dates:
Submitted: | Sep 16, 2004 |
Accepted: | Jan 26, 2005 |
Published online: | Mar 2, 2005 |
Published print: | May 3, 2005 |
Identifiers:
Web of science | WOS:000228203100025 |
Scopus | 2-s2.0-15344339462 |
Elibrary | 13497081 |
Chemical Abstracts | 2005:240079 |
Chemical Abstracts (print) | 143:285951 |
OpenAlex | W1970492630 |