Mechanistic Insights into Alkene Epoxidation with HO by Ti- and other TM-Containing Polyoxometalates: Role of the Metal Nature and Coordination Environment.
The oxidation of alkenes by HO catalyzed by Ti(IV)-containing polyoxometalates (POMs) as models of Ti single-site catalysts has been investigated at DFT level and has been compared with other early transition-metal-substituted polyoxometalates. We have studied in detail the reaction mechanism of the...
| Publicado en: | Journal of the American Chemical Society Vol. 132; no. 21; pp. 7488 - 7498 |
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| Autores principales: | , , , , |
| Formato: | Artículo |
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American Chemical Society
6/2/2010
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| Materias: | |
| Acceso en línea: | Ver este registro en EBSCOhost |
| fields | @attributes: recordID: 1 pdfLink: plink: https://search.ebscohost.com/login.aspx?direct=true&db=hlh&AN=51251165&site=ehost-live header: @attributes: shortDbName: hlh uiTerm: 51251165 longDbName: Humanities International Complete uiTag: AN controlInfo: bkinfo: jinfo: jid: 00027863 ACS jtl: Journal of the American Chemical Society issn: 00027863 maglogo: N pubinfo: dt: 6/2/2010 vid: 132 iid: 21 pid: 997 pub: American Chemical Society artinfo: ui: 51251165 10.1021/ja1023157 ppf: 7488 ppct: 10 formats: tig: atl: Mechanistic Insights into Alkene Epoxidation with HO by Ti- and other TM-Containing Polyoxometalates: Role of the Metal Nature and Coordination Environment. aug: au: Antonova, Nadya S. Carbó, Jorge J. Kortz, Ulrich KhoIdeeva, Oxana A. Poblet, Josep M. affil: Department de Química Física i Inorgànica, Universitat Rovira i Vigili, Marcel 11 Domingo s/n, 43007 Tarragona, Spain School of Engineering and Science, Jacobs University, P.O. Box 750561, 28725 Bremen, Germany Boreskov Institute of Catalysis, Russian Academy of Sciences, Lavrentiev Avenue 5, Novorsibirsk 630090, Russia su: Alkenes Polyoxometalates Catalysts Titanium Oxidation-reduction reaction Epoxy compounds sug: subj: Alkenes Polyoxometalates Catalysts Titanium Oxidation-reduction reaction Epoxy compounds ab: The oxidation of alkenes by HO catalyzed by Ti(IV)-containing polyoxometalates (POMs) as models of Ti single-site catalysts has been investigated at DFT level and has been compared with other early transition-metal-substituted polyoxometalates. We have studied in detail the reaction mechanism of the CH epoxidation with HO mediated by two different POMs, the Ti-monosubstituted Keggin-type POM [PTi(OH)WO] and the Ti-disubstituted sandwich-type POM [Ti(OH)AsWO(HO)]. These species exhibit well-defined 6and 5-coordinated titanium environments. For both species, the reaction proceeds through a two-step mechanism: (i) the Ti-OH groups activate HO with a moderate energy barrier yielding either Ti-hydroperoxo (Ti-OOH) or Ti-peroxo (Ti-OO) intermediate, and (ii) the less stable but more reactive Ti-hydroperoxo species transfers oxygen to alkene to form the epoxide, this latter step being the ratedetermining step. The higher activity of the sandwich anion was attributed to the absence of dimer formation, and its higher selectivity to the larger energy cost of homolytic O-O bond breaking in the hydroperoxo intermediate. We also propose several requisites to improve the efficiency of Ti-containing catalysts, including flexible and 5-fold (or lower) coordinated Ti environments, as well as reagent-accessible Ti sites. Calculations on other TM-containing Keggin-type POMs [PTM(OH)WO] (TM = Zr(IV), V(V), Nb(V), Mo(Vl), W(Vl), and Re(Vll)) showed that when we move from the left to the right in the periodic table the formation of the epoxide via peroxo intermediate becomes competitive because of the higher mixing between the orbitals of the TM and the O-O unit. pubtype: Academic Journal doctype: Article src: R language: English refInfo: copyright: @attributes: flag: Y dt: @attributes: year: 2010 holdings: @attributes: islocal: N |
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