Structural Assessment and Catalytic Consequences of the Oxygen Coordination Environment in Grafted Ti—Calixarenes.
Calixarene-Ti complexes were grafted onto SiO (0.18-0.24 Ti nm) to form isolated and accessible Ti centers persistently coordinated to multidentate calixarene ligands. Grafted Ti-tert-butylcalix-[4]arenes gave Ti K-edge absorption spectra with pre-edge features at 4968.6-4968.9 eV, independently of...
| Publicado en: | Journal of the American Chemical Society Vol. 129; no. 5; pp. 1122 - 1132 |
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| Autores principales: | , , , , , |
| Formato: | Artículo |
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American Chemical Society
2/7/2007
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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=23995691&site=ehost-live header: @attributes: shortDbName: hlh uiTerm: 23995691 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: 2/7/2007 vid: 129 iid: 5 pid: 997 pub: American Chemical Society artinfo: ui: 23995691 10.1021/ja065830c ppf: 1122 ppct: 10 formats: tig: atl: Structural Assessment and Catalytic Consequences of the Oxygen Coordination Environment in Grafted Ti—Calixarenes. aug: au: Notestein, Justin M. Andrini, Leandro R. Kalchenko, Vitaly I. Requejo, Felix G. Katz, Alexander Iglesia, Enrique affil: Department of Chemical Engineering, University of California at Berkeley, Berkeley, California 94720 Departamento de Física, Facultad de Ciencias Exactas, Universidad Nacional de La Plata and IFLP-INIFTA (CONIGET), 1900 La Plata, Argentina Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanskaya Str., 5, 02094, Kyiv-94, Ukraine su: Calixarenes Coordination compounds Complex compounds Catalysis Chemistry sug: subj: Calixarenes Coordination compounds Complex compounds Catalysis Chemistry ab: Calixarene-Ti complexes were grafted onto SiO (0.18-0.24 Ti nm) to form isolated and accessible Ti centers persistently coordinated to multidentate calixarene ligands. Grafted Ti-tert-butylcalix-[4]arenes gave Ti K-edge absorption spectra with pre-edge features at 4968.6-4968.9 eV, independently of Ti surface density and of their use in epoxidation catalysis. The structure and reactivity of grafted Ti-calix[4]arenes were weakly dependent on thermal treatment below 573 K, and the relative epoxidation rates of trans- and cis-alkenes showed that calixarene ligands did not restrict access to Ti centers more than corresponding calcined Ti-SiO materials. For all materials, C NMR and UV-visible spectroscopies confirmed the presence of Ti-O-Si connectivity and identical ligand-to-metal transitions. Grafted Ti-homooxacalix[3]arene complexes, however, gave weaker pre-edge features at higher energies (~4969.5 eV), consistent with greater Ti 3d occupancy and coordination numbers greater than four, and 20-fold lower cyclohexene epoxidation rate constants (per Ti) than on calix[4]arene-based materials. These different rates and near-edge spectra result from aldehyde formation caused by unimolecular cleavage of ether linkages in homooxacalix[3]arene ligands during grafting, leading to higher coordination and electron density at Ti centers. Materials based on tert-butylcalix[4]arene and homooxacalix[3]arenes led to similar epoxidation rates and near-edge spectra after calcination, consistent with the conversion of both materials to isolated Ti centers with identical structure. These materials provide a systematic approach for relating oxidation reactivity to Ti 3d occupancy, a descriptor of Lewis acid strength, and Ti coordination, because they provide Ti centers with varying electron density and coordination, but maintain accessible active centers with uniform structure and unrestricted access to reactants. pubtype: Academic Journal doctype: Article src: R language: English refInfo: copyright: @attributes: flag: Y dt: @attributes: year: 2007 holdings: @attributes: islocal: N |
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