The Role of Outer-Sphere Surface Acidity in Alkene Epoxidation Catalyzed by Calixarene—Ti(IV) Complexes.
Cooperativity between Brønsted acidic defect sites on oxide surfaces and Lewis acid catalyst sites consisting of grafted calixarene—Ti(IV) complexes is investigated for controlling epoxidation catalysis. Materials are synthesized that, regardless of the surface or calixarene substituent, demonstrate...
| Publicado en: | Journal of the American Chemical Society Vol. 129; no. 50; pp. 15585 - 15596 |
|---|---|
| Autores principales: | , , , , , |
| Formato: | Artículo |
| Publicado: |
American Chemical Society
12/19/2007
|
| 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=28156744&site=ehost-live header: @attributes: shortDbName: hlh uiTerm: 28156744 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: 12/19/2007 vid: 129 iid: 50 pid: 997 pub: American Chemical Society artinfo: ui: 28156744 10.1021/ja074614g ppf: 15585 ppct: 11 formats: tig: atl: The Role of Outer-Sphere Surface Acidity in Alkene Epoxidation Catalyzed by Calixarene—Ti(IV) Complexes. aug: au: Notestein, Justin M. Solovyov, Andrew Andrini, Leandro R. Requejo, Felix G. Katz, Alexander Iglesia, Enrique affil: Department of Chemical Engineering, University of California, Berkeley, Berkeley, California 94720 Department of Chemical and Biological Engineering, Northwestern University, Evanston IL 60208 INIFTA e IFLP (CONICET), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 1900 La Plata, Argentina su: Alkenes Calixarenes Aromatic compounds Surface chemistry Physical & theoretical chemistry sug: subj: Alkenes Calixarenes Aromatic compounds Surface chemistry Physical & theoretical chemistry ab: Cooperativity between Brønsted acidic defect sites on oxide surfaces and Lewis acid catalyst sites consisting of grafted calixarene—Ti(IV) complexes is investigated for controlling epoxidation catalysis. Materials are synthesized that, regardless of the surface or calixarene substituent, demonstrate nearly identical UV—visible ligand-to-metal charge-transfer bands and Ti K-edge X-ray absorption near edge spectral features consistent with site-isolated, coordinatively unsaturated Ti(IV) atoms. Despite similar Ti frontier orbital energies demonstrated by these spectra, replacing a homogeneous triphenylsilanol ligand with a silanol on a SiO surface increases cyclohexene epoxidation rates with tert-butyl hydroperoxide 20-fold per Ti site. Supporting calixarene—Ti active sites on fully hydroxylated AlO or TiO, which possess lower average surface hydroxyl pK than that of SiO, reduces catalytic rates 50-fold relative to SiO. These effects are consistent with SiO surfaces balancing two competing factors that control epoxidation rates—equilibrated hydroperoxide binding at Ti, disfavored by stronger surface Brønsted acidity, and rate-limiting oxygen transfer from this intermediate to alkenes, favored by strongly H-bonding intermediates. These observations also imply that Ti—OSi rather than Ti-OCalix bonds are broken upon hydroperoxide binding to Ti in kinetically relevant steps, which is verified by the lack of a calixarene upper-rim substituent effect on epoxidation rate. The pronounced sensitivity of observed epoxidation rates to the support oxide, in the absence of changes to the Ti coordination environment, provides experimental evidence for the importance of outer-sphere H-bonding interactions for the exceptional epoxidation reactivity of titanium silicalite and related catalysts. pubtype: Academic Journal doctype: Article src: R language: English refInfo: copyright: @attributes: flag: Y dt: @attributes: year: 2007 holdings: @attributes: islocal: N |
|---|