Dynamics of Silica-Supported Catalysts Determined by Combining Solid-State NMR Spectroscopy and DFT Calculations.
The molecular dynamics of a series of organometallic complexes covalently bound to amorphous silica surfaces is determined experimentally using solid-state nuclear magnetic resonance (NMR) spectroscopy and density functional theory calculations (DFT). The determination is carried out for a series of...
| Publicado en: | Journal of the American Chemical Society Vol. 130; no. 18; pp. 5886 - 5901 |
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| Autores principales: | , , , , , , , , , , |
| Formato: | Artículo |
| Publicado: |
American Chemical Society
5/7/2008
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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=31960062&site=ehost-live header: @attributes: shortDbName: hlh uiTerm: 31960062 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: 5/7/2008 vid: 130 iid: 18 pid: 997 pub: American Chemical Society artinfo: ui: 31960062 10.1021/ja077749v ppf: 5886 ppct: 15 formats: tig: atl: Dynamics of Silica-Supported Catalysts Determined by Combining Solid-State NMR Spectroscopy and DFT Calculations. aug: au: Blanc, Frédéric Basset, Jean-Marie Copéret, Christophe Sinha, Amritanshu Tonzetich, Zachary J. Schrock,, Richard A. Solans-Monfort, Xavier Clot, Eric Eisenstein, Odile Lesage, Anne Emsley, Lyndon affil: Laboratoire de Chimie, Catalyse, Polymères et Procédés (UMR 5265), Chimie Organoinérallique de Surface, ESCPE Lyon, Université de Lyon, 43 Bd du 11 Novembre 1918, F-69616 Villeurbanne, France Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachussets 02139 Department de Química, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain Institut Charles Gerhardt Montpellier (UMR 5253, CNRS, UM2, UM1, ENSCM); Université Montpellier 2, cc 1501, Place E. Bataillon, F-34095 Montpellier, France Laboratoire de Chimie (UMR 5182), ENS Lyon, Université de Lyon, 46 Allée d'Italie, F-69364 Lyon, France su: Nuclear magnetic resonance Silicon compounds Carbon compounds Density functionals Catalysts Anisotropy sug: subj: Nuclear magnetic resonance Silicon compounds Carbon compounds Density functionals Catalysts Anisotropy ab: The molecular dynamics of a series of organometallic complexes covalently bound to amorphous silica surfaces is determined experimentally using solid-state nuclear magnetic resonance (NMR) spectroscopy and density functional theory calculations (DFT). The determination is carried out for a series of alkylidene-based catalysts having the general formula [(≡]SiO)M(ER)(=CH(t)Bu)(R′)] (M = Re, Ta, Mo or W; ER = CtBu, NAr or CHtBu; R′ = CHtBu, NPh, NCH). Proton-carbon dipolar coupling constants and carbon chemical shift anisotropies (CSA) are determined experimentally by solid-state NMR. Room-temperature molecular dynamics is quantified through order parameters determined from the experimental data. For the chemical shift anisotropy data, we validate and use a method that integrates static values for the CSA obtained computationally by DFT, obviating the need for low-temperature measurements. Comparison of the room-temperature data with the calculations shows that the widths of the calculated static limit dipolar couplings and CSAs are always greater than the experimentally determined values, providing a clear indication of motional averaging on the NMR time scale. Moreover, the dynamics are found to be significantly different within the series of molecular complexes, with order parameters ranging from <S> = 0.5 for [(≡]SiO)Ta(=CHtBu)(CHtBu)] and [(≡]SiO)Re(≡]CtBu)(=CHtBu)(CHtBu)] to <S> = 0.9 for [(≡]SiO)Mo(≡]NAr)(=CHtBu)(R′) with R′ = CHtBu, NPh, NCH. The data also show that the motion is not isotropic and could be either a jump between two sites or more likely restricted librational motion. The dynamics are discussed in terms of the molecular structure of the surface organometallic complexes, and the orientation of the CSAs tensor at the alkylidene carbon is shown to be directly related to the magnitude of the alpha-alkylidene CH agostic interation. pubtype: Academic Journal doctype: Article src: R language: English refInfo: copyright: @attributes: flag: Y dt: @attributes: year: 2008 holdings: @attributes: islocal: N |
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