Linked Life Data

18402450

Source:http://linkedlifedata.com/resource/pubmed/id/18402450

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PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
18
pubmed:dateCreated
2008-4-30
pubmed:abstractText
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 [([triple bond]SiO)M(ER)(=CH(t)Bu)(R')] (M = Re, Ta, Mo or W; ER = C(t)Bu, NAr or CH2(t)Bu; R' = CH2(t)Bu, NPh2, NC4H4). 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(z)> = 0.5 for [([triple bond]SiO)Ta(=CH(t)Bu)(CH2(t)Bu)2] and [([triple bond]SiO)Re([triple bond]C(t)Bu)(=CH(t)Bu)(CH2(t)Bu)] to <S(z)> = 0.9 for [([triple bond]SiO)Mo([triple bond]NAr)(=CH(t)Bu)(R') with R' = CH2(t)Bu, NPh2, NC4H4. 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.
pubmed:language
eng
pubmed:journal
pubmed:status
PubMed-not-MEDLINE
pubmed:month
May
pubmed:issn
1520-5126
pubmed:author
pubmed:issnType
Electronic
pubmed:day
7
pubmed:volume
130
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
5886-900
pubmed:year
2008
pubmed:articleTitle
Dynamics of silica-supported catalysts determined by combining solid-state NMR spectroscopy and DFT calculations.
pubmed:affiliation
Laboratoire de Chimie, Catalyse, Polymères et Procédés (UMR 5265), Chimie Organométallique de Surface, ESCPE Lyon, Université de Lyon, 43 Bd du 11 Novembre 1918, F-69616 Villeurbanne, France.
pubmed:publicationType
Journal Article