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    Grafting trimethylaluminum and its halogen derivatives on silica: general trends for Al-27 SS-NMR response from first principles calculations

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    Type
    Article
    Authors
    Kerber, Rachel Nathaniel
    Kerber, Torsten
    Rozanska, Xavier
    Delbecq, Francoise
    Sautet, Philippe
    KAUST Grant Number
    UK-C0017
    Date
    2015
    Permanent link to this record
    http://hdl.handle.net/10754/673083
    
    Metadata
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    Abstract
    Al-27 NMR is the method of choice for studying grafted Al species on a large area solid support, such as co-catalysts for alpha-olefin oligomerization involving mesoporous silica materials. Here, we show how to interpret the Al-27 solid-state NMR spectrum and parameters for various types of Al monomeric and dimeric alkyl and halogen compounds grafted on silica, based on the trends obtained from first-principles calculations. Since most alkylaluminum species tend to form dimers in the gas phase, we chose as prototypes both the AlMe3 monomer and the Al2Me6 dimer. On top of that the influence of chlorine substituents on the NMR parameters is explored considering all possible isomers. There are two main effects on the Al NMR parameters observed in the case of monomers: (i) the larger pi-donating character of the ligands (from Me to Cl for example) leads to a decrease of the quadrupolar coupling constant C-Q and (ii) the larger sigma-attracting character of the ligand (from Cl to F for example) yields an upfield variation of the Al chemical shift delta(ISO) while in contrast C-Q is increased. The same is true also in the case of dimeric species, with an additional specific effect. By Al-27 solid state NMR we can differentiate clearly between terminal and bridge positions for the substituents. The reason for this phenomenon is explained in terms of different natural localized MO (NLMO) contributions to the C-Q parameter. This aspect is important because the surface sites for this type of system are expected to be mostly dinuclear Al species, grafted on the silica surface via either two terminal or two bridging siloxy ligands.
    Citation
    Kerber, R. N., Kerber, T., Rozanska, X., Delbecq, F., & Sautet, P. (2015). Grafting trimethylaluminum and its halogen derivatives on silica: general trends for 27Al SS-NMR response from first principles calculations. Physical Chemistry Chemical Physics, 17(40), 26937–26945. doi:10.1039/c5cp04109k
    Sponsors
    This publication is based on work supported by Award No. UK-C0017, made by King Abdullah University of Science and Technology (KAUST).
    Publisher
    ROYAL SOC CHEMISTRY
    Journal
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS
    DOI
    10.1039/c5cp04109k
    Additional Links
    http://xlink.rsc.org/?DOI=C5CP04109K
    ae974a485f413a2113503eed53cd6c53
    10.1039/c5cp04109k
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