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    Heterolytic cleavage of ammonia N-H bond by bifunctional activation in silica-grafted single site Ta(V) imido amido surface complex. Importance of the outer sphere NH3 assistance

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    Type
    Article
    Authors
    Gouré, Eric
    Avenier, Priscilla
    Soláns, Xavier Luis
    Veyre, Laurent
    Baudouin, Anne Christine
    Kaya, Yasemin
    Taoufik, Mostafa
    Basset, Jean-Marie cc
    Eisenstein, Odile
    Quadrelli, Elsje Alessandra
    KAUST Department
    Chemical Science Program
    KAUST Catalysis Center (KCC)
    Physical Science and Engineering (PSE) Division
    Date
    2011
    Permanent link to this record
    http://hdl.handle.net/10754/561647
    
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    Abstract
    Ammonia N-H bond is cleaved at room temperature by the silica-supported tantalum imido amido complex [(≡SiO)2Ta(NH)(-NH2)], 2, if excess ammonia is present, but requires 150 °C to achieve the same reaction if only one equivalent NH3 is added to 2. MAS solid-state 15N NMR and in situ IR spectroscopic studies of the reaction of either 15N or 2H labeled ammonia with 2 show that initial coordination of the ammonia is followed by scrambling of either 15N or 2H among ammonia, amido and imido groups. Density functional theory (DFT) calculations with a cluster model [{(μ-O)[(H3SiO) 2SiO]2}Ta(NH)(-NH2)(NH3)], 2 q·NH3, show that the intramolecular H transfer from Ta-NH2 to TaNH is ruled out, but the H transfers from the coordinated ammonia to the amido and imido groups have accessible energy barriers. The energy barrier for the ammonia N-H activation by the Ta-amido group is energetically preferred relative to the Ta-imido group. The importance of excess NH3 for getting full isotope scrambling is rationalized by an outer sphere assistance of ammonia acting as proton transfer agent, which equalizes the energy barriers for H transfer from coordinated ammonia to the amido and imido groups. In contrast, additional coordinated ammonia does not favor significantly the H transfer. These results rationalize the experimental conditions used. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011.
    Citation
    Gouré, E., Avenier, P., Solans-Monfort, X., Veyre, L., Baudouin, A., Kaya, Y., … Quadrelli, E. A. (2011). Heterolytic cleavage of ammonia N–H bond by bifunctional activation in silica-grafted single site Ta(V) imido amido surface complex. Importance of the outer sphere NH3 assistance. New Journal of Chemistry, 35(5), 1011. doi:10.1039/c1nj20032a
    Publisher
    Royal Society of Chemistry (RSC)
    Journal
    New Journal of Chemistry
    DOI
    10.1039/c1nj20032a
    ae974a485f413a2113503eed53cd6c53
    10.1039/c1nj20032a
    Scopus Count
    Collections
    Articles; Physical Science and Engineering (PSE) Division; Chemical Science Program; KAUST Catalysis Center (KCC)

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