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    Cooperative effect by monopodal silica-supported niobium com-plexes pairs enhancing catalytic cyclic carbonate production

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    Type
    Article
    Authors
    D’Elia, Valerio cc
    Dong, Hailin
    Rossini, Aaron J
    Widdifield, Cory M. cc
    Vummaleti, Sai V. C. cc
    Minenkov, Yury cc
    Poater, Albert cc
    Abou-Hamad, Edy cc
    Pelletier, Jeremie D. A.
    Cavallo, Luigi cc
    Emsley, Lyndon
    Basset, Jean-Marie cc
    KAUST Department
    Chemical Science Program
    KAUST Catalysis Center (KCC)
    Physical Science and Engineering (PSE) Division
    Date
    2015-06-15
    Online Publication Date
    2015-06-15
    Print Publication Date
    2015-06-24
    Permanent link to this record
    http://hdl.handle.net/10754/552780
    
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    Abstract
    Recent discoveries highlighted the activity and the intriguing mechanistic features of NbCl5 as a molecular catalyst for the cycloaddition of CO2 and epoxides under ambient conditions. This has inspired the preparation of novel silica supported Nb-species by reacting a molecular niobium precursor [NbCl5•OEt2] with silica dehydroxylated at 700 °C (SiO2-700) or at 200 oC (SiO2-200) to generate diverse surface complexes. The product of the reaction between SiO2-700 and [NbCl5•OEt2] was identified as a monopodal supported surface species [≡SiONbCl4•OEt2] (1a). The reactions of SiO2-200 with the niobium precursor, according to two different protocols, generated surface complexes 2a and 3a presenting significant, but different, populations of the monopodal surface complex along with bipodal [(≡SiO)2NbCl3•OEt2]. 93Nb SSNMR spectra of 1a-3a and 31P SSNMR on their PMe3 derivatives (1b-3b) led to the unambiguous assignment of 1a as a single site, monopodal Nb-species while 2a and 3a were found to present two distinct surface-supported components, with 2a being mostly monopodal [≡SiONbCl4•OEt2] and 3a being mostly bipodal [≡S ONbCl3•OEt2]. Double-quantum/single-quantum 31P NMR correlation experiment carried out on 2b supported the existence of vicinal Nb centers on the silica surface for this species. 1a-3a were active heterogeneous catalysts for the synthesis of propylene carbonate from CO2 and propylene oxide under mild catalytic conditions; the performance of 2a was found to significantly surpass that of 1a and 3a. With the support of a systematic DFT study carried out on model silica surfaces, the observed differences in catalytic efficiency were correlated with an unprece-dented cooperative effect between two neighboring Nb centers on the surface of 2a. This is in an excellent agreement with our previous discoveries regarding the mechanism of the NbCl5 catalyzed cycloaddition in the homogeneous phase.
    Citation
    Cooperative effect by monopodal silica-supported niobium com-plexes pairs enhancing catalytic cyclic carbonate production 2015:150507190632009 Journal of the American Chemical Society
    Publisher
    American Chemical Society (ACS)
    Journal
    Journal of the American Chemical Society
    DOI
    10.1021/jacs.5b02872
    PubMed ID
    25950495
    Additional Links
    http://pubs.acs.org/doi/abs/10.1021/jacs.5b02872
    ae974a485f413a2113503eed53cd6c53
    10.1021/jacs.5b02872
    Scopus Count
    Collections
    Articles; Physical Science and Engineering (PSE) Division; Chemical Science Program; KAUST Catalysis Center (KCC)

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