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    Concerning the Deactivation of Cobalt(III)-Based Porphyrin and Salen Catalysts in Epoxide/CO 2 Copolymerization

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    Type
    Article
    Authors
    Xia, Wei
    Salmeia, Khalifah A.
    Vagin, Sergei I.
    Rieger, Bernhard
    KAUST Grant Number
    UK-C0020/KSA-C0069
    Date
    2015-02-05
    Online Publication Date
    2015-02-05
    Print Publication Date
    2015-03-09
    Permanent link to this record
    http://hdl.handle.net/10754/597827
    
    Metadata
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    Abstract
    © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Functioning as active catalysts for propylene oxide (PO) and carbon dioxide copolymerization, cobalt(III)-based salen and porphyrin complexes have drawn great attention owing to their readily modifiable nature and promising catalytic behavior, such as high selectivity for the copolymer formation and good regioselectivity with respect to the polymer microstructure. Both cobalt(III)-salen and porphyrin catalysts have been found to undergo reduction reactions to their corresponding catalytically inactive cobalt(II) species in the presence of propylene oxide, as evidenced by UV/Vis and NMR spectroscopies and X-ray crystallography (for cobalt(II)-salen). Further investigations on a TPPCoCl (TPP=tetraphenylporphyrin) and NaOMe system reveal that such a catalyst reduction is attributed to the presence of alkoxide anions. Kinetic studies of the redox reaction of TPPCoCl with NaOMe suggests a pseudo-first order in cobalt(III)-porphyrin. The addition of a co-catalyst, namely bis(triphenylphosphine)iminium chloride (PPNCl), into the reaction system of cobalt(III)-salen/porphyrin and PO shows no direct stabilizing effect. However, the results of PO/CO2 copolymerization by cobalt(III)-salen/porphyrin with PPNCl suggest a suppressed catalyst reduction. This phenomenon is explained by a rapid transformation of the alkoxide into the carbonate chain end in the course of the polymer formation, greatly shortening the lifetime of the autoreducible PO-ring-opening intermediates, cobalt(III)-salen/porphyrin alkoxides. CO2 saves: The deactivation of cobalt(III)-porphyrin and salen catalysts in propylene oxide/carbon dioxide copolymerization is systematically investigated, revealing a proposed mechanism for the catalyst reduction (see scheme).
    Citation
    Xia W, Salmeia KA, Vagin SI, Rieger B (2015) Concerning the Deactivation of Cobalt(III)-Based Porphyrin and Salen Catalysts in Epoxide/CO 2 Copolymerization . Chem Eur J 21: 4384–4390. Available: http://dx.doi.org/10.1002/chem.201406258.
    Sponsors
    W.X. and K.A.S. thank the King Abdullah University of Science and Technology (KAUST) for the financial support of this work (UK-C0020/KSA-C0069).
    Publisher
    Wiley
    Journal
    Chemistry - A European Journal
    DOI
    10.1002/chem.201406258
    PubMed ID
    25656829
    ae974a485f413a2113503eed53cd6c53
    10.1002/chem.201406258
    Scopus Count
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