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    Improved molecular weight control in ring-opening metathesis polymerization (ROMP) reactions with ru-based olefin metathesis catalysts using n. donors and acid: a kinetic and mechanistic investigation

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    Authors
    Dunbar, M.
    Balof, S.
    Labeaud, L.
    Yu, B.
    Lowe, Andrew
    Valente, E.
    Schanz, H.
    Date
    2009
    Type
    Journal Article
    
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    Citation
    Dunbar, M. and Balof, S. and Labeaud, L. and Yu, B. and Lowe, A. and Valente, E. and Schanz, H. 2009. Improved molecular weight control in ring-opening metathesis polymerization (ROMP) reactions with ru-based olefin metathesis catalysts using n. donors and acid: a kinetic and mechanistic investigation. Chemistry - A European Journal. 15 (45): pp. 12435-12446.
    Source Title
    Chemistry - A European Journal
    DOI
    10.1002/chem.200901013
    ISSN
    0947-6539
    School
    Nanochemistry Research Institute
    URI
    http://hdl.handle.net/20.500.11937/47800
    Collection
    • Curtin Research Publications
    Abstract

    The effect of the addition of H3PO4 on the ROMP activity of cyclooctene (COE) with first- [Cl2(PCy3) 2Ru=CHPh] and second-generation [(H2IMeS)Cl 2(PCy3)Ru=CHPh] Grubbs' catalysts 1 and 4 (Cy = cyclohexyl, Ph = phenyl, Mes = 2,4,6-trimethylphenyl (mesityl)), their inhibited mixtures with 1-methylimidazole (MIM), as well as their isolated bis-N,N'-dimethylaminopyridine (DMAP) derivatives [Cl2(PCy 3)(DMAP)2Ru=CHPh)] (Sb) and [Cl2(H 2IMeS)(DMAP)2Ru= CHPh] (7b) (DMAP = dimethylaminopyridine) , a novel catalyst, has been investigated. The studies include the determination of their initiation rates, as well as a determination of the molecular weights and molecular weight distributions of the polymers obtained with these catalysts and catalyst mixtures from the exo-7-oxanorbornene derivative 11. The structure of catalyst 7b was confirmed by means of X-ray diffraction. All N-donor-bearing catalysts or N-donor-containing catalyst mixtures not only exhibited elevated activity in the presence of acid, but also increased initiation rates. Using the reversible inhibition/activation protocol with MIM and H3PO 4 enabled us to conduct controlled ROMP with catalyst 4 producing the isolated exo-7-oxanorbornene-based polymer 12 with predetermined molecular weights and narrow molecular weight distributions. This effect was based on fast and efficient catalyst initiation in contrast to the parent catalyst 4. Hexacoordinate complex 5 b also experienced a dramatic increase in initiation rates upon acidaddition and the ROMP reactions became well-controlled in contrast to the acid-free reaction. In contrast, complex 7b performs well-controlled ROMP in the absence of acid, whereas the polymerization of the same monomer becomes less controlled in the presence of H3PO 4. The closer evaluation of catalysts 5 b and 7 b demonstrated that their initiation rates exhibit a linear dependency on the substrate concentration in contrast to catalysts 1 and 4. As a consequence, their initiation rates are determined by an associative step, not a dissociative step as seen for catalysts 1 and 4. A feasible associative metathesis initiation mechanism is proposed. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.

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