Get access
Advertisement

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

Authors

  • Miles A. Dunbar,

    1. Department of Chemistry and Biochemistry, The University of Southern Mississippi, 118 College Drive, # 5043, Hattiesburg, MS 39406-5043 (USA), Fax: (+1) 601-2665708
    Search for more papers by this author
  • Shawna L. Balof,

    1. Department of Chemistry and Biochemistry, The University of Southern Mississippi, 118 College Drive, # 5043, Hattiesburg, MS 39406-5043 (USA), Fax: (+1) 601-2665708
    Search for more papers by this author
  • Lawrence J. LaBeaud,

    1. Department of Chemistry and Biochemistry, The University of Southern Mississippi, 118 College Drive, # 5043, Hattiesburg, MS 39406-5043 (USA), Fax: (+1) 601-2665708
    Search for more papers by this author
  • Bing Yu Dr.,

    1. Department of Chemistry and Biochemistry, The University of Southern Mississippi, 118 College Drive, # 5043, Hattiesburg, MS 39406-5043 (USA), Fax: (+1) 601-2665708
    Search for more papers by this author
  • Andrew B. Lowe Dr.,

    1. Centre for Advanced Macromolecular Design (CAMD), School of Chemical Sciences and Engineering, The University of New South Wales, Sydney, NSW 2052 (Australia)
    Search for more papers by this author
  • Edward J. Valente Dr.,

    1. Department of Chemistry, University of Portland, 500 N. Willamette Blvd., Portland, OR 97203 (USA)
    Search for more papers by this author
  • Hans-Jörg Schanz Dr.

    1. Department of Chemistry and Biochemistry, The University of Southern Mississippi, 118 College Drive, # 5043, Hattiesburg, MS 39406-5043 (USA), Fax: (+1) 601-2665708
    Search for more papers by this author

Abstract

The effect of the addition of H3PO4 on the ROMP activity of cyclooctene (COE) with first- [Cl2(PCy3)2Ru[DOUBLE BOND]CHPh] and second-generation [(H2IMes)Cl2(PCy3)Ru[DOUBLE BOND]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(PCy3)(DMAP)2Ru[DOUBLE BOND]CHPh)] (5 b) and [Cl2(H2IMes)(DMAP)2Ru[DOUBLE BOND]CHPh] (7 b) (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 7 b 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 H3PO4 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 acid-addition and the ROMP reactions became well-controlled in contrast to the acid-free reaction. In contrast, complex 7 b performs well-controlled ROMP in the absence of acid, whereas the polymerization of the same monomer becomes less controlled in the presence of H3PO4. 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.

Get access to the full text of this article

Ancillary