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, University of Southern Mississippi
Shawna L. L. Balof, University of Southern MississippiFollow
Lawrence J. J. LaBeaud, University of Southern MississippiFollow
Bing Yu, University of Southern MississippiFollow
Andrew B. Lowe, University of New South Wales
Edward J. Valente, University of Portland
Hans-Jörg Schanz, University of Southern Mississippi

Document Type

Article

Publication Date

1-1-2009

Department

Chemistry and Biochemistry

School

Mathematics and Natural Sciences

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)Cl₂(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(PCy₃)(DMAP)₂RuCHPh)] (5 b) and [Cl₂(H₂IMes)(DMAP)₂Ru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.

Publication Title

Chemistry - A European Journal

Volume

15

Issue

45

First Page

12435

Last Page

12446

Recommended Citation

Dunbar, M. A., Balof, S. L., LaBeaud, L. J., Yu, B., Lowe, A. B., Valente, E. J., 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), 12435-12446.
Available at: https://aquila.usm.edu/fac_pubs/8922