Ring-opening polymerization metathesis (ROMP), a type of olefin metathesis, is a powerful synthetic tool to create polyolefins from strained cyclic monomers. While most metathesis reactions are catalyzed by either Grubbs- or Schrock-type catalysts. However, many of these catalysts suffer from poor sensitivity to air or moisture, selectivity issues, or low catalytic efficiency. Consequently, there is a strong need for more robust catalysts in the synthesis of polymers and materials. Previously, our group examined a ruthenium phosphinimine complex, herein referred to as [Ru1], for cross metathesis of 1-hexene. It was found that [Ru1] acted as a fast initiator for this reaction. However, it was found that ethylene, a common biproduct of olefin metathesis, caused catalyst decomposition. Therefore, we hypothesized that [Ru1] would be a strong candidate for ROMP given that no ethylene is generated. Kinetic studies using various cyclic monomers were conducted showing a first-order reaction with respect to all monomers. Turnover frequencies (TOF) as high as 40,000 s^-1 and turnover numbers (TON) of up to 232,000 were observed for norbornene. Using an empirical rate-law, a rate-constant of 7.9 x 10⁸ M^-1 s^-1 was calculatedfor this system, which is near rate of diffusion in tetrachloromethane, 7x 10⁹ M^{-1 s}-1. Other substrates such as cis-cyclooctene, 1,5-cyclooctadiene, and dicyclopentadiene were also investigated. GPC analysis of these polymers indicates the formation of high molecular weight polymers with narrow dispesities (<1.4). Notably, [Ru1] can polymerize up to 250,000 equivalents of monomer in five hours. This new ruthenium phosphinimine complex can therefore offer fast access to ultra-high molecular weight ROMP polymers with fast rection times. Further details, as well as current and future efforts will be presented.

Patricia Calvo

Kansas State University

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