A Highly Controllable Latent Ruthenium Schiff Base Olefin Metathesis Catalyst: Catalyst Activation and Mechanistic Studies

A ruthenium Schiff base catalyst (5), bearing an N-heterocyclic carbene ligand, was found to be a latent catalyst for the ring-opening metathesis polymerization of cis,cis-1,5-cyclooctadiene and dicyclopentadiene and is activated efficiently on addition of hydrochloric acid. A benchmark study was performed using the Grubbs first (1), second (2), and third (3) generation catalyst. Results further illustrate that the catalyst can be stored in dicyclopentadiene at a monomer/catalyst ratio of 15,000/1 without any significant polymerization during at least 12 months. After activation of the catalyst with a Bronsted acid, no undesired loss of performance can be detected. This concept of activation can be easily adapted to a Reaction Injection Molding process, and reaction control is obtained via the in situ generation of the cocatalyst as the outcome of the reaction of alcohols with Lewis acids. Insight into the activation mechanism was gained through an in-depth nuclear magnetic resonance study, and a plausible mechanism is proposed. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 302-310, 2010