NIH Public Access Author Manuscript Organometallics. Author manuscript; available in PMC 2012 December 26. NIH-PA Author Manuscript Published in final edited form as: Organometallics. 2011 December 26; 30(24): 6713–6717. doi:10.1021/om200911e. Thermally Stable, Latent Olefin Metathesis Catalysts Renee M. Thomas, Alexey Fedorov, Benjamin K. Keitz, and Robert H. Grubbs The Arnold and Mabel Beckman Laboratories of Chemical Synthesis, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125 Robert H. Grubbs:
[email protected] Abstract NIH-PA Author Manuscript Highly thermally stable N-aryl,N-alkyl N-heterocyclic carbene (NHC) ruthenium catalysts were designed and synthesized for latent olefin metathesis. These catalysts showed excellent latent behavior toward metathesis reactions, whereby the complexes were inactive at ambient temperature and initiated at elevated temperatures, a challenging property to achieve with second generation catalysts. A sterically hindered N-tert-butyl substituent on the NHC ligand of the ruthenium complex was found to induce latent behavior toward cross-metathesis reactions, and exchange of the chloride ligands for iodide ligands was necessary to attain latent behavior during ring-opening metathesis polymerization (ROMP). Iodide-based catalysts showed no reactivity toward ROMP of norbornene-derived monomers at 25 °C, and upon heating to 85 °C gave complete conversion of monomer to polymer in less than 2 hours. All of the complexes were very stable to air, moisture, and elevated temperatures up to at least 90 °C, and exhibited a long catalyst lifetime in solution at elevated temperatures. Introduction NIH-PA Author Manuscript Olefin metathesis is widely used as a method of constructing carbon-carbon double bonds.1 Toward this end, highly efficient metathesis catalysts have been designed through improvement of activity,2 stability,3 and selectivity of the catalysts.4 Recently, efforts have been directed toward the development of latent metathesis catalysts.5,6 Latent catalysts are defined as complexes that show little or no activity at a particular (usually ambient) temperature and initiate only upon activation. This activation can be caused by a variety of different stimuli, including heat,7,8 acid,9 light,10-13 and chemical activation.14 Latent metathesis catalysts primarily have applications in polymer chemistry.14 One such application is the advantage of prepari