Article in Organometallics — 2011. — №
30. — С. 6713-6717 doi:10.1021/om200911e.
Abstract
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.
