Highly Active Ruthenium Catalysts for Olefin Metathesis: The Synergy of N-Heterocyclic Carbenes and Coordinatively Labile Ligands

Two N-heterocyclic carbene ligands at once may be one too many , at least if you intend to have highly active ruthenium catalysts for olefin metathesis. Density functional calculations recommend the replacement of the second carbene ligand in the successful ROMP catalysts 1 by coordinatively more labile ligands as in 2 or 3 . In both cases, the catalytic activity is greatly improved.