Synthesis and activity of a new generation of ruthenium-based olefin metathesis catalysts coordinated with 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ligands

[GRAPHICS] A new family of 1,3 dimesityl-4,5-dihydroimidazol-2-ylidene ruthenium based complexes 9a-c has been prepared starting from RuCl2(=CHPh)(PCy3)(2) 2. These air and water tolerant complexes were shown to exhibit an increased ring-closing metathesis activity at elevated temperature when compared to that of the parent complex 2 and the previously developed complex 3, In many instances the activity of these complexes also rivaled or exceeded that of the alkoxy-imido molybdenum complex 1. Catalyst loadings of as low as 0.05 mol % could be used.