Design and synthesis of new ruthenium-based catalysts for improved activity in challenging Z-selective metathesis reactions

Our group has recently reported a series of ruthenium-based metathesis catalysts that contain a chelating NHC. These catalysts demonstrate high Z-selectivity in a variety of metathesis reactions including cross metathesis, ring-closing metathesis and ring-opening metathesis polymn. However, the substrate scope has so far been limited to relatively unhindered olefins. In order to probe the origin of this selectivity, a series of catalysts with N-heterocyclic carbene (NHC) substituents of varying steric bulk were prepd. These catalysts were subsequently examd. for improved reactivity in a range of olefins that contain bulky substituents. In addn., the mechanism of the C-H-activation step in the synthesis of such catalysts was probed through variation of the sterics and electronics of both the adamantyl and aryl NHC substituents.