Probing the Relevance of NHC Ligand Conformations in the Ru‐Catalysed Ring‐Closing Metathesis Reaction

Cat power: Judicious backbone substitution of N-heterocyclic carbenes (NHCs) leads to stable Ru metathesis catalysts with frozen NHC conformations. This finding not only permits the isolation of complexes that are among the most active catalysts in the ring-closing metathesis of hindered olefins (see graphic; Ts=p-toluenesulfonyl), but also provides fundamental mechanistic insights on the role of N-aryl substituent conformations on catalyst activity.