cis-Dichloro Sulfoxide Ligated Ruthenium Metathesis Precatalysts

Ruthenium Olefin Metathesis Catalysts Bearing a Macrocyclic N-Heterocyclic Carbene Ligand: Improved Stability and Activity

Formation of sterically hindered C-C double bonds via catalytic olefin metathesis is considered a very challenging task for Ru catalysts. This limitation led to the development of specialised catalysts bearing sterically reduced N-heterocyclic carbene (NHC) ligands that are very active in such transformations, yet significantly less stable as compared to general purpose catalysts. To decrease the small-size NHC catalysts susceptibility to decomposition, a new NHC ligand was designed, in which two sterically reduced aryl arms were tied together by a C-8 alkyl chain. The installation of this macrocyclic ligand on the ruthenium centre led to the formation of an olefin metathesis catalyst (trans-Ru6). Interestingly, this complex undergoes transformation into an isomer bearing two Cl ligands in the cis-arrangement (cis-Ru6). These two isomeric complexes exhibit similarly high thermodynamic stability, yet different application profiles in catalysis.

Light-Driven gem Hydrogenation: An Orthogonal Entry into "Second-Generation" Ruthenium Carbene Catalysts for Olefin Metathesis

The newly discovered light-driven gem hydrogenation of alkynes opens an unconventional yet efficient entry into five-coordinate Grubbs-type ruthenium carbene complexes with cis-disposed chloride ligands. Representatives of this class featuring a chelate substructure formed by an iodo-substituted benzylidene unit react with (substituted) 2-isopropoxystyrene to give prototypical "second-generation" Grubbs-Hoveyda complexes for olefin metathesis. The new approach to this venerable catalyst family is safe and versatile as it uses a triple bond rather than phenyldiazomethane as the ultimate carbene source and does not require any sacrificial phosphines.