Effect of Ligand Bulk in Ruthenium-Catalyzed Olefin Metathesis: IPr* vs IPr

Novel ruthenium catalysts, [RuCl 2 (IPr*)(PPh 3 )(3-phenylindenylidene)] ( 1 ) and [RuCl 2 (IPr*)(Py)(3-phenylindenylidene)] ( 2 ), bearing the very bulky ligand IPr* are reported. The complexes were tested in ring closing and cross-metathesis, and their activities were compared to that displayed by [RuCl 2 (IPr)(PPh 3 )(3-phenylindenylidene)] ( 3 ) and the new [RuCl 2 (IPr)(Py)(3-phenylindenylidene)] ( 4 ), in order to assess how the steric hindrance of the N -heterocyclic carbene influences the catalytic activity of the resulting ruthenium complexes.