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

Novel ruthenium catalysts, [RuCl2(IPr*)­(PPh3)­(3-phenylindenylidene)] (1) and [RuCl2(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 [RuCl2(IPr)­(PPh3)­(3-phenylindenylidene)] (3) and the new [RuCl2(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.