Anionic Ligand Exchange in Hoveyda−Grubbs Ruthenium(II) Benzylidenes

A series of Hoveyda−Grubbs benzylidenes, Ru(X)2(IMesH2)(CH-2-(2-PrO)C6H4) (X = Cl, Br, CF3CO2, C2F5CO2; IMesH2 = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) were demonstrated to undergo intermolecular anionic ligand exchange when mixed. The implication is that anionic ligand exchange is occurring between identical ruthenium benzylidenes at all times in solution. A mechanism involving bridged dimers is invoked.