The Cl2(PCy3)(IMes)Ru(CHPh) catalyst: olefin metathesis versus olefin isomerization

While investigating RCM of substrates requiring elevated temperatures and extended reaction times, significant isomerization of one of the double bonds in the starting diene was observed with the recently developed [RuIMes] catalyst. This isomerization appeared as an important drawback of the catalyst, but a judicious selection of solvent and additive can completely eliminate this side reaction.