Metal-centered oxidations facilitate the removal of ruthenium-based olefin metathesis catalysts

Commercially available catalysts (SIMes)(PCy3)Cl2Ru(double bond; length as m-dashCHPh) (2) and (SIMes)Cl2Ru(double bond; length as m-dashCH-o-O-i-PrC6H4) (3) (SIMes = 1,3-dimesitylimidazolin-2-ylidene) were found to display reversible Ru oxidations via a series of electrochemical measurements. The redox processes enabled the catalysts to be switched between two different states of activity in ring opening metathesis polymerizations and ring closing metathesis reactions, primarily through changes in catalyst solubility. Moreover, treating a solution of 2 dissolved in C6H6/CH2Cl2/[1-butyl-3-methylimidazolium][PF6] (6:1:1.1 v/v/v) with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone was found to remove >99.9% of the catalyst, as determined by UV/vis spectroscopy. The methodology described herein establishes a new approach for controlling the activities displayed by commercially available olefin metathesis catalysts and for removing residual Ru species using redox-driven processes.