Rate Studies and Mechanism of Ring-Closing Olefin Metathesis Catalyzed by Cationic Ruthenium Allenylidene Arene Complexes

Rate studies of the ring-closing metathesis reaction of N,N-diallyltosylamide catalysed by [(h6-p-cymene)(PCy3)RuCl(=C=C=CPh2)]OTf, performed by 1H NMR in benzene-d6 and in dichloromethane-d2, indicate that the rate limiting process is the reaction itself above 50 °C, or the thermal activation of the complex at lower temperatures. While the reaction is inhibited by addition of PCy3 and not of p-cymeme, spectroscopic studies indicate that the activation process involves primarily a transformation of the allenylidene moiety into a ruthenium-indenylidene species.