A convenient system for improving the efficiency of first-generation ruthenium olefin metathesis catalysts

The performance of certain olefin metathesis reactions catalyzed by Grubbs catalysts has been enhanced by the simple addition of phenol. Addition of phenol to self-metathesis reactions catalyzed by 1 produced very small quantities of unwanted byproducts and allowed for room-temperature metathesis at high substrate:catalyst loadings. The efficiency of cross-metathesis reactions between methyl acrylate and 1-decene catalyzed by 2 was also significantly increased by addition of p-cresol to the reaction mixture. Mechanistic studies, including NMR spectroscopy and DFT calculations, established that phenol is playing a number of positive roles in the active metathesis cycle, including altering the relative rates of phosphine loss and rebinding, activating the carbene carbon for reaction with olefinic substrate, and hemilabile stabilization of the key 14-electron intermediate species.