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Published January 31, 2001 | Supplemental Material
Journal Article Open

New Insights into the Mechanism of Ruthenium-Catalyzed Olefin Metathesis Reactions


Over the past two decades, olefin metathesis has emerged as a mild and efficient method for the formation of carbon−carbon double bonds. In particular, (PCy_3)_2(Cl)_2RuCHPh (1)^2 has found extensive use in organic and polymer chemistry due to its high reactivity with olefins in the presence of a diverse array of functional groups. Recently, a new family of ruthenium-based olefin metathesis catalysts have been prepared by the substitution of a single PCy_3 ligand of 1 with an N-heterocyclic carbene. These new alkylidenes, particularly [Figure 1], exhibit dramatically increased activity over the parent system in ring-opening metathesis polymerization, ring-closing metathesis,4a and cross metathesis reactions. The mechanism of olefin metathesis reactions catalyzed by 1 has received intense investigation in our group and others and early studies established that phosphine dissociation is a crucial step along the reaction coordinate. As such, it has been suggested that the high activity of 2 and its analogues is due to their increased ability to promote this critical phosphine dissociation step. We report herein a detailed mechanistic study of phosphine exchange and initiation kinetics in alkylidenes 1 and 2. This study provides new and surprising evidence concerning the origin of the large activity differences between these two catalysts.

Additional Information

© 2001 American Chemical Society. Received 4 October 2000. Published online 6 January 2001. Published in print 1 January 2001. We thank Dr. Ola Wendt and Dr. Jeffrey Yoder for assistance with magnetization transfer experiments. Dr. Adam Matzger, Dr. Jennifer Love, Annita Zhong, and Diego Benitez are acknowledged for helpful discussions. This research was supported by the NSF.

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