ORGN 35 |
| R. H. Grubbs1, Anatoly Chlenov2, and Soon Hyeok Hong1. (1) California Institute of Technology, Arnold and Mabel Beckman Laboratory of C, Pasadena, CA 91125, (2) Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125 |
| Olefin metathesis is widely used in the synthesis of biologically relevant compounds. One of the most powerful applications is the formation of large macrocycles via ring-closing metathesis with Ru catalysts. Currently available first and second generation Grubbs catalysts work well in the majority of applications. However, high catalyst loadings are often required to compensate for catalyst decomposition during the reaction, especially at elevated temperatures. It is highly desirable to synthesize a more stable olefin metathesis catalyst that would afford the ring-closing metathesis of less reactive substrates in improved yields with reduced catalyst loadings as well as induce reactions that are not currently possible. Investigations of the active catalytic species (Ru methylidene complex) derived from second generation Grubbs catalyst showed that it decomposes via initial dissociation of the phosphine followed by its attack on the methylidene, eventually leading to the formation of the carbon-bridged Ru dimer. With this information in hand we designed a modified catalyst where N-heterocyclic carbene ligand is varied to improve catalyst stability. Details of catalyst design and early results of catalyst activity and stability will be presented. |
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Metal-Mediated Reactions and Syntheses
8:00 AM-12:00 PM, Sunday, August 22, 2004 Pennsylvania Convention Center -- 201B, Oral
Division of Organic Chemistry |