Date: 2009. 10. 16, 4:00 PM Place: Mogam Hall, Bldg 500 -Abstract- Over the past decade, olefin metathesis has emerged as a powerful method for the formation of carboncarbon double bonds. In particular, ruthenium olefin metathesis catalysts based on the L2X2Ru=CHR scaffold have been used extensively in organic and polymer chemistry due to their high activity and functional group tolerance. Despite these advances, one of the major limiting factors for the use of ruthenium carbene catalysts in many reactions is the lifetime and efficiency of these catalysts. As a result, the ring-closing of large rings requires increased catalyst loadings in high-dilution conditions, and the metathesis of highly substituted and/or electron-deficient olefins still requires elevated temperatures and extended reaction times. Furthermore, catalyst decomposition sometimes leads to unwanted side reactions, such as olefin isomerizations. To address these problems, decomposition mechanism of current ruthenium olefin metathesis catalysts has been investigated. Based on the information from the decomposition study, a method to prevent undesirable isomerization reaction has been developed. This mild, inexpensive, and effective method to block olefin isomerization increases the synthetic utility of olefin metathesis by improving product yield and purity. Besides, a highly active water-soluble metathesis catalyst that shows unprecedented activity in aqueous media has been developed. Potential industrial applications of the developed method and the water-soluble catalyst will be discussed.