The long term objectives of this research are to achieve both detailed mechanistic understandings and to develop new synthetic methods for a number of different alkyne coupling reactions. Transition metal- catalyzed alkyne coupling reactions have been extensively utilized in the synthesis of a wide range of natural products. Transition metal sigma-acetylide complexes are considered to be important intermediate species in some of these reactions. This research proposes to study the fundamental reactivity of coordinatively unsaturated ruthenium-acetylide complexes toward the coupling reactions of alkynes with alkenes and carbonyl compounds. This research proposes to examine the mechanisms of these alkyne coupling reactions. Specific plans are presented to explore the catalytic activity of unsaturated ruthenium-acetylide species in these reactions. Metallacyclopentadiene complexes have been widely implicated as key intermediate species in a number of different alkyne oligomerization reactions. The newly formed ruthenacyclopentadiene complex was shown to catalyze the linear coupling reactions of acetylenes and olefins. The proposal describes specific plans to study the reactivity and catalytic activity of the ruthenacyclopentadiene complexes towards linear alkyne coupling reactions. The specific goals of this research are to study the fundamental reactivity and catalytic activity of the ruthenium-acetylide and ruthenacyclopentadiene complexes toward the alkyne coupling reactions, and to establish the detailed mechanisms of these reactions.