This award in the Inorganic, Bioinorganic, and Organometallic Program is made to Dr. Frank J. Feher of the Chemistry Department of the University of California at Irvine to support work on transition-metal-containing silsesquioxanes. In previous work, a vanadium complex of this type was found to catalyze polymerization of ethylene and propylene. In this study, the structure of the active polymerization catalyst and the mechanism by which it operates will be investigated. The results may be relevant to the reaction chemistry of silica-supported transition metal complexes generally. The understanding of silica surface structure and reactivity is of practical importance for applications in catalysis, ceramics, adsorbents, abrasives, thickeners, and lubricants. Large, incompletely condensed silsesquioxanes with structural similarities to silicon dioxide polymorphs have been prepared and used to prepare polyhedral oligometallasilsesquioxanes (POMSS). Vanadium, zirconium, titanium, molybdenum, and chromium complexes will be prepared, their catalytic reactivity tested, and the structure of their active sites determined. Solid state NMR will be used extensively.