Silica, a porous solid material made by purifying and melting sand, is used widely as a solid support for industrial catalysts. Such catalysts often consist of metal atoms or metal-containing molecules partially buried in the silicon-oxygen framework at the silica surface. In work preliminary to that proposed here molecules based on the silicon-oxygen framework, but soluble in organic solvents, were synthesized. Metal adducts of these molecules are expected to be excellent models of the silica-based catalysts, with the advantage that they can be studied by a variety of techniques to which surface catalysts are not amenable. The studies should lead to a more profound understanding of silica-based catalysts and provide information needed for the rational design of better catalysts. The aim of our research is to develop a new class of transition- metal-containing siloxane macromolecules, called polyhedral oligometallasilsequioxanes(POMSS), that can be used to model reaction processes that occur on silica-supported metal-oxide catalysts. The proposed research is focussed on three major areas: 1) Synthesis and Reactivity Studies of Ti and Zr- Containing POMSS: By examining the reactivity of Ti and Zr- containing POMSS with substrates such as carbon monoxide, hydrogen, oxygen, ethylene, acetylene, etc., it is proposed to "finger-print" the inherent chemical reactivity of these interesting new complexes. 2) Reactivity Studies of V-Containing POMSS: V-containing POMSS will be used to gain access to reactive intermediates that are believed to be involved in VO(OR)3-catalyzed oxidations of hydrocarbons by alkyl hydroperoxides and hydrogen peroxide. 3) Synthesis of POMSS Containing Group VII and VIII Transition-Metals: Several synthetic approaches to POMSS containing late transition-metals will be used in efforts to develop the trisilanol ligand into a general ligand that can be used as a silica model with virtually any transition-metal.
