Polyhedral oligometallasilsesquioxanes as models for silica-supported olefin polymerization catalysts

The hydrolytic condensation of cyclopentyl- and cyclohexyltrichlorosilane results in the formation of incompletely condensed polyhedral oligosilsesquioxanes. Our research efforts have focussed on the reactivity of trisilanol {dollar}rm Cysb7Sisb7Osb9(OH)sb3{dollar} with transition metal and main group elements. Silica-supported transition metal complexes have gained use a olefin polymerization catalysts. Since silsesquioxanes have a highly silecious oxide framework, the potential of polyhedral oligosilsesquioxanes as soluble models for silica-supported transition metal catalysts was investigated.; The discovery that {dollar}rm Cysb7Sisb7Osb{lcub}12{rcub}V(O){dollar} was capable of polymerizing ethylene in the presence of trimethylaluminum led to the survey of the reactivity of {dollar}rm Cysb7Sisb7Osb{lcub}12{rcub}V(O){dollar} with other Lewis acids. For example, the addition of GaCl{dollar}sb3{dollar} to {dollar}rm Cysb7Sisb7Osb{lcub}12{rcub}V(O){dollar} produced Lewis adduct {dollar}rm Cysb7Sisb7Osb{lcub}12{rcub}V(O){dollar}-GaCl{dollar}sb3.{dollar} The addition of {dollar}rm (Mesb3SiCHsb2)sb3Al{dollar} to solutions of {dollar}rm Cysb7Sisb7Osb{lcub}12{rcub}V(O){dollar} at {dollar}-{dollar}78{dollar}spcirc{dollar}C also produced a Lewis adduct. However, upon warming to room temperature, the vanadium center is alkylated and the aluminum atom is partially incorporated into the silsesquioxane framework. {dollar}sp{lcub}51{rcub}{dollar}V and {dollar}sp{lcub}17{rcub}{dollar}O NMR spectroscopy played an important part in the characterization of these new complexes.; The synthesis and reactivity of simpler alkyloxovanadium siloxide complexes were also investigated. The addition of triphenylsilanol to a solution of {dollar}rm (Mesb3SiCHsb2)sb3V(O){dollar} produced dialkyl complex {dollar}rm (Phsb3SiO)V(O)(CHsb2SiMesb3)sb2{dollar} and monoalkyl complex {dollar}rm (Phsb3SiO)sb2V(O)(CHsb2SiMesb3){dollar} in good yield. The addition of {dollar}rm (Mesb3SiCHsb2)sb3Al{dollar} to solutions of {dollar}rm (Phsb3SiO)V(O)(CHsb2SiMesb3)sb2{dollar} and {dollar}rm (Phsb3SiO)sb2V(O)(CHsb2SiMesb3){dollar} also produce Lewis adduct complexes. {dollar}sp{lcub}51{rcub}{dollar}V and {dollar}sp{lcub}17{rcub}{dollar}O NMR spectroscopy once again played an important part in the characterization of these complexes.; Finally, the chromate ester {dollar}rm Cysb7Sisb7Osb9(OSiMesb3)(Osb2CrOsb2){dollar} was synthesized and structurally characterized. {dollar}rm Cysb7Sisb7Osb9(OSiMesb3)(Osb2CrOsb2){dollar} also exhibited olefin polymerization activity upon addition of alkylaluminum reagents. The efforts to elucidate the mechanism of the catalyst forming reaction will be discussed.