Tris zirconocenes, preparation

A new development in silsesquioxane chemistry is the combination of sil-sesquioxanes with cyclopentadienyl-type ligands. Recently, several synthetic routes leading to silsesquioxane-tethered fluorene ligands have been developed.86,87 The scenario is illustrated in Scheme 47. A straightforward access to the new ligand 140 involves the 1 1 reaction of 2 with 9-triethoxysilylmethylfluorene. Alternatively, the chloromethyl-substituted c/ovo-silsesquioxane derivative 141 can be prepared first and treated subsequently with lithium fluorenide to afford 140. Compound 141 has been used as starting material for the preparation of the trimethylsilyl and tri-methylstannyl derivatives 142 and 143, respectively, as well as the novel zirconocene complex 144. When activated with MAO (methylalumoxane), 144 yields an active ethylene polymerization system. 

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