Polymeric lithium cyclopentadienyl derivatives

FIGURE 15. Solid-state stmctures of polymeric lithium cyclopentadienyl derivatives 

Molecular fractions of polymeric lithium cyclopentadlenyl derivatives 

FIGURE 16. Molecular fractions of polymeric lithium cyclopentadienyl derivatives in the solid-state. The cations of the lithocene anions 47 and 48 (Ph4P+ and [(12-crown-4)2Li], respectively) have been omitted for clarity. With 55 the cation is [(THF)4Li]+. AU three are solvent-separated ion pairs. 

FIGURE 17. Donor-base-coordinated monomeric lithium cyclopentadienyl derivatives in the solid- 

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A new development in silsesquioxane ehemistry is the eombination of sil-sesquioxanes with cyclopentadienyl-type ligands. Reeently, several synthetie routes leading to silsesquioxane-tethered fluorene ligands have been developed. The scenario is illustrated in Seheme 47. A straightforward aeeess to the new ligand 140 involves the 1 1 reaction of 2 with 9-triethoxysilylmethylfluorene. Alternatively, the chloromethyl-substituted c/oxo-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, respeetively, as well as the novel zirconoeene complex 144. When activated with MAO (methylalumoxane), 144 yields an active ethylene polymerization system. 

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