Cyclopentadienyl derivatives substitution polymerization

Annulated derivatives of cyclopentadienyl, such as indenyl and fluorenyP (Figure 3.15), as well as acenaphthyl-substituted cyclopentadienyl, and pentalenyl, are some of the most important cyclopentadienyl derivatives. They, and their derivatives with interarmular bridges, play a major role in controlling stereochemistry during the metal-catalyzed polymerization of olefins, as is described in Chapter 21. A number of permethylindenyl complexes have been reported.- ... 

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. 

The induction of chirality in Cp- metal derivatives may also be studied. There are different ways that even achiral substituents on a cyclopentadienyl ring can give chiral metal complexes. The induction of chirality can proceed through their substitution pattern and/or a hindered ring or substituent rotation. The isotactic polymerization of propylene by means of metallocene catalysts is one example where such a metallocenic chirality has already been employed in an important stereoselective synthesis. 

A particular subset of these ligated dialkyls are those in which the ligand is tethered to the cyclopentadienyl ligand. Thus, chromacyclopentane and cycloheptane derivatives stabilized by the (7/ 7/ -Me4C5CH2CH2NMe2) ligand have been prepared and their reactivity supports the intermediacy of such metallacycles in the catalytic trimerization of ethylene. A variety of donor-ligand-substituted cyclopen-tadienylchromium(III) complexes with amino and phosphino substituents has been prepared and screened for an ethylene polymerization activity. ... 

Metallocene derivatives are the most extensively studied class of homogeneous catalysts for the polymerization of olefins. Less saturated and less hindered mono-Gp group 4 metal species of the type [Cp MR2]+ (Cp denotes Cp or a substituted cyclopentadienyl ring) may also behave as useful catalysts or initiators for olefin polymerization. Catalysts for syndiospecific polymerization of styrene based on mono-Cp titanium derivatives with different substituents on the Gp ligand and with various types of tetraphenylborates have been examined. A good relationship between the... 

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