Indenyl—cyclopentadienyl zirconium

Scheme 15 Reactivity of mixed indenyl-cyclopentadienyl zirconium complexes toward...

Complex 18 polymerises propene to crystalline isotactic polypropene after activation with methylaluminoxane. X-ray crystallography shows that 18 has a C2 symmetry axis and that both coordination sites are equally shielded. The related complexes, bis l-(5-cholesten-3a-yl)indenyl zirconium dichloride and diraethylsilyl-his(2-methyl-4-r-butyl-cyclopentadienyl) zirconium dichloride, can also be activated by methylaluminoxane for the stereoselective polymerisation of propene. i . ... 

A comprehensive study of 15 zirconecene monomethyl monochloro compounds and their exchange of chloride for methyl with AlMe3 indicates that the exchange process is a function of the electron deficiency at the metal.62 With low electron densities, the zirconium is more likely to exchange chloride for methyl. The study revealed low electron densities at the metal for the indenyl compounds by comparison to the cyclopentadienyl compounds. The study also revealed that steric effects are minor compared to the electronic effects of the ligands on the zirconium. 

Figure 10.20. Cyclopentadienyl-indenyl zirconium catalyst for hemispecific polymerisation...

Stereoblock polypropylene is synthesized by unbridged metallocenes such as bis(neomenthyl)zirconium dichloride (7) with cyclopentadienyl or phenyl substituted indenyl ligands [55, 56]. The stereoblock length increases at lower polymerization temperatures. Products containing isotactic and atactic blocks are elastomeric if the isotactic block length is short. Rieger [57] obtained similar polypropylenes by bridged fluorenyl-substituted indenyl zirconium complexes. 

To date, two types of metallocene complexes have been used in the polymerization of olefins at CNT surfaces by PFT a ruthenium alkylidene complex anchored by two routes onto SWCNTs via a pyrene derivative spacer [94], and zirconium complexes of general formula [(R)2ZrCl2], R being a derivative of cyclopentadienyl or indenyl, anchored onto CNTs modified with MAO [97]. 

The thallium salt of (l,5-bis(cyclopentadienyl)-hexamethyltrisiloxyl)(indenyl)zirconium dichloride reacts with />tolylsulfonyl-treated silica to form a tethered metallocene with a cyclopentadiene group bound to the surface (Scheme 9). This catalyst polymerizes ethylene in the presence of MAO with activities much higher than those of Cp(Ind)ZrCl2 supported on silica, but still less than that of the homogeneous catalyst. ... 

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