Monocyclopentadienyl titanium derivatives

Monocyclopentadienyl titanium derivatives are the most active precursors for catalysts possessing high syndiospecific polymerisation activity for styrene and ring-substituted styrenes. The polymerisation activity of biscyclopentadie-nyl titanium compounds activated with methylaluminoxane is lower than that of other soluble titanium-based catalysts [73]. 

Probably substitution of the cyclopentadienyl ligand on alcoholysis and hydrolysis, and its transfer in reactions of di- and monocyclopentadienyl-titanium derivatives with FeClj or iron(II) acetylacetonate, follows a mechanism common for 77-ligand exchange in other metal 77-complexes (see later). 

Several cationic titanium and zirconium monocyclopentadienyl derivatives, [Cp MR2]+ (M = Ti, Zr), have been synthesized by the reaction of MR3Cp ... 

Among titanium-based precursors, monocyclopentadienyl compounds of the type CpTiCl3 or Cp TiCl3 activated by MAO or B(C6F5)3 showed the best performance, although several substituted mono-Cp or indenyl derivative and Cp-free compounds as Ti(CH2Ph)4 and Ti(OR)4 (R = alkyl, aryl) are quite active as well. In short, practically any soluble titanium compound can be used as precatalyst.154-158... 

Syndiotactic polystyrene was first obtained only recently by Ishihara et al. [5] in polymerisation with a homogeneous catalyst derived from a transition metal compound such as monocyclopentadienyltitanium trichloride and methylalu-minoxane in toluene. Since then, several authors have reported on the synthesis of syndiotactic polystyrene promoted by different catalysts based on metal hydrocarbyls such as benzyl compounds, half-sandwich metallocenes (e.g. monocyclopentadienyl, monopentamethylcyclopentadienyl and monoindenyl metal derivatives), metal alkoxides, metallocenes and some other compounds. These catalysts are commonly derived from titanium or zirconium compounds, either activated with methylaluminoxane or aluminium-free, such as those activated with tris(pentafluorophenyl)boron, and promote the syndiospecific polymerisation of styrene and substituted styrenes [5-10,21,48-70], Representative examples of the syndiospecific polymerisation of styrene using catalysts based on various titanium compounds and methylaluminoxane are shown in Table 4.2 [6,52,53,56,58],... 

The reactivity of such compounds has been studied in detail 201-212). Substitution of the 7r-cyclopentadienyl group has been investigated for monocyclopentadienyl halogen and alkoxytitanium derivatives, dicyclo-pentadienyltitanium halides and alkoxides 201-211), and for (77-a llyl) (77-cyclopentadienyl)palladium 212a). The stereochemistry of these complexes has been confirmed unequivocally by physical methods including X-ray studies. The structures of (77-allyl)(7T-cyclopentadienyl)palladium 213) and of (77-cyclopentadienyl)titanium trichloride 214) are shown. 

In 1985, Ishihara [10] at Indemitsu, Japan, reported that monocyclopentadienyl, indenyl, or fluorenyl titanium complexes, with different substituents on the Cp derivatives, were highly active for styrene polymerization, producing syndiotactic polystyrene with high melting temperature. Ishihara smdied early transition metals from group 3 or 4 systems based on late transition metals such as Ni were inactive for styrene homo- or copolymerization. Monocyclopentadienyl complexes, also... 

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