Substituted indenyl and cyclopentadienyl catalysts

Chapter 3 Substituted Indenyl and Cyclopentadienyl Catalysts for Stereoselective... 

According to an early hypothesis21, stereoregular isotactic polymerization requires the presence of chirality within the catalyst. Thus, with achiral metallocenes mostly atactic polymers are obtained. Chiral ansa-metallocenes with substituted cyclopentadienyl ligands, or especially with indenyl and tetrahydroindenyl ligands, are effective in stereoselective polymer synthesis. 

Polymers of a similar microstructure are obtained if unbridged substituted metallocenes having a significant rotational isomerisation barrier are used as catalyst (Fig. 16). Early attempts concentrated on substituted cyclopentadienyl and indenyl compounds [134—138],... 

Mw = 19,000, and Tm = 155 °Cwithapolymerizationactivityof 10 kg PP/mmolZr h, as compared to Mw = 920,000 and 880 kg PP/mmol Zr h obtained with the 2-methyl-4-naphthyl-substituted bis(indenyl) catalyst 9 under similar polymerization conditions (see Chapter 3 for a further discussion of cyclopentadienyl ligand substitution pattern effects in propylene polymerization). 

A strategy for stereoblock propylene polymerization that can be viewed as a hybrid between those described in Sections 8.3.2 and 8.3.3 consists of using metallocene catalysts with hapto-fiexible cyclopentadienyl-aryl ligands.The catalyst precursors in these systems are Ti(IV) or Zr(IV) complexes bearing a (substituted) cyclopentadienyl or indenyl ligand bridged to a neutral aromatic moiety such as a (substituted) phenyl or naphthyl. A typical example is 4 (Scheme 8.5), which... 

---