Metallocene Molecular Symmetry and the Catalysts Syndiotactic Specificity

Metallocene Molecular Symmetry and the Catalyst s Syndiotactic Specificity 

All syndiotactic-specific catalysts that have been discussed so far had one principal element in common their precatalyst s metallocene molecules in solid phase all presented bilateral molecular symmetry or a vertical plane of S5mimetry (ffy) in the solid state. However, from the discussions in Sect. 4.3 it is clear that the whole notion of a perfect molecular symmetry, bilateral or otherwise, in the solution phase should be handled with caution and not t taken very literally. We saw that even with initially perfect bilateral symmetric metallocene molecules like 1 (2) and 6 (7), the perfect symmetry may be lost, at least in part, in solution and during different stages of the polymerization due to incessant t, and possibly t  

1 Syndio- and Nonsyndiospecific Catalyst Systems with C Symmetric Metallocene Structures 

A disappointing example of this kind is the performance of the bilaterally symmetric 

As mentioned in Sect. 2.4, complex 8 is prepared by selective hydrogenation of the fluorenyl moiety of the parent highly syndiotactic-specific metallocene molecule 6. Its crystal structure is presented in Fig. 23. Complex 8 fulfills all symmetry requirements that one would expect a priori from a would-be syndiotactic-specific precatalyst molecule, nevertheless, after its activation with MAO and its exposure to propylene, complex 8 produces polypropylene chains with perfectly atactic microstructure [28, 30]. 

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