Ziegler-Natta olefin polymerization active cationic species

On the technical scale, olefin polymerization is based on the activation of a suitable zirconocene precursor, typically Cp2ZrMe2 or Cp2ZrCl2, by a strong Lewis acid as co-catalyst. Mechanistic studies on Ziegler-Natta-like polymerization have long focused on the role of cationic alkylzirconocene species in the catalysis. There have been previous mass spectrometric studies of isolated metallocene ions in the gas phase, most notably by Richardson and co-workers. The failure to observe olefin oligomerization in this study was attributed to incomplete thermaliza-... 

An important development over the last two years has been the confirmation that cationic Group IV metal alkyl complexes are the catalytically active species in olefin polymerizations with homogeneous Ziegler-Natta catalysts. A number of complexes of the type [Cp2MR(L)] (M = Ti, Zr, Hf) have now been prepared, particularly when stabilized by donor ligands such as L = THF. The chemistry of zirconium complexes of this type has been reviewed. Some cationic benzyl complexes with stereorigid ligands (29)... 

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