Nature of the Active Sites in Soluble Ziegler-Polymerization Catalysts Generated from Titanocene Halides and Organoaluminum Lewis Acids

Abstract

That the active site in Ziegler-Natta polymerization catalysts is the transition metal-carbon bond receives strong support from the finding that pure transition metal alkyls, such as tetrabenzyltitanium [1], can themselves polymerize ethylene and propylene, even in the complete absence of any main-group alkyl. However, it is also evident that combinations of transition-metal salts or organometallics with main-group alkyls often display greatly enhanced catalytic activity and stereoregular polymerization in such processes [2]. The isotactic polymerization of propylene by TiCl₃ and Et₂AlCl [3] and the greatly accelerated polymerization of ethylene by Cp₂ZrMe₂ and (MeAlO)_n [4] are cases in point.

Part 44 of the series, “Organometallic Compoinds of Group III”.