Ziegler-Natta catalysts alkene oligomerization

Since cationic titanium complexes have been proposed as intermediates in alkene polymerization by soluble Cp2TiCl2/AlR3-based Ziegler-Natta catalysts see Ziegler-Natta Catalysts), there has been considerable interest in the synthesis and reactivity of cationic titanium complexes (see Oligomerization Polymerization by Homogeneous Catalysis). 

Alkenes.— A text on Ziegler-Natta catalysts has been published and polymerization by transition-metal hydrides, alkyls, and allyl compounds heis been reviewed. A reaction model for Ziegler-Natta polymerization has also been formulated. The conventional mechanism for alkene dimerization, oligomerization, and polymerization has, however, been questioned because there are no unambiguous examples of metal-alkyl-alkene compounds which unda go alkene insertion into the metal-alkyl bond. Also, catalysts which effect Ziegler-Natta polymerization are often active for alkene metathesis reactions and so a similiar mechanism for both has been proposed (Schrane 2). ... 

Ziegler-Natta-type catalysts, which are active in polymerization and oligomerization of alkenes. are also influenced by adding CO2 to the reaction mixture. The addition of CO2 changes the molecular we t and crystallinity of the products or the activity and selectivity of the catalyst, both in polyethylene [307,308] and in polypropylene production [309-312]. 

Busico, V. Cipullo, R. Corradini, P. Ziegler-Natta oligomerization of 1-alkenes A catalyst s fingerprint. 1. Hydrooligomerization of propene in the presence of a highly isospecific MgCl2-supported catalyst. Makromol. Chem. 1993,194,1079-1093. 

Alkenes. —Reviews on Ziegler-Natta catalysis and the stereoregular and sequence-regular polymerization of butadiene have been published and the stereoselective oligomerizations of isoprene by lithium and palladium catalysts have been compared. Semi-empirical MO calculations suggest that Ziegler-Natta polymerization proceeds via a bis-alkene complex and a metallacyclo-pentane intermediate. ... 

The most important representatives are the lowest 1-alkenes, ethylene and propene. Ethylene is not particularly easily polymerized by radical or ionic mechanisms. Its importance as a monomer was greatly enhanced by the discovery of coordination polymerizations. Propene is oligomerized by radical and ionic initiators. This explains the importance of Natta s modification [1] of Ziegler [2,3] catalysts, enabling inferior raw materials to yield high-quality polymers. 

The 1963 Nobel Prize in Chemistry was awarded to Karl Ziegler and Giulio Natta for their research on catalysts (see Catalysis) for the oligomerization see Oligomer) and polymerization see Polymerization) of alkenes under mild conditions of temperature and pressure. Their discoveries have grown into a multibillion dollar industry for the production of plastics, elastomers, and inexpensive feedstock chemicals for copolymers, surfactants, and other useM additives. ... 

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