Alkene polymerization Ziegler-Natta catalysis

34 and 23.35), and repetition of these last two steps results in polymer growth. In propene polymerization, the stereoselective formation of isotactic polypropene is thought to be controlled by the catalyst s surface structure which imposes restrictions on the possible orientations of the coordinated alkene relative to the metal-attached alkyl group. 

Propene polymerization by the Ziegler-Natta process can be summarized as follows. 

Comment on the type of polymer produced and the need for selectivity for this form of polypropene. 

In this section, we describe selected commercial applications of heterogeneous catalysts. The examples have been chosen to illustrate a range of catalyst types, as well as the development of motor vehicle catalytic converters. 

Surface site with vacant coordination site 

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Alkene polymerization Ziegler-Natta catalysis and metallocene catalysts... 

The discovery of the stereoregular polymerization of alkenes by Ziegler-Natta catalysis opened a possible route to optically active polymers by a suitable modification of the catalyst. Indeed, Natta, in 1961, succeeded in polymerizing ben-zofurane 2 (Scheme 2) under the influence of a catalyst obtained by a combining of AICI3 and phenylalanine. Optical activity was detected for the polymer [15]. This reaction seems the first example of homogeneous asymmetric catalysis by a metal complex, however it is difficult to estimate the efficiency of the process from the specific rotation of the polymer. The asymmetric polymerization of... 

Stable transition-metal complexes may act as homogenous catalysts in alkene polymerization. The mechanism of so-called Ziegler-Natta catalysis involves a cationic metallocene (typically zirconocene) alkyl complex. An alkene coordinates to the complex and then inserts into the metal alkyl bond. This leads to a new metallocei e in which the polymer is extended by two carbons, i.e. 

One of the great discoveries of organomctallic chemistry was the catalyzed polymerization of alkenes at atmospheric pressure and ambient temperature. Vast quantities of polyethylene and polypropylene (over 15 million tons annually) are made by Ziegler-Natta catalysis. Ziegler and Natta received the Nobel prize in chemistry in 1963, and the importance of their work w stimulating interest in organometallic chemistry should not be underestimated. 

The 1963 the Nobel Prize in Chemistry was awarded to Karl Ziegler and Giulio Natta for their discoveries in the field of the chemistry and technology of high polymers . The polymerization of alkenes by heterogeneous Ziegler-Natta catalysis is of vast importance to the polymer industry. In... 

An Organometallic Com pound That Occurs Naturally Coenzyme B,2 591 Organocopper Reagents 592 Palladium-Catalyzed Cross-Coupling 595 Homogeneous Catalytic Hydrogenation 597 Olefin Metathesis 600 Ziegler-Natta Catalysis of Alkene Polymerization 603 Summary 606 Problems 608... 

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. ... 

Ziegler-Natta type catalysis is one of two methods used commercially to produce high density polyethylene, the other being metal oxide catalysis. Ziegler-Natta catalysis is very flexible the variety of catalyst systems that fall into this family is immense. In addition to ethylene, many other alkenes may also be polymerized, to produce either homopolymers when reacted in isolation or copolymers when... 

The first example of homogeneous transition metal catalysis in an ionic liquid was the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate (mp. 78 °C), described by Parshall in 1972 (Scheme 5.2-1, a)) [1]. In 1987, Knifton reported the ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [Bu4P]Br, a salt that falls under the now accepted definition for an ionic liquid (see Scheme 5.2-1, b)) [2]. The first applications of room-temperature ionic liquids in homogeneous transition metal catalysis were described in 1990 by Chauvin et al. and by Wilkes et ak. Wilkes et al. used weekly acidic chloroaluminate melts and studied ethylene polymerization in them with Ziegler-Natta catalysts (Scheme 5.2-1, c)) [3]. Chauvin s group dissolved nickel catalysts in weakly acidic chloroaluminate melts and investigated the resulting ionic catalyst solutions for the dimerization of propene (Scheme 5.2-1, d)) [4]. 

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