Coordination polymerization definition

Definitions, chemical and physical properties, and general features of the most relevant catalyst types used in coordination polymerizations are described in Section 5.3, after the classification by type of monomers most frequently used and studied in this kind of polymerization reactions. 

According to Eliel s definition, the cationic coordinated polymerization of the cis and trans isomers of l-chloro-2-isobutoxy-... 

Since the development of the Ziegler catalyst based on crystalline TiCU, many more catalyst systems have been foimd that can be activated in a similar manner by alkylaluminium compoimds to promote the coordination polymerization of ethene. Therefore, the definition of a Ziegler catalyst refers to a system that combines ... 

The most famous mechanism, namely Cossets mechanism, in which the alkene inserts itself directly into the metal-carbon bond (Eq. 5), has been proposed, based on the kinetic study [134-136], This mechanism involves the intermediacy of ethylene coordinated to a metal-alkyl center and the following insertion of ethylene into the metal-carbon bond via a four-centered transition state. The olefin coordination to such a catalytically active metal center in this intermediate must be weak so that the olefin can readily insert itself into the M-C bond without forming any meta-stable intermediate. Similar alkyl-olefin complexes such as Cp2NbR( /2-ethylene) have been easily isolated and found not to be the active catalyst precursor of polymerization [31-33, 137]. In support of this, theoretical calculations recently showed the presence of a weakly ethylene-coordinated intermediate (vide infra) [12,13]. The stereochemistry of ethylene insertion was definitely shown to be cis by the evidence that the polymerization of cis- and trans-dideutero-ethylene afforded stereoselectively deuterated polyethylenes [138]. 

The discussion of Mnetic work will be here preceded by a summarized description of the chemical nature of the polymerization, to which we have attributed a mechanism of anionic coordinated type. Such a definition of the reaction mechanism depends upon the fact that the catalyst is a complex in which, generally, a transition metal acts as a coordinating agent and that a carbon atom, which belongs to the extremity of a growing polymeric chain, is coordinated to such a complex and, in the activated state, it possesses a negative charge. 

Perhaps the best studied group of titanium(IV) complexes is the alkoxides. The metal alkoxides generally have received a great deal of attention because of their ease of hydrolysis and reactivity with hydroxylic molecules, and their tendency to increase the coordination number of the metal which is opposed by the steric effect of the alkyl group. These properties result in materials, the characteristics of which range from polymeric solids to volatile liquids. The definitive review of this area is that by Bradley. ... 

N2 ligand is not able to induce appreciable surface mobility or relaxation. The tendency toward strong relaxation in the presence of adsorbates differentiates the chemistry of transition metal ions on silica from the chemistry of the same ions on crystalline oxides (on which relaxation and mobility are definitely smaller). This property is likely to play a fundamental role in determining the properties of Cr2+ (Ni2+) on silica in catalytic processes (e.g., ethene polymerization) for which a large number of coordination vacancies are needed. 

Within this overview of copper(I), lithium, and magnesium thiolate complexes, one of the aims is to highlight the influence that (intramolecular) nitrogen coordination exerts on the structure of such species, since intermolecular (auxiliary) coordination of heteroatoms often leads to poorly defined species. An example of this poor species definition is the reaction behavior of polymeric copper(I) thiophenolate, [Cu(SPh)]. with triphenylphosphine Several P-coordinated aggregates with variable stoichiometry were reported (Scheme 1) (27-29). This behavior makes it difficult to study one specific species in cop-per(I) thiolate catalyzed organic reactions since equilibria are likely to occur. 

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