Alkyl halides Compounds with halogen Table

The addition of a third component to the metal-alkyl is a widespread practice with MgCI2 catalysts in order to improve their performance and to control the polymer molecular structure. In ethylene polymerization the addition of modifiers (alkyl-halides, Lewis acids such as A1C13, halogens such as I2, and others) is rather limited and is principally used to modify the MWD (see Table 11 in Ref.53)). On the other hand, the addition of modifiers is almost indispensable to obtain satisfactorily stereoregular propylene polymers. The additives used for this purpose are generally electron donor compounds (Lewis bases) and a wide variety has been described in patent and scientific literature. 

Ester- and amide-substituted radicals bearing an adjacent stereocenter abstract hydrogen with high diastereoselectivity1. The radicals are generated via intra- or intermolecular radical addition to alkenes, halogen abstraction from alkyl halides or reductive cleavage of alkylmercury compounds. Some examples are shown in Table 1. 

Table 3 lists pure cultures, capable of co-reducing halogenated aliphatic compounds. Frequently, these organisms possess transition metal complexes that react with the alkyl halides. Among the most important of these complexes are the cytodm>mes, cerrinoids, frictor F430, and vitamin C 4]. 

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