Nickel catalyst, diene polymerization

Many recent publications have described the stereospecific polymerization of dienes by ir-allyl compounds derived from Cr, Nb, Ni, etc. Of particular interest is the work of Durand, Dawans, Teyssie who have shown that ir-allyl nickel catalysts (XXI) in the presence of certain additives polymerize butadiene stereospecifically (87, 38). The active center results from reaction of acidic additives with the transition metal. 

Subsequent hydrogenation (Scheme 5) using a nickel catalyst affords the saturated ditetrahydrofurfuryl propane (19) (59). Ditetrahydrofurfuryl propane (60) is a solvent and co-catalyst for the selective polymerization of dienes to 1,2-poly dienes. 

Soluble cobalt and nickel catalysts for conjugated diene polymerization are usually prepared in the presence of monomer with the formation of a TT-allylic structure as a relatively stable intermediate, but the nature of attachment of other ligands to the active site is not known. Aluminium halides and cobalt halides react to form complexes of the structure (IX) [57]... 

Subjects specifically excluded are cycloolefin polymerizations catalyzed by naked nickel catalysts, palladium-catalyzed ethylene/carbon monoxide alternating copolymerizations, metathesis polymerizations of cyclic olefins, and diene polymerizations... 

Nakano, M. Yao, Q. Usuki, A. Tanimura, S. Matsuoka, T. Stereo- and regiospecific polymerization of cyclic conjugated dienes using highly active nickel catalysts. Chem. Commun. 2000, 2207-2208... 

Dienes or olefins are polymerized in the presence of a 7r-allylnickel complex and a phosphate as catalysts to afford the polymers having a Tt-allyl group at the end position as shown in eq. (19.50). Then they are able to easily copolymerize with styrene or isocyanates [61,72,92-96]. Further, the polymerization of isocyanate and cyclohexadiene has been tried in the presence of nickel catalysts [94,95]. 

The dienol phosphates are known to be less reactive and more stable than the corresponding dienic iodides or bromides. However, under iron catalysis, the oxidative addition step is easier than with palladium or nickel catalysts. This methodology circumvents the conventional use of dienyl iodides or bromides. Since these reagents are known to be sensitive and prone to polymerization, this strategy constitutes a substantial improvement for the synthesis of stereodefined conjugated dienes. 

The catalyst activity is so high that uranium concentration lower than 0.1 millimoles per liter allows a complete conversion of butadiene to be obtained in a few hours, at 20°C, The transfer reaction of uranium based catalyst is similar to that of conventional 3d-block elements (titanium, cobalt, nickel) so that the molecular weight of the polymer is affected by polymerization temperature, polymerization time and monomer concentration in the customary way. This is in contrast, as we shall see later on, to some catalysts based on 4 f-block elements. Uranium based catalysts are able to polymerize isoprene and other dienes to high cis polymers the cis content of polyisoprene is 94%, somewhat inferior to titanium based catalysts. In contrast, with 3d-block elements an "all cis", random butadiene-isoprene... 

Nickel is frequently used in industrial homogeneous catalysis. Many carbon-carbon bond-formation reactions can be carried out with high selectivity when catalyzed by organonickel complexes. Such reactions include linear and cyclic oligomerization and polymerization reactions of monoenes and dienes, and hydrocyanation reactions [1], Many of the complexes that are active catalysts for oligomerization and isomerization reactions are supposed also to be active as hydrogenation catalysts. 

The transition group compound (catalyst) and the metal alkyl compound (activator) form an organometallic complex through alkylation of the transition metal by the activator which is the active center of polymerization (Cat). With these catalysts not only can ethylene be polymerized but also a-olefins (propylene, 1-butylene, styrene) and dienes. In these cases the polymerization can be regio- and stereoselective so that tactic polymers are obtained. The possibilities of combination between catalyst and activator are limited because the catalytic systems are specific to a certain substrate. This means that a given combination is mostly useful only for a certain monomer. Thus conjugated dienes can be polymerized by catalyst systems containing cobalt or nickel, whereas those systems... 

The adoption of reaction models available for the polymerization of conjugated dienes by Ni- and Ti-catalysts to the polymerization of BD by Nd catalysis is justified by the similarities of the respective metal carbon bonds. In each of these mechanistic models the last inserted monomer is bound to the metal in a 3-allyl mode. The existence of Ni- -allyl-moieties was demonstrated by the reaction of the deuterated nickel complex [ rf- C4D6H)NiI]2 with deuter-ated BD (deuterated in the 1- and 4-position). After each monomer insertion a new 3-allyl-bond is formed [629]. As TT-allyl-complexes are known for Ti and Ni this knowledge has been adopted for Nd-based polymerization catalysts [288,289,293,308,309,630-636,638-645]. 

The acid-catalyzed hydrocarboxylation of alkenes (the Koch reaction) can be performed in a number of ways. In one method, the alkene is treated with carbon monoxide and water at 100-350°C and 500-1000-atm pressure with a mineral acid catalyst. However, the reaction can also be performed under milder conditions. If the alkene is first treated with CO and catalyst and then water added, the reaction can be accomplished at 0-50°C and 1-100 atm. If formic acid is used as the source of both the CO and the water, the reaction can be carried out at room temperature and atmospheric pressure.The formic acid procedure is called the Koch-Haaf reaction (the Koch-Haaf reaction can also be applied to alcohols, see 10-77). Nearly all alkenes can be hydrocarboxylated by one or more of these procedures. However, conjugated dienes are polymerized instead. Hydrocarboxylation can also be accomplished under mild conditions (160°C and 50 atm) by the use of nickel carbonyl as catalyst. Acid catalysts are used along with the nickel carbonyl, but basic catalysts can also be employed. Other metallic salts and complexes can be used, sometimes with variations in the reaction procedure, including palladium, platinum, and rhodium catalysts. The Ni(CO)4-catalyzed oxidative carbonylation with CO and water as a nucleophile is often called Reppe carbonylationP The toxic nature of nickel... 

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