Heterogeneous catalysis alkene polymerization

The range of reactions which have been examined is wide (248) and includes hydrogenations (256), ammonia synthesis (257), polymerizations (257), and oxidations (258). Little activity has occurred in this area during the past few years. Recent reports of the effects of sonication on heterogeneous catalysis include the liquefaction of coal by hydrogenation with Cu/Zn (259), the hydrogenation of olefins by formic acid with Pd on carbon (260), and the hydrosilation of 1-alkenes by Pt on carbon (261). 

Polymerizations of alkenes, with or without functional groups, are very important industrial processes. The industrial manufacture of polyethylene (PE) and polypropylene (PP), two of the largest plastics by tonnage, are based mainly on heterogeneous catalysts. However, the importance and relevance of homogeneous catalysis in polymerization reactions have increased significantly for two reasons. 

Zr and Hf hydrides have been proposed as intermediates or by-products in heterogeneous and homogeneous catalysis of alkene isomerization, polymerization, and trimerization reactions.388 657-659 For example, heating the well-characterized silica-bound Zr(neopentyl)ra (n 1, 2) with dihydrogen afforded silica supported Zr-hydrides as indicated by IR spectroscopy. 58 Interestingly, this silica-supported Zr hydride exchanged via cr-bond metathesis with alkanes to produce the corresponding Zr alkyl derivatives.388,660,661... 

In a similar vein, a series of papers published between 2002 and 2008 contains spectacular claims of highly enantioselective asymmetric additions of water to styrenes, unsaturated carboxylic acids, or simple terminal alkenes [34-Al]. The catalysts used are of the heterogeneous type and based on chiral biopolymers such as wool, gelatin, or chitosan as solid supports (sometimes in combination with silica or ion-exchange resins) that are doped with transition metal salts. This series of papers contains spectacular claims, insufficient experimental data, and erroneous chemical structures for the biopolymers used. As earlier work from the same group of authors on asymmetric catalysis on bio-polymeric supports is irreproducible [42], one is well advised to await independent confirmation of those results. 

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... 

Finally, actinide complexes such as [MCp 2R2] (M = Th or U, R = alkyl or H) are very active catalysts for the hydrogenation and polymerization of olefins. The complexes [U(allyl)3X] (X = Cl, Br, I) are excellent initiators for the stereospecific polymerization of butadiene, which produces rubbers that have remarkable mechanical properties. Some other complexes are active for the heterogeneous CO reduction and alkene metathesis. The field of catalysis using organoactinide complexes should considerably expand in the near future. 

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