Polymerization cobalt-catalyzed

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]. 

Neither the thermal nor the cobalt-catalyzed decomposition of 3-butene-2-hydroperoxide in benzene at 100 °C. produced any acetaldehyde or propionaldehyde. In the presence of a trace of sulfuric acid, a small amount of acetaldehyde along with a large number of other products were produced on mixing. Furthermore, on heating at 100°C., polymerization is apparently the major reaction no volatile products were detected, and only a slight increase in acetaldehyde was observed. Pyrolysis of a benzene or carbon tetrachloride solution at 200°C. in the injection block of the gas chromatograph gave no acetaldehyde or propionaldehyde, and none was detected in any experiments conducted in methanol. 

Scheme 6.10. Hawker et al. s[44] cobalt catalyzed polymerization affording polyester macromolecules. The degree of branching was determined to be ca. 49% based on degradative product distribution assessment.

Childers (5) found that a cobalt-catalyzed polymerization terminated with C14 labelled alcohol resulted in activity in the polymer, whereas H3 hydroxyl labelled alcohol gave inactive polymer. He deduced, therefore, that the mechanism was cationic. The organometal compound used in this catalyst was ethylaluminum sesquichloride, and his observations have been confirmed (26). We carried out virtually the same experiment as Childers except that AlEt2Cl was used instead of AFEtsCh with the opposite conclusion—namely, the growth was anionic (8). 

Metal—Carbon Bonds in Cobalt-Catalyzed Polymerization. Concentrations of metal-carbon bonds were determined (using tritium labelled alcohol) with increase in conversions. Experiments were made in two solvents (petrol and benzene) with two cobalt salts (chloride and naphthenate) under conditions giving rise either to liquid mixed structure or to high trans polybutadiene. The data are summarized in Table XI. Table XII and Figure 11 shows optical properties of some cobalt salts and complexes. 

The most interesting application from an industrial point of view is the cobalt-catalyzed one-step synthesis of 2-vinylpyridine from acetylene and acrylonitrile (eq. (10)). In this way the fine chemical can be manufactured using equal amounts by weight of the comparatively inexpensive components, acetylene and acrylonitrile. The 2-vinylpyridine synthesis must be carried out in pure acrylonitrile below 130-140 °C, otherwise acrylonitrile and the product 2-vinylpyridine undergo thermal polymerization [34]. Therefore only very active catalysts can be applied in the reaction of eq. (10). The best results were obtained using i/ -l-phenyl-borininatocobalt cod as the catalyst (productivity 2.78 kg 2-vinylpyridine per g cobalt [5 ej. 

To achieve a high-level of control over polymerizations, and resulting polymer microstructures, the preparation of pure exo isomers of the monomers were targeted. Exo-endo mixtures that were obtained as the cycloaddition adducts were not always separable by selective reciystallizations. Compounds 5, 6, 8, and 9 were separated from their endo isomers through selective recrystallization to give white crystalline solids. Cobalt-catalyzed transformation of the anhydride into a substituted imide linkage resulted in the protected amine functionalized monomer structure in excellent yield. For monomers 6, 8 and 9, pure exo isomer was isolated by successive recrystallizations from cold ether overall yields were 40 to 56%. 

Cobalt-Catalyzed Chain Transfer Polymerization A Review... 

Cobalt-Catalyzed Chain Transfer Polymerization A Review S Slavin, K McEwan, and DM Haddleton... 

Homogeneous catalysts play an important role in industry as well as in research laboratories. Established applications include, for example, polymerization processes with zirconocene and its derivatives, rhodium- or cobalt-catalyzed hydroformylation of olefins, and enantioselective isomerization catalysts for the preparation of menthol. In contrast to heterogeneous catalysts, more experimental studies of reaction mechanisms are available and the active species can be characterized experimentally in some cases. Most catalysts are based on transition metal compounds, for which electronic structures and properties are well studied theoretically. A substantial number of elementary reactions, such as reductive elimination, oxidative addition, alkene or carbonyl migratory insertion, etc., have been experimentally Studied in detail by means of isotopic, NMR, and IR studie.s, as well as theoretically. ... 

Cobalt( III)bis (ethy lenediamine) glycine, polymers with a,a -diaminosebacic acid, 174 Condensation polymerizations, base-catalyzed, 1... 

In the presence of catalytic amounts of vitamin B12, it has been possible to couple 1,1-disubstituted alkenes with defined regiochemistry under mild conditions in environmentally benign solvent system such as ethanol/water (Table 1). The mechanistic studies led the authors to conclude that organic free radicals are formed in this reaction. In the current process, the rate of combination of two radicals is increased by removing the persistent Co(ll) radical with Ti(in) or Zn. This is in contrast to cobalt-catalyzed free-radical chain transfer and cobalt-mediated living radical polymerization in which the cobalt macrocycle s role is to reduce the steady-state concentration of free radicals (Equation (33)). ... 

The breadth of reactions catalyzed by cobalt compounds is large. Some types of reactions are hydrotreating petroleum (qv), hydrogenation, dehydrogenation, hydrodenitrification, hydrodesulfurization, selective oxidations, ammonoxidations, complete oxidations, hydroformylations, polymerizations, selective decompositions, ammonia (qv) synthesis, and fluorocarbon synthesis (see Fluorine compounds, organic). 

The stereospecific polymerization of alkenes is catalyzed by coordination compounds such as Ziegler-Natta catalysts, which are heterogeneous TiCl —AI alkyl complexes. Cobalt carbonyl is a catalyst for the polymerization of monoepoxides several rhodium and iridium coordination compounds... 

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