Ligand, catalyst cobalt

The physical properties of low melting point (60—105°C) syndiotactic polybutadienes commercially available from JSR are shown in Table 1. The modulus, tensile strength, hardness, and impact strength all increase with melting point. These properties are typical of the polymer made with a cobalt catalyst modified with triphenylphosphine ligand. 

Cobalt carbonyl complexes with tertiary phosphine ligands are not volatile. This makes possible a distillative separation of the reaction products from the cobalt catalyst system (Fig. 5). 

Interestingly, the activity of the corresponding cobalt catalyst possessing a pincer-type ligand is higher than that of the iron complex. In addition, the cobalt complex also acts as a catalyst in asymmetric mtermolecular cyclopropanations. 

Enediynes 38 undergo [2+2+2] cycloaddition reactions to afford polycyclic cyclohexadienes 39 in presence of a cobalt catalyst (Scheme 5.11) [14]- In this system, the presence of a NHC ligand improved the catalytic power of cobalt when compared with phosphine ligands. In addition to increased yields, lower ligand... 

In the hydroformylation of lower alkenes using a modified cobalt catalyst complex separation is achieved by distillation. The ligands are high-boiling so that they remain with the heavy ends when these are removed from the alcohol product. Distillation is not possible when higher alcohols or aldehydes are produced, because of decomposition of the catalyst ligands at the higher temperatures required. Rhodium complexes can usually also be removed by distillation, since these complexes are relatively stable. 

In 1968 Wilkinson discovered that phosphine-modified rhodium complexes display a significantly higher activity and chemoselectivity compared to the first generation cobalt catalyst [29]. Since this time ligand modification of the rhodium catalyst system has been the method of choice in order to influence catalyst activity and selectivity [10]. 

Lin, J. J. (Texaco Development Corp.) Process for synthesis of amidoacids using a cobalt catalyst and a bidentate phosphine ligand Eur. Pat. Appl. 263,624 1988. Chem. Abstr. 1989, 110, 154881. 

Alkyldiphosphines turned out to be very useful in a different reaction, namely the carbonylation/hydrogenation of ethylene oxide to give 1,3-propanediol also using cobalt catalysts. Interestingly, the ligand contains two phobane units bridged by 1,2-ethenediyl. The process was commercialised by Shell [18]. 

Comparison of the different types of cobalt catalysts shows that the in situ system [Eq.(2)] is most accessible while the Rep-, R(ind)-, and bori-ninato ligands having electron-withdrawing substitutents are the most active. The difference between the 14e" and the 12e core complexes makes itself apparent in the chemoselectivity of the reaction. Catalysts containing a 14-electron core favor pyridine formation, whereas those containing a 12-electron core (i.e., the rj -allylcobalt systems) favor the formation of benzene derivatives by cyclotrimerization of the alkynes. For example, in the reaction of propyne and propionitrile at 140°C in the presence of a 12-electron system (5), a 2 1 ratio of benzene to pyridine product is formed, whereas a catalyst containing the cpCo moiety (a 14-electron system) leads (under identical conditions) to the predominant formation of pyridine derivatives (84HCA1616). 

The Y ligand remains attached to Co during the catalytical cycle. Thus, changing the Y ligand has a major effect on the generation and activity of the cobalt catalyst in the pyridine synthesis (Fig. 3). Whereas varying L does not affect catalyst activity at 150°C (Fig. 2), quite different activity at... 

The steps by which this metal hydride forms the observed organic products are perhaps similar to those already discussed for cobalt catalysts. Steps which may be involved are intramolecular hydride migration to produce a formyl ligand ... 

The activity of rhodium complexes with phosphine or phosphite ligands is about three to four orders of magnitude higher than that of cobalt catalysts.21-23 [RhH(CO)(PPh3)3] preformed or prepared in situ has proved to be the active species when triphenylphosphine is used as ligand. Despite the high cost of rhodium, the mild reaction conditions and high selectivities make rhodium complexes the catalyst of choice in hydroformylation. 

The use of cobalt carbonyls, modified cobalt catalysts, and ligand-modified rhodium complexes, the three most important types of catalysts in hydroformylation,... 

In the unmodified catalyst system (Scheme 1), the rate shows a first-order dependence on hydrogen pressure and an inverse first-order dependence on carbon monoxide pressure, so that the rate is nearly independent of total pressure. The reaction is first order in alkene and first order in cobalt at higher CO pressures. With phosphine-modified cobalt catalysts, the rate-determining step depends on the ligand and the alkene. 

The obvious choice (at least from the standpoint of availability) to test the role of the salen ligand chelating Co(II) was to buy Jacobsen s cobalt catalyst, 2330 (Scheme 12). This species would introduce several new structural and stereoelectronic factors at the same time (relative to the... 

In principle, with cobalt catalysts similar pathways for deactivation exist. Because of the low price of cobalt compared to rhodium, this is less important in unmodified cobalt catalysis, but the deposition of cobalt clusters and metallic cobalt can cause nozzles and valves to plug up, resulting in the shutdown of the plant. In case of a ligand-modified cobalt catalysis, the same problems of ligand deterioration e.g., by oxygen and peroxides, arise, necessitating a meticulous purification of the starting materials. 

The first-generation catalyst, a cobalt carbonyl ligand, was employed in the BASF process. In the next generation, phosphine species were added to milden the reaction conditions and to optimize the linear to branched ratio. In the third... 

Fell also described the hydroformylation of fatty acids with heterogenized cobalt carbonyl and rhodium carbonyl catalysts [37]. The products of the reaction with polyunsaturated fatty acids were, depending on the catalyst metal, poly- or monoformyl products. The catalyst carrier was a silicate matrix with tertiary phosphine ligands and cobalt or rhodium carbonyl precursors on the surface. The cobalt catalyst was applied at 160-180°C and gave mostly monofunctionalized fatty acid chains. With linoleic acid mixtures, the corresponding rhodium catalyst gave mono- and diformyl derivatives. Therefore, the rhodium catalyst was more feasible for polyfunctionalized oleocompounds. The reaction was completed in a batch experiment over 10 h at 100 bar and 140°C rhodium leaching was lower than 1 ppm. 

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