Nickel-complex Catalysts

Cyclization with various nickel complex catalysts gives up to 97% selectivity to a mixture of cyclooctatetraene derivatives, with only 3% of benzene derivatives. The principal isomer is the symmetrical l,3,5,7-cyclooctatetraene-l,3,5,7-tetramethanol (29). 

Shell Higher Olefin Process) plant (16,17). C -C alcohols are also produced by this process. Ethylene is first oligomerized to linear, even carbon—number alpha olefins using a nickel complex catalyst. After separation of portions of the a-olefins for sale, others, particularly C g and higher, are catalyticaHy isomerized to internal olefins, which are then disproportionated over a catalyst to a broad mixture of linear internal olefins. The desired fraction is... 

Furthermore, 2,2-difluoro-3-hydroxyesters are readily obtained from ClCF2COOMe and carbonyl compounds by electrolysis in a one-compartment cell using a sacrificial zinc anode and a nickel-complex catalyst [26], The catalytic cycle is shown in Scheme 3.11 and nickel zinc exchange is a key step. 

Rehmann [90] has employed ultrasound to improve the yield of polyphenylene, thought at one time to have a future as a conducting material. Using dibromobenzene and a nickel complex catalyst he investigated both bath and probe systems and found that sonication led to improved yield when compared to the conventional synthesis (i. e. reflux) and also had the advantage of allowing the use of a lower temperature (20 °C). 

The production of 1-alkenes from ethylene oligomerization was carried out with high selectivity in ionic liquids in the presence of a cationic nickel complex catalyst (ri -methallyl)-[bis(diphenylphosphino)methane-monoxide-K -P,0]nickel(II) hexafluoroantimonate, [(mall)-Ni(dppmo)]Sbp6 (240). The overall reaction rate of... 

It was shown that room-temperature molten salts derived from the combination of 1,3-dialkylimidazolium chloride and A1C13 can be used as solvents in two-phase catalytic dimerization of propene to give hexenes catalyzed by Ni(II) compounds (125). The effects of phosphane ligands coordinated to nickel and operating variables were also investigated (126). The dimerization products separate as an organic layer above the molten salt. This reaction has been carried out with n-butenes as the reactant and cationic nickel complex catalysts dissolved in organochloroaluminate liquids (127). 

Polymerisation with Homogeneous Nickel-complex Catalysts... 

Vinyl and aryl halides have been electrochemically coupled using nickel complex catalysts and these methods have been reviewed previously825. 

When applied to triple bonds, hydrocarboxylation gives a,p-unsaturated acids under very mild conditions. Triple bonds give unsaturated acids and saturated dicar-boxylic acids when treated with carbon dioxide and an electrically reduced nickel complex catalyst. Alkynes also react with NaHFe(CO)4, followed by CuCl2 2 H2O, to give alkenyl acid derivatives. A related reaction with CO and palladium catalysts in the presence of SnCE also leads to conjugated acid derivatives. Terminal alkynes react with CO2 and Ni(cod)2, and subsequent treatment with DBU (p. 1132) gives the a,p-unsaturated carboxylic acid. ... 

In this stoichiometric reaction sequence, a Poisson distribution of a-oletin products is obtained. The main disadvantage of this process is the large amount of aluminium alkyls needed in an industrial plant. To overcome this drawback, improvements of the process were developed by several companies. Only the two most important examples, the Gulf process and the Ethyl process, will be described in more detail. Shell developed a different route based on a nickel complex catalyst. Though other processes based on different transition metal catalysts have been developed, only the three processes mentioned above became important [16]. 

These chloroaluminate anions proved to be weakly coordinating toward nickel complex catalyst involved in our system. Moreover, the nickel active species is efficiently stabilized in the ionic medium, which plays both solvent and co-catalyst roles. 

Mechanistic investigations with special nickel complex catalysts have shown that nickel hydrides with chelating P-0 groups are the catalytically active species. The metal hydride reacts with ethylene to give alkylnickel intermediates, which can grow further by ethylene insertion or eliminate the corresponding a-olefins. A simplified mechanism is shown in Scheme 3-8 [9],... 

Scheme 3-8 Schematic of ethylene oligomerization with nickel complex catalysts [9]...

This was the appearance of publications by W. Reppe and co-workers in followed by Badische Anilin und Soda Fabrik patents/ They showed that various triphenylphosphine complexes of nickel, especially [Ni(CO)2(PPh5)2](Ph = QHs), were more effective than other nickel complex catalysts for the polymerization of olefinic and acetylenic substances and that others, especially [NiBr2(PPh3)2], catalyzed the formation of acrylic acid esters from alcohols (ROH), acetylene, and carbon monoxide ... 

These data indicate, what system Ni(ll)(acac)2+L based on nickel complex catalyst, may serve as catalyst for the alkylarens oxidation not only ethylbenzene but also toluene and cumene, - to the corresponding hydroperoxides. 

Liu Zhanxian, Linear oligomerization of propylene with chelated nickel complex catalyst, Gaodeng Xuexiao Huaxue Xuebao, 6, 1127, 1985 (Chinese) Chem. Abstr, 104, 20778U, 1986. 

Electrolysis at a nickel electrode (with no catalyst) led to N2 and H2 evolution, in contrast to the results with the nickel complex catalysts which gave N2 in close to 100% yield no significant amounts of H2 or NO were detected. 

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