Cyclooctene, catalytic dimerization

An obvious method to investigate the formation and the nature of the catalytically active nickel species is to study the nature of products formed in the reaction of complexes such as 3 or 4 with substrate olefins. This has been investigated in some detail in the case of the catalytic dimerization of cyclooctene to 1-cyclooctylcyclooctene (17) and dicy-clooctylidene (18) [Eq. (4)] using as catalyst 7r-allylnickel acetylacetonate (11) or 7r-allylnickel bromide (1) activated by ethylaluminum sesquihalide or aluminum bromide (4). In a typical experiment, 11 in chlorobenzene was activated with excess ethylaluminum sesquichloride cyclooctene was then added at 0°C and the catalytic reaction followed by removing... 

The following conclusions can be drawn (a) ir-Allylnickel compounds are probably not involved in the catalytic dimerization of cyclooctene, because the highest reaction rate occurs when only traces of these compounds can be detected further, the concentration of the new 7r-allyl-nickel compound (19) becomes significant only after the catalytic reaction has ceased, (b) The complex formed between the original 7r-allylnickel compound (11) and the Lewis acid is transformed immediately upon addition of cyclooctene to the catalytically active nickel complex or complexes. In contrast to 7r-allylnickel compounds, this species decomposes to give metallic nickel on treatment of the catalyst solution with ammonia, (c) The transformation of the catalytically active nickel complex to the more stable 7r-allylnickel complex occurs parallel with the catalytic dimerization reaction. This process is obviously of importance in stabilizing the catalyst system in the absence of reactive olefins. In... 

The selective, Ni-catalyzed, biphasic dimerization of 1-butene to linear octenes has been studied in the author s group. A catalytic system well loiown for its ability to form linear dimers from 1-butene in conventional organic solvents - namely the square-planar Ni-complex (q-4-cycloocten-l-yl](l,l,l,5,5,5,-hexafluoro-2,4-pen-tanedionato-0,0 )nickel [(H-COD)Ni(hfacac)] [103] - was therefore used in chloroaluminate ionic liquids. 

The transformation of the catalytically active species (21 or 24) into the complex (19) at the end of the catalytic reaction requires the abstraction of a hydrogen atom from the cyclooctene dimer and is accompanied by hydrogenation of the monomer to give cyclooctane [Eq. (5)] ... 

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