Olefins nickel-catalyzed oligomerization

Nickel-based catalyst systems constitute one of the important catalysts for olefin oligomerization, because nickel is the only metal that can control the mode of linking of olefins. The specific activity is high, and it is one of the less expensive transition elements. Because of these advantages, much research has gone into the study of nickel-catalyzed oligomerization [148-1811. 

The Ni-catalyzed oligomerization of olefins in ionic liquids requires a careful choice of the ionic liquid s acidity. In basic melts (Table 5.2-2, entry (a)), no dimerization activity is observed. FFere, the basic chloride ions prevent the formation of free coordination sites on the nickel catalyst. In acidic chloroaluminate melts, an oligomerization reaction takes place even in the absence of a nickel catalyst (entry (b)). FFowever, no dimers are produced, but a mixture of different oligomers is... 

Selectivity Control in Nickel-Catalyzed Olefin Oligomerization... 

In the present chapter an attempt is made to summarize the available material concerning the control of selectivity in the nickel-catalyzed homogeneous oligomerization of olefins and related reactions [for a previous review of this topic, see Bogdanovic et al. (4)]. No attempt has, however, been made to give a complete literature survey. 

The oligomerization of ethylene to higher a-olefins is catalyzed by nickel(II) chelate complexes such as (22-XXXIV). The active species is a nickel hydride, generated in situ,... 

Recent Developments in Theoretical Organometallic Chemistry, 15, 1 Redistribution Equilibria of Organometallic Compounds, 6, 171 Redistribution Reactions of Transition Metal Organometallic Complexes, 23, 9S Redistribution Reactions on Silicon Catalyzed by Transition Metal Complexes, 19, 213 Remarkable Features of (t) -Conjugated Diene) zirconocene and -hafnocene Complexes, 24, 1 Selectivity Control in Nickel-Catalyzed Olefin Oligomerization, 17, lOS Silyl, Germyl, and Stannyl Derivatives of Azenes, N H Part I. Derivatives of Diazene, N3H2, 23, 131... 

Many transition metals catalyze oligomerization reactions between dienes and olefins or alkynes. Possible reaction products are legion. But it is almost exclusively with zerovalent nickel that cyclic products are formed. Addition of olefins or alkynes to catalysts mentioned in the previous section suppresses the cyclooligomerization and instead gives cyclo-co-oligomerization products. 

Based on Ziegler s work at the MPl fiir Kohlenforschung in Miilheim/Germany, Wilke and co-workers learned how to control the selectivity of nickel-catalyzed reaction by use of ligands. Keim, then at Shell at Emeryville, introduced P-O chelate ligands and carried out the basic research for the oligomerization process. The whole process was developed in a collaboration between Shell Development in the US and the Royal Shell Labs in Amsterdam/The Netherlands. Today there are two locations producing nearly 1 MMt of a-olefins per year. 

Extensive studies of the oligomerization of dienes by nickel catalysts were conducted by WUke and co-workers. More recently, Brookhart and co-workers reported the synthesis, isolation, and structural characterization of the active intermediate in nickel-catalyzed butadiene oligomerization (Equation 22.39). This species is formed from a cationic nickel-allyl species in the presence of butadiene. The coordination sphere of tlais complex contains one allyl and two olefin donors in a single hydrocarbon ligand that was formed from three butadiene ligands and the starting allyl group. 

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