Nickel displacement reactions

In 1954, Ziegler and coworkers observed that the course of the reaction of ethene with trialkylalanes was drastically altered by the presence of traces of nickel salts [25]. Instead of low molecular weight polyethylene, the only product was 1-butene. Obviously, the transition metal strongly supports the displacement reaction of the alkyl group bonded to the aluminum by ethylene, a reaction which can be formally described as transfer of a hydridoalane. 

The electrochemical series corresponds only to the standard condition, i.e., for unit activity of the ions, since a change to another ionic concentration can alter the order of the electrode potentials of the elements very markedly. The case of nickel plating mentioned earlier may be taken as typically illustrative of the many practical examples of the effects and the consequences of nonstandard conditions. It must also be mentioned in the context of the examples of displacement reactions provided earlier that the concentrations and the electrode potentials frequently vary during a displacement reaction. 

Another simple oligomerization is the dimerization of propylene. Because of the formation of a relatively less stable branched alkylaluminum intermediate, displacement reaction is more efficient than in the case of ethylene, resulting in almost exclusive formation of dimers. All possible C6 alkene isomers are formed with 2-methyl-1-pentene as the main product and only minor amounts of hexenes. Dimerization at lower temperature can be achieved with a number of transition-metal complexes, although selectivity to 2-methyl-1-pentene is lower. Nickel complexes, for example, when applied with aluminum alkyls and a Lewis acid (usually EtAlCl2), form catalysts that are active at slightly above room temperature. Selectivity can be affected by catalyst composition addition of phosphine ligands brings about an increase in the yield of 2,3-dimethylbutenes (mainly 2,3-dimethyl-1-butene). 

In 1971, Otsuka etal63,64, and Klein and Nixon65 simultaneously reported the formation of nickel 7r-complexes of azobenzene. The tr-bonded structure (type IV, Fig. 3) was assigned on the basis of displacement reactions and spectroscopic evidence. Treatment of (jr-Ph—N=N-Ph)Ni (PR3)2, (R = Me, Bu, Ph), with aqueous ethanol or with dimethylglyoxime in THF resulted in the reduction of the diazeno... 

Insignificant impurities of heavy metals (e.g. nickel) in a reactive medium or equipment material can cause a secondary displacement reaction which forms higher olefines ... 

Reactions of organomagnesium compounds with dialkyl sulfates or alkyl sulfonates often give satisfactory yields of the products of displacement of sulfate or sulfonate. Side-reactions have been observed, but they can often be avoided for example, an excess of the sulfate or sulfonate should be used with Grignard reagents, as some is consumed by nucleophilic attack by halide ion [A]. The dialkyl sulfates are reactive, but hazardous. Toluenesulfonates (tosylates) are less reactive, but their reactions are catalysed by copper complexes the reactions of trifluoromethanesulfonates (triflates) are catalysed by nickel complexes. Reactions of Grignard reagents with secondary tosylates appear to follow an Sn2 mechanism, with inversion of configuration [43],... 

If it is now assumed that cyclododecatriene-nickel could be an intermediate in the cyclododecatriene synthesis, this compound should undergo displacement reactions with other electron donors and especially with butadiene. 

The two compounds, bis (cyclo-octadiene) nickel and (cyclo-octatetraene) nickel, can also be synthesized directly by reduction of nickel acetylacetonate in the presence of olefins. But bis (cyclo-octatetraene) nickel is obtained only by a displacement reaction on the centro-nickel compound. 

Displacement Reaction. Much of what has been said about the alkylation reaction is also valid for the displacement reaction. Here also it is of importance to keep the nickel level as low as possible, not only to prevent isomerization and branching during displacement, but especially to circumvent trouble during the subsequent separation of TEA from olefins. 

At least 20 p.p.m. of nickel (TEA basis) are required in order to obtain 97 to 99% displacement within 2 hours (200° F., 2000 p.s.i. of ethylene). After completion of the reaction, when the ethylene pressure is released, a displacement reaction product containing traces of nickel catalyst tends to revert to alkylaluminum. This reaction takes place slowly at room temperature and atmospheric pressure, but the rate accelerates at the conditions required for TEA-olefin separation. It is no surprise, then, that even after only a few seconds contact a significant amount of back-alkylation will take place. 

In the course of these investigations, an experiment was carried out to prepare hexyl and octyl derivatives of aluminum by reaction of triethylaluminum with ethylene. Instead of the anticipated aluminum alkyls, an almost quantitative yield of 1-butene was obtained. After a strenuous investigation, Ziegler and his coworkers found that an extremely small trace of metallic nickel caused this change in the course of the reaction. The nickel, present from a previous hydrogenation experiment, catalyzed the displacement reaction (Reaction 2) of 1-butene from butylaluminum (Reaction 3),... 

Nickel(0)-olefin complexes are often prepared by displacement reactions on [Ni(l,5-COD)2] - ... 

The reactivity of aryl chlorides can be increased by adding lithium bromide, and at aryl sulfonates with lithium chloride or bromide [43,49]. This observation is based on the well known palladium- or nickel-catalysed displacement reaction of chloride (or aryl sulfonates) to more reactive bromide, what increases the reaction rate [51,52]. 

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