7r-Allylnickel halides

Method B2 A modification of method B4 for the preparation of catalysts starting from organonickel halides consists in the exchange of the halide anion by an anion of a strong complex acid, HY. This has been accomplished by reacting 7r-allylnickel halides (1) or their phosphine adducts (2) with silver salts (65) ... 

It has been known that 7r-allylnickel halides are catalysts for polymerization of butadiene (50, 51). When the halide is chloride, the polymer formed is cis-polybutadiene when the halide is iodide, the polymer is trans-polybutadiene. Porri and co-workers (50) interpret this effect in terms of the ease of dissociation of the dimeric complex 29 by butadiene. The chloride complex... 

A greater variety of substituted isocoumarins is available from the reaction of 7r-allylnickel halides with the sodium salts of 2-bromobenzoic acids. Use of the sodium salt is necessary to prevent debromination through an intramolecular proton transfer from the carboxyl group. The initial products, 2-allylbenzoic acids, undergo a palladium-assisted ring closure to isocoumarins. 

The discovery that, in strongly polar media, 7r-allylnickel halides react with a wide variety of organic halides has introduced what promises to be a most useful method for the selective combination of unlike groups (22)... 

A second mode of reaction is available in which unreacted allyl halide or 7r-allylnickel halide complex apparently reacts with either (XXII), or the acyl chloride formed from (XXII), and with (XXIII) to give the... 

Polymerization was carried out in benzene in the presence of bis-(7r-allylnickel halides). The latter were prepared from nickel carbonyl and allyl halide (allyl bromide, crotyl chloride, bromide, or iodide etc.). The results of the polymerization runs are reported in Table I. The data indicate that all of the bis(7r-allylnickel halides) initiate by themselves the stereospecific butadiene polymerization yielding a polymer with 97-98% 1,4-units. The cis-l,4/trans-l,4 ratio depends on the halide in the dimeric r-allylnickel halide but not on the nature of allylic ligand. The case of bis(7r-crotylnickel halides) shows the effect of halide on microstructure, for whereas (C4H7NiCl)2 initiates cis- 1,4-polybutadiene formation, trans-1,4 polymers are produced by (C4H7NiI)2. The reactivity increase in the series Cl < Br < I. 

The stability of halide bridges in dimeric r-allylic complexes against the action of bases depends on the nature of the halogen the chloride complexes are the least stable. According to Burger (3) the dimers of bis(7r-allylnickel halides) are hydrolyzed with destruction of bridges and monohydrate formation. 

This article describes further progress in the chemistry of 7r-allylnickel compounds. First, preparative methods for 7r-allylnickel halides, alkoxides, amides, and alkyls are described. Next, some chemical properties of these compounds—e.g., a recently observed disproportionation reaction—are discussed. Then, the use of 7r-allylnickel halides as homogeneous catalysts is discussed. Whereas bis (7r-allyl) nickel is a catalyst for butadiene cyclotrimerization, 7r-allylnickel halides combined with Lewis acids, such... 

The common preparative method for 7r-allylnickel halides is at the moment the reaction of nickel(O) olefin complexes like bis(cycloocta-1,5-diene) nickel, (IV), with allylic halides (23). The olefin complex, IV, can be prepared easily by reducing nickel(II) salts (like nickel acetyl-acetonate) with aluminum organic compounds in the presence of cycloocta-1,5-diene (5). 7r-Allylnickel halides and substituted 7r-allylnickel halides prepared according to this method are listed in Table I. 

Table I. 7r-Allylnickel Halides Prepared from Bis ( cycloocta-1,5 -diene) nickel ( 0 )...

In connection with the investigation of 7r-allylnickel halides, we synthesized some compounds of the type 7r-allylnickel X, where X is the anion of a proton acid. Two preparative methods have been used (a)... 

TT-Allylnickel halides are more stable, and thermal disproportionation is not observed even at higher temperatures. Recently, we found that TT-allylnickel halides can be disproportionated easily by treating them in solution with excess gaseous ammonia (2). Bis(7r-allyl)nickel and ammonia adducts of nickel dihalides are obtained in quantitative yields and can be separated easily. In fact, the disproportionation reaction represents at the moment the easiest way to synthesize bis (7r-allyl) nickel type compounds since as mentioned, all types of 7r-allylnickel halides can be prepared easily. The advantage of the new method lies in the fact that bis (TT-allyl) nickel type compounds can be prepared without prior preparation of organometallic allyl compounds, such as Grignard compounds, which are sometimes diflBcult to prepare. The disproportionation of TT-allylnickel halides has an analog in the chemistry of alkyl-mercuric halides, some of which disproportionate under the influence of ammonia (12). 

In considering dimeric 7r-allylnickel halides as homogeneous catalysts it should be remembered that solutions of 7r-allylnickel halides in toluene, for example, show only poor catalytic activity toward olefins like ethylene or propylene. Under forcing conditions of temperature and pressure a slow oligomerization of these olefins to a mixture of dimers, trimers, etc., is observed. 

Some experiments designed to obtain information about the nature of the catalytically active species have been carried out (15, 16), Complex formation between 7r-allylnickel halides and aluminum halides can be followed by the shift of the Trallyl protons in the H-NMR spectrum. By adding n electron donors, such as ethers or amines, the catalytically active complexes, XIII, are decomposed. 

The transfer of halide from 7r-allylnickel halide to aluminum to give a haloaluminum anion results in a strong decrease in the electron density and formation of free coordination positions on nickel. The presence and number of free coordination positions can be demonstrated by reaction with carbon monoxide. The catalytically active complex, XIII, reacts at —40°C. with 2 moles of carbon monoxide to give the inactive XIV which can be isolated. In XIII, there are accordingly two free coordination positions. During catalysis, these positions are presumably occupied by olefins in the form of 7r-complexes. A stable olefin 7r-complex, 7r-allylnickel (7T-cycloocta-l,5-diene) aluminum tetrabromide, XV, can actually be isolated by adding cycloocta-l,5-diene to a solution of the active complex, XIII. 

The dimerization reaction has been carried out under two different conditions. In laboratory experiments, the reaction is conveniently carried out under 1 or less than 1 atmosphere and at a temperature of —20° to — 10°C. These relatively low temperatures are necessary to obtain a sufficient concentration of ethylene or propylene in the catalyst solution. The dimerization catalyst for laboratory experiments is usually prepared by mixing, for example, chlorobenzene solutions of a 7r-allylnickel halide and an aluminum halide (or alkylhalide) in molar ratio of at least 1 1. The phosphine-modified catalyst is obtained by simply adding 1 mole of a phosphine per mole of nickel to the solution of the catalyst. When ethylene or propylene is introduced into the catalyst solution, reaction starts immediately, as evidenced by a sudden rise in temperature. Dimerization is exothermic to the extent of about 28 kcal./mole propylene dimer. Hence, the mixture must be stirred and cooled intensively during the reaction. Under these conditions (Table V), reaction rates of about 6 kg. 

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