Allyl nickel compounds

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... 

Insertion reactions with allyl-nickel compounds have also been investigated. No carboxylate intermediate could be observed in the condensation of bis-rj -allyhnickel with carbon dioxide, althou the reaction, however, produced y butyrolaClone in a 32% yield based on nickel [49.50]. 

Keywords Allylation Carbonyl compound Dienes Homoallylation Nickel catalysis Reductive coupling... 

Many recent publications have described the stereospecific polymerization of dienes by ir-allyl compounds derived from Cr, Nb, Ni, etc. Of particular interest is the work of Durand, Dawans, Teyssie who have shown that ir-allyl nickel catalysts (XXI) in the presence of certain additives polymerize butadiene stereospecifically (87, 38). The active center results from reaction of acidic additives with the transition metal. 

The primary (7, 47) and most commonly used organonickel compounds have been the dimeric 7r-allyl- (or substituted Tr-allyl-) nickel halides (1) (Scheme 1) or their monophosphine adducts (2) in the presence of Lewis acids such as aluminum halides or alkylaluminum halides (4, 48-53). The... 

Examples of w-allylnickel-X compounds (X = anionic ligand) other than 77-allylnickel halides which have been used in combination with (alkyl)aluminum halides as olefin oligomerization catalysts are 7r-allyl-nickel acetylacetonate (11) (Section III), 7r-allylnickel aziridide (4, 56), and bis(7r-allyl)nickel (6) (59). In addition to ir-allylnickel halides, organo-nickel halides such as tritylnickel chloride (60, 61) and pentafluoro-phenylbis(triphenylphosphine)nickel bromide (62), or hydridonickel halides, e.g., trans-hydridobis(triisopropylphosphine)nickel chloride (12) (Section III), give active catalysts after activation with aluminum halides... 

Mechanistic studies of the nickel-catalyzed cyclization of butadiene have been carried out. The formation of various cyclic compounds catalyzed by nickel complexes is explained via the intermediacy of ir-allylic nickel complexes 11 and 12. 

Bis(ir-allyl)nickel is not formed in this reaction, but the compound be made by condensing nickel vapor with tetraallyltin (131) ... 

In a sense the tr-allyl compounds of the transition metals can be regarded as the simplest of the sandwich molecules. Bis(jr-allyl)nickel, the best known of such complexes, has been shown by x-ray crystallography (104,105) to have a staggered arrangement of tr-allyl moieties and hence a C2h molecular conformation. The electronic structure of the ground state of bis(jr-allyl)nickel has been investigated by both semiempirical (47) and ab initio (274,275) methods, and a semiempirical computation has been performed on bis(7r-allyl)palladium (47). 

The second compound of this type was the very simple one, bis(ir-allyl)-nickel (20). 

The discovery of bis(7r-allyl)nickel led to the recognition that most of the transition metals form such complexes in which exclusively allyl groups are attached to the central metal atom (24).4 Further investigation demonstrated very clearly that in the transition allyl metal compounds both types of metal-carbon bonds, tj and it, play important roles, and that even differences in the participation of the two types of bonds are possible. By a rather peculiar... 

Hegedus and Varaprath studied the reactions of various bromodienes with Ni(CO)4 and with bis(cyclooctadiene)nickel. l-Bromo-2,5-hexadiene and 2-bromomethyl-1,3-butadiene give the stable products 62 and 63, respectively, which resemble allyl nickel halides in their properties (217). Similar compounds had been prepared several years previously from geranyl halides (218). l-Bromo-2,4-pentadiene and l-bromo-2,4-hexadiene, however, formed intractable materials which could not be isolated and purified. In these cases the red color of the solution which was first produced faded and NiBr2 was deposited. The desired compounds, however, could be generated in situ at — 30° C and used in coupling reactions with aryl, alkenyl, and allyl halides (217). 

On the other hand, there are indications that our expectations must not be set too high. A great variety of chemically extraordinary interesting transition metal organometallics has been prepared during the past decades. I think in particular of the types known as "sandwich compounds", exemplified by ferrocene, bisbenzenechromium, bis 7-allyl nickel and cyclobutadienemetal complexes ... 

It has been noted that unlike the palladium and platinum complexes, the nickel derivatives afford nickel iodide instead of the free metal. The reaction is accompanied by carbon monoxide evolution, which is increased in the presence of iodine. Independently of the stoichiometric ratio of Pd to Fe employed, the reaction consumes approximately half the amount of allyl-palladium compound. Hence the present authors assume that iron enneacarbonyl produces two moieties under the conditions of reaction ... 

The dimeric allylic nickel halide complexes are simpler in that no problems of reaction with organo-aluminium compounds are involved. They are of low activity and give polymer of low molecular weight owing to a rapid monomer transfer reaction [61]. The active centre is formed by dissociation of the complex in the presence of monomer and since the rate is proportional to [Ni] and [M] the extent of dissociation is small and the complex with monomer of low stability. 

The kinetics of butadiene polymerized by bis(7T-allyl nickel trifluoro-acetate) has been studied by Teyssie et al. [173]. Equilibrium constants for the formation of the complex (with aromatic compounds which give the equibinary polymer), calculated from cryoscopic measurements or polymer micro-structure, are 6—7 and 26—35 respectively for benzene and nitrobenzene. The higher concentration of active centres compared with... 

TJ ecent articles of this series (18) reported investigations of the synthe-sis of cyclododecatriene from butadiene (6) using a nickel catalyst. These investigations culminated in isolating a crystalline intermediate of this cyclization reaction (19). Strong support for the proposed structure of the intermediate, I was obtained by synthesizing bis (7r-allyl) nickel II (20). Subsequently, several 7r-allyl compounds of many transition metals were synthesized (21). 

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... 

Although, in principle, it is possible to displace one allyl group from bis (TT-allyl) nickel with any proton acid of greater acidity than propylene in fact, reaction with proton acids like water or alcohols is slow. In such cases, TT-allylnickel X-type compounds, can be prepared, for example, by treating 7r-allylnickel bromide with the alkali salt of the corresponding acid. In this way, 7r-allylnickel alkoxides, VII (with R= —CH3, —CoH.-) and —C, Hr,), (3), 7r-allylnickel amides (2), the 7r-allylnickel aziridide, VIII, and TT-allylnickel diphenylamide, were prepared. 

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