Allyl-nickel derivatives

The RMgX is added to a suspension of the Ni salt in ether at low T. When the reaction is complete, the solvent is evaporated and the product isolated by crystallization from pentene or by sublimation. The resultant bis(allyl)nickel derivatives have limited thermal stability decomposition occurs between 20°C and — 30°C depending on the nature of the substituents (see Table 4). A procedure is available for Ni(i -C3H5)2 Alternatively, the... 

Carbon-carbon bonds can be formed between unlike groups by reaction of n-allyl nickel derivatives (formed from nickel carbonyl) and alkyl halides. ... 

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 first example illustrated in Scheme 13 portrays a novel route to the cephalosporin derivative (47) [28, 29] through the intermediacy of the allyl nickel species (46). The second example provides... 

Several nickel derivatives of the type [ANiXfi (A = allyl, X = halogen) are known, but they are very much less stable to air than the palladium compounds (76, 77). The small dipole-moment of bis (ally lnickel bromide) may mean that the nickel-bromine bridges are not coplanar (76). 

The allyl group itself may also be attached to a cyclopentadienyl-metal residue, giving compounds of the type (CjHsJMCCsHs). These are known for nickel (77, 152), palladium (232), and platinum (232a). The palladium and platinum compounds are remarkably stable the nickel derivative is. liquid at room temperature, and decomposes very readily in oxygen. 

In principle pentadienyls can bond to transition elements in at least three basic ways, tj3, and tjs (Fig. 1). These can be further subdivided when geometrical factors are considered. If r 5 coordination could be converted to rj3 orr/1, one or two coordination sites could become available at the metal center, and perhaps coordinate substrate molecules in catalytic processes. Little is known about the ability of pentadienyl complexes to act as catalysts. Bis(pentadienyl)iron derivatives apparently show naked iron activity in the oligomerization of olefins (144), resembling that exhibited by naked nickel (13). The pentadienyl groups are displaced from acyclic ferrocenes by PF3 to give Fe(PF3)5 in a way reminiscent of the formation of Ni(PF3)4 from bis(allyl)nickel (144). 

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 ... 

In their studies on the use of silyl-substituted ligands as thermal and oxidative stabilizers of transition metals, Pannell and collaborators [79] show that tram- -trimethylsilyl-3- / -allyl(trimethyl)tin can be prepared in an approximate 50% yield by the Barbier reaction of a trialkyl or triarylmetal chloride with magnesium metal and l-trimethylsilyl-3-chloroprop-l-ene. With nickel(II) chloride, magnesium, a trace of mercuric(ll) chloride, and 2-trimethylsilyl-3-chloroprop-l-ene, the thermally and oxidatively stable bis( / -2-trimethylsilylallyl)nickel derivative is prepared in 36% yield. The unsubstituted derivative is thermally unstable and ignites in air. 

An interesting synthesis of isocoumarins uses the n-allyl nickel halides and n-olefin palladium complex, while another involves an aromatic nucleophilic substitution by the carbanion derived from acetone... 

Unsymmetrical allyl complexes react almost exclusively at the less substituted end of the al-lylic system. Santalene 71 has been prepared from 69 and 16 in two ways. Coupling the Grignard reagent 70 MX = MgBr with 16 gives 20% yield16 while the allyl nickel complex 70 MX = Nil couples with 16 in 95% yield.17 This is a major development from the allyl derivatives of Mg and Li, which tend to react at the more substituted end of the allyl system, and are in any case less well behaved than the nickel complexes. 

Modern developments have included allyl groups functionalised at the ends, particularly those derived from silylated enals such as 72. The application shown here creates a cyclopentenone 74 by combination of the allyl nickel 73 with an alkyne and CO rather in the style of the Pauson-Khand reaction (chapter 6).18... 

This last example succeeds partly because nickel catalyses the union of the three reagents in the second step. Similar things happen in the combination of nickel allyls with zinc borates 76. The allyls are derived from unsymmetrical allylic acetates 75 and react at the end remote from the phenyl group (R1 is an alkyl group and R2 is an aryl or alkyl group).19... 

Reduction to the alcohol, tosylation and conversion to the C-22 iodo derivative provides the substrate for reaction with a-(dimethyl allyl) nickel bromide. This coupling reaction gives the desmosterol side chain directly [scheme (7)] ... 

Coupling of Allyl Halide Derived Nickel-Allyl Complexes with Alkyl Halides and Other Electrophiles... 

Recently, Ni-catalyzed allylic substitutions of simple alkenes for the formation of 1,4-dienes 174 have been described by Jamison and Matsubara. Allylic alcohol derivatives 172, bearing a variety of leaving groups, can be coupled with a wide range of simple alkenes 173 including gaseous ethylene and propylene. The key for the reaction was the use of the appropriate nickel-phosphine complex and a stoichiometric amount of a silyl triflate. Reactions of 1-alkyl-substituted alkenes... 

In contrast to the transition metal catalysts above, nickel complexes have been studied intensely for the polymerization of CHD and its derivatives. jr-Allylnickel-based complexes were employed by Dolgoplosk et al. for CHD polymerization. They used n-alkenylnickel halides, for example, K-metallyl nickel dichloride and it-allyl nickel dibromide, combined with electron acceptors such as chloranil (tetrachloro-/ -quinone) or nickel trichloroacetate. Unfortunately, the true propagating species of the above catalytic systems are not clear, but they were moderately active for CHD polymerization and the polymer obtained appeared to have a predominantly 1,4-linked structure. However, the stereoregularity of the polymer was not very high based on its Tm (270 °C). 

Bis(allyl)nickel complexes react with alkyl derivatives of 2,3-dihydro-l,3-diborole to give the first n -allyl tetradecker complexes (14) to be isolated. ... 

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