Crotylnickel chloride

Bis(7r-crotylnickel chloride) is inactive in water medium with bromide a low yield of polymer with 50-60% trans, 40-50% cis-1,4, and 2-3% 1,2-units was obtained. (C4H7NiI)2 produces trans- 1,4-polybutadiene with 14-20% conversion. 

The authors suggested that the structure of bis(syn-7r-crotylnickel chloride) is inconsistent with the assumed mechanism of cis unit formation. From our point of view the apparent contradiction does not prove anything since in the reactive intermediate the nickel atom might not be linked with halide ligands. Different stereospecificity and reactivity of (C4H7NiCl)2 and (C4H7NiI)2 in hydrocarbon and water media indicate that the nature of active sites is not the same in both cases. 

However, the structural identity of polybutadienes prepared with bis(7r-crotylnickel chloride) and with (C4H7NiX)2+ Lewis acids system suggests that the nature of the active sites is similar for these catalysts. 

Taking into account the lability of the dimer with chloride bridges we suggest that butadiene attacks the bis(7r-crotylnickel chloride) with destruction of the halide bridges and formation of complexes like those formed by the interaction of crotylnickel halide with Lewis bases ... 

The active center formed by the interaction of butadiene with bis( r-crotylnickel chloride) or the products of the reaction of (C4H7NiX)2 + Lewis acids does not contain halides, and there is no steric hindrance for syn complex to be isomerized into an anti complex, which is more stable thermodynamically according to Bank (2). 

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. 

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