Crotylnickel iodide

Thus, the butadiene polymerization in water medium initiated by the catalytic system KI + (C4H7NiX)2 (X = Cl, Br) is apparently effected by bis(7r-crotylnickel iodide). The reactivity and stereospecificity of the latter arise evidently from the stability of iodide bridges to hydrolysis. 

Since the electron density of nickel in bis(7r-crotylnickel iodide) is high, the formation of five-coordinate complexes is favored for compounds with vacant orbitals readily attached by dative bonds (11). The bases might be classed into two types by this characteristic ... 

Bases of the second class decrease the catalyst activity. The polymer yield obtained with bis(7r-crotylnickel iodide) is significantly higher than that produced by catalysts (C4H7NiI)2 -f- 2B [B = pyridine, P(C6H5)3 andP(C4H9)3]. 

Our experimental finding supports the view that the active site of butadiene polymerization in the presence of bis(7r-crotylnickel iodide) is the complex with nickel bound to iodide. Thus, the butadiene addition across syn-7r-allyllic bond produces trans-1,4-polybutadiene. 

More recently it has been shown that in the polymerization with TT-crotylnickel iodide the order in monomer falls from a value close to unity at [M] below 0.5 mole 1" to below 0.5 at [M] > 4 mole 1 . These observations have been interpreted in terms of scheme (c) on p. 162, namely coordination of two monomer molecules with the catalyst and with most of the catalyst existing in the complex (inactive) state. The molecular weights of the polymers are double those calculated from the kinetic scheme put forward [61] and this is attributed to coupling of live polymer chains on termination [251]. Molecular weight distributions are binodal consistent with slow propagation and transfer. 

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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