Stereospecific polymerization of butadiene by catalysts prepared from π‐allyl nickel halides

Butadiene has been polymerized by π‐allyl‐Ni‐halides (I) to low molecular weight stereoregular polymers, with either benzene, n‐pentane, tetrahydrofuran, cyclohexanol, or ethyl alcohol used as solvents. Solid polymers and oily products were simultaneously obtained as polymerization products. In benzene as solvent, π‐allyl‐Ni‐I and π‐allyl‐Ni‐Br gave predominantly trans‐1,4 polymers, while π‐allyl‐Ni‐Cl gave polymers largely composed of cis‐1,4 units. In the other solvents predominantly trans‐1,4 polymers were obtained, irrespective of the nickel derivative used. By reacting π‐allyl‐Ni‐Br, in benzene solution, with either AlBr3, Al2(O‐i‐C3H7)3Br3, BF3 or TiCl2 (O‐i‐C3H7)2, complexes were obtained (II) which polymerize butadiene to predominantly cis‐1,4 polymers. Evidence is reported that these complexes are of ionic type and contain the cation magnified image The different stereospecificity observed in the polymerizations by I and II is interpreted on the basis of the different mode of coordination of butadiene to Ni of the complexes I and II, respectively.