Role of back‐biting in the stereoselectivity of Ni(II)‐catalyzed butadiene polymerization

Remarkable information on the relevance of back-biting to determining the stereoselectivity in the polymerization of butadiene is reported. The first insertion of the butadiene unit in the metal–methyl σ bond is preferentially 1,4-trans, whereas during chain propagation, more than 90% of the monomer is in a 1,4-cis arrangement. The experimental results have been rationalized by the fact that during the first insertion, anti–syn isomerization of the allyl group is favored.