Mechanistic insight into the selective trans-1,4-polymerization of butadiene by terpyridine-iron(II) complexes - A computational study

The density functional theory (DFT) method has been employed to unravel mechanistic intricacies of the 1,4-polymerization of 1,3-butadiene mediated by the [(eta(3)-RC3H4)Fe-II(C15H11N3)(eta(2)-C4H6)]+ terpyridine-iron(II) active catalyst species. The pi-allyl-insertion mechanism is operative for chain growth, whilst the alternative sigma-allyl-insertion mechanism has been explicitly demonstrated as being inoperable. This study elucidates the mechanism of cis-trans regulation and unveils the factors that govern the observed high trans-1,4 stereoselectivity, in particular, the discriminative role of allylic isomerization. An atactic trans-1,4-polydiene is expected from polymerization of a terminally monosubstituted butadiene, the experimental results of which have not been reported thus far.