Cyclopolymerization of 1,5-hexadiene by enantiomerically-pure zirconium salan complexes. Polymer optical activity reveals α-olefin face preference

A study was conducted to investigate cyclopolymerization of 1,5-Hexadiene by enantiomerically-pure zirconium salan complexes. Stereochemical directing equivalence between a bulky (R,R)-(Δ)-salan-Zr complex and the (S,S)-EBTHI-Zr complex was also derived. It was presumed on the basis of the proved relationship between ligand steric bulk and isotacticity induction that the Salan-Zr complexes of less bulky ligands would give poly(methylene-1,3- cyclopentane) (PMCP) with negligible optical rotations. It was found that such equivalence may be explained as quadrant similarity between these two systems and in the case of less bulky ligands a more complex stereochemical control seems to operate. It was also demonstrated that the ansa-metallocenes, which is a broad variety of enantiomerically pure Salan-Zr complexes can be prepared directly from the chiral ligands.