Redox-controlled syndio-specific polymerization of styrene catalyzed by ferrocenyl functionalized half-sandwich scandium complexes.

Redox-controlled polymerization is one of the new and efficient strategies to precisely construct the microstructures of polymeric materials, and thus has received increasing attention in the chemical community. Salt metathesis of ScCl with 1 equiv. of Fc(1-CH)Li (where Fc = ferrocenyl group), followed by the addition of 2 equiv. of LiCHCHNMe-o in THF at room temperature gave the ferrocenyl functionalized half-sandwich scandium bis(o-dimethylaminobenzyl) complex [Fc(1-CH)]Sc(CHCHNMe-o) (1) in 89% isolated yield. This complex was characterized by elemental analysis, FT-IR spectroscopy, NMR spectroscopy and single-crystal X-ray diffraction. Treatment of 1 with 1 equiv. of [PhC][B(CF)] in THF generated the THF-coordinated cationic half-sandwich scandium mono(o-dimethylaminobenzyl) complex {[Fc(1-CH)]Sc(CHCHNMe-o)}{[B(CF)]} (2-THF). Switching in situ between the oxidized and reduced forms of active THF-free species (originally generated from 1/[PhC][B(CF)] in situ) resulted in the redox-controlled syndio-specific polymerization of styrene.