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

Abstract

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 ScCl₃ with 1 equiv. of Fc(1-C₉H₆)Li (where Fc = ferrocenyl group), followed by the addition of 2 equiv. of LiCH₂C₆H₄NMe₂-o in THF at room temperature gave the ferrocenyl functionalized half-sandwich scandium bis(o-dimethylaminobenzyl) complex [Fc(1-C₉H₆)]Sc(CH₂C₆H₄NMe₂-o)₂ (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 [Ph₃C][B(C₆F₅)₄] in THF generated the THF-coordinated cationic half-sandwich scandium mono(o-dimethylaminobenzyl) complex {[Fc(1-C₉H₆)]Sc(CH₂C₆H₄NMe₂-o)}{[B(C₆F₅)₄]} (2-THF₂). Switching in situ between the oxidized and reduced forms of active THF-free species (originally generated from 1/[Ph₃C][B(C₆F₅)₄] in situ) resulted in the redox-controlled syndio-specific polymerization of styrene.