Divalent Lanthanide Tetraisobutylaluminates: Reactivity and Living Isoprene Polymerization

Abstract

Lanthanide (Ln) tetraisobutylaluminates constitute key components in commercial 1,3-diene polymerization catalysts, and likewise are the homogeneous rare-earth-metal catalysts of prime industrial importance. Discrete divalent rare-earth-metal complexes [Ln(AliBu4)2] (Ln=Sm, Eu, Yb) reported here display the first structurally characterized homoleptic metal tetraisobutylaluminates. Treatment of [Ln(AliBu4)2] with C2Cl6 gives access to SmII/SmIII mixed-valence cluster [Sm6Cl8(AliBu4)6] and the YbII cluster [Yb4Cl4(AliBu4)4], respectively. Reaction with B(C6F5)3 leads to hydride abstraction and formation of arene-coordinated hydroborates such as [Sm{HB(C6F5)3}2(toluene)2]. Complexes [Ln(AliBu4)2] engage in single-component isoprene polymerization, affording high cis-1,4 polyisoprenes with narrow molecular weight distributions. Binary [Yb(AliBu4)2]/[HNPhMe2][B(C6F5)4] fabricates polyisoprene in a perfectly living manner. The catalytically active species are scrutinized by NMR spectroscopy.