Divalent Lanthanide Tetraisobutylaluminates: Reactivity and Living Isoprene Polymerization.

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(AliBu 4 ) 2 ] (Ln=Sm, Eu, Yb) reported here display the first structurally characterized homoleptic metal tetraisobutylaluminates. Treatment of [Ln(AliBu 4 ) 2 ] with C 2 Cl 6 gives access to Sm II /Sm III mixed-valence cluster [Sm 6 Cl 8 (AliBu 4 ) 6 ] and the Yb II cluster [Yb 4 Cl 4 (AliBu 4 ) 4 ], respectively. Reaction with B(C 6 F 5 ) 3 leads to hydride abstraction and formation of arene-coordinated hydroborates such as [Sm{HB(C 6 F 5 ) 3 } 2 (toluene) 2 ]. Complexes [Ln(AliBu 4 ) 2 ] engage in single-component isoprene polymerization, affording high cis-1,4 polyisoprenes with narrow molecular weight distributions. Binary [Yb(AliBu 4 ) 2 ]/[HNPhMe 2 ][B(C 6 F 5 ) 4 ] fabricates polyisoprene in a perfectly living manner. The catalytically active species are scrutinized by NMR spectroscopy.