Ancillary Ligand-Free Mixed Chlorido/Isobutylaluminato Lanthanide Complexes in Isoprene Polymerization

Abstract

Ternary catalyst mixtures are employed for industrial-scale rare-earth-metalpromoted diene polymerization. Thereby, the role of organoaluminum compounds in activating the rare-earth-metal component is still poorly understood. Mixed chlorido/ amido complexes [Ln{N(SiMe 3 ) 2 } 2 (μ-Cl)(THF)] 2 are selected as well-defined precursors according to the chlorination/alkylation activation sequence. The heteroleptic lanthanide tetraisobutylaluminate complexes [Ln{N(SiMe 3 ) 2 }(AliBu 4 )(μ-Cl)] 2 (Ln = La, Nd) form when [Ln{N(SiMe 3 ) 2 } 2 (μ-Cl)(THF)] 2 is treated with triisobutylaluminum. By contrast, the [La{N(SiMe 3 ) 2 } 2 (μ-Cl)(THF)] 2 /AlMe 3 reaction afforded the isolable heteroaluminate complex [La{N(SiMe 3 ) 2 }{(μ-CH 3 )(μ-N(SiMe 3 ) 2 )AlMe 2 }(μ-Cl)] 2 , highlighting the distinct reactivity of aluminum alkyls. Complex [Nd{N(SiMe 3 ) 2 }(AliBu 4 )(μ-Cl)] 2 features catalytic activity in isoprene polymerization for the fabrication of high cis-selective polyisoprene and displays single-component polymerization activity. Compounds [Ln{N(SiMe 3 ) 2 } 2 (μ-Cl)(THF)] 2 are best accessed from La[N(SiMe 3 ) 2 ] 3 /LaCl 3 (THF) mixtures since starting out from LaCl 3 (THF)/K[N(SiMe 3 ) 2 ] leads to alkali-metal contaminations as revealed by the isolation of the mixed hydrido/isobutylaluminato complex [K(iBu 3 Al-μ−H-AliBu 3 )] n , formed upon reaction with triisobutylaluminum.