Rare-Earth Metal Bis(alkyl) Complexes Bearing the FluCH(2)-THF Ligand: Synthesis, Structures, and Catalysis toward Polymerizations of Conjugated Dienes

A series of constrained-geometry-configuration (CGC) rare-earth metal complexes bearing the ligand fluorenylmethylene-tetrahydrofuranyl (15-FluCH2-THF)Ln(CH2SiMe3)2(THF) (Ln = Y, 1; Lu, 2) have been synthesized by the alkane elimination reaction between the FluCH2-THF ligand and the rare-earth metal trialkyls and fully characterized by nuclear magnetic resonance and X-ray diffraction analyses. Complexes 1 and 2 are monomeric THF solvates, in which the CGC ligand adopts the 15/ Kappa 1 bonding mode with the central metals via coordination of five carbon atoms from the fluorenyl fragment and the tetrahydrofuranyl oxygen atom. Upon activation with AliBu3 and [Ph3C][B(C6F5)4], complex 1 showed high activity toward conjugated diene polymerization, to afford up to 98.5% cis-1,4-polybutadiene and 69.0% 3,4-unit-enriched polyisoprene. The reason behind this was elucidated.