Ultimately Specific 1,4‐cis Polymerization of 1,3‐Butadiene with a Novel Gadolinium Catalyst

Novel complexes [(C₅Me₅)₂Ln][B(C₆F₅)₄] (Ln = Pr, Nd, or Gd) were prepared, which in combination with ⁱBu₃Al efficiently induce highly 1,4‐cis‐specific polymerization of butadiene. The activity of the Gd complex/ⁱBu₃Al system is high enough to exhibit good catalytic activity even at low temperature. Polymerization at −78 °C gave polybutadiene with nearly perfect 1,4‐cis microstructure (>99.9%) with sharp molecular weight distribution (M _w/M _n = 1.45) and in reasonable yield.

ORTEP drawing of 2b . Selected bond distances (Å): Pr‐F1 = 2.549(2), Pr‐F19 = 2.625(2).