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

Novel complexes [(C 5 Me 5 ) 2 Ln][B(C 6 F 5 ) 4 ] (Ln = Pr, Nd, or Gd) were prepared, which in combination with i Bu 3 Al efficiently induce highly 1,4‐cis‐specific polymerization of butadiene. The activity of the Gd complex/ i Bu 3 Al 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). magnified image ORTEP drawing of 2b . Selected bond distances (Å): Pr‐F1 = 2.549(2), Pr‐F19 = 2.625(2).