Discrete Trivalent Lanthanide Isobutylaluminates in Isoprene Polymerization: Elucidation of Cationized Active Species

Triisobutylaluminum (TIBA) is a main component applied in industrial Ziegler-type mixed catalysts for conjugated diene polymerization. Despite this importance, discrete crystalline trivalent lanthanide tetraisobutylaluminates have not yet been examined in polymerization. The present study revealed that discrete complexes Ln[N(SiMe3)(2)](HAliBu(3))(AliBu(4)) (Ln = La, Pr, Nd, Gd) promote highly stereoselective isoprene polymerization with >99% cis selectivity. Mechanistic studies with borate cocatalysts, supported by single crystal X-ray diffraction, and NMR spectroscopy, disclose the formation of dicationic neodymium complex [Nd{N(SiMe3)(2)}(PhNMe2)(2)][B(C6F5)(4)](2) from the binary system Nd[N(SiMe3)(2)](HAliBu(3))(AliBu(4))/[PhNMe2H][B(C6F5)(4)]. Complex [Nd{N(SiMe3)(2)}(PhNMe2)(2)][B(C6F5)(4)](2) engages in single-component isoprene polymerization.