The activation of the tris(ally1)neodymium complex Nd(q3-C3H& * dioxane with alkylaluminoxanes (MA0 or HIBAO) results in highly selective catalysts for the 1,4-cispolymerization of butadiene (&-selectivity up to 80%). Under standard conditions (50"C, toluene), the turnover frequency (TOF) of the catalysVMA0 system amounts to 10-15 000 mol butadiene/(mol Nd h). Molecular weight determinations indicate the formation of only one polymer chain per neodymium center as in a living polymerization reaction, and for the catalyst/HIBAO system the rate law r, = k, [Nd][C4H6] with k, = 8,7 * lo-' mol/(Ls) (at 25°C) has been derived. As the catalytically active species, a cationic monobutenyl neodymium(II1) complex is discussed, which is stabilized through coordinative interaction with the counter anion as well as the growing polybutadiene chain. This cationic complex reacts under insertion with butadiene in a bimolecular fashion.
EinfiihrungSeit Anfang der 80er Jahre werden fur die groBtechnische Erzeugung von 1,4-cis-Polybutadien, das ubenviegend zur Fahrzeugreifen-Herstellung Venvendung findet, a) 50. Mitteilung uber Komplexkatalyse, 49. Mitteilung vgl. Lit.'" 0 1997, Hiithig &