Komplexkatalyse LIX. Die Katalyse der 1,4-trans-Polymerisation des Butadiens mit Tris(allyl)neodym(III) Nd(η3-C3H5)3 als Einkomponentenkatalysator—Kinetik und Reaktionsmechanismus

The solvate-free Nd(η3-C3H5)3 (1) catalyses the 1,4-trans polymerization of butadiene in toluene at 50°C with a selectivity of 80–85%. In the investigated range of concentrations [BD]0=1 and 2 moll−1 and [Nd]=8–15×10−4 moll−1 the rate law rP=kP[Nd][BD] is to be valid with the rate constants kP=0.51 and 0.28 lmol−1s−1, respectively, in dependence of the butadiene initial concentration [BD]0. In the used turnover range of 20–70% the average molar mass increases linearly with the reacted butadiene per Nd, like in a living polymerization. The polydispersity is correspondingly very low PD≤1.3, and from the ratio of calculated and experimentally determined average mol mass follows the formation of 2 or 3 polymer chains per Nd at [BD]0=1 or 2 moll−1, respectively. To explain the catalytic properties of 1 a reaction model is presented, which is based on the successive formation of 2 catalyst complexes, a bis- and a tris(polybutadienyl)neodymium(III) complex, which catalyse the chain growth in dependence of the extent and the mode of butadiene coordination according to the π-allyl insertion mechanism.