Organolanthanide Chemistry: Rare–Earth-based Ziegler–Natta Catalysts
The rare-earth elements or lanthanides display important components in the concert of Ziegler–Natta catalysis. On the one hand side, metallocene derivatives, „lanthanidocenes“, are excellent models for clarifying the active sites of Ziegler–Natta catalysts via emulation of the major initiation, propagation, and termination steps. On the other hand side, multicomponent systems (Ziegler-Mischkatalysatoren) represent so far the only class of homogeneous rare-earth catalysts which are commercially applied. Stereospecific polymerization of 1,3-dienes, e.g., butadiene, isoprene, and 2,3-dimethylbutadiene, is efficiently initiated by neodymium-based catalysts for the industrial-scale production of high-quality synthetic rubbers (cis-1,4-polymers). Our interest in Ziegler–Natta-related organolanthanide chemistry is multifacetted including the investigation of single-component catalyst precursors such as lanthanidocenes, hemi-lanthanidocenes, and O- and N-based post-metallocenes, that is non-metallocenes featuring dialkoxide and diamide ligands. We are also exploring classical multicomponent systems derived from tailor-made rare earth carboxylates and alkoxides. Alkylaluminate derivatives are examined not only to learn more about the role of organoaluminum cocatalysts but also to provide acitve sites (e.g., alkyl, hydride, cationic species) for the stereoselective olefin polymerization. Monomers under study comprise ethylene, propylene, styrene, acrylonitrile, acrylates, and 1,3-dienes.