Rare-Earth Metals and Aluminum Getting Close in Ziegler-Type Organometallics

A prolific and synergetic interplay of rare-earth metal components and organoaluminum reagents is of fundamental importance in Ziegler-type catalysts used in diene polymerization. The present article surveys organoaluminum-promoted alkylation/cationization activation pathways which have been elaborated for various lanthanide compounds, i.e., halides, carboxylates, alkoxides, aryloxides, (silyl)amides, and hydrides. Special emphasis is put on the identification of stable discrete Ln/Al heterobimetallic complexes and the interpretation of their solution and solid-state structure (LnX n Al coordination modes). Surpassing the pure model character of many structurally evidenced Ln/Al heterobimetallics their applicability and performance in the manufacture of polydienes will be highlighted and emerging structure-reactivity relationships will be addressed. Consideration is also given to various heterogenized variants involving organopolymeric and inorganic support materials.