Lanthanide Ziegler-Natta model

The relevance of Ln/Al heterobimetallic complexes for the emulation of zirconocene-based polymerization catalysis [13-15] was later on also stressed by the Lanthanide Ziegler-Natta Model [16]. Accordingly, lanthanidocene alkyl complexes were not only successfully employed for clarifying major initiation, propagation, and termination steps (Scheme 3) [17,18]. 

Beyond this exclusive lanthanide Ziegler-Natta model, Ziegler-type multicomponent systems ( Mischkatalysatoren ) represent the only class of homogeneous rare-earth metal catalysts of considerable commercial relevance [40-43]. High-czs-1,4-polydienes are industrially produced from 1,3-dienes (butadiene and isoprene) in aliphatic or aromatic hydrocarbons by a number of Mischkatalysatoren based on the transition metals titanium, cobalt, and nickel, and the lanthanide element neodymium [40-47]. The... 

By replacing cyclopentadienyl by pentamethylcyclopentadienyl, steric compression at the metal centre is greatly increased, especially at lutetium, the smallest lanthanide. The complex Cp LuCHdOEt ) polymerizes ethene and oligomerizes propene. (Cp = / -C-MeJ. Its behaviour thus provides a good model for Ziegler-Natta catalysis. The insertion of propene into the Lu—CH bond and some further propagation steps have been followed by n.m.r. spectroscopy. Clear examples of such insertions are rare in d-block chemistry (p. 380). Termination can occur either by j -H transfer or by -methyl transfer the latter is a novel process which has yet to be observed for d-block elements. 

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