Lanthanides olefin dimerization

Group NIB and f-BIOCk Metallocenes. The need for expensive cocatalysts has always hampered the development of metallocene catalysts for olefin polymerization. It was recognized early on that substitution of the Group IVB metal with a lanthanide or Group IIIB element in the -1-3, state would represent a cocatalyst-free analogue of the Kaminsky system. Active catalysts are indeed obtained from bis-Cp lanthanocenes and yttrium- and scandium-based congeners. The lutetium dimer 29 has an activity of >7 kg/mmol(Lu)/h/atm for ethylene polymerization in cyclohexane (95). (This remarkable compound can also break the C—H bonds of alkanes.)... 

The insertion of alkenes into M-H bonds has been examined in Chap. 4. This reaction is very important because, it leads to the dimerization, oligomerization and polymerization of alkenes. It is broad and concerns not only transition metals, but also main-group metals (group 13 Lewis acids), lanthanides and actinides. For instance, AlEt3 is an excellent initiator of olefin polymerization. This reaction can also be considered as the hydrometallation or the hydroelementation of an olefin, and stoichiometric examples have been shown. If the element E does not have the property of a Lewis acid allowing olefin pre-coordination onto a vacant site and thus facilitating insertion, the insertion reaction is not possible without a catalyst. 

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