Actinide oligomeric complexes

The hydride complexes of actinides usually contain a coligand, such as, for example, OR, dmpe, or Cp, and can be monomeric or oligomeric. Thus, the borohydrides An(BH4)4 produced according to (5.68) are polymeric (An = Th, U) or monomeric (An = Np, Pu), whereas the An(BH3Me)4 are all monomeric. Their volatility increases from Th to Pu, whereas their stability goes in the opposite direction [282] ... 

The unsubstituted para-t-butyl calixarenes themselves complex metals via their aryloxide groups. Since aryloxide complexes are frequently oligomeric, the simple calixarenes do not give monomeric complexes. Aryloxides are hard ligands, therefore they readily form complexes with oxo-philic hard metal ions such as alkali metals, early transition metals, lanthanides, and actinides. Complexation is often inferred because the calixarene acts as a carrier for the metal ion from an aqueous to an organic phase. With the /wa-/-butylcalix[ ]arenes in alkaline solution, a value of n = 6 gives the best carrier for lithium(I), sodium(I), and potassium(I), with a value of n 8 giving the best carrier for rubidium(I) and caesium(I).15,16 Titanium(IV) complexes have been characterized,17-19 as well as those of niobium(V) and tantalum(V).20-22 These complexes are classified as... 

Olefin insertion has been observed for complexes of nearly every transition metal and most lanthinides and actinides as well, the notable exception being group 17 metals. As discussed in section V.A, low insertion barriers have been computed for most classes of catalytically active complexes as well. One might speculate that any metal alkyl complex with the potential for a vacant coordination site would make polymer. This expectation is not experimentally realized because chain termination pathways compete with propagation. These termination pathways can be activated by a number of factors. Polymerization catalysts can be converted to oligomerization or dimerization catalysts simply by changes in the solvent or counteranion. The commonly proposed termination pathways are discussed below. 

We have shown in this review that neutral and cationic organoactinide complexes have been extensively studied, in the last decade, as catalysts for several organic transformations [9-12, 111]. Polymerization of alkenes[112,113], oligomerization of terminal alkynes [55, 114], hydrosilylation of terminal alkynes [41], and 1,1-insertion of isonitriles into terminal alkynes [28] comprise some other studied processes not presented here. However, due to the high oxophilicity of the actinide complexes (as mentioned above), substrates containing oxygen have been excluded because of the expected and predictable oxygen—actinide interaction. 

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