Recent Advances in the Reductive Chemistry of the Rare Earth and Actinide Metals
Abstract: It is now known that the formal +2 oxidation state is accessible in crystallographically characterizable molecular complexes for all the rare earth metals, except radioactive Pm. Previously, complexes of the +2 ions had only been crystallized for Eu, Yb, Sm, Tm, Dy, and Nd. The new oxidation states were found in the tris(cyclopentadienyl) coordination environments, (Cp'3)3- and (Cp"3)3-, where Cp' = C5H4SiMe3 and Cp" = C5H3(SiMe3)2. In these ligand fields, reduction of 4fn Ln3+ lanthanide precursor complexes formed 4fn5d1 products rather than the traditional 4fn+1 Ln2+ ions of Eu, Yb, Sm, Tm, Dy, and Nd. Complexes of new +2 actinide ions of Th, U and Pu have also been discovered in these tris(cyclopentadienyl) coordination environments.
The synthetic studies of the past few years have led to a coherent generalization of ligand effects on the reduction reactions that led to complexes of these new +2 ions.This postulated that in the coordination environment of three Cp' or Cp" ligands, crystallograpically characterizable complexes of +2 ions can be isolated, but that with more strongly donating ligands such as C5Me4H, C5Me5, and N(SiMe3)2, the analogous +2 species are too reactive to isolate. On the other hand, reductions of LnA3 complexes (Ln = rare-earth metal; A = anion) of the latter, strongly donating ligands are excellent routes to reduced dinitrogen complexes containing side-on bound (N=N)2- ligands, but reductions of Cp' and Cp" ligated complexes do not readily form (N=N)2- products.This presentation will describe how recent synthetic results have shown that these generalizations require significant modification!
This seminar will describe how the reductive chemistry of these metals continues to evolve.