The actinyl chemistry of soft-donor ligands

The presentation by Stéphanie Cornet of The University of Manchester, England, was diverse in terms of the multitude of actinide compounds and synthesis routes described. The basis of the talk was the linear dioxoactinyl cation of the general structure (O=An=O)ⁿ⁺ (where n = 1 or 2); for example, the plutonyl (V) cation (O=Pu=O)⁺, and the plutonyl(VI) cation, (O=Pu=O)²⁺. Generally, four to six additional ligands can coordinate in the equatorial plane.
Many of the synthetic procedures were based on the work of Carol Burns and co-workers at Los Alamos, who developed a simple one-pot dehydration of UO₂Cl₂.xH₂O for the preparation of UO₂Cl₂(THF)₃ (THF = tetrahydrofuran); these compounds prove to be an excellent starting material for the synthesis of a variety of uranyl (VI) complexes. For example, the following are a few of the interesting structures that have been previously reported:

This talk was particularly focused on nitrogen- or phosphorus-containing soft-donor ligands. Cornet described the synthesis of phosphine oxide and phosphinimine complexes [UO₂Cl₂(R₃PX)₂] (R=Ph or Cy, X=O or NH) by addition of two equivalents of the phosphine oxide or phosphinimine ligand to the uranyl–THF starting material. Moreover, the reaction with the N-donor phosphinimines (R₃PNH) to solutions of UO2Cl2(R₃PO)2 resulted in the selective displacement of the P=O ligands and the formation of the phosphinimine complexes UO₂Cl₂(R₃PNH)₂.¹H and ³¹P nuclear magnetic resonance (NMR) spectra exhibited the presence of both trans and cis isomers in solution and the UO₂Cl₂(Cy₃PNH)₂ have been structurally characterized in both configurations. A short U–N bond length was also observed, suggesting a strong U–N interaction.

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