Evaluating Electron-Transfer Reactivity of Complexes of Actinides in +2 and +3 Oxidation States by using EPR...

The possibility that the relative reactivity of complexes of actinide metals in the +2 and +3 oxidation states could be investigated by examining reactions between An^III and An^II species of Th and U with rare-earth metal reagents that provide EPR confirmation of electron transfer reactivity has been explored. Neither Cp''₃ Th^III nor Cp''₃ U^III will reduce Cp''₃ La^III or Cp'₃ Y^III (Cp'=C₅ H₄ SiMe₃ , Cp''=C₅ H₃ (SiMe₃ )₂ ). However, both [K(2.2.2-cryptand)][Cp''₃ Th^II ] and [K(2.2.2-cryptand)][Cp''₃ U^II ] reduce Cp''₃ La^III and Cp'₃ Y^III to form [Cp''₃ La^II ]^1- and [Cp'₃ Y^II ]^1- , respectively, which were identified by EPR spectroscopy. The reverse reactions also occur which indicates that the reduction potentials are similar. [Cp''₃ La^II ]^1- reduces Cp'₃ Y^III and the reverse Y^II /La^III combination also occurs. In both cases, the reactions generate EPR spectra indicative of multiple species in the mixtures of La^II and Y^II , which is consistent with ligand exchange and demonstrates that numerous heteroleptic complexes of these Ln^II ions exist.