Evaluating electrochemical accessibility of 4f5d and 4f Ln(II) ions in (CHSiMe)Ln and (CMeH)Ln complexes.

The reduction potentials (reported Fc/Fc) for a series of Cp'Ln complexes (Cp' = CHSiMe, Ln = lanthanide) were determined electrochemistry in THF with [BuN][BPh] as the supporting electrolyte. The Ln(III)/Ln(II) reduction potentials for Ln = Eu, Yb, Sm, and Tm (-1.07 to -2.83 V) follow the expected trend for stability of 4f, 4f, 4f, and 4f Ln(II) ions, respectively. The reduction potentials for Ln = Pr, Nd, Gd, Tb, Dy, Ho, Er, and Lu, that form 4f5d Ln(II) ions ( = 2-14), fall in a narrow range of -2.95 V to -3.14 V. Only cathodic events were observed for La and Ce at -3.36 V and -3.43 V, respectively. The reduction potentials of the Ln(II) compounds [K(2.2.2-cryptand)][Cp'Ln] (Ln = Pr, Sm, Eu) match those of the Cp'Ln complexes. The reduction potentials of nine (CMeH)Ln complexes were also studied and found to be 0.05-0.24 V more negative than those of the Cp'Ln compounds.