Evaluating electrochemical accessibility of 4fn5d1 and 4fn+1 Ln(ii) ions in (C5H4SiMe3)3Ln and (C5Me4H)3Ln complexes

The reduction potentials (reported vs. Fc+/Fc) for a series of Cp'3Ln complexes (Cp' = C5H4SiMe3, Ln = lanthanide) were determined via electrochemistry in THF with [nBu4N][BPh4] 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 4f7, 4f14, 4f6, and 4f13 Ln(II) ions, respectively. The reduction potentials for Ln = Pr, Nd, Gd, Tb, Dy, Ho, Er, and Lu, that form 4fn5d1 Ln(II) ions (n = 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'3Ln] (Ln = Pr, Sm, Eu) match those of the Cp'3Ln complexes. The reduction potentials of nine (C5Me4H)3Ln complexes were also studied and found to be 0.05-0.24 V more negative than those of the Cp'3Ln compounds.