The cyclopentadienyl complexes (C5H5)3M (M = Sm, Yb, and Eu) and (MeC5H4)3Sm undergo chemically reversible electrochemical reduction in tetrahydrofuran at platinum, gold, and mercury electrodes under purified nitrogen to give [(C5H5)3M]- species, (C5H5)3M + e- → [(C5H5)3M]-. As required by this reaction, reversible electrochemical oxidation of KSm(C5H5)3 to give (C5H5)3Sm has also been observed. The reversible half-wave potentials, Er1/2 (approximately equal to the standard redox potential E°), are considerably more negative than for reduction of M(III) to M(II) in water, indicating that both solvent and ligand terms are important in lanthanoid redox chemistry. The Er1/2 values show that thermodynamic stability of the divalent species toward oxidation falls in the sequence M = Eu > Yb > Sm. The kinetic reactivity with adventitious moisture and/or oxygen follows the thermodynamic sequence with [(C5H5)3Sm]- being particularly sensitive to traces of water. Reaction of (C6F5)2Yb with cyclopentadiene and (C6F5)2Hg provides a new synthesis of (C5H5)3Yb.
|Number of pages||5|
|Publication status||Published - 1986|