Light Lanthanide Metallocenium Cations Exhibiting Weak Equatorial Anion Interactions

As the dysprosocenium complex [Dy(Cp-ttt)(2)][B(C6F5)(4)] (Cp-ttt=C(5)H(2)tBu(3)-1,2,4, 1-Dy) exhibits magnetic hysteresis at 60 K, similar lanthanide (Ln) complexes have been targeted to provide insights into this remarkable property. We recently reported homologous [Ln(Cp-ttt)(2)][B(C6F5)(4)] (1-Ln) for all the heavier Ln from Gd-Lu; herein, we extend this motif to the early Ln. We find, for the largest Ln(III) cations, that contact ion pairs [Ln(Cp-ttt)(2){(C6F5-kappa(1)-F)B(C6F5)(3)}] (1-Ln; La-Nd) are isolated from reactions of parent [Ln(Cp-ttt)(2)(Cl)] (2-Ln) with [H(SiEt3)(2)][B(C6F5)(4)], where the anion binds weakly to the equatorial sites of [Ln(Cp-ttt)(2)](+) through a single fluorine atom in the solid state. For smaller Sm-III, [Sm(Cp-ttt)(2)][B(C6F5)(4)] (1-Sm) is isolated, which like heavier 1-Ln does not exhibit equatorial anion interactions, but the Eu-III analogue 1-Eu could not be synthesised due to the facile reduction of Eu-III precursors to Eu-II products. Thus with the exception of Eu and radioactive Pm this work constitutes a structurally similar family of Ln metallocenium complexes, over 50 years after the [M(Cp)(2)](+) series was isolated for the 3d metals.