Light Lanthanide Metallocenium Cations Exhibiting Weak Equatorial Anion Interactions

摘要

As the dysprosocenium complex [Dy(Cp^ttt)2][B(C6F5)4] (Cp^ttt=C5H2 tBu3‐1,2,4, >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‐κ¹‐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.