Isolation of reactive Ln(ii) complexes with C5H4Me ligands (CpMe) using inverse sandwich countercations: synthesis and structure of [(18-crown-6)K(μ-CpMe)K(18-crown-6)][CpMe3LnII] (Ln = Tb, Ho)

Although attempts to make the Y(ii) complex, (Cp^Me₃Y)¹⁻ (Cp^Me = C₅H₄Me), by reduction of Cp^Me₃Y with potassium were unsuccessful and the products of potassium reduction of Cp^Me₃Ln for Ln = La and Pr led to ring-opening reduction of THF, we report that crystallographically-characterizable Ln(ii) complexes of Tb and Ho can be isolated by reducing Cp^Me₃Ln(THF) with KC₈ in THF in the presence of 18-crown-6 (18-c-6). X-ray crystallography revealed that these complexes are isolated with a methylcyclopentadienide inverse sandwich countercation: [(18-c-6)K(μ-Cp^Me)K(18-c-6)][Cp^Me₃Ln] (Ln = Tb, Ho). Although reduction of Cp^Me₃Ln with potassium in the presence of the 2.2.2-cryptand (crypt) chelate has not generally provided fully-characterizable, crystalline products, in the case of Dy, crystals of [K(crypt)][Cp^Me₃Dy] could be isolated. [ABSTRACT FROM AUTHOR]