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).

ABSTRACT

Although attempts to make the Y(ii) complex, (CpMe3Y)1- (CpMe = C5H4Me), by reduction of CpMe3Y with potassium were unsuccessful and the products of potassium reduction of CpMe3Ln 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 CpMe3Ln(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-CpMe)K(18-c-6)][CpMe3Ln] (Ln = Tb, Ho). Although reduction of CpMe3Ln 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)][CpMe3Dy] could be isolated.