Lanthanide(ii) complexes of a phosphine-borane-stabilised carbanion

Abstract

The reaction between two equivalents of the potassium salt [(Me₃Si)₂{Me₂P(BH₃)}C]K (4) and SmI₂(THF)₂ in refluxing THF yields the dialkylsamarium(II) compounds [(Me₃Si)₂{Me₂P(BH₃)}C]₂Sm(THF) (5a) or [(Me₃Si)₂{Me₂P(BH₃)}C]₂Sm(THF)₃ (5b), depending on the crystallisation conditions, in good yield as air- and moisture-sensitive crystalline solids. X-ray crystallography shows that, whereas both alkyl ligands chelate the samarium(II) ion in 5a, in 5b one alkyl ligand chelates the metal centre and one binds the metal only through its borane hydrogen atoms. The reaction between YbI₂ and two equivalents of 4 in refluxing benzene yields the solvent-free dialkylytterbium(II) compound [(Me₃Si)₂{Me₂P(BH₃)}C]₂Yb (8). In contrast to 5a and 5b, compound 8 reacts rapidly with THF to give the free phosphine-borane (Me₃Si)₂{Me₂P(BH₃)}CH as the only identifiable product.