Synthesis and structural characterisation of alkali metal complexes of heteroatom-stabilised 1,4- and 1,6-dicarbanions

Easy Access to Phosphine-Borane Building Blocks

In this paper, we highlight the synthesis of a variety of primary phosphine-boranes (RPH2 ⋅BH3 ) from the corresponding dichlorophosphines, simply by using Li[BH4 ] as reductant and provider of the BH3 protecting group. The method offers facile access not only to alkyl- and arylphosphine-boranes, but also to aminophosphine-boranes (R2 NPH2 ⋅BH3 ) that are convenient building blocks but without the protecting BH3 moiety thermally labile and notoriously difficult to handle. The borane-protected primary phosphines can be doubly deprotonated using n-butyllithium to provide soluble phosphanediides Li2 [RP⋅BH3 ] of which the phenyl-derivative Li2 [PhP⋅BH3 ] was structurally characterized in the solid state.

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

The reaction between two equivalents of the potassium salt [(Me(3)Si)(2){Me(2)P(BH(3))}C]K (4) and SmI(2)(THF)(2) in refluxing THF yields the dialkylsamarium(II) compounds [(Me(3)Si)(2){Me(2)P(BH(3))}C](2)Sm(THF) (5a) or [(Me(3)Si)(2){Me(2)P(BH(3))}C](2)Sm(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 YbI(2) and two equivalents of 4 in refluxing benzene yields the solvent-free dialkylytterbium(II) compound [(Me(3)Si)(2){Me(2)P(BH(3))}C](2)Yb (8). In contrast to 5a and 5b, compound 8 reacts rapidly with THF to give the free phosphine-borane (Me(3)Si)(2){Me(2)P(BH(3))}CH as the only identifiable product.