Germanium(II) and Tin(II) Complexes of a Sterically Demanding Phosphanide Ligand

The reaction between PhPCl(2) and 1 equiv of RLi, followed by in situ reduction with LiAIH(4) and an aqueous workup yields the secondary phosphane PhRPH [R = (Me(3)Si)(2)CH]. Treatment of PhRPH with n-BuLi in diethyl ether generates the lithium phosphanide (RPhP)Li(Et(2)O)(n) [15(Et(2)O)], which may be crystallized as the tetrahydrofuran (THF) adduct (RPhP)Li(THF)(3) [15(THF)]. Compound 15(Et(2)O) reacts with 1 equiv of either NaO-tBu or KO-tBu to give the corresponding sodium and potassium phosphanides (RPhP)Na(Et(2)O)(n) (16) and (RPhP)K(Et(2)O)(n) (17), which may be crystallized as the amine adducts [(RPhP)Na(tmeda)](2) [16(tmeda)] and [(RPhP)K(pmdeta)](2) [17(pmdeta)], respectively. The reaction between 2 equiv of 17 and GeCl(2)(1,4-dioxane) gives the dimeric compound [(RPhP)(2)Ge](2)center dot Et(2)O (18 center dot Et(2)O). In contrast, the reaction between 2 equiv of 15 and SnCl(2) preferentially gives the ate complex (RPhP)(3)SnLi(THF) (19) in low yield; 19 is obtained in quantitative yield from the reaction between SnCl(2) and 3 equiv of 15. Crystallization of 19 from n-hexane/THF yields the separated ion pair complex [(RPhP)(3)Sn][Li(THF)(4)] (19a); exposure of 19a to vacuum for short periods leads to complete conversion to 19. Treatment of GeCl(2)(1,4-dioxane) with 3 equiv of 15 yields the contact ion pair (RPhP)(3)GeLi(THF) (20), after crystallization from n-hexane/THF. Compounds 15(THF), 16(tmeda), 17(pmdeta), 18 Et(2)O, 19a, and 20 have been characterized by elemental analyses, multielement NMR spectroscopy, and X-ray crystallography. While 15(THF) is monomeric, both 16(tmeda) and 17(pmdeta) are dimeric in the solid state. The diphosphagermylene 18 center dot Et(2)O adopts a dimeric structure in the solid state with a syn,syn-arrangement of the phosphanide ligands, and this structure appears to be preserved in solution. The ate complex 19a crystallizes as a separated ion pair, whereas the analogous ate complex 20 crystallizes as a discrete molecular species. The structures of 19 and 20 are retained in non-donor solvents, while dissolution in THF yields the separated ion pairs 19a and [(RPhP)(3)Ge][Li(THF)(4)] (20a).