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

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posted on 17.05.2010, 00:00 authored by Keith Izod, John Stewart, Ewan R. Clark, William Clegg, Ross W. Harrington
The reaction between PhPCl2 and 1 equiv of RLi, followed by in situ reduction with LiAlH4 and an aqueous workup yields the secondary phosphane PhRPH [R = (Me3Si)2CH]. Treatment of PhRPH with n-BuLi in diethyl ether generates the lithium phosphanide (RPhP)Li(Et2O)n [15(Et2O)], which may be crystallized as the tetrahydrofuran (THF) adduct (RPhP)Li(THF)3 [15(THF)]. Compound 15(Et2O) reacts with 1 equiv of either NaO-tBu or KO-tBu to give the corresponding sodium and potassium phosphanides (RPhP)Na(Et2O)n (16) and (RPhP)K(Et2O)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 GeCl2(1,4-dioxane) gives the dimeric compound [(RPhP)2Ge]2·Et2O (18·Et2O). In contrast, the reaction between 2 equiv of 15 and SnCl2 preferentially gives the ate complex (RPhP)3SnLi(THF) (19) in low yield; 19 is obtained in quantitative yield from the reaction between SnCl2 and 3 equiv of 15. Crystallization of 19 from n-hexane/THF yields the separated ion pair complex [(RPhP)3Sn][Li(THF)4] (19a); exposure of 19a to vacuum for short periods leads to complete conversion to 19. Treatment of GeCl2(1,4-dioxane) with 3 equiv of 15 yields the contact ion pair (RPhP)3GeLi(THF) (20), after crystallization from n-hexane/THF. Compounds 15(THF), 16(tmeda), 17(pmdeta), 18·Et2O, 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·Et2O 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)3Ge][Li(THF)4] (20a).