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

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