Synthesis, characterization, and solution dynamics of alkali-metal chloride, aluminate, and borate adducts of the tridentate amido diphosphine ligand precursor LiN(SiMe(2)CH(2)PPr(2)(i))(2)

The preparation of LiCl, LiAlMe(4), LiAlEt(4), LiBEt(4), and NaBE(4) adducts of the lithium salt of the potentially tridentate ligand precursor LiN(SiMe(2)CH(2)PPr(2)(i))(2) is reported. The reaction of HN(SiMe(2)CH(2)Cl)(2) with LiPPr2i (3 equiv) in THF at -78 degrees C leads to the isolation of {LiN(SiMe(2)CH(2)PPr(2)(i))(2)}2LiCl, under certain conditions. The X-ray crystal structure shows it to exist as a 2:1 adduct with pseudo C-2 symmetry in which a LiCl molecule is sandwiched between two LiN(SiMe(2)CH(2)PPr(2)(i))(2) monomers. The LiCl molecule and two Li-N units form a planar six-membered core which can best be described as a three-rung ladder. The solution IH NMR spectrum is consistent with this geometry. Variable-temperature P-31 and Li-7 NMR spectroscopy indicate that the basic structural features of this compound are maintained in solution. This is confirmed by a Li-7 NOESY experiment. The addition of LiAlMe(4) to LiN(SiMe(2)CH(2)PPr(2)(i))(2) results in the formation of {LiN(SiMe(2)CH(2)PPr(2)(i))(2) . LiAlMe(4)}(2); the same product is formed upon the addition of MeLi (4 equiv) to AlCl2[N(SiMe(2)CH(2)PPr(2)(i))(2)]. The X-ray crystal structure of this product indicates that a 2:2 dimer of C-2 symmetry is present. Variable-temperature NMR studies are consistent with a highly fluxional molecule under ambient conditions. The variable-temperature Li-6 NMR spectra of the multiply labeled derivative {(LiN)-Li-6-N-15(SiMe(2)CH(2)PPr(2)(i))(2) .(6)LiAlMe(4)}(2) indicate that lithium exchange is occurring faster than phosphine exchange. Interaggregate lithium exchange is present under ambient conditions, while at lower temperatures, intraaggregate exchange is more favorable. The behavior of this species varies greatly upon dissolution in coordinating solvents. LiAlEt(4) and LiBEt(4) adducts of LiN(SiMe(2)CH(2)PPr(2)(i))(2) were also formed but could not be crystallized and thus studied in the solid state. The addition of NaBEt(4) to LiN(SiMe(2)CH(2)PPr(2)(i))(2) affords {LiN(SiMe(2)CH(2)PPr(2)(i))(2) . NaBEt(4)}(x). The X-ray crystal structure of this compound shows it to be an infinite one-dimensional polymer. In this case, the elucidated structure is the result of aggregation upon solvent evaporation. Comparison of the three crystal structures illustrates that even with varying adducts (i.e., LiCl, LiAlMe(4), and NaBEt(4)) the basic geometries of the LiN(SiMe(2)CH(2)PPr(2)(i))(2) unit remain similar.