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) a dducts of the lithium salt of the potentially tridentate ligand precur sor 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 add uct with pseudo C-2 symmetry in which a LiCl molecule is sandwiched be tween two LiN(SiMe(2)CH(2)PPr(2)(i))(2) monomers. The LiCl molecule an d two Li-N units form a planar six-membered core which can best be des cribed as a three-rung ladder. The solution IH NMR spectrum is consist ent with this geometry. Variable-temperature P-31 and Li-7 NMR spectro scopy 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 produc t indicates that a 2:2 dimer of C-2 symmetry is present. Variable-temp erature NMR studies are consistent with a highly fluxional molecule un der ambient conditions. The variable-temperature Li-6 NMR spectra of t he 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 fast er 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 great ly upon dissolution in coordinating solvents. LiAlEt(4) and LiBEt(4) a dducts 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 compoun d shows it to be an infinite one-dimensional polymer. In this case, th e elucidated structure is the result of aggregation upon solvent evapo ration. Comparison of the three crystal structures illustrates that ev en with varying adducts (i.e., LiCl, LiAlMe(4), and NaBEt(4)) the basi c geometries of the LiN(SiMe(2)CH(2)PPr(2)(i))(2) unit remain similar.