Lithium synthetic reagents: dimerization and intramolecular association. Double bridging in "dianions"

Abstract

-The dimerization energies of lithium compounds, 2LiX-(LiX)9, are quite large and depend principally on the electronegativity of X. Intramoleular association, the equivalent of dimerization, is comparably favorable energetically. Thus, many polylithium compounds, including many synthetically useful "dianions", are found by molecular orbital calculations to prefer structures in which the lithium atoms bridge symmetrically. An example is o,o'-dilithiobiphenyl, whose predicted structure has now been confirmed by X-ray spectroscopy. Dilithiated species based on propene (CH9CHCHLi9), propane (LiCH9CH9CH9Li), acetaldehyde (Li CHCHO), acetone (LiCH2COH Li ahd Li CHCOCH), ahd mies (e.g., HCOLi9) are amog 1,3-double bridging examles. Besies o,o -dilithiobiphenyl, 1,4-double lithium bridging is exhibited by 1,4-dilithiobutane, 1,4-dilithio-2-cis-butene, and 1,4-dilithio-1,3-cis,cis-butadiene. While electrostatic interactions provide the simplest explanation for these structures, multi center covalent bonding also is important in determining geometrical details and energetic differences.

Mono-anionic acetophenone imine ligands: synthesis, ortho-lithiation and first examples of group (v) metal complexes

“…It is postulated that upon lithiation, the acetophenone imine ligands form either large clusters or polymerized species in which the ligands gather around groups of lithium ions. [53][54][55][56] The formation of aggregates of this type can result in superstructures with lower overall symmetry, explaining the inequivalence of the two 1 H NMR resonances for the -OCH 2 O-moiety. This lack of symmetry can result in one or both of the methylene protons falling in the shielded region due to the ring current of aryl groups from the imines or other acetophenone moieties.…”

Alkali Metal Diphenylmethanides: Synthetic, Computational and Structural Studies

“…Due to the interesting structural features displayed by many of these compounds, theoretical studies have focused on the various metal–ligand binding modes, resulting in considerable theory, focusing primarily on rationalizing metal–ligand binding trends and the degree of σ‐ or π‐bonding in these systems 4. 8–15 Even with significant attention focused on the alkali metal derivatives, the limited range of preparative methods and difficulties regarding stability and solubility have prevented the investigation of several worthwhile ligand systems. Particularly interesting among these is the diphenylmethanide anion.…”

Lithium Bonds in Lithium Batteries

“…Subsequently, the first experimental proof of the existence of Li bond complexes X⋅⋅⋅Li–Y (X=NH 3 , Me 3 N, H 2 O, Me 2 O; Y=Cl, Br) was obtained in a matrix isolation IR study in 1975 . The Li bond theory has developed continuously since these reports …”