LITHIUM SYNTHETIC REAGENTS: DIMERIZATION AND INTRAMOLECULAR ASSOCIATION. DOUBLE BRIDGING IN "DIANIONS"

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