Spectroscopic Studies of some Cryptated Lithium Carbanions and Related Species

Complexation of alkali cations by macroheterobicyclic ligands leads to a now well-known class of complexes, called cryptates, in which the cation is included within the central molecular cavity of the ligand [1]. Solutions of these alkali metal cryptates have been studied by different techniques [2], however, only few data exist concerning their physicochemical properties in low polarity aprotic solvents [3]. This information is needed in order to elucidate the mechanism and the kinetics of the anionic polymerization of heterocyclic and vinyl monomers with cryptates as counterions [4]. Thus we have examined the behavior and the structure of some lithium ion pairs and of their complexes with cryptands, namely the [211], in THF and in toluene by two complementary techniques : UV and visible spectrophotometry, and by 1H 7Li and NMR.