EFFECTS OF LIGANDS ON ION-PAIRING BEHAVIOR OF BENZYLIC LITHIUM COMPOUNDS

Article abstract of DOI:10.1016/S0022-328X(00)84678-1

The 1/1/ adduct of t-butyllithium and α-methylstyrene (II) has been generated in cyclopentane in the presence of a variety of ether and t-amine ligands as well as unsolvated, giving stable solutions in every case.NMR spectra of the solvated species are the same for all ligands but differ from that of the unsolvated compound.The results are consistent with a salt which contains a conjugated t-benzylic anion and exists as a loose ion-pair in the presence of ligands and as a tight ion-pair in cyclopentane alone.In contrast, benzyllithium behaves like a tight ion-pair in the presence of all ligands tried.Steric hindrance to tight ion-pairing at C_α of II is concluded to be responsible for the results observed.A covalently-bonded dilithium compound, 4,4-dimethyl-2-lithio-2-(p-lithio-phenyl)pentane has been generated.