LOW-TEMPERATURE H-1, C-13, SE-77, AND TE-125 NMR-STUDIES ON THE APICAL-APICAL LIGAND-EXCHANGE VIA THE HYPERVALENT TELLURIUM AND SELENIUM ATE COMPLEXES [10-M-3(C3), M=SE, TE] IN THE REACTIONS OF DIARYL TELLURIDES AND SELENIDES WITH ARYLLITHIUM REAGENTS

Pentafluorophenyl phenyl telluride (1) and 3,5-dichloro-2,4,6-trifluorophenyl phenyl telluride (2) react with pentafluorophenyllithium or 3,5-dichloro-2,4,6-trifluorophenyllithium in THF at low temperatures to form the corresponding tellurium ate complexes (A) and (B) as sole intermediates in the ligand exchange on the hypervalent tellurium atom. The corresponding selenides (3) and (4) also react with identical aryllithium reagents in THF to form the discrete intermediates, selenium ate complexes (C) and (D), in the exchange reactions. In these ligand exchange reactions of tellurides and selenides, electron-withdraw ing ligands occupy the apical positions and the exchange lakes place between these apical-oriented groups. The low-temperature H-1, C-13, Se-77, and Te-125 NMR spectroscopic techniques are effective methods for detection of unstable tellurium and selenium ate complexes.