First Crucial Evidence for Apical-Apical Exchange via a Hypervalent Tellurium Ate Complex in the Reactions of Diaryl Tellurides with Aryllithium Reagents

Abstract

Pentafluorophenyl phenyl telluride and 3,5-dichloro-2,4,6-trifluorophenyl phenyl telluride reacted with pentafluorophenyllithium or 3,5-dichloro-2,4,6-trifluorophenyllithium at low temperature to form the corresponding tellurium ate complexes as sole intermediates of the ligand exchange on the hypervalent tellurium centers. In these tellurium ate complexes electron-withdrawing aryl ligands were arranged at apical positions and the ligand exchanges took place between the apical-directing groups.

Low‐temperature 1H, 13C, 77Se, and 125Te 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

“…These lzsTe NMR spectra are rationalized in terms of the increase in the electron density at the central tellurium atom of the hypervalent ate complexes as well as the triphenyltellurium ate complex previously reported [3]. On warming the reaction mixture in an NMR tube, these ' "Te NMR signals shift again to 527.5 and 549.6 ppm, which are assigned as those of tellurides (1) and (2) at room temperature, and the ratios are nearly identical to those of the isolated tellurides, demonstrating that the exchange reaction between two carbon ligands takes place at rwm temperature.…”

“…These tellurium-lithium exchange reactions have attracted considerable attention, since the reactions provide a convenient procedure for the generation of numerous, synthetically useful organolithium reagents, as presented by Sonoda and co-workers [ 13. Furthermore, the mechanism of the exchange reaction has been investigated by Reich et al [2] and Furukawa et al [3]. They have confirmed that the exchange reaction proceeds via two steps involving the initial formation of discrete intermediates, ate complexes of [10-Te-3(C3)], using 'H, 13C, and Te NMR techniques at low temperatures.…”

“…Consequently, the NMR chemical shifts observed in the present reactions indicate that the hypervalent telluranes [ate complexes,] are also formed in the reactions of tellurides (1) and (2) with pentafluorophenyllithium. Alternatively, when pentafluorophenyl phenyl and 3 3 dichloro-2,4,6-trifluorophenyl phenyl selenides (3) and (4) were treated with pentafluorophenyllithium or 3,5-dichloro-2,4,6-trifluorophenyllithium at -78"C, similar 'H, 13C, I9F, and 77Se NMR behavior was observed in the reactions of selenides with aryllithiums. This is the first observation of the formation of selenium ate complexes [ 10-Se-3(C3)] having three carbon ligands.…”

When a very fast radical probe cyclization hints at a carbanionic intermediate rather than at a radical one: a further proof of a polar mechanism for the aryl bromide–alkyllithium exchange reaction

“…Beak and co-workers 6 ,7 rationalized their isotope labeling experiments on aryl bromides by the involvement of S N 2 or of ate complexes and discarded both an ET and a four-center concerted mechanism. Such ate complexes were detected by Reich and co-workers 8,9 and Ogawa et al 10 for iodoaromatics. More recently Boche and co-workers carried out comprehensive ab initio electronic structure calculations on Ph-I-CH 3 (-) and other ate complexes.…”

“…On the other hand, for alkyl halides, the iodides, which are the best electron acceptors in the series F, Cl, Br, I are also, by far, the most prone to form ate-type complexes. [8][9][10] As a consequence the ET participation in the reactivity of alkyl iodides is generally not observed (see, however, ref. 30).…”