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- Title
The Role of Ate Complexes in the Lithium-Sulfur, Lithium-Selenium and Lithium-Tellurium Exchange Reactions.
- Authors
Reich, Hans J.; Gudmundsson, Birgir Ö.; Green, D. Patrick; Bevan, Martin J.; Reich, Ieva L.
- Abstract
Hypervalent ate complexes are presumptive intermediates in the metal-halogen, metal-tellurium, and related exchange reactions. The effect of o, o′-biphenyldiyl vs. diphenyl substitution on formation of tellurium ate complexes was studied by a kinetic technique and by NMR spectroscopy. Only a modest increase in the association constant ( Kate) was measured. When Li/M exchanges of o, o′-biphenyldiyl sulfides and selenides were made intramolecular by means of a m-terphenyl framework ( 12-S, 12-Se, 21), enormous increases (>109) in the rate of Li/S and Li/Se exchange were observed compared to acyclic models. Apparently, these systems are ideally preorganized to favor the T-shaped geometry of the hypervalent intermediates. For the selenium systems, ate complex intermediates ( 20-Se, 26) were detected spectroscopically in THF- or THF/HMPA-containing solutions. A DNMR study showed that Li/Se exchange was substantially faster than exchange of the lithium reagents with the ate complex. Therefore, these ate complexes are not on the actual Li/Se exchange pathway.
- Publication
Helvetica Chimica Acta, 2002, Vol 85, Issue 11, p3748
- ISSN
0018-019X
- Publication type
Article
- DOI
10.1002/1522-2675(200211)85:11<3748::AID-HLCA3748>3.0.CO;2-0