Are ate complexes true intermediates in lithium-metalloid exchange? Subtle effects of ion-pair structure in lithium-tellurium and lithium-selenium exchange reactions.

The lithium±metalloid exchange reaction is widely used to prepare synthetically valuable organolithium reagents. The full synthetic potential of one of the most important of these reactions, the Li/I exchange, was not realized (e.g., in the synthesis of alkyllithium reagents) until mechanistic studies showed that it was a well-behaved polar process without a significant radical component.[1a,b,2] Ate complexes, first proposed by Wittig and Schˆllkopf,[3] are presumptive intermediates in these reactions [Eq. (1)]. Ate complexes of