Are Ate Complexes True Intermediates in Lithium–Metalloid Exchange? Subtle Effects of Ion-Pair Structure in Lithium–Tellurium and Lithium–Selenium Exchange Reactions

Li/Te exchange via the ate complex with no contribution from direct exchange (i.e., kd=0) was demonstrated by NMR studies on an intermolecular reaction (see scheme; M=Te, Ar=5-diphenylphosphanyl-2-thienyl). In contrast, in an intramolecular Li/Se exchange reaction, direct exchange bypasses the observable ate complex (kd≫kate).