Structure of 2-lithiobenzofuran-tmeda and 2-lithiobenzothiophene-tmeda in the solid state and in solution.
The solid-state structure of 2-lithiobenzofuran-tmeda, detd. by single-crystal x-ray diffraction, consists of dimeric species in which benzofuryl rings bridge the Li atoms and tmeda acts as chelating ligand. The O atom of one of the benzofuryl rings shows an interaction with Li. The x-ray structure of 2-lithiobenzothiophene-tmeda dimer also shows chelating tmeda ligands to be present, but no S-Li contacts. The distortion of the C(ipso)-Li-C(ipso)'-Li' ring, which also is found for dimeric phenyllithium-tmeda, is explained by steric effects. In soln. (toluene) both species are revealed by NMR to have dimeric structures with C2v symmetry. NMR shows the same to be true for 2-lithiobenzoselenophene-tmeda in toluene.
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