The solution structures of [bis (diethylamino)phenylsilyl] lithium (1), [(diethylamino)diphenylsilyl] Lithium (2), and [(diethylamino)phenylmethylsilyl] lithium (3) were investigated by C-13, Si-29, Li-7, and N-15 NMR spectroscopic experiments. The Si-29-Li-7(6) coupling can be observed in each species at low temperature. The coupling patterns indicate that these three species exist as monomers in THF. Using a N-15-enrichment technique, the Si-29-N-15 couplings in 1 and 2 are observed. Next, the solid-state structures of [(diphenylamino)diphenylsilyl] lithium ((Ph2N)Ph2Si-X; X = Li) (4) and its fluoro (X = Fl (16), stannyl (X SnMe3) (17), and hydro (X H) (18) derivatives were revealed by crystallographic studies as well as by solid-state 29Si NMR experiments. In the solid state, 4 exists as a monomer solvated with three THF molecules arising from the reaction solvent. The electropositive substituent X, such as lithium, causes the elongation of the Si-C and Si-N bonds, reduction of the sum of the C-Si-N (or C) angles, and a downfield shift of the 29Si resonances.