Crystal structures and Si-29 NMR calculations of amino-functionalized silyllithium compounds

X-ray structural analysis of the amino-functionalized silyllithium compound s tris(tetrahydrofuran) [bis(diethylamino)phenylsilyl]lithium (4.3THF) and tris(tetrahydrofuran) [(diethylamino)bisphenylsilyl]lithium (7.3THF) are pr esented. Both compounds are monomeric in the solid state as well as in solu tion. Despite the formal negative charge at the silicon atom, the nitrogen centres are flattened. No Li-N interactions were observed, in contrast to t he homologous (lithiomethyl)amines, RI-DFT calculations give an explanation for the variation of experimental Si-Li bond lengths of 2.627(4)Angstrom ( 4.3THF), 2.682(8)Angstrom (7.3THF) and 2.732(7) Angstrom {tris(tetrahydrofu ran)[bis(diphenylamino)phenylsilyl]lithium} (1.3THF). N-Si orbital interact ions, influenced by the type of substituents located at the nitrogen centre , affect these structural parameters as well as the Si-29 NMR chemical shif ts. The apparently unusual experimental values of the Si-29 NMR resonance s ignals at delta = 20.3 (for 7.3THF) and delta = 28.4 (for 4.3THF) can be ex plained by DFT-IGLO calculations and are a consequence of the combination o f electronegative and electropositive substituents at the silicon centre.