Crystal structures of unsolvated lithiosilanes with Si-Si bonds

The molecular structures of lithiopentamethyldisilane ([LiSiMe2SiMe3](4), l a), 2-lithio-1,1,2,3,3-pentamethyl-1,3-diphenyltrisilane ([LiSi(SiMe2Ph)(2) Me](2), Ib), and 2-lithio-1,1,1,3,3,3-hexamethyl-2-phenyltrisilane ([LiSi(S iMe3)(2)Ph](2), Ic) have been determined by X-ray diffraction. The silyllit hium la is a tetramer in the solid state with intramolecular Li ... CH3 ago stic interactions. The silyllithiums Ib and Ic are dimers with intramolecul ar lithium-phenyl interactions. The latter adopts a molecular structure wit h not only an intramolecular Li-Ph interaction, but also an intermolecular Li ... CH3 agostic interaction. The structures of these organometallic deri vatives show novel features not observed in solvent-coordinated lithiosilan es. These features provide valuable insights into structures that differ ma rkedly from those of lithiosilanes containing coordinated donor solvent mol ecules.