Structures of Tetrasilylmethane Derivatives (XMe2Si)2C(SiMe3)2 (X = H, Cl, Br) in the Gas Phase, and their Dynamic Structures in Solution

The structures of the molecules (XMe2Si)(2)C(SiMe3)(2), where X = H, Cl, Br, have been determined by gas electron diffraction (GED) using the SARACEN method of restraints, with all analogues existing in the gas phase as mixtures of C-1- and C-2-symmetric conformers. Variable temperature H-1 and Si-29 solution-phase NMR studies, as well as C-13 NMR and H-1/Si-29 NMR shift correlation and H-1 NMR saturation transfer experiments for the chlorine and bromine analogues, are reported. At low temperatures in solution there appear to be two C-1 conformers and two C-2 conformers, agreeing with the isolated-molecule calculations used to guide the electron diffraction refinements. For (HMe2Si)(2)C(SiMe3)(2) the calculations indicated six conformers close in energy, and these were modeled in the GED refinement.