Structures of tetrasilylmethane derivatives C(SiXMe2)4 (X = H, F, Cl, Br) in the gas phase and their dynamic structures in solution.

The structures of the molecules C(SiXMe2)4 (X = H, F, Cl, Br) have been determined by gas electron diffraction (GED). Ab initio calculations revealed nine potential minima for each species, with significant ranges of energies. For the H, F, Cl, and Br derivatives nine, seven, two, and two conformers were modelled, respectively, as they were quantum-chemically predicted to be present in measurable quantities. Variable-temperature 1H and 29Si solution-phase NMR studies and, where applicable, 13C NMR, 1H/29Si NMR shift-correlation, and 1H NMR saturation-transfer experiments are reported for C(SiXMe2)4 (X = H, Cl, Br, and also I). At low temperature in solution two conformers (one C1-symmetric and one C2-symmetric) are observed for each of C(SiXMe2)4 (X = Cl, Br, I), in agreement with the isolated molecule ab initiocalculations carried out as part of this work for X = Cl, Br. C(SiHMe2)4 is present as a single C1-symmetric conformer in solution at the temperatures at which the NMR experiments were performed

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)2C(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 C1- and C2-symmetric conformers. Variable temperature 1H and 29Si solution-phase NMR studies, as well as 13C NMR and 1H/29Si NMR shift correlation and 1H NMR saturation transfer experiments for the chlorine and bromine analogues, are reported. At low temperatures in solution there appear to be two C1 conformers and two C2 conformers, agreeing with the isolated-molecule calculations used to guide the electron diffraction refinements. For (HMe2Si)2C(SiMe3)2 the calculations indicated six conformers close in energy, and these were modeled in the GED refinement

The gas-phase structure and some reactions of the bulky primary silane (Me₃Si)₃CSiH₃ and the solid-state structure of the bulky dialkyl disilane [(Me₃Si)₃CSiH₂]₂

The molecular structure of the bulky primary silane, (Me3Si)3CSiH3, in the gas phase has been determined by electron diffraction. Photolysis of (Me3Si)3CSiH3 affords a convenient route to the bulky dialkyl disilane, [(Me3Si)3CSiH2]2, which is the first 1,2-dialkyldisilane to be structurally characterised by single-crystal X-ray diffraction. The disilane has an unusually large Si–Si–C angle of 120.05(9)°.</p