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Title: Tetrasilylmethane derivatives : synthesis, structures and their potential as precursors to silyl cations
Author: Bätz, Karin
ISNI:       0000 0001 3452 2825
Awarding Body: Imperial College London (University of London)
Current Institution: Imperial College London
Date of Award: 2006
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This thesis describes studies of the gas phase structures and dynamic behaviour of several tetrasilylmethane derivatives as well as the use of silanes bearing the trisyl ligand (Tsi), (Me3Si)3C-, or closely related ligands in attempts to prepare silyl cations R3Si+. Hydride abstraction reactions between the silanes TsiSiMe2H, TsiSi(OMe)2H, (PhMe2Si)3CSiMe2H and (Me3Si)2C(SiMe2H)2 and the trityl salt Ph3C+B(C6F5)4⁻ in a chlorobenzene/toluene-d8 solvent mixture were carried out and monitored by 1H, 29Si and 13C NMR spectroscopy, which indicated that several species appeared to be present in dynamic equilibria in solution. A range of compounds such as TsiSiCl3, CDCl3, Et2O and CH3CN were added to the equilibrium mixtures to trap any silyl cationic species present and the reactions monitored by NMR spectroscopy and G. C. mass spectrometry. The results obtained indicate that complicated mixtures were formed but a detailed analysis has not been possible. The structures of the molecules TsiSiH3, (XMe2Si)4C where X = H, F, Cl and Br and (XMe2Si)2C(SiMe3)2 where X = H, Cl and Br were determined by gas-phase electron diffraction. Ab initio calculations revealed that the compound TsiSiH3 was present in the gas phase as a single C1 (pseudo-C3) conformer. (XMe2Si)4C where X= H, F, Cl and Br were calculated to exist as two different conformers of C1 symmetry and a third conformer of C2 symmetry in varying proportions. The gas-phase mixtures of (XMe2Si)2C(SiMe3)2 where X = Cl and Br were determined to consists of a C1 and a C2 conformer in different ratios, whereas that of (HMe2Si)2C(SiMe3)2 comprised of a single C2 conformer. Variable temperature 1H and 29Si NMR studies and where applicable 13C NMR, 1H/29Si NMR shift correlation and 1H NMR saturation transfer experiments of (XMe2Si)4C where X = H, Cl and Br and (XMe2Si)2C(SiMe3)2 where X = H, Cl and Br are reported. At low temperature, there appears to be a C1 and a C2 conformer of (XMe2Si)4C where X = Cl and Br and two C2 as well as two C1 conformers of (XMe2Si)2C(SiMe3)2 where X = Cl and Br. (HMe2Si)4C and (HMe2Si)2C(SiMe3)2 seem to be present as single conformers only at low temperature in solution. Solid state 13C{1H} and 29Si{1H} MAS NMR spectra of (XMe2Si)2C(SiMe3)2 where X = Cl and Br at ambient temperature were also obtained.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral