The chemistry of the hypersilyl and related ligands

• Main Author: Chan, W. T. K.
• Published: University of Cambridge 2009
• Subjects: 546.3
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597417

This thesis is mainly focused on the investigation of the chemistry and reactivity of the hypersilyl ligand {[(Me₃Si)₃Si]^-}, and the rationalisation of the use of siloxanes as precursors ([(R₂SiO)_n]). A total of ten new compounds have been prepared from these studies, and X-ray crystallography forms a central basis of the analysis of these species, along with NMR spectroscopy and various other analytical techniques. The first novel compound described is [(Ph₃Si)(Me₃Si)₂SiK^.18-crown-6] (3). Despite isolating 3 in pure both crystalline and powder form the difficulty in synthesising the compound in large scale meant that its reactivity could not be investigated fully. A series of Si-M complexes was made in the form of [(Me₃Si)₃Si^.MX₃]^-[K^.18-crown-6]⁺(4-6, M = Al or Ga, X = Cl or Br), as well as [(Ph₃Si)(Me₃Si)₂Si^.GaCl₃]^-[K^.18-crown-6]⁺ through the reaction of the respective silyl anion with the corresponding group 13 halides. Due to yield considerations, 6 was chosen as a precursor to study the thermal decomposition behaviour of this type of compounds. The reaction between (Me₃Si)₃SiK^.18-crown-6 (1a) with (P₄) led to the formation of the unusual {P₈[(Me₃Si)₃Si]₂^.K^.18-crown-6}^-[K^.18-crown-6^.(THF)₂]⁺ (8). The discovery of 8 allows an investigation into the relatively poorly understood mechanism for this type of reaction, and a proposed mechanism, supported by computational calculations, is discussed. The reaction between hypersilyl potassium (1a) and mesityl nitrile gave 6,8-dimethyl-1-amino-3-mesityl-isoquinoline. Finally, the unexpected formation of [2-PySi(Me)₂LiO]₆ and {[18-crown-6^.]GaCl₄}_∞ are also described.