Silicon-fluorine bond, reactivity

The first observation of penta- and hexaeoordinate silicon compounds was reported at the beginning of the 19th century by Gay-Lussac [87] and Davy [88], Subsequent investigation of hypercoordination in silicon compounds stimulated widespread use of nucleophilic activation and catalysis in the application of organosilicon compounds as reactive species in organic synthesis. Synthetic application for silicon-fluorine bond formation can be found in several reviews over the last two decades, and this section focuses on recent advances in the use of hypervalent organosilicon compounds in selective organic synthesis, in particular, selective carbon-carbon bond formation [89]. 

This might account for the failure to synthesize FH2CSi derivatives by treatment of (monochloro-methyl)silanes with fluorinating agents like AgF, KF, or SbFs, which led to a breakdown of the (chloromethyl)silicon moiety to give the corresponding fluorosilanes [7]. Additional indications of the reactivity of the C-F bond have been obtained by studying the thermal decomposition of these compounds. 

Interest in such compounds has arisen as a result of the extensive studies being carried out on the stereochemical aspects associated with phosphorus in coordination number five. The observation of distinct axial and equatorial P—F environments for the tetrafluorophosphoranes, by NMR techniques, is possible, whereas this observation is not common to the corresponding hydrocarbon-phosphorus bonded tetrafluorophosphoranes. Further substitution at phosphorus is possible, the tetrafluorophosphoranes and trifluorophosphoranes are reactive compounds, and it is possible to substitute further F atoms for other groups. The experimental techniques described here can be applied to the preparation of other amino fluoro phosphoranes. Further, the same techniques are applicable to other reactions involving phosphorus-fluorine compounds and silicon compounds. 

The conditions giving the best yields for the vinylation with trimethylvinylsilane were applied to the coupling reaction of 1-trimethylsilyl-l-octene [Eq.(7)]. However, the silicon reagent was recovered totally intact. We considered that the polarization of the C-Si bond of this reagent was lowered by the hexyl substituent. Accordingly, to induce the polarization of the Si-C bond, we replaced one to three methyl(s) on Si by fluorine(s) and were pleased to find that fluoro(dimethyl)silane (n = 1) or difluoro(methyl)silane (n = 2) was reactive enough [8]. 

The elements in group 18 have full outer shells of electrons. This is a stable electron arrangement and these elements only form compounds with the most reactive elements, notably fluorine. The first two elements in group 14, carbon and silicon, have outer shells which are half full. These two elements generally do not form simple ions but instead form covalent bonds. (However, carbon reacts with metals to form a number of metal carbides.)... 

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