Silane with silicon ions

Several aromatic and heterocyclic acyl trimethylsilanes have been used as acyl anion equivalents by treatment with fluoride ion (Scheme 81, path a) d33,i54b,i60,i9i,i92 Provided that the acyl substituent is electron-withdrawing, and that there are no aryl substituents on the silicon atom, acyl anions can be trapped by various electrophiles in moderate to good yields indeed, acyl anions and pentacoordinate silicon anionic species have both been detected in gas-phase reactions of acyl silanes with fluoride ion . 

Reaction of allylic silanes with aldehydes and ketones can also be induced by fluoride ion, which is usually supplied by the THF-soluble salt tetrabutylammonium fluoride (TBAF). Fluoride adds at silicon to form a hypervalent anion with much enhanced nucleophilicity.73 An alternative reagent to TBAF is tetrabutylammonium triphenyldi-fluorosilicate.74... 

Crucial for the success of the Hiyama Coupling is the polarization of the Si-C bond. Activation of the silane with base or fluoride ions (TASF, TBAF) leading to a pentavalent silicon compound is a first necessary step. 

Isomerization of methyl-substituted allylsilanes. Substrates of this type when heated with fluoride ion in THF rearrange to allyl silanes in which the silicon atom is bonded to the less-substituted carbon atom of the allylic group. 

Silane 5 attacks ion 4 or 8 with the double-bond carbon atom that is in y-position to the silicon atom. This generates carbocation 11, which is stabilized by the silicon in the P-position. Nucleophilic attack at the silicon regenerates the double bond with an overall allylic rearrangement of the double bond. 

When a silane such as 742 is treated with fluoride ion, fluoride attacks the silicon and displaces the carbanion 743. If the anion is generated in the presence of an electrophile, typical carbanion reactions occur. It is unlikely that the carbanion (743) has a significant lifetime as a discrete entity. Indeed, it need not exist at all,... 

Like the reactions of silicon ions with silane, the reactions of silicon ions with silicon tetrafluoride can provide information about both the ions and neutral silicon fluoride species (Weber and Armentrout, 1988). Reactions (15) to (17), analogous to processes (6) to (8), are the only reactions observed. 

Increased functionality of the organometallic moiety will lead to more intricate supramolecular assemblies. A suggestive organometallic example is provided by tetra(p-cyanophenyl)silane, Si(C6H4CN-p)4, which forms a three-dimensional self -organized supramolecular network of interpenetrating double layers by coordination with silver ions [27] and a layered supramolecular structure with TiCU [28], both imposed by the directionality of tetrahedral silicon centers. Supramolecular assemblies are defined as "extended polymolecular arrays presenting a more or less... 

An alternative rearrangement pathway may be observed when the silicon atom bears aryl substituents or when simple aUcanoyl triaUcylsilanes are used. This pathway is similar to one suggested, but not observed, by Brook for reaction of acyl silanes with aikoxide Addition of fluoride ion to silicon induces a migration to the carbonyl car-... 

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