Silicon tetra fluoride

Contact with liquid hydrogen fluoride causes violent evolution of silicon tetra-fluoride. (The same is probably true of metal silicides and other silicon compounds generally.)... 

The desired extent of fluorination of the starting material may dictate the fluorinating agent to be used. For example, fluorine converts silicon tetrachloride to silicon tetra-fluoride, whereas antimony(III) fluoride promotes the reactions which produce the chlorofluorides, SiCl3F, SiCl2F2, and SiCIFs. 

Quite often additional trifluorosilane can be obtained by simply returning the unreacted silane to the reaction vessel and allowing additional reaction time. A single reaction period yields about 1.5 g. (65% based on HSiCl3 employed) of product having an observed molecular weight of 86.9 (calcd. 86.1) and an infrared spectrum consistent with pure trifluorosilane.11 However, on some occasions the product is contaminated with silicon tetra-fluoride due to a reaction of the antimony compounds with the trifluorosilane. The silicon tetrafluoride impurity does not interfere with the preparation of tetracarbonyl(trifluorosilyl)cobalt. 

The hydrated compound (CrF.5H2O)SiF0 is stable in dry air or in a vacuum but in contact with moist air it slowly loses silicon tetra-fluoride, and ultimately yields hydrated chromic fluoride, Cr2F5.7ll20. 

Boron trifluoride is similar in many ways to silicon tetra-fluoride, including its physical properties and reactions with water and alkalies. It could be prepared by an analogous method ... 

At the turn of the 18th century many scientists believed that silica, or silica earth, contained an unknown chemical element and tried to isolate it in a free state. H. Davy attempted to decompose silica with an electric current—the method by which a number of alkali metals had already been prepared—but without success. The scientist s attempt to prepare free silicon by passing metallic potassium vapour over red-hot silicon oxide also failed. In 1811 L.J. Gay Lussac and L. Thenard applied themselves to the problem. They observed a vigorous reaction between silicon tetra-fluoride and metallic potassium a reddish brown compound was formed in the reaction. The scientists could not reveal the nature of the product most likely, it was contaminated amorphous silicon. 

The sodium beryllium fluoride product is soluble in water and can be leached out, together with some aluminium, excess sodium silicofluoride, and small amounts of other impurities. Unfortunately a high proportion of the valuable fluorine is lost as the gaseous and highly toxic silicon tetra-fluoride, or as undissolved sodium aluminium fluoride. However, the escape of volatile silicon tetrafluoride can be prevented if a small amount of sodium fluoride is present with the sodium silicofluoride, owing to the reaction... 

Both soluble and insoluble fluorides are converted into silicon tetra-fluoride (b.p. -65 C) on warming with quartz sand (silica) and concentrated sulfuric acid ... 

Antimony.—The chlorotrifluoromethylstibines (CFs)jSbCl and CFs-SbCl, have been obtained by treatment of trichloromethyltrifluorosilane with antimony trifluoride in the absence of solvent. Treatment of the silane with a stoicheiometric amount of antimony trifluoride in ether gives silicon tetra-fluoride and tristrichloromethylstibine, which decomposes into antimony trichloride and the chlorocarbons CClj, C2CI4, and CaClj when warmed similar fluorination with an excess of antimony trifluoride yields the halo-genomethanes CHF, CHF2CI, and CHFCla. =... 

The following striking differences between silicon and germanium tetra-fluoride are apparent (i) germanium tetrafluoride forms more stable complexes with cyclic ethers and dimethyl ether than does silicon tetrafluoride ... 

Noyori and coworkers found that tetrafluorosilane or trimethylsilyl tri-flate catalyzes the condensation of appropriately protected glycopyranosyl fluorides with trimethylsilyl ethers or alcohols. The strong affinity of silicon for fluorine was considered to be the driving force for this reaction. In the case of Sip4, attack of a nucleophile on the glycosyl cation-SiFj ion-pair intermediate was anticipated. Thus, condensation of 2,3,4,6-tetra-O-benzyl-a- and - -D-glucopyranosyl fluorides (47a and 47fi) with methyl... 

Alkynes are viable substrates for the tandem intramolecular silylformylation/allylsilyla-tion reaction. The 1,5-diastereoselechvity is reversed from that observed with alkene substrates, as the 1,5-anti product predominates (Scheme 5.24) [38]. Synthetic flexibility was demonstrated in that either of two carbon-silicon cleavage procedures may be employed. Protodesilylahon with tetra-n-butylammonium fluoride followed by acetylation (determi-... 

An interesting case of simultaneous exchange of two fluorides has been reported recently22. In compounds 2g and 2h there is one tetra- and one pentacoordinate silicon. Fluoride transfer from the pentacoordinate silicate to the silane was found to be inter-molecular, with a large negative entropy of activation. It was concluded that exchange takes place simultaneously between two complexes, through a cyclophane-like transition... 

MICHAEL ADDITIONS Alumina. Aluminum chloride. Cesium fluoride-Silicon(lV) cthoxidc. 1,4-Diazabicyclo[2.2.2]octanc. l,8-Diazabicyclo[5.4.0]-7-undecene. Ketene r-butyldimethylsilyl methyl acetal. Lithium acetylides. (S)-( + )-2-Mcthoxymethylpyrrolidine. Methyl lithiodithioacetate. Methyl (phcnylsulfinyl)acetate. Methyl 2-trimcthylsilylacrylate. Nickel carbonyl. Organocopper reagents. 8-Phenylmcnthol. Phenyl 2-(trimethylsilyl)ethynyl sulfone. Tetra-n-butylammonium fluoride. Tiianium(IV) chloride. 3-Triisopropylsilylpropynyllithiuni. Zirconium(IV) n-propoxiilc... 

However, an efficient synthesis of the spirovetivane-sesquiterpene a-Vetispirene 392 was achieved initiating the cleavage of the silicon-cyclopropane carbon bond of 160 by fluoride ion. This was effected with anhydrous tetra-n-butyl ammonium fluoride in THF solution containing acetone at reflux temperature for 10 hr. The pentadienyl anion 387 thus generated experienced highly regioselective addition of acetone at the... 

It is a palladium-catalyzed cross-coupling reaction between organosilanes (vinyl, ethynyl and allylsilanes) and organic halides (aryl, vinyl and allyl halides). Allylpal-ladium chloride dimmer [( ri -C3H5PdCl)2] and either tris(diethylamino)sulfonium difluorotrimethylsilicate (TASF) or tetra-n-butylammonium fluoride (TBAF) are used as catalysts. Fluoride ion acts as an activator for the coupling, forming an intermediate hypervalent anionic silicon species, which can then transmetallate with palladium as a preliminary reaction to coupling. 

Finally, the / er butyldimethylsilyl (TBS) ether is cleaved with tetra- -butylammonium fluoride (TBAF) to provide alcohol 22. TBAF is suitable for this deprotection step because silicon has a high affinity for fluorine. Thus, fluoride attacks a d-orbital of the silicon atom in 46 providing the negatively charged pentacoordinate intermediate 47, which then breaks down with loss of the alkoxide 49 to give 48. 

Naked enolates without any complexation can be made from silyl enol ethers using fluoride ion, a very selective nucleophile for silicon 49, and a non-metallic cation, usually a tetra-alkylammonium ion. The commonest reagent is TBAF (TetraButylAmmonium Fluoride Bu4N+ F ). In this way the naked enolate 50 was made. It proved to be acylated with acetic anhydride exclusively at oxygen to give the enol acetate 53 and alkylated with Mel at carbon to give the ketone 51 in 84% isolated yield.18... 

Lithium enolates 85 and silyl enol ethers 86 are probably widest in application in modern organic synthesis. The basic rules of selectivity were laid down in chapters 2-4 where many examples were given. We shall simply summarise the position and add some extra versatility from chapters 5-9. These two methods must be taken together because easy interconversion means that a way of making one is a way of making another. In addition, the silyl enol ethers 86 are a source of naked enolates 87 when fluoride is used to remove silicon in the absence of a metal cation. Tetra-alkyl ammonium fluorides such as TBAF (Bu4N+ I ) are usually used. 

Tebbe olefination, 441 Tebbe olefinations, 368 Tebbe s reagent, 457 Tedania ignis, 246 Tedanolide, 246 tedanolide, 256 TEMPO, 250, 301 temporary silicon tether, 103 Tennant quinoline synthesis, 7 tetra-n-butylammonium fluoride (TBAF), 214 2-(7-aza-1 H-benzotriazole-1 -yl)-1,1,3, 3-tetramethyluronium hexafluorophosphate (HATU), 25... 

---