Silane fluoro

This excellent method of oxidative cleavage (/) of carbon-silicon bonds requires that the silane carry an electronegative substituent (2), such as alkoxy or fluoro. Either hydrogen peroxide or mcpba may be used as oxidant, and the alcohol is produced with retention of configuration (3). Fluoride ion is normally a mandatory additive in what is believed to be a fluoride ion-assisted rearrangement of a silyl peroxide, as shown below ... 

Radical-mediated silyldesulfonylation of various vinyl and (a-fluoro)vinyl sulfones 21 with (TMSlsSiH (Reaction 25) provide access to vinyl and (a-fluoro)vinyl silanes 22. These reactions presumably occur via a radical addition of (TMSlsSi radical followed by /)-scission with the ejection of PhS02 radical. Hydrogen abstraction from (TMSlsSiH by PhS02 radical completes the cycle of these chain reactions. Such silyldesulfonylation provides a flexible alternative to the hydrosilylation of alkynes with (TMSlsSiH (see below). On oxidative treatment with hydrogen peroxide in basic aqueous solution, compound 22 undergoes Pd-catalyzed cross-couplings with aryl halides. 

The nomenclature of the RP is not consequent. The RP most often used contains octyl (RP C8) or octadecyl (RP C18) groups. There is no differentiation even when two methyl groups are introduced additionally with the silane (as with monofunctional silanes) or only one (difunctional) or none (trifunctional silane). Some manufacturer use silanes with bulky side groups (e.g., isopropyl groups) to improve the hydrolytic stability of the bonded phases, but here also, only the longest alkyl group is used in nomenclature. RP C8 and RP C18 are the work horses in HPLC. Shorter chains (RP4) are used in protein separations, and special selectivity can be obtained with bonded phenyl, cyano, amino or fluoro groups. 

Chloro-, hydroxy-, alkoxy- and siloxysilanes are converted by sulfur tetrafluoride into fluoro-silanes. Thus, chlorotrimethylsilane, trimethylsilanol and hexamethyldisiloxane react at 20 "C to give fluorotrimethylsilane in 42-77% yield.231... 

Reaction of silicon tetrafluoride with phenylmagnesium bromide at 0 C in diethyl ether provides fluorotriphenylsilane and fluorodiphenylsilane in 59.5 and 5% yield, respectively.3 Chloro(cy-clohexyl)(l-naphthyl)silane is converted into (cyclohexyl)fluoro(l-naphthyl)silane by reaction with a reagent which is prepared by bubbling silicon tetrafluoride through a mixture of tet-rahydrofuran and water.12... 

Biaryls have also been prepared by coupling support-bound aryl halides with aryl-zinc compounds (Figure 5.20) or with aryl(fluoro)silanes [203]. As with Suzuki or Stille couplings, these reactions also require transition metal catalysis. An additional strategy for coupling arenes on solid phase is the oxidative dimerization of phenols (Figure 5.20). 

Mixed Organofluorine - Organosilicon Chemistry. Part 9. Aldol Reactions of Acylsilanes and (Difluoroenoxy)silanes. Application to the Synthesis of 2-Fluoro 1,3-Diketones ... 

Silane (Dichloro-fluoro-niethyl)-trimethyl- ElOb,. 407/413 (Educt)... 

Silane Dimcthyl-fluoro-(l. 1,2-trimcthyl-propvl)- ElOa. 613 (Cl -> F)... 

This explains why di- and trisubstitution of the six-membered ring with fluoro-silanes and -boranes is possible. These groups decrease the basic character of the ring and its tendency to ring contraction. 

However, the reaction rate is also increased by using silanes with R groups such as fluoro or alkoxy instead of alkyl. In fact, there are only a few successful examples of coupling reactions using trimethylsilane derivatives. 

Bell and co-workers 24, 25) have investigated the generation of tri-fluoromethyl radicals from photolysis of HFA in the presence of silanes. Abstraction of the proton is observed in the case of trichlorosilane (24), while methyl(fluoro)silanes lead to the formation of CFjH, CjF, and CF CH 2(25). 

The cross-coupling reaction of alkenyl(fluoro)silanes with aryl halides sometimes produces, in addition to the desired ipso-cowpled products, small amounts of cmc-coupled products [14]. The czne-coupling is often striking in the reaction with organotin compounds. The isomer ratio of products produced by the reaction of l-fluoro(dimethyl)silyl-l-phenylethene with aryl iodides is found to depend on the electronic nature of a substituent on aryl iodides (Eq. 11) an electron-withdrawing group like trifluoromethyl and acetyl favors the formation of the ipso-coupled product. To explain the substituent effect, the mechanism depicted in Scheme 3 is proposed for the transmetalation of alkenylsilanes with palladium(ll) complexes. It is considered that an electron-donating substituent on Ar enhances... 

High molecular weight perfluorinated tertiary alcohols can be prepared by the reaction of (perfluoroalkyl)- and (perfluorooxaalkyl)trimethylsilanes with fluoro ketones (vide supra). The reaction has been extended to carbonyl compounds other than ketones acid fluorides gave ketones, but no reaction was observed with esters. a-Oxo esters react with trimethyl(tri-fluoromcthyl)silane with fluoride initiation in tetrahydrofuran /(./(. -trifluoro lactic acid derivatives are produced in good yields in one step. 

Trifluoro(trimethylsilyl)ethene (1) is also formed by the reaction of bromotrifluoroethene with chlorotrimethylsilane in the presence of tris(diethylamino)phosphane in benzonitrile at room temperature. " Trifluoro(trimethylstannyl)ethene (2) is obtained via a similar route in 80% yield and dimethylbis(trifluorovinyl)silane in 56% yield from dichlorodimethylsilane. " Tri-fluoro(triethylgermanyl)ethenc is available from trifluoroiodoethene and chlorotriethylger-mane." ... 

Thus, reaction of the silane, in the presence of cesium fluoride in acetonitrile, with per-fluoro(3-azapent-2-ene) and perfluoro(5-azanon-4-ene) gave phenylazaalkenes 9. 

The reaction of trimethyl(perfluorophenyl)silanc with carbonyl centers occurs under mild reaction conditions, similar to those used for trimethyl(trifluoromethyl)silane. Acetyl fluoride in acetonitrile in the presence of catalytic amounts of potassium fluoride gives l-fluoro-l-(penta-fluoropheny )ethyl acetate (12) in 65% yield. When the bifunctional acid fluoride perfluoro-glutaryl difluoride reacts with trimethyl(perfluorophcnyl)silane in acetonitrile in the presence of potassium fluoride, the perfluorinated diketone perfluoro(l,5-diphenylpcntane-l,5-dione)... 

Fig. 2. Mole fraction of gaseous products formed by the IR-multiphoton decomposition of (fluoro-methyl)silanes (reprinted from reference [25])...

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