Fluoro phosphane

The mechanism of the formation of organic fluorides from silyl etliers and fluoro-/. -phosphanes has been studied in some detail for tetrafluoro(phcnyl)-A -phosphane. The first step, which is usually quantitative at low temperatures, is the formation of an intermediate alkoxyfluoro-A -phosphane 1 and fluorotrimethylsilanc. 

Organolithium compounds can also react with fluorinated phosphorus derivatives. For example, aryl(difluoio)phosphanes 18 are formed by reaction of the corresponding aiyllithium compounds with phosphorus chloride difluoridc. The overall reaction is shown in Table I. This procedure has also been extended to the preparation of several cyclopentadienyl(di-fluoro)phosphane derivatives. ... 

The reactivity of fluoro(organyl)phosphanes depends on the nucleophilicity of phosphorus For mstance the phosphanes may add to the carbonyl carbon to form phosphiniio phosphoranes (equation 36) or may react with acid fluondes to form acyldifhiorophosphoranes [37] (equation 37)... 

There do not appear to be any simple phosphines that bear a CH2F group. However, fluorine NMR spectra of phosphonates, phosphane oxides, and phosphonium compounds with CH2F and —CHF- bound to phosphorous have been reported. Examples are given in Scheme 3.26, including spectral data for the useful Horner-Wadsworth-Emmons reagent, triethyl 2-fluoro-2-phosphonoacetate. 

The electrochemical oxidation of tertiary phosphanes, R3P, can be carried out with a platinum electrode in acetonitrile with the addition of pentylammonium fluoride and with the electrolyte tetraethyl ammonium tetrafluoroborate.65 The observed product is the trialkyldi-fluoro-25-phosphane R3PF2. The electrolysis is carried out in a galvanostatic mode with a current density from 3.3 to 6.7 mA cm-2. The anodic oxidation may be represented by the following equation ... 

The second product in this reaction, the difluorotris(perfluoroalkyl)-A5-phosphane, does not dissolve in aryl fluorides and, because of its greater density, forms a lower layer which can be easily separated. In this way the difluoro-A5-phosphanes are regenerated almost quantitatively and can be used in the synthesis many times. An example is the decomposition of 4-nitrobenzene-diazonium trifluorotris(heptafluoropropyl)phosphate at 87 C which provides l-fluoro-4-ni-trobenzene in 82% yield and difluorotris(heptafluoropropyl)-A5-phosphane in quantitative yield.6 This method is a convenient modification of the Balz-Schiemann reaction (see Section 26.1.3.). 

Decomposition of the diazonium trifluorotris(perfluoroalkyl)phosphates proceeds mildly, without formation of tars (since no strong Lewis acid evolves), and with high yields of the substituted fluorobenzenes. For example, l-fluoro-4-nitrobenzene is obtained in a far better yield (82%) than from 4-nitrobenzenediazonium hexafluorophosphate or tetrafluoroborate [cf. formation of 2 (R = 4-N02)]. The coproduced difluorotris(perfluoroalkyl)-A5-phosphanes are not soluble in the resulting fluorobenzene derivatives and, because of their high density, form a lower layer which is readily separated. Thus, these difluoro-25-phosphanes can be regenerated quantitatively and used repeatedly. 

Phosphane Difluoro-(4-fluoro-phcnyl)- ElOa. 515 (Educt)... 

Whereas the solvent influence on the and chemical shifts of the apolar tetramethylsilane is comparatively small (Ad ca. 0.5... 1.5 ppm), much greater effects are observed in the case of dipolar molecules such as 4-fluoro-nitrosobenzene and triethyl-phosphane oxide (Ad ca. 3. .. 25 ppm) as well as for the thallium(I) ion (Ad > 2000 ppm ). 

The conversion of silyl ethers into fluorides may serve as an indirect method for the conversion of hydroxy compounds into fluorides, but in some cases the silyl ethers are not formed from the corresponding alcohols and then a step is saved by direct conversion into the fluorides. Two classes of fluorinating reagents have been used so far to transform silyl ethers into fluorides these are nuoro-A -phosphanes, which were used first, and fluoro-/, -suIfanes. 

The ability of fluoro-2 -phosphanes to transform silyl ethers into fluorides was first observed during a study of the reactions of phosphorus pentafluoride and its derivatives R PF5 (n = 1, 2, 3 R = hydrocarbon group) with trimethylsilyl ethers. Subsequently, this reaction was proposed as a new method for the preparation of C-F compounds from silyl ethers or silicic acid esters with fluoro-A -phosphanes. Pentafluorophenyl-substituted fluoro-A -phos-phanes were found to react similarily, Other workers found that tctrafluoro(phenyl)-A -phos-phane. which was chosen as the most convenient reagent with regard to reactivity and stability, gave considerable amounts of elimination products, especially with primary and cyclic alcohols. Good yields of fluorinated products are obtained when stable carbocations can be formed at the site of substitution, such as in tertiary alcohols, but 2-phcnylethanol. benzyl alcohol and diphcnylmethanol, on the other hand, give only poor yields of fluorinated products ethers and polymers are the main products. ... 

Ammonio- and phosphoniohexafluorocyclobutanide ylides 11, prepared from pcrfluorocy-clobutene and tertiary amines or phosphanes, are soluble in a wide range of (even nonpolar) organic solvents and transfer fluoride, and therefore can be used as an easily soluble source of fluoride anions. Although they contain no ionic fluoride they react with fluoride anion acceptors such as silicon derivatives with elimination of thermodynamically favored fluoro-trimethylsilane to produce carbanions which can be quenched with suitable electrophiles. The reaction proceeds upon slightly heating the reactants in tetrahydrofuran or dimethylform-amide solution. 

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." ... 

The A -phosphane 1, formed in the reaction of triphenylphosphane with hcxafluoro-propene, reacts further with hcxafluoroacetone in the presence of the fluoride ion. affording triphenylphosphane oxide and perfluoro(2-methylpcnt-2-ene) (2). Formation of fluoro-A -phos-phancs underlies the method for the reduction of perfluoroalkenes which involves the reaction of an alkene with tributylphosphane and subsequent hydrolysis of the A -phosphanc formed. ... 

When perflluoro(2-methylpropene) reacts with tributylphosphane in acetonitrile at — 30"C, the reaction does not stop with the formation of fluoro-2 -phosphanes, and, as a result of a series of transformations, perfluorodiene 3 and conjugated cross-triene 4 are formed. When the reaction is carried out with triphenylphosphane in acetonitrile without cooling triene 4 is obtained in 67 % yield.On the other hand, the reaction of perfluoro(2-methylpropcnc) with tributylphosphane in diethyl ether at — 70 C leads to the corresponding fluoro-A -phos-phane treating this compound with potassium fluoride dihydrate in tetraglyme gives 1,1,1,3-tetrafluoro-2-(trifluoromethyl)hept-3-ene in 75% yield,... 

When perfluoro(2-methylpent-2-ene) reacts with phosphanes, carbanion 5 is formed. It is known that internal alkenes isomerize into the terminal alkenes in the presence of basic reagents, so that 5 reacts with this isomeric form and the end product of the reaction is per-fluoro(3-ethyl-2.5-dimcthylocta-2.4-dieiie) (6). 

On the other hand, in the reaction of trifluoroiodomethane and tris(diethylamino)phos-phane other products are formed, namely bis(diethylamino)(trifluoromethyl)phosphanc [(EtjNlaPCFj] and the salt (Et2N)4P l The salt 16 is stable up to its melting point. The high positive charge on the phosphorus atom in this compound promotes the reaction with the fluoride ion (arising from CsF, TASF, etc.). The fluoro-A -phosphane 17 is formed as an intermediate in this reaction. It reacts, for example, with benzaldehyde to form the alcohol 18. ... 

Perfluoroalkenes react readily with tertiary phosphanes to form various products depending on the position of the multiple bond in the alkene. Internal alkenes (perfluorobut-2-ene and perfluorocyclobutene) undergo addition of phosphane at the multiple bond with subsequent 1,2-migration of the fluorine atom to form stable phosphanes. Terminal fluoroalkenes under similar conditions form the corresponding fluoro(perfluorovinyl)-/5-phosphanes. The exception is perfluoro(2-methylpropene) which reacts with triphenylphosphane to form the triene... 

By reaction of a 1,1-difluoroethene with tributylphosphane in the presence of boron trifluoride-diethyl ether complex, the vinylphosphonium salt is obtained. On subsequent hydrolysis the selectivity of formation of the Z- and F-isomer is 100%, but it diminishes after the introduction into the alkene. together with the perfluoroalkyl group, of substituents such as phenyl and 4-methoxyphcnyl. In accordance with this methodology, a method of substitution of fluorine by hydrogen at the fluoroolefinic double bond has been developed.194,206 The first stage of this reaction includes the formation of a fluoro-/5-phosphane from the fluoroalkene and tributylphosphane. The decomposition of this /l5-phosphane in the aqueous solvent leads to a fluoroalkene, e.g. formation of l.206... 

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