Difluoro phosphane

Tabic 1. Aryl(difluoro)phosphanes from the Reaction of Aryllithium Compounds with Phosphorus Chloride Difluoride... 

Organolithium compounds can also react with fluorinated phosphorus derivatives. For example, aryl(difluoro)phosphanes 18 are formed by reaction of the corresponding aryllithium compounds with phosphorus chloride difluoride. The overall reaction is shown in Table l.K This procedure has also been extended to the preparation of several cyclopentadienyl(di-fluoro)phosphane derivatives.9... 

It should be noted that under some conditions reaction of internal perfluoroalkenes and -cycloalkenes with tributylphosphane and triphenylphosphane results in dimerization, preceded by defluorination and formation of a 1,3-diene and an appropriate difluoro-/ -phosphane. For example, reaction of perfluoroalkenes containing three perfluoroalkyl groups at the double bond w ith a phosphane [tributylphosphane. triphenylphosphane, tris(diethylamino)phosphane] results in reductive dimerization of these alkenes, to give 1,3-dienes and difluoro-/5-phosphanes. 

Sulfur tetrafluoride acts as an oxidative fluorinating agent towards organometalloid compounds. Triphenylphosphane and triphenylarsane are converted at 100-150C into difluoro-triphenyl-l5-phosphane (16) and difluorotriphenyl-l5-arsane (17), respectively.219... 

Similarly, the reaction between sulfur tetrafluoride and tris(dimethylamino)phosphane proceeds with oxidation of the phosphane in addition to fluorine transfer to give tris(dimethylamino)-difluoro-A5-phosphane (18) as the main product. In contrast, the reaction with tris(methyl-sulfanyl)phosphane does not give a straightforward fluorination extensive Arbuzov-type rearrangements and fluorination reactions occur.220... 

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-trifhioromclhyl-F.IOa. 515 (PC12 - pr,) E10b2. 69 f. (F.duct)... 

Phosphane (1.2-Difluoro-elhenyl)-methoxy-( tetrafluoro-1 H-ethyl)-EI0b2, 153 (— F2 - En PH - P-OR)... 

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

Phosphane Difluoro-(pentafluoro-phenyl)- ElOa. 514f. 

Diniethoxynaplithyl(difluoro)phosphancwas formed in46% yield from 2,3-dimelhoxynaphthalcne via lithiation at 30 C for 20 h. b From 3IP and FNMR this also showed the presence of 2-methoxy-4-(tri-fluoromcthyl)phenyl(ditluoro)phosphane (32% yield). 

The Hiyama-Hatanaka cross-coupling reaction is a more recent arylation coupling reaction that was reported by these workers in 1988 [12e, 31]. These workers demonstrated that trimethylsilylethy-lene reacts with aryl halides in the presence of a Pd(0) catalyst, a base, and a source of fluoride ion to give styrene derivatives [12e]. The source of Pd can be (it-CjHjPdCOj, Pd(Ph3P)4, or even Pdjfdbalj the base could be a hydroxide, an acetate, a phosphane, or a phosphite and the source of the fluoride ion could be tris(diethylamino)sulfonium difluoro(trimethyl)silicate (TASF), tetrabutylammonium fluoride (TBAF) or even KF (See Scheme 1.14a). The role of this reagent is shown in the catalytic cycle... 

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