Fluoride ion catalysts

A recent modification of the Peterson reaction involves the use of fluoride ion catalysts. Reaction of bis(trimethylsilyl)methyl derivatives 166 and carbonyl compounds gives the expected alkenes 167 (as shown in equation 137) in high yields, especially for non-enolisable carbonyl compounds, and in some cases with high stereoselectivity209. 

Carboxylic acid fluorides undergo addition to fluoroalkenes in the presence of a fluoride ion catalyst, e.g. antimony(V) fluoride to give products 1, or cesium fluoride to give products 2 ... 

Elias, A.J. Kirchmeier, R.L. Shreeve, J.n.M. Polyfluoroalkoxy and aryloxy cyclic phosphazenes an alternative synthetic route to substitution reactions using siloxanes in the presence of fluoride ion catalysts. Inorg. Chem. 1994, 55(13), 2727-2734. 

Cesium fluoride as fluoride ion catalyst Migration of fluorine Perfluoro compounds... 

Solid cesium fluoride is a good fluoride ion catalyst for certain reactions requiring the formation of a carbanion intermediate. F. e. s. R. D. Dresdner, F. N. Tlumac, and J. A. Young, J. Org. Ghem. 30, 3524 (1965). 

Fujita and Hiyama have developed a homogeneous fluoride ion catalyst system consisting of tetrabutylammonium fluoride (TBAF) or tris(diethylamino)sulfonium difluorotiimethylsilicate (TASF) in hexamethylphosphoric triamide (HMPA), which can promote and complete the hydrosilylation of aldehydes and ketones at room temperature or lower temperatures within one hour in most cases (equation The relative... 

When C,0,0-tris(trimethylsilyl)ketene acetals such as 14S are subjected to the reaction with aldehydes in the presence of a catalytic amount of a Lewis acid followed by hydrolysis, the a,/ -unsaturated carboxylic acids are formed in a highly E-selective manner (Scheme 2.93) [265, 266]. Fluoride ion catalysts such as NaF and CsF are also used instead of the Lewis acids. 

Fluoresceins 21, 795 Fluoride ion catalyst, cesium fluoride as 21, 781 Fluorides (s. a. Halides, Replacement)... 

Fluorides. Tantalum pentafluoride [7783-71-3] TaF, (mp = 96.8° C, bp = 229.5° C) is used in petrochemistry as an isomerization and alkalation catalyst. In addition, the fluoride can be utilized as a fluorination catalyst for the production of fluorinated hydrocarbons. The pentafluoride is produced by the direct fluorination of tantalum metal or by reacting anhydrous hydrogen fluoride with the corresponding pentoxide or oxychloride in the presence of a suitable dehydrating agent (71). The ability of TaF to act as a fluoride ion acceptor in anhydrous HF has been used in the preparation of salts of the AsH, H S, and PH ions (72). The oxyfluorides TaOF [20263-47-2] and Ta02F [13597-27-8] do not find any industrial appHcation. 

When potassium fluoride is combined with a variety of quaternary ammonium salts its reaction rate is accelerated and the overall yields of a vanety of halogen displacements are improved [57, p 112ff. Variables like catalyst type and moisture content of the alkali metal fluoride need to be optimized. In addition, the maximum yield is a function of two parallel reactions direct fluorination and catalyst decomposition due to its low thermal stability in the presence of fluoride ion [5,8, 59, 60] One example is trimethylsilyl fluoride, which can be prepared from the chloride by using either 18-crown-6 (Procedure 3, p 192) or Aliquot 336 in wet chlorobenzene, as illustrated in equation 35 [61],... 

Cordes et al995 carried out alkaline hydrolyses of p-nitrophenylhexanoate 55 (PNPH) in the presence of poly-4-vinylpyridine partially quaternized with dodecyl-bromide and ethylbromide (QPVP). They also found that the polyelectrolytes are increasingly effective as catalysts with an increasing ratio of dodecyl to ethyl groups, and the hydrophobic interactions are important in determining the catalytic efficiency. They observed the inhibitory effects of several gegen-anions fluoride ions are the weakest inhibitor, and nitrate is the strongest (F- < Cl < S04 [Pg.159]

Dichloro monomers can also be polymerized with bisphenols in the presence of fluorides as promoting agents.78 The fluoride ions promote the displacement of the chloride sites to form more reactive fluoride sites, which react with phenolate anion to form high-molecular-weight polymers. Adding 5-10 mol % phase transfer catalysts such as A-alkyl-4-(dialkylamino)pyridium chlorides significantly increased the nucleophilicity and solubility of phenoxide anion and thus shortened the reaction time to one fifth of the uncatalyzed reaction to achieve the same molecular weight.79... 

The fluoride ion is an effective catalyst for conjugate additions involving relatively acidic carbon nucleophiles.292 The reactions can be done in the presence of excess... 

B. Potassium allyl- and crotyltrifluoroborates undergo addition to aldehydes in biphasic media as well as water to provide homoallylic alcohol in high yields (>94%) and excellent diastereoselectivity (dr >98 2). The presence of a phase-transfer catalyst (e.g., B114NI) significantly accelerates the rate of reaction, whereas adding fluoride ion retards the reaction (Eq. 8.70).165 The method was applied to the asymmetric total synthesis of the antiobesity agent tetrahydrolipstatin (orlistat).166... 

The stannylation and silylation of heteroaryl halides has also been studied. The stannylation of 4-iodo pyrimidine was conducted with hexamethyl and hexa-ra-butyl ditin in the presence of fluoride ion and Pd(PPh3)2(OAc)2 as catalyst. The stannylation of 5-bromopyrimidine occurred in the highest yields in the presence of the ligandless catalyst bis(7r-allylpalladium chloride).175 The silylation of bromopyridines, bromopyrimidines, and bromoquinolines also occurred after 96 h at 160 °C with Pd(PPh3)4 as catalyst in HMPT solvent.162... 

Cyclization reactions of vinyl- and alkynylsilanes have been reviewed100. The course of the reaction of the cyclohexenone derivative 184 depends on the catalyst employed ethylaluminium dichloride gives solely the product 185 of 1,6-addition, whereas tetrabuty-lammonium fluoride yields a mixture containing 69% of the 1,4-adduct 186 and 31% of the bridged compound 187 (equation 89)101. Intramolecular addition reactions of allylic silanes102 may also be catalysed by Lewis acids (equation 90) or fluoride ions, and in this case an allyl anion or a pentavalent silicon intermediate may be involved (equation 91). Such reactions are exemplified by the formation of a 1 5 mixture of the diastereomers 189 and 190 when the cyclohexenone derivative 188 is treated with ethylaluminium dichloride (equation 92). In the presence of fluoride anion the ratio of the isomers is reversed103. 

Alkynylsilanes will react with bis(tributyltin) oxide in the presence of fluoride ion as catalyst to give the stannylalkynes in excellent yield and hexamethyldisiloxane, which can be removed under reduced pressure (Equation (82)).68 244... 

The addition of nitromethane to chalcones has been studied using N-benzylquininium chloride as the chiral phase-transfer catalyst and fluoride ion as the base (46). The enantiomeric excess was moderate (up to 26%). No conclusions were drawn from this study. 

The reaction of the carbanion derived from diethyl methylphosphonate with perhalogenated aromatics may result in substitution of halide to yield perhaloaryl(hetaryl)methylphosphonates, which can be converted into tris- or bis-(perhaloaryl)methanes. Displacement of fluoride ion has been reported in the reaction of dimethoxycarbene with l-fluoro-2,4-dinitrobenzene and with hexafluorobenzene. The hydrodehalogenation of halogenated aryl ketones may be facilitated using hydrogen over a Pt/C catalyst. " ... 

The stability of dialkylimidazolium cation-containing ionic liquids can be a problem even at moderate temperatures in the presence of some reagents or catalysts. For example, when CsF and KF were used in the ionic liquid [BMIM]PFg to perform a halogen exchange reaction in an attempt to replace Br from bromo-carbons with F , it was found that alkyl elimination from the [BMIM] cation took place, forming methyl imidazole, 1-butene, 1-fluorobutane, and other unidentified products at 150°C overnight 69). The fluoride ion acted as a base that promotes elimination or substitution processes. 

Group transfer polymerization (GTP) requires either a nucleophilic or Lewis acid catalyst. Bifluoride (HF2) and fluoride ions, supplied by soluble reagents such as tris(dimethylamino)-sulfonium bifluoride, [(CH3)2N]3SHF2, and (w-C NF, are the most effective nucleophilic catalysts, although other nucleophiles (CN , acetate, p-nitrophenolate) are also useful. Zinc... 

The hydrolytic decomposition of a potential fluorophosphite ligand would generate free fluoride ions which would be expected to be detrimental to the activity of a hydroformylation catalyst. The patent literature contains abundant references to the detrimental effects of halogens (6) on hydroformylation catalysts, and based on the patent information, one could not reasonably expect a halophosphite to be a successful hydroformylation ligand. However, a second publication by Klender (7) shows that exposure of / and other fluorophosphites to moisture at temperatures of 250°C to 350°C does not generate fluoride, even at part per million levels. 

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