Phosphorus, bonding fluorides

Fluorides with fluorine-phosphorus bonds also react with Lewis acids tert-Butylpentafluorocyclotriphosphazenes are arylated in the presence of aluminum chlonde [26] (equation 18)... 

The valence shell of the phosphorus atom In phosphorus(v) fluoride contains ten electrons five from the phosphorus and one each from the five fluorine atoms. The shape will be a trigonal bIpyramId with bond angles of 120°, 180° and 90° (Figure 14.3). 

In contrast to phosphorus esters, sulfur esters are usually cleaved at the carbon-oxygen bond with carbon-fluorine bond formation Cleavage of esteri nf methanesulfonic acid, p-toluenesidfonic acid, and especially trifluoromethane-sulfonic acid (tnflic acid) by fluoride ion is the most widely used method for the conversion of hydroxy compounds to fluoro derivatives Potassium fluoride, triethylamine trihydrofluoride, and tetrabutylammonium fluoride are common sources of the fluoride ion For the cleavage of a variety of alkyl mesylates and tosylates with potassium fluoride, polyethylene glycol 400 is a solvent of choice, the yields are limited by solvolysis of the leaving group by the solvent, but this phenomenon is controlled by bulky substituents, either in the sulfonic acid part or in the alcohol part of the ester [42] (equation 29)... 

The magnetic criterion is particularly valuable because it provides a basis for differentiating sharply between essentially ionic and essentially electron-pair bonds Experimental data have as yet been obtained for only a few of the interesting compounds, but these indicate that oxides and fluorides of most metals are ionic. Electron-pair bonds are formed by most of the transition elements with sulfur, selenium, tellurium, phosphorus, arsenic and antimony, as in the sulfide minerals (pyrite, molybdenite, skutterudite, etc.). The halogens other than fluorine form electron-pair bonds with metals of the palladium and platinum groups and sometimes, but not always, with iron-group metals. 

Carbon-phosphorus double bonds are also formed in addition reactions of tris(trimethylsilyl)phosphine 1692 (which can be readily prepared from white phosphorus, sodium, and TCS 14 [13a,b,c]) to give oxazohum fluorides 1691 which then give the azaphospholes 1694, via 1693 [3, 14]. On addition of 1692 to 1695, the diazaphosphole 1696 [3, 15] is prepared, whereas l,3-azaphospholo[l,2a]pyridines 1698 [16] are formed from 1692 and 1697, and 1,3-thiaphospholes 1700 are formed from the dithiohum fluorides 1699 [17]. l,3-Benzodiphospholyl anions 1703 are generated by reaction of acid chlorides with the dihthium salts 1701, via 1702 [18] (Scheme 11.3). 

A Lewis base must have valence electrons available for bond formation. Any molecule whose Lewis stmcture shows nonbonding electrons can act as a Lewis base. Ammonia, phosphorus trichloride, and dimethyl ether, each of which contains lone pairs, are Lewis bases. Anions can also act as Lewis bases. In the first example of adduct formation above, the fluoride ion, with eight valence electrons in its 2 s and 2 p orbitals, acts as a Lewis base. 

Preparative details and extensive i.r., n.m.r., and mass spectra have been described for the phosphoranes (87).48 These phosphoranes have a TBP structure, and for (87a)—(87c) their n.m.r. spectra are temperature-independent, and indicate that the fluorines bonded to phosphorus are equivalent. The authors have suggested an explanation based on rapid intramolecular isomerization, and discussed the possibility that a facile TR pathway exists for this process.46 Octahedral adduct formation between (87) and fluoride ion or trimethylphosphine has also been described,46 as shown in (88). 

Phosphorotrithioite, 21 61 Phosphorus, 33 106-107 acids, pK values of, 3 383 bond angles in trihalides, 13 365 bromochlorides, 7 12 bromofluorides, 7 8-9, 10 chalcogenide halides, 23 400 chloFofluorides, 7 8, 9-10 complexes, xenon fluoride reactions, 46 86 compounds... 

Table 6.4 contains some bond length and bond angle data for the hydrides, fluorides and chlorides of nitrogen, phosphorus and arsenic. The differences in the electronegativity coefficients (Allred-Rochow) in the compounds are also given. 

It was decided to study the system tetrakis (trifluorophosphine) nickel- (0) -ammonia (23) in some detail a smooth reaction was observed when the complex, condensed on excess ammonia at liquid air temperature, was allowed to warm up gradually. Precipitation of colorless crystals, identified as ammonium fluoride in almost stoichiometric amount, based on complete ammonolysis of the phosphorus-fluorine bonds, was observed at temperatures as low as —90° to —80°. Removal of the ammonium fluoride by filtration at temperatures not higher than —50°, and subsequent slow evaporation of the ammonia from the filtrate invariably led to a brown-yellow solid, although a colorless, crystalline material was formed initially. The product was decomposed almost instantaneously by water with precipitation of elemental nickel. Analysis of the hydrolyzate obtained in aqueous hydrochloric acid revealed a nickel-phosphorus-nitrogen atom ratio close to 1 4 4, corresponding to an apparently polymeric condensation product. 

Thus, a stable derivative of phosphorus triamide, P(NH2)3, could not be obtained. Such expectations were encouraged by recent work of Kodama and Parry (12), who succeeded in ammonolyzing phosphorus trifluoride-borane, F3P.BH3, with formation of a stable phosphorus triamide-borane, (H2N)3P.BH3. Ammonolysis of boron- or phosphorus-fluorine rather than -chlorine bonds is advantageous, since ammonium fluoride is insoluble in liquid ammonia and can easily be separated, while ammonium chloride is readily soluble. 

Moissan and his colleague Meslans then tried other methods for C —F bond synthesis.121 Alkyl fluorides could not be made via reactions of alcohols with hydrogen fluoride or phosphorus fluorides. However, silvcr(l) fluoride was found to function as a halogen-exchange reagent and several alkyl fluorides were made and characterized, all being fairly resistant to alkaline hydrolysis. 

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