Xenon difluoride bonding

In xenon difluoride, the electronic structure shows three lone pairs around the xenon, and two covalent bonds to the two fluorine atoms hence it is believed that here xenon is using one p (doublepear) orbital to form two bonds ... 

Xenon difluoride fluorinates adamantane in low yield [45] (equation 22) When the carbon-hydrogen bond is activated by an a-sulfur atom, fliiorination occurs readily The reactions involve intermediates that contain sulfur-fluorine bonds. At-Fluoropyridinium reagents behave similarly [99, 100, 101, 102] (equations 55-57)... 

On the other hand, oxidizing fluonnating agents like silver difluoride, xenon difluoride, or bromine trifluoride replace one chlorine group and then cleave the sulfur-nitrogen bond [56],... 

Xenon difluoride is characteristic in reacting with polarized double bonds (glycals and enol acetates ) in the presence of acid or Lewis acid catalyst,... 

Xenon difluoride reacts with carbon-carbon single, double, and triple bonds giving addition fluoroorganic compounds, e.g.,... 

Phenyl-substituted alkenes with halogen atoms at the double bond react with xenon difluoride in dichloromethane in the presence of hydrogen fluoride forming vicinal difluorides in 50% yield.35... 

Alkenes react with xenon difluoride in the presence of some auxiliary reagent to form unsymmetrical addition products. Treatment of indene (8) with xenon difluoridc and methanol in the presence of hydrogen fluoride leads to fluoromethoxylation of the C = C bond, dia-stereomers of 1-alkoxy-2-fluoroindane are formed as the major product, difluoroindane was detected in trace quantities. In the presence of a boron trifluoride-diethyl ether complex the crossover l-fluoro-2-alkoxylated indanes have been obtained as major products.48,49... 

To overcome problems associated with the removal of iodobenzene and its derivatives formed upon fluorination of arylalkenes and arylalkynes with (difluoroiodo)arenes, polymer-supported (difluoroiodo)arenes were proposed.139 With these agents, the separation procedures are reduced to filtration of the iodinated polymer. For this purpose popcorn polystyrene is io-dinated and then transformed into the difluoroiodide by treatment with xenon difluoride in the presence of hydrogen fluoride in dichloromelhane at 25 C. The amount of active fluorine bonded to iodine atoms on the polymer support is estimated by iodometric titration. The reactions with phenyl-substituted alkenes result in rearranged gew-difluorides. The procedure provides the same fluorination products as with (difluoroiodo)benzenc (see Section 4.13.) but in much higher yields, e.g. PhCF2CH2Ph (96%), PhCF2CH(Me)Ph (95%). PhCH2CF2H (86%), and l,l-difluoro-2-phenylcyclopentanc (91 %). 

A combination of xenon difluoride and water in HF was found to be a potent oxidizing agent. At ambient temperature this reagent is able to oxidize poly-fluorobenzenes and derivatives of F-cyclohexadiene-1,4. The oxidation is selective, and the C=C bond bearing Xe+ fragment does not participate in the reaction [127,128] ... 

Finally, halogens can be introduced by electrophilic addition to a double bond (Scheme 3.4b). For example, the reaction of glucal with xenon difluoride in the presence of a catalytic amount of BF3 OEt2 gives a 2-deoxy-2-fluoro-glucosyl fluoride as a mixture of anomers.19... 

Korytnyk and coworkers have shown that reactions of xenon difluoride with acetylated glycals in the presence of boron trifluoride are a convenient route for the synthesis of 1,2-difluoro sugars, while the addition of fluorine to the double bond occurred predominantly from the less hindered side and cis adducts were mainly formed75, 76. Stereoselective transformation of tri-O-acetyl-D-galactal with xenon difluoride at -20 to +5 °C, without a catalyst in CFC13, after hydrolysis, afforded 2-deoxy-2-fluoro-D-galactose in 63% yield77. 

Transformations of phosphines to difluorophosphoranes proceed with xenon difluoride under mild conditions and in high yields, and the phosphorus-hydrogen bond is stable chlorine atoms are replaced by fluorine in chlorine-phosphorus molecules, while triphenyl and trimethyldifluorophosphorane are isolated in 90-100% yield130-132. Reactions of compounds containing P—N, P—O and P—S bonds with xenon difluoride proceed by fragmentation or dimerization133 (Scheme 55). 

Alkylaluminium compounds were transformed by xenon difluoride mainly to fluorides, while Al-carbon bond cleavage is accompanied with bright chemiluminescence141-144. 

Possible interactions between xenon difluoride and xenon tetrafluoride molecules as a result of bond dipoles. The magnitude of x would be larger than that ofy, because the Xe atom is polarized in two directions (by two fluorine atoms) in the difluoride and in four directions (by four fluorine atoms) in the tetrafluoride. 

Another example of the simultaneous addition of fluorine and oxygen to a C = C bond is the fluorination of diphenylacetylene with xenon difluoride in the presence of trifluoroacetic acid ° how ever, the yield of the desired l-fluoro-l,2-diphenyl-2-(trifluoroacetoxy)ethene is only 3%, so there is no preparative use for this method. 

Of course, most reactive metal fluorides, such as cobalt trifluoride [268] and vanadium pentafluoride, will react with alkenes but the reactions can be very difficult to control, except for haloalkenes [269]. Much easier control is possible with xenon fluorides [137], the reactivity decreasing in the series XeFe > Xep4 > Xep2. Since the first report of the use of xenon difluoride for the addition of fluorine to double bonds, many studies have been published and reviewed [54, 135] (Figure 3.61). 

Xenon difluoride is easy to make, and relative to other xenon fluorides, safe to handle. It is therefore attractive as a reagent. Because of its low average bond energy ( 30 kcal. mole- ) and the "inertness of its reduction product (Xe) it has considerable potential in oxidative fluorinations. However, others have shown that the compound has considerable kinetic stability, e.g. it may be retrieved from aqueous solution in which it is thermodynamically unstable towards hydrolysis. 

The bonding in xenon difluoride may be accounted for by the resonance hybrid (F—Xe)+F and F (Xe—F)+ ). (This description maintains both classical valence concepts the octet and the electron pair bond.) High bond polarity is associated with such a description since the negative charge borne... 

From theoretical considerations Jortner, Rice, and Wilson in 1963 concluded that the bond ionicity in xenon difluoride was approximately F - -Xe —and on this basis they predicted that the enthalpy of sublimation, AlPstib> should be 13.3 I I moI ... 

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