C6F5XeF, a versatile starting material in xenon–carbon chemistry
Routes to diorgano xenon coumpounds starting from ArXeF.
Introduction
The first examples of xenon(II)–carbon compounds, salts containing the [C6F5Xe]+ cation, were prepared independently by Naumann [1] and Frohn [2] in 1989 and were structurally characterised by X-ray crystallography [3]. The development of the following decade which included alkynyl-, cycloalkenyl-, and alkenyl- in addition to arylxenon(II) compounds was summarised in two reviews [4]. Additionally, one example of a xenon(IV)–carbon compound is known: [C6F5XeF2] [BF4] [5].
Principally, three potential classes of xenon(II)–carbon compounds can be discussed: (a) salts with a xenonium cation [OrgXe]+ Y−, (b) neutral molecules with one or two xenon–carbon bonds OrgXe–Y or Org2Xe, and (c) salts with a xenon–carbon fragment in the anions M [OrgXeY2] or M [Org2XeY]. The latter class has been unknown until now as well as the inorganic prototype M [XeF3].
This paper contributes to class b. In addition to the symmetric molecules (ArF)2Xe the asymmetric ones ArFXe(ArF)′ and ArFXeY are subjects of this paper. C6F5XeF (1) as starting material for both aims can be obtained by two different procedures: the F−-catalysed transfer of the aryl group C6F5 from C6F5SiMe3 to XeF2 [6] or the addition of the “naked” fluoride ion to the [C6F5Xe]+ cation in the corresponding [AsF6]− salt [7]. The first procedure always delivers an admixture of Xe(C6F5)2.
In our previous work, we have shown the introduction of a second organo group into 1 [7]. With Cd(C6F5)2 in CH2Cl2 we obtained the symmetric molecule Xe(C6F5)2 (2) (Eq. (1)).
Me3SiCN and its isotopomers Me3SiN and Me3SiC reacted spontaneously with 1 forming the asymmetric molecules C6F5XeCN (3a), C6F5XeN (3b), and C6F5XeC (3c), respectively (Eq. (2)).
Different to the reaction described in Eq. (2), no reaction took place between 1 and the silylated nucleophile (Nu) Me3SiC6F5.
In this paper, we will elucidate the usefulness of cadmium organyls and silyl compounds for the substitution of xenon-bonded fluorine in 1 by suitable nucleophiles. We will discuss the driving forces for the synthesis of new C6F5XeNu compounds as well as the influence of the Lewis acidity of the transfer reagents.
Section snippets
The substitution of fluorine in 1 by aryl groups
Analogously to (Eq. (1)), 1 reacted with the less fluorinated diarylcadmium Cd(2,4,6-C6H2F3)2 and formed the desired asymmetric diarylxenon compound 2,4,6-C6H2F3XeC6F5 (4) but in addition the symmetric compounds Xe(C6F5)2 (2) and Xe(2,4,6-C6H2F3)2 (5) were obtained.
This dismutation is a new phenomenon in xenon–carbon chemistry. We have performed some control experiments to check the migration of
Conclusion
The high polarity of the Xe–F bond in ArXeF offers this class of molecules for introducing new organic groups into the C–Xe moiety. They are also potential and promising starting materials for proving the possiblities of new Xe–E bond combinations. Further work is in progress.
Experimental
The , , , and NMR spectra were recorded on Bruker spectrometers WP 80 SY ( at 80.13 MHz and at 75.39 MHz), AVANCE 300 ( at 300.13 MHz, at 75.47 MHz, at 282.40 MHz, and at 83.02 MHz), and DRX 500 ( at 125.76 MHz, at 470.59 MHz, and at 138.34 MHz). The chemical shifts are referenced to TMS (, ), CCl3F (, with C6F6 as secondary reference (−162.9 ppm)), and XeOF4 , with XeF2 in MeCN (c→0) as secondary reference at 24 °C (−1813.28 ppm).
All
Acknowledgements
We gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.
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2011, TetrahedronCitation Excerpt :These reactions do have the characteristics of electrophilic substitutions and formation of intermediates 3 is consistent with XeF2 reacting as FXeδ+⋯F→Pyrexδ− (i.e., as an FXe+ equivalent). A number of aryl xenon species of the type Ar–Xe–X have been isolated and characterized, including Ar–Xe–F25–27 and Ar–Xe–OCOR.28,29 These species do undergo ligand coupling with elimination of Xe,25 and there is evidence that the hypervalent C–Xe bond undergoes homolytic cleavage.26,30