C6F5XeF, a versatile starting material in xenon–carbon chemistry

Journal of Fluorine Chemistry 125 (2004) 981–988

C6F5XeF, a versatile starting material in xenon–carbon chemistry Hermann-Josef Frohn*, Michael Theißen Institute of Chemistry, Inorganic Chemistry, University Duisburg-Essen, Lotharstr. 1, D-47048 Duisburg, Germany Received 13 June 2003; received in revised form 12 October 2003; accepted 3 January 2004

Abstract The molecules ArFXeF (ArF ¼ C6 F5 , 2,4,6-C6H2F3) with a more polar Xe–F bond than XeF2 are versatile starting materials for substitution reactions. Fluorine-aryl substitutions with Cd(ArF)2, C6F5SiMe3/[F], and C6F5SiF3 formed symmetric and/or asymmetric diarylxenon compounds. Applying C6F5BF2, with a higher F-affinity than the corresponding aryltrifluorosilane, in contrast gave the salt [RXe] [ArFBF3]. Using the alkenyl and alkyl compounds CF2 ¼ CFSiMe3 /[F], CF3SiMe3/[F], and Cd(CF3)2 in reactions with C6F5XeF, the perfluoroalkenyl or -alkyl transfer reagents were consumed without observing C6 F5 XeCF ¼ CF2 or C6F5XeCF3 but the formation of Xe(C6F5)2 (dismutation product) and in the latter case C6F5CF3 (coupling product), gave hints of the desired intermediates. # 2004 Elsevier B.V. All rights reserved. Keywords: Noble gas chemistry; Xenon–carbon compounds; Xenon–fluorine substitution; Polyfluoroorgano transfer reagents; NMR spectroscopy

1. Introduction The first examples of xenon(II)–carbon compounds, salts containing the [C6F5Xe]þ 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]þ 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)0 and ArFXeYare 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]þ cation in the corre-

sponding [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)). 2C6 F5 XeF þ CdðC6 F5 Þ2 ! XeðC6 F5 Þ2 þ CdF2 #

(1)

2

1

Me3SiCN and its isotopomers Me3Si13 CN and Me3SiC15 N reacted spontaneously with 1 forming the asymmetric molecules C6F5XeCN (3a), C6F5Xe13 CN (3b), and C6F5XeC15 N (3c), respectively (Eq. (2)). C6 F5 XeF þ Me3 SiCN ! C6 F5 XeCN þ Me3 SiF 1

(2)

3a

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 xenonbonded 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. 2. Results and discussion 2.1. The substitution of fluorine in 1 by aryl groups

*

Corresponding author. Tel.: þ49-203-379-3310; fax: þ49-203-379-2231. E-mail address: [email protected] (H.-J. Frohn). 0022-1139/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jfluchem.2004.01.019

Analogously to (Eq. (1)), 1 reacted with the less fluorinated diarylcadmium Cd(2,4,6-C6H2F3)2 and formed the

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H.-J. Frohn, M. Theißen / Journal of Fluorine Chemistry 125 (2004) 981–988

Table 1 NMR spectroscopic data (d (ppm), J (Hz)) of the Xe–C compounds C6F5XeF (1), 2,4,6-C6H2F3XeF (6), (C6F5)2Xe (2), (2,4,6-C6H2F3)2Xe (5), and 2,4,6C6H2F3XeC6F5 (4) Compound

Solvent

T (8C)

19

129

F 3

( J(F, Xe) d(p-F)

d(o-F) a,b

c

3

( J(F, F)

d(m-F)

d(Xe–F)

1

J(F ,Xe)

Xe

d(Xe)

1

J(Xe, F)

3

J(Xe, F)

1 6a

CD2Cl2 CD2Cl2

78 70

129.3 100.4

81 71

146.9 102.0

20 d

156.5 –

3.5 7.8

4013 3767

3789 3872

4014 3740

82 73

2e 2

(CD3)2CO 60 CD2Cl2 78

131.6 133.1

n.d.

153.7 154.1

20 21

158.7 159.0

– –

– –

4148 4152

– –

41

h

–

–

–

4209

–

53i

k

– 159.7

– –

– –

4176

–

n

f

5

CD2Cl2

70

103.8

54

110.7

4j 4l

CD2Cl2

78

104.6 132.1

65

109.0 155.8

m

21

g

n.d., Not determinable. a Addition of traces of [NMe4] F. b 13 C{19 F} 86.4 (dm, 2 J(C, Xe–F) ¼ 115, 1 J(C, Xe) ¼ 111, C-1), 137.1 (s, C-3,5), 143.1 (s, C-4), 143.9 (s, C-2,6). c4 J(F, Xe–F) ¼ 19 {m-F}. d3 J(F, H) ¼ 8. e 13 C{19 F} 123.2 (s, 1 J(C, Xe) ¼ 315, C-1), 137.0 (s, 3 J(C, Xe) ¼ 19, C-3,5), 141.3 (s, C-4), 143.8 (s, 2 J(C, Xe) ¼ 20, C-2,6). f3 J(F, Xe) ¼ 43 {m-F}. g t1=2 ¼ 150 Hz. h3 J(F, H) and 4 J(F, F) are overlapping. i 1 { H}, non-decoupled t1=2 ¼ 138 Hz. j 2,4,6-C6H2F3 group of 4. k3 J(F, H) ¼ 8. l C6F5 group of 4. m3 J(F, Xe) ¼ 22 2 {m-F}. n t1=2 ¼ 191 Hz.

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.

check the migration of fluorinated aryl groups in CH2Cl2 under the influence of CdF2 (surface reaction) or soluble [NMe4] F. We found out that 1 and CdF2 do not interact and do not form 2. The 4 did not convert to 1 or 2,4,6C6H2F3XeF (6) when reacted with [NMe4] F. The 19 F NMR shift values of 4 (Table 1) and the results of ab initio calculations (Table 2) allow us to interpret the dismutation process. In 4, the C6F5 group carries more negative partial charge (higher anionic character) than the 2,4,6-C6H2F3 group. We propose that 4 with a permanent dipole moment undergoes an intermolecular interaction with the terminal

22C6 F5 XeF þ Cdð2; 4; 6-C6 H2 F3 Þ2 1

! 22; 4; 6-C6 H2 F3 XeC6 F5 ðmain productÞ 4

þ CdF2 # þ XeðC6 F5 Þ2 þ Xeð2; 4; 6-C6 H2 F3 Þ2

(3)

5

2

This dismutation is a new phenomenon in xenon–carbon chemistry. We have performed some control experiments to

Table 2 Calculated (Gaussian 94, RHF, LANL2DZ) geometric parameters and charges (Mulliken) of Y–Xe–Z molecules Y

Z

C6F5 C6H2F3 C6F5 C6H2F3 C6H2F3 C6F5 C6F5

F F C6F5 C6H2F3 C6F5 CF¼CF2 CF3

Selected geometric parametersa

Symmetry

1 6 2d 5d 4d 8 9

CS CS C1 C1 C1 C1 CS

b

Selected Mulliken charges c

Y–Xe

Xe–Z

ff

ff

ff at Xe

Xe

Y

C(1, Y)

Z

C(1, Z)

2.20 2.18 2.34 2.34 2.27 2.33 2.32

2.13 2.16 2.34 2.34 2.43 2.34 2.43

117.7 116.6 117.4 115.6 116.5 117.5 117.8

– – 117.4 115.6 116.5

180.0 180.0 180.0 180.0 180.0 180.0 180.0

1,148 1.111 0.980 0.952 0.965 0.927 0.909

0.415 0.355 0.490 0.476 0.374 0.490 0.446

1.001 1.035 0.687 0.763 0.830 0.720 0.728

0,733 0.756 0.490 0.476 0.591 0.437 0.463

– – 0.687 0.763 0.591 0.177 0.463

˚ ] or [8]. In [A Angle C(2)–C(1)–C(6) in Y. c Angle C(2)–C(1)–C(6) in Z. d Both aryl groups are perpendicular to each other. e Angle F–C(1)–C(2) of the CF ¼ CF2 group ¼ 118.6. f Angle F–C–F of the CF3 group ¼ 106.4. a

b

e f

H.-J. Frohn, M. Theißen / Journal of Fluorine Chemistry 125 (2004) 981–988 δ− δ+

R

C6F5

R

2.

Xe

1.

δ+

F

R'

F

F

Xe

F

Si

C6F 5

δ−

F

1.

2.

+

Xe

F

R

R

Xe R'

Xe

983

Scheme 2.

Scheme 1.

fluorine atom of the polar starting material 1 (Scheme 1). The Xe. . .F–Xe bridge allows the C6F5 group of 4 to migrate to the more positively charged Xe-centre of 1 and 2 results beside 6. The latter can react with Cd(2,4,6-C6H2F3)2 forming 5. This step was verified separately (Eq. (4)).

When 1 reacted with C6F5BF2, a Lewis acid of higher fluoride affinity than C6F5SiF3, only fluoride abstraction took place and the xenonium salt [C6F5Xe] [C6F5BF3] was formed in a good yield (Eq. (7)). C6 F5 XeF þ C6 F5 BF2 ! ½C6 F5 Xe ½C6 F5 BF3 1

2 2; 4; 6-C6 H2 F3 XeF þ Cdð2; 4; 6-C6 H2 F3 Þ2

(7)

7

6

! 2Xeð2; 4; 6-C6 H2 F3 Þ2 þ CdF2 #

(4)

5

The important driving force for the formation of the symmetric or asymmetric diarylxenon compounds 2, 4, and 5 from the corresponding arylxenonfluorides and diaryl cadmium compounds is the lattice energy of the by-product CdF2. Despite the polarity of the Xe–F bond in 1 being higher relative to XeF2, C6F5SiMe3 is not a suitable reagent for the direct transfer of the C6F5 group even if we consider the higher Si–F bond enthalpy relative to the Si–C bond enthalpy. The inertness of C6F5SiMe3 is opposite to the reactivity of Me3SiCN [7]. When we used the method elaborated for XeF2 as starting material by Naumann we found that the result of the reaction of 1 depended strongly on the concentration. For concentrations <0.03 mol l1 C6F5SiMe3 was consumed but 1 was not converted (Eq. (5a)). Using concentrations >0.05 mol l1 the conversion of 1 into 2 became the main reaction channel (Eq. (5b)). ½F

C6 F5 XeF þ C6 F5 SiMe3 ! C6 F5 XeF; C6 HF5 ; Me3 SiF

Recently we published work on salts containing the alkenylxenonium cation [9]. But until now there has been no proof for the existence of alkylxenon compounds [10,4a]. Using the stabilising effect of the C6F5 group we tried to realise a first example of C6F5XeOrg compounds with Org ¼ alkenyl and alkyl. When 1 was treated with CF2 ¼ CFSiMe3 in CH2Cl2 at 78 8C no reaction proceeded. After addition of catalytic amounts of [NMe4] F, 1 and CF2 ¼ CFSiMe3 were consumed. The main products of the vinyltrimethylsilane were Me3SiF and CF2 ¼ CHF. The 1 ended up with Xe(C6F5)2 (2) and minor amounts of C6HF5 and (C6F5)2. The latter both are typical decomposition products of 2. The unexpected formation of 2 can be rationalised by a dismutation where 1 was involved (compare the dismutation of 4 (Scheme 1)). The high amount of CF2 ¼ CHF may result from a competing decomposition of the [CF2 ¼ CFSiMe3 F] anion and its attack on the solvent and not predominantly from C6 F5 XeCF ¼ CF2 or Xe(CF ¼ CF2 )2 (Eq. (8a)).

low conc:

1

(5a) ½F

! XeðC6 F5 Þ2 þ Me3 SiF

high conc:

2.2. The substitution of fluorine in 1 by alkenyl and alkyl groups

C6 F5 XeF þ CF2 ¼ CFSiMe3

F =CH2 Cl2

!

Me3 SiF

< C6 F5 XeCF ¼ CF2 > 8

(8a)

(5b)

2 < C6 F5 XeCF ¼ CF2 >! XeðC6 F5 Þ2 þ < XeðCF ¼ CF2 Þ2 >

2

(8b)

The negative result without fluoride catalysis showed that the nucleophilicity of C6F5 in C6F5SiMe3 itself is not high enough and the basicity of fluorine in the XeF-fragment of 1 is too small to generate the ‘‘[C6F5SiMe3F]’’ anion. This encouraged us to test C6F5Si-compounds of higher acidity for transferring the aryl group. Indeed, C6F5SiF3 in CH2Cl2 allowed the synthesis of 2 at 78 8C (Eq. (6), Scheme 2). It is important to mention that C6F5SiF3 was successfully used for the substitution of one fluorine atom in halogen fluorides like IF5, BrF5, and BrF3 [8] but failed in the case of XeF2 [4a].

An analogous result was obtained when 1 was treated with an equimolar amount of CF3SiMe3. No reaction proceeded in CH2Cl2 at 78 8C. After addition of catalytic amounts of [NMe4] F, CF3SiMe3 was converted totally into Me3SiF but only approximately 50% of 1 reacted to give C6HF5, C6F5CF3, (C6F5)2, and Xe(C6F5)2. The CF3 group was found in CHF3 (main product), CClF3, and C6F5CF3 (Eq. (9c)). For the dismutation assisted by 1, see Scheme 1 and Eq. (9b).

C6 F5 XeF þ C6 F5 SiF3 ! XeðC6 F5 Þ2 þ SiF4

C6 F5 XeF þ CF3 SiMe3

1

2

(6)

< XeðCF ¼ CF2 Þ2 >

CH solvent

!

Xe þ 2CF2 ¼ CHF

½F =CH2 Cl2

!

Me3 SiF

< C6 F5 XeCF3 > 9

(8c)

(9a)

984

H.-J. Frohn, M. Theißen / Journal of Fluorine Chemistry 125 (2004) 981–988

2 < C6 F5 XeCF3 >! XeðC6 F5 Þ2 þ < XeðCF3 Þ2 >

(9b)

< C6 F5 XeCF3 >! C6 F5 CF3 þ Xe

(9c)

CH2 Cl2

< XeðCF3 Þ2 > ! Xe þ CHF3 ðmainÞ þ CClF3

(9d)

Additionally the substitution of fluorine by the CF3 group was attempted using Cd(CF3)2 as reagent and 1 in excess.

In CH2Cl2, no reaction was detected by 19 F NMR at 78 8C. The stepwise heating of the mixture up to 10 8C followed by cooling to 78 8C was accompanied by the complete consumption of dialkylcadmium. The CF3 group was found as C6F5CF3 (coupling product presumably resulting from C6F5XeCF3, see (Eq. (9c))), CHF3, and CClF3 (the latter both from CF3 radical attacks on CH2Cl2, see (Eq. (9d))).

-128.9 -129.0 -129.1 -129.2 -129.3 -129.4 -129.5 -129.6 -129.7

-128.9 -129.0 -129.1 -129.2 -129.3 -129.4 -129.5 -129.6 -129.7 -129.8

(a)

(ppm)

-128.9 -129.0 -129.1 -129.2 -129.3 -129.4 -129.5 -129.6 -129.7 -129.8

(c)

(ppm)

(b)

(ppm)

-128.9 -129.0 -129.1 -129.2 -129.3 -129.4 -129.5 -129.6 -129.7 -129.8

(d)

(ppm)

Fig. 1. The 19 F NMR signal of the o-F atoms of C6F5XeF (1) in CD2Cl2 at 78 8C: (a) after addition of [NMe4] F, (b) without an addition of [NMe4] F, (c) like a), but 129 Xe decoupled; (d) like (a), but selective 19 F decoupling of the m-F atoms.

H.-J. Frohn, M. Theißen / Journal of Fluorine Chemistry 125 (2004) 981–988

2.3. The NMR spectroscopic behaviour and the results from ab initio calculations of the arylxenonfluorides 1, 6, the diarylxenon compounds 2, 5, 4, and the pentafluorophenylxenon compounds with an alkenyl or alkyl groups 8, 9 The constitution of compounds 1, 6, 2, 5, and 4 was confirmed by heteronuclear NMR spectroscopy (19 F, 129 Xe, 13 C; Table 1, Figs. 1 and 2).

-100.10

-100.20

-100.40

-100.50

-100.60

-1.0 -2.0 -3.0 -4.0

-5.0 -6.0 -7.0 -8.0 -9.0 -10.0 -11.0 -12.0 -13.0 -14.0 -15.0

(ppm)

The xenon-bonded fluorine in 1 and 6 is sensitive to fluorine exchange even in non-coordinating CD2Cl2 (19 F) [6,7]. This exchange which is known e.g. from the [XeF5] anion [11] can be suppressed by adding small quantities of a soluble fluoride like [NMe4] F and has a significant effect on the shape of the o-F signal (Figs. 1 and 2). Without addition of fluoride the o-fluorine signal of 1 appears as pseudodoublet with 129 Xe satellites (Fig. 1b). After adding fluoride the o-fluorine signal changed to a pseudo-triplet with 129 Xe

-101.7

-100.70

(ppm)

(a)

(c)

-100.30

985

-101.8

-101.9

(b)

-3855

-102.0

-102.1

-102.2

-3880

-3885

(ppm)

-3860

-3865

-3870

(ppm)

(d)

Fig. 2. The NMR signals of C6H2F3XeF (6) in CD2Cl2 solution with an addition of [NMe4] F at 78 8C.

19

-3875

F: (a) o-F, (b) p-F, and (c) Xe–F; (d)

129

Xe.

986

H.-J. Frohn, M. Theißen / Journal of Fluorine Chemistry 125 (2004) 981–988

satellites (Fig. 1a) generated by the 4 J(o-F, XeF) coupling of 19 Hz. Some tendencies in the NMR spectra will be discussed using the information from the ab initio calculations. The resonance of the xenon-bonded fluorine became shielded from 1 to 6 parallel to the increase of negative partial charge. The p-F resonance of a polyfluorinated aryl group is a good indicator for the charge of this group. The comparison (19 F) of 1, 2, and 4 reveals a stepwise shielding of the p-F resonance of the C6F5 group which is in agreement with the increase of the negative Mulliken charge (MC) of the group in the same order. Similar, but less obvious behaviour is found for the p-F resonance of the 2,4,6-C6H2F3 group in 6 and 5. In 4 with two different aryl groups bonded to xenon, the 2,4,6-C6H2F3 group is the less electronegative one and takes over more positive charge from xenon than the C6F5 group in 2 and, parallel, the C6F5 group takes over more anionic character. We can describe the situation in 4 by the non-bonding resonance formula [2,4,6-C6H2F3Xe]þ [C6F5] which fits well with the p-F shift values and the Mulliken charges of both aryl groups. The 129 Xe shift values in CD2Cl2 solution follow the decrease of the Mulliken charge of xenon in the order 1 > 6 > 2 > 4 > 5. Within the class of diarylxenon compounds the dependence of d(129 Xe) from the Mulliken charge can be expressed by the linear correlation d(129 Xe) ¼ 2027.1 (MC) 6136.8 with R2 ¼ 0:9742. The 1 J(F, Xe) values of the XeF compounds 1 and 6 as well as XeF2 (5621 Hz) and [FXe]þ (7230 Hz) [12] show an excellent linear correlation with the calculated (Table 2) and reported [12] distances d(XeF) in pm: 1 J(F, Xe) ¼ 100.9 d(Xe F) þ 25589 with R2 ¼ 0:9983. Finally, we want to comment on the results of the calculations for 8 and 9; neither compound could be proven by low temperature NMR. The Mulliken charges of the C6F5 group, on C(1) of this group, and on Xe are approximately comparable to 2. Even the total charge of the CF ¼ CF2 or the CF3 group is in the range of the C6F5 group in 2. The significant difference concerns the charge on C(1) of the alkenyl or alkyl group. In 8, this C(1) carries a charge 0.177 and in 9 even a positive charge of 0.463 which seems to be responsible for the kinetic instability [10].

3. 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.

4. Experimental The 1 H, 13 C, 19 F, and 129 Xe NMR spectra were recorded on Bruker spectrometers WP 80 SY (1 H at 80.13 MHz and

19

F at 75.39 MHz), AVANCE 300 (1 H at 300.13 MHz, 13 C at 75.47 MHz, 19 F at 282.40 MHz, and 129 Xe at 83.02 MHz), and DRX 500 (13 C at 125.76 MHz, 19 F at 470.59 MHz, and 129 Xe at 138.34 MHz). The chemical shifts are referenced to TMS (1 H, 13 C), CCl3F (19 F, with C6F6 as secondary reference (162.9 ppm)), and XeOF4 129 Xe, with XeF2 in MeCN (c ! 0) as secondary reference at 24 8C (1813.28 ppm). All experiments were carried out under an atmosphere of dry argon in FEP traps. Cd(2,4,6-C6H2F3)2 was prepared similar to Cd(C6F5)2 [13] from the Grignard reagent 2,4,6C6H2F3MgBr and CdCl2 in Et2O and sublimated before use (19 F 84.7 m 3 J(F, 111 and113 Cd) 137 Hz, o-F; 109.2 tm, 3 J(F, H) 9 Hz, p-F; 1 H 6.69 m, m-H. 2,4,6-C6H2F3BF2 was prepared by the reaction sequence 2,4,6-C6H2F3MgBr, M [2,4,6-C6H2F3B(OMe)3], K [2,4,6-C6H2F3BF3], and 2,4,6-C6H2F3BF2 [14]. Cd(CF3)2 was obtained donor-free by the reaction of CdEt2 and CF3I in CD2Cl2 at 50 8C. Excess of CF3I and EtI were removed in vaccum at 25 8C (19 F 39.4, s, 2 J(F, 111 Cd) 508, 2 J(F, 113 Cd) 519 Hz [15]. C6F5SiMe3 was obtained from C6F5MgBr and Me3SiCl in Et2O, C6F5SiF3 from the reaction of C6F5SiCl3 and SbF3 [16]. CF3SiMe3 was purchased from Aldrich, and CF2 ¼ CFSiMe3 was synthesised by the reaction of CF3CH2F in Et2O with two equivalent of BuLi/n-hexane at  60 8C and subsequent reaction with Me3SiCl at 78 8C. [17] 19 F 89.0, dd, 3 J(F-2trans, F-2cis) 70, 3 J(F-2trans, F-1) 25 Hz, F-2trans; 118.3, dd, 3 J(F-2cis, F-1) 117 Hz, F-2cis; 200.0, dd, F-1. [C6F5Xe] [AsF6] resulted from the reaction of XeF2 with B(C6F5)3 and following metathesis with AsF5 [18]. [2,4,6-C6H2F3Xe] [BF4] was prepared analogous to the method described in [19] by the reaction of XeF2 and 2,4,6-C6H2F3BF2 and [NMe4] F was obtained similar to lit [20]. 4.1. Preparation of arylxenonfluorids 4.1.1. C6F5XeF (1) [NMe4] F (25 mg, 0.27 mmol) dissolved in 78 8C cold CH2Cl2 (1 ml) was added to the stirred cold CH2Cl2 suspension (1.5 ml) of [C6F5Xe] [AsF6] (131 mg, 0.27 mmol). The reaction suspension was vigorously stirred at 78 8C for 2 days. The mother liquor was separated and the solid residue was washed with CH2Cl2 (78 8C, 0.5 ml). The combined CH2Cl2 solutions contained C6F5XeF (0.19 mmol, 70%, determined by the quantitative NMR standard C6F6). After storage (2 days with stirring at 78 8C) over a 10-fold excess of CsF for removing traces of HF, the CH2Cl2 phase was separated. The solvent and volatile by-products like C6HF5 were removed at 50 8C/102 hPa, and the solid residue was washed three times at 78 8C with cold n-pentane and dried for 1.5 h at 40 8C/102 hPa yielding 69% of 1. The 1 decomposed totally within 4 h when warmed to 20 8C. For NMR characterisation see Table 1.

H.-J. Frohn, M. Theißen / Journal of Fluorine Chemistry 125 (2004) 981–988

4.1.2. 2,4,6-C6H2F3XeF (6) The 6 was obtained by using the procedure described in Section 4.1.1 starting with [2,4,6-C6H2F3Xe] [BF4] (92 mg, 0.26 mmol) and [NMe4] F (24 mg, 0.26 mmol). The nonoptimised yield of 6 was 19 %. For NMR characterisation see Table 1.

987

extracted three times with n-pentane (78 8C, each 1 ml) and dried at 40 8C/102 hPa. In the cold acetone-d6 solution (70 8C) the [C6F5Xe]þ cation (19 F 126.3, m, 3 J(F, Xe) ¼ 87 Hz, o-F; 143.0, t 3 J(F, F) ¼ 21 Hz, p-F; 155.8, m, m-F) with a fluorosilicate anion, presumably [SiF5] (19 F 135.2, s, 1 J(F, Si) ¼ 140 Hz [21]) was obtained in addition to 2 (main product).

4.2. Preparation of diarylxenon 4.2.1. A reaction of C6F5XeF with Cd(C6F5)2 The cold solution of Cd(C6F5)2 (18 mg, 0.04 mmol) in CH2Cl2 (0.5 ml, 78 8C) was added to a stirred solution of 1 (0.08 mmol, determined by the quantitative NMR standard C6F6) in CH2Cl2 (78 8C, 1.5 ml). After 5 min the precipitation of CdF2 was observed and after 10 min the reaction was finished (19 F). The mother liquor was separated from the solid residue which was washed five times with CH2Cl2 (78 8C, 0.4 ml each portion). The combined CH2Cl2 phases contained 0.06 mmol (75% yield) Xe(C6F5)2 (2). The solvent and volatile by-products like C6HF5 were removed at 50 8C/102 hPa, and the solid residue was washed at 78 8C with cold n-pentane and dried for 1 h at 40 8C/102 hPa. Yield of 2 was approximately 70%. Solid 2 decomposed spontaneously at 20 8C. For NMR characterisation see Table 1. 4.2.2. Reactions of C6F5XeF with C6F5SiMe3 in the presence of [NMe4] F 4.2.2.1. In a diluted solution (<0.03 mol l1). C6F5SiMe3 (15 ml, 0.08 mmol) was added to the cold stirred CH2Cl2 solution (2.5 ml, 78 8C) of 1 (0.07 mmol, determined by the quantitative NMR standard C6F6) and [NMe4] F (3 mg, 0.03 mmol). At 78 8C the ‘‘naked’’ fluoride had already been consumed after 5 min, but 2 was not detected in traces. Among non-reacted 1 and a reduced amount of C6F5SiMe3 the resulting products of the silane, C6HF5 and Me3SiF, were observed (19 F). 4.2.2.2. In a more concentrated solution (>0.05 mol l1). The 1 (0.10 mmol), C6F5SiMe3 (0.09 mmol), and [NMe4] F (3 mg, 0.03 mmol) together in 1.9 ml CH2Cl2 (78 8C) were stirred and formed a suspension. 19 NMR control showed that C6F5SiMe3 had reacted totally. The molar ratio of C6F5 compounds in the mother liquor was 1:2:C6HF5:(C6F5)2 ¼ 1:2:4:2. 4.2.3. The reaction of C6F5XeF with C6F5SiF3 C6F5SiF3 (14 ml, 0.09 mmol) was dropped on the cold wall of the FEP-trap containing 1 (0.07 mmol, determined by the quantitative NMR standard C6F6) dissolved in cold CH2Cl2 (2 ml, 78 8C). After mixing a white solid precipitated and in the CH2Cl2 phase 2 was detected (19 F) in addition to C6HF5 and (C6F5)2 and the slightly shifted signals of C6F5SiF3 (19 F 125.9, 142.7, 159.0, 133.9). The solvent was removed in vacuum at 40 8C and the solid was

4.2.4. The reaction of C6F5XeF with C6F5BF2 A cold solution (CH2Cl2, 78 8C, 0.25 ml) of C6F5BF2 (0.10 mmol, determined by the quantitative NMR standard CCl2FCClF2) was added to a cold CH2Cl2 solution (78 8C, 1 ml) of 1 (0.09 mmol, determined by the quantitative NMR standard C6F6). Spontaneously a colourless solid precipitated. The mother liquor was separated after 15 min and the solid was washed twice with cold CH2Cl2 (78 8C, each 1 ml). The salt was dried for 1 h at 35 8C/102 hPa and then dissolved at 40 8C in MeCN. [C6F5Xe] [C6F5BF3] was formed in approximately 90% yield. 19 F {[C6F5Xe]þ}: 125.3 (m, 3 J(F, Xe) ¼ 69 Hz, o-F); 142.0 (tt, 3 J(F, F) ¼ 20 Hz, 4 J(F, F) ¼ 5 Hz, p-F); 154.8 (m, m-F); 19 F {[C6F5BF3]}: 135.5 (m, o-F); 160.4 (t, 3 F(F, F) ¼ 20 Hz p-F); 164.9 (m, m-F); 135.4 (m, BF3). Traces of [BF4] 19 F 149.0 (s) were detected. 4.2.5. The reaction of C6F5XeF with Cd(2,4,6-C6H2F3)2 2,4,6-C6H2F3XeC6F5 (4) was obtained by using the procedure described in Section 4.2.1 starting with C6F5XeF (0.08 mmol, determined by the quantitative NMR standard C6F6) in 0.7 ml CD2Cl2 and Cd(2,4,6-C6H2F3)2 (16 mg, 0.04 mmol) in 0.3 ml CD2Cl2. The mother liquor of the reaction contained 4, 2, 5, 2,4,6-C6H2F3-C6F5, 2,4,6C6H2F3D, C6F5D, and (C6F5)2 in the relative molar ratio 10:2:  1:1:1:1:1. In this case the purifcation by extraction with n-pentane was limited due to the high thermal instability of 4. 4.2.6. The reaction of 2,4,6-C6H2F3XeF with Cd(2,4,6-C6H2F3)2 Xe(2,4,6-C6H2F3)2 (5) was obtained by using the procedure described in Section 4.2.1 starting with 2,4,6C6H2F3XeF (6) (0.07 mmol, determined by the quantitative NMR standard C6F6) in 0.7 ml CD2Cl2 and Cd(2,4,6C6H2F3)2 (13 mg, 0.035 mmol) in 0.3 ml CD2Cl2. Yield of 5 was 27%. For NMR characterisation see Table 1. 4.3. Attempts to substitute the terminal fluorine in C6F5XeF by perfluoroalkenyl and -alkyl groups 4.3.1. The reaction of C6F5XeF with perfluoroethenyltrimethylsilane A cold CH2Cl2 solution (78 8C, 0.2 ml) of CF2 ¼ CFSiMe3 (0.02 mmol, containing an admixture of hexane) was added to a stirred CH2Cl2 solution (78 8C, 1 ml) of 1 (0.08 mmol). 19 F NMR control after 1 h indicated that no reaction had proceeded. After the addition of [NMe4] F

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(5 mg, 0.05 mmol) dissolved in cold CH2Cl2 (78 8C, 0.5 ml) the mixture changed the colour to brown and the 19 F NMR displayed the consumption of the starting materials and formation of the products 2, CF2 ¼ CFH, C6HF5, (C6F5)2, and Me3SiF in the molar ratio 5:40:5:1:60. C6 F5 CF ¼ CF2 was not detected. 4.3.2. The reaction of C6F5XeF with trifluoromethyltrimethylsilane and bis(trifluoromethyl)cadmium 4.3.2.1. The reaction of C6F5XeF with trifluoromethyltrimethylsilane. The reaction was performed corresponding to Section 4.2.1 using the following quantities: 1 (0.16 mmol), CF3SiMe3 (25 ml, 0.16 mmol), [NMe4] F (5 mg, 0.05 mmol), and CH2Cl2 (78 8C, 1 ml). The reaction started spontaneously after the addition of the ‘‘naked’’ fluoride and CF3SiMe3 reacted completely. The quantity of products was determined by 19 F: Me3SiF (0.135 mmol), 1 (0.055 mmol), 2 (0.005 mmol), C6F5–CF3 (0.007 mmol), C6HF5 (0.021 mmol), (C6F5)2 (0.003 mmol), CHF3 (0.087 mmol), CClF3 (0.008 mmol). 4.3.2.2. The reaction of C6F5XeF with bis(trifluoromethyl) cadmium. Cd(CF3)2 (10 mmol) dissolved in CH2Cl2 (0.2 ml, 78 8C) was added to an excess of 1 (55 mmol) dissolved in cold CH2Cl2 (1.5 ml, 78 8C). No reaction could be detected by 19 F at 78 8C. The temperature had been raised stepwise to 40, 20, and 10 8C and maintained for 10 min on each step before being cooled down to 78 8C. 19 F NMR control now confirmed the complete consumption of Cd(CF3)2. In addition to non-reacted 1 (33 mmol) the mother liquor also contained C6F5–CF3 (3 mmol), CHF3 (3 mmol), CClF3 (2 mmol), and C6HF5 (15 mmol). Acknowledgements We gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.

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