Reactions of methyl(pentafluorophenyl)- and methyl(pentafluorophenyl)phenylsilanes with electrophiles. A convenient preparative route to halogeno(methyl)pentafluorophenylsilanes C6F5SiMe2X and C6F5SiMeX2 (X=F, Cl and Br)

Article abstract of DOI:10.1016/S0022-328X(98)00805-5

Halogeno(methyl)pentafluorophenylsilanes C₆F₅SiMe_nX_3-n (n=1, 2) (X=F, Cl, Br) were prepared in good yields from the corresponding phenylsilanes C₆F₅SiMe_nPh_3-n by reactions with the electrophiles aHF, HCl-AlCl₃, Br₂-AlBr₃ or AlX₃ (X=Cl, Br) halogenated hydrocarbons. Additionally, reactions of C₆F₅SiMe₃ and (C₆F₅)₂SiMe₂ with selected electrophiles were studied.

Full text of DOI:10.1016/S0022-328X(98)00805-5

Journal of Organometallic Chemistry 570 (1998) 255–263
Reactions of methyl(pentafluorophenyl)- and
methyl(pentafluorophenyl)phenylsilanes with electrophiles. A
convenient preparative route to
halogeno(methyl)pentafluorophenylsilanes C6F5SiMe2X and
C6F5SiMeX2 (X=F, Cl and Br)
H.-J. Frohn a,*, A. Lewin a, V.V. Bardin b
a Fachgebiet Anorganische Chemie, Gerhard-Mercator-Uni6ersita¨t Duisburg, Lotharstrasse 1, D-47048 Duisburg, Germany
b Institute of Organic Chemistry, 630090 No6osibirsk, Russia
Received 6 May 1998
Abstract
Halogeno(methyl)pentafluorophenylsilanes C6F5SiMenX3−n (n=1, 2) (X=F, Cl, Br) were prepared in good yields from the
corresponding phenylsilanes C6F5SiMenPh3−n by reactions with the electrophiles aHF, HCl–AlCl3, Br2–AlBr3 or AlX3 (X=Cl,
Br) halogenated hydrocarbons. Additionally, reactions of C6F5SiMe3 and (C6F5)2SiMe2 with selected electrophiles were studied.
© 1998 Elsevier Science S.A. All rights reserved.
Keywords: Silanes; Electrophilic substitution
1. Introduction
CF3C(O)OH (reflux) [5,6], and of C6F5SiMe3 with ex-
cess of iodine in MeCN (reflux, 2 h) [3] failed. Treat-
ment of C6F5Si(h-Np)PhMe with BrCl in CHCl3
(−78–20°C) led to the regiospecific cleavage of the
naphthyl group and the formation of C6F5SiPhMeCl
[7]. It should be noted that reactions of pen-
tafluorophenylsilanes with electrophiles can be pro-
moted by Lewis base co-ordination at the silicon atom.
By that procedure pentafluorophenyl derivatives of
polyvalent bromine- [8] and iodinefluorides [9] were
successfully prepared from the silanes C6F5SiMe3,
(C6F5)2SiMe2 and C6F5SiF3. Some pentafluorophenyla-
tion reactions of other electrophilic substrates were
known from literature [10] (see also review [11]).
A well-known method of regiospecific functionalisa-
tion of aromatic hydrocarbons is the replacement of the
alkylsilyl group –SiAlk3 in ArSiAlk3 under the action
of electrophiles [1]. However, in the case of pen-
tafluorophenylsilanes there are only few examples of
electrophilic desilylation reactions known. Tetra-
kis(pentafluorophenyl)silane formed pentafluoroben-
zene when refluxed in 6 N HCl in THF [2] or bro-
mopentafluorobenzene in low yield in reactions with
excess of bromine in MeCN (reflux, 2 h) [3]. Sulfodesi-
lylation of C6F5SiMe3 with SO3 in CF2ClCFCl2
(−196–25°C) showed a better conversion and gave
C6F5S(O)2OSiMe3 in a 69% yield [4]. On the other
hand, reactions of (C6F5)4Si with aq. 6 N HCl (reflux, 5
h) [2], of (C6F5)2SiMe2 and (C6F5)2SiMeH with
Recently we reported the facile preparation of
halogeno(pentafluorophenyl)silanes
(C6F5)nSiX4−n
(X=F, Cl; n=1, 2) by fluoridation and chloridation of
the corresponding ethoxy(pentafluorophenyl)silanes
and investigated some reactions of C6F5SiF3 with elec-
* Corresponding author.
0022-328X/98/$ - see front matter © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00805-5

256
H.-J. Frohn et al. / Journal of Organometallic Chemistry 570 (1998) 255–263
1,2,4,5-tetrafluoro[bis(trimethylsilyl)]benzene and CF3S-
O3D in high yield within a few minutes.
trophiles and nucleophiles [12]. The high resistance of
the carbon–silicon bond in C6F5SiF3 to the elec-
trophilic desilylation allowed us to plan alternative
syntheses of halogeno(pentafluorophenyl)silanes from
either methyl(pentafluorophenyl)phenyl or methyl(pen-
tafluorophenyl)silanes under the action of strong elec-
trophilic reagents. Although the C–Si bond in SiMe4
easily undergoes cleavage with superacids like FSO3H
or CF3SO3H under formation of the esters
FS(O)2OSiMe3 or CF3S(O)2OSiMe3, respectively [13],
the favoured C–Si reaction site in silanes with C6F5–
Si–Me fragments was not an obvious priority. How-
ever, the predominant cleavage of the phenyl group in
C6F5SiMenPh3−n in reactions with electrophiles under
formation of C6F5SiMe2X and C6F5SiMeX2 (X=F, Cl,
Br) was expected. While silanes C6F5SiMe2X can princi-
pally be obtained on pathways (1) and (2) [6,14–20],
there was no convenient preparative route to the inter-
esting bifunctional dihalogeno(methyl)pentafluoro-
phenylsilanes.
Weaker electrophiles (CF3CO2H, reflux, 4 h; [NO2]+
[BF4]− in CH3CN, r.t., 3 days) did not react with silane
1. However, nitrodesilylation of silane 1 was possible
with [NO2]+[BF4]− in sulfolane (100 °C, 2 h).
The aryl–silicon bond in C6F5SiMe3
1
and
(C6F5)2SiMe2 3 was successfully cleaved with elec-
trophilic brominating agents. Bromodesilylation with
liquid bromine at r.t. proceeded slowly and silane 3
showed less reactivity in comparison to silane 1. Never-
theless, both silanes 1 and 3 were converted into bro-
mopentafluorobenzene 4 within a few minutes under
the action of liquid bromine and AlBr3.
2. Results
2.1. Reactions of methyl(pentafluorophenyl)silanes
The complex trimethyl(pentafluorophenyl)silane 1 re-
acted with anhydrous HF (aHF) at room temperature
(r.t.) under formation of pentafluorobenzene 2 and
fluorotrimethylsilane. The stronger protic acids FSO3H
and CF3SO3H caused the same regiospecific aryl–sili-
con bond cleavage. In both cases the methyl–silicon
bond remained uneffected.
Bromopentafluorobenzene 4 was also obtained from
silane 3 in a fast reaction with a sub-stoichiometric
amount of AlBr3 and an excess of bromine in 1,2-dibro-
moethane (DBE) in a 93% yield as well as 7% pen-
tafluorobenzene 2.
Surprisingly, we found a slow reaction of silane 3
with AlBr3 in DBE to pentafluorobenzene 2 and bro-
mo(dimethyl)pentafluorophenylsilane 5 in a molar ratio
of 1:1.
Those results allowed us to carry out the simple
preparation of deuterated polyfluoroaromatics. Indeed,
1,4-dideuterotetrafluorobenzene was obtained from

H.-J. Frohn et al. / Journal of Organometallic Chemistry 570 (1998) 255–263
257
Similar results were obtained in the reactions of
silane 3 with AlCl3 in CD2Cl2 or CDCl3. In CDCl3 the
products 2 (H containing) and 6 were detected in the
reaction mixture as well as traces of C6F5CDCl2. The
latter suggests the participation of carbocationic species
as reactive intermediates. However, the main path in
the slow reactions of (C6F5)2SiMe2 with AlX3 in halo-
genated hydrocarbons (also in deuterated ones) was
protodesilylation. In spite of careful handling the influ-
ence of moisture as a source of H can not be totally
excluded, especially in the case of long-time reactions.
Substantial acceleration of the protodesilylation reac-
tion was achieved when gaseous HCl was passed into
the suspension of AlCl3 in the CDCl3 solution of silane
3 at r.t.
Dichloro(methyl)pentafluorophenylsilane 12 was pre-
pared in a similar way from silane 8, HCl gas and AlCl3
in hexane. However, the more convenient route to
silane 12 is the reaction of silane 8 with AlCl3 in
CH2Cl2 at r.t. The initial reaction product was
chloro(methyl)pentafluorophenyl(phenyl)silane 13 which
finally underwent replacement of the residual phenyl
group by chlorine. The same result was obtained in
acetyl chloride.
That useful approach was successfully extended to
the synthesis of bromosilane
5
and dibro-
mo(methyl)pentafluorophenylsilane 14. Both com-
pounds were easily prepared from the correspond-
ing silanes 7 and 8 under the action of AlBr3 in DBE
at r.t.
2.2. Reactions of methyl(pentafluorophenyl)phenylsilanes
In contrast to methyl(pentafluorophenyl)silanes 1
and 3 the reactions of dimethyl(pentafluorophenyl)
phenylsilane 7 and methyl(pentafluorophenyl)diphenyl-
silane 8 with electrophilic agents proceeded more read-
ily and principally under phenyl–silicon bond cleavage.
Treatment of silanes 7 and 8 with aHF gave in high
yields fluoro(dimethyl)pentafluorophenylsilane 9 and
difluoro(methyl)pentafluorophenylsilane 10, respec-
tively. Fluoro(methyl)pentafluorophenyl(phenyl)silane
11 was detected as an intermediate by 19F-NMR spec-
trometry in the reaction of 8 to 10.
It should be mentioned, that difluorosilane 10 can
also be obtained in addition to the procedure described
in equation 16 by the reaction of dichloro(methyl)-
pentafluorophenylsilane 12 with xenon difluoride simi-
lar to the preparation of C6F5SiMe2F from C6F5Si-
Me2Cl and XeF2 [21].

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H.-J. Frohn et al. / Journal of Organometallic Chemistry 570 (1998) 255–263
Table 1
1H- and 29Si-NMR spectra of pentafluorophenylsilanes C6F5SiXYZ (CDCl3, 35°C)
X
Y
Z
l(H)/ppm
l(Si)/ppm J/Hz
−0.75
CH3 CH3 CH3 0.42
CH3 CH3 Cl
0.83a
16.66
(CH3, F2) 1.8
CHb3 CH3 Br
−2.60
−7.03
−9.58d
−17.01
e
CHb3 CH3 C6H5 7.66–7.45 (C6H5), 0.81 (CH3)
CH3 CH3 C6F5 0.80 (CH3)c
(CH3, F2) 1.8
(CH3, F2) 1.6, (Si, F2) 55.0, (Si, CH) 7.4
(HCSiF) 6.1, (CH3, F2) 1.5, (Si, F) 288.2, (Si, F2) 6.4, (Si,
F3) 3.4, (Si, F4) 1.0
CH3
F
F
0.75
CH3 Cl
CH3 Br
Cl
Br
1.19
1.51
10.34
−6.71
−12.78
(CH3, F2) 2.4
(CH3, F2) 3.4, (Si, F2) 6.5, (Si, F3) 3.2, (Si, F4) 1.2
(H3, H4) 7.4, (CH3, F2) 2.3
CH3 C6H5 C6H5 7.57 (H-2, 6), 7.47 (H-4), 7.41 (H-3, 5),
0.98 (CH3)
a Lit. 0.92 ppm (in benzene) [27]. b In CD2Cl2. c Present work, lit. see [19,28,29]. d Lit. −8.3 ppm [30]. e Lit. see [19,28].
3. Conclusions
WP 80 SY (1H at 80.13, 19F at 75.39 MHz), AM 400
(13C at 100.58, 29Si at 79.49 MHz) and Avance DRX
500 (1H at 500.13, 13C at 125.76, 19F at 470.59, 29Si at
99.36 MHz) with respect to TMS and C6F6. The 19F
chemical shifts were related to CFCl3 using l(F)=
−162.9 ppm for C6F6. IR spectra were measured on a
Nicolet 20 DXB instrument (KBr pellets) and Raman
spectra on a Bruker FT-spectrometer IFS 66 equipped
with a Raman device FRA 106 (Nd: YAG laser AD-
LAS) (glass capillary sealed under dry argon). GCMS
measurements of mixtures were performed with a gas
chromatograph HP 5890 (HP 5 capillary, 30 m) com-
bined with a mass spectrometer AMD 604.
The reactivity of methyl(pentafluorophenyl)silanes
towards strong electrophiles like HY (Y=F, OSO2F,
OSO2CF3), HCl–AlCl3, bromine, Br2–AlBr3 or AlX3
(X=Cl, Br) halogenated hydrocarbons demonstrated
that aryl–Si bond cleavage was also possible in the case
of electron-poor phenyl groups like the C6F5-group.
Under similar conditions phenylsilanes C6F5Si(Me)n
Ph3−n underwent regiospecific replacement of the
phenyl group(s) by halogen atom(s) while the C6F5–Si
fragments stayed unchanged. Those circumstances al-
lowed us to elaborate a general and simple preparative
route to halogeno(methyl)pentafluorophenylsilanes.
Considerations about the pathways and the rates of
those reactions will be included in our next publication
in the field of pentafluorophenylsilane chemistry [22].
Pentafluorophenylsilanes 1 [23] and 3 [19] were pre-
pared by literature methods. Hydrogen fluoride was
dried by electrolysis (stainless steel cell, Ni electrodes).
HCl gas was dried by bubbling through concentrated
H2SO4. FSO3H, CF3SO3H and AcCl were distilled,
AlCl3 and AlBr3 sublimed before use. [NO2]+[BF4]−
(Fluka) and CF3CO2H (Solvay) were used without
additional purification. Hexane, ether, benzene,
CH2Cl2, CHCl3 and 1,2-dibromoethane were dried by
4. Experimental section
NMR spectra were recorded on Bruker spectrometers
Table 2
19F-NMR spectra of pentafluorophenylsilanes C6F5SiXYZ (CDCl3, 35°C)
X
Y
Z
l(F)/ppm
J(F, F)/Hz
F-2, 6
F-4
F-3, 5
CH3
CHa3,b
CHa3
CHc3
CHa3,d
CHa3
CH3
CHe3
CH3
CH3
CH3
CH3
CH3
CH3
C6H5
C6H5
C6H5
F
Cl
Br
C6H5
C6F5
F
Cl
C6H5
F
Cl
Br
−128.06
−128.83
−126.62
−128.41
−127.80
−125.97
−124.94
−128.67
−127.28
−126.72
−150.60
−152.30
−152.60
−150.92
−149.75
−149.58
−151.42
−147.30
−147.50
−147.43
−162.03
−162.60
−162.34
−161.83
−161.31
−161.38
−161.86
−160.82
−160.73
−160.67
(2, 4) 4.5, (3, 4) 19.8
(2, 4) 3.6, (3, 4) 19.7
(2, 4) 3.7, (3, 4) 19.5
(2, 4) 3.9, (3, 4) 19.9
(2, 4) 4.3, (3, 4) 19.7
(2, 4) 4.7, (3, 4) 19.9
(2, 4) 4.0, (3, 4) 20.1
(2, 4) 5.2, (3, 4) 19.9, (F, Si) 288.2
(2, 4) 5.6, (3, 4) 20.1
(2, 4) 5.7, (3, 4) 20.1
Cl
Br
a In CD2Cl2. b Present work, lit. see [19,28]. c Present work, lit. see [19,28,29]. d l(F) (F–Si) −162.25 ppm. e l(F) (F–Si) −131.17 ppm.

H.-J. Frohn et al. / Journal of Organometallic Chemistry 570 (1998) 255–263
259
literature methods and stored over molecular sieves
(ether over Na). All reactions were carried out in
stoppered FEP traps under dry argon atmosphere ex-
cept where alternative handling is described. Solid ma-
terials were manipulated in a Braun glove box with a
gas purification MB-100.
and FS(O)2OSiMe3 had taken place after 5–7 min
(1H-, 19F-NMR).
4.3.3. With CF3SO3H
At r.t. silane 1 (250 mg, 1.04 mmol) was added to
CF3SO3H (0.3 ml) under stirring. Within a few min-
utes the total conversion of silane 1 into pen-
tafluorobenzene 2 and CF3S(O)2OSiMe3 was observed
(19F-NMR).
NMR, IR and Raman spectral data are given in
Tables 1–4.
4.1. Methyl(pentafluorophenyl)diphenylsilane 8
4.3.4. With CF3CO2H
Silane 1 (2.0 g, 8.3 mmol) and CF3CO2H (5 ml)
were refluxed for 4 h. The system was diluted with
water (10 ml), the phases were separated, the organic
phase was washed with aq. NaHCO3 and water and
finally dried with MgSO4. In total 1.8 g (90%) of
silane 1 were recovered.
Bromopentafluorobenzene (13.6 g, 54.9 mmol) and
ether (100 ml) were placed in a flask equipped with
dropping funnel, reflux condenser and magnetic stirrer
under dry argon and cooled to −78°C. A sample of
BuLi (1.6 M in hexane, 34.5 ml, 54.9 mmol) was added
dropwise under stirring. The reaction mixture was
maintained at −78°C for 3 h before a solution of
Ph2SiMeCl (12.8 g, 54.9 mmol) in ether (100 ml) was
added. Overnight the reaction mixture was allowed to
warm to r.t. After hydrolysis the organic phase was
separated, the aqueous phase was extracted with ether
and the combined extracts were dried with MgSO4.
Silane 8 (15.4 g, 77%) was isolated by vacuum-distilla-
tion, b.p. 117−120°C (0.04 hPa).
4.3.5. With [NO2]+[BF4]− in sulfolane
A solution of silane 1 (84 mg, 0.35 mmol) and
[NO2]+[BF4]− (70 mg, 0.53 mmol) in sulfolane (0.2
ml) was stirred in a flask at 100°C for 2 h. After
cooling to 30–35°C a mixture of silane 1, nitropen-
tafluorobenzene (1:1.5, M) and a resonance at l(F)=
−144.9 ppm, possibly the result of an addition
between sulfalane and BF3, was observed by 19F-
NMR spectrometry.
Found: C 62.3, H 3.46, F 26.1. C19H13F5Si. Re-
quired: C 62.6, H 3.57, F 26.1.
4.3.6. With [NO2]+[BF4]− in acetonitrile
4.2. Dimethyl(pentafluorophenyl)phenylsilane 7
No reaction was detected between silane 1 (61 mg,
0.25 mmol) and [NO2]+[BF4]− (60 mg, 0.45 mmol) in
acetonitrile (0.15 ml) at 22°C after stirring for 3 days
in a glass NMR tube (19F-NMR).
Within 15 min P(NEt2)3 (7.7 g, 31 mmol) was
added dropwise under stirring to a 5–8°C cold solu-
tion (flask) of bromopentafluorobenzene (6.5 g, 26
mmol) and PhMe2SiCl (3.7 g, 26 mmol) in benzene
(20 ml). The resulting suspension was stirred for a
further 1 h, washed with concentrated H2SO4 (2×5
ml) and finally with water till neutral. After drying
with MgSO4 silane 7 (4.3 g, 55%) was isolated by
vacuum-distillation, b.p. 142–145°C (3 hPa) (lit.
94.5–95.5°C (0.2 hPa) [24]).
4.3.7. With bromine
A mixture of silane 1 (180 mg, 0.75 mmol) and
1
bromine (247 mg, 1.54 mmol) was stirred at r.t. H-
and 19F-NMR monitoring showed the slow formation
of C6F5Br and BrSiMe3 (20, 28 and 55% conversion
of silane 1 after 13, 22 and 90 h, respectively).
4.3. Reactions of pentafluorophenyltrimethylsilane 1
with electrophiles
4.3.8. With bromine and AlBr3
Silane 1 (68 mg, 0.28 mmol) was added to a solu-
tion of AlBr3 (58 mg, 0.22 mmol) in bromine (0.1 ml)
at −20°C. After warming to r.t. (15 min) the 19F-
NMR spectrum showed the total conversion of silane
1 into bromopentafluorobenzene 4. A violent reaction
took place when the reactants were mixed at r.t.
4.3.1. With aHF
Silane 1 (200 mg, 0.83 mmol) and aHF (0.4 ml)
were stirred at r.t. The conversion of silane 1 into
pentafluorobenzene 2 was 30% after 12 h and 100%
after 30 h (19F-NMR).
4.4. 1,4-Dideuterotetrafluorobenzene
4.3.2. With FSO3H
Silane 1 (200 mg, 0.83 mmol) was added to FSO3H
(0.4 ml) under stirring at −60°C. At −60°C no re-
action was detected after 5 min while at −20°C the
total conversion of silane 1 into pentafluorobenzene 2
At
−20°C
1,2,4,5-tetrafluoro[bis(trimethylsi-
lyl)]benzene (1.0 g, 3.4 mmol) was added to a stirred
solution of CF3SO3D, obtained from D2O (0.2 g, 10

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H.-J. Frohn et al. / Journal of Organometallic Chemistry 570 (1998) 255–263
Table 3
13C-NMR spectra of pentafluorophenylsilanes C6F5SiXYZ (CDCl3, 35°C)
X
Y
Z
l (C)/ppm
J/Hz
CH3 CH3 CH3 C6F5: 149.37 (C-2, 6), 142.25 (C-4), 137.52 (C-3, 5),
111.23 (C-1); CH3: 1.98
C6F5: (C2, F2) 241.5, (C4, F4) 253.9, (C4, F3) 13.6, (C4, F2)
6.0, (C3, F3) 253.5, (C1, F2) 29.5
CHa3 CH3 C6H5 C6F5: 149.88 (C-2, 6), 142.81 (C-4), 137.96 (C-3, 5),
110.47 (C-1); C6H5: 136.63 (C-1), 134.29 (C-3, 5),
130.43 (C-4), 128.65 (C-2, 6); CH3: −1.03
C6F5: (C2, F2) 241.8, (C3, F3) 250.8, (C4, F4) 253.8, (C4,
F3) 13.5, (C4, F2) 6.0, (C1, F2) 32.4, (C1, F3) 3.5, (C1, F4)
3.5; C6H5: (C3, H3) 158.6, (C4, H4) 160.1, (C4, H3) 7.0,
(C2, H2) 159.6; CH3: (C, F2) 3.5, (C, H) 121.7, (C, Si) 56.8
C6F5: (C2, F2) 243.3, (C4, F4) 256.3, (C4, F3) 13.5, (C4, F2)
6.0, (C3, F3) 252.8, (C1, F2) 30.7; CH3: (C, F2) 3.1, (C, Si)
58.8
CH3 CH3 C6F5 C6F5: 148.99 (C-2, 6), 142.74 (C-4), 137.33 (C-3, 5),
107.84 (C-1); CH3: −0.14
CH3 C6H5 C6H5 C6F5: 149.25 (C-2, 6), 142.48 (C-4), 137.32 (C-3, 5),
108.27 (C-1); C6H5: 134.63 (C-3, 5), 133.79 (C-1),
C6F5: (C2, F2) 251.8, (C4, F4) 255.8, (C4, F3) 13.5, (C4, F2)
5.8, (C3, F3) 244.3, (C1, F2) 31.1, (C1, F3) 3.4, (C1, F4) 3.4;
C6H5: (C3, H3) 160.6, (C4, H4) 160.6, (C4, H3) 7.4, (C2,
H2) 162.1; CH3: (C, F2) 4.0, (C, H) 122.3
130.12 (C-4), 128.10 (C-2, 6); CH3: −1.52
CH3
F
F
C6F5: 149.34 (C-2, 6), 144.23 (C-4), 137.47 (C-3, 5),
102.59 (C-1); CH3: −2.49
C6F5: (C2, F2) 247.8, (C3, F3) 254.8, (C4, F4) 259.3, (C4,
F3) 13.2, (C4, F2) 5.9; CH3: (C, SiF) 15.7
CH3 Cl
CH3 Br
Cl
C6F5: 148.78 (C-2, 6), 144.03 (C-4), 137.54 (C-3, 5),
106.47 (C-1); CH3: 7.92
C6F5: (C2, F2) 249.1, (C3, F3) 254.3, (C4, F4) 259.3, (C4,
F3) 13.3, (C4, F2) 6.6, (C1, F2) 26.6, (C1, F3) 3.1, (C1, F4)
3.1; CH3: (C, F2) 3.5, (C, Si) 75.8
C6F5: (C2, F2) 249.3, (C3, F3) 254.8, (C4, F4) 259.8, (C4,
F3) 13.2, (C4, F2) 5.9, (C1, F2) 26.2, (C1, F3) 3.2, (C1, F4)
3.2; CH3: (C, F2) 3.7
Br
C6F5: 148.63 (C-2, 6), 144.08 (C-4), 137.51 (C-3, 5),
106.90 (C-1); CH3: 10.77
a In CD2Cl2.
mmol) and (CF3SO2)2O (2.0 g, 7 mmol). After 10–15
min the 19F-NMR spectrum showed the formation of
1,4-C6D2F4. The compound 1,4-C6D2F4 (0.4 g, 77%)
was isolated by distillation, b.p. 84–86°C.
4.5.4. With AlCl3 (1.9 equi6alents) in CD2Cl2
The reaction of silane 3 (57 mg, 0.15 mmol) with
AlCl3 (35 mg, 0.26 mmol) and CD2Cl2 (0.2 ml) led to a
mixture of compounds 3, 6 and 2 (42.9, 28.6 and 28.6
molar%, respectively) as well as Me2SiCl2 (1H- and
19F-NMR).
4.5. Reactions of dimethyl[bis(pentafluorophenyl)]silane
3 with electrophiles
4.5.5. With AlCl3 (0.33 equi6alents) in CDCl3
A sample of AlCl3 (11 mg, 0.08 mmol) was added at
r.t. to a solution of silane 3 (99 mg, 0.25 mmol) in
CDCl3 (0.4 ml) and the resulting reaction mixture was
stirred for 13 days. The organic phase contained silanes
3, 6, 2 and C6F5CDCl2 (62, 18, 18 and 2 molar%,
respectively) as well as Me2SiCl2 (1H-, 19F-NMR and
GCMS).
4.5.1. With bromine
In a reaction with bromine (0.3 ml) at r.t. 20% of
silane 3 (34 mg, 0.08 mmol) were converted into bro-
mopentafluorobenzene 4 and traces of pentafluoroben-
zene 2 (19F-NMR) within 8 days.
4.5.2. With bromine and AlBr3
A sample of AlBr3 (23 mg, 0.09 mmol) was added at
r.t. to a solution of silane 3 (57 mg, 0.15 mmol) in
bromine (0.3 ml). After 15 min the reaction mixture was
4.5.6. With AlCl3 (1.9 equi6alents) in CDCl3
The reaction of silane 3 (36 mg, 0.09 mmol) with
AlCl3 (22 mg, 0.16 mmol) and CDCl3 (0.4 ml) gave a
mixture of 3, 6, 2 and C6F5CDCl2 (29, 29, 29 and 13
molar%, respectively) as well as Me2SiCl2 (1H-, 19F-
NMR and GCMS).
diluted with CDCl3 (0.05 ml). The H- and 19F-NMR
1
spectra showed the total conversion of silane 3 into
bromopentafluorobenzene and Me2SiBr2.
4.5.3. With bromine and AlBr3 in DBE
A solution of silane 3 (52 mg, 0.13 mmol) in DBE
(0.2 ml) was added to AlBr3 (19 mg, 0.07 mmol) and the
resulting solution was stirred for 0.5 h at r.t. Bromosi-
lane 5, pentafluorobenzene 2 (1:1, M) and silane 3 (5%
conversion) were detected by 19F-NMR spectrometry. A
total of 0.5 h after the addition of bromine (65 mg, 0.4
mmol) C6F5Br and C6F5H (93:7, M) were the only
polyfluoroaromatic products (19F-NMR).
4.5.7. With HCl and AlCl3 in CDCl3
Gaseous HCl was bubbled into a stirred suspension
of AlCl3 (29 mg, 0.22 mmol) in a CDCl3 (2 ml) solution
of silane 3 (157 mg, 0.40 mmol) at r.t. After 1 h silanes
3, 6 and pentafluorobenzene 2 (24, 29 and 47 molar%,
respectively) were detected along with Me2SiCl2 (1H-
and 19F-NMR).

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261

262
H.-J. Frohn et al. / Journal of Organometallic Chemistry 570 (1998) 255–263
4.6. Reactions of dimethyl(pentafluorophenyl)phenyl-
silane 7 with electrophiles
reaction mixture by 19F-NMR spectrometry showed the
following composition (molar%):
4.6.1. With aHF
A two phase system of silane 7 (1.25 g, 4.12 mmol),
aHF (1 ml) and CH2Cl2 (3 ml) was stirred at r.t. After
0.5 h aHF was evaporated under argon and the residual
solution was treated with NaF. Compound 9 (0.95 g,
94%) was isolated by distillation, b.p. 155–158°C (lit.
157–159°C [21]).
Reaction
time,
minutes
Silane 8
(%)
Silane 13
(%)
Silane 12
(%)
15
30
45
52
—
—
48
50
—
—
50
100
4.6.2. With AlBr3 in DBE
A sample of AlBr3 (109 mg, 0.41 mmol) was added to
a stirred solution of silane 7 (433 mg, 1.43 mmol) in
DBE (2 ml) at 5°C. After 10 min the suspension was
diluted with hexane (8 ml) and filtered. The filtrate was
washed with 10% HCl and water and dried with
MgSO4. Separation of the mother liquid and evapora-
tion of the solvent gave product 5 (380 mg, 87%).
4.7.4. With AlCl3 (0.7 equi6alents) in CH2Cl2
A solution of silane 8 (1.18 g, 3.2 mmol) in CH2Cl2 (3
ml) was added to a stirred suspension of AlCl3 (297 mg,
2.2 mmol) in CH2Cl2 (1 ml). After 45 min the 19F-NMR
spectrum showed the total conversion of silane 8 into
product 12 which was isolated in a 66% yield (603 mg)
by distillation, b.p. 171°C (lit. 63–65°C (4 hPa) [26],
71°C (10 hPa) [18]).
4.7. Reactions of methyl(pentafluorophenyl)diphenyl-
silane 8 with electrophiles
4.7.1. With aHF
4.7.5. With AlCl3 (7.7 equi6alents) in AcCl
A sample of aHF (2 ml) was added to a solution of
silane 8 (1.25 g, 3.4 mmol) in CH2Cl2–CD2Cl2 (3:1) (4
ml) at −78°C. The two phase system was stirred and
warmed to r.t. Periodic control of the reaction mixture
by 19F-NMR spectrometry showed the following com-
position (molar%):
A solution of silane 8 (26 mg, 0.07 mmol) in AcCl
(0.1 ml) was added to a stirred solution of AlCl3 (73
mg, 0.55 mmol) in AcCl (0.15 ml). After 20 min the
19F-NMR spectrum showed the total conversion of
silane 8 into product 12.
4.7.6. With AlBr3 (0.5 equi6alent) in DBE
A solution of silane 8 (1.36 g, 3.7 mmol) and AlBr3
(498 mg, 1.9 mmol) in DBE (25 ml) was stirred for 10
min. The 19F-NMR spectrum showed the total conver-
sion of silane 8 into product 14 which was isolated in a
65% yield (897 mg) by distillation, b.p. 199°C.
Reaction
time, h
Silane 8
(%)
Silane 11
(%)
Silane 10
(%)
0.5
4
23.5
78
—
—
22
51
—
—
49
100
4.8. Reaction of dichloro(methyl)pentafluorophenylsilane
12 with XeF2
When the total conversion of silane 8 into silane 10
was achieved, aHF was removed in vacuum at −30°C
and product 10 (531 mg, 63%) was isolated by distilla-
tion, b.p. 150°C (lit. 144°C [25]).
A sample of xenon difluoride (0.80 g, 4.73 mmol) was
added in one portion to a stirred solution of dichloro-
silane 12 (1.28 g, 4.55 mmol) in CH2Cl2 (5 ml) at r.t.
Within a few minutes xenon started to evolve. After 30
min the reaction mixture was warmed to reflux, the
solvent was distilled off and difluorosilane 10 (0.83 g,
74%) was isolated by distillation, b.p. 137–138°C (lit.
144°C [25]).
4.7.2. With HCl and AlCl3 in hexane
At r.t. gaseous HCl was bubbled into a stirred sus-
pension of AlCl3 (100 mg, 0.75 mmol) in a hexane (10
ml) solution of silane 8 (525 mg, 1.44 mmol) for 60 min.
The 19F-NMR spectrum of the mother liquid showed
the quantitative conversion of silane 8 into product 12.
Acknowledgements
4.7.3. With AlCl3 (one equi6alent) in CH2Cl2
The authors gratefully acknowledge Volkswagen
Stiftung and Fonds der Chemischen Industrie for finan-
cial support and Solvay Fluor und Derivate GmbH for
the contribution of chemicals.
A solution of silane 8 (1.21 g, 3.3 mmol) in CH2Cl2 (3
ml) was added to a stirred suspension of AlCl3 (429 mg,
3.2 mmol) in CH2Cl2 (1 ml). Periodic control of the

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263
D.H. O’Brien, C.M. Harbordt, J. Organomet. Chem. 21 (1970)
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