Preparation of halogeno(pentafluorophenyl)silanes (C6F5)nSiX4-n (X=F, Cl and Br; N=2, 3) from pentafluorophenyl(phenyl)silanes (C6F5)nSiPh4-n

Article abstract of DOI:10.1016/S0022-328X(98)00720-7

Halogeno(pentafluorophenyl)silanes (C₆F₅)_nSiX_4-n (X=F, Cl and Br; n=2, 3) were prepared in good yields from the corresponding phenylsilanes (C₆F₅)_nSiPh_4-n by reactions with the electrophiles aHF, FSO₃H, HCl-AlCl₃ or with AlX₃ (X=Cl, Br)-halogenated hydrocarbons. The relative leaving ability of the organyl groups (C₆F₅, C₆H₅, Me) bonded to the silicon atom and the strength of the electrophilic reagent are discussed.

Full text of DOI:10.1016/S0022-328X(98)00720-7

Journal of Organometallic Chemistry 568 (1998) 233–240
Preparation of halogeno(pentafluorophenyl)silanes (C6F5)nSiX4−n
(X=F, Cl and Br; n=2, 3) from pentafluorophenyl(phenyl)silanes
(C6F5)nSiPh4−n
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; received in revised form 22 May 1998
Abstract
Halogeno(pentafluorophenyl)silanes (C6F5)nSiX4−n (X=F, Cl and Br; n=2, 3) were prepared in good yields from the
corresponding phenylsilanes (C6F5)nSiPh4−n by reactions with the electrophiles aHF, FSO3H, HCl–AlCl3 or with AlX3 (X=Cl,
Br)–halogenated hydrocarbons. The relative leaving ability of the organyl groups (C6F5, C6H5, Me) bonded to the silicon atom
and the strength of the electrophilic reagent are discussed. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Silanes; Electrophilic substitution; Silicon
1. Introduction
2. Results
Our previous paper dealt with the facile prepara-
tion of halogeno(methyl)pentafluorophenylsilanes C6F5-
SiMenX3−n (X=F, Cl, Br; n=1, 2) in reactions of the
corresponding phenylsilanes C6F5SiMenPh3−n with
electrophilic reagents [1]. The substantial differences in
the leaving ability of pentafluorophenyl and phenyl
groups prompted us to extend that approach to the
synthesis of halogeno(pentafluorophenyl)silanes (C6F5)n
SiX4−n starting with easily available compounds
(C6F5)nSiPh4−n. All up to date known routes to
halogeno(pentafluorophenyl)silanes have some disad-
vantages, e.g. multistep reactions, low yields of the
desired products, formation of complex reaction mix-
tures or the use of specific laboratory equipment (see [2]
and references cited there).
The starting material pentafluorophenyl(phenyl)-
silanes (C6F5)2SiPh2 1 and (C6F5)3SiPh 2 were readily
produced by nucleophilic substitution of chlorine in the
easily available chloro(phenyl)silanes Ph2SiC12 and Ph-
SiCl3, respectively, with C6F5Li in ether–hexane using
modified literature methods [3,4]. However, the situa-
tion was different for C6F5SiPh3. We were not able to
work out a preparative route to silane C6F5SiPh3 by
reaction of Ph3SiCl with C6F5MgBr or with C6F5Br and
P(NEt2)3. From C6F5Li and Ph3SiCl [4] we always got
a raw product of low purity in low yields. In the past
the lack of a simple synthesis for C6F5SiPh3 was already
reported by Fearon and Gilman [3]. Because of the lack
of availability of C6F5SiPh3 we concentrated our inves-
tigations of the reactivity of pentafluorophenyl-
(phenyl)silanes with electrophiles exclusively on silanes
1 and 2.
* Corresponding author.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00720-7

234
H.-J. Frohn et al. / Journal of Organometallic Chemistry 568 (1998) 233–240
2.1. Reactions of pentafluorophenyl(phenyl)silanes with
protic acids
(DCE) should facilitate the reaction with HCl–AlCl3
due to the higher solubility of the catalyst and the
higher polarity of media. Indeed, quantitative forma-
tion of dichlorosilane 7 took place within a few min
when silane 1 was treated with HCl and AlCl3 in DCE
at r.t.
No reaction was detected between silane 1 and an
excess of aHF at room temperature (r.t.) over 26 h, but
a slow replacement of one phenyl group by fluorine
took place in dichloromethane or chloroform solutions.
However, the treatment of silane 1 with a mixture of
aHF and FSO3H led to the formation of difluoro-[bis-
(pentafluorophenyl)]silane 3 in good yields within 1.5 h.
1+HCl+1.4AlCl3 ꢀDꢀCꢀEꢀꢁ 7 (100%)
(9)
10 min
It was surprising that the replacement of the C6H5
group by chlorine also occurred in the absence of HCl.
We studied that unexpected reaction in detail and de-
veloped a convenient preparative route to halogeno
(pentafluorophenyl)silanes.
(C6F5)2SiPh2+aHF (1) ꢀꢀꢀꢀꢀꢁ No reaction
(1)
RT, 26 h
CHCl
3
1+aHF ꢀꢀꢀꢀꢀꢀꢀꢁ (C6F5)2SiPhF (4) (20% conversion of 1)
RT, 7 days
(2)
CH Cl
2
2
2.2. Reactions of pentafluorophenyl(phenyl)silanes with
aluminum trichloride and tribromide–halogenated
hydrocarbons
1+aHF ꢀꢀꢀꢀꢀꢀꢀꢁ (C6F5)2SiPhF (4) (72% yield)
RT, 8 days
+(C6F5)2SiF2 (3) (10% yield)
(3)
(4)
1+aHF+FSO3H ꢀꢀꢀꢀꢀꢀꢀꢁ 3 (72% yield)
RT, 1.5 h
Treatment of phenylsilane 1 with 0.5 equivalents of
AlCl3 in CH2Cl2 at r.t. for 1 h gave dichlorosilane 7. In
chloroform the analogous reaction was completed after
3 h. Increasing the amount of AlCl3 accelerated the
reaction rate in dichloromethane and chloroform. On
no account was pentafluorophenyl–silicon bond cleav-
age detected.
Silane
2
was unreactive towards aHF in
dichloromethane, but reacted rapidly with fluorosul-
fonic acid to give fluoro[tris(pentafluorophenyl)]silane 5
and benzenesulfonyl fluoride. Likely, fluorosilane 5 was
formed by thermal decomposition of the ester
(C6F5)3SiOSO2F in FSO3H (cf. similar displacement of
the fluorosulfato group by fluorine in Me3SiOSO2F and
related compounds [5]).
CH Cl or CHCl
2
2
3
1+n AlCl3 ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢁ (C6F5)2SiCl2
(10)
RT
7 (100%)
n=1.0 (35 min),
CH Cl
2
2
(C6F5)3SiPh+aHF ꢀꢀꢀꢀꢀꢀꢀꢀꢁ No reaction
(5)
RT, 4 days
in CH Cl :
2
n=0.5 (60 min),
n=5.0 (10 min)
n=5.0 (15 min)
2
CH Cl
2
2
in CHCl :
3
n=0.5 (180 min), n=1.0 (40 min),
2+FSO3H ꢀꢀꢀꢀꢀꢁ (C6F5)3SiF+PhSO2F (5) (83% yield)
RT, 1.5 h
(6)
A similar picture was observed in the reaction of
phenylsilane 2 with AlCl3. In CH2Cl2 the total conver-
sion into chlorosilane 8 was achieved within 1 h
whereas 4 h were required for the complete reaction in
CHCl3.
Anhydrous HCl reacted with both silanes 1 and 2 in the
presence of AlCl3 in hexane to give chlorosilanes 6, 7 or
8, respectively. Total consumption of silane 1 was
achieved within 1 h, but further substitution of the
residual phenyl group in silane 6 by chlorine proceeded
CH Cl (55 min) or
2
2
CHCl (240 min)
3
2+0.5 AlCl3ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢁ (C6F5)3SiCl (8) (100%) (11)
slowly. Silane
2
with three electron-poor pen-
RT
tafluorophenyl groups was less reactive than silane 1
and the conversion of 2 into chlorosilane 8 was incom-
plete after 2–3 h even in the presence of five equivalents
of AlCl3.
Hexane
1+HCl+nAlCl3 ꢀꢀꢀꢀꢀꢁ (C6F5)2SiPhCl+(C6F5)2SiCl2
Dibromo[bis(pentafluorophenyl)]silane 9 and bromo-
[tris(pentafluorophenyl)]silane 10 were easily prepared
by the homogenous reaction of the corresponding
silanes 1 and 2 with less stoichiometric amounts of
AlBr3 in 1,2-dibromoethane (DBE).
DBE
1+0.5 AlBr3 ꢀꢀꢀꢀꢀꢀꢀꢁ (C6F5)2SiBr2 (9) (100%)
n=0.9,
8 h,
6 (27%),
7 (73%);
(12)
RT, 20 min
n=3,
3 h,
7 (100%)
(7)
DBE
2+0.5 AlBr3 ꢀꢀꢀꢀꢀꢀꢀꢁ (C6F5)3SiBr (10) (100%)
(13)
Hexane
2+HCl+nAlCl3 ꢀꢀꢀꢀꢀꢁ(C6F5)3SiCl
RT, 90 min
n=2,
3 h,
8 (59% conversion of 2);
(8)
n=5,
2 h,
8 (64% conversion of 2)
3. Discussion
Because of the negligible solubility of AlCl3 in hex-
ane, the low reaction rate can be assigned to the
heterogeneous conditions of reaction. It was expected
that the use of polar halogenated hydrocarbons such as
dichloromethane, chloroform or 1,2-dichloroethane
The results presented here have close relations to the
formation of halogeno(methyl)pentafluorophenylsilanes
reported in our previous paper [1] and that circum-
stance caused us to discuss both results together. The

H.-J. Frohn et al. / Journal of Organometallic Chemistry 568 (1998) 233–240
235
elaboration and understanding of simple synthetic
routes to halogeno(pentafluorophenyl)silanes was the
goal of our work. With phenylsilanes as starting mate-
rial we have not analysed further the path of the phenyl
leaving group under the influence of the different
electrophiles.
of silane 1 in aHF–CH2Cl2 was 36% (21 h) and only
20% in aHF–CHC13 (7 days). Those results correlate
with the lower solubility of aHF in chloroform with
respect to that in dichloromethane (see Section 4). The
second aspect is the positive influence of a high dielec-
tric constant of the solvent on the electrophilic bond
cleavage, e.g. in CH2Cl2 with the higher dielectric con-
stant (m=8.9) reactions are faster than in CHCl3 (m=
4.8). The third important factor is the direct partici-
pation of halogenated hydrocarbon solvents in the reac-
tions when AlX3 was present. Reactions of pentafluo-
rophenylsilanes with AlX3 in halogenated hydrocarbons
probably proceeded via an intermediate generation of a
carbocationic species like [ClCHl2 + ·Cl4All−] which are
the reactive electrophilic key agents. The higher elec-
trophilicity of carbocation [ClCH2]+ with respect to
[Cl2CH]+ and the higher dielectric constant of CH2Cl2
were responsible for the higher reactivity of AlCl3 in
CH2Cl2 in comparison to CHCl3. Moreover, the high
solubility of the stronger Lewis acid AlBr3 in DBE
(m=4) and the higher polarisation of the carbon–
bromine bond in [BrCH2CHl2 + ·Br4All−] made that
system the most effective electrophile in the series
AlCl3–CHCl3, AlCl3–CH2Cl2 and AlBr3–DBE.
Principally, catalytic amounts of AlX3 were satisfac-
tory to run those processes. Our previous [1] and
present work demonstrated clearly the acceleration of
the reaction rate with increasing relative amounts of
aluminum trihalide. In the case of the high soluble
system AlBr3–DBE a higher relative amount of AlBr3
increased the concentration of the electrophile. In
CH2Cl2, CHCl3, DCE and hexane with very low solu-
bilities of AlCl3 the reaction rate depended mainly on
the active surface of the catalyst. In the course of the
reaction the active surface could be reduced by deposi-
tion of by-side products like [–CHCl(C6H4)]n which
resulted from consecutive reactions of the phenyl leav-
ing group under electrophilic conditions. By-side alky-
lation of the phenyl group in the case of the reagent
halogenated alkane AlHal3, is a source of H–Hal which
forms H+ as additional electrophile in the presence of
AlHal3. Our observation that in such cases the opera-
tion in a closed system compared with an open one is
accompanied by a faster cleavage of the C6H5–Si bond
means that the protolytic cleavage is faster than the
carbocationic.
3.1. Relati6e rate of carbon–silicon bond clea6age in
C6F5(Ph)SiXY
In all pentafluorophenyl(phenyl)silanes C6F5(Ph)Si-
XY only substitution of the phenyl group by halogen
took place, independent of the nature of the elec-
trophile. Comparison of the time for the total con-
sumption of the starting silanes under similar
conditions (temperature, concentration) gave the fol-
lowing sequences.
Electrophile Rate of consumption of
C6F5(Ph)SiXY
HF–CH2C12 X, Y: C6F5, C6F5 ꢀC6F5, PhBPh,
MeBMe, Me
1 AlCl3–
CH2C12
0.5 AlBr3–
DBE
X, Y: C6F5, C6F5BC6F5, Ph ꢁ Ph,
Me
X, Y: C6F5, C6F5BC6F5, PhBPh,
Me ꢁMe, Me.
It is noteworthy, that only strong electrophilic
reagents like CF3SO3H, FSO3H, Br2–AlBr3 or Br2–
AlBr3–DBE were reactive enough to cleave the pen-
tafluorophenylsilicon bond in the methyl(pentafluoro-
phenyl)silanes (C6F5)nSiMe4−n (n=1, 2). The methyl–
silicon bond stayed unchanged in all cases [1]. The rate
of carbon–silicon bond cleavage by electrophiles in-
creased in the series: CH3ꢀC6F5BC6H5.
The electrophilic character of those processes was
proved by the following considerations: (a) replacement
of the phenyl group in phenyl(pentafluorophenyl)
silanes occurred more readily than the pentafluo-
rophenyl group while the latter was preferentially elimi-
nated in the silicate anion [C6F5Si(C6H5)XYNu]− and
(b) the rate of the C6F5–Si bond cleavage in methyl
(pentafluorophenyl)silanes depended clearly on the
strength of the protic acids (CF3SO3H\FSO3H\
aHF) and Lewis acids (Br2–AlBr3\AlBr3–DBE\
AlCl3–CH2C12).
The unexpected and very slow reaction of AlCl3 with
(C6F5)2SiMe2 in CD2Cl2 and CDCl3 under formation of
C6F5H and C6F5SiMe2Cl [1] is explainable if we as-
sume–despite of a dry argon atmosphere–that small
amounts HCl were formed by partial hydrolysis of
AlCl3 by penetration of water vapour into the FEP trap
with PTFE stopper during the long-time processes (13
days).
3.2. Role of sol6ent and AlX3 (X=Cl, Br)
Solvents can influence the conversion rate of pen-
tafluorophenylsilanes under the action of electrophiles
in three ways. The first aspect is the solubility of the
electrophilic reagent or catalyst. Indeed, the conversion

236
H.-J. Frohn et al. / Journal of Organometallic Chemistry 568 (1998) 233–240
4. Experimental section
mmol) and ether (70 ml) were placed in a flask
equipped with a dropping funnel, a reflux condenser
and a magnetic stirrer and cooled to −78°C under dry
argon. BuLi (1.6 M in hexane, 60 ml, 96.0 mmol) was
added dropwise under stirring. The reaction mixture
was maintained at −78°C for 1 h before a solution
of PhSiCl3 (7.15 9, 33.8 mmol) in ether (40 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. The solvent was distilled off and the residue
was sublimed at 130°C (0.04 hPa). Sublimate 2 was
purified by crystallisation from hexane and re-sublima-
tion at 110°C (0.04 hPa) (yield 12.6 9, 67%), m.p. 138°C
(lit. m.p. 136–137°C [3], b.p. 180°C (0.8 hPa), m.p.
149°C [4]).
The NMR spectra were recorded on Bruker spec-
trometers WP 80 SY (1H at 80.13 MHz, 19F at 75.39
MHz) and Avance DRX 500 (1H at 500.13 MHz, 13C at
125.76 MHz, 19F at 470.59 MHz, 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. The IR spectra were measured on a Nicolet 20
DXB instrument (KBr pellets) and the Raman spectra
on a Bruker FT spectrometer IFS 66 equipped with a
Raman device FRA 106 (Nd: YAG laser ADLAS)
(glass capillary sealed under dry argon).
Pentafluorophenylsilanes
(C6F5)2SiPh2
1
and
(C6F5)3SiPh 2 were obtained by modified literature
methods [3] (see below). Hydrogen fluoride was dried
by electrolysis (stainless steel cell, Ni electrodes), HCl
by bubbling through H2SO4. FSO3H was distilled and
aluminum trihalogenides AlX3 were sublimed before
use. Ether, hexane, dichloromethane, chloroform, 1,2-
dichloroethane and 1,2-dibromoethane were dried by
literature methods and stored over molecular sieves
(ether over Na). All reactions were carried out in
stoppered FEP or PFA traps under dry argon atmo-
sphere except when alternative handling is described.
Solid materials were manipulated in a Braun glovebox
with a gas purification MB-100.
4.3. Reactions of bis(pentafluorophenyl)diphenylsilane 1
with electrophiles
4.3.1. With aHF
A suspension of silane 1 (80 mg, 2.4 mmol) in aHF
(0.5 ml) was stirred at r.t. for 26 h. After removal of
aHF in vacuum at −20°C and dissolution of the solid
residue (74 mg) in CH2Cl2 silane 1 was recovered
unchanged (19F-NMR).
The solubility of aHF in CDCl3 (4.0 mg ml−1, 0.19
mmol ml−1), CD2Cl2 (14.4 mg ml−1, 0.72 mmol ml−1
)
4.3.2. With aHF in dichloromethane
and in DCE (38.5 mg ml−1, 1.92 mmol ml−1) at 1°C
was determined by 19F-NMR spectrometry using C6F6
as a quantitative internal reference.
A sample of aHF (2 ml) was added to a stirred
solution of silane 1 (1.21 g, 2.4 mmol) in CH2Cl2–
CD2Cl2 (2:1) (3 ml) at −78°C. The two phase system
was warmed to r.t. After 3 days the reaction mixture
contained silanes 1, 4 and 3 (15, 80 and 5 M%). After
8 days only 4 and 3 were present in a molar ratio of
4.1. Bis(pentafluorophenyl)diphenylsilane 1
Bromopentafluorobenzene (13.0 g, 52.6 mmol) and
ether (50 ml) were placed in a flask equipped with a
dropping funnel, a reflux condenser and a magnetic
stirrer and cooled to −78°C under dry argon. BuLi
(1.6 M in hexane, 34 ml, 54.4 mmol) was added drop-
wise under stirring. The reaction mixture was main-
tained at −78°C for 1 h before Ph2SiCl2 (7.42 g, 29.3
mmol) 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 1 was isolated by vacuum-distillation,
b.p. 140–155°C (0.04 hPa) and crystallised from hexane
(yield 7.85 g, 58%), m.p. 149–151°C (lit. m.p. 151–
152°C [3], b.p. 175°C (0.15 hPa), m.p. 152°C [4]).
Found: C 55.9, H 2.03. C24H10F10Si. Required: C 55.8,
H 1.95.
Table 1
1H and 29Si-NMR spectra of pentafluorophenylsilanes (C6F5)2SiXY
(CDCl3, 35°C)
X
Y
l(H)/ppm
l(Si)/ppm J/Hz
C6Ha5 C6H5 7.71 (H-2, 6),
−25.11
−33.17
−14.40
(H2, H4) 1.6, (H3,
H4) 7.5
7.60 (H-4),
7.51 (H-3, 5)
C6F5 C6H5 7.58 (H-2, 6),
(H2, H4) 1.3, (H3,
H4) 7.5
7.52 (H4),
7.42 (H-3, 5)
7.71 (H-2, 6)
C6H5
C6Fa5
F
F
(H3, H4) 6.9, (Si,
F) 286.1
7.60 (H-4),
7.50 (H-3, 5)
—
—
—
−20.23
−22.70
−33.39
(Si, F) 288.5
C6F5 Cl
C6F5 Br
4.2. Tris(pentafluorophenyl)phenylsilane 2
A sample of bromopentafluorobenzene (23.0 g, 93.0
a In CD2Cl2.

H.-J. Frohn et al. / Journal of Organometallic Chemistry 568 (1998) 233–240
237
Table 2
19F-NMR spectral data of pentafluorophenylsilanes (C6F5)2SiXY(CDCl3, 35°C)
X
Y
l(F)/ppm
J(F,F)/Hz
F-2,6
F-4
F-3,5
C6Ha5,b
C6Fb5
C6H5
C6H5
C6H5
Fc
−123.89
−125.86
−127.12
−149.41
−147.86
−147.13
−160.91
−160.51
−160.57
(2, 4) 4.4, (3, 4) 19.9
(2, 4) 4.7, (3, 4) 20.2
(2, 4) 5.0, (3, 4) 20.0,
(F, Si) 285.8, (FSiCCF) 12.4
(2, 4) 5.2, (3, 4) 19.9
(2, 4) 5.9, (3,4) 20.3
C6H5
Cl
Br
−125.81
−126.88
−147.39
−145.80
−160.47
−160.03
C6Fa5,b
a In CD2Cl2.
b Present work, lit. see [14].
c l(F) −163.43 ppm.
85:15 (19F-NMR). The volatile compounds were re-
moved in vacuum at −50°C. Product 4 was isolated by
vacuum distillation in 72% yield (788 mg) (b.p. 90°C
to the formation of 6 and 7 in a molar ratio of 54:46 (1
h) and 11:89 (2 h). After 3 h only silane 7 was detected
in the reaction mixture by 19F-NMR spectrometry.
1
(10 hPa)) and characterised by H, 13C, 19F, 29Si-NMR,
IR and Raman spectra (Tables 1–4).
4.3.7. With HCl and AlCl3 (1.4 equi6alent) in DCE
HCl was bubbled into a stirred suspension of
AlCl3 (73 mg, 0.55 mmol) in a DCE (1 ml) solution
of silane 1 (194 mg, 0.38 mmol) at r.t. Silane 7
was formed in quantitative yield within 10 min (19F-
NMR).
4.3.3. With aHF in CDCl3
A sample of aHF (0.4 ml) was added to a solution of
silane 1 (25 mg, 0.05 mmol) in CDCl3 (0.4 ml) at
−78°C and kept at r.t. for 7 days. The organic phase
contained silanes 1 and 4 (80 and 20 M%). No addi-
tional resonances of polyfluoroaromatics were detected
in the acidic phase (19F-NMR).
4.3.8. With AlCl3 (0.5 equi6alent) in CH2Cl2
A sample of AlCl3 (54 mg, 0.41 mmol) was added
to a stirred solution of silane 1 (421 mg, 0.82 mmol)
in CH2Cl2 (2 ml). After 50 min the total consump-
tion of silane 1 was detected and 6 and 7 were for-
med in a molar ratio of 18:82. Complex 7 was the
only polyfluoroaromatic reaction product after 60
min.
4.3.4. With aHF and FSO3H
A sample of aHF (6 ml) and FSO3H (1 ml) were
added in sequence to silane 1 (1.10 g, 2.12 mmol) in a
FEP trap (ƒi=23 mm) at −10°C. The reaction mix-
ture was stirred at r.t. for 1.5 h until the solid silane
disappeared. The acidic phase was extracted with
CH2Cl2 (2×3 ml). The combined extracts were treated
with NaF, filtered and the solvent was removed in
vacuum. Silane 3 (0.61 g, 72%) was isolated by vacuum
distillation, b.p. 76–78°C (6.7 hPa) (lit. b.p. 90°C (13.3
hPa), 207°C [6], 126°C (80 hPa) [2]) and identified by
19F-NMR spectrometry [2].
4.3.9. With AlCl3 (0.9 equi6alent) in CH2Cl2
Similarly, the reaction of AlCl3 (241 mg, 1.8 mmol)
with silane 1 (1.07 g, 1.2 mmol) in CH2Cl2 (3 ml) gave
silanes 6 and 7 in a molar ratio of 25:75 (30 min). After
40 min silane 7 was the only product. Product 7 (622
mg, 69%) was isolated by vacuum-distillation, b.p.
100–105°C (1.0 hPa) (lit. b.p. 100–103°C (2.0 hPa) [2],
180–182°C (21.3 hPa) [8]) and was identified by 13C,
19F and 29Si-NMR spectra [2].
4.3.5. With HCl and AlCl3 (0.9 equi6alent) in hexane
HCl was bubbled into a stirred suspension of AlCl3
(161 mg, 1.21 mmol) in a hexane (10 ml) solution of
silane 1 (663 mg, 1.28 mmol) at r.t. After 1 h 19F-NMR
spectrometry showed the total conversion of silane 1
into 6 and 7 (88 and 12 M%). Further treatment of the
reaction mixture with HCl for 8 h gave compounds 6
and 7 in a molar ratio of 27:73.
4.3.10. With AlCl3 (5.0 equi6alent) in CD2Cl2
The treatment of silane 1 (32 mg, 0.06 mmol) in
CD2Cl2 (0.3 ml) with AlCl3 (45 mg, 0.34 mmol) at r.t.
resulted after 10 min in the quantitative formation of
silane 7 (19F-NMR).
4.3.6. With HCl and AlCl3 (3.2 equi6alent) in hexane
In a similar way, the bubbling of HCl into a stirred
suspension of AlCl3 (82 mg, 0.62 mmol) in a hexane (2
ml) solution of silane 1 (101 mg, 0.20 mmol) at r.t. led
4.3.11. With AlCl3 in CHCl3
Reactions of AlCl3 (n equivalents) with silane 1
(0.4 mmol) in CHCl3 (2 ml) were performed in a

238
H.-J. Frohn et al. / Journal of Organometallic Chemistry 568 (1998) 233–240
Table 3
13C-NMR spectra of pentafluorophenylsilanes (C6F5)2SiXY(CDCl3, 35°C)
X
Y
l(C)/ppm
J/Hz
C6Fa5 C6H5 C6F5: 149.63 (C-2, 6), 143.56 (C-4), 137.99 (C-3, 5),
C6F5: (C2, F2) 245.3, (C4, F4) 256.3, (C4, F3) 13.6, (C4, F2) 5.9,
(C3, F3) 252.3, (C1, F2) 28.7
106.83 (C-1)
C6H5: 135.93 (C-3, 5) 131.45 (C-4), 128.66 (C-2, 6),
129.90 (C-1)
C6F5 C6H5 C6F5: 149.24 (C-2, 6), 143.69 (C-4), 137.57 (C-3, 5),
104.54 (C-1)
C6F5: (C2, F2) 246.8, (C4, F4) 258.9, (C4, F3) 13.3, (C4,F2) 6.4,
(C3,F3) 254.1, (C1, F2) 27.4
C6H5: 134.45 (C-3, 5) 131.56 (C-4), 128.44 (C-2, 6),
127.60 (C-1)
C6H5: (C3, H3) 160.6, (C4, H4) 161.1, (C4, H3) 6.9), (C2, H2)
163.1
C6H5
F
C6F5: 149.29 (C-2, 6), 144.17 (C4), 137.56 (C-3, 5),
104.22 (C-1)
C6F5: (C2, F2) 247.8, (C4, F4) 259.4, (C4, F3) 13.2, (C4, F2) 6.8,
(C3, F3) 255.3
C6H5: 133.66 (C-3, 5), 132.54 (C-4), 128.66 (C-2, 6),
128.56 (C-1)
C6H5: (C3, H3) 159.6, (C4, H4) 161.6, (C4, H3) 7.6, (C2, H2)
161.1
C6F5
F
C6F5: 149.92 (C-2, 6), 145.34 (C-4), 138.19 (C-3, 5),
103.10 (C-1)
C6F5: 149.21 (C-2, 6), 144.53 (C-4), 137.65 (C-3, 5),
103.77 (C-1)
C6F5: (C2, F2) 246.8, (C4, F4) 260.3, (C4,F3) 13.0, (C4, F2) 6.0,
(C3, F3) 254.8, (C1, F2) 26.9, (C1, SiF)16.0
C6F5: (C2, F2) 248.8, (C4, F4) 261.3, (C4, F3) 13.3, (C4, F2) 5.8,
(C3, F3) 255.3, (C1, F2) 24.2
C6F5 Br
a In CD2C12.
similar manner and showed the following results
(19F-NMR).
(2:1) (3 ml) at −78°C and kept at r.t. for 4 days.
After removal of aHF and dichloromethane in vac-
uum the unchanged silane
quantitatively.
2
was recovered
n
Time (min)
Silane 6 (%)
Silane 7 (%)
0.5
0.5
0.5
0.5 190
1.0
1.0
30
55
70
47
24
18
—
40
—
53
76
82
100
60
100
4.4.2. With FSO3H in CH2Cl2
A sample of FSO3H (0.7 ml) was added at r.t. to a
stirred solution of silane 2 (550 mg, 0.90 mmol) in CH2Cl2
(1 ml) (PFA trap: ƒi=11.7 mm). After 1 h the 19F-NMR
spectrum of the organic phase showed the quantitative
formation of silane 5 and PhSO2F [l( F) 64.1 ppm)] (1:1,
molar). The organic phase was separated and the acidic
phase was extracted with CH2Cl2 (2 ml). The combined
extracts were treated with NaF, filtered and the volatile
substances were removed in vacuum at B90°C. Silane
5 (0.41 g, 83%) was obtained as residue and was identified
by 19F-NMR [2] and additionally characterised by 13C
and 29Si-NMR spectrometry (Tables 1 and 3).
30
40
Similarly, the treatment of silane 1 (27 mg, 0.05 mmol)
with AlCl3 (36 mg, 0.27 mmol) in CDCl3 (0.4 ml) gave
silane 7 (100% yield, 19F-NMR) within 15 min.
4.3.12. With AlBr3 (0.5 equi6alent) in DBE
A solution of silane 1 (223 mg, 0.43 mmol) in DBE (2
ml) was added to a stirred solution of AlBr3 (56 mg, 0.21
mmol) in DBE (1 ml) at r.t. After 20 min the 19F-NMR
spectrum showed the quantitative conversion of silane 1
into dibromosilane 9 [7,14].
4.4.3. With HCl and AlCl3 (2.0 equi6alent) in hexane
A sample of HCl was bubbled into a stirred suspension
of AlCl3 (52 mg, 0.39 mmol) in a hexane (10 ml) solution
of silane 2 (119 mg, 0.20 mmol) at r.t. The molar ratio
of silane 2 to chlorosilane 8 was 41:59 (3 h) and 38:62
(4 h) (19F-NMR).
4.3.13. With AlBr3 (1.0 equi6alent) in DBE
Similarly, after 10 min dibromosilane 9 was obtained
in quantitative yield by the reaction of silane 1 (114 mg,
0.22 mmol) with AlBr3 (59 mg, 0.22 mmol) in DBE (2
ml) at r.t. (19F-NMR).
4.4.4. With HCl and AlCl3 (5.1 equi6alent) in hexane
A sample of HCl was bubbled into a stirred suspension
of AlCl3 (112 mg, 0.84 mmol) in a hexane (2.5 ml)
solution of silane 2 (101 mg, 0.17 mmol) at r.t. After 2
h the molar ratio of silane 2 to chlorosilane 8 was 36:64
(19F-NMR).
4.4. Reactions of tris(pentafluorophenyl)phenylsilane 2
with electrophiles
4.4.1. With aHF in dichloromethane
A sample of aHF (3 ml) was added to a stirred solu-
tion of silane 2 (710 mg, 1.2 mmol) in CH2Cl2–CD2Cl2
4.4.5. With AlCl3 (0.5 equi6alent) in CH2Cl2
A solution of silane 2 (344 mg, 0.57 mmol) in CH2Cl2

H.-J. Frohn et al. / Journal of Organometallic Chemistry 568 (1998) 233–240
239

240
H.-J. Frohn et al. / Journal of Organometallic Chemistry 568 (1998) 233–240
(2 ml) was added to a stirred suspension of AlCl3 (38
mg, 0.28 mmol) in CH2Cl2 (1 ml). After 35 min the
molar ratio of silane 2 to chlorosilane 8 was 13:87.
Complex 8 was the only polyfluoroaromatic product
after 55 min (19F-NMR).
(19F-NMR). The reaction mixture was evaporated to
dryness in a vacuum (50°C, 0.04 hPa) and the residue
was sublimed at 110°C (0.04 hPa) to give bromosilane
10 (543 mg, 83%), m.p. 108–110°C (lit. 83–85°C [9,13],
103–107°C [10]). Compound 10 was identified by 19F-
[14], 13C and 29Si-NMR spectra, IR and Raman spectra
(Tables 1–4).
4.4.6. With AlCl3 (1.2 equi6alent) in CH2Cl2
A solution of silane 2 (923 mg, 1.5 mmol) in CH2Cl2
(6 ml) was added to a stirred suspension of AlCl3 (246
mg, 1.8 mmol) in CH2Cl2 (1 ml). After 55 min chlorosi-
lane 8 was the only polyfluoroaromatic product. The
reaction mixture was evaporated to dryness in vacuum
(0.04 hPa) and after repeated sublimation at 92°C (0.04
hPa) silane 8 was obtained in 82% yield (700 mg), m.p.
93–95°C (lit. 78.5–79.5°C [9], 83–85°C [10], 83–86°C
[11], 91–93°C [12]). Compound 8 was identified by 13C,
19F [2] and 29Si-NMR spectra, IR and Raman spectra
(Tables 1 and 4).
4.4.10. With AlBr3 (4.1 equi6alent) in DBE
AlBr3 (38 mg, 0.14 mmol) dissolved in DBE (0.15 ml)
was added to a stirred solution of silane 2 (21 mg, 0.04
mmol) in DBE (0.1 ml) at r.t. After 10 min a quantita-
tive conversion of silane 2 into bromosilane 10 was
detected by 19F-NMR spectrometry.
4.5. Con6ersion of chlorotris(pentafluorophenyl)silane
into fluorotris(pentafluorophenyl)silane
A sample of chlorosilan 8 (32 mg, 0.06 mmol) was
dissolved in CD2Cl2 (0.3 ml). At −78°C 0.3 ml aHF
was added. The two-phase system was stirred and
warmed to r.t. After 90 min the CD2Cl2 phase was
separated. Compound 8 was quantitatively converted
into fluorosilane 5 (19F-NMR).
4.4.7. With AlCl3 (0.5 equi6alent) in CHCl3
A solution of silane 2 (361 mg, 0.60 mmol) in CHCl3
(1 ml) was added to a stirred suspension of AlCl3 (40
mg, 0.30 mmol) in CHCl3 (1 ml) at r.t. 19F-NMR
monitoring showed the following results.
Acknowledgements
Reaction time (min) Silane 2 (%) Silane 8 (%)
We gratefully acknowledge Volkswagen Stiftung and
Fonds der Chemischen Industrie for financial support.
35
55
240
78
51
—
22
49
100
References
[1] H.-J. Frohn, A. Lewin, V.V. Bardin, J. Organomet. Chem.
(submitted for publication).
4.4.8. With AlBr3 (0.5 equi6alent) in DBE
[2] H.-J. Frohn, M. Giesen, A. Klose, A. Lewin, V.V. Bardin, J.
Organomet. Chem. 506 (1996) 155.
[3] F.W.G. Fearon, H. Gilman, J. Organomet. Chem. 10 (1967) 409.
[4] M. Schmeißer, N. Wessal, M. Weidenbruch, Chem. Ber. 101
(1968) 1897.
Silane 2 (121 mg, 0.20 mmol) dissolved in DBE (1
ml) was added to a stirred solution of AlBr3 (26 mg,
0.10 mmol) in DBE (1 ml) at r.t. 19F-NMR monitoring
showed the following results.
[5] (a) D.H. O’Brien, T.J. Hairston, Organomet. Chem. Rev. 7A
(1971) 95. (b) D.H. O’Brien, C.M. Harbordt, J. Organomet.
Chem. 21 (1970) 321. (c) C.M. Harbordt, D.H. O’Brien, J.
Organomet. Chem. 111 (1976) 153. (d) D.D. Hopf, D.H.
O’Brien, J. Organomet. Chem. 111 (1976) 161.
[6] G. Ha¨gele, M. Weidenbruch, Chem. Ber. 105 (1972) 173.
[7] H.G. Horn, M. Probst, Monatsh. Chem. 126 (1995) 1169.
[8] A. Whittingham, A.W.P. Jarvie, J. Organomet. Chem. 13 (1968)
125.
[9] R.R. Schrieke, B.O. West, Aust. J. Chem. 22 (1969) 49.
[10] (a) G.S. Kalinina, B.I. Petrov, O.A. Kruglaya, N.S. Vyazankin,
Zh. Obshch. Khim. 42 (1972) 148. (b) G.S. Kalinina, B.I. Petrov,
O.A. Kruglaya, N.S. Vyazankin, Chem. Abstr. 77 (1972) 19767.
[11] M.F. Lappert, J. Lynch, J. Chem. Soc. Chem. Commun. (1968)
750.
Reaction time (min) Silane 2 (%) Silane 10 (%)
20
35
45
90
43
19
9
57
81
91
—
100
4.4.9. With AlBr3 (1.0 equi6alent) in DBE
A solution of silane 2 (647 mg, 1.2 mmol) in DBE (10
ml) was added to a stirred solution of AlBr3 (302 mg,
1.1 mmol) in DBE (1 ml) at r.t. After 25 min the molar
ratio of silane 2 to bromosilane 10 was 30:70 and after
40 min 10 was the only polyfluoroaromatic product
[12] E. Hengge, E. Starz, W. Strubert, Monatsh. Chem. 99 (1968)
1787.
[13] M. Weidenbruch, N. Wessal, Angew. Chem. Int. Ed. Engl. 9
(1970) 467.
[14] G. Ha¨gele, M. Weidenbruch, Chem. Ber. 106 (1973) 460.