Structural characterization of bismuth(III) and antimony(III) chlorotriflates: Key intermediates in catalytic Friedel-Crafts transformations

Article abstract of DOI:10.1002/ejic.200400281

Chlorotriflates of antimony and bismuth Cl_nM(OSO ₂CF₃)_3-n (n = 1 or 2) are believed to be metallic intermediates of major importance in Friedel-Crafts reactions that use Bi(OSO₂CF₃)₃, Sb(OSO₂CF ₃)₃, the systems BiCl₃/CF₃SO ₂OH or SbCl₃/CF₃SO₂OH as catalysts. Unknown until now, the compounds ClBi(OSO₂CF₃)₂ (1) and Cl₂Sb(OSO₂CF₃) (2) have been synthesized by reaction of MCl₃ (M = Bi, Sb) with triflic acid. After crystallization from THF, 1 and 2 were investigated in the solid state by X-ray crystallography. Their use as catalysts in benzoylation of toluene, acylation of m-xylene, and sulfonylation of toluene led to conclusive results, thus giving weight to their key role as intermediates in Friedel-Crafts reactions. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200400281

SHORT COMMUNICATION
Structural Characterization of Bismuth(III) and Antimony(III) Chlorotriflates:
Key Intermediates in Catalytic Friedel؊Crafts Transformations
[a]
[a]
[a]
[a]
´
`
Stephane Mazieres,* Christophe Le Roux,* Magali Peyronneau, Heinz Gornitzka,
and Nicolas Roques[b]
Keywords: Bismuth / Antimony / Triflate / X-ray diffraction / FriedelϪCrafts reactions
Chlorotriflates of antimony and bismuth ClnM(OSO2CF3)3−n
(n = 1 or 2) are believed to be metallic intermediates of major
importance in Friedel−Crafts reactions that use Bi(-
OSO2CF3)3, Sb(OSO2CF3)3, the systems BiCl3/CF3SO2OH or
ated in the solid state by X-ray crystallography. Their use as
catalysts in benzoylation of toluene, acylation of m-xylene,
and sulfonylation of toluene led to conclusive results, thus
giving weight to their key role as intermediates in
SbCl3/CF3SO2OH as catalysts. Unknown until now, the com- Friedel−Crafts reactions.
pounds ClBi(OSO2CF3)2 (1) and Cl2Sb(OSO2CF3) (2) have
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
been synthesized by reaction of MCl3 (M = Bi, Sb) with triflic Germany, 2004)
acid. After crystallization from THF, 1 and 2 were investig-
Introduction
aromatic compounds that use BiIII and SbIII triflate based
catalysts, and their direct use as catalysts in these reactions.
The number of bismuth compounds structurally charac-
terized by X-ray crystallographic methods has greatly in-
creased over the past decades, showing the growing interest
in these structures.[1] For our topic, we will focus on BiIII
and also SbIII halides, which are found to be useful in a
number of applications;[2] of major interest is the use of
bismuth or antimony derivatives in catalysis. For
FriedelϪCrafts acylations, reactions which are mainly de-
veloped on an industrial scale using at least a stoichiometric
amount of a Lewis acid such as AlCl3 or TiCl4,[3] BiCl3 and
recently bismuth() trifluoromethanesulfonate (triflate) ap-
peared to be among the best catalysts for the acylation of
aromatic compounds.[4Ϫ6] In 1988, Olah had already
showed the catalytic activity of boron(), aluminium()
and gallium() triflates in alkylation and acylation reac-
tions with 50mol % metallic triflates.[7] Later various met-
allic salts of triflic acid such as rare earth[8Ϫ11] and anti-
mony() triflates[12,13] were reported. The catalytic ef-
ficiency of bismuth() triflate was confirmed, especially in
the sulfonylation of arenes,[14] a reaction that belongs to the
most important group of aromatic electrophilic substi-
tutions.[3,4] In the present work we describe the preparation
of mixed chlorotriflates of bismuth and antimony, which
are involved in the process of acylation and sulfonylation of
Results and Discussion
In the mechanism for both acylation and sulfonylation
reactions,[6,8Ϫ13] it clearly appears that the main electro-
philic agent is a mixed anhydride such as trifluoromethane-
sulfonic carboxylic- or trifluoromethanesulfonic arenesul-
fonic anhydrides (RCOϪOϪSO2CF3 or ArSO2ϪOϪ
SO2CF3), which are known to be strong acylating or sulfon-
ylating reagents.[15] The formation of mixed anhydrides re-
sults from ligand exchanges at the metal (Scheme 1, path a).
[a]
´ ´
´
Laboratoire Heterochimie Fondamentale et Appliquee, UMR
Scheme 1
5069,
118 route de Narbonne, 31062 Toulouse Cedex 04, France
Fax: (internat.) ϩ33-5-61-558204
E-mail: mazieres@chimie.ups-tlse.fr
Following the formation of the anhydride and its reaction
with the aromatic compound (Scheme 1, path b), the
[b]
Rhodia Organique Fine, Centre de Recherche de Lyon,
`
85 rue des freres Perret, 69192 Saint-Fons, France
Eur. J. Inorg. Chem. 2004, 2823Ϫ2826
DOI: 10.1002/ejic.200400281
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2823

`
S. Mazieres, C. Le Roux, M. Peyronneau, H. Gornitzka, N. Roques
SHORT COMMUNICATION
mechanism involves the reaction of the metal() chloride
with triflic acid (CF3SO2OH), leading to the mixed metallic
intermediate (Scheme 1, path c). The metal acts as a shuttle
for the triflic acid. Such types of mixed compounds have
been previously related with fluorosulfonic acid and result
from the reaction of BiCl3 and fluorosulfonic acid; however,
they have been poorly characterized.[16] In fact, it appears
that these metallic intermediates play a key role with regard
to the entire mechanism. Until now their existence was
postulated,[8Ϫ13] but no real proof was given for their exact
structure. One goal was to isolate such mixed metallic chlo-
rotriflates. The reaction between the metal() chloride and
an excess of triflic acid did not lead to metal tristriflate[17]
but to compounds 1 and 2 in appreciable yields (Scheme 2).
Figure 1. Molecular structure of 1·4THF in the solid state; selected
˚
distances (A) and angles (°): BiϪCl1 2.465(4), BiϪO1 2.386(11),
BiϪO4 2.613(13), BiϪO5 2.879(15), Cl1ϪBiϪO8 156.4(3),
Cl1ϪBiϪO4 80.4(3), Cl1ϪBiϪO5 131.2(3)
Scheme 2
With bismuth, the only product is the chlorobistriflate 1,
while antimony leads exclusively to the dichlorotriflate 2. It
appears that the trifluoromethanesulfonate ligand exhibits
a strong electronic effect, which modifies the strength of the
remaining MϪCl bonds. Only one ligand exchange oc-
curred with antimony, while two with bismuth. 1 is stable
up to 250 °C,[18] and this thermostability can indicate the
strength of the bonds involved.
In the synthesis of these compounds, the use of toluene
as solvent proved to be crucial; while BiCl3 is mainly soluble
in π-donor solvents, the solvation of SbCl3 with donor sol-
vents can be greatly compromised by strong complexation,
which inhibits further reactivity. Indeed, these complexes
known as Mentshutkin complexes[19,20] are responsible for
the inefficiency of SbCl3 in the catalysis of Friedel- Crafts
reactions of activated aromatics.[21] Compounds 1 and 2 are
crystalline, and their THF adducts were obtained from a
THF/pentane solution. Single crystals suitable for an X-ray
structure determination were grown at Ϫ20 °C.
Figure 2. Molecular structure of 2·2THF in the solid state; selected
˚
distances (A) and angles (°): SbϪCl1 3.3628(8), SbϪCl2 2.3629(8),
SbϪO1A 2.876(3), SbϪO2 2.911(3), SbϪO3 3.084(3),
Cl1ϪSbϪCl2 92.75(3), Cl1ϪSbϪO1A 82.57(5), Cl1ϪSbϪO2
158.83(5), Cl1ϪSbϪO3 153.55(5)
The structure of the THF adduct of 2 may be best de-
scribed as a distorted octahedron in which one SO2 group
The structure analysis of the THF complexes in the solid occupies an axial position (Figure 2). This structure is as-
state shows a monomeric form in the case of the bismuth sociated into dimeric units through two weak coordinations
compound and a dimeric form for the antimony compound by two triflate ligands of different units thereby bridging
(Figure 1 and Figure 2). In both compounds, primary the two Sb centers. The antimony atoms are thus seven-co-
˚
˚
MϪCl bonds (BiϪCl1 2.465 A and SbϪCl1 2.362 A, ordinate.
˚
SbϪCl2 2.363 A) appear shorter than MϪCl bond lengths
These newly synthesized and fully characterized mixed
in MCl3 or MCl3 with oxygen donor interactions;[22] this is chlorotriflates are believed to be the mixed metallic inter-
in accordance with the observed stability of these MϪCl mediates involved in the mechanism, but nothing is known
bonds. For the THF adduct of 1, the chlorine atom, in good about the real mixture in solution during the process. By
approximation, occupies the axial position of a distorted changing the stoichiometry of the reactants, triflic acid and
pentagonal bipyramid (Figure 1).
metal chloride, it was not possible to isolate or even charac-
The two triflate ligands are connected to the bismuth terize Cl2Bi(OSO2CF3) or ClSb(OSO2CF3)2 in solution;
˚
atom through oxygen atoms, BiϪO1 2.386 A and BiϪO4 this is probably due to their lack of stability. In both cases
˚
2.613 A, the latter bond length is longer, probably due to we only obtained products 1 and 2.
˚
another weak interaction (BiϪO5 2.879 A) which destroys
Finally, experiments were performed in which 1 and 2
the ideal geometry of the bipyramid.
were used as catalysts in benzoylation, acylation and sulfon-
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 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2004, 2823Ϫ2826

Structural Characterization of Bismuth(III) and Antimony(III) Chlorotriflates
Table 1. Catalytic activity of 1 and 2 in benzoylation, acylation and sulfonylation reactions
SHORT COMMUNICATION
Entry
Reaction
Catalyst
Mol (%)
Yield (%)
o/m/p
1
2
3
4
5
6
7
8
benzoylation of toluene
acylation of m-xylene
sulfonylation of toluene
Bi(OSO2CF3)3
10
10
10
30
5
5/10
5
95[6]
60
22/2/76
21/2/77
1
Sb(OSO2CF3)3
77[13]
74
2
1
99
39/6/55
39/6/55
40/6/54
38/6/56
BiCl3/CF3SO2OH
2
SbCl3/CF3SO2OH
95[23]
99
5/5
99
Ϫ Cl]ϩ, 393 (8) [MϪClϪOSO2CF3]ϩ. C2BiClF6O6S2 (542.57):
calcd. C 4.43, Cl 6.53, F 21.01, S 11.82; found C 4.43, Cl 6.05, F
21.09, S 11.87.
ylation of aromatic compounds (Table 1). In these catalytic
systems, the ratio of triflate ligand, which leads to the mixed
anhydride (Scheme 1, path a) is the main factor that influ-
ences the efficiency of the catalytic process.
For the benzoylation of toluene (Table 1, entries 1 and
2), the use of ClBi(OSO2CF3)2 1 at 10 mol % led to 60%
yield, and gave a similar result to that obtained with Bi-
(OSO2CF3)3.[6] The yield for 1 is lower, but 1 only has two
triflate ligands instead of three as is the case for Bi-
(OSO2CF3)3.
Cl2Sb(OSO2CF3) 2 provided identical results (74% yield)
for the acylation of m-xylene (Table 1, entries 3 and 4) with
n-pentCOCl to that obtained by the catalytic system de-
scribed by Kobayashi.[13] For the sulfonylation of toluene
(Table 1, entries 5 to 8), where the mixed species play a key
role, a 99% yield of tolylphenylsulfones was obtained with
1 [similar to that obtained by the catalytic system BiCl3/
CF3SO2OH (5 mol %/10 mol %)],[23] and a 99% yield was
also obtained with 2 [the same as that obtained by the cata-
lytic system SbCl3/CF3SO2OH (5 mol %/5 mol %)]. In ad-
dition, all the selectivities proved to be similar.
Cl2Sb(OSO2CF3) (2): The same procedure was used as for 1, and
the reaction mixture was heated at 110 °C for 5 h. 2 (4.6 g, 61%
yield) was recrystallized from a THF/pentane solution at Ϫ20 °C.
M.p. 61 °C(decomp.). 13C NMR (100.6 MHz, [D6]DMSO, TMS):
1
δ ϭ 120.5 (q, JC,F ϭ 322 Hz) ppm. 19F NMR (376.4 MHz,
[D6]DMSO, CF3COOH): δ ϭ 1.5 ppm. IR (CH3CN): ν˜ ϭ 588, 515
(SϪO in OSO2CF3), 353 (SbϪCl) cmϪ1. RAMAN: ν˜ ϭ 356
(SbϪCl) cmϪ1. MS (DCI/CH4): m/z ϭ 343 (16) [MH]ϩ, 193 (19)
[M Ϫ OSO2CF3]ϩ. It was not possible to obtain satisfactory
elemental data.
Benzoylation of Toluene: PhCOCl (1.97 g, 14 mmol), toluene
(2.58 g, 28 mmol), and catalyst (14 mmol) were added together in
a 20 mL flask. After 5 h at 110 °C, dichloromethane (20 mL) was
added, and the organic layer was extracted with a 6% aqueous HCl
(2 ϫ 10 mL), dried (MgSO4), and concentrated. After purification
by flash chromatography (silica, pentane/ether, 9:1), methylbenzo-
phenones were isolated. The use of 10 mol % of Bi(OSO2CF3)3 led
to 95% yield (o/m/p, 22/2/76)[6] and 10 mol % of 1 led to 60% yield
(o/m/p, 21/2/77).
With regard to the yields and the selectivities, the results
for the catalytic activity of 1 and 2 are conclusive, and these
mixed metallic chlorotriflates are strongly believed to be the
key intermediates in these FriedelϪCrafts reactions.
Acylation of m-Xylene: Following the procedure described by Ko-
bayashi,[13] n-pentCOCl (0.20 g, 1.49 mmol), m-xylene (4.69 g,
44.2 mmol), and Sb(OSO2CF3)3 (83 mg, 1.46 mmol) were added to-
gether, and the mixture was heated at 100 °C. After 24 hours, 1-
(2,4-dimethylphenyl)hexan-1-one was obtained in 77% yield. With
the same procedure, the use of 30 mol % of 2 led to 74% yield.
Experimental Section
Sulfonylation of Toluene: (a) 1 as the catalyst: following the pro-
cedure described in ref. 23, 99% yield (o/m/p, 39/6/55) was obtained
using 5 mol % of 1, the system BiCl3/CF3SO2OH (5 mol %/10
mol %) provided 95% yield (o/m/p, 39/6/55). (b) 2 as the catalyst:
following the typical procedure, PhSO2Cl (3.25 g, 18.4 mmol), tolu-
ene (3.39 g, 36.8 mmol) and catalyst (5 mol %, 0.92 mmol) were
heated at 110 °C for 12 hours. Dichloromethane (40 mL) was then
added, and the organic layer was extracted with aqueous HCl
(40 mL of a 2  solution), neutralized by saturated NaHCO3 solu-
tion (40 mL), and analyzed by GC with tetradecane as external
standard.
Syntheses of 1 and 2 were performed under a dry and oxygen-free
argon atmosphere. Solvents were dried by appropriate methods.
Melting points were determined in capillaries sealed under argon
and are uncorrected.
ClBi(OSO2CF3)2 (1): Triflic acid (10.5 g, 70.0 mmol) was added
dropwise at 0 °C to a solution of bismuth() chloride (9.1 g,
28.9 mmol) in toluene (60 mL). The reaction mixture was then
stirred for 10 min at room temperature and heated to 110 °C for
90 min. After cooling, the mixture was filtered, and the residue
was washed twice with dichloromethane (100 mL). Solvents were
X-ray Structure Determination for the THF Adducts of 1 and 2:
removed in vacuo, and 1 was obtained as a white powder (14.0 g, Crystal data were collected at low temperatures [T ϭ 193(2) K]
89% yield) and was recrystallized from a THF/pentane solution at
using an oil-coated shock-cooled crystal on a Bruker-AXS CCD
1000 diffractometer with Mo-Kα radiation (λ ϭ 0.71073 A). Semi-
Ϫ20 °C. M.p. Ͼ250 °C. 13C NMR (100.6 MHz, [D6]DMSO, TMS):
˚
1
δ ϭ 125.9 (q, JC,F ϭ 322 Hz) ppm. 19F NMR (376.4 MHz, empirical absorption corrections were employed.[24] The structures
CD3CN, CF3COOH): δ ϭ 0.9 ppm. IR (CH3CN): ν˜ ϭ 635, 585,
515 (SϪO in OSO2CF3), 310 (BiϪCl) cmϪ1. RAMAN: ν˜ ϭ 307 the least-squares method on F2.[26] Experimental details are given
(BiϪCl) cmϪ1. MS (DCI/CH4): m/z ϭ 543 (4) [MH]ϩ, 507 (5) [M
in Table 2.
were solved by direct methods (SHELXS-97)[25] and refined using
Eur. J. Inorg. Chem. 2004, 2823Ϫ2826
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`
S. Mazieres, C. Le Roux, M. Peyronneau, H. Gornitzka, N. Roques
SHORT COMMUNICATION
Table 2. Crystal Data for 1·4THF and 2·2THF
1·4THF
2·2THF
Empirical formula
Molecular mass
Crystal system
Space group
C18H32BiClF6O10S2
830.99
monoclinic
P21/c
17.018(2)
18.394(2)
8.960(1)
C9H16Cl2F3O5SSb
485.93
triclinic
¯
P1
˚
a (A)
8.299(2)
9.515(2)
11.395(2)
105.791(2)
96.575(2)
106.136(2)
814.0(3)
2
˚
b (A)
˚
c (A)
α (°)
β (°)
γ (°)
93.232(2)
3
˚
V (A )
2800.3(5)
4
6.626
0.1 ϫ 0.2 ϫ 0.6
0.377188
24516
3985
0.0870
343
0.0646
0.1631
4.498
Z
Abs. coeff. (mmϪ1
Crystal size (mm)
)
2.196
0.3 ϫ 0.5 ϫ 0.6
0.702541
7073
4060
0.0269
190
0.0330
0.0906
2.098
Max. and min. transmission
Reflections collected
Independent reflections
Rint
No. of parameters
R1 [I Ͼ 2σ(I)]
wR2 (all data)
Largest diff. peak (e A
CCDC
Ϫ1
˚
)
199266
199267
[11]
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Eur. J. Inorg. Chem. 2004, 2823Ϫ2826