Siloxa-bridged-cyclophanes featuring benzene, thiophene and pyridine units

Article abstract of DOI:10.1039/b211045h

Two octamethyldisiloxa-bridged [3.3]cyclophanes (1 and 2) and a dodecamethyltrissiloxa-bridged [3.3.3]-cage compound (3) were prepared by hydrolysis of the chlorosilyl monomers. This general route was also employed for the preparation of two octamethyldisiloxa-bridged [3.3]heterophanes featuring two thiophene (14) or pyridine (17) moities.

Full text of DOI:10.1039/b211045h

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Siloxa-bridged-cyclophanes featuring benzene, thiophene and
pyridine unitsy
´
Audrey Moores, Christian Defieber, Nicolas Mezailles, Nicole Maigrot, Louis Ricard and
Pascal Le Floch*
´ ´ ´ ´
´
Laboratoire Heteroelements et Coordination (CNRS UMR 7653), Departement de Chimie,
Ecole Polytechnique, 91128, Palaiseau cedex, France. E-mail: lefloch@poly.polytechnique.fr;
Fax: +33 1 69 33 39 90; Tel: +33 1 69 33 45 70
Received (in Montpellier, France) 8th November 2002, Accepted 5th February 2003
First published as an Advance Article on the web 14th May 2003
Two octamethyldisiloxa-bridged [3.3]cyclophanes (1 and 2) and a dodecamethyltrissiloxa-bridged [3.3.3]-cage
compound (3) were prepared by hydrolysis of the chlorosilyl monomers. This general route was also employed
for the preparation of two octamethyldisiloxa-bridged [3.3]heterophanes featuring two thiophene (14) or
pyridine (17) moities.
Introduction
Since their discovery in 1949 by Brown and Farthing,1 cyclo-
phanes and their functional derivatives have been intensely stu-
died. Their attractive geometry has been exploited in many
different fields such as polymer science, biology, molecular
recognition and organometallic chemistry.2 Furthermore, it
Scheme 1 Reduction of a diphosphacyclophane.
has long been known that small strained cyclophanes that
allow p-stacking are well-suited materials for the study of elec-
tron transfer (ET) processes between aromatic structures.3 In
this regard, in 2001 we reported on the use of [3.3](2,6)phos-
phininophanes as a model for the ET process between
phosphinine rings.4 In that study we showed that the mono-
electronic reduction of the siloxa-bridged [3.3](2,6)phosphinino-
phane I resulted in the formation of a monoanionic species II
featuring a one-electron phosphorus-phosphorus single bond
(Scheme 1). This finding prompted us to enlarge this study
to similar structures incorporating other types of aromatic
rings. Herein, we report on the syntheses of siloxa-bridged
cyclo- and heterophanes incorporating either benzene, thio-
phene or pyridine units.
tris(chlorodimethylsilyl)benzene.9 The first step, which consists
in a reductive self-coupling promoted by Na, furnished
1,2,9,10,17,18-hexasila[2.2.2](1,3,5)cyclophane featuring three
Si–Si bonds with an extremely low yield of 0.22%. In a second
step, oxidation of this cage-like phane with Et3NO yielded
macrocycle 3 in a nearly quantitative yield .
Various new synthetic approaches to cyclophanes 1–3 can
be proposed. Among different possibilities, we deliberately
favoured that which relies on coupling of the readily available
Si–Cl derivatives with water. The general scheme of this
approach is presented in Scheme 3. The first step consists in
synthesis of the substituted 1,3-bis-, 1,4-bis- or 1,3,5-tris(ethoxy-
dimethylsilyl)benzene derivatives 7, 8 and 9, obtained through
a Grignard reaction from the corresponding bromoarene com-
pounds 4, 5 and 6. The second step allows conversion of 7–9
into the respective chlorosilyl derivatives 10–12 using acetyl
chloride. Compounds 10 and 11 have already been prepared
by Tilley et al.10 using the same sequence, and the 1,3,5-tris-
(chlorodimethylsilyl)benzene derivative 12 was obtained by
Plenio by chlorination of the corresponding Si–H compound
in CCl4 .11 Though the tris(ethoxydimethylsilyl) derivative 9
could not be obtained in pure form (90% purity), we found
our approach much more convenient since it avoids the use
Results and discussion
Syntheses and X-ray analysis
A search of electronic databases indicated that three cyclo-
phanes featuring two or three tetramethyldisiloxane groups
as linkers were already known (shown in Scheme 2). The meta-
cyclophane 1 was synthesized in 1999 by reacting 1,3-bis(di-
methylhydroxysilyl)benzene with DMAP (overall yield of
21% from the 1,3-dibromobenzene).5,6 The isomeric para deri-
vative 2 was prepared in 1964 by thermal cracking of the cor-
responding poly(tetramethyl-p-silphenylsiloxane) polymer in
the presence of NaOH at 300 ꢀC and obtained with an overall
yield of 2.6% from the 1,4-dibromobenzene. Unfortunately, no
NMR or structural data for 2 are available.7,8 Finally, the cage
compound 3 was prepared by a two-step sequence from 1,3,5-
y Electronic supplementary information (ESI) available: crystal data
and X-ray structure of [3.3](1,4)cyclophane (2). See http://www.
rsc.org/suppdata/nj/b2/b211045h/
Scheme 2 Three siloxa-bridged cyclophanes.
994
New J. Chem., 2003, 27, 994–999
DOI: 10.1039/b211045h
This journal is # The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2003

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Scheme 3 Synthetic strategy.
of chlorine. Compound 12 was obtained after reaction of 9
with acetyl chloride with a nearly quantitative yield.
Syntheses of the respective macrocycles 1–3 (Scheme 4) were
conducted in THF at room temperature in the presence of
water. As expected, we found that dilution and the amount
of water used played a crucial role in the cyclization process
and many experiments were carried out to determine the best
experimental conditions. In all cases, the use of high concen-
trations resulted exclusively in the formation of polymers
whose compositions were not determined. Using a rather high
dilution (between 7 and 11.4 mmol Lꢁ1) and an excess of water
(5 equiv. for 1 and 2 and 15 equiv. for 3) the expected macro-
cycles were formed in modest to good yields. Nevertheless, in
all cases these yields were found to be higher than those pre-
viously reported. Cyclophane 1 was obtained with a yield of
65% (36% from 1,3-dibromobenzene). On the other hand,
the paracyclophane 2 was isolated with an overall yield of
28% (17.3% from the 1,4-dibromobenzene). This compound
was fully characterized by NMR techniques (1H and 13C), ele-
mental analyses and its formulation was definitely ascertained
by X-ray crystallography (given in the Electronic supplemen-
tary information, ESI).
Fig. 1 ORTEP view of one molecule of 3. The numbering is arbitrary
and different from that used in the 13C NMR spectrum. All hydrogen
atoms have been deliberately omitted for clarity.
defined by the rings (Y between 5ꢀ and 7ꢀ). Apart from this,
the structure of 3 does not deserve special comments and bond
lengths within the ring fall in the usual range (see Table 1).
These first encouraging results prompted us to investigate
the synthesis of similar siloxa-bridged heterophanes incorpor-
ating thiophene and pyridine units. The strategy employed
slightly differs from that depicted above in that the synthesis
of 2,5-bis(chlorodimethylsilyl)thiophene was not realized using
the same Grignard-mediated approach. Two routes have
already been reported for the synthesis of 13: an electrochemi-
cal method that involves the coupling13 between 2,5-dibro-
mothiophene and Me2SiCl2 and a palladium-mediated route
that relies on the coupling of the 2,5-bis(dimethylsilyl)thio-
phene with CCl4 .14 We found that the trapping reaction of
the readily available 2,5-dilithiothiophene with Me2SiCl2 is
a more straightforward approach.
In compound 2, the two benzene rings do not lie exactly
above one another, as was also reported for [3,3]paracyclo-
phane.12 The inter-ring distance is 3.607 A. The most signifi-
˚
cant structural feature concerns the Si–C bonds, which
deviate from the planes defined by the two rings (Y between
7ꢀ and 9ꢀ). This distorsion, observed for [3.3]paracyclophane
too, shows that a substantial cyclic strain exists in 2.
Having this compound in hand, synthesis of the thiopheno-
phane derivative 14 could be achieved (Scheme 4), albeit in a
very low yield that could not be improved despite many
attempts. This new cyclophane was successfully characterized
by NMR techniques, elemental analyzes and its formulation
was further confirmed by an X-ray crystallographic study
(selected parameters given in Table 2). In the solid state, 14
adopts an anti conformation (Fig. 2), the two thiophene rings
defining two roughly parallel planes that are separated by
The most significant synthetic improvement was obtained in
the synthesis of cyclophane 3, which was isolated with an over-
all yield of 15%. This macrocycle was also fully identified by
NMR spectroscopy, by comparison with reported data, ele-
mental analyses and its X-ray structure was recorded (shown
9
˚
in Fig. 1). At 3.503 A, the inter-ring distance is slighly shorter
than that in the paracyclophane 2. As noted above for 2,
though the two aromatic rings are roughly planar the three
Si–C(ring) bonds significantly deviate from the mean planes
˚
3.15 A. As noted above in the structures of 2 and 3, a cyclic
strain is also visible in 14 since the Si–C bonds are not coplanar
with the two ring planes (Y between 5ꢀ and 9ꢀ).
Preparation of the siloxa-bridged pyridinophane 17 also
constituted an interesting goal. 2,6-Bis(bromodimethylsilyl)-
pyridinium bromide (15) was selected as precursor. In 1992,
Plenio had devised a very convenient route to this salt, which
relies on trapping of 2,6-dimagnesiopyridine with Me2SiHCl,
˚
Table 1 Selected bond lengths (A) and angles (deg) for compound 3
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(1)–C(6)
Si(1)–C(1)
Si(1)–O(1)
1.404(2)
1.399(2)
1.400(2)
1.393(2)
1.403(2)
1.399(2)
1.877(1)
1.633(1)
Si(1)–O(1)–Si(2)
O(1)–Si(1)–C(1)
C(2)–C(1)–Si(1)
C(6)–C(1)–Si(1)
C(6)–C(1)–C(2)
C(3)–C(2)–C(1)
148.68(8)
109.47(6)
120.9(1)
121.9(1)
117.1(1)
122.8(1)
Scheme 4 Synthesis of cyclophanes 1, 2 and 3 and [3,3]thiopheno-
phane 14.
New J. Chem., 2003, 27, 994–999
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˚
Table 2 Selected bond lengths (A) and angles (deg) for compound 14
S(1)–C(1)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–S(1)
Si(1)–C(4)
Si(2)0–C(1)
Si(1)–O(1)
Si(2)–O(1)
1.723(2)
1.371(2)
1.417(2)
1.376(2)
1.724(2)
1.862(2)
1.866(2)
1.636(1)
1.644(1)
C(1)–S(1)–C(4)
C(2)–C(1)–S(1)
O(1)–Si(1)–C(4)
Si(1)–O(1)–Si(2)
C(1)–C(2)–C(3)
C(4)–C(3)–C(2)
C(3)–C(4)–S(1)
C(3)–C(4)–Si(1)
S(1)–C(4)–Si(1)
94.42(8)
108.9(1)
109.28(6)
144.48(7)
114.2(1)
113.6(1)
108.9(1)
126.9(1)
123.9(1)
followed by a Si–H to Si–Br exchange using bromine.11 Hydro-
lysis of 15 was carried out in THF despite the low solubility
of the salt and the desired bispyridinium macrocycle 16 was
isolated in very good yield (80%).
This new pyridinophane, which was found to be insoluble in
most common organic solvents and only sparingly soluble in
MeCN, was fully characterized by NMR techniques and ele-
mental analyses. Though the two acidic protons could not be
detected in the 1H NMR spectrum of 16, the formation of
the salt was clearly apparent from the downfield shifts of the
H4 protons, which appear as a triplet at d(CD3CN) ¼ 8.48
ppm with 3J(H–H) ¼ 7.8 Hz. However, a final proof of the
structure was given by X-ray crystallography. An ORTEP
view of one molecule of 16 is presented in Fig. 3 and selected
geometrical parameters in Table 3. In the solid state, 16 adopts
a syn conformation, as shown in Scheme 5, but there is no
steric hindrance between the two pyridinium protons, which
Fig. 3 ORTEP view of one molecule of 16. The numbering is arbi-
trary and different from that used in the 13C NMR spectrum. All
hydrogen atoms, except those bound to nitrogen atoms, as well as
one of the two bromide counteranions, have been deliberately omitted
for clarity.
dent on the length of the connecting chains and on the substi-
tution pattern of the cyclophane. For instance, [2.2]- and
[3.4]cyclophane and derivatives adopt the anti conformation
whereas [3.3]metacyclophane adopts the syn conformation.15
Shinmyozu et al. and Semmelhack et al. showed that dynamic
NMR experiments could give precious conformational infor-
mation for this type of macrocycles.15,16 First, they proved that
the barrier to aromatic nucleus inversion between syn and anti
is very low (no freezing of the process down to 180 K).
Secondly, when the syn conformation is favoured, bridge-iso-
merization between syn(chair-chair), syn(chair-boat) and syn-
(boat-boat) becomes observable (Scheme 6). A 48.5 kJ molꢁ1
barrier between conformers syn(chair-chair) and syn(chair-
boat) was observed in the case of d4-[3.3]metacyclophane.15
Subsequent studies in which methylene moieties of the
bridge were replaced by NH, S or Se and/or pyridine was sub-
stituted by benzene led to the same type of results, namely, fast
inversion of the preferred syn geometry and slower bridge
isomerization.16,17 It was thus interesting to study the variable
temperature NMR for the metacyclophanes reported in this
article, especially in the case of pyridinophane 17 whose con-
formation was unknown. As noted above, the crystal structure
for cyclophanes 1 and 14 revealed a preferred anti conforma-
tion. Dynamic 1H NMR studies on these two species con-
firmed that this geometry is also preferred in solution.
Indeed, we could not detect the freezing of the ring inversion
down to 180 K. The same experiment was conducted on com-
pound 17 and the spectra can be seen in Fig. 4. The CH3
groups are equivalent at room temperature and down to 208
K. They split into two singlets (one for the axial group and
˚
lie 2.584 A apart.
Conversion of 16 into the neutral pyridinophane 17 proved
to be problematic and many combinations of bases and sol-
vents were tested without success. Finally we found that direct
abstraction of the two acidic protons with MeLi as a base in
hexane at 0 ꢀC proved to be the most convenient way to gen-
erate 17 (Scheme 5). Using this simple approach, 17 could be
isolated pure by simple filtration of the LiBr salt with a very
good yield (78%). Compound 17, which turned out to be
slightly moisture sensitive, was successfully characterized by
means of NMR spectroscopy and elemental analyses. Unfortu-
nately, no structural information could be gained and all our
attempts to crystallize 17 have failed so far.
1
Dynamic H NMR study
[3.3]Metacyclophanes can adopt two conformations, syn and
anti, and the preference for one of the two is strongly depen-
˚
Table 3 Selected bond lengths (A) and angles (deg) for compound 16
N(1)–C(1)
N(1)–C(5)
N(1)–H(1N)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
Si(1)–O(1)
Si(1)–C(1)
1.353(4)
1.351(4)
.82(4)
C(5)–N(1)–C(1)
N(1)–C(1)–C(2)
N(1)–C(1)– Si(1)
C(2)–C(1)–Si(1)
C(3)–C(2)–C(1)
C(2)–C(3)–C(4)
C(3)–C(4)–C(5)
N(1)–C(5)–C(4)
126.7(3)
116.0(3)
120.2(3)
123.8(3)
120.7(4)
120.8(4)
119.7(4)
116.0(4)
1.382(5)
1.368(6)
1.376(6)
1.398(5)
1.634(2)
1.901(4)
Fig. 2 ORTEP view of one molecule of 14. The numbering is arbi-
trary and different from that used in the 13C NMR spectrum. All
hydrogen atoms have been deliberately omitted for clarity.
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Scheme 5 Synthesis of the pyridinium-based cyclophane 16 and
[3,3]pyridinophane 17.
Fig. 4 Variable temperature NMR spectra (in ppm) of compound 17
in CD2Cl2 .
one for the equatorial) upon further lowering of the tem-
perature. This clearly indicates that what we observe is a syn-
(chair-chair) to syn(chair-boat) to syn(boat-boat) bridge
interconversion. From the NMR data we could extract an
analyses were performed by the ‘‘Service d’Analyse du
CNRS’’ at Gif sur Yvette, France.
activation barrier for this interconversion of 43.2 kJ molꢁ1 18
,
Syntheses
which is consistent with what was previously observed for
such a process.17
1,1,3,3,10,10,12,12-Octamethylsil-2,11-oxa[3.3](1,3)cyclophane
(1). 1,3-Bis(chlorodimethylsilyl)benzene (10; 1.5 g, 5.7 mmol)
was dissolved in THF (200 mL) and water (0.5 mL, 27.8 mmol)
was added in one portion at room temperature. The resulting
solution was stirred for 3 days and the solvent was evaporated.
The white solid obtained was then successively washed with
ether (2 ꢂ 10 mL) and hexane (2 ꢂ 20 mL). After drying, cyclo-
phane 1 was obtained as a white powder. Yield: 0.77 g (65%);
mp 208 ꢀC. For spectroscopic characterizations, see ref. 5.
In conclusion, we have developed a new route for the synth-
esis of three siloxa-bridged cyclophanes relying on the direct
coupling of Si–Cl derivatives with water. In all cases, this
new procedure proved to be much more convenient than those
reported so far, especially for preparation of the cage com-
pound 3. Though the yield still remains modest, this improve-
ment should now allow the host–guest properties of this new
edifice to be explored. Additionally, this new synthetic
approach was employed to prepare two new siloxa-bridged
[3.3]heterophanes incorporating thiophene or pyridine units.
1,1,3,3,10,10,12,12-Cctamethylsilyl-2,11-oxa[3.3](1,4)cyclophane
(2). 1,4-Bis(chlorodimethylsilyl)benzene (11; 0.90 g, 3.40 mmol)
was dissolved in THF (500 mL) and water (0.310 mL, 17.2
mmol) was added in one portion at room temperature. The
resulting solution was stirred for 3 days and the solvent was
evaporated. After washing with ether (20 mL) and hexanes
(20 mL), macrocycle 2 was isolated as a white powder. Yield
Experimental
General
1
0.20 g (28%); mp 208 ꢀC. H NMR (CDCl3): d 0.37 (24H, s,
All reactions were routinely performed under an inert atmo-
sphere of nitrogen by using Schlenk and glove-box techniques
and dry deoxygenated solvents. Dry THF and hexanes were
obtained by distillation from Na/benzophenone and dry
CH2Cl2 and CDCl3 from P2O5 . Nuclear magnetic resonance
spectra were recorded on a Bruker Avance 300 spectrometer
operating at 300 MHz for 1H, 75.5 MHz for 13C. Solvent peaks
SiMe2), 7.00 (s, 8H, H of C6H4); 13C {1H} NMR (CDCl3): d
0.5 (s, SiMe2), 132.3 (s, CH of C6H4), 138.8 (s, Cipso of
C6H4). MS (m/z, %): 417 (M, 100). Anal. calcd for
C20H32O2Si4 : C, 57.63; H, 7.74; found: C, 57.34; H, 7.39%.
1,1,3,3,10,10,12,12,19,19,21,21-Dodecamethylsilyl-2,11,20-oxa-
[3.3.3](1,3,5)cyclophane (3). 1,3,5-Tris(chlorodimethylsilyl)ben-
zene (12; 5.00 g, 14 mmol) was dissolved in THF (2 L) and
water (4 mL, 222 mmol) was added in one portion at room
temperature. The resulting solution was stirred for 5 days
and then evaporated to dryness. The orange oil obtained was
subjected to chromatography on silica gel using hexane as sol-
vent. After having eluted a first fraction that mainly contained
polymeric materials and traces of 3, the macrocycle was
obtained in a second fraction (Rf ¼ 0.13, SiO2 , hexane). 3 was
recovered as a yellow powder after evaporation of solvents.
Yield: 585 mg (overall 15%). For spectroscopic characteriza-
tions, see ref. 9.
are used as internal reference relative to Me4Si for 1H and 13
C
chemical shifts (ppm) and coupling constants are expressed in
Hertz. The following abbreviations are used: b; broad, singlet;
d, doublet; t, triplet; m, multiplet. Mass spectra were obtained
at 70 eV with an HP 5989B spectrometer coupled to an HP
5980 chromatograph by the direct inlet method. Elemental
1,3,5-Tris(ethoxydimethylsilyl)benzene (9). Bis(ethoxy)dimethyl-
silane (40.8 mL, 238 mmol), magnesium (6.9 g, 287.5 mmol)
and THF (200 mL) were placed into a 500 mL flask under
nitrogen. The resulting mixture was heated at 50 ꢀC and a
solution of tribromobenzene (6; 25.0 g, 79.4 mmol) in THF
(70 mL) was added dropwise (duration: 3 h). The solution
was then heated for 25 h under reflux. After cooling to room
temperature, the solution was filtered. After evaporation of
the solvent, the brown oil obtained was extracted twice with
hexane (2 ꢂ 30 mL) to yield an orange oil. This oil did not
Scheme 6 The two dynamical processes in [3,3]metacyclophanes.
New J. Chem., 2003, 27, 994–999
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Table 4 X-Ray data and structural refinement details for compounds
3, 14 and 16
contain exclusively 9 and traces of 1,3-bis(ethoxydimethyl-
1
silyl)benzene were detected in the H and 13C NMR spectrum
(between 5 to 8%). Unfortunately, further attempts to purify
9 by distillation led to a partial decomposition of the com-
pound. Yield: 19 g (62%). 1H NMR (CDCl3): d 0.41 (s, 18
H, SiMe2), 1.21 [t, 9 H, 3J(H–H) ¼ 6.98, Me], 3.71 [q, 6 H,
3J(H–H) ¼ 6.98, OCH2], 7.85 (s, 3 H, H of C6H3). 13C {1H}
NMR (CDCl3): d ꢁ1.6 (s, SiMe2), 18.5 (s, Me of OEt), 58.8
(s, OCH2), 136.3 (s, C1,3,5 of C6H3), 139.8 (s, CH of C6H3).
MS: m/z (%): 384 (2) [M ꢁ 1], 368 (100) [M ꢁ CH3], 324 (20)
[M ꢁ CH3 ꢁ OC2H5], 281 (18) [M ꢁ Si(CH3)2OC2H5], 267
Compound
3
14
16
Molecular formula
C
24H42O3Si6 C16H28O2S2Si4 C18H32Br2N2O2Si4ꢃC4H8O
FW
T/K
547.12
150.0(10)
0.71069
428.86
150.0(10)
0.71069
652.74
150.0(10)
0.71069
Orthorhombic
Pnma
˚
l/A
Crystal system
Monoclinic
P21/c
Triclinic
Pꢁ1
Space group
˚
a/A
˚
17.0411(3)
12.0953(2)
16.9900(2)
90.00
6.7411(2)
8.2744(2)
11.44040(10)
72.939(2)
23.444(5)
12.699(5)
10.521(5)
90.00
b/A
˚
c/A
(40)
[M ꢁ Si(CH3)2OC2H5 ꢁ CH3],
177
(60)
[M ꢁ 2
a/deg
b/deg
g/deg
Si(CH3)2OC2H5].
114.0700(10) 72.984(2)
90.00
90.00
90.00
3197.43(9)
4
73.3800(10)
569.18(2)
1
1,3,5-Tris(chlorodimethylsilyl)benzene (12). Compound 9 (5 g,
13 mmol) and acetyl chloride (10 mL), which was used both as
reagent and solvent, were heated at 80 ꢀC for 15 h. After
evaporation of the excess acetyl chloride and ethyl acetate,
compound 12 was recovered as a brownish oil. After disti-
llation, 12 was recovered as a colourless oil (purity 95%). Yield:
4.62 g ( > 99%). For spectroscopic charcaterizations, see ref. 11.
3
˚
U/A
3132(2)
4
Z
m(MoKa)/cmꢁ1
Reflect. measured
Indep. reflect.
Reflections used
Rint
0.283
15394
9244
0.452
4544
2.765
6591
3296
2782
3592
2757
7331
0.0212
0.0388
0.1104
0.0277
0.0346
0.0967
0.0249
0.0455
0.1388
a
R1 [I > 2s(i)]
b
wR2 [I > 2s(I)]
2,5-Bis(chlorodimethylsilyl)thiophene(13). The 2,5-bis(chloro-
dimethylsilyl)thienyl derivative was obtained through the
reaction of the dilithium salt with Me2SiCl2 in excess. A solu-
tion of butyllithium (1.6 M in hexane; 40 mmol, 25 mL) was
added dropwise at room temperature to a solution of thio-
phene (1.64 g, 20 mmol) and TMEDA (4.64 g, 40 mmol).
The resulting mixture was then heated under reflux for 90
min. After cooling to ꢁ20 ꢀC, Me2SiCl2 (51.84 g, 400 mmol)
was added and the resulting solution was heated under reflux
for 2 h. After evaporation of the excess Me2SiCl2 , the orange
residue obtained was distilled. Compound 13 was recovered as
a colourless oil. Yield: 3.77 g (70%). For spectroscopic charac-
terizations, see ref. 14.
a
b
2
R1 ¼ S|F0| ꢁ |Fc|/S|F0|. wR2 ¼ (SwkF0| ꢁ |Fck /Sw|F0|2)1/2
.
dichloromethane was added and the resulting solution was fil-
tered on celite. The pink powder obtained was successively
washed with hexane (5 mL) and Et2O (2 ꢂ 5 mL), after eva-
poration of the solvent. After drying, pyridinophane 17 was
recovered as a slightly coloured pink solid. Yield: 0.17 g
(78%); mp > 260 ꢀC. 1H NMR (CDCl3): d 0.61 (s, 24H,
3
SiMe2), 7.4 [d, 4 H, J (H–H) ¼ 7.6 Hz, H3 of C5H3N], 7.65
[t, 2 H, J (H–H) ¼ 7.8 Hz, H4 of C5H3N]. 13C {1H} NMR
3
(CDCl3): d 0.6 (s, SiMe2), 127.7 (s, C3 of C5H3N), 132.8 (s,
C4 of C5H3N), 171.23 (s, C2 of C5H3N). MS (m/z, %): 429
(M, 100). Anal. calcd for C18H30N2O2Si4 : C, 51.62; H, 7.22;
found: C, 51.50; H, 7.29%.
1,1,3,3,9,9,11,11-Octamethylsilyl-2,10-oxa[3.3](2,5)thiopheno-
phane (14). 13 (4 g, 15 mmol) was dissolved in THF (1.5 L) and
water (1.35 g, 65 mmol) was added in one portion at room
temperature. The resulting solution was stirred for 1 week.
After evaporation of the solvent, the orange residue obtained
was crystallized in methanol (10 mL) at room temperature.
After filtration, compound 14 was recovered as a white solid.
Yield: 0.20 g (7%); mp 175 ꢀC. 1H (CDCl3): d 0.36 (s, 24H,
4 ꢂ SiMe2), 7.26 (s, 4H, H of C4H2S). 13C {1H} NMR
(CDCl3): d 0.3 (s, SiMe2), 134.1 (s, CH of C4H2S), 158.1 (s,
Cipso of C4H2S). MS (m/z, %): 429 (M, 100). Anal. calcd for
C16H28O2S2Si4 : C, 44.81; H, 6.58; found: C, 44.70; H, 6.63%.
X-Ray structural determination
Single crystals of compound 3 suitable for X-ray crystallogra-
phy were obtained by recrystallization from hexane. Single
crystals of compound 14 were obtained by diffusing methanol
into a toluene solution of the compound. Single crystals of
compound 16 were obtained by diffusing THF into a benzoni-
trile solution of the compound. Data were collected on a Non-
ius Kappa CCD diffractometer using an Mo Ka (l ¼ 0.71073
˚
A) X-ray source and a graphite monochromator. Experimental
Precursor 16. The 2,6-bis(bromodimethylsilyl)pyridine
hydrobromide salt (15; 5 g, 11.5 mmol) was dissolved in
THF (700 mL) and water (0.4 g, 22.2 mmol) was added in
one portion at room temperature. After 5 days of stirring,
macrocycle 16 was collected by filtration and washed with
ether (20 mL). After drying, 16 was recovered as a white solid.
details are described in Table 4. The crystal structures were
solved using SIR 9719 and SHELXL-97.20 ORTEP drawings
were made using ORTEP III for Windows.21
CCDC reference numbers 203273–203276. See http://www.
rsc.org/suppdata/nj/b2/b211045h/ for crystallographic data
in CIF or other electronic format.
1
Yield: 2.66 g (80%); mp > 260 ꢀC. H NMR (CD3CN): d 0.88
(s, 24H, SiMe2), 8.19 [dd, 4 H, 3J(H–H) ¼ 7.8 Hz, 4J(H–H) ¼
1.3 Hz, H3 of C5H3N], 8.48 [t, 2 H, 3J(H–H) ¼ 7.8, H4 of
C5H3N]. 13C {1H} NMR (CD3CN): d 0.0 (s, SiMe2), 134.0
(s, C3 of C5H3N), 143.5 (s, C4 of C5H3N), 160.3 (s, C2 of
C5H3N). MS (m/z, %): 419 (100) [M ꢁ 1], 282 (75)
[M ꢁ C5H5NSiMe2]. Anal. calcd for C18H32Br2N2O2Si4 : C,
37.24; H, 5.56; found: C, 37.30; H, 5.65%.
Acknowledgements
The authors thank the CNRS and the Ecole Polytechnique for
the financial support of this work.
References
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999