Synthesis of 5,5,6,6,21,21,22,22-octamethyl-5,6,21,22-tetragerma[10.10] paracyclophane

Article abstract of DOI:10.1016/S0022-328X(03)00432-7

A [10,10]paracyclophane, 5,5,6,6,21,21,22,22-octamethyl-5,6,21,22- tetragerma[10.10]paracyclophane (4a), with two - R¹R²GeGeR¹R²- moieties in the center of two bridges, was prepared. An attempt to synthesize cyclophanes, 4b (R¹=Me; R²=Ph) and 4c (R¹=R²=Ph) was also made. The products were not analytically pure even after strenuous purification procedure to indicate that a double Wurtz coupling reaction is extremely difficult and necessarily accompanied by formation of polymeric by-products.

Full text of DOI:10.1016/S0022-328X(03)00432-7

Journal of Organometallic Chemistry 678 (2003) 61ꢁ67
/
www.elsevier.com/locate/jorganchem
Synthesis of 5,5,6,6,21,21,22,22-octamethyl-5,6,21,22-
tetragerma[10.10]paracyclophane
Yoshito Takeuchi *, Yoshitake Suzuki, Fumiyasu Ono, Kenji Manabe
Department of Chemistry, Faculty of Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka-shi 259-1293, Japan
Received 17 March 2003; received in revised form 26 April 2003; accepted 7 May 2003
Abstract
A
[10,10]paracyclophane, 5,5,6,6,21,21,22,22-octamethyl-5,6,21,22-tetragerma[10.10]paracyclophane (4a), with two
R1R2GeGeR1R2Ã moieties in the center of two bridges, was prepared. An attempt to synthesize cyclophanes, 4b (R1ꢀ
R2ꢀPh) and 4c (R1ꢀR2ꢀ
Ph) was also made. The products were not analytically pure even after strenuous purification procedure
Ã
/
/
/
Me;
/
/
/
to indicate that a double Wurtz coupling reaction is extremely difficult and necessarily accompanied by formation of polymeric by-
products.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Wurtz coupling; Cyclophanes; Organogermanium compound; ditopic host
1. Introduction
ma[2.2]paracyclophane (1), was reported by Sekiguchi et
al. [7]. This compound has a variety of interesting
feature: firstly, the synthesis itself is a challenge since a
Cyclophanes are one of the most interesting classes of
organic compounds from a structural point of view.
Since the first report of this class of compounds [1], a
large number of analogous compounds have been
reported [2]. One interesting aspect of cyclophanes is
their ability to act as hosts of a variety of chemical
species [3].
GeÃ
/
Ge bond is weaker than the corresponding CÃ
/C
bond, secondly, a comparison of structural parameters
such as bond lengths and bond angles with those of
silicon- and carbon-analogues, 1,1,2,2,9,9,10,10-octa-
methyl-1,2,9,10-tetrasila[2.2]paracyclophane (2), and
1,1,2,2,9,9,10,10-octamethyl[2.2]paracyclophane
(3),
and thirdly a similar comparison of the extent of pꢁp
/
Attempts have been made to improve the selectivity
or the ability of cyclophanes to act as hosts by
introducing side chains on the aromatic ring containing
heteroatoms. Further attempts have been made to
modify cyclophanes by introducing side chains of the
aromatic ring containing heteroatoms [4]. Attempts
have also been made to introduce heteroatoms into
appropriate positions on the bridge [5].
interaction between two parallel aromatic rings in these
cyclophanes [8].
We believed that enlarging the cavity of 1, which
consisted of two aromatic rings and two bridges made of
two germanium atoms, would allow the cavity to act as
a kind of heteroditopic host, i.e. a host which can
interact both a cationic and an anionic guest. Thus, this
molecule could capture and/or transport zwitterionic
species such as amino acids.
It had previously been established that germanium-
containing large rings can capture and transport halide
ions [9]. A possible cation-p interaction [10] between the
positive side of the guest and the aromatic rings allowed
the cyclophane with an enlarged cavity to act as a
heteroditopic host.
As a part of our extensive study of novel hosts
containing germanium [6], we were interested in cyclo-
phanes modified with a germanium-containing moiety.
The
first
germanium-containing
1,1,2,2,9,9,10,10-octamethyl-1,2,9,10-tetrager-
cyclophane,
* Corresponding author. Tel: ꢂ
/
81-463-59-4111; fax: ꢂ81-463-58-
/
With this in mind, we attempted to synthesize a
germacyclophane with a much larger cavity, viz.
9684.
E-mail address: yoshito@chem.kanagawa-u.ac.jp (Y. Takeuchi).
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00432-7

62
Y. Takeuchi et al. / Journal of Organometallic Chemistry 678 (2003) 61ꢁ67
/
5,5,6,6,21,21,22,22-octamethyl-5,6,21,22-tetrager-
ma[10.10]paracyclophane (4a). Preliminary MM2 calcu-
lations indicated that the size of the cavity of 2 was ca.
Route A is a ring closure by a Grignard reaction
which is probably the most frequently used pathway.
Thus, Sakurai et al. [11] synthesized the first cyclophane,
2, which has a bridge made of silicon, although in low
yield (1.6%). Routes B and C are intra- and intermole-
cular Wurtz coupling reactions, respectively. Routes A
9A (e.g. C11Ã
/
C30ꢀ
/
9.220 A) by ca. 12 A (e.g. Ge5Ã
/
Ge22ꢀ12.011 A), which was large enough to accom-
/
modate small amino acids.
2. Results and discussion
and B involve a digermane with a relatively weak GeÃ
Ge bond and thus there is always some danger of a GeÃ
/
/
Ge bond cleavage during the final ring closure [12].
Furthermore, the intermediate digermane is difficult to
synthesize.
Regarding route C, intermolecular cyclizations of this
type have an apparent statistical disadvantage since the
2.1. Strategy of synthesis
Several methods are possible for the synthesis of
macrocyclic organogermanium compounds as are de-
picted in Scheme 1.
Scheme 1. Possible synthetic procedure of tetragerma-macrocycles.

Y. Takeuchi et al. / Journal of Organometallic Chemistry 678 (2003) 61ꢁ
/67
63
intermolecular coupling necessarily competes with the
intramolecular cyclization. On the other hand, route C
use bromine to prepare bromogermane from phenylger-
mane [14]. This method is not, however, always applic-
able particularly when the compound contain a benzyl
has an advantage in that the weaker GeÃ/Ge bond is
(or ArCH2ꢃ) moiety that is susceptible to the Geꢁ
benzyl
/
formed at the final stage of the reaction and that the
synthesis of the precursor is relatively easy. Taking these
factors into consideration, we decided to employ the
route C for our attempt to synthesize 4a.
bond cleavage by bromine. Recently, it was found that
boron tribromide, BBr3, is an excellent reagent for
affecting phenylꢁ
/
bromine exchange without cleavage
bromine
of the Geꢁbenzyl bond [15]. The phenylꢁ
/
/
The necessary precursor of 4a, 1,4-bis(4-(bromodi-
methylgermyl)butyl)benzene (5a) was prepared as
shown in Scheme 2. It was thought that hydrogermyla-
tion of 1,4-bis-(3-butenyl)benzene, (8), with dimethyl-
phenylgermane (7a) is the method of choice to prepare
5a.
exchange with BBr3 took place smoothly to convert 6a
into 5a in 39.5% yield while bromination with Br2
resulted in poor yield.
In the final stage of the synthesis, a double Wurtz
coupling of 5a was attempted under various conditions.
The best result was obtained when the reaction was
carried out in toluene with Na in the presence of a
catalytic amount of tetraphenylethylene (TPE) [16].
After a series of strenuous purification procedures, a
small amount of 5,5,6,6,21,21,22,22-octamethyl-
5,6,21,22-tetragerma[10.10]paracyclophane (4a) was ob-
tained as a colorless oil. The yield of 4a was as low as
0.86%, which was not unexpected for a double Wurtz
coupling reaction. A large amount of uncharacterisable
polymeric materials was also obtained. Sakurai et al.
[11] reported that the yield of the cyclic product by the
Wurtz coupling reaction was improved in the presence
of 18-crown-6. The Wurtz reaction was attempted in this
manner, but 4a was not obtained.
We prepared 8 in 64% yield by a coupling reaction
between 3-bromopropene and 1,4-bis(chloromethyl)-
benzene, (9), in the presence of Mg. Linder et al. [13]
also prepared 8 from 1,4-bis(bromomethyl)benzene in
63% yield. Since the yields are comparable, the synthesis
described in this paper may be regarded as superior, as
the chloride precursor is considerably cheaper than the
1
bromide. It is noteworthy, however, that the H-NMR
data reported by Linder et al. was different from the
data presented in this paper. There is no ambiguity in
the assignment of 1H-NMR data presented in this paper,
since it is based on HÃ
/
H and HÃ
/
C COSY experiments.
The germanium compound dimethylphenylgermane
7a was prepared from tetrachlorogermane via tetraphe-
nylgermane, dibromodiphenylgermane, dimethyldiphe-
nylgermane,
bromodimethylphenylgermane
and
2.2. Characterization of 4a
dimethylphenylgermane, other germanium compounds
were prepared in a similar manner.
Hydrogermylation of 8 with 7a gave 1,4-bis(4-(di-
methylphenylgermyl)butyl)benzene (6a) in 49% yield. It
is a standard method of organogermanium chemistry to
The most persuasive evidence for the formation of 4a
was given by EI-MS measurements. The expected
molecular ion peak was observed in the EI-MS spectrum
at m/e 786, and, furthermore, peaks around the
Scheme 2. Synthesis of 4.

64
Y. Takeuchi et al. / Journal of Organometallic Chemistry 678 (2003) 61ꢁ67
/
calculated pattern for species containing four germa-
nium atoms (b). The agreement between (a) and (b) is
reasonable, indicating that 4a does contain four germa-
nium atoms.
Other evidence for the structure of 4a included the
1H- and 13C-NMR spectra of 8, 9, 6a, 5a and 4a. The
relevant NMR data are given in Tables 1 and 2. For ease
of comparison the numbering of 8, 9, 6a and 5a for
NMR data follows that of 4a.
The connectivity was established by means of HÃ
and HÃC COSY experiments. It is evident that the ÃCÃ
CÃCÃCÃ moiety is present in all these compounds.
/H
/
/
/
/
/
/
2.3. Attempts to synthesize other germacyclophanes
Based on the MS and NMR spectral data, it was
confirmed that the Wurtz coupling of dibromogermane,
5a, gave the desired cyclic tetragermane 4a in low yield.
However, experimental evidence [17] suggested that
organogermanium hosts show poor ability to capture
and transport anions unless the alkyl substituent on the
germanium atom is replaced by the halogen.
Fig. 1. Characteristic mass spectral pattern of compounds containing
four germanium atoms.
With this in mind, we attempted to prepare 5,6,21,22-
tetramethyl-5,6,21,22-tetraphenyl-5,6,21,22-tetrager-
ma[10.10]paracyclophane (4b) and 5,5,6,6,21,21,22,22-
octaphenyl-5,6,21,22-tetragerma[10.10]paracyclophane
molecular ion peak form a characteristic pattern that is
associated with a species containing four germanium
atoms. Fig. 1 shows the observed pattern (a) and
Table 1
1H-NMR spectral data of 8, 6a, 6b, 5a, 5b, 5c, 4a and 4b in CDCl3
a
8
H1
H2
H3
H4
2.68 (t, vicJꢀ
2.39ꢁ2.33 (m)
5.86 (transJꢀ17.1 Hz; cisJꢀ
4.97cis (cisJꢀ10.3 Hz; gemJꢀ
5.04trans (transJꢀ17.1 Hz; gemJꢀ
/
7.8 Hz)
/
/
/
10.3 Hz; vicJꢀ
1.8 Hz; allylJꢀ
1.8 Hz; allylJꢀ
/
0.0 Hz)
1.7 Hz)
1.7 Hz)
/
/
/
/
/
/
H31
7.11
GeMe
ꢁ/
8 b
6a c
2.54 (t, vicJꢀ
6b
2.53 (t, vicJꢀ
5a
2.60 (t, vicJꢀ
7.8 Hz)
H1
H2
2.95 (t, vicJꢀ
/7.8 Hz)
/7.8 Hz)
/7.8 Hz)
/
2.68ꢁ
6.22ꢁ
5.36ꢁ
7.38
/
2.60 (m)
6.08 (m)
5.24
1.64ꢁ
1.48ꢁ
0.99ꢁ
7.03
0.35
/
1.58 (m)
1.41 (m)
0.96
1.66ꢁ
1.54ꢁ
1.29ꢁ
6.99
0.61
/
1.60 (m)
1.48 (m)
1.25
1.70ꢁ
1.59ꢁ
1.22ꢁ
7.08
0.67
/
1.64 (m)
1.53 (m)
1.19
H3
/
/
/
/
H4
/
/
/
/
H31
GeMe
GePh
ꢁ/
7.46ꢁ
/
7.32
7.46ꢁ
/
7.31
ꢁ/
5b
2.58 (t, vicJꢀ
5c
4a
4b
H1
H2
H3
H4
H31
/7.8 Hz)
2.56
2.53 (t, vicJꢀ
1.59ꢁ1.53 (m)
1.37ꢁ
0.81ꢁ
/
7.6 Hz)
2.52 (t)
1.70ꢁ1.58 (m)
1.70ꢁ
1.53ꢁ
7.04
/
1.80ꢁ
1.80ꢁ
1.80ꢁ
7.00
/
1.63 (m)
1.63 (m)
1.63
/
1.62ꢁ
1.45ꢁ
1.20ꢁ
/
1.53 (m)
1.34 (m)
0.99
/1.58 (m)
/
/
1.30 (m)
/
/1.50
/
/0.78
/
7.05
7.05
GeMe 1.00
ꢁ/
0.13
0.39
GePh 7.58ꢁ/7.40
7.59ꢁ/7.33
ꢁ/
7.27ꢁ/7.23
a
This study.
Ref. [13].
b
c
Aromatic ring bonded to germanium; 7.46ꢁ7.32 (m, 10H).
/

Y. Takeuchi et al. / Journal of Organometallic Chemistry 678 (2003) 61ꢁ
/67
65
Table 2
13C-NMR spectral data of 8, 6a, 6b, 5a, 5b, 5c, 4a and 4b in CDCl3
a
No.
8
8 b
6a
6b
5a
35.0
5b
34.9
5c
4a
35.0
4b
34.8
C1
C2
35.0
35.5
35.6
35.2
35.0
35.0
34.3
36.2
138.7
114.8
139.8
129.3
35.1
24.8
35.0
24.7
34.3
23.6
21.5
139.6
128.3
3.4
34.2
24.1
34.8
25.5
34.7
25.4
C3
C4
138.2
114.8
139.3
128.3
24.3
19.4
15.9
139.8
128.1
14.5
139.5
128.2
20.7
16.4
139.7
128.3
15.7
139.7
127.9
C30
C31
GeMe
GePh
137.7
128.4
2.2
135.6
128.4
ꢁ
/
ꢁ
/
ꢃ
/
3.6
ꢃ
/
5.2
ꢁ
/
ꢃ
/
3.8
ꢃ5.0
/
127.8
128.1
133.1
141.8
128.0
128.5
133.9
139.8
128.3
130.0
132.7
139.6
128.1
130.1
133.5
139.4
127.8
128.3
133.8
141.1
a
This study.
Ref. [13].
b
(4c), since both 4b and 4c may be converted to the
corresponding bromide by a phenylꢁbromine exchange
reaction with BBr3.
3. Experimental
/
1H-NMR spectra were determined on a JEOL EX-400
spectrometer operating at 400 MHz, and the chemical
shifts were reported in d (ppm) with respect to Me4Si.
13C-NMR spectra were determined on a JEOL EX-400
spectrometer operating at 100 MHz and the chemical
shifts were reported in d (ppm) with respect to Me4Si.
Mass spectra were recorded on JEOL NS-MP09 mass
spectrometer operating in the EI mode at 70 eV or on a
PerSeptive Biosytemes DE MALDI-TOF mass spectro-
meter, Voyager Elite XL. Elemental analysis was carried
In principle 4b and 4c could be prepared in a similar
manner as the preparation of 4a, as shown in Scheme 2,
if appropriate precursors 5b and 5c were synthesized.
5b was prepared by two methods. The first method,
(method A), was the bromination of 1,4-bis(4-(methyl-
diphenylgermyl)butyl)benzene (6b). 6b was obtained by
the hydrogermylation of 8 with methyldiphenylgermane
(7b). The other method, (method B), was the hydro-
germination of 8 with bromomethylphenylgermane (7b?)
(Scheme 2).
out with a PerkinꢁElmer Series II CHNS/O Elemental
/
Analyzer or by the Microanalytical Laboratory, Depart-
ment of Chemistry, The Graduate School of Science,
The University of Tokyo.
A Wurtz coupling reaction of 5b afforded a small
1
amount of 4b, as was verified by H- and 13C-NMR
spectroscopy. Because of the inevitable contamination
by various by-products, an analytically pure sample of
4b was not obtained. It is interesting to notice that the
obtained sample was a mixture of stereoisomers as was
indicated by the NMR spectra.
3.1. 1,4-Bis(3-butenyl)benzene (8)
To a solution of 2.4 g (0.1 mol) of magnesium
turnings in Et2O (75 ml) was added dropwise 12.2 g
(0.1 mol) of 3-bromopropene in Et2O (75 ml). The
mixture was refluxed for 1 h at room temperature. A
solution containing 5.2 g (0.03 mol) of 1,4-bis(chlor-
omethyl)benzene (9) in THF (50 ml) was added and the
mixture was refluxed for 2 h, which was hydrolyzed by
water (15 ml) and aq. NH4Cl (25 ml). The ether layer
was separated, dried and the solvent was evaporated.
The crude product was distilled under reduced pressure
(9 mmHg, 110 8C) to yield a colorless liquid of 8 (3.5 g,
0.02 mol, 64%).
The precursor 5c was prepared via the hydrogermyla-
tion of 8 with bromodiphenylgermane (7c?). A Wurtz
coupling reaction of 5c also afforded a small amount of
1
4c, as was verified by H- and 13C-NMR spectroscopy.
Here again, due to the contamination by various by-
products, separation of an analytically pure sample of 4c
was unsuccessful. Preparations of the necessary organo-
germanium species 7b, 7b? and 7c? are carried out by the
methods described in the literature.
These results indicated that the synthesis of pure
cyclophanes with germanium atom(s) in the bridge was
extremely difficult, and was impractical as a method of
synthesizing more than trace amounts of the respective
host molecule. It appeared that the synthesis of cyclo-
phanes with side arms containing a germanium moiety
on the aromatic ring would be more feasible. Further
study along these lines is in progress in our laboratory.
The preparations of 7a [17], 7b [17] and 7c? [18] were
previously described in the literature.
3.2. Bromomethylphenylgermane (7b?)
A mixture of methylphenylgermane [18] (1.07 g, 6.4
mmol) and NBS (1.14 g, 6.4 mmol) in hexane (16 ml)

66
Y. Takeuchi et al. / Journal of Organometallic Chemistry 678 (2003) 61ꢁ67
/
mmol, 0.86%). EIMS; m/z: 786 ([Mꢂ]: C36H Ge72-
70
64
was refluxed for 4 h. The solvent was evaporated after
the remaining NBS was filtered off. The crude product
was distilled under reduced pressure (20 mmHg, 130 8C)
to yield a colorless liquid of 7b? (1.02 g, 4.2 mmol, 65%).
Anal. Calc. for C7H9GeBr: C, 34.22; H, 3.69. Found: C,
Ge74Ge2, 786.19).
3.6. 1,4-Bis(4-(methyldiphenylgermyl)butyl)benzene
(6b)
1
34.43; H, 3.69. H-NMR (CDCl3, 400 MHz): d 1.16
(3H, d, Jꢀ
7.42ꢁ7.62 (m, 5H, GeÃ
MHz): d 1.8 (GeÃCH3), 128.6, 130.5, 133.0, 135.4 (GeÃ
Ph).
/
2.3 Hz, GeÃ
/
CH3), 5.85 (m, 1H, GeÃ
/
H),
A mixture of 8 (1.86 g, 10 mmol) and methyldiphe-
nylgermane (7b) (5.34 g, 20 mmol) was stirred at 100 8C
for 1 h. The mixture was further stirred for 7 h after the
/
/
Ph). 13C-NMR (CDCl3, 100
/
/
catalytic amount of H2PtCl6×
/
6H2O was added. The
mixture was extracted by Et2O and the solvent was
evaporated. The crude product was distilled under
reduced pressure to remove volatile material. The
resulting solution was purified by means of column
chromatography (silica gel, CHCl3) to yield a pale
yellow oil of 1,4-bis(4-(methyldiphenylgermyl)bu-
tyl)benzene (6b) (4.70 g, 7.0 mmol, 70%). Anal. Calc.
for C40H46Ge2: C, 71.49; H, 6.90. Found: C, 71.20; H,
6.80.
3.3. 1,4-Bis(4-(dimethylphenylgermyl)butyl)benzene
(6a)
A mixture of 7a (2.63 g, 15 mmol) and 8 (1.25 g, 6.45
mmol) was stirred at 100 8C for 1 h. The mixture was
further stirred for 7 h after the catalytic amount of
H2PtCl6×/6H2O was added. The mixture was extracted
by Et2O and the solvent was evaporated. The crude
product was distilled under reduced pressure (9 mmHg,
120 8C) to remove volatile material. The resulting
solution was purified by GPC with CHCl3 to yield a
colorless oil of 6a (1.40 g, 2.6 mmol, 40%). Anal. Calc.
for C30H42Ge2: C, 65.77; H, 7.73. Found: C, 65.64; H,
7.74.
3.7. 1,4-Bis(4-
(bromomethylphenylgermyl)butyl)benzene(5b)
3.7.1. Method A
To a refluxing solution of 6b (4.7 g, 7.0 mmol) in CCl4
(50 ml) was added dropwise Br2 (3.2 g, 20 mmol) in CCl4
(10 ml) in 2 h with refluxing and stirring, which was
continued for 5 h. The solvent was evaporated and the
residue was purified by GPC with CHCl3 to yield a pale
brown oil of 5b (0.52 g, 0.8 mmol, 11%). Anal. Calc. for
C28H36Br2Ge2: C, 49.63; H, 5.35. Found: C, 49.45; H,
5.21.
3.4. 1,4-Bis(4-(bromodimethylgermyl)butyl)benzene
(5a)
To a solution of 6a (5.87 g, 11 mmol) in 65 ml of
CH2Cl2 was added dropwise boron tribromide (21 ml (1
M in CH2Cl2), 21 mmol). The mixture was stirred for 1
h below 0 8C and additional 6 h at room temperature.
The remaining boron tribromide was inactivated by 20
ml of water and the mixture was extracted by CH2Cl2.
The solvent was evaporated and the residue was purified
by GPC with CHCl3 to yield a pale yellow oil of 5a (2.54
g, 4.6 mmol, 42%), DE MALDI-TOFMS; m/z: 574.23,
576.22, 577.23, 578.23, 579.24, 580.24, 581.23, 582.23,
583.22, 584.22. (C18H32Ge2Br2, 576.92).
3.7.2. Method B
A mixture of 8 (1.86 g, 10.0 mmol) and 7b (5.89 g, 24.0
mmol) was stirred at 100 8C for 1 h. The mixture was
further stirred for 11 h after the catalytic amount of
H2PtCl6×
/
6H2O was added. The mixture was extracted
by Et2O and the solvent was evaporated. The crude
product was distilled under reduced pressure to remove
volatile material. The resulting solution was purified by
GPC with CHCl3 to yield a colorless oil of 5b (2.73 g, 4.0
mmol, 63%).
3.5. 5,5,6,6,21,21,22,22-octamethyl-5,6,21,22-
tetragerma[10.10]Paracyclophane (4a)
A mixture of Na (3.17 g; 140 mmol) and toluene (190
ml) was refluxed for 3 h in the atmosphere of argon. The
mixture was cooled to room temperature, to which TPE
(0.229 g; 0.69 mmol) was added and stirred for 2 h. A
toluene solution (100 ml) of 5 (3.77 g; 6.8 mmol) was
added dropwise in 19 h with stirring. The stirring was
continued for 276 h at room temperature. The remain-
ing Na was filtered off, and the polymeric by-produces
was removed by means of column chromatography
3.8. Attempted preparation of 5,6,21,22-tetramethyl-
5,6,21,22-tetraphenyl-5,6,21,22-
tetragerma[10.10]paracyclophane (4b)
(a) In THF: A mixture of Na (1.20 g, 50 mmol) and
TPE (0.1 g, 0.3 mmol) in THF (80 ml) was stirred for 1 h
at room temperature in the atmosphere of nitrogen. A
THF solution (40 ml) of precursor 5b (2.16 g; 2.08
mmol) was added dropwise in 19 h with stirring. The
stirring was continued for 67 h at room temperature.
The remaining Na was filtered off, and the polymeric
by-produces were removed by means of column chro-
(silica gel; CH2Cl2:Et2Oꢀ1:1). The eluate was evapo-
/
rated and the remaining material was purified by means
of GPC to afford colorless liquid of 4a (46 mg, 0.058

Y. Takeuchi et al. / Journal of Organometallic Chemistry 678 (2003) 61ꢁ
/67
67
matography (silica gel, hexaneÃ
/
CH2Cl2Ã
/
Et2Oꢀ
/
4:1:0ꢁ
/
Acknowledgements
0:1:1). The eluate was evaporated and the remaining
material was purified by means of GPC to afford
colorless liquid of 4b (10 mg, 0.01 mmol) in 0.46% yield.
(b) In toluene: The reaction was carried out in
toluene. The result was much the same with the reaction
in THF. The yield of 4b was 10 mg (0.46%).
This work was partly supported by The High-tech
Research Center Project from The Ministry of Educa-
tion, Culture, Sports, Science and Technology.
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(silica gel, CH2Cl2Ã
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