Use of the extended one-pot (EOP) procedure for the preparation of ethynylated thiophene derivatives and related palladium-ethynylthiophene organometallic oligomers

Article abstract of DOI:10.1021/om010312q

The palladium-catalyzed coupling (Stille coupling) of 2,5-diiodothiophene (1) with tributyl(ethynyl)tin forms the 2,5-bis(ethynyl)thiophene (3) and tributyltin iodide as side product (step 1). Addition of lithium diisopropylamide (LDA) to this mixture causes deprotonation of the bis-alkyne and its reaction with the tin halide present in the medium to form the 2,5-bis[(tributyltin)ethynyl]thiophene (4) (step 2). To this mixture was subsequently added trans-dichlorobis(tri-n-butylphosphine)palladium (5), and the corresponding trans-bis(tri-n-butylphosphine)-μ-[2,5-bis(ethynyl)thiophene]palladium oligomer (6) was obtained (step 3). Alternatively, the same route can be directed toward the formation of ethynylated thiophene oligomers: after formation of the 2,5-bis[(tributyltin)ethynyl]thiophene (4) (step 2), addition of 2-iodothiophene (8) or 2-iodo-5-(trimethylsilyl)thiophene (10) led to the formation of 2,5-bis(2-thienylethynyl)thiophene (9) (step 3) and [2-trimethylsilyl(ethynyl)thiophene]-2,5-bisethynylthiophene (11) (step 3′), respectively. The latter can be easily desilylated to obtain the [2-(ethynyl)thiophene]-2,5-bisethynylthiophene (13), while treatment of 9 with sec-BuLi/I₂ formed the 2,5-[2,2′-(5,5′-diiodo)bisthienyl]bisethynylthiophene (12). Through a sequence of transformations similar to steps 1-3, the oligo(iodo)ethynylthiophene 12 has been connected to the bis(tri-n-butylphosphine)palladium moiety to form the trans-bis(tri-n-butylphosphine)-μ-[2,2′-bis(ethynyl)thiophene]-2,5-bise thynylthiophene]palladium polymer (15). To compare the advantages of the above extended one-pot (EOP) procedures over classical routes, polymers 6 and 15 were also prepared by the copper-catalyzed reaction of trans-dichlorobis(tri-n-butylphosphine)palladium (5) with 2,5-bis(ethynyl)thiophene (3) and [2-(ethynyl)thiophene]-2,5-bisethynylthiophene (13).

Full text of DOI:10.1021/om010312q

4
360
Organometallics 2001, 20, 4360-4368
Use of th e Exten d ed On e-P ot (EOP ) P r oced u r e for th e
P r ep a r a tion of Eth yn yla ted Th iop h en e Der iva tives a n d
Rela ted P a lla d iu m -Eth yn ylth iop h en e Or ga n om eta llic
Oligom er s
,
†
‡
,‡,⊥
Patrizia Altamura,* Giorgio Giardina, Claudio Lo Sterzo,*
Maria Vittoria Russo§
and
Dipartimento di Chimica, Universit a` di Salerno, Via S. Allende, 84081 Baronissi, Italy, and
Centro CNR di Studio sui Meccanismi di Reazione and Dipartimento di Chimica,
Universit a` “La Sapienza”, Box 34-Roma 62, Piazzale Aldo Moro, 5, 00185 Roma, Italy
Received April 17, 2001
The palladium-catalyzed coupling (Stille coupling) of 2,5-diiodothiophene (1) with tributyl-
ethynyl)tin forms the 2,5-bis(ethynyl)thiophene (3) and tributyltin iodide as side product
step 1). Addition of lithium diisopropylamide (LDA) to this mixture causes deprotonation
(
(
of the bis-alkyne and its reaction with the tin halide present in the medium to form the
,5-bis[(tributyltin)ethynyl]thiophene (4) (step 2). To this mixture was subsequently added
2
trans-dichlorobis(tri-n-butylphosphine)palladium (5), and the corresponding trans-bis(tri-
n-butylphosphine)-µ-[2,5-bis(ethynyl)thiophene]palladium oligomer (6) was obtained (step
3
). Alternatively, the same route can be directed toward the formation of ethynylated
thiophene oligomers: after formation of the 2,5-bis[(tributyltin)ethynyl]thiophene (4) (step
), addition of 2-iodothiophene (8) or 2-iodo-5-(trimethylsilyl)thiophene (10) led to the
2
formation of 2,5-bis(2-thienylethynyl)thiophene (9) (step 3) and [2-trimethylsilyl(ethynyl)-
thiophene]-2,5-bisethynylthiophene (11) (step 3′), respectively. The latter can be easily
desilylated to obtain the [2-(ethynyl)thiophene]-2,5-bisethynylthiophene (13), while treatment
of 9 with sec-BuLi/I
Through a sequence of transformations similar to steps 1-3, the oligo(iodo)ethynylthiophene
2 has been connected to the bis(tri-n-butylphosphine)palladium moiety to form the trans-
2
formed the 2,5-[2,2′-(5,5′-diiodo)bisthienyl]bisethynylthiophene (12).
1
bis(tri-n-butylphosphine)-µ-[2,2′-bis(ethynyl)thiophene]-2,5-bisethynylthiophene]palladi-
um polymer (15). To compare the advantages of the above extended one-pot (EOP) procedures
over classical routes, polymers 6 and 15 were also prepared by the copper-catalyzed reaction
of trans-dichlorobis(tri-n-butylphosphine)palladium (5) with 2,5-bis(ethynyl)thiophene (3)
and [2-(ethynyl)thiophene]-2,5-bisethynylthiophene (13).
In tr od u ction
Organometallic polymers having a backbone com-
posed of conjugated polyynes and transition metals are
attracting increasing attention in material science
potential applications, efficient routes to organometallic
conjugated polymers are required.
Preparation of polymeric materials of type [-CtC-
M-CtC-Ar-]n (M ) Ni, Pd, Pt) was first developed
5
by Hagihara by means of a dehydrohalogenation reac-
1
2
because they may exhibit liquid crystalline, magnetic,
tion using Cu-catalyzed coupling of terminal alkynes
3
4
optical, and electronic properties. These technologi-
cally important characteristics arise from the unique
electronic delocalization in these materials along the
entire polymer backbone, including metal atoms and
bridging acetylide spacers. Because of these important
(
H-CtC-Ar-CtC-H) and transition metal halides
(L2MCl2). Although this procedure is quite efficient and
has also allowed the preparation of polymers containing
5
c
mixed metals into the polymer backbone, this synthetic
route suffers from a major drawback of preparing and
handling pure terminal alkynes, which are quite reac-
tive materials, occasionally manifesting uncontrollable
*
Corresponding authors.
Universit a` di Salerno.
Centro CNR di Studio sui Meccanismi di Reazione, Universit a` “La
†
‡
6
reactivity. Terminal alkynes are also used for the
Sapienza”.
§
Dipartimento di Chimica, Universit a` “La Sapienza”.
E-mail: Claudio.Losterzo@uniroma1.it.
preparation of polymers containing Pt-Pt bonds, and
⊥
7
gold-containing polymers obtained by Puddephatt; the
(1) Takahashi, S.; Takai, Y.; Morimoto, H.; Sonogashira, K.; Hagi-
hara, N. Mol. Cryst. Liq. Cryst. 1982, 32, 139.
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Met. 1993, 55-57, 3299. (b) Hmyene, M.; Yassar, A.; Escorne, M.;
Percheron-Guegan, A.; Garnier, F. Adv. Mater. 1994, 6, 564.
(
(5) (a) Takahashi, S.; Kariya, M.; Yatake, T.; Sonogashira, K.;
Hagihara, N. Macromolecules 1978, 11, 1063. (b) Sonogashira, K.;
Fujikura, Y.; Yatake, T.; Toyoshima, N.; Takahashi, S.; Hagihara, N.
J . Organomet. Chem. 1978, 145, 101. (c) Sonogashira, K.; Kataoka,
S.; Takahashi, S.; Hagihara, N. J . Organomet. Chem. 1978, 160, 319.
(d) Hagihara, N.; Sonogashira, K. Takahashi, S. Adv. Polym. Sci. 1980,
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(
3) (a) Blau, W. J .; Byrne, H. J .; Cardin, D. J .; Davey, A. P. J . Mater.
Chem. 1991, 1, 245. (b) Long, N. J . Angew. Chem., Int. Ed. Engl. 1995,
4, 21.
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of Conducting Polymers, 2nd ed.; Marcel Dekker: New York, 1998.
3
(
1
0.1021/om010312q CCC: $20.00 © 2001 American Chemical Society
Publication on Web 09/14/2001

Preparation of Ethynylated Thiophene Derivatives
Organometallics, Vol. 20, No. 21, 2001 4361
Sch em e 1
latter are prepared from the reaction of metal chlorides
with the appropriate diethynylarene (H-CtC-Ar-Ct
C-H) in the presence of a base. Also Marder and co-
respectively leading to poly(arylene ethynylene) copoly-
mers [-CtC-Ar-CtC-Ar′-]n (path a1) or poly-
(metalla ethynylene)(arylene ethynylene) copolymers
[-CtC-M-CtC-Ar-]n (path a2).
8
workers have made use of terminal dialkynes to form
rhodium-containing polyynes which are obtained by
reductive elimination of methane and loss of a phos-
phine ligand in the reaction of unsubstituted diynes
Both EOP procedures (path a1 and path a2) consist of
three straightforward steps which are consecutively
carried out in the same reaction pot, just by sequentially
(
H-CtC-Ar-CtC-H) and Rh(PR3)4Me.
9
Recently Lewis has proposed an alternative route
(6) (a) Neenan, T. X.; Whitesides, G. M. J . Org. Chem. 1988, 53,
to linear-chain, metal-containing polymers based on
the polycondensation of bis(trimethylstannyl)diynes
2489, and references therein. (b) Alami, M.; Ferri, F.; Linstrumelle,
G. Tetrahedron Lett. 1993, 6403. (c) Nguyen, P.; Todd, S.; Van den
Biggelaar, D.; Taylor, N. J .; Marder, T. B.; Wittmann, F.; Friend, R.
H. Synlett 1994, 299. (d) Bleicher, L.; Cosford, N. D. P. Synlett 1995,
(
Me3Sn-CtC-Ar-CtC-SnMe3) with metal halides.
With respect to Hagihara’s procedure, Lewis’ method
1
115. (e) Diederich, F.; Rubin, Y.; Chapman, O. L.; Goroff, N. S. Helv.
Chim. Acta 1994, 77, 1441. (f) Berris, B. C.; Hovakeemian, G. H.; Lai,
Y.-H.; Mestdagh, H.; Vollhardt, K. P. C. J . Am. Chem. Soc. 1985, 107,
5670. (g) Giesa, R. Rev. Macromol. Chem. Phys. 1996, C36, 631.
was extended to Fe, Ru, Os, Rh, and Co, in addition to
group 10 metals. However if the Lewis synthetic ap-
proach widened the array of organometallic polymers
attainable, it also introduced the demanding necessity
of transformation of the alkynes into the corresponding
trimethyltin derivatives. Such a transformation must
be unavoidably performed by using noxious tin reagents.
Moreover, after the formation of the polymeric products,
one must deal with the trimethyltin chloride side
(7) (a) J ia, G.; Puddephatt, R. J .; Scott, J . D.; Vittal, J . J . Organo-
metallics 1993, 12, 3565. (b) Irwin, M. J .; J ia, G.; Payne, N. C.;
Puddephatt, R. J . Organometallics 1996, 15, 51. (c) Irwin, M. J .; J ia,
G.; Vittal, J . J .; Puddephatt, R. J . Organometallics 1996, 15, 5321. (d)
Puddephatt, R. J . Chem. Commun. 1998, 1055.
(8) (a) Fyfe, H. B., Mlekuz, M.; Zargarian, D.; Taylor, N. J .; Marder,
T. B. J . Chem. Soc., Chem. Commun. 1991, 188. (b) Fyfe, H. B., Mlekuz,
M.; Zargarian, D.; Marder, T. B. Organometallics 1991, 10, 204.
(9) (a) Davies, S. J .; J ohnson, B. F. G.; Kan, M. S.; Lewis, J . J . Chem.
Soc., Chem. Commun. 1991, 187. (b) Davies, S. J .; J ohnson, B. F. G.;
Kan, M. S.; Lewis, J . J . Organomet. Chem. 1991, 401, C43. (c) J ohnson,
B. F. G.; Kakkar, A. K.; Kan, M. S.; Lewis, J . J . Organomet. Chem.
1
0
product, the most toxic tin reagent.
More recently Wolf11 has used the copper-catalyzed
1
991, 409, C12. (d) J ohnson, B. F. G.; Kakkar, A. K.; Kan, M. S.; Lewis,
coupling of ethynyltributyltin detivatives and ruthe-
nium chlorides to form ruthenium oligothienylacetylide
complexes. In this latter case, although the highly toxic
trimethyltin derivatives have been replaced by much
less hazardous tributyltin derivatives, the synthesis of
pure terminal alkynes precursors is still necessary.
J .; Dray, A. E.; Friend, R. H.; Wittmann, F. J . Mater. Chem. 1991, 1,
485. (e) Atherton, Z.; Faulkner, C. W.; Ingham, S. L.; Kakkar, A. K.;
Kan, M. S.; Lewis, J .; Long, N. J .; Raithby, R. P. J . Organomet. Chem.
1
993, 462, 265.
(10) (a) Zybill, C. E. In Synthetic Methods of Organometallic and
Inorganic Chemistry; Hermann, W. A., Ed.; Thieme: Stuttgart,
Germany, 1997; pp 264-270. (b) Pereyre, M.; Quintard, J .-P.; Rahm,
A. Tin in Organic Synthesis; Butterworth & Co.: London, England,
1987.
Within this field we have recently proposed a new use
of the Stille12 reaction, consisting of an original one-pot
(11) Zhu, Y.; Millet, D. B.; Wolf, M. O.; Rettig, S. J . Organometallics
1
999, 18, 1930.
12) (a) Stille, J . K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508. (b)
route straightforwardly leading from aromatic halides
to the corresponding ethynyltributyltin aromatic deriva-
tives and, further, to their direct use to form polyacety-
lenes and polymetallaacetylenes. This novel approach
to highly ethynylated materials has been named the
(
Mitchell, T. N. In Metal-catalyzed Cross-coupling Reactions; Diederich,
F., Stang, P. J ., Eds.; Wiley-VCH: Weinheim, Germany, 1998; p 167.
(
c) Farina, V.; Krishnamurthy, V.; Scott, W. J . The Stille Reaction; J ohn
Wiley & Sons: New York, 1998.
13) (a) Antonelli, E.; Rosi, P.; Lo Sterzo, C.; Viola, E. J . Organomet.
(
Chem. 1999, 578, 210. (b) Lo Sterzo, C. Synlett 1999, 11, 1704. (c)
Giardina, G.; Rosi, P.; Ricci, A.; Lo Sterzo, C. J . Polym. Sci. Part A:
Polym. Chem. 2000, 38, 260
1
3
extended one-pot (EOP) procedure. In Scheme 1 two
EOP pathways (path a1 and path a2) are outlined,

4
362 Organometallics, Vol. 20, No. 21, 2001
Altamura et al.
Sch em e 2
adding reactants up to the formation of the polymeric
product.
iophene spacers into the polymer backbone. The differ-
ent synthetic approaches are compared and discussed.
In the first step, a diiodoaromatic compound (I-Ar-
I) is reacted in THF solvent with 2 equiv of tributyl-
Resu lts a n d Discu ssion
(ethynyl)tin (Bu3Sn-CtC-H) in the presence of zero-
valent palladium. In this reaction the bisethynylaro-
matic compound (H-CtC-Ar-CtC-H) is formed along
with 2 equiv of Bu3SnI side product. To this mixture,
cooled to -20 °C, 2 equiv of LDA is added, causing
deprotonation of the terminal acetylenic functionalities
and their recombination with the Bu3SnI side product
to form the corresponding tin acetylides (Bu3Sn-CtC-
Ar-CtC-SnBu3). Following this transformation, al-
ternatively a second diiodoaromatic compound (I-Ar′-
I) (path a1) or a metal diiodide compound (I-M-I) (path
a2) is added to the reaction mixture; these reac-
tion conditions still are suitable to perform a second
F or m a tion of tr a n s-bis(tr i-n -bu tylp h osp h in e)-µ-
2,5-bis(eth yn yl)th ioph en e]palladiu m oligom er (6).
[
In Scheme 2 are represented the three complementary
synthetic approaches (path a, path b, and path c) that
we performed in order to prepare the trans-bis(tri-n-
butylphosphine)-µ-[2,5-bis(ethynyl)thiophene]palladi-
um oligomer (6).
Path a represents the classical synthetic route5 to
access transition metal σ-acetylide complexes and poly-
mers, consisting of the (i) Pd-catalyzed TMSA-diiodide
coupling, (ii) TMS deprotection, and (iii) copper-cata-
lyzed dehydrohalogenation. In this route both the TMS
intermediate (2) and the terminal alkyne intermediate
palladium-promoted carbon-carbon coupling or
a
palladium-promoted metal-carbon coupling to afford
(
3) need to be isolated and purified before their use in
the corresponding poly(arylene ethynylene) copolymers
[
-CtC-Ar-CtC-Ar′-]n (path a1) or poly(metalla
the subsequent step. The Pd-catalyzed TMSA-2,5-
diiodothiophene coupling to obtain the bis[(trimethyl-
silyl)ethynyl]thiophene (2) was performed introducing
some modifications to the procedure described by
ethynylene)(arylene ethynylene) copolymers [-CtC-
M-CtC-Ar-]n (path a2). At the end of the overall
process, not only is the polymeric material isolated by
simple precipitation and washing with methanol, but
from the filtrate, the Bu3SnI side product may be
recovered by distillation and reused, thus allowing a
recycling of the tin reagent.1
In this work we report on different uses of our
extended one-pot (EOP) procedure (i) to conveniently
access ethynylthiophene and oligoethynylthiophene de-
rivatives and their subsequent uses to prepare organo-
metallic oligomers by classical routes and (ii) to prepare
organometallic polymers by straightforward formation
and insertion of ethynylthiophene and oligoethynylth-
6
a
14
Whitesides and Raithby, consisting of the use of an
ultrasound bath to break up the solid mass formed in
the flask during the reaction and the use of sublimation
instead of chromatographic separation to isolate the
final product. These modifications conveniently allowed
isolation of 2 in 96% yield. Formation of 3 was ac-
complished by treatment of 2 under standard desilyla-
3c
6a
tion conditions, and after workup, pure 3 was isolated
(14) Lewis, J .; Long, N. J .; Raithby, R. P.; Shields, G. P.; Wong, W.-
Y.; Younus, M. J . Chem. Soc., Dalton Trans. 1997, 4283

Preparation of Ethynylated Thiophene Derivatives
Organometallics, Vol. 20, No. 21, 2001 4363
by Kugelrohr distillation. The pure product, isolated as
a colorless liquid, is a quite sensitive and hazardous
6
a
14
material that became dark upon standing. However
if stored under argon at -20 °C in sealed vials, it
crystallizes and remains indefinitely stable. Reaction of
F igu r e 1
3
with trans-dichlorobis(tri-n-butylphosphine)palladium
tage of the EOP procedure to form the 2,5-bis[(tribu-
(5) was performed under standard dehydrohalogenation
tyltin)ethynyl]thiophene (4) (first part of path b), since
5
conditions. Reactants were dissolved in diethylamine
and stirred at 50 °C in the presence of CuI. The progress
1
8
the unavoidable residual presence of palladium cata-
lyst (from the first step of path b) would mask the
possible copper catalysis in path c. As a consequence,
to cleanly perform path c, 4 must be prepared in a pure
of the reaction was periodically checked by 1 P NMR.
3
15
When variations no longer were observed in the 3P
1
NMR spectrum (15 h), the solution was filtered and
concentrated to a minimum volume. Addition of metha-
nol caused precipitation of a red-brown material, which
was filtered, washed with methanol, and dried under
vacuum. Subsequent chromatographic purification and
characterization showed that the product resulted from
coupling of 3 and 5 (vide infra).
1
9
form by the reaction of pure 3 and Et2NSnBu3. Re-
action of 4 and 5 was carried out in refluxing chloroben-
zene in the presence of 10% CuI. After 15 h a sample of
1
4
13
the reaction mixture examined by P NMR showed
only the presence of a broad peak at 11 ppm. After
cooling, filtration, and evaporation to a minimum vol-
ume, addition of methanol caused the formation of a
dark precipitate, which after workup was identified as
the bimetallic complex 7.
Starting from the same diiodide (1), the EOP route
(path b) was started with the reaction of 1 with tributyl-
(ethynyl)tin in THF at 70 °C in the presence of 0.1% of
F or m a t ion of t h e [2-(E t h yn yl)t h iop h en e]-2,5-
biseth yn ylth iop h en e Sp a cer (13). The introduction
of different types of organic spacers in organometallic
conjugated polymers should result in a different degree
of electronic communication between metal centers and
consequently in the tuning of related properties mani-
fested by these materials. In this respect we studied
suitable routes to form and then to connect the oligo-
ethynylthiophene 13 (Figure 1) with the bis(tri-n-
butylphosphine)palladium moieties.
Pd(PPh3)4. After overnight stirring, a sample of the
reaction mixture examined by H NMR showed quan-
titative transformation into 2,5-bis(ethynyl)thiophene
1
16
(3) and tributyltin iodide side product. The reaction
mixture was then cooled at -20 °C, and lithium diiso-
propylamide (LDA) was added. The addition of the base
provoked deprotonation of the alkyne and its recombi-
nation with the tin halide, to form the 2,5-bis[(tribu-
tyltin)ethynyl]thiophene (4). Also this transformation
1
16
was clearly evidenced by H NMR analysis of a sample
of the reaction mixture. To this mixture was added
trans-dichlorobis(tri-n-butylphosphine)palladium (5), and
the reaction flask was maintained for an additional 24
h at 70 °C. After cooling and vacuum evaporation to a
minimum volume, addition of methanol caused precipi-
tation of a red-brown material. This residue when
treated with THF, CH2Cl2, or CHCl3 leaves some
insoluble material.17 The soluble part, purified by
column chromatography, proved to be the product of
coupling of 4 and 5 (vide infra).
Two different one-pot routes (path a and path b of
Scheme 3) have been performed in order to prepare
precursors 9 and 11, which, after further transfor-
mations, will be used in the EOP and Hagihara syn-
thetic protocols, respectively, to connect the oligoethy-
nylthiophene spacer 12 to the palladium unit.
Preparation of 9 and 11 have in common with Scheme
2
the first two steps leading from 2,5-diiodothiophene
(1) to 2,5-bis[(tributyltin)ethynyl]thiophene (4). In the
present case, following formation of 4, 2-iodothiophene
(8) or alternatively 2-iodo-5-(trimethylsilyl)thiophene
(10) was directly added to the same reaction mixture
where 4 was formed, and after 24 h of further warming
at 70 °C, 9 and 11 were formed, respectively.
From the filtrate, after evaporation of volatiles and
vacuum distillation of the oily residue, it was possible
to recover most of the Bu3SnCl formed as side product.
Path c has been performed according to the procedure
1
1
used by Wolf consisting of the copper-catalyzed cou-
pling of ethynyltributyltin detivatives and metal chlo-
rides. Although this route has been used only to form
ruthenium oligothienylacetylides, we decided to try it
for the formation of polymeric materials of type 6 since
the use of tributyltin derivatives presents lesser envi-
ronmental and safety concerns10 than the use of tri-
methyltin derivatives as in the case of Lewis’ method.
In this synthetic route it is not possible to take advan-
As in the case of the EOP route to form 6 (path b of
Scheme 2), each step of transformations of path a and
path b can be conveniently monitored by 1H NMR
spectroscopy.
Adopting the procedure described by Wakefield,20
treatment of 2,5-bis(2-thienylethynyl)thiophene (9) with
sec-BuLi in the presence of TMDA and I2 afforded 2,5-
[2,2′-(5,5′-diiodo)bisthienyl]bisethynylthiophene (12) (eq
1
), a material suitable for use in the EOP protocol to be
linked to metal moieties. Under different reaction
conditions Cava and co-workers have attempted conver-
sion of 9 into 12 by the action of n-BuLi and I2. However
(
15) A sample of the reaction mixture (0.4 mL) was loaded in a 5
mm NMR tube. To this a little amount of C
lock purpose.
6 6
D (0.1 mL) was added for
(
16) The sequential check of the transformation progresses was
typically performed by withdrawing a sample of the reaction mixture
0.1-0.2 mL), stripping off the solvent under reduced pressure (10-
5 mmHg/25 °C, 20 min), redissolution with CDCl , and recording the
H NMR spectrum. It is recommended not to use a vacuum oil pump
to dry samples since Bu SnCtCH is volatile enough to be lost under
(
(18) 2,5-Bis[(tributyltin)ethynyl]thiophene (4) is a high-boiling oily
material whose purification is very difficult. Attempts of performing
vacuum distillation lead to thermal decomposition; chromatographic
separation partially cleaves tributyltin groups.
1
3
1
3
these condition, thus obtaining wrong information on completion of
step 1.
(19) Viola, E.; Lo Sterzo C.; Crescenzi, R.; Frachey, G., J . Organomet.
Chem. 1995, 493, C9.
(20) Wakefield, B. J . Organolithium Methods; Academic Press:
London, 1988.
(17) Formation of insoluble material might be related to the forma-
tion of insoluble higher-order polymers.

4
364 Organometallics, Vol. 20, No. 21, 2001
Altamura et al.
Sch em e 3
Sch em e 4
they reported21 that under their conditions an insepa-
rable mixture of 12 and the corresponding monoiodo
derivative is obtained.
p h en e]p a lla d iu m P olym er (15). The synthesis of the
oligoethynylthiophene spacers 11 and 12 allowed a
complementary approach to the formation of the orga-
nometallic species 15. In Scheme 4 are represented (i)
the classical TMS deprotection/CuI-catalyzed dehydro-
halogenation sequence (path a) and (ii) the EOP route
(path b), both leading to the trans-bis(tri-n-butylphos-
phine)-µ-[2,2′-bis(ethynyl)thiophene]-2,5-bisethynyl-
thiophene]palladium oligomer (15).
Path a starts with removal of the protecting trimeth-
ylsilyl groups on 11. With respect to the standard pro-
cedure, since 11 is insoluble in methanol, the desily-
lation reaction was carried out in a 1:1 THF/MeOH
mixture in the presence of a small amount of an aqueous
KOH solution. Following workup and chromatographic
F or m a tion of tr a n s-bis(tr i-n -bu tylp h osp h in e)-µ-
2,2′-b is(e t h yn yl)t h iop h e n e ]-2,5-b ise t h yn ylt h io-
6a
[
(21) Tormos, G. V.; Nugara, P. N.; Lakshmikantham, M. V.; Cava,
M. P. Synth. Met. 1993, 53, 271

Preparation of Ethynylated Thiophene Derivatives
Organometallics, Vol. 20, No. 21, 2001 4365
the EOP procedure affords slightly higher oligomers. It
is remarkable that the value of the degree of polymer-
3
1
ization as estimated by P NMR is in substantial
agreement with the value of the polymerization degree
2
2
as estimated by GPC.
The fact that independently of the different adopted
procedures, in the case of formation of either polymer 6
and 15, only short-term oligomers were obtained is
indicative of the general difficulties encountered in the
formation of palladium-based metallapolyynes.24 In this
respect it may be of significance that the palladium-
based species are the most rarely reported. Despite this
limitation, because of their intrinsic value, we main-
tained our interest in oligomeric materials of type 6 and
15. This confidence is based on the fact that for
conjugated polymers electronic and photoactive proper-
ties are little related to polymer chain length, since
these properties rapidly tend to saturation with the
F igu r e 2
separation, pure 13 was isolated in 67% yield as a yellow
oil, which showed to be quite unstable, turning dark
upon standing. Because of its sensitivity, this compound
was used immediately after its preparation. In the
subsequent step, 13 was reacted with trans-dichlorobis-
(
tri-n-butylphosphine)palladium (5) under typical Hagi-
5
hara conditions. However, using diethylamine as sol-
vent and in the presence of a catalytic amount of CuI,
the dehydohalogenation route afforded a mixture of
products, which after chromatographic separation were
identified as being short oligomers of type 15 (vide infra)
and the bimetallic complex 16 (Figure 2).
2
3b,25
increase of chain length.
As a confirmation of this,
Path b was performed under the same conditions
previously used for the formation of polymer 6 (Scheme
preliminary results obtained using oligomeric material
of type 15, as obtained in the present work, have shown
an excellent behavior when used for the fabrication of
sensitive membranes for gas and vapor detection.26
Recover y a n d Recyclin g of Tin , a F u lly In te-
gr a ted P r ocess. The organometallic materials 6 and
15 formed by the EOP routes outlined in path b of
Schemes 2 and 4 were isolated and purified by precipi-
tation and repeated washings with methanol. In addi-
tion to the polymeric product we also obtained a
methanolic rinsing solution containing the reaction
solvent, lower oligomers, residual phosphine ligand, and
2
). The Stille coupling of 12 with tributyl(ethynyl)tin
in refluxing THF in the presence of Pd(PPh3)4 afforded
2-(ethynyl)thiophene]-2,5-bisethynylthiophene (13) and
tributyltin iodide as side product. Upon cooling at -20
C, addition of LDA to this mixture caused deprotona-
[
°
tion of the alkyne and its recombination with the tin
halide to form [2-tributyltin(ethynyl)thiophene]-2,5-
bisethynylthiophene (14). To this mixture trans-dichlo-
robis(tri-n-butylphosphine)palladium (5) was subse-
quently added, and the reaction mixture was warmed
to reflux for an additional 24 h. After cooling, precipita-
tion, and washing with methanol, a red-brown powder
was isolated. Evaporation of the filtrate and vacuum
distillation of the oily residue allowed almost complete
recovery of the Bu3SnI side product. The red-brown
material consisting of 15 upon treatment with THF,
the Bu SnCl side product. From this solution, upon
3
evaporation of the volatiles, a dark, viscous residue
remained, from which it was possible to recover up to
92% of pure Bu SnCl by vacuum distillation. The
3
recovered Bu SnCl was subsequently utilized in the
3
reaction with the lithium acetylide ethylenediamine
1
7
27
CH2Cl2, or CHCl3 left some insoluble residue. The
soluble part analyzed by GPC proved to be the product
of coupling of 14 and 5 (vide infra).
complex to form new Bu SnCtCH (eq 2), which is the
3
coupling partner of the thiophene derivatives 1 and 12
at the beginning of the three EOP processes outlined
in Scheme 3 and path b of Schemes 2 and 4.
Ch a r a cter iza tion of th e P r od u cts. Materials ob-
tained as a result of the coupling between the ethynyl
thiophene spacers 3 and 13 with trans-dichlorobis(tri-
n-butylphosphine)palladium (5), using the different
synthetic approaches, have been characterized by gel
permeation chromatography and NMR spectroscopy. In
Table 1 are reported molecular weight, molecular weight
distribution, and degree of polymerization of the differ-
ent materials estimated using the GPC techniques
The possibility of using the Bu3SnCl recovered at the
end of the polymerization process to form new Bu3SnCt
(22) Evidently, polymetallaacetylene polymers are a special class
of rodlike polymers. Thus, factors that are generally limiting the
reliability of polystyrene calibration in the use of the GPC technique
for the determination of molecular weights of organic rodlike
(
relative to polystyrene standard); also given is the
6
a,23
polymers
23) (a) Pearson, D. L.; Schumm, J . S.; Tour, J . M. Macromolecules
1994, 27, 2348. (b) Tour, J . M. Chem. Rev. 1996, 96, 537.
24) (a) Sonogashira, K.; Kataoka, S.; Takahashi S.; Hagihara, N.
in this case are balanced by other effects.
3
1
degree of polymerization as estimated by P NMR
spectroscopy, by measure of internal vs terminal relative
intensities of phosphorus signals. It is important to note
that with the use of the EOP procedure in the case of
formation of both 6 and 15, after precipitation, part of
the isolated material remained insoluble1 (entries 2,
(
(
J . Organomet. Chem. 1978 160, 319. (b) Takahashi, S.; Morimoto, H.;
Murata, E.; Kataoka, S.; Sonogashira, K.; Hagihara, N. J . Polym.
Sci.: Polym. Chem. Ed. 1982 20, 565 (c) Onitsuka, K.; Yamamoto S.;
Takahashi, S. Angew. Chem., Int. Ed. 1999, 38, 174
7
(25) (a) Altmann, M.; Enkelmann, V.; Beer, F.; Bunz, U. F. H.
4
). In the formation of polymer 6 (entries 1, 2), besides
Organometallics 1996, 15, 394. (b) Wautelet, P.; Moroni, M.; Oswald,
L.; Le Moigne, J .; Pham, A.; Bigot, J . Y.; Luzzati, S. Macromolecules
yields, only slight differences were found between the
characteristics of materials obtained from the two
different procedures (paths a and b of Scheme 2). In both
cases, only short oligomers were obtained. The situation
is slightly different in the case of formation of 15 (entries
1
996, 29, 446. (c) ten Hoeve, W.; Wynberg, H.; Havinga, E. E.; Meijer,
E. W. J . Am. Chem. Soc. 1991, 113, 5887.
(26) (a) Russo, M. V.; Furlani, A.; Altamura, P.; Fratoddi, I.; Lo
Sterzo, C.; Bearzotti. Proceedings of the IV Conference “Sensors and
Microsystems” AISEM 99; Di Natale, C., D’Amico, A., Eds.; World
Science Publishers: Singapore, 2000; p 228. (b) Lo Sterzo, C.; Furlani,
A.; Altamura, P.; Cianfriglia, P.; Bearzotti A.; Russo M. V. Proceedings
of the VIII Conference “Syntheses and Methodologies in Inorganic
Chemistry”, Daolio, S., Fabrizio, M., Tondello, E., Armelao, L., Vigato,
P. A., Eds.; 1998; Vol. 8, p 82.
3
and 4). Using the dehydrohalogenation procedure an
appreciable amount (37%) of the bimetallic compound
6 accompanies the formation of short oligomers, while
1

4
366 Organometallics, Vol. 20, No. 21, 2001
Altamura et al.
Ta ble 1. Yield s a n d Molecu la r Weigh ts for P olym er s 6 a n d 15 Obta in ed w ith Differ en t P r oced u r esa
yield (%)
Mwb
Mnc
MWDd
DP(Mw)e
DP(Mn)f
DP(NMR)g
6
4
(1) dehydrohalogenation
2) extended one pot (EOP)
(3) dehydrohalogenation
4) extended one pot (EOP)
57
76
60
73
3000
2750
2200
4000
1300
1700
1000
1500
2.3
1.6
2.2
2.6
5
4
3
5
2
3
1
2
3
5
3
6
(
1
(
a
Calculated on the soluble part of the polymeric material. b Weight-average molecular weights. c Number-average molecular weights.
d
e
f
Molecular weight distribution (Mw/Mn). Degree of polymerization; calculated on the basis of the Mw value. Degree of polymerization;
calculated on the basis of the Mn value. Degree of polymerization; calculated by P NMR on the basis of internal vs terminal relative
g
31
intensities of phosphorous signals.
F igu r e 3
CH allows us to reintroduce the tributyltin moiety into
the polymerization process. Figure 3 represents the fully
integrated process composed by the three steps of the
EOP procedure (steps 1-3) and the recovery and recycle
of tin.
and THF as eluent and polystyrene as a standard. Solvents,
including those used for NMR and chromatography, and all
other liquids were thoroughly degassed before use. Chromato-
graphic separations were performed with 70-230 mesh silica
gel. Elemental analyses were performed at the Dipartimento
di Chimica of the Universit a` di Roma “La Sapienza”.
A key aspect of the process depicted in Figure 6 is
recycling of the tin reagent, which overcomes a major
drawback of the Stille reaction, that is, the environ-
mental concern related with the use of toxic and costly
Standard techniques, with Schlenk type equipment for the
manipulation of air-sensitive compounds under argon atmo-
sphere, were employed. All solvents were dried (sodium-
potassium alloy for tetrahydrofuran and diethyl ether and Na
for the hexanes and amines) and argon-satured prior to use.
The compounds trans-bis(tributylphosphine)palladium(II) chlo-
1
0
organostannanes. In this respect we believe that the
present work is in accord not only with the desirability
of Stille protocols catalytic in tin28 but also with the
31
32
ride (5), 2-iodo-5-[(trimethylsylyl)ethynyl]thiophene (9), 2,5-
2
9
19
“atom economy” concept recently developed by Trost
bis[(tributylstannyl)ethynyl]thiophene (4), and bis(acetonitrile)-
palladium(II) chloride33 were prepared by reported procedures.
Other chemicals were purchased from Aldrich or Strem and
used as received unless otherwise specified.
and the design of environmentally benign chemical
3
0
processes.
P r ep a r a tion of 2,5-[(Tr im eth ylsilyl)eth yn yl]th iop h en e
2). To a mixture of 2,5-diiodothiophene (1) (12.01 g, 49.65
Exp er im en ta l Section
(
mmol), (CH CO Cu (0.5 g, 2.75 mmol), PdCl (CH CN) (1.05
3
2
)
2
2
3
2
FT-IR and far-IR spectra were recorded as Nujol mulls,
liquids, or casted films on a Fourier Transform Perkin-Elmer
g, 4.05 mmmol), and triphenylphosphine (1.48 g, 5.64 mmol)
in diisopropylamine (50 mL) was added dropwise trimethyl-
silylacetylene (13.21 g, 134.5 mmol) during 1 h under stirring
at room temperature. The reaction mixture was then refluxed
for 3 h. During this time the color of the reaction mixture
changed from light green to black, and most of the initial slurry
changed to a solid mass. From time to time immersion into
an ultrasound bath helped to break up the solid mass. After
cooling, the precipitated ammonium iodide was filtered off and
washed with dichloromethane (2 × 50 mL). The combined
filtrates were treated with a 5% acqueous solution of HCl (2
1
13
31
1
720 spectrometer. H NMR, C NMR, and P NMR were
recorded on a Bruker AC300P spectrometer at 300, 75, and
21.5 MHz, respectively. The 1H NMR chemical shifts are
reported in ppm downfield vs Me Si, assigning the residual
H NMR impurity signal in the solvent (CDCl ) to the
resonance at 7.24 ppm. The C NMR chemical shifts are
1
4
1
3
1
3
1
3
31
referenced to the C triplet of CDCl
spectra were referenced to external 85% H
3
at 77.00 ppm. P NMR
PO . Molecular
3
4
weights of the materials were determined with a Perkin-Elmer
GPC-HPLC instrument with a UV detector, using a Perkin-
×
50 mL), then with water (3 × 50 mL), and dried over
Elmer PL gel 10µ mixed N. 0258-2135 column, using CHCl
3
magnesium sulfate. After addition of Celite, the solvent was
evaporated under reduced pressure and the residue was
(
27) (a) Renaldo, A. F.; Labadie, J . W.; Stille, J . K. Org. Synth. 1989,
-2
6
1
7, 86. (b) Bottaro, J . C.; Hanson, R. N.; Seitz, D. E. J . Org. Chem.
981, 46, 5221.
sublimed at 90 °C and 10 Torr, cooling the coldfinger at -10
°C. In the event of the presence of a little amount of
(
28) Maleczka, R. E.; Gallagher, W. P.; Terstiege, I. J . Am. Chem.
Soc. 2000, 122, 384
29) (a) Trost, B. M. Science 1991, 254, 1471. (b) Trost, B. M.; Sorum,
M. T.; Chan, C.; Harms, A. E.; Ruter, G. J . Am. Chem. Soc. 1997, 119,
98. (c) Trost, B. M.; Krische, M. J . Synlett 1998, 1.
30) Anastas, P. T.; Warner, J . C. Green Chemistry: Theory and
Practice; Oxford University Press: New York, 1998; pp 29-55.
(
(31) Saito, T.; Munakata, H.; Imoto, H. Inorg. Synth. 1977, 17, 87
(32) Viola, E.; Lo Sterzo, C.; Trezzi, F. Organometallics 1996, 15,
4352.
(33) Hegedus, L. S. In Organometallics in Synthesis; Schlosser, M.,
Ed.; J ohn Wiley & Sons: Chichester, England, 1994; p 448.
6
(

Preparation of Ethynylated Thiophene Derivatives
Organometallics, Vol. 20, No. 21, 2001 4367
contaminating bis(trimethylsilyl)butadiyne, this side product
can be eliminate by collecting and discarding the first amount
istics were identical to those of the material obtained with the
dehydrohalogenation route.
of the sublimate. The product (13.15 g, 96%) was isolated as
P a th c: Cop p er -Ca ta lyzed -CtC-Sn Bu /Cl-P d Cou p -
3
1
white solid. H NMR (CDCl
IR (Nujol): 2147 (s), 1250 (s), 1173 (s), 845 (s) cm . Spectro-
3
ppm): 7.02 (s, 2H), 0.23 (s, 18H).
lin g. To a degassed solution of trans-Cl Pd (PBu ) (5) (0.202
2
3 2
-
1
g, 0.35 mmol) and CuI (6.7 mg, 0.035 mmol) in chlorobenzene
(20 mL) was added 2,5-bis[(tributylstannyl)ethynyl]thiophene
scopic data are in agreement with literature reports.6
a,14
(
4) (0.250 g 0.35 mmol). The solution was heated to reflux
P r ep a r a tion of 2,5-Bis(eth yn yl)th iop h en e (3). To a
solution of 2,5-[(trimethylsilyl)ethynyl]thiophene (2) (0.49 g,
overnight (15 h) and then cooled to room temperature. The
mixture was then filtered through Celite to eliminate the spent
catalyst, and the filtrate was reduced under vacuum to a small
volume. Addition of methanol precipitated a red-brown solid,
which was collected by filtration, washed repeatedly with
methanol, and dried under vacuum. The solid was purified
chromatographically using a silica gel column and toluene/
THF (8:2 v/v) as the eluent. Removal of the solvent under
1
.77 mmol) in degassed methanol (30 mL) was added 0.1 mL
of a 0.5 M solution (0.05 mmol) of KOH in water. The solution
was stirred at room temperature for 1 h, then diluted with
water (50 mL), and extracted with pentane (3 × 30 mL). The
combined organic layers were dried over sodium sulfate, and
after filtration, the solvent was removed under reduced
pressure at room temperature. The liquid residue was purified
-
1
reduced pressure yielded 0.083 g (39%) of product (7) as dark
by Kugelrohr distillation (40 °C, 2 × 10 mbar) to give 0.20 g
1
solid. H NMR (CDCl
3
ppm): 6.59 (s, 2H, thiophene), 1.91-
CH CH CH ) 1.56-1.36 (m, 48H,
) 0.90 (t, 36H, J ) 7.1 Hz, P(CH CH
). C NMR (CDCl ppm): 127.2, 126.1 (thiophenes)
02.0 (t, J ) 14 Hz, (Pd-CtC-), 98.4 (br, Pd-CtC-), 26.4
(P(CH CH CH CH 24.4 (t, J ) 7 Hz, P(CH CH CH CH
22.8 (t, J ) 14 Hz, P(CH CH CH CH ), 13.8 (P(CH CH
). P NMR (CDCl , ppm): 10.7. IR (casted film):
(86%) of product as a colorless oil. Pure 3 if left standing in
1
.85 (m, 24H, P(CH
P(CH CH CH CH
CH CH
2
2
2
3 3
)
air at room temperature rapidly turns dark. However, if stored
2
2
2
3
)
3
2
2
-
under argon in sealed vials at -20 °C it crystallizes and
1
3
1
2
3
)
3
3
remains indefinitely stable. H NMR (CDCl
3
ppm): 7.09 (s,
1
2
H), 3.32 (s 2H). IR (liquid): 2106 (m), 1214 (s), 1209 (m), 808
-
1
2
2
2
3
)
3
2
2
2
3 3
) ,
(s) cm . Spectroscopic data are in agreement with literature
6
a,14
2
2
2
3
)
3
2
2
-
reports.
3
1
CH
857-2871 (s), 2089 (m) cm . Anal. Calcd for C56
Pd S: C, 61.92; H, 7.09. Found: C, 62.12; H, 7.2.
P r epar ation of 2,5-(2,2′-Bisth ien yl)biseth yn ylth ioph en e
9). To a solution of 0.25 g (0.22 mmol) of Pd(PPh and 0.92
2
CH
3
)
3
3
P r ep a r a t ion of P oly{2,5-b is(et h yn yl)t h iop h en eb is-
tr ibu tylp h osp h in e)p a lla d iu m } (6). P a th a : Deh yd r oh a -
-
1
2
2 4
H110Cl P -
(
2
logen a tion Rou te. 2,5-Bis(ethynyl)thiophene (3) (0.13 g, 0.98
mmol) was dissolved in 20 mL of diethylamine, and to this
solution trans-Cl Pd (PBu ) (5) (0.57 g, 0.98 mmol), followed
2 3 2
(
3 2
)
g (2.68 mmol) of 2,5-diiodothiophene in 50 mL of THF was
added 1.69 g (5.4 mmol) of ethynyltributyltin. After overnight
stirring at 70 °C, 1H NMR analysis indicated complete
consumption of the starting tin reagent with formation of 3
and Bu SnI. After cooling to -20 °C, 3.5 mL (7.02 mmol) of a
solution of LDA (2.0 M in THF/heptane/ethylbenzene) was
added and the mixture allowed to warm to room temperature.
by CuI (5 mg), was added. After 15 h of stirring at room
temperature the reaction mixture was filtered on a glass frit
covered with Celite and reduced to a minimum volume by
evaporation under vacuum. Upon addition of methanol to the
filtrate, a red-brown solid precipitated, which was collected
on a glass frit and washed with methanol. The residue was
redissolved in a minimum amount of dichloromethane and
purified chromatographically using a silica gel column and
15
3
1
A sample of the reaction mixture examined by H NMR
analysis15 indicated complete conversion of the alkyne moieties
into the corresponding tributyltinalkynyl functionalities. To
toluene as the eluent. Removal of the solvent left 0.4 g (57%)
1
of product as a red-brown solid. H NMR (CDCl
3
ppm): 6.56
). C NMR (CDCl
ppm): 127.0, 116.9 (thiophene), 105.7, 97.5 (-CtC-), 26.7,
this solution was added 1.13 g (5.4 mmol) of 2-iodothiophene
1
3
(
s, 2H, thiophene), 2.1-0.86 (m, 54H, PBu
3
3
1
(8), and the mixture was warmed to reflux. After 24 h H NMR
15
analysis indicated complete consumption of reactants and
formation of 9. After cooling, the solvent was evaporated under
reduced pressure and 50 mL of diethyl ether was added to the
reaction mixture, followed by the addition of 100 mL of a 50%
solution of KF in water. The mixture was rapidly stirred for
30 min while argon was bubbled through the solution and then
transferred into a separatory funnel. The ether solution was
washed with water (3 × 50 mL), dried over magnesium sulfate,
and filtered. Celite (10 g) was added to the filtrate, and the
mixture was evaporated to dryness in vacuo. The residue was
chromatographed on silica gel using hexanes as the eluent to
yield 0.41 g (1.39 mmol, 52%) of a pale yellow powder. An
analytical sample was obtained by sublimation at 95 °C/4.5 ×
3
1
2
4.61 (m), 13.9 (PBu
3 3
). P NMR (CDCl , ppm): 11.39 (P
terminal), 7.14 (P internal). IR (Nujol): 2088 (s) 1510 (m) 394
-
1
(
w) cm . Anal. Calcd for C32
Found: C, 58.98; H, 7.27.
P a th b: EOP Rou te. To a solution of 0.010 g (0.008 mmol)
of Pd(PPh and 0.147 g (0.43 mmol) of 2,5-diiodothiophene
1) in 20 mL of THF was added 0.270 g (0.86 mmol) of tributyl-
56 2
H P PdS: C, 59.94; H, 8.80.
3 4
)
(
(
1
ethynyl)tin. After overnight stirring at 70 °C, H NMR
1
5
analysis indicated complete consumption of the starting tin
reagent with formation of 3 and Bu SnI. After cooling to -20
C, 0.5 mL (10.0 mmol) of a solution of LDA (2.0 M in THF/
3
°
heptane/ethylbenzene) was added, and the mixture allowed
to warm to room temperature. A sample of the reaction
-
6
1
10 mbar, cooling the coldfinger at -10 °C. H NMR (CDCl
3
1
15
mixture examined by H NMR analysis indicated complete
conversion of the alkyne moieties into the corresponding
tributyltinalkynyl functionalities. To this solution was added
ppm): 7.01 (m, 2H J ) 5 Hz, J ) 3.8 Hz), 7.13 (s, 2H) 7.28 (m,
2H, J ) 1.0 Hz, J ) 5 Hz) 7.31 (m, 2H J ) 1.0 Hz, J ) 5.0
Hz). IR (casted film): 3104 (w), 2197 (w), 1410 (w), 1195 (s),
-
1
trans-Cl
2
Pd (PBu
3
)
2
(5) (0.250 g, 0.43 mmol), and the mixture
699 (s) cm . Spectroscopic data are in agreement with
literature reports.
P r ep a r a tion of [2-Tr im eth ylsilyleth yn ylth iop h en e]-
2,5-bis(eth yn yl)th iop h en e (11). To a solution of 0.21 g (0.19
mmol) of Pd(PPh3)2 and 0.78 g (2.28 mmol) of 2,5-diiodo-
thiophene in 50 mL of THF was added 1.43 g (4.6 mmol) of
1
15
21
was warmed to reflux. After 24 h H NMR analysis indicated
complete consumption of reactants; then, after cooling, the
mixture was filtered over Celite to eliminate the spent catalyst
and the filtrate was evaporated under vacuum to a small
volume. Upon addition of methanol, a red-brown solid pre-
cipitated, which was collected by filtration, washed repeatedly
with methanol, and dried under vacuum. The crude product
was purified by chromatography over silica by using toluene
as the eluent. The product (0.210 g, 76%) was obtained as a
dark solid. Evaporation under reduced pressure of the metha-
nolic rinsing solution afforded a dark oil, which was submitted
1
ethynyltributyltin. After overnight stirring at 70 °C, H NMR
analysis15 indicated complete consumption of the starting tin
reagent with formation of 3 and Bu SnI. After cooling to -20
3
°C, 3.0 mL (6.0 mmol) of a solution of LDA (2.0 M in THF/
heptane/ethylbenzene) was added, and the mixture allowed
to warm to room temperature. A sample of the reaction
-
2
1
15
to vacuum distillation (Kugelrohr, 120 °C/10 Torr), giving
.257 g (92%) of tributyltin chloride. Spectroscopic character-
mixture examined by H NMR analysis indicated complete
conversion of the alkyne moieties into the corresponding
0

4
368 Organometallics, Vol. 20, No. 21, 2001
Altamura et al.
tributyltinalkynyl functionalities. To this solution was added
.40 g (4.6 mmol) of 2-iodo-5-[(trimethylsilyl)ethynyl]thiophene
graphed on a silica gel column using the same solvent as the
eluant. First was eluted 16 (0.22 g, 37%), followed by 15 (0.21
1
1
(
10), and the mixture was warmed to reflux. After 24 h
H
g, 60%).
1
5
1
NMR analysis indicated complete consumption of reactants
and formation of 11. After cooling, the solvent was evaporated
under reduced pressure, and 50 mL of diethyl ether was added
to the reaction mixture, followed by the addition of 100 mL of
a 50% solution of KF in water. The mixture was rapidly stirred
for 30 min while argon was bubbled through the solution and
then transferred into a separatory funnel. The ether solution
was washed with water (3 × 50 mL), dried over magnesium
sulfate, and filtered. Celite (10 g) was added to the filtrate,
and the mixture was evaporated to dryness in vacuo. The
residue was chromatographed on a silica gel column packed
with hexanes using a gradient elution first with hexanes and
Ch a r a cter iza tion of 15. H NMR (CDCl
3
ppm): 6.68-7.09
3
1
(m, 6H, thiophenes), 2.06-0.81 (m, 54H, PBu
(CDCl , ppm): 11.85 (P terminal), 7.41 (P internal). IR (casted
film): 2182 (w), 2099 (m), 1193 (w), 800 (m), 390 (w) cm
Anal. Calcd for C44 Pd: C, 61.92; H, 7.09. Found: C,
61.33; H, 7.56. When a 13/trans-Cl Pd (PBu molar ratio of
1:2 was used, only the bimetallic complex 16 was formed (73%).
3
). P NMR
3
-
1
.
60 3 2
H S P
2
3 2
)
1
3
Ch a r a cter iza tion of 16. H NMR (CDCl ppm): 7.08 (s,
2H central thiophene), 7.05 (d, 2H, J ) 3.7 Hz lateral
thiophenes), 6.69 (d, 2H, J ) 3.7 Hz lateral thiophenes), 1.89
(m, 12H, P(CH
CH ), 1.46 (m, 12H, P(CH
7.1 Hz, P(CH CH CH CH
2
CH
2
CH
2
CH
3
)
2
3
), 1.52 (m, 12H, P(CH
CH CH CH , 0.91 (t, 18 H, J )
). C NMR (CDCl ppm): 132.3,
2 2 2
CH CH -
3
)
3
2
3
2
3 3
)
1
then with a mixture of hexanes/CH
2
Cl
2
(95:5 v/v). Evaporation
2
2
2
3
)
3
3
of the solvent yielded 0.67 g (60%) of 11 as a pale yellow
131.7, 131.1, 127.6, 124.4, 119.1 (thiophenes), 106.8 (t, J ) 16
Hz, (Pd-CtC-)) 97.9 (br, Pd-CtC-) 88.0, 88.1 (-CtC-),
1
powder. H NMR (CDCl
3
ppm): 7.09 (s, 4H), 7.14 (s, 2H) 0.23
2
6.3 (P(CH
2
CH
2
CH
2
CH
3
)
3
24.3 (t, J ) 6.3 Hz, P(CH
2 2 2
CH CH -
(
1
s, 18H). IR (casted film): 2963-2852 (m), 2143 (m), 1415 (w),
202 (s), 801 (s) cm-1. Spectroscopic data are in agreement
CH ) , 22.9 (t, J ) 13.4 Hz, P(CH CH CH CH ) ), 13.7 (P(CH -
3
3
2
2
2
3
3
2
3
1
3
4
2 2 3 3 3
CH CH CH ) ). P NMR (CDCl , ppm): 11.06. IR (casted
with literature reports.
film): 2857-2871 (s), 2189 (w), 2100 (s), 2099 (m), 1194 (w),
P r epa r a tion of 2,5-[2,2′-(5,5′-Diiodo)bisth ien yl]biseth y-
n ylth iop h en e (12). A flask was charged with 0.41 g (3.5
mmol) of N,N,N′,N′-tetramethylethylenediamine (TMEDA),
-
1
7
5
99 (m), 359 (w) cm . Anal. Calcd for C68
6.90; H, 8.00. Found: C, 56.96; H, 8.13.
114 3 2 4 2
H S Cl P Pd : C,
P a th b: EOP Rou te. To a solution of 0.006 g (0.006 mmol)
of Pd(PPh and 0.16 g (0.26 mmol) of 2,5-[2,2′-(5,5′-diiodo)-
0
.52 g (1.8 mmol) of 2,5-(2,2′-dithienyl)diethynylthiophene (9),
3 4
)
and 50 mL of hexane. To this solution was added 2.7 mL (3.5
mmol) of sec-BuLi (1.3 M in cyclohexane) by syringe, and the
reaction mixture was refluxed for 30 min. After this time the
reaction mixture was left to reach room temperature and then
bisthienyl]bisethynylthiophene (12) in 40 mL of THF was
added 0.18 g (0.54 mmol) of ethynyltributyltin. After overnight
stirring at 70 °C, 1H NMR analysis indicated complete
consumption of the starting tin reagent with formation of 13
15
2
was cooled to 0 °C. I (0.9 g, 3.5 mmol) was added and the
and Bu SnI. After cooling to -20 °C, 0.34 mL (0.70 mmol) of
3
mixture stirred at room temperature for 30 min. To the
reaction mixture was then added water (100 mL), and the
mixture was extracted with benzene (3 × 50 mL). The organic
layer was further washed with water (4 × 100 mL), dried over
sodium sulfate, and filtered. Celite was added to the filtrate,
and after removal of the solvent, the coated product was
chromatographed on silica gel (hexane) to yield 0.31 g (40%)
a solution of LDA (2.0 M in THF/heptane/ethylbenzene) was
added, and the mixture allowed to warm to room temperature.
1
A sample of the reaction mixture examined by H NMR
analysis15 indicated complete conversion of the alkyne moieties
into the corresponding tributyltinalkynyl functionalities. To
2 3 2
this solution was added trans-Cl Pd (PBu ) (5) 0.128 g (0.22
1
mmol), and the mixture was warmed to reflux. After 24 h, H
NMR analysis15 indicated complete consumption of reactants;
the mixture was then cooled and filtered over Celite to
eliminate the spent catalyst, and the filtrate was reduced
under vacuum to a small volume. Addition of methanol caused
formation of a precipitate that was collected by filtration,
washed repeatedly with methanol, and dried under vacuum.
The product (0.2 g, 73%) was isolated as a dark red solid.
Evaporation under reduced pressure of the methanolic rinsing
solution afforded a dark oil, which was submitted to vacuum
1
of the product, which was recrystallized from EtOH. H NMR
(
CDCl ppm): 7.13 (d, J ) 3.8 Hz, 2H), 6.92 (d, J ) 3.8 Hz,
3
13
2
1
2
3
H) 7.13 (s, 1H). C NMR (CDCl ppm): 137.2, 133.7, 132.5,
28.5, 124.4, 75.8 (thiophene), 87.6, 86.4 (CtC). IR (Nujol):
193 (w), 1190 (m), 799 (s), 501 (s) cm-1. Anal. Calcd for
C
16
H
6
S
3
I
2
: C, 35.06; H, 1.10. Found: C, 35.5; H, 1.15.
P r ep a r a tion of [2-Eth yn ylth iop h en e]-2,5-biseth yn yl-
th iop h en e (13). This compound was prepared with the same
procedure used for 2,5-bis(ethynyl)thiophene (3) by treating
0
.29 g (0.61 mmol) of [2-trimethylsilylethynylthiophene]-2,5-
-2
distillation (Kugelrohr, 120 °C/10 mmHg), giving 0.064 g
bis(ethynyl)thiophene (11), dissolved in a mixture of THF and
MeOH (1:1), with 0.5 mL of a 0.5 M solution (0.25 mmol) of
KOH in water. The product was isolated by chromatography
on a silica gel column using a mixture of hexanes/THF (9:1)
as the eluent. Removal of the solvent yielded 0.14 g (0.41 mmol,
(
90%) of tributyltin chloride. Spectroscopic characteristics were
identical to those of the material obtained with the dehydro-
halogenation route.
Ack n ow led gm en t. This work was supported by the
Consiglio Nazionale delle Ricerche (CNR Roma), with
the “Progetto Finalizzato C.N.R.-Materiali Speciali per
Tecnologie Avanzate II”, contract no. 97.00946.PF34,
and the “Progetto Finalizzato CNR-Materiali e Dis-
positivi per l’Elettronica a Stato Solido”, contract no.
6
7%) of the product as a yellow oil that darkened upon
standing. This compound was used immediately after its
1
preparation. H NMR (CDCl
7
3
ppm): 7.14 (d, J ) 3.8 Hz, 2H),
.11 (d, J ) 3.8 Hz, 2H), 7.15 (s, 2H), 3.38 (s, 2H). IR (casted
film): 3282 (m), 2199 (w), 2098 (w), 1197 (m), 800 (s) cm
Spectroscopic data are in agreement with literature reports.34
-
1
.
9
7.01350.PF48. Thanks are also given to CNR/RAS
Russian Academy of Science-Moscow) bilateral agree-
P r ep a r a tion of P oly{[2-eth yn ylth iop h en e]-2,5-biseth y-
n ylt h iop h en eb is(t r ib u t h ylp h osp h in e)p a lla d iu m } (15).
P ath a: Deh ydr oh alogen ation Rou te. [2-Ethynylthiophene]-
(
ment for financial support. The authors acknowledge
Prof. Giancarlo Sleiter for the kind revision of the
manuscript.
2
,5-bisethynylthiophene (13) (0.14 g, 0.41 mmol) was dissolved
in 20 mL of diethylamine, and to this solution was added trans-
Cl Pd (PBu (5) (0.24 g, 0.41 mmol) followed by CuI (5 mg).
2
3 2
)
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra
accounting for the sequence of transformations from 1 to 9 and
related explanatory text. 1H NMR and C NMR spectra of
compound 16 and related description. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
After 15 h of stirring at room temperature all volatile
components were removed under reduced pressure. The re-
13
sulting residue was redissolved in CHCl
3
and chromato-
(34) Buttinelli, A.; Antonelli, E.; Viola, E.; Lo Sterzo, C. Organome-
tallics 1998, 17, 2574.
OM010312Q