A new stereoselective approach to (E)-poly(arylenevinylene)s

Article abstract of DOI:10.1055/s-2007-1000836

A new synthetic protocol for the one-pot, stereoselective synthesis of (E)-poly(arylenevinylene)s via palladium-catalyzed Hiyama cross-coupling of dihaloarenes with cyclic gem-bis(silyl)ethene or isopropoxydimethylvinylsilane is described. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-1000836

LETTER
41
A New Stereoselective Approach to (E)-Poly(arylenevinylene)s
Stereoselective
A
pproac
i
h
to
(
E
e
)-Poly(aryl
s
ł
Department of Organometallic Chemistry, Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
Fax +48(61)8291508; E-mail: marcinb@amu.edu.pl
Received 16 October 2007
far fully exploited. Recently, Ozawa and co-workers re-
Abstract: A new synthetic protocol for the one-pot, stereoselective
ported a stereocontrolled synthesis of trans- and cis-oli-
synthesis of (E)-poly(arylenevinylene)s via palladium-catalyzed
Hiyama cross-coupling of dihaloarenes with cyclic gem-bis(si-
go(arylenevinylene)s
using
Hiyama-type
polycondensation of substituted 1,4-diiodobenzenes with
1,4-bis(silyl-ethenyl)benzenes.8c,10 An interesting silicon-
assisted alternative for the synthesis of PAV seems to be
also palladium-catalyzed poly-Heck reaction of bisarene-
diazonium salts with vinyltriethoxysilane.11 However, ap-
plication of this particular method has been limited be-
cause of commercial unavailability of bisarene-diazonium
salts, whose synthesis from very toxic aryl diamines is
challenging even for the most common PAV precursors.
lyl)ethene or isopropoxydimethylvinylsilane is described.
Key words: poly(arylenevinylene)s, cross-coupling, palladium
catalyst, organometallic reagents, silicon derivatives
Poly(arylenevinylene)s (PAV) constitute a group of p-
conjugated polymers that have attracted considerable in-
terest because of their potential applications in electronic
and optoelectronic devices including light-emitting di-
odes, solar cells, plastic lasers, fluorescent sensors, re-
chargeable batteries, field-effect transistors, etc.1 In the
context of their wide applications, synthetic design of
PAV has attracted a great deal of recent interest.2
Therefore, we wish to report herein the first, unprecedent-
ed, one-pot, palladium-catalyzed Hiyama-type strategy
for the stereoselective synthesis of (E)-poly(arylenevi-
nylene)s using aryl dihalides and isomeric bis(si-
lyl)ethenes as new double-bond equivalents.
Conventional approaches to poly(arylenevinylene)s in-
volve dehydrohalogenative polycondensation of bis(ha-
lomethyl)benzenes (Gilch reaction),3 thermolysis of
sulfonium polymer precursors (Wessling route),4 Wittig–
Horner polycondensation of xylylene diphosphonates
with phthalaldehydes,5 palladium-catalyzed Heck reac-
tion of ethylene6 or divinylarenes7 with dihaloarenes as
well as palladium-catalyzed Suzuki–Miyaura coupling of
difunctional arylboronic derivatives with di(haloalke-
nyl)arenes.8
During the course of our studies on the reactivity of gem-
inal bis(silyl)alkenes towards carbon electrophiles, we
have unexpectedly found that 2,2,4,4-tetramethyl-1,5-di-
oxa-3-methylene-2,4-disilacycloheptane (1), in the reac-
tion with 2 equivalents of aryl iodides (iodobenzene and
4-iodoanisole), under standard cross-coupling conditions
forms exclusively (instead of the expected 1,1-di-
arylethenes) cine-substitution products – (E)-stilbene and
(E)-4,4¢-dimethoxystilbene, respectively, with perfect ste-
reoselectivity and almost quantitative yield (Scheme 1).12
The palladium-catalyzed and fluoride-promoted cross-
coupling of unsaturated organosilicon compounds with
aryl halides (Hiyama coupling) has been recently em-
ployed as a mild and efficient alternative to the well-es-
tablished Stille and Suzuki reactions due to commercial
availability, high stability, and low toxicity of the silicon
derivatives.9 Although there are many reports on the suc-
cessful applications of the Hiyama coupling in the synthe-
sis of molecular p-conjugated organic frameworks, the
potential use of this particular method for the synthesis of
arylenevinylene oligomers and polymers has not been so
Although cine-substitution of 1-aryl-1-silylethenes in pal-
ladium-catalyzed cross-coupling with aryl iodides or aryl-
diazonium salts has been previously reported,13 the
simultaneous ipso- and cine-substitution of geminally si-
lylated ethenes under Hiyama conditions is unprecedent-
ed.
Since the starting compound 1 can be easily prepared with
high yield in a two-step process from inexpensive chlo-
rodimethylvinylsilane and ethylene glycol using silyla-
R
Me
Pd2(dba)3
Me
I
Si
Si
Me
Me
+
THF, 65 °C, 2 h
O
O
R
R
1
(2 equiv)
R = H, OMe (92–96%)
Scheme 1
SYNLETT 2008, No. 1, pp 0041–0044
x
x.
x
x.
2
0
0
7
Advanced online publication: 11.12.2007
DOI: 10.1055/s-2007-1000836; Art ID: G33807ST
© Georg Thieme Verlag Stuttgart · New York

42
W. Prukała et al.
LETTER
tion–ruthenium-catalyzed
silylative
coupling–exo- lower yield (Table 1, entry 5) and an increase of the
cyclization sequence,14 this novel bis(silyl)ethene trans- amount of Pd catalyst (from 0.5 to 2 mol% per silyl group)
formation is expected to be an attractive alternative for the as well as a longer reaction time did not appreciably affect
synthesis of arylenevinylene polymers.
the rate of this process.
We began our investigations with the cross-coupling be- It is worth noting that all the coupling processes proceed-
tween cyclic 1,1-bis(silyl)ethene 1 and 1,4-diiodobenzene ed in stereoselective manner to yield products containing
using Pd2(dba)3 as a catalyst and TBAF as an activator. only (E)-vinylene units in the polymer chain. Moreover,
Under standard cross-coupling reaction conditions (30– the application of more available and cheaper aryl dibro-
40 °C), the expected product was not observed, whereas at mides to our new silicon-assisted methodology has signif-
55 °C the low conversion of diiodoarene has been detect- icantly broadened its utility. The conversion of 1,4-
ed (ca 40%). Increasing the temperature to 80 °C complet- dibromobenzene and 4,4¢-dibromobiphenyl has been only
ed this reaction in 16 hours with only 0.5 mol% loading of slightly lower than that of 1,4-diiodobenzene under the
Pd2(dba)3 per silyl group.
analogous reaction conditions (Table 1, entry 2, 7).
These optimal conditions were applied to the other aryl di- With the optimized conditions established for cyclic 1,1-
iodides providing almost quantitative yields (94–98%) of bis(silyl)ethene, we turned our attention towards the one-
the desired polymeric products (Table 1).15 Only 1,4-di- pot synthesis of PAV by successive silylative coupling –
iodotetrafluorobenzene gave the expected polymer with Hiyama coupling proceeding via (E)-1,2-bis(silyl)ethene
intermediate. In the first step, unsaturated organosilicon
Table 1 Synthesis of (E)-Poly(arylenevinylene)s via Palladium-
Catalyzed Cross-Coupling of Cyclic 1,1-Bis(silyl)ethene with Aryl
alyzed silylative coupling of the respective vinylsilane
Dihalidesa
precursors were synthesized using ruthenium hydride cat-
and then the post reaction mixture was treated with an ap-
propriate dihaloarene under the Hiyama cross-coupling
conditions (Scheme 2). In this process, isopropoxydi-
methylvinylsilane (8) was used to facilitate the next palla-
dium-catalyzed cross-coupling.
Me
Si
Me
Me
[Pd2(dba)3]
Ar
Si
Me
+
X-Ar-X
n
TBAF, 80 °C
dioxane
O
O
n
n
X = I, Br
1
The silylative coupling of 8 successfully proceeded in the
presence of [RuHCl(CO)(PPh3)3] (2 mol%) in dioxane,
and the starting vinylsilane was efficiently transformed
into an almost equimolar mixture of isomeric (E)-1,2-
bis(isopropoxydimethylsilyl)ethene A and 1,1-bis(iso-
propoxydimethylsilyl)ethene B (Scheme 2) in 16 hours at
110 °C. Moreover, the use of CuCl (2 mol%) as a co-cat-
alyst caused a slight increase in the catalytic activity of the
ruthenium–hydride complex. Although toluene or chlo-
robenzene could also be employed without affecting ei-
ther the activity of the catalytic system or the selectivity
of this process, the use of dioxane seemed to be the most
favorable due to its higher effectiveness in the following
palladium-catalyzed coupling.
F
F
F
(7)
Ar =
(2),
(5),
(6),
(3),
(4),
S
F
Entry Aryl dihalide
Time (h) Product17 Yield (%)b
1
2
3
4
5
6
7
8
1,4-I2C6H4
1,4-Br2C6H4
1,3-I2C6H4
1,2-I2C6H4
1,4-I2C6F4
16
24
24
24
48
24
24
24
2
2
3
4
5
6
6
7
96
94
98
97
35
98
95
97
4,4¢-I2C6H4-C6H4
Similarly to the reactions with 1, palladium-catalyzed
coupling of the isomeric bis(silyl)ethenes A and B with
aryl dihalides in the presence of TBAF and Pd2(dba)3 (1
mol%) catalyst proceeded stereoselectively to give satis-
factory yields of the desired poly(arylenevinylene)s
4,4¢-Br2C6H4-C6H4
2,5-I2C4H2S
a [1]:[XArX]:[TBAF]:[Pd2(dba)3] = 1:0.9:2.4:0.01, dioxane, 80 °C.
b Isolated yields of products.
SiMe2(Oi-Pr)
n X-Ar-X
(i-PrO)Me2Si
RuHCl(CO)(PPh3)3
CuCl
A
[Pd2(dba)3]
Ar
2n
SiMe2(Oi-Pr)
+
TBAF, 80 °C
dioxane
dioxane, 16 h, 110 °C
n
8
(i-PrO)Me2Si
SiMe2(Oi-Pr)
B
n
yield: 99%
selectivity: a/b = 1:1
Scheme 2
Synlett 2008, No. 1, 41–44 © Thieme Stuttgart · New York

LETTER
Stereoselective Approach to (E)-Poly(arylenevinylene)s
Table 3 Physical Properties of the Polymers 2–7
43
(Table 2).16 This particular reaction proceeded via com-
petitive stereospecific coupling of (E)-bis(silyl)ethene in-
termediate and afore-mentioned rearrangement of
geminal bis(silyl)ethene derivatives. The results of the
one-pot silylative coupling–Hiyama coupling are depicted
in Table 2.
Compound
UV λmax ([nm)
369.8
Mn
1530a
Mw/Mn
–
2
3
4
5
6
7
307.2
840a
2670b
2200a
11700b
3220b
–
p-Arylene polymers were isolated by simple filtration
from the reaction mixture. The PAV containing o-phen-
ylene or thienylene units were isolated by column chro-
matography. All polymers were washed with acetone in
order to remove traces of oligomers and catalyst and dried
under vacuum. Due to the lack of polar lateral substitu-
ents, these polymers were found to be only poorly soluble
in CHCl3 and partly in THF. Molecular weights of THF
soluble fractions of polymers obtained were measured by
GPC using THF as an eluent and polystyrene standards.
299.4
1.27
–
305.8
338.2
1.19
1.18
384.0
a Calculated by MALDI-MS.
b Calculated by GPC.
1
corresponding H NMR signals fall in the region of aro-
matic protons and could be assigned only for (E)-
poly(1,4-phenylenevinylene) oligomers 2 (J = 19 Hz) and
(E)-poly(tetrafluorophenylenevinylene)s 5 (J = 16 Hz). It
may be noted that the presence of 1,1-diarylenevinylene
defects in the polymers, which are usually formed during
other palladium-catalyzed processes was not detected.
Due to the insolubility of the resulting products, the ma-
trix-assisted laser desorption–ionization mass spectrome-
try (MALDI-MS) was also applied for estimation of their
molecular weights. The MALDI-MS spectra of 2 and 5 in
ditranol as a matrix revealed only short chain polymers:
11–18-mer and 6–10-mer, respectively. The LSIMS of
these compounds in NBA as matrix revealed chains till In conclusion, we have developed a new, efficient, highly
25-mer characterized by very low intensity peaks and high stereoselective, one-pot synthetic methodology for the
polydispersity. The polymers in solution subjected on UV construction of (E)-poly(arylenevinylene)s based on pal-
light (366 nm) emit intensive blue (2–6) or green (7) light. ladium-catalyzed Hiyama cross-coupling of cyclic bis(si-
Representative physical properties of the selected prod- lyl)ethene or sequential silylative coupling–Hiyama
ucts are presented in Table 3.
cross-coupling of isopropoxydimethylvinylsilane with
aryl dihalides. The availability of starting materials, the
simplicity of the experimental technique, and the use of
aryl dibromides instead of aryl diiodides are favorable
features of this new catalytic approach to stereodefined
PAV polymers.
The structure of the resulting polymers was proved by FT-
1
IR and H NMR spectroscopy. The presence of (E)-vi-
nylene functionality was unambiguously confirmed by
the appearance of FT-IR bands attributable to CH bending
of trans-vinylene at 936–971 cm–1. Unfortunately, the
Table 2 One-Pot Synthesis of (E)-Poly(arylenevinylene)s via Se-
quential Ruthenium-Catalyzed Silylative Coupling–Palladium-Cata-
lyzed Cross-Coupling of Isopropoxydimethylvinylsilanea
Acknowledgment
This work was made possible by a grant PBZ-KBN 118/T09/17
from Ministry of Education and Science (Poland).
n X-Ar-X
RuHCl(CO)(PPh3)3
CuCl
Ar
[Pd2(dba)3]
2n
SiMe2(Oi-Pr)
References and Notes
dioxane, 110 °C
TBAF, 80 °C
dioxane
n
8
(1) For reviews, see: (a) Functional Organic and Polymeric
Materials; Richardson, T. H., Ed.; John Wiley and Sons:
Chichester England, 2000. (b) Samuel, I. P. W.; Turnbull,
G. A. Chem. Rev. 2007, 107, 1272. (c) Coropceanu, V.;
Cornil, J.; da Silva Filho, D. A.; Olivier, Y.; Silbey, R.;
Bredas, J. L. Chem. Rev. 2007, 107, 926. (d) Thomas, S.
W.; Joly, G. D.; Swager, T. M. Chem. Rev. 2007, 107, 1339.
(e) Günes, S.; Neugebauer, H.; Sariciftci, N. S. Chem. Rev.
2007, 107, 1324. (f) Hoeben, F. J. M.; Jonkheijm, P.; Meijer,
E. W.; Schenning, A. P. H. Chem. Rev. 2005, 105, 1491.
(g) Segura, J. L.; Martin, N.; Guldi, D. M. Chem. Soc. Rev.
2005, 34, 31.
Entry
Aryl dihalide
1,4-I2C6H4
Time (h) Product
Yield (%)b
1
2
3
4
5
6
8
16
24
24
24
48
24
24
2
2
3
4
5
6
7
98
92
90
90
43
98
90
1,4-Br2C6H4
1,3-I2C6H4
1,2-I2C6H4
1,4-I2C6F4
4,4¢-I2C6H4-C6H4
2,5-I2C4H2S
(2) (a) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew.
Chem. Int. Ed. 1998, 37, 402. (b) Scherf, U. Top. Curr.
Chem. 1999, 201, 163. (c) Akcelrud, L. Prog. Polym. Sci.
2003, 28, 875.
a Silylative coupling conditions:
(3) (a) Gilch, H. G.; Wheelwright, W. L. J. Polym. Sci., Part A:
Polym. Chem. 1966, 4, 1337. (b) Hsieh, B. R.; Yu, Y.; Van
Laeken, A. C.; Lee, H. Macromolecules 1997, 30, 8094.
[8]:[RuHCl(CO)(PPh3)3]:[CuCl] = 1:0.02:0.02; dioxane (1 M),
110 °C, 16 h. Hiyama coupling conditions: [ViSiMe2(Oi-
Pr)]:[XArX]:[TBAF]:[Pd2(dba)3] = 2:0.9:2.4:0.01, dioxane, 80 °C.
b Isolated yields of products
Synlett 2008, No. 1, 41–44 © Thieme Stuttgart · New York

44
W. Prukała et al.
LETTER
(4) (a) Wessling, R. A.; Zimmerman, R. G. US 3 401 152, 1968.
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for Organic Synthesis, Vol. 1; Negishi, E., Ed.; Wiley-
Interscience: New York, 2002, 285. (b) Hiyama, T. In
Metal-Catalyzed Cross-Coupling Reactions; Diederich, F.;
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J. Organomet.Chem. 2003, 49, 676.
was heated at 80 °C for 16–48 h under an argon atmosphere.
The degree of conversion of the substrates was estimated by
GC and TLC analyses. Then, the reaction mixture was
cooled and the precipitated solid was filtered and washed
extensively with acetone. The final product was separated
using filtration (2, 6) or chromatography column (3–5, 7)
with silica (THF–EtOAc). The desired products were
obtained by combining both fractions of solids to afford the
desired polymeric products.
(16) One-Pot Synthesis of PAV from Isopropoxydimethyl-
vinylsilane
The glass minireactor (10 mL, equipped with a magnetic
stirring bar, argon bubbling tube and thermostated heating
oil bath) was evacuated and flushed with argon. Then,
[RuH(Cl)(CO)(PPh3)3] (19.05 mg, 0.02 mmol), CuCl (1.98
mg, 0.02 mmol), isopropoxydimethylvinylsilane (0.144 g,
1.0 mmol), and anhyd dioxane (1.0 mL) were added to the
reactor (in the case of reaction with 4,4¢diiodobiphenyl and
2,5-diiodothiophene 2 mL of dioxane). The reaction mixture
was heated at 110 °C for 16 h under an argon flow. After the
reaction was completed [GC-MS and 1H NMR analyses
confirmed the formation of the mixture of (E)-1,2-bis(iso-
propoxydimethylsilyl)ethene A and 1,1-bis(isopropoxy-
dimethylsilyl)ethene B], palladium catalyst [Pd2(dba)3]
(0.005 mmol), TBAF (1 M solution in THF, 320 mg, 1.2
mmol), and respective dihaloarene (0.45 mmol) were added
and the mixture was heated at 80 °C for 16–48 h under an
argon atmosphere. The degree of conversion of the
substrates was estimated by GC and TLC analyses. Then, the
reaction mixture was cooled and the precipitated solid was
filtered and washed extensively with acetone. The final
product was separated using filtration (2, 6) or chromatog-
raphy column (3–5, 7) with silica (THF–EtOAc). The
desired products were obtained by combining both fractions
of solids to afford the desired polymeric product.
(11) Sengupta, S.; Sadhukhan, S. K. J. Chem. Soc., Perkin Trans.
1 1999, 2235.
(12) Reaction of Cyclic 1,1-Bis(silyl)ethene (1) with Aryl
Iodides
(17) Spectroscopic Data of the Selected Products
(E)-Poly(1,4-phenylenevinylene)s (2)
The glass reactor (100 mL, two-necked, round-bottomed
flask equipped with a magnetic stirring bar, reflux
condenser, argon bubbling tube and thermostated heating oil
bath) was evacuated and flushed with argon. Compound 1 (1
g, 4.95 mmol) and anhyd THF (20 mL) were added to the
reactor. At r.t. 14.8 mmol of TBAF (1 M soln in THF) was
added and the mixture was stirred for 10 min. After this time,
9.9 mmol of the respective aryl iodide and 56.8 mg (9 mmol)
of Pd2(dba)3 were added and the reaction mixture was stirred
under argon for 2 h at 65 °C. After the reaction was
completed (GC-MS analysis) the volatiles were evaporated
under vacuum and the crude product was chromatographed
on silica gel (eluent: hexane–EtOAc, 10:1) to afford the
analytically pure products. Isolated yields: (E)-stilbene,
96%; (E)-4,4¢-dimethoxystilbene, 92%.
IR (KBr): 740.5 (s), 834.8 (s), 964.7 (s), 1015.2 (s), 1256.0,
1488.6, 1512.8, 1596.6, 1695.9 (s, br), 2922.6, 2953.9,
3021.6 (s) cm–1. 1H NMR (300 MHz, DMSO-d6): d = 0.15 (s,
SiCH3), 0.21 (s, SiCH3), 6.50 (d, J = 19.2 Hz, PhCH=), 6.94
(d, J = 19.2 Hz, PhCH=), 7.41 (d, J = 8.5 Hz, H in phenyl
ring), 7.54 (d, J = 8.5 Hz, H in phenyl ring) ppm. 13C NMR
(75 MHz, DMSO-d6): d = 0.1, 0.5, 0.8, 29.0, 31.3, 128.2,
128.7, 129.2, 132.4 ppm. Anal. Calcd for (C8H6)n: C, 94.07;
H, 5.92. Found: C, 91.58; H, 5.43.
(E)-Poly(2,3,5,6-tetrafluorophenylenevinylene)s (5)
IR (KBr): 758.7 (s), 938.6, 979.5, 1091.1 (s, br), 1215.7,
1486.4, 1527.7, 1617.3, 1652.9, 2928.8, 2961.1, 3019.3 (s)
cm–1. 1H NMR (300 MHz, CDCl3): d = 0.10 (s, SiCH3), 0.20
(s, SiCH3), 7.09 (d, J = 16 Hz, PhCH=), 7.75 (d, J = 16 Hz,
PhCH=) ppm. 13C NMR (75 MHz, CDCl3): d = –0.2, 0.6,
29.4, 29.7, 30.3, 125.4, 128.4, 128.9, 130.5, 143.4 ppm.
Anal. Calcd for (C8F4H2)n: C, 55.19; H, 1.19. Found: C,
55.37; H, 1.43.
(13) (a) Hatanaka, Y.; Hiyama, T. J. Organomet.Chem. 1994, 97,
465. (b) Ikenaga, K.; Matsumoto, S.; Kikukawa, K.;
Matsuda, T. Chem. Lett. 1988, 873. (c) Babudri, F.;
Farinola, G. M.; Lopez, L. C.; Mattinelli, M. G.; Naso, F.
J. Org. Chem. 2001, 66, 3878.
(E)-Poly(2,5-thiophenylenevinylene)s (7)
(14) Pawluc, P.; Marciniec, B.; Hreczycho, G.; Gaczewska, B.;
Itami, Y. J. Org. Chem. 2005, 70, 370.
IR (KBr): 790.6 (s, br), 935.8, 1039.4 (s, br), 1070.1, 1258.5,
1444.5, 1618.6, 1655.2, 1722.2, 2924.3, 2957.4, 3065.4
cm–1. 1H NMR (300 MHz, CDCl3): d = 0.08 (s, SiCH3), 0.20
(s, SiCH3), 6.40–7.80 (m, H in thiophenyl ring and ArCH=)
ppm. 13C NMR (75 MHz, CDCl3): d = 0.1, 0.9, 14.2, 19.6,
23.1, 29.8, 30.4, 124.2, 125.4, 128.3, 128.7, 128.8, 130.4,
130.8, 143.2 ppm. Anal. Calcd for (C6H4S)n: C, 66.62; H,
3.72; S, 29.64. Found: C, 62.58; H, 3.03; S, 28.33.
(15) Synthesis of PAV from Cyclic 1,1-Bis(silyl)ethene (1)
[Pd2(dba)3] (9.16 mg, 0.01 mmol), dioxane (4 mL), 2,2,4,4-
tetramethyl-3-methylene-1,5-dioxa-2,4-disilacycloheptane
(1, 202 mg, 1 mmol), TBAF (640 mg, 2.4 mmol), and
respective dihaloarene (0.9 mmol) were placed in an
evacuated and flushed with argon 25 mL flask. The mixture
Synlett 2008, No. 1, 41–44 © Thieme Stuttgart · New York

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