Synthesis and characterization of an oligomeric conjugated metal-containing poly(p-phenylenevinylene) analogue

Article abstract of DOI:10.1039/c0dt00121j

A new nickel-containing bis(bromobenzyl)salphen monomer suitable for Gilch polymerization was prepared. Reaction with KO^tBu in THF-DMF afforded primarily gels, but also soluble, conjugated oligomers that are red-shifted in the absorption spectr

Full text of DOI:10.1039/c0dt00121j

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PAPER
www.rsc.org/dalton | Dalton Transactions
Synthesis and characterization of an oligomeric conjugated metal-containing
poly(p-phenylenevinylene) analogue†
Jian Jiang, Alfred C. W. Leung and Mark J. MacLachlan*
Received 11th March 2010, Accepted 29th April 2010
First published as an Advance Article on the web 7th June 2010
DOI: 10.1039/c0dt00121j
A new nickel-containing bis(bromobenzyl)salphen monomer suitable for Gilch polymerization was
prepared. Reaction with KOtBu in THF–DMF afforded primarily gels, but also soluble, conjugated
oligomers that are red-shifted in the absorption spectrum when compared to the monomer. This
spectral change, consistent with an enhanced conjugation length, was also compared with a suitable
model compound for the polymer. Our results indicate that Gilch polymerization may be a useful route
to fully conjugated metal-containing polymers if attention is paid to ensuring solubility of the product.
complexes in the backbone are known, we were able to ensure
Introduction
solubility with the use of long alkyl substituents. The dearth of
Conjugated polymers have been the subject of intense research
viable synthetic routes to conjugated metal-containing polymers,
since the discovery in 1977 that doped polyacetylene is metallic.1
as well as the difficulty of producing soluble polymers has impeded
The conjugation in these organic materials is facilitated by unsat-
progress in this field.
urated bonding within the backbone that enables delocalization of
Since the discovery of electroluminescence in poly(p-phenylene-
vinylene) (PPV, 1) in 1990,13 many derivatives of PPV have been
prepared, particularly for application in light-emitting diodes
(LEDs).14,15 PPV derivatives with bulky alkoxy side groups have
been most extensively studied as these substituents enhance
both solubility and quantum efficiency.16 Various approaches
to synthesize soluble dialkoxy PPVs have been reported in the
literature including the Gilch route,17 the Wittig reaction,18 and
aryl-ethylene coupling via Heck or Suzuki reactions.19 Among
these methods, the Gilch route is commonly used because it is
a simple one-pot process. In the Gilch polymerization route, a
1,4-di(halogenomethyl)benzene structure is postulated to undergo
an elimination reaction to form a quinodimethane intermediate
that polymerizes, as shown in Scheme 1.20 In a second step, elimi-
nation of HX affords the conjugated PPV. Most research based on
the synthesis of PPV by the Gilch route has focused on changing
the functional groups on the monomer precursor in order to form
the quinodimethane intermediate more readily. A few papers have
reported the synthesis of poly(fluorenevinylene) derivatives by
Gilch polymerization in which electrons transfer over four double
bonds to give the quinodimethane intermediate.21 We are aware
of only two papers that show a more complicated system, in
which researchers attempted to incorporate porphyrin units22 and
1,3,4-oxadiazole segments23 into the copolymer backbone. These
copolymers contained less than 2 mol% of porphyrin and less than
electrons within the p-orbitals, and gives rise to a band structure.
In general, the conjugation in organic polymers is limited by
defects and rotation of bonds within the backbone. By preventing
the rotation of the components in the conjugated polymer, the
conjugation may be extended, improving the extent of exciton
delocalization and charge carrier migration.2 Efforts to hinder
rotation have included using conjugated and saturated linkers
between segments of the backbone.3 Metal complexation may
be used to modify the conjugation by hindering rotation of the
polymer. For example, Swager and coworkers have used this
mechanism to inhibit the conjugation in polythiophene segments,
leading to measurable property changes that can be used in
sensing.4
There is a growing interest in the synthesis and character-
ization of metal-containing conjugated polymers due to their
potential in materials science.5,6 In addition to affecting the
conformation of the polymer, the introduction of a metal center
into the conjugated polymer chain may produce a range of
characteristics that differ from those of conventional organic
polymers, e.g. redox, magnetic, optical and electronic properties.7
Incorporation of chromophores, such as Schiff-base complexes,8
into polymers has been investigated for developing catalysts9
and luminescent materials for potential application in light-
emitting diodes (LEDs).10 Schiff-base complexes incorporated
into polymers via electropolymerization offer binding sites for the
4-electron reduction of oxygen to water.11 We have reported con-
jugated poly(p-phenyleneethynylene)s that incorporate Schiff-base
complexes of Ni2+, VO2+, Zn2+, and Cu2+.12 The metal complexes
strongly influence the optical properties of the conjugated polymer.
Although intractable conjugated polymers containing Schiff-base
Department of Chemistry, University of British Columbia, 2036 Main
Mall, Vancouver, BC, Canada V6T 1Z1. E-mail: mmaclach@chem.ubc.ca;
Fax: 604-822-2847; Tel: 604-822-3070
† Electronic supplementary information (ESI) available: NMR spectra,
mass spectra, and other supplementary data. See DOI: 10.1039/c0dt00121j
Scheme 1 Synthesis of PPV by the Gilch polymerization.
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30% of oxadiazole segments. It was not possible to include larger
quantities of porphyrin and oxadiazole into the polymer due to
solubility limitations.
We report here the design and synthesis of a new Schiff-base
metal complex that functions as a monomer for the preparation
of a metal-containing PPV analogue. The synthesis and char-
acterization of the conjugated homopolymer, as well as a new
conjugated model compound, are discussed. During the formation
of the quinodimethane intermediate in our system, an elimination
reaction over seven double bonds must occur.
pound 3 was then converted into 2,5-bis(methoxymethyl)anisole
4
in 95% yield upon treatment with excess NaOMe in
THF.27 Selective oxidation of compound 4 with 2,3-dichloro-
5,6-dicyanobenzoquinone (DDQ) in 10 : 1 CH2Cl2–H2O gave 2-
methoxy-4-(methoxymethyl)benzaldehyde 5.27 In this reaction, the
product obtained is a mixture of 5 and its isomer 3-methoxy-4-
(methoxymethyl)benzaldehyde in a 5 : 1 ratio. As the separation of
the isomers was difficult at this stage, the mixture was used for the
next step without purification. In the final step, a simultaneous
deprotection of the phenol as well as the benzyl methyl ether with
BBr3 gave the desired compound 6. This product could be purified
by flash chromatography on SiO2 (in 1 : 2 DCM : hexanes) and
stored in the fridge. The by-product was easily separated from
the desired compound 6 by this method. It is noteworthy that
compound 6 is relatively unstable; attempts to concentrate it by
rotary evaporation at > 30–40 ◦C resulted in decomposition to a
thick, brown paste with visible HBr production.
Results and discussion
The best method to ensure complete metallation of a conjugated
polymer is to polymerize the metal-containing monomer, rather
than post-polymer modification. We proposed to synthesize a
new monomer 2 containing two benzylbromide substituents as
a possible precursor to a metallo-PPV analogue. This monomer
features branched alkoxy groups with stereogenic centers for
solubility and a square planar nickel(II) center to maintain
planarity and, thus, conjugation in the monomer. In this monomer,
the elimination reaction would extend over a distance of 16 atoms,
as will be discussed.
Schiff-base condensation of 6 with 4,5-diamino-1,2-bis(2-
ethylhexyloxy)benzene 7 in the presence of nickel(II) acetate
yielded monomer 2 in 56% yield, Scheme 3. The 1H NMR
spectrum of 2 was extremely broad in CDCl3, suggesting strong
aggregation that results in a decrease of the T2 relaxation time for
the protons. Upon addition of a trace of THF-d8, sharp peaks were
observed and could be assigned to the resonances of the protons
expected for compound 2. In particular, the imine resonance was
observed at 7.78 ppm, and the resonance of the protons on the
bromomethyl substituents was present as a singlet at 4.35 ppm.
Other characterization was also consistent with the complex.
To synthesize monomer 2, we required 4-bromomethyl-2-
hydroxybenzaldehyde 6, a previously unknown compound. Al-
though 5-halomethyl-2-hydroxybenzaldehyde can be prepared
easily by chloro- or bromomethylation of salicylaldehyde,24 we
knew it would be much more difficult to obtain the isomer we
desired in 6. There is one report of a related compound (4-
chloromethyl-2-hydroxybenzaldehyde).25
Scheme 3 Synthesis of nickel-containing monomer 2.
t
Polymerization of 2 with an excess of BuOK in a mixture of
THF and DMF afforded the new polymer 8, Scheme 4. The low
yield was attributed to the formation of a gel that would not
dissolve in any solvent we tried. Gelation is a common problem
for Gilch polymerization reactions, but the source of its formation
remains under discussion.28 Our attempts to obtain polymer 8 were
severely frustrated by gel formation. Researchers have published
the polymerization procedure under many different conditions
to overcome gelation, several of which we tried to optimize the
preparation of polymer 8.29 Table 1 summarizes some of the
Scheme
2 illustrates our route to compound 6. 1,4-
Bis(bromomethyl)anisole 3 was prepared via free-radical bromi-
nation of commercially available 2,5-dimethylanisole.26 Com-
Scheme 2 Synthesis of compound 6.
Scheme 4 Synthesis of Schiff base polymer 8.
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Table 1 Summary of conditions used for polymerization of 2
GPC of the polymer (see ESI†) indicated that the highest
molecular weight fractions had a molecular weight of only ca.
5600 Da (Mn), indicating that the oligomer contains only 7–8
repeat units in its structure. Nevertheless, this is still respectable
for conjugated metallopolymers, which are rarely soluble and
generally synthesized in low molecular weights. The required
electron transfer/elimination reaction through the entire ligand
during the polymerization may also inhibit polymerization and
prevent the generation of high molecular weight polymer. El-
emental analysis was also consistent with ca. 3–4 repeat units
in the polymer, assuming terminal CH2Br substituents. We have
found that elemental analysis of our metal-containing polymers
often underestimates the amount of carbon present in the polymer,
possibly due to coordination of water.
T/◦C Yielda
Mn
b
Solvent
Reagents
THF
THF
THF
tBuOK
tBuOK
50
20
Gelation
10%
Gelation
—
3300
—
tert-Butylbenzylchloride + 20
tBuOK
THF
DMF
DMF
KOH + Bu4NBr
0
Less than 5% 240
Gelation
73%
tBuOK
50
20
20
—
tBuOK
1000
5560
THF + DMF tBuOK
34%
a Yield of soluble fraction. b Measured by GPC (THF) relative to
polystyrene standards
conditions we tried to obtain the soluble polymer. In general,
most of the procedures afforded exclusively or primarily insoluble
material. In an attempt to terminate the end groups with p-tert-
butylbenzyl groups, p-tert-butylbenzylchloride was added to the
reaction (entry #3), but still only insoluble material was obtained.
Typically, the elimination reaction in the first step of the Gilch
polymerization proceeds over a single benzene ring as illustrated
for PPV in Scheme 1. In the case of monomer 2, the elimination
reaction to afford a quinodimethane intermediate must occur
through the entire structure. We rationalized that positioning the
benzylic halide groups para to the imine groups on 2 would allow
electron transfer through the entire ligand system to occur, giving
a quinodimethane-like intermediate, as shown in Scheme 5.
TGA of the product showed decomposition at 250 ◦C, more
than 50 ◦C higher than for the monomer. The char that remained
(11.4 mass%) corresponds to the expected mass if the product is
primarily NiO.
Comparison of the IR spectra obtained from the polymer and
the monomer confirms that the Schiff-base complex is still intact
-1
=
in the polymer. The C N vibration appears at 1602 cm in the
polymer. A peak at 1275 cm-1 is attributed to the C–O stretching
vibration of the phenol structure. The two bands near 530 cm-1 and
455 cm-1 belong to the vibration of Ni–O and Ni–N, respectively.
Importantly, a new peak appears at 1695 cm-1 in the IR spectrum
of the polymer, Fig. 1. This medium strength band is assigned to
=
the C C stretching vibration of PPV chains. The band observed in
the both monomer and compound 6 at 669 cm-1, which is assigned
to the C–Br stretch vibration, is absent in the IR spectrum of 8.
Scheme 5 Proposed elimination step in monomer 2 to give the quin-
odimethane-like intermediate, which undergoes polymerization to form
polymer 8.
During the polymer preparation, we were concerned that
tBuOK could react with the imine on the monomer, possibly
destroying the complex during the reaction. Deprotonation of
t
the imine functionality with BuOK has been reported.30 To test
whether this was a problem, a simple nickel(II) salphen molecule
was reacted under similar conditions to monomer 2 with excess
tBuOK. After the experiment, the reaction was quenched with
methanol and the product was analyzed. NMR spectroscopy
indicated that the complex was stable, though it is possible that the
monomer was deprotonated during the polymerization reaction,
and this could be one cause of the gel formation.
Based on our experiments, we found that polymerization in
a mixture of THF and DMF gave less gelation and higher
molecular weight than in pure THF or DMF. The resulting red
material is soluble in THF and DCM, and was characterized by
gel permeation chromatography (GPC), elemental analysis, and
thermogravimetric analysis (TGA), as well as by UV-vis, IR, and
NMR spectroscopies.
Fig. 1 IR spectra of (a) polymer 8 and (b) monomer 2 between
-1
-1
=
1400–1800 cm , showing the C C stretching mode at 1695 cm in the
polymer.
The 1H NMR spectrum of 8 is very broad, suggestive of
aggregation, and unlike the spectrum for 2, the spectrum for 8
does not become sharp upon addition of coordinating solvents.
1
The H NMR spectrum of the polymer in CD2Cl2 (with a trace
of THF-d8) is consistent with the proposed polymer structure and
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indicates the absence of residual monomer or short oligomers that
would be expected to show sharp resonances. A broad peak at 7.6–
8.0 ppm is assigned to the imine resonance. A broad peak between
6 and 7.5 ppm is attributed to the protons of aromatic and ethenyl
groups. There is also a small peak at 3.9 ppm assigned to protons
on OCH2. We could not observe a peak near 4.35 ppm where the
CH2Br peak in monomer 2 was located, but it may be very weak
if only due to end groups in the polymer. The aggregation of the
polymer prevented us from obtaining useful 13C NMR data.
To provide further confirmation of the polymer structure, we
prepared model compound 10 as shown in Scheme 6. Treatment
of monomer 2 with triphenylphosphine in DMF afforded the
extended conjugation. The bandgaps calculated from UV-vis are
2.0 eV and 2.2 eV for the polymer and the monomer, respectively.
Overall, the features in the visible region of the spectrum are
similar for the monomer, the polymer, and the model compound.
These are quite likely dominated by charge-transfer bands within
the complex.
Experimental
2,5-Dimethylanisole, sodium methoxide (25% in methanol),
N-bromosuccinimide
(NBS),
2,3-dichloro-5,6-dicyano-1,4-
benzoquinone (DDQ), boron tribromide (BBr3), nickel(II)
acetate, and triphenylphosphine (PPh3) were obtained from
Aldrich. Deuterated solvents were obtained from Cambridge
Isotope Laboratories, Inc. Tetrahydrofuran was distilled from
sodium/benzophenone under N2. 2,5-Di(bromomethyl)anisole
1
Wittig reagent 9. H, 13C, and 31P NMR and MS data for this
compound were consistent with its structure. Condensation with
benzaldehyde gave the distilbene model compound 10 in 72% yield.
NMR and MS data for this compound were in agreement with its
structure.
(3),26 2-methoxy-4-(methoxymethyl)benzaldehyde (4),27 and
31
4,5-diethylhexyloxy-1,2-phenylenediamine
literature methods.
were prepared by
All reactions were carried out under a nitrogen atmosphere
using Schlenk techniques or in a N2 glovebox (MBraun) unless
otherwise noted. 1H and 13C NMR spectra were recorded on
Bruker AV-400 and AV-300 spectrometers. 13C NMR spectra were
recorded using a proton decoupled pulse sequence. UV-Vis spectra
were obtained in distilled THF on a Varian Cary 5000 UV-
Vis/near-IR spectrometer using a 1 cm quartz cuvette. IR spectra
were obtained as neat in the solid state on a Thermo Nicolet
6700 FT-IR spectrometer. Molecular weights were estimated by
gel permeation chromatography (GPC) in THF using a Waters
liquid chromatograph. Narrow molecular weight polystyrene
standards were used for calibration purposes. Electrospray (ESI)
mass spectra were obtained at the UBC Microanalytical Services
Laboratory on a Micromass LCT time-of-flight (TOF) mass
spectrometer equipped with an electrospray ion source. MALDI-
TOF mass spectra were obtained in a dithranol matrix (cast
from THF) on a Bru¨ker Biflex IV instrument where spectra were
acquired in the positive reflection mode with delay extraction.
Melting points were obtained on a Fisher-John’s melting point
apparatus.
Scheme 6 Synthesis of model compound 10.
Fig. 2 displays the UV-vis spectra of homopolymer 8, together
with the spectra of monomer 2 and model compound 10.
Compared to the spectrum of monomer 2, the UV-vis absorption
spectrum of 8 was broader and slightly red-shifted, consistent with
Synthesis of 2-hydroxy-4-(bromomethyl)benzaldehyde 6
To a mixture of 1 g (3.4 mmol) of 2,5-di(methoxymethyl)anisole
(4) in 300 mL of 10 : 1 dichloromethane–water was added 1.15 g
(5.0 mmol) of DDQ and the reaction mixture was vigorously
stirred at room temperature overnight. The red mixture was then
poured into saturated sodium bicarbonate and stirred for 30 min.
After the mixture separated, the aqueous layer was extracted with
dichloromethane (3 ¥ 50 mL). The combined organic fractions
were washed with brine then water, and dried over MgSO4. After
filtration and concentration by rotary evaporation, the crude
product was used for the next step without further purification.
1H NMR spectroscopy indicated that the product was a mixture
of 2-methoxy-4-(methoxymethyl)benzaldehyde and 3-methoxy-4-
(methoxymethyl)benzaldehyde, but the product was not easily
separated at this stage.
Under an atmosphere of nitrogen the crude product from
above was dissolved in 200 mL of anhydrous dichloromethane.
The solution was cooled by dry ice/acetone and 1 mL of BBr3
Fig. 2 UV-vis spectra (1.0 cm cell, 298 K, THF) of monomer 2, polymer
8, and model compound 10 in THF.
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(10.4 mmol) was added. The red solution was stirred overnight
allowing the reaction mixture to slowly warm to room temperature.
After pouring the reaction onto ice, the product was extracted with
dichloromethane (3 ¥ 50 mL). The combined organic fractions
were dried over MgSO4, filtered, and dried by rotary evaporation.
During rotary evaporation, the temperature of the water bath
must be lower than 30 ◦C to prevent rapid decomposition. The
crude yellow solid was purified by flash column chromatography
on SiO2 with DCM : hexanes = 1 : 2. Rotary evaporation of the
solvent at low temperature afforded a yellow solid. The compound
decomposes on standing at room temperature and must be stored
in the fridge. Yield: 0.17 g (0.78 mmol, 24%) based on 2 steps. 1H
NMR(CDCl3): d = 11.04 (s, 1H), 9.87 (s, 1H), 7.55 (d, 1H), 7.02 (d,
1H), 6.99 (s, 1H), 4.40 (s, 2H) ppm. 13C NMR (CDCl3): d = 196.1,
161.9, 147.1, 134.4, 120.8, 120.5, 118.2, 31.9 ppm. EI-MS: m/z =
214, 216 (M)+, 135 (M+ - CH2Br). Anal. calc’d for C8H7BrO2: C
44.68, H 3.28; Found C 44.35, H 3.39. UV/Vis (DCM): 227, 268,
335 nm. IR: 3200, 1654, 1565, 1502, 1448, 1436, 1388, 1287, 1224,
1189, 1128, 1012, 974, 868, 802, 745, 664, 558, 453 cm-1. M.P.:
50 ◦C (dec.).
866, 790, 723, 609, 530, 455 cm-1. Theor. Anal. calc’d for HBr-
terminated oligomers BrH(C38H46N2NiO4)4HBr: C 65.77, H 6.75,
N 4.04; Found: C 64.27, H 7.24, N, 4.18. GPC in THF showed
oligomers, including a fraction with a molecular weight of Mn =
5560 Da.
Synthesis of complex 9
A mixture of 0.33 g (0.4 mmol) of 2 and 0.21 g (0.8 mmol) of PPh3
in 40 mL of anhydrous DMF was heated to reflux for 8 h under
nitrogen. After cooling to room temperature, the reaction mixture
was poured into diethyl ether. The precipitate was collected on a
Buchner funnel, washed with 100 mL of diethyl ether, and dried
1
under vacuum. Yield: 0.26 g (0.24 mmol, 56%) of red solid. H
NMR (DMSO-d6): d = 8.92 (s, 2H), 7.3–7.9 (m, 48H), 6.65 (s,
2H), 6.10 (d, 2H), 5.09 (d, 4H), 3.95 (t, 4H), 0.8–1.8 (m, 30H)
ppm. 13C NMR (DMSO-d6): d = 163.9, 153.8, 150.6, 136.1,
135.2, 134.5, 130.5, 123.0, 121.2, 118.5, 117.7, 99.77, 77.4, 39.9,
31.3, 29.4, 23.9, 23.3, 14.3, 11.6 ppm. 31P NMR (DMSO-d6):
d = 23.45 ppm. HRMS (ESI): C74H77N2NiO4P2 Calc. 1177.4790,
Found 1177.4712. UV/Vis (THF): 259, 389 nm. IR: 3053, 3013,
2953, 2925, 2858, 1602, 1512, 1435, 1374, 1278, 1191, 1109, 995,
870, 806, 743, 716, 687, 646, 606, 531, 503, 461 cm-1. M.P.: 260 ◦C
(dec.).
Synthesis of monomer 2
A solution of 0.144 g (0.66 mmol) of 6 and 0.122 g (0.33 mmol)
of 7 in 20 mL of degassed THF was stirred under N2 at room
temperature overnight. Nickel(II) acetate tetrahydrate (0.08 g,
4.5 mmol) was added and the red solution was stirred for an
additional 12 h at room temperature. The solution was poured
into 150 mL methanol, yielding a red precipitate. The precipitate
was collected by filtration and reprecipitated 2 more times for
Synthesis of model compound 10
To a mixture of 0.1 g (0.07 mmol) of compound 9 and 0.015 g
(0.14 mmol) of benzaldehyde was added 10 mL of dry THF
and 10 mL of dry DMF. The mixture was stirred at R.T. for
10 min until all of the solid was dissolved. The solution was added
under nitrogen by syringe to a flask containing 5 mL of dry THF
containing 0.05 g (0.45 mmol) of tBuOK. After stirring for 8 h, the
reaction mixture was poured into methanol. The precipitate was
recovered by filtration and washed with 10 mL methanol. Yield:
0.042 g (0.05 mmol, 72%). 1H NMR (CD2Cl2): d = 8.02 (br, 2H),
1
purification. Yield: 0.15 g (0.18 mmol, 56%). H NMR(trace of
THF-d8 in CDCl3): d = 7.78 (s, 2H), 7.12 (d, 2H), 7.02 (s, 2H),
6.97 (s, 2H), 6.65 (d, 2H), 4.35 (s, 4H), 3.95 (d, 4H) 1.8–0.9 (m,
30H) ppm. 13C NMR (CDCl3): d = 165.2, 151.6, 150.4, 144.0,
136.3, 134.1, 121.9, 120.3, 116.6, 98.4, 77.4, 72.1, 39.9, 33.9, 30.8,
29.4, 24.2, 23.3, 14.3, 11.5 ppm. ESI-MS: m/z = 814 (M+). Anal.
Calc’d for C38H48Br2N2NiO4: C 55.98, H 5.93, N 3.44; Found C
55.58, H 6.27, N 3.84. UV/Vis (THF): 263, 301, 391, 487 nm.
IR: 3051, 3017, 2955, 2921, 2856, 1607, 1584, 1518, 1440, 1370,
1276, 1188, 1117, 1030, ◦944, 867, 824, 787, 744, 669, 617, 542,
458 cm-1. M.P.: 160–162 C.
6.90–7.60 (br, m, 22H), 3.95 (br, 4H), 0.8–1.5 (br, 30H) ppm. 13
C
NMR (CDCl3): d = 165.8, 151.6, 150.0, 143.6, 137.3, 136.3, 133.3,
132.5, 131.6, 130.4, 129.36, 128.8, 128.3, 127.5, 127.1, 122.2, 120.4,
119.9, 116.9, 114.2, 98.5, 77.4, 72.2, 39.8, 30.8, 29.4, 24.1, 23.3,
14.3, 11.5 ppm.32 HRMS (ESI): C52H58N2NiO4 Calc. 833.3750,
Found 833.3828. Anal calc’d for 10.2H2O (C52H62N2NiO6): C
71.81, H 7.19, N 3.22; Found: C 71.67, H 6.81, N 3.43. UV/Vis
(THF): 301, 406, 495 nm. IR: 3055, 3023, 2953, 2923, 2856, 1601,
1581, 1515, 1463, 1434, 1361, 1276, 1181, 1112,◦1026, 958, 875,
778, 689, 634, 593, 529, 454 cm-1. M.P.: 125–130 C.
Synthesis of polymer 8
To a stirred solution of 0.2 g (0.25 mmol) of monomer 2 in 10 mL
of anhydrous THF and 10 mL of anhydrous DMF was added
t
a solution of 0.05 g (4.5 mmol) of BuOK in 5 mL THF. The
resulting mixture was stirred for 48 h at room temperature before
it was poured into methanol (150 mL). The red solid was collected
by filtration and washed with methanol, then stirred in hexane at
room temperature for 1 h. After drying in the funnel, the crude
product was placed in a Soxhlet extractor and extracted into hot
THF over 2 d. After cooling, the THF was removed by rotary
Conclusions
We have applied the Gilch polymerization method to construct a
conjugated metal-containing analogue of poly(phenylenevinylene)
(PPV). We synthesized a new monomer and demonstrated that
polymerization affords gels or soluble oligomers. From GPC,
the longest oligomers were ca. 7–8 repeat units in length. A
model compound that represents a piece of the polymer was
synthesized using a Wittig reaction. Our results show that the
Gilch polymerization method may be applied to complex, metal-
containing monomers to form novel soluble metallopolymers.
1
evaporation to give a dark red solid (0.055 g, 34%). H NMR
(trace of THF-d8 in CD2Cl2) d = 9.0–8.2 (br), 8.0–6.4 (br), 4.0–
3.6 (br) 1.8–0.9 (br) ppm. It was not possible to obtain a 13C
NMR spectrum. UV/Vis (THF): 225, 394 nm. IR: 3052, 3014,
2952, 2921, 2853, 1694, 1602, 1501, 1463, 1361, 1275, 1177, 1007,
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872.
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We thank the Natural Sciences and Engineering Research Council
(NSERC) of Canada (Discovery Grant) and the University of
British Columbia for funding this research. We are grateful to
Joseph Hui for obtaining MALDI-TOF mass spectra and to Prof.
Derek Gates for access to his GPC (NSERC RTI grant).
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6508 | Dalton Trans., 2010, 39, 6503–6508
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