Poly(salphenyleneethynylene)s: Soluble, conjugated metallopolymers that exhibit unique supramolecular crosslinking behavior

Article abstract of DOI:10.1039/b618833h

The synthesis of new soluble conjugated metallopolymers 4a-c and 5a-c containing Zn, Ni and Cu salphen derivatives is reported. The structures of the high molecular weight polymers are confirmed by NMR, IR, UV-vis, and fluorescence spectroscopic studies.

Full text of DOI:10.1039/b618833h

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Poly(salphenyleneethynylene)s: soluble, conjugated metallopolymers that
exhibit unique supramolecular crosslinking behavior{{
Alfred C. W. Leung and Mark J. MacLachlan*
Received 2nd January 2007, Accepted 23rd February 2007
First published as an Advance Article on the web 13th March 2007
DOI: 10.1039/b618833h
The synthesis of new soluble conjugated metallopolymers 4a–c and 5a–c containing Zn, Ni and
Cu salphen derivatives is reported. The structures of the high molecular weight polymers are
confirmed by NMR, IR, UV-vis, and fluorescence spectroscopic studies. Zinc-containing
metallopolymer 4a exhibits strong aggregation behavior in solution and in the solid state, and
dissociation of the aggregates occurs upon addition of coordinating bases such as pyridine. A
significant change to the luminescence of 4a is observed, suggesting its potential application as a
sensor for Lewis bases.
polymerizable metal-containing monomers and the polymers’
insolubilities.16
Introduction
Recent developments in conjugated organic polymers, such as
In 2002, Lavastre and co-workers reported a large library of
poly(p-phenylene)s (PPPs) and poly(p-phenylenevinylene)s
new luminescent conjugated polymers from a combinatorial
synthesis and screening method.17 Preliminary in-situ studies of
(PPVs), have met with tremendous success and have led to
useful applications such as organic light-emitting diodes,1
the polymers indicated that the postulated structures 1
semiconductors,2 and photovoltaic devices.3 Among the large
variety of these conjugated polymers, poly(phenyleneethynyl-
ene)s (PPEs) are a relatively new and distinct class of
conjugated polymers that have drawn a great deal of attention.
Extensive research efforts have focused on the synthesis of new
polymeric PPE materials,4 along with other oligomeric
structures such as macrocycles,5 foldamers,6 and dendrimers.7
Potential applications for these materials are especially
promising in the area of chemosensing and biosensing, where
various PPE derivatives were demonstrated to function as
sensors for chemical analytes such as trinitrotoluene (TNT)
and biological agents such as DNA and carbohydrates.8 Other
potential applications as electroluminescent materials,9 non-
linear optical (NLO) materials,10 and liquid crystals11 were
also explored.
incorporating Zn2+ and Ni2+ salphen complexes possessed
excellent luminescent characteristics, suggesting that they may
be candidates for electroluminescent materials. We found that
these polymers are insoluble, and we reported in a previous
communication the synthesis of soluble high molecular weight
derivatives, polymers 2.18 Studies of their luminescent proper-
ties indicated that these polymers were poorly emissive, and
would not be suitable for electroluminescent devices.
In the search for novel PPEs with new and useful properties,
researchers have synthesized and combined a diverse library of
monomers, attaching functional units such as crown ethers12
and carbohydrates13 to the conjugated polymers. In particular,
PPEs containing metal complexes such as porphyrins
and ferrocenes have demonstrated unique electronic proper-
ties14 and supramolecular behavior.15 Although these organo-
metallic PPEs exhibit attractive properties, relatively few
examples of these metallopolymers have appeared in the
literature, largely due to the synthetic difficulties in obtaining
Department of Chemistry, University of British Columbia, 2036 Main
Mall, Vancouver, BC V6T 1Z1, Canada.
E-mail: mmaclach@chem.ubc.ca; Fax: +1-604-822-2847;
Tel: +1-604-822-3070
{ This paper is part of a Journal of Materials Chemistry issue
highlighting the work of emerging investigators in materials chemistry.
{ Electronic supplementary information (ESI) available: general
experimental details, analytical data and synthetic procedures for
compounds 7–9. See DOI: 10.1039/b618833h
Although polymers 1 and 2 do not possess good lumines-
cence, we anticipated these materials to have interesting
properties in other areas due to the fact that Schiff base metal
complexes, such as complexes of N,N9-bis(salicylidene)ethyl-
enediamine, 3 (‘‘M(salen)’’), are known to exhibit interesting
magnetic,19 NLO,20 oxygen transport,21 catalytic,22 and
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sensory23 properties. In addition, our research group has
investigated many macrocycles that contain salen complexes,
and these may be thought of as cyclic oligomers of the
polymers described in this paper. These macrocycles exhibit
interesting supramolecular behavior, forming molecular clus-
ter complexes and self-assembling into tubular assemblies.24
Coordination and binding of small molecules to the macro-
cycles were found to strongly affect the optical properties of
these materials, making them good candidates for sensors.
Other researchers have reported the incorporation of salen-
type complexes into conjugated backbones with variable
success, and these have been utilized as catalysts, electro-
luminescent materials, and microspheres for photonic applica-
tions.25 In this article, we report the synthesis of a new series of
conjugated metallopolymers 4 and 5 designed to form linear
and helical or zig-zag conformations, respectively. We report
on their optical properties as well as the aggregation behavior
of the zinc-containing polymers.
the salphen monomer. Although the resulting polymers were
soluble in THF, long periods of stirring and heating were
necessary to fully dissolve the polymers, and they become less
soluble upon aging. Therefore, we sought to prepare PSPE
derivatives with improved solubility through the addition of
racemic 2-butyloctyloxy substituents, branched chains with
chiral centers. Scheme 1 shows the synthetic route to the
required precursor, substituted phenylenediamine 9. Efforts to
prepare compound 7 using standard Williamson ether synth-
esis conditions with K2CO3 or NaOH as the base led only to a
low yield (24%) of 7, with large amounts of mono-substituted
side-product and unreacted catechol remaining even after
2 weeks of heating at reflux. The efficiency of this procedure
can be significantly improved using NaH as the base, first
forming salts of 6 followed by slow addition of 1-bromo-2-
butyloctane; compound 7 was obtained as a colorless oil in
excellent yield (96%). Compound 7 was subsequently nitrated
with HNO3 and reduced with Raney Ni and hydrazine to
afford the target diamine 9. Soluble salphen ligand 11 was
prepared by reaction of 5-iodosalicylaldehyde 10 and diamine
9 under nitrogen in THF, and was isolated as a bright orange
solid in 79% yield, Scheme 2. Reaction of 11 with Zn(OAc)2,
Ni(OAc)2, and Cu(OAc)2 afforded salphen monomers 12a–c as
yellow, red, and brown solids, respectively, in 85–92% yield.
These monomers with iodo functionality opposite the hydroxyl
groups are expected to give linear polymers.
In an effort to develop metallopolymers with the potential to
form helices,26 we constructed Schiff base monomers with a
bent structure. Schiff base ligand 14 with iodo functionality
meta to the hydroxyl moiety was prepared from 4-iodosalicyl-
aldehyde 13 in 73% yield, Scheme 3. Subsequent reaction with
Zn(OAc)2, Ni(OAc)2, and Cu(OAc)2 yielded metal-containing
monomers 15a–c, respectively, in 90–93% yield.
Compounds 12a–c and 15a–c were reprecipitated 2–3 times
to afford pure compounds, and their compositions and purities
were confirmed with 1H and 13C NMR spectroscopy, IR
spectroscopy, UV-vis spectroscopy, MALDI-TOF mass spec-
trometry, and elemental analysis. The monomers all display an
intense CLN stretching mode at 1600–1615 cm21 in their IR
spectra. Mass spectra of monomers 12a–c and 15a–c showed
the expected molecular mass, and dimeric species were
observed for both Zn monomers 12a and 15a. UV-vis spectra
Results and discussion
Synthesis
Previously we prepared soluble poly(salphenyleneethynylene)s
(PSPEs) by incorporating two dodecyloxy substituents onto
Scheme 1 Synthesis of phenylenediamine 9.
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Scheme 2 Synthesis of monomers 12a–c.
Scheme 3 Synthesis of monomers 15a–c.
of the monomers all show multiple bands in the region between
200 and 550 nm, with strong absorption peaks centered at ca.
400 nm, and broad tails that extend to 550 nm. Fluorimetry
measurements indicated that none of the monomers fluoresce,
not surprising since they all have iodide substituents.
strong interchain interactions that can lead to aggregation.
Consistent with this, polymers 5 do not readily form films, and
they were isolated as waxy solids.
Polymer characterization
1H NMR spectra of polymers 4a–b and 5a–b in CDCl3 showed
very broad peaks in the expected aromatic and alkyl regions,
including a broad peak characteristic of the imine residue at ca.
8.5 ppm, Fig. 2.27 The severe broadening is likely due to slow
tumbling of the rigid polymers in the viscous solution,
combined with strong aggregation between the polymer
strands. The absence of terminal alkyne signals, residual
monomer, or oligomer corroborated the formation of poly-
mers with high molecular weight. IR spectroscopy confirms
the absence of any starting monomers, and the presence of the
vCLN (1600–1615 cm21) stretching mode verified that the
salphen moiety remained intact. A new signal at ca. 2200 cm21
was observed in all of the polymers, corresponding to the CMC
stretching mode as expected with the formation of alkyne
linkages in the polymeric backbone. UV-vis spectroscopy of
the polymers showed peaks that are broader than for the
Polymerization of 12a–c proceeds via Pd-catalyzed
Sonogashira cross coupling in a mixture of THF–HNiPR2,
affording high molecular weight polymers 4a–c in 72–90%
yield after 3–4 precipitations from THF into acetone and
methanol, Scheme 4. Polymers 5a–c were prepared employing
an identical procedure, Scheme 5, but the resulting polymers
were more soluble in organic solvents and were therefore
purified by 3–4 precipitations from THF into methanol and
hexane. Polymers 4a–c readily dissolve in THF, but remain
insoluble in other common organic solvents such as chloro-
form and toluene. These polymers form flexible free standing
films, suggesting that their molecular weights are high enough
to ensure substantial interchain entanglement, Fig. 1. Polymers
5a–c are much more soluble, dissolving in solvents such as
chloroform and THF. The improved solubility of 5 is likely a
result of the polymers’ helical or coil structures, inhibiting
Scheme 4 Synthesis of conjugated metallopolymers 4a–c.
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Scheme 5 Synthesis of conjugated metallopolymers 5a–c.
monomers, but the general absorption pattern resembled the measured correspond to degrees of polymerization ranging
starting salphen complexes. Absolute molecular weights of
the polymers were established to be between ca. 19 000 and
74 000 Da (Mw) using GPC. The high molecular weights
from 14 to 55, and the molecular weights and other related
information of the individual polymer samples are summarized
in Table 1.
Schiff base complexes have been incorporated into polymers
to generate high temperature materials.28 Thermal gravimetric
analysis (TGA) indicated that PSPEs 4a–c and 5a–c are stable
to ca. 200 uC, with less than 2% mass loss below this
temperature. Differential scanning calorimetry (DSC) studies
were performed on all of the polymers, but no noticeable
transitions occurred between temperatures of 260 and 300 uC.
UV-vis spectra of polymers 4a–c and 5a–c show strong
absorption peaks between ca. 400 and 500 nm, Fig. 3. Linear
polymers 4a–c all have similar absorption peaks centered at
shorter wavelength (ca. 410 nm) and broad shoulders that
extend toward 575 nm. On the other hand, absorption spectra
of non-linear polymers 5a–c possess broad peaks with less
obvious shoulders. The linear polymers 4 all show significant
blue-shifts in absorption relative to the non-linear analogues 5.
We postulate that there is extended conjugation through the
aromatic system on the salphen unit in the case of non-linear
polymers 5, whereas in linear polymers 4 the conjugation
pathway is interrupted by the metal centers, leading to shorter
conjugation length and thus a blue-shifted absorption. To
support our observations, the absorption spectra of model
compounds 17 and 18 with phenylacetylene substituents para
and meta to the phenol moiety, respectively, were compared.
As shown in Fig. 4, the absorption spectrum of 18 is slightly
red-shifted in comparison to that of 17, but the absorption
shoulder extends to significantly longer wavelength (ca. 20 nm
shift). This observed change in absorption behavior between
Fig. 1 Intensely colored films of polymers 4a–c were obtained
through simple suction filtration. The polymers dissolve in THF to
give red solutions.
Table 1 Molecular weights (Mw, Mn) and polydispersities of poly-
mers 4a–c and 5a–c. Measurements were made with a GPC system
equipped with triple detection (refractive index, light-scattering, and
viscosity)
4a
4b
4c
5a
5b
5c
Mw
Mn
PDI
18700
17200
1.09
73600
52000
1.42
33700
32400
1.04
32800
24300
1.35
60400
42400
1.43
63200
50700
1.25
Fig. 2 1H NMR spectrum of polymer 4a (CDCl3 + 1% pyridine-d5).
Inset: Expanded view of region from 3 to 9 ppm.
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Fig. 4 UV-vis absorption (normalized) spectra of 17 and 18 in
Fig. 3 UV-vis absorption (normalized) spectra of polymers 4a–c and
5a–c in CH2Cl2.
CH2Cl2.
the phenolic oxygen and Zn2+ metal center of Zn salphen
moieties.24,30 In these phenyleneethynylene-type macrocycles,
strong aggregation was observed in non-polar solvents, but
deaggregation occurred upon the addition of coordinating
ligands such as pyridine that competitively coordinate to the
zinc ions.
the model compounds agrees with the observed trend for the
polymers, correlating the absorption changes with increase of
conjugation.
Zinc-containing Schiff base polymer 4a is insoluble in most
organic solvents, such as CH2Cl2. Upon addition of ca. 1%
pyridine to a sample of 4a in CH2Cl2, the polymer dissolved.
On the other hand, when 2,6-lutidine was added instead of
pyridine, the polymer was not dissolved, even in pure lutidine.
Lutidine is a stronger base than pyridine, but bulky methyl
substituents inhibit coordination to metal centers. This
observation suggested that the coordination of pyridine to
the polymer was necessary to disrupt strong intermolecular
interactions between the polymer strands.
To further probe this interaction, we studied the addition of
Lewis bases to the polymer in solution. The UV-vis spectrum
of polymer 4a in CH2Cl2 shows an absorption peak at 400 nm
with a broad shoulder that extends to approximately 550 nm.
Fluorescence measurements in CH2Cl2 indicated that the
polymer is weakly luminescent, having a quantum yield of
only 0.073%. Upon the addition of pyridine to a solution of 4a
in CH2Cl2, a gradual but minor decrease in the absorption
maximum at ca. 400 nm was observed, together with small
increases to the absorption shoulder at ca. 500 nm, Fig. 6a. A
pseudo-isosbestic point was observed at ca. 530 nm, but was
Aggregation
Self-association of Zn salen complexes is well documented in
the literature, forming dimeric complexes in solution and the
solid state. In rigid salphen ligands, the Zn2+ ion is unable to
acquire a tetrahedral geometry, and therefore dimerizes to
expand its coordination number as shown in Fig. 5.29 We have
reported the reversible aggregation of zinc-containing Schiff
Fig. 5 Illustration of dimerization in Zn salphen complexes. Strong
interactions between the Zn2+ center and the phenolic oxygens of the
metal complexes hold the dimer together.
…
base macrocycles mediated by a Zn O interaction between
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Fig. 7 UV-vis and fluorescence spectra of 18 (CH2Cl2, 5.00 6
Fig. 6 UV-vis and fluorescence spectra of 4a (CH2Cl2, 5.00 6
1026 M) titrated with a) pyridine (1.03 6 1026 to 1.03 6 1025 M;
step size: 1.03 6 1026 M) and b) 4,49-bipyridine (4.30 6 1025 to
6.45 6 1024 M; step size: 4.30 6 1025 M).
1026 M) titrated with a) pyridine (1.03 6 1028 to 1.65 6 1027 M;
step size: 1.03 6 1028 M) and b) 4,49-bipyridine (1.08 6 1026 to
2.40 6 1025 M; step size: 1.08 6 1026 M).
polymer becomes more soluble. The polymer emission also
increases in intensity and undergoes a blue shift, supporting
the disruption of an excimer-like species.
not well defined, consistent with the complexity of the polymer
deaggregation process as pyridine binds to the metal salphen
complexes. In the emission spectra, a much more pronounced
effect was observed upon the addition of pyridine, where the
fluorescence maximum at ca. 580 nm increased about four-fold
after 2 equivalents of pyridine were added (W = 0.27% after
saturation). A blue shift from 590 to 546 nm was also observed
in the fluorescence spectrum. When 2,6-lutidine was added to
solutions of polymer 4a in solution, no changes in the
absorption or emission spectra were observed.
We investigated the addition of 4,49-bipyridine to polymer
4a to see whether a ladder polymer would form, where the
metal ions are bridged by the bipyridine ligand. A similar
approach to porphyrin-based PPE ladder polymers has been
reported by Anderson and co-worker.31 Addition of bipyridine
to 4a in CH2Cl2 yielded similar changes to the absorption
spectrum as for the addition of pyridine, but an abrupt
decrease of the emission peak was observed, Fig. 6b. The
decrease in emission ceased after ca. 0.2 equivalents of
4,49-bipyridine were added to the sample, and the Stern–
Volmer plot for the fluorescence quenching shows a non-linear
curve, indicative of static quenching. The observed behavior is
consistent with the formation of polymers with the bidentate
4,49-bipyridine ligand bridging the polymer strands.
For comparison, we examined model compound 18, a Zn
salphen complex that is monomeric in solution. As shown in
Fig. 7, the absorption spectrum of 18 changes gradually with
the addition of pyridine or 4,49-bipyridine, but no significant
changes to the fluorescence spectra are observed.
These results suggest that in solution polymer 4a exists in an
…
aggregated (crosslinked) state held together by Zn O inter-
Polymer 5a is expected to adopt a helical or coil structure in
which inter-strand interactions are reduced in comparison to
4a, inhibiting aggregation. Polymer 5a is considerably more
soluble than 4a, suggesting that there are fewer crosslinks
within the polymer. Moreover, the optical properties of
polymer 5a are affected by Lewis bases in a different way
actions. In this form, the luminescence is mostly quenched due
to excimer-like inter-strand interactions, along with energy
transfer of the polymer absorption into localized states of the
metal complexes. Upon addition of a Lewis base that can
coordinate to the Zn2+ ions, the crosslinks are broken and the
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Fig. 9 Cartoon illustrating the disruption of the polymer crosslinks
upon the addition of pyridine.
designing a polymer structure that reduces interchain interac-
tions, as in polymer 5a. This new reversible crosslinking
…
mechanism involving Zn O interactions, illustrated in Fig. 9,
is potentially useful for developing thermoplastic and elasto-
meric materials.
Conclusions
In summary, we have prepared a new series of high molecular
weight conjugated PPE polymers containing Zn, Ni, and Cu
salphen metal complexes in the backbone. The insolubility of
the rigid metallopolymers was overcome through the addition
of racemic branched alkoxy substituents, and the introduction
of a bent geometry to the conjugated backbone. We have
observed strong aggregation of the linear Zn metallopolymers
…
that is facilitated by the presence of Zn O interactions.
Deaggregation occurs when the polymer is treated with a
coordinating base such as pyridine, and a strong response in
polymer emission makes these polymers possible sensors for
Lewis bases. Future work will probe the effects of different
Lewis bases on the optical properties of polymer 4a, with the
goal of making a conjugated polymer with optical properties
that can be tuned by addition of ligands.
Fig. 8 UV-vis and fluorescence spectra of 5a (CH2Cl2, 5.00 6
1026 M) titrated with a) pyridine (1.03 6 1026 to 1.03 6 1025 M;
step size: 1.03 6 1026 M) and b) 4,49-bipyridine (4.30 6 1025 to
3.01 6 1024 M; step size: 4.30 6 1025 M).
Experimental
than polymer 4a. As shown in Fig. 8, gradual changes were
observed in the absorption spectra upon addition of pyridine
or 4,49-bipyridine, suggesting that coordination of the ligands
occurs as in the case of polymer 4a. However, only a very
minor increase to the polymer’s emission at 590 nm was
observed upon addition of pyridine, and a similarly small
decrease to the fluorescence peak occurred in response to the
addition of 4,49-bipyridine. These results from UV-vis and
fluorescence spectroscopy, along with sharper signals in the 1H
NMR spectrum and the good solubility of this material,
confirm that the polymer 5a has a weaker tendency to form
strong aggregates in the dilute CH2Cl2 solution. However, it is
likely that intramolecular association of the salphen moieties
leads to the weak luminescence (W = 0.15%).
Polymers 4b–c and 5b–c containing square planar Ni2+ and
Cu2+ ions showed no significant changes to their absorption
spectra upon the addition of coordinating bases. The lack of
response from these polymers is expected as the metal centers
are square planar in geometry and do not readily expand their
coordination numbers.
Materials
Copper(I) iodide, zinc(II) acetate, nickel(II) acetate, and
copper(II) acetate were obtained from Aldrich. Tetrakis-
(triphenylphosphine)palladium was obtained from Strem
Chemicals, Inc. Deuterated solvents were obtained from
Cambridge Isotope Laboratories, Inc. Tetrahydrofuran was
distilled from sodium/benzophenone under N2. NHiPr2 was
distilled from NaOH under N2. 5-Iodosalicylaldehyde 10,
4-iodosalicylaldehyde 13, and 1,4-dihexadecyloxy-2,5-diethy-
nylbenzene 16 were prepared by literature methods.32 The
synthesis of model compound 18 was previously reported by
our group,30 and compound 17 was prepared by an analogous
procedure.
UV-vis and fluorescence measurements
Polymers 4a–c and 5a–c were initially dissolved in a small
amount of THF (ca. 2 mL) and diluted to appropriate
concentrations (1.0
6 M for quantum efficiency
1026
measurements, 5.0 6 1026 M for titration studies) with
CH2Cl2 so that the final concentration of THF was ,0.1%.
Titration experiments were performed in a 1 cm cuvette. The
…
Overall, we believe that the Zn O interaction is involved in
crosslinking conjugated polymer 4a. This supramolecular
interaction can be disrupted by addition of bases or by
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addition of appropriate Lewis bases in CH2Cl2 to the polymer
samples with a microsyringe was followed by a short period of
mixing and subsequent UV-vis and fluorescence measure-
ments. No significant differences in the absorption and
emission spectra were found between samples of polymers 5a
prepared via the above method and samples prepared by
dilution in pure CH2Cl2.
1411, 1368, 1318, 1279, 1245, 1224, 1184, 1140, 1115, 1017,
933, 821, 787; dH (400 MHz, CDCl3) 7.77, (s, 2H, CHLN), 7.52
(s, 2H, aromatic CH), 7.32 (d, J = 9.2 Hz, 2H, aromatic CH),
6.90 (s, 2H, aromatic CH), 6.73 (d, J = 8.8 Hz, 2H, aromatic
CH), 3.94 (d, J = 5.2 Hz, 4H, OCH2), 1.83 (m, 2H, CH2), 1.33
(m, 32H, CH2), 0.89 (m, 12H, CH3); dC (100.6 MHz, CDCl3)
164.7, 151.2, 150.5, 142.5, 140.8, 135.8, 124.2, 123.0, 98.0, 75.6,
72.4, 38.3, 32.2, 31.5, 31.2, 30.0, 29.4, 27.2, 23.3, 23.0, 14.4; m/z
(MALDI-TOF) 992.3 (M+, Calc. 992.2); mp decomp. .260 uC.
Syntheses
Synthesis of Schiff base ligand (11). A solution of 9 (0.500 g,
1.05 mmol) and 10 (0.572 g, 2.31 mmol) in 20 mL of THF was
heated to reflux for 24 h. After cooling to room temperature,
50 mL of MeOH was added to the reaction mixture under air
to precipitate the orange product. Precipitation in THF–
MeOH was repeated once to afford 11 (0.735 g, 0.785 mmol,
79%) as an orange solid (Found: C, 56.41; H, 6.64; N, 3.24.
Calc. for C44H62I2N2O4 requires C, 56.41; H, 6.67; N, 2.99%);
Synthesis of copper monomer (12c). Monomer 12c was
prepared by a procedure identical to that for 12a except copper
acetate was used in the place of zinc acetate. The monomer was
isolated as a brown solid (92%) (Found: C, 53.33, H, 6.12, N,
3.18. Calc. for C44H60I2N2O4Cu requires C, 52.94; H, 6.06; N,
2.81%); lmax (CH2Cl2)/nm 255 (log e 6.08), 373 (2.50), 420
(3.40); nmax(KBr)/cm21 2924, 2855, 1894, 1732, 1607, 1589,
1507, 1457, 1371, 1316, 1246, 1220, 1175, 1138, 1118, 1017,
956, 824, 776, 726; m/z (MALDI-TOF) 997.8 (M+, Calc.
998.3); mp 230–232 uC.
l
max (CH2Cl2)/nm 361 (log e 1.67), 390 (1.60); nmax(KBr)/cm21
2956, 2926, 2856, 1889, 1612, 1557, 1510, 1471, 1351, 1272,
1220, 1410, 1351, 1272, 1220, 1180, 1130, 1018, 933, 870, 845,
819, 766, 727; dH (400 MHz, CDCl3) 13.19 (s, 2H, OH), 8.53,
(d, J = 6.8 Hz, 2H, CHLN), 7.65 (d, J = 2 Hz, 2H, aromatic
CH), 7.55 (q, J = 2, 10.8 Hz, 2H, aromatic CH), 6.81 (d, J =
8.8 Hz, 2H, aromatic CH), 6.74 (s, 2H, aromatic CH), 3.91 (d,
J = 5.6 Hz, 4H, OCH2), 1.83 (m, 2H, CH2), 1.25–1.60 (m, 32H,
CH2), 0.87 (m, 12H, CH2); dC (100.6 MHz, CDCl3) 161.0,
160.2, 150.0, 141.4, 140.3, 135.0, 121.8, 120.1, 104.2, 79.8, 72.5,
38.4, 32.1, 31.6, 31.4, 30.0, 29.3, 27.1, 23.3, 22.9, 14.3; m/z
(MALDI-TOF) 937.3 (M + H+, Calc. 937.3); mp 166–168 uC.
Synthesis of Schiff base ligand (14). A solution of 9 (0.617 g,
1.29 mmol) and 13 (0.706 g, 2.85 mmol) in 20 mL of THF was
heated to reflux for 24 h. After cooling to room temperature,
50 mL of MeOH was added to the reaction mixture under air
to precipitate the orange product. Precipitation in THF–
MeOH was repeated once to afford 14 (0.883 g, 0.942 mmol,
73%) as an orange solid (Found: C, 56.58; H, 6.67; N, 3.16.
Calc. for C44H62I2N2O4 requires C, 56.41; H, 6.67; N, 2.99%);
lmax (CH2Cl2)/nm 289 (log e 3.12), 344 (2.19), 387 (1.93);
n
max(KBr)/cm21 2927, 2857, 1601, 1553, 1515, 1484, 1464,
Synthesis of zinc monomer (12a). Compound 11 (0.300 g,
0.320 mmol) and zinc acetate dihydrate (0.084 g, 0.038 mmol)
were combined in 10 mL of THF under air. The reaction was
heated to reflux for 24 h to give a yellow solution. Cooling to
room temperature followed by addition of 40 mL of MeOH
furnished 12a (0.289 g, 0.289 mmol, 90%) as a yellow solid
(Found: C, 55.24; H, 6.53; N, 3.19. Calc. for C44H60I2N2O4Zn
requires 52.84; H, 6.05, N, 2.80%); lmax (CH2Cl2)/nm 304 (log e
1.96), 402 (2.34); nmax(KBr)/cm21 2918, 2859, 1888, 1614,
1504, 1466, 1374, 1309, 1263, 1218, 1170, 1139, 1119, 1018,
961, 937, 873, 826, 773, 726; dH (400 MHz, DMSO-d6) 8.94, (d,
J = 6.8 Hz, 2H, CHLN), 7.77 (d, J = 2 Hz, 2H, aromatic CH),
7.45 (s, 2H, aromatic CH), 7.38 (q, J = 2.4, 11.2 Hz, 2H,
aromatic CH), 6.54 (d, J = 8.8 Hz, 2H, aromatic CH), 3.98 (d,
J = 4.8 Hz, 4H, OCH2), 1.76 (b, 2H, CH2), 1.2–1.5 (m, 32H,
CH2), 0.87 (m, 12H, CH3); dC (100.6 MHz, DMSO-d6) 170.8,
159.5, 149.3, 143.1, 141.1, 132.5, 125.8, 122.6, 100.3, 71.9, 71.0,
1358, 1268, 1252, 1018, 1060, 1018, 939, 905, 860, 850, 793; dH
(400 MHz, CDCl3) 13.38 (s, 2H, OH), 8.51, (s, 2H, CHLN),
7.42 (s, 2H, aromatic CH), 7.24 (q, J = 0.8, 8.8 Hz, 2H,
aromatic CH), 7.03 (d, J = 8.0 Hz, 2H, aromatic CH), 6.75 (s,
2H, aromatic CH), 3.91 (d, J = 5.2 Hz, 4H, OCH2), 1.83 (m,
2H, CH2), 1.2–1.6 (m, 32H, CH2), 0.87 (m, 12H, CH3); dC
(100.6 MHz, CDCl3) 161.5, 161.3, 149.9, 135.0, 133.0, 128.5,
127.1, 119.0, 104.7, 99.9, 72.6, 38.4, 32.1, 31.6, 31.3, 30.0, 29.4,
27.1, 23.3, 22.9, 14.1; m/z (MALDI-TOF) 937.3 (M + H+,
Calc. 937.3); mp 99–101 uC.
Synthesis of zinc monomer (15a). Compound 14 (0.300 g,
0.320 mmol) and zinc acetate dehydrate (0.084 g, 0.038 mmol)
were combined in 10 mL of THF under air. The reaction was
heated to reflux for 24 h to give a yellow solution. Cooling to
room temperature followed by addition of 40 mL of MeOH
furnished 15a (0.294 g, 0.294 mmol, 92%) as a yellow solid
(Found: C, 52.48; H, 6.20; N, 3.20. Calc. for C44H60I2N2O4Zn
requires C, 52.84; H, 6.05; N, 2.80%); lmax (CH2Cl2)/nm 312
(log e 3.04), 390 (3.28); nmax(KBr)/cm21 2925, 2856, 1610,
1579, 1502, 1463, 1405, 1376, 1268, 1217, 1174, 1117, 911, 865,
833, 774, 732; dH (300 MHz, DMSO-d6) 8.92, (s, 2H, CHLN),
7.43 (s, 2H, aromatic CH), 7.17 (d, J = 9 Hz, 2H, aromatic
CH), 7.11 (s, 2H, aromatic CH), 6.85 (q, J = 3.0, 9.0 Hz, 2H,
aromatic CH), 3.98 (d, J = 3.0 Hz, 4H, OCH2), 1.75 (b, 2H,
CH2), 1.2–1.5 (m, 32H, CH2), 0.86 (m, 12H, CH3); dC
(100.6 MHz, DMSO-d6) 171.2, 160.3, 149.2, 137.0, 132.5,
131.6, 121.8, 119.3, 111.1, 102.5, 100.5, 71.1, 31.3, 31.0, 30.6,
37.6, 31.3, 31.0, 30.6, 29.2, 28.6, 26.3, 22.5, 22.1, 13.9; m/z
+
(MALDI-TOF) 998.3 (M+, Calc. 998.2), 2000.5 (dimer M2
,
calc. 1996.4); mp decomp. .290 uC.
Synthesis of nickel monomer (12b). Monomer 12b was
prepared by a procedure identical to that for 12a except nickel
acetate was used in the place of zinc acetate. The monomer was
isolated as a red solid (85%) (Found: C, 53.11; H, 6.44; N, 2.96.
Calc. for C44H60I2N2O4Ni requires 53.19, H, 6.09; N, 2.82%);
lmax (CH2Cl2)/nm 267 (log e 7.11), 387 (3.80), 493 (1.42);
n
max(KBr)/cm21 2928, 2854, 1607, 1590, 1556, 1515, 1452,
1930 | J. Mater. Chem., 2007, 17, 1923–1932
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29.2, 28.6, 26.3, 22.5, 22.1, 13.9; m/z (MALDI-TOF) 998.3
(M+, Calc. 998.2), 1997.4 (dimer (M2 + H)+, Calc. 1996.4); mp
decomp. .320 uC.
film (Found: C, 72.44; H, 9.36; N, 2.35. Calc. for
C86H129N2O6Ni requires C, 76.76; H, 9.66; N, 2.08%); lmax
(CH2Cl2)/nm 277 (log e 5.81), 412 (9.33); nmax(KBr)/cm21
2922, 2204, 1732, 1610, 1494, 1453, 1378, 1274, 1181, 1029,
829, 756; GPC (THF) Mw = 73 600 (Mw/Mn = 1.42).
Synthesis of nickel monomer (15b). Monomer 15b was
prepared by a procedure identical to that for 15a except nickel
acetate was used in the place of zinc acetate. The monomer was
isolated as a red solid (93%) (Found: C, 53.35; H, 6.17; N, 2.91.
Calc. for C44H60I2N2O4Ni requires C, 53.19; H, 6.09; N,
2.82%); lmax (CH2Cl2)/nm 262 (log e 6.19), 320 (4.21), 390
(6.59), 473 (2.52); nmax(KBr)/cm21 2926, 2856, 1608, 1585,
1496, 1463, 1420, 1368, 1279, 1245, 1224, 1186, 1115, 1015,
917, 856, 776; dH (300 MHz, CDCl3) 7.57, (s, 2H, CHLN), 7.33
(d, J = 1.2 Hz, 2H, aromatic CH), 6.87 (s, 2H, aromatic CH),
6.83 (q, J = 1.5, 9.9 Hz, 2H, aromatic CH), 6.73 (d, J = 8.4 Hz,
2H, aromatic CH), 3.90 (d, J = 5.4 Hz, 4H, OCH2), 1.82 (m,
2H, CH2), 1.42 (m, 32H, CH2), 0.90 (m, 12H, CH2); dC
(75.5 MHz, CDCl3) 164.4, 151.5, 150.4, 136.0, 134.0, 130.5,
124.7, 120.0, 102.5, 97.8, 72.2, 38.4, 32.2, 31.6, 31.2, 30.0, 29.4,
27.3, 23.3, 23.0, 14.4; m/z (MALDI-TOF) 992.7 (M+, Calc.
992.2); mp 190–192 uC.
Synthesis of copper polymer (4c). Polymer 4c was prepared
by a procedure identical to that for 4a, starting with monomer
12c. Precipitations furnished polymer 4c (80%) as a dark red
film (Found: C, 76.09; H, 9.64; N, 2.40. Calc. for
C86H129N2O6Cu requires C, 76.48, H, 9.63; N, 2.07%); lmax
(CH2Cl2)/nm 279 (log e 4.55), 412 (9.25); nmax(KBr)/cm21
2923, 2852, 2204, 1735, 1609, 1586, 1516, 1454, 1414, 1376,
1325, 1274, 1216, 1174, 1124, 1019, 832, 753; GPC (THF) Mw =
33 700 (Mw/Mn = 1.04).
Synthesis of zinc polymer (5a). Polymer 5a was prepared
using a procedure identical to that for 4a, starting with
monomer 15a. Purification of the polymer was performed by
precipitation from THF into hexane twice, and into MeOH
twice. Polymer 5a (77%) was isolated as a dark red solid
(Found: C, 72.57; H, 9.37; N, 2.10. Calc. for C86H129N2O6Zn
requires C, 76.38; H, 9.61; N, 2.01%); lmax (CH2Cl2)/nm 341
(log e 3.10), 430 (6.06); nmax(KBr)/cm21 2926, 2850, 2206,
1606, 1503, 1467.21, 1413, 1379, 1270, 1215, 1175, 1116, 1018,
986, 867, 723; dH (400 MHz, CDCl3, 1% pyridine-d5). 8.8–8.5
(broad, s), 6.5–7.8 (broad, m) 3.7–4.3 (broad, d), 2.4–0.7
(broad, m); GPC (THF) Mw = 32 800 (Mw/Mn = 1.35).
Synthesis of copper monomer (15c). Monomer 15c was
prepared by a procedure identical to that for 15a except copper
acetate was used in the place of zinc acetate. The monomer was
isolated as a brown solid (90%) (Found: C, 53.18; H, 6.22; N,
2.94. Calc. for C44H60I2N2O4Cu requires C, 52.94; H, 6.06; N,
2.81%); lmax (CH2Cl2)/nm 274 (log e 3.40), 327 (3.84), 366
(2.96), 416 (5.02); nmax(KBr)/cm21 2928, 2858, 1606, 1581,
1499, 1461, 1416, 1375, 1275, 1244, 1222, 1182, 1138, 1116,
1057, 1018, 943, 914, 859, 839, 777, 731; m/z (MALDI-TOF)
997.8 (M+, Calc. 998.3); mp 128–130 uC.
Synthesis of nickel polymer (5b). Polymer 5b was prepared by
a procedure identical to that for 5a, starting with monomer
15b. Precipitations furnished polymer 5b (72%) as a dark red
solid (Found: C, 70.34; H, 8.93; N, 2.10. Calc. for
C86H129N2O6Ni requires C, 76.76; H, 9.66; N, 2.08%); lmax
(CH2Cl2)/nm 277 (log e 4.74), 402 (3.43); nmax(KBr)/cm21
2927, 2852, 2201, 1732, 1604, 1494, 1468, 1275, 1217, 1029,
866, 722; dH (400 MHz, CDCl3, 1% pyridine-d5). 8.2–6.6
(broad, m), 3.5–4.5 (broad), 3.2–0.4 (broad, m); GPC (THF)
Mw = 60 400 (Mw/Mn = 1.43).
Synthesis of zinc polymer (4a). Monomers 12a (0.2007 g,
0.2007 mmol) and 16 (0.1218 g, 0.2007 mmol) were combined
in a 100 mL vessel. To these solids were added 10 mL of
distilled THF and 4 mL of distilled NHiPr2 via syringe. The
reaction mixture was then degassed by three freeze/pump/thaw
cycles. In a glovebox, 5 mol% of Pd(PPh3)4 and 5 mol% CuI
were added. The brown reaction mixture was subsequently
freeze/pump/thawed one more time and heated to 75 uC for
24 h. The reaction mixture was then filtered through glass wool
and precipitated with 400 mL of MeOH to yield an orange
solid. Further purification was performed by precipitating the
polymer once from THF into MeOH, and twice into acetone.
During the dissolution of the polymer into THF, a very fine
beige precipitate would sometimes appear, and was removed
by filtration. This procedure yielded polymer 4a (0.229 g, 85%)
as a dark red film (Found: C, 74.22; H, 9.47; N, 2.28. Calc. for
C86H129N2O6Zn requires C, 76.38; H, 9.61; N, 2.01%); lmax
(CH2Cl2)/nm 331 (log e 3.64), 404 (7.60); nmax(KBr)/cm21
2854, 2203, 1732, 1620, 1506, 1469, 1413, 1379, 1319, 1274,
1216, 1168, 1125, 1025, 881, 853, 833, 750, 721; dH (400 MHz,
CDCl3, 1% pyridine-d5). 9–6 (broad, m), 3.3–4.5 (broad), 3.2–
0.1 (broad, m); GPC (THF) Mw = 18 700 (Mw/Mn = 1.09).
Synthesis of copper polymer (5c). Polymer 5c was prepared
by a procedure identical to that for 5a, starting with monomer
15c. Precipitation furnished polymer 5c (90%) as a dark red
solid (Found: C, 70.80; H, 8.89; N, 2.01. Calc. for
C86H129N2O6Cu requires C, 76.48, H, 9.63; N, 2.07%); lmax
(CH2Cl2)/nm 276 (log e 3.85), 344 (3.27), 448 (7.00); nmax(KBr)/
cm21 2913, 2866, 2204, 1734, 1610, 1523, 1490, 1464, 1379,
1273, 1186, 1142, 1113, 1013, 984, 872, 825, 791, 721; GPC
(THF) Mw = 63 200 (Mw/Mn = 1.25).
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