Evaluation of Cyclooctatetraene-Based Aliphatic Polymers as Battery Materials: Synthesis, Electrochemical, and Thermal Characterization Supported by DFT Calculations

Article abstract of DOI:10.1002/cplu.201700356

Organic electrode materials for rechargeable batteries are becoming a viable alternative for existing technologies. In particular, redox polymers have shown great performances. While many cathode-active derivatives are known, the development of their anode-active counterparts, required for the design of full-organic batteries, lacks behind. Here we present investigation on the suitability of cyclooctatetraene (COT)-based aliphatic polymers as anode-active battery materials, inspired by the known reversible reduction chemistry of COT at low electrochemical potential. We found that both synthesized polystyrene derivatives, side-group functionalized with COT, showed limited electrochemical reversibility of the reduction processes, whereas reductions proceeded reversibly in model compounds of these polymers. Differential scanning calorimetry measurements and density-functional theory calculations showed that this incomplete reversibility was due to cross-linking reactions occurring between COT units in the polymers. For the future of COT-based redox polymers, we propose a molecular design that prevents these cross-linking reactions.

Full text of DOI:10.1002/cplu.201700356

Accepted Article
Title: Evaluation of cyclooctatetraene-based aliphatic polymers as
battery materials: Synthesis, electrochemical and thermal
characterization, supported by DFT-calculations
Authors: Martin E Speer, Christopher Sterzenbach, and Birgit Esser
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Evaluation of cyclooctatetraene-based aliphatic polymers as
battery materials: Synthesis, electrochemical and thermal
characterization, supported by DFT-calculations
[
a]
[b]
[a]
Martin E. Speer, Christopher Sterzenbach, and Birgit Esser*
Abstract: Organic electrode materials for rechargeable batteries are
becoming a viable alternative for existing technologies. In particular,
redox polymers have shown great performances. While many
cathode-active derivatives are known, the development of their
anode-active counterparts, required for the design of full-organic
batteries, lacks behind. Here we present our investigation on the
suitability of cyclooctatetraene (COT)-based aliphatic polymers as
anode-active battery materials, inspired by the known reversible
reduction chemistry of COT at low electrochemical potential. We
found that both synthesized polystyrene derivatives, side-group
functionalized with COT, showed limited electrochemical reversibility
of the reduction processes, while reductions proceeded reversibly in
model compounds for these polymers. Differential scanning
calorimetry measurements and density-functional theory calculations
showed that this incomplete reversibility was due to cross-linking
reactions occurring between COT units in the polymers. For a future
design of COT-based redox polymers we propose to employ a
molecular design that prevents these cross-linking reactions.
planar and stable dianion (Scheme 1). This reduction can be
[
13]
[14]
performed chemically
as well as electrochemically.
The
electrochemical reversibility of this process has rendered COT of
[
15]
interest to the design of molecular actuators,
conformational change from tub-shape to planar upon reduction,
due to the
[
16–18]
and for the storage of electrons in battery applications.
In
order to be employed as electrode-active battery material, the
incorporation of the COT unit into a polymeric architecture is
required to provide insolubility in solvents commonly used for
[
6]
battery electrolytes. While molecules containing several COT
[
17,19–22]
units have been reported before,
to the best of our
knowledge, there is no account of polymers incorporating COT
units in the side group.
2–
e–
e–
1
Scheme 1. Two-step reduction of cyclooctatetraene (1) to its dianion.
Introduction
We herein describe the synthesis and electrochemical
characterization of the two aliphatic polymers P1 and P2, which
are side-group functionalized with COT, as well as their
electrochemical characterization. The thermal properties of these
polymers were investigated, supported by DFT calculations,
showing cross-linking reactions in the solid state. We furthermore
report on the synthesis and electrochemical investigation of the
four COT model compounds 2-5, whose electrochemical
properties guided the design of the polymers mentioned above.
The development of organic electrode materials for batteries is a
[
1–6]
growing field of research.
In order to find suitable organic
materials, new monomeric and polymeric compounds have to be
identified, which show an electrochemically highly reversible
[
7]
redox chemistry. While the majority of organic electrode
materials developed is of p-type and can be reversibly oxidized at
+
[6,8]
potentials of up to 4.1 V vs. Li/Li ,
making them suitable as
battery cathode materials, fewer examples for n-type and
[
9,10]
potential anode-materials exist.
These, however, are
R
necessary to build full-organic batteries. Cyclooctatetraene (COT,
n
n
1
) could be ideally suited as n-type, redox-active unit. Its redox
[
11–13]
chemistry has interested chemists for almost 60 years.
Upon
two-electron reduction, COT is transformed to a 10 π-aromatic,
2-5
[
a]
b]
M. E. Speer, Prof. Dr. B. Esser
Institute for Organic Chemistry
University of Freiburg
Albertstr. 21, 79104 Freiburg, Germany
E-mail: besser@oc.uni-freiburg.de
C. Sterzenbach
P1
O
O
Ph
R =
O
O
P2
[
2
3
4
5
Kekulé-Institute for Organic Chemistry
University of Bonn
Figure 1. Cyclooctatetraene-based polymers P1 and P2 and model compounds
-5 investigated in this study.
Gerhard-Domagk-Str. 1, 53121 Bonn, Germany
2
Supporting information for this article is given via a link at the end of
the document.
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+
Results and Discussion
Fc/Fc . A similar solvent dependence of the electrochemical
[
26–28]
behaviour of COT has been observed before.
O
A variety of different aliphatic polymer backbones are available,
which could be used to incorporate COT as a side group. Initially,
the direct free-radical polymerization of vinyl-COT was attempted,
however, did not lead to any polymerized material. Hence model
compounds 2–5 were synthesized in order to identify a suitable
polymer backbone, which would allow for a reversible reduction
of the COT unit. 2 and 3 represent models for polystyrene
derivatives, in which the COT unit is directly attached to the
styrene unit (2) or separated by an ethyl linker (3). 4 is a model
compound for an acrylate polymer, and 5 for a polystyrene
derivative, in which the COT unit is attached via an ester group.
Ac O
-DMAP
O
2
4
Pyridine
rt, 3 h
1
. (i) n-BuLi, 2.5 h
ii) DMF, 2.5 h
THF, –78 ºC to rt
OH
Br
(
6
6%
4
2. NaBH4
Benzoyl
chloride
4-DMAP
THF/H2O, rt, 1 h
O
Ph
6
9
22%
O
Et N/CH Cl
2
3
2
rt, 3 h
8%
8
5
Br
Pd(PPh ) , NaOH
3
4
+
Scheme 3. Synthesis of model compounds 4 and 5.
B
THF/H O
2
O
O
4
0 ºC, 3 h
8%
6
6
7
2
1
. (i) 9-BBN, THF
ii) 6, Pd(OAc) , RuPhos, KF
(
2
THF, rt, 28 h
BF K
3
2
. PhBr, Pd(OAc) , RuPhos
2
8
K CO , toluene/H O
2
3
2
15 h, 70 ºC
3
2%
3
Scheme 2. Synthesis of model compounds 2 and 3.
Model compounds 2–5 were synthesized starting from bromo-
Figure 2. Cyclic voltammograms of 2 in DMF (top) and THF (bottom) (1 mM,
[
23]
COT (6). A Suzuki-Miyaura coupling with p-tolyl boronic ester
−1
4 6
scan rate 100 mV s , with 0.1 M n-Bu NPF , glassy carbon electrode).
[
24]
7
afforded model compound 2 in 68% yield (Scheme 2). For the
[
25]
synthesis of 3 a procedure by Molander et al. was employed.
Potassium vinyltrifluoroborate (8) was hydroborated with 9-BBN
in situ, yielding a 1,2-dibora intermediate. This was then subjected
to two sequential Suzuki-Miyaura couplings with bromo-COT (6)
followed by bromobenzene to afford model compound 3 in 32%
overall yield. For the synthesis of model compounds 4 and 5, the
bromo functionality in 6 was replaced by an aldehyde group,
which was subsequently reduced to alcohol 9 (Scheme 3). 9 was
then transformed to esters 4 and 5 through reaction with acetic
anhydride and benzoyl chloride, respectively, employing standard
protocols.
The reductions of model compound 3 with an ethyl linker were
slightly less reversible, as shown in Figure 3. In DMF two separate
reduction waves appeared at half-wave potentials of E1/2 = −2.26
+
and −2.42 V vs. Fc/Fc . In THF both reductions took place at the
+
same half-wave potential of E1/2 = −2.41 V vs. Fc/Fc , however, in
the anodic scan direction a shoulderis visible at about −2.44 V vs.
+
Fc/Fc , indicating that re-oxidation to the radical anion and neutral
COT took place at two separate potentials. Compared to model
compound 2, the reductions of 3 are shifted to more negative
potentials by ca. 0.1 V. This is likely due to electronic conjugation
between the p-tolyl and COT groups in 2, which is absent in 3.
In compounds 4 and 5 the reductions were irreversible, likely
Cyclic voltammetry measurements in solution were performed
on model compounds 2–5 to provide information on the
reversibility of the reduction process of the COT unit. Depending
on the solvent, derivative 2 showed one or two chemically
reversible reduction waves of the COT moiety (Figure 2). While in
DMF the two one-electron reductions leading to the COT radical
[29]
due to the redox activity of the ester functionalities (see SI).
Hence, the highest reversibility of the COT reductions was found
for model compounds 2 and 3, and for this reason a poly(styrene)
backbone was chosen for the COT polymers with a direct
connection to the COT unit (P1) or connected via an ethyl linker
anion and dianion appeared at separate half-wave potentials of
+
E
1/2 = −2.17 and −2.30 V vs. Fc/Fc , in THF only one two-electron
(
P2).
reduction wave was visible at a half-wave potential of −2.33 V vs.
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reversibility. In THF P1 showed one reduction wave for both
electron transfers, as was observed for model compound 2, with
+
a cathodic peak potential of Epc = −2.38 V vs. Fc/Fc . For P2 the
reduction occurred at a cathodic peak potential of Epc = −2.64 V
+
vs. Fc/Fc in THF (Figure 5).
Figure 3. Cyclic voltammograms of 3 in DMF (top) and THF (bottom) (1 mM,
−
1
4 6
scan rate 100 mV s , with 0.1 M n-Bu NPF , glassy carbon electrode).
The synthesis of polymers P1 and P2 proceeded from bromo-
COT (6), as shown in Scheme 4. Suzuki-Miyaura coupling of 6
with styrene boronic ester 10 provided monomer 11 in 96% yield.
Monomer 12 was synthesized employing the procedure
Figure 4. Cyclic voltammograms of P1 in DMF (top) and THF (bottom) (1 mM,
−
1
4 6
scan rate 100 mV s , with 0.1 M n-Bu NPF , glassy carbon electrode).
[
25]
mentioned above by Molander et al.:
6 and 1-bromo-4-
vinylbenzene were sequentially coupled to the 1,2-dibora
intermediate generated by hydroboration of vinyltrifluoroborate (8)
with 9-BBN. This provided monomer 12 in 44% yield. The free-
radical polymerizations of 11 led to polymer P1 with a molecular
−
1
n
weight of M = 10,900 g mol and a PDI of 1.90, while P2 was
−
1
obtained from 12 with a molecular weight of M
n
= 37,000 g mol
and a PDI of 2.90.
−
1
Figure 5. Cyclic voltammogram of P2 in THF (1 mM, scan rate 20 mV s , with
0.1 M n-Bu NPF , glassy carbon electrode).
Br
Pd(PPh3)4
4
6
NaOH
AIBN
P1
+
THF/H O
reflux, 3 h
Toluene
60 ºC
2
B
O
O
We assume that the incomplete reversibility of the reduction
processes in P1 and P2 was partly due to inter- and
intramolecular dimerization processes between COT units. These
were observed when the thermal properties of P1 and P2 were
investigated. While thermal gravimetric analysis (TGA) indicated
a high thermal stability and no decomposition below 435 ºC for P1
and 402 ºC for P2 (see SI), the DSC measurements showed the
occurrence of strongly exothermic reactions upon heating above
200 ºC (Figure 6). To gain information on the enthalpy change
2
3
4 h
8%
9
6%
6
1
0
11
1
. (i) 9-BBN, THF
ii) 6, Pd(OAc) , RuPhos, KF
(
2
THF, rt, 28 h
AIBN
BF K
P2
3
2
. 1-Bromo-4-vinyl-benzene,
Pd(OAc) , RuPhos, K CO
Toluene
60 ºC
3
8
2
2
3
during this reaction, the DSC curves were evaluated using the
6 h
0%
toluene/acetone/H O
[30]
2
5
method by Borchardt and Daniels.
This single scan method
7
0 ºC (23 h) to rt (18 h)
allows for a fast determination of the activation energy of an nth
order reaction, proceeding from the general rate equation (for
further details see SI). For P1 the exothermic reaction occurred
4
4%
1
2
‡
−1
Scheme 4. Synthesis of polymers P1 and P2.
with an activation enthalpy of ΔH = 22.7 kcal mol (per COT
subunit) in a reaction order of n = 1.3 and with a total enthalpy
−
1
change of ΔH = −21.4 kcal mol (per COT subunit). For P2 the
‡
−1
In order to evaluate the reversibility of the reduction processes
in COT-polymers P1 and P2, cyclic voltammetry measurements
were performed. In DMF P1 showed two reduction waves in close
activation enthalpy amounted to ΔH = 48.8 kcal mol per COT
subunit (reaction order of n = 2) and the total enthalpy change to
−
1
ΔH = −27.7 kcal mol (for details see SI).
proximity with cathodic peak potentials of Epc = −2.25 V and
+
−
2.34 V vs. Fc/Fc , but reoxidation occurred with incomplete
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isomers were optimized with 14 being the most stable one
(
Scheme 5). The activation enthalpy for the valence
tautomerization of 13 to 14 was calculated to be
‡
−1
ΔH = 24.3 kcal mol
(PW6B95-D3/def2-QZVP(COSMO-RS,
benzene)//TPSS-D3/def2-TZVP, see also Figure 7). This
corresponds well with the activation enthalpy experimentally
determined by Huisgen for the rearrangement of 13 to 14 of
‡
−1 [33,34]
ΔH = 25 kcal mol ,
activation enthalpy obtained from the DSC heating curve of P1 of
and with the experimental value of
‡
−1
ΔH = 22.7 kcal mol per COT subunit.
Ph
H
Ph
Ph
1
/2
Figure 6. Differential scanning calorimetry (DSC) heating curves of P1 (top) and
H
−
1
2
P2 (bottom) (Heating rate 10 K min , N ). The DSC measurements show the
1
3
14
15
Ph
occurrence of strongly exothermic reactions at 258 °C (P1) and 286 °C (P2). No
glass transition appeared during heating.
Scheme 5. Valence tautomerization of phenyl-COT (13) as a model compound
for P1 to the bicyclo[4.2.0]-octa-2,4,7-triene 14 and [4+2]-cycloaddition to 15.
COT is known to undergo dimerization processes upon
heating in the bulk state or even upon standing at room
[
11]
Once 14 is formed it can undergo dimerization in form of a
temperature.
valence tautomerization of the COT units to bicyclo[4.2.0]-octa-
,4,7-triene through disrotatory ring closure (see Scheme 5),
The initial reaction of this process is either a
[
4+2]-cycloaddition. The structures of eight different dimers were
optimized, of which 15 was the most stable. With
2
‡
−1
ΔH = 7.9 kcal mol
(PW6B95-D3/def2-QZVP(COSMO-RS,
which can act both as diene and dienophile in a [4+2]-
cycloaddition, or a direct [4+2]-cycloaddition between two COT
benzene)//TPSS-D3/def2-TZVP) the activation enthalpy for the
dimerization of 14 to 15 is significantly lower than that for the
valence tautomerization of 13 to 14. The reaction enthalpy for the
[
11,12]
units.
Both the initial adducts can undergo further
rearrangement or bond-forming processes leading to a number of
[
11,31,32]
whole process 13
à
15 was calculated to be
dimeric products that have been well characterized.
In
−
1
ΔH = −13.6 kcal mol (normalized to one molecule of 13), while
order to investigate whether the experimental values from the
DSC measurements correspond to cycloaddition reactions
between COT units in P1 and P2, density functional theory (DFT)
calculations were performed (for details see Experimental Section
and SI) using phenyl-COT (13) as a model compound for P1 and
methyl-COT (16) for P2. 13 can undergo valence tautomerization
to a bicyclo[4.2.0]-octa-2,4,7-triene, of which four constitutional
the experimental reaction enthalpy obtained from the DSC
–
1
heating curve of P1 amounted to ΔH = −21.4 kcal mol per COT
subunit. This deviation can be rationalized by assuming that the
dimerization products of the COT units in P1 can undergo further
exothermic reactions.
Figure 7. Calculated reaction path for the valence tautomerization of 13 to 14 followed by dimerization through [4+2]-cycloaddition to 15 (PW6B95-D3/def2-
QZVP(COSMO-RS, benzene)//TPSS-D3/def2-TZVP).
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Methyl-COT (16) served as a model compound for P2 Experimental Section
(
Scheme 6). The calculated activation enthalpy for the valence
‡
−1
tautomerization of 16 to 17 amounts to ΔH = 25.2 kcal mol
PW6B95-D3/def2-QZVP(COSMO-RS, benzene)//TPSS-
D3/def2-TZVP), which is close to that calculated for the phenyl
Chemicals were obtained from commercial suppliers and used without
further purification. Experiments with water- or oxygen-sensitive
substances were carried out under an argon atmosphere using glassware
dried by heating under vacuum and standard Schlenk-techniques.
(
‡
−1
derivative 13. With ΔH = 48.8 kcal mol per COT subunit the
experimental value from the DSC curve of P2, however, deviates
significantly. The reason for this is not clear. The reaction enthalpy
2 2
Anhydrous solvents (THF, toluene, CH Cl ) were obtained from a solvent
purification system (MB-SPS-800) and stored over 3 Å molecular sieves.
Other anhydrous solvents were obtained by drying over activated
molecular sieves (3 Å) for several days. Ethyl acetate and cyclohexane for
flash chromatography were purchased in technical grade and purified by
distillation using a rotary evaporator. Other solvents were purchased and
for the whole process 16
à 18 was calculated to be
−
1
ΔH = −10.9 kcal mol (normalized to one molecule of 16), while
the experimental reaction enthalpy obtained from the DSC
−
1
1
13
1
heating curve of P2 amounted to ΔH = −27.7 kcal mol per COT
subunit. Again, this deviation is likely due to the fact that the COT
units in P2 can undergo further exothermic reactions once
structures such as 18 are formed.
used in analytical or HPLC grade. H and C{ H}NMR spectra were
recorded on Bruker Avance dpx 400, dpx 300, III HD 300 and II 400
spectrometers at room temperature and referenced to the residual proton
[
35]
or carbon resonance of the deuterated solvent. EI-MS spectra were
recorded on a MAT 90 or a MAT 95 XL sector field device from Thermo
Finnigan. HRMS spectra were measured on a Thermo Fisher Scientific Inc.
Exactive or LCQ Advantage via atmospheric pressure chemical ionization
Me
ΔH = 25.2
H
ΔH = 9.5
kcal mol
Me
Me kcal mol–1
–1
(
APCI) with an orbitrap analyzer. Polymer molecular weights were
1
/2
ΔH = 5.9
ΔH = –16.8
kcal mol
determined using a GPC unit by Agilent Technologies. As eluent THF was
used with a flow rate of 1 mL/min, and measurements were calibrated
against polystyrene standards by PSS Polymer Standard Service GmbH.
Cyclic voltammograms in solution were measured inside a glovebox using
a PGSTAT128N by Metrohm Autolab. As working, counter, and reference
electrode a glassy carbon disc electrode (2 mm diameter), a platinum rod,
and a Ag/AgNO3 electrode containing a silver wire immersed in an inner
kcal mol–
1
H
–1
1
6
17
18
Me
Scheme 6. Valence tautomerization of methyl-COT (16) as a model compound
for P1 to bicyclo[4.2.0]-octa-2,4,7-triene 17 and [4+2]-cycloaddition to 18
including calculated activation and reaction enthalpies (PW6B95-D3/def2-
QZVP(COSMO-RS, benzene)//TPSS-D3/def2-TZVP).
chamber filled with 0.1 M AgNO
3 4 6
and 0.1 M n-Bu NPF were used,
respectively. The ferrocene/ferrocenium redox couple was used as internal
©
reference. For TGA measurements a TGA/STAA851 (SF 1100 °C, MT 1,
2
N atmosphere) by Mettler Toledo was used with an Alox 40 μL melting
These dimerization reactions of COT units in P1 and P2 were
likely responsible for the lower observed electrochemical
reversibility of the reduction processes compared to model
compounds 2 and 3. Furthermore, the resulting cross-linking
between polymer chains in P1 and P2 already occurred at room
temperature, since these polymers turned insoluble in organic
solvents after storing them for several days on the bench.
e
pot by Mettler Toledo. DSC measurements were done on a DSC823
HSS7, N atmosphere, liquid N cooling) by Mettler Toledo with a standard
aluminum 40 μL melting pot by Mettler Toledo.
(
2
2
(
(1E,3Z,5Z,7Z)-1-(4-(Methyl)phenyl)cycloocta-1,3,5,7-tetraene (2). Aq.
NaOH (2.5 mL, 1 mM) was added to a mixture of 2-(4-methylphenyl)-
[24]
4
.4.5.5-tetramethyl-1.3.2-dioxaborolane
(7, 275 mg, 1.26 mmol) and
[
23]
(
1Z,3Z,5Z,7Z)-1-bromocycloocta-1,3,5,7-tetraene
(6,
.93 mmol) in THF (70 mL). The solution was degassed with three freeze-
(80 mg, 0.069 mmol) was added. The
mixture was stirred at 40 °C for 3 h. H O (5 mL) was added, and the
mixture was extracted with EtOAc. The combined organic layers were
dried (MgSO ), filtered, and the solvent was removed under reduced
pressure. Column chromatography (silica gel, cyclohexane) afforded 2
353 mg,
1
3 4
pump-thaw cycles, and Pd(PPh )
Conclusions
2
In conclusion we have reported on the synthesis of two novel
aliphatic polymers P1 and P2, side-group-functionalized with
cyclooctatetraene (COT) units, and on four model compounds 2-
4
1
(
168 mg, 68%) as a slightly yellow oil. R
f
0.48 (cyclohexane); H NMR (300
5
.
Electrochemical investigations showed the reduction
MHz, CDCl ): δ 7.29-7.26 (m, 2H), 7.13-7.10 (m, 2H), 6.21-5.85 (m, 7H),
3
1
3
processes of the COT units to occur with high reversibility in
model compounds 2 and 3, while electrochemical reversibility was
slightly reduced in the structurally similar polymers P1 and P2.
This was ascribed to thermal dimerization and cross-linking
reactions between COT units in P1 and P2, which were
investigated using differential scanning calorimetry (DSC) and
density functional theory (DFT) calculations. Hence, due to the
limited electrochemical reversibility of the reduction processes in
P1 and P2, these COT-polymers are not suitable for an
application as electrode-active battery material. In a more
advanced design of COT redox polymers, such cross-linking
processes will have to be prevented to achieve high
electrochemical reversibility of the redox processes, e.g. by
adding more space between COT subunits along the polymer
chain.
2.33 (s, 3H); C NMR (101 MHz, CDCl
3
): δ* 142.1, 137.6, 137.4, 133.3,
1
32.5, 132.3, 131.9, 131.6, 129.1, 127.3, 126.2, 21.2; HRMS (APCI+): m/z
+
calculated for C15H15O: 211.1117 [M+O+H] , found: 211.1117. *One
missing signal could not be assigned due to line broadening.
1Z,3Z,5Z,7Z)-1-(Phenethyl)cycloocta-1,3,5,7-tetraene (3). A degassed
(
solution of 9-borabicyclo(3.3.1)nonane (3.6 mL, 1.80 mmol, 0.5 M in THF)
in dry THF (10 mL) was added to potassium vinyltrifluoroborate (8, 234 mg,
1
.75 mmol). After stirring for 4 h at room temperature the mixture was
added to Pd(OAc)2 (8.5 mg, 38 µmol), RuPhos (35 mg, 75 µmol) and
potassium fluoride (230 mg, 3.95 mmol). (1E,3Z,5Z,7Z)-1-
bromocycloocta-1,3,5,7-tetraene (6, 320 mg, 1.75 mmol) was added, and
the resulting mixture was stirred at room temperature for 24 h. The solvent
was removed under reduced pressure, and Pd(OAc)
RuPhos (33 mg, 71 µmol), K CO (725 mg, 5.2 mmol) and a degassed
mixture of toluene (10 mL) and H O (1 mL) were added. Bromobenzene
320 mg, 0.21 mL, 1.75 mmol) was added dropwise, and the mixture was
stirred at 80 °C for 5 h and at 70 °C for 10 h. H O (15 mL) was added, and
the mixture was extracted with ethyl acetate. The organic layer was
washed with brine, dried (MgSO ), filtered, and the solvent was removed
2
(5 mg, 22 µmol),
2
3
2
(
2
4
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1
3
under reduced pressure. Column chromatography (silica gel,
1.5 Hz, 1H), 7.47-7.42 (m, 2H), 5.95-5.83 (m, 7H), 4.75 (s, 2H); C NMR
(75 MHz, CDCl ): δ 166.3, 138.7, 133.4, 133.1, 132.3, 132.1, 131.9, 131.4,
131.2, 130.3, 130.1, 129.8, 128.5, 67.6.
cyclohexane) afforded 3 (118 mg, 32%) as slightly yellow oil. R
f
0.37
): δ 7.30-7.26 (m, 2H), 7.21-7.16
m, 3H), 5.87-5.77 (m, 6H), 5.56 (s, 1H), 2.74 (t, J = 8.1 Hz, 2H), 2.34 (t, J
3
1
(
cyclohexane); H NMR (400 MHz, CDCl
3
(
1
3
=
1
3
8.1 Hz, 2H); C NMR (101 MHz, CDCl ): δ* 144.0, 142.0, 134.3, 132.4,
4
,4,5,5-Tetramethyl-2-(4-vinylphenyl)-1,3,2-dioxaborolane (10).
A
32.0, 131.6, 131.1, 128.6, 128.4, 126.8, 125.9, 39.9, 35.4; MS (EI+), m/z
solution of n-BuLi (1.6 M in hexanes, 9.40 mL, 15.0 mmol) was added
dropwise to a solution of 1-bromo-4-vinylbenzene (1.79 mL, 13.7 mmol) in
dry THF (90 mL) at −78 °C. After stirring for 1.5 h at −78 °C, 2-isopropoxy-
+
•
+•
+•
(
(
%): 208 (18) [M] , 117 (100) [M–C
APCI+): calculated for C16
7
H
7
] , 91 (45) [M–C
9
H
9
] ; HRMS
+
H
16: 208.1252 [M] , found: 208.1254. *One
1
3
missing signal could not be assigned due to line broadening. The C NMR
spectrum contained some impurities due to cycloaddition reactions
between COT units.
4
,4,5,5-tetramethyl-1,3,2-dioxaborolane (3.62 mL, 17.8 mmol) was added
dropwise. After stirring at −78 °C for another hour, the cold bath was
removed, and the reaction mixture was stirred at rt for 2.5 h. The reaction
mixture was quenched with sat. aq. NH
organic phase was separated, and the aqueous phase was extracted with
Et O (3 x 30 mL). The combined organic layers were washed with brine
(100 mL), dried (MgSO ), and the solvent was removed under reduced
pressure. Column chromatography (silica gel, cyclohexane/EtOAc: 20/1)
afforded 10 (2.92 g, 93%) as colorless liquid. = 0.42
(cyclohexane/EtOAc: 20/1); H NMR (300 MHz, CDCl ): δ 7.77 (d, J =
4 2
Cl (40 mL) and H O (30 mL). The
(
1E,3Z,5Z,7Z)-Cycloocta-1,3,5,7-tetraene-1-carbaldehyde. A solution of
n-BuLi (1.6 M in hexane, 8.19 mL, 13.1 mmol) was added dropwise to a
solution of (1E,3Z,5Z,7Z)-1-bromocycloocta-1,3,5,7-tetraene (6, 2.01 g,
2
4
1
0.9 mmol) in dry THF (40 mL) at –78 °C. After stirring at –78 °C for 2.5 h,
dry DMF (6.00 mL, 77.5 mmol) was slowly added, and the reaction mixture
was stirred at room temperature for 2.5 h. The reaction mixture was
a
R
f
1
3
quenched with aq. 1 M HCl (90 mL) and extracted with Et
The organic layer was washed with H O (5 x 200 mL) and brine (100 mL).
The combined organic layers were dried (MgSO ), and the solvent was
removed under reduced pressure. Column chromatography (silica gel,
cyclohexane/Et O: 10/1) afforded (1E,3Z,5Z,7Z)-cycloocta-1,3,5,7-
tetraene-1-carbaldehyde (350 mg, 24%) as an orange oil. 0.26
) δ 9.47 (s, 1H), 6.75
2
O (5 x 50 mL).
8.1 Hz, 2H), 7.41 (d, J = 7.9 Hz, 2H), 6.73 (dd, J = 10.9, 17.6 Hz, 1H), 5.81
(dd, J = 17.6, 0.9 Hz, 1H), 5.29 (dd, J = 10.9, 0.9 Hz, 1H), 1.35 (s, 12H);
2
1
3
4
3
C NMR (75 MHz, CDCl ): δ* 140.3, 137.0, 135.2, 125.7, 115.0, 83.9,
+
+
25.0; MS (EI+, 70 eV), m/z (%): 230 (95) [M] , 215 (60) [M−CH
3
] , 147 (10)
+
+
2
[M−C
6
H
13] , 130 (100) [M−C
6
H
13O] ; HRMS (APCI+): m/z calculated for
+
R
f
C
14
H
20BO
2
: 231.1551 [M+H] , found: 231.1552. *One missing signal could
1
(
(
cyclohexane/Et
2
O: 10/1); H NMR (300 MHz, CDCl
3
not be assigned because of signal broadening.
bs, 1H), 5.76-6.01 (m, 6H).
(
1E,3Z,5Z,7Z)-1-(4-Vinylphenyl)cycloocta-1,3,5,7-tetraene
(11).
(
(1E,3Z,5Z,7Z)-Cycloocta-1,3,5,7-tetraen-1-yl)methanol (9). NaBH
50.9 mg, 1.34 mmol) was added to a solution of (1E,3Z,5Z,7Z)-cycloocta-
,3,5,7-tetraene-1-carbaldehyde (350 mg, 2.69 mmol) in THF (8 mL) and
4
Pd(PPh (89.6 mg, 77.6 µmol) was added to a degassed solution of
3 4
)
(
(1E,3Z,5Z,7Z)-1-bromocycloocta-1,3,5,7-tetraene (6, 284 mg, 1.55 mmol),
4,4,5,5-tetramethyl-2-(4-vinylphenyl)-1,3,2-dioxaborolane (10, 393 mg,
1.71 mmol) and aq. NaOH (2.33 mL, 4.65 mmol, 1 M) in THF (15 mL). The
1
H
1
2
O (0.27 mL). The resulting mixture was stirred at room temperature for
h. After adding H O (5 mL), the reaction mixture was extracted with Et
2
2
O
reaction mixture was heated under reflux for 3 h. H
and the organic layer was separated. The aqueous layer was extracted
with Et O (3 x 50 mL). The combined organic layers were dried (MgSO ),
2
O (20 mL) was added,
(
3 x 25 mL), washed with aq. 1 M HCl (50 mL) and brine (100 mL). The
combined organic layers were dried (MgSO ), and the solvent was
removed under reduced pressure. Column chromatography (silica gel,
cyclohexane/Et O: 10/1) afforded 9 (337 mg, 93%) as a yellow oil. R
.40 (cyclohexane/EtOAc: 2/1); H NMR (300 MHz, CDCl
4
2
4
and the solvent was removed under reduced pressure. Column
2
f
=
chromatography (silica gel, cyclohexane), afforded 11 (307 mg, 96%) as
1
1
0
3
): δ 5.94-5.81
m, 7H), 4.04 (s, 2H), 1.62 (s, 1H); C NMR (75 MHz, CDCl ): δ* 143.7,
33.5, 132.2, 131.9, 131.7, 131.6, 127.5, 66.5. *One missing signal could
not be assigned due to line broadening.
an orange oil. R
f
= 0.42 (cyclohexane); H NMR (400 MHz, CDCl
3
): δ 7.35
1
3
(
3
(s, 4H), 6.72 (dd, J = 17.6, 10.9 Hz, 1H), 6.25-5.90 (m, 7H), 5.75 (ddd, J =
1
3
1
17.6, 0.8, 0.8 Hz, 1H), 5.25 (ddd, J = 10.9, 0.8, 0.8 Hz, 1H); C NMR (101
MHz, CDCl ): δ* 141.8, 139.8, 137.0, 136.6, 133.0, 132.6, 132.4, 132.3,
3
1
31.8, 128.1, 126.4, 126.3, 113.9; MS (EI+, 70 eV), m/z (%): 206 (100)
+
+
+
+
[
M] , 191 (40) [M-CH
3
] , 178 (28) [M-C
2
H
4
] , 91 (40) [M-C
9
H
7
] ; HRMS
(
(1E,3Z,5Z,7Z)-Cycloocta-1,3,5,7-tetraen-1-yl)methyl acetate (4). 4-
Dimethylaminopyridine (3.23 mg, 26.1 µmol) and acetic anhydride (74 µL,
82 µmol) were added to a solution of ((1E,3Z,5Z,7Z)-cycloocta-1,3,5,7-
tetraen-1-yl)methanol (9, 100 mg, 745 µmol) in dry pyridine (5 mL). The
reaction mixture was stirred at room temperature for 3 h. H O (10 mL) was
+
(
APCI+): m/z calculated for C16
H
15: 207.1168 [M+H] , found: 206.1167.
*
One missing signal could not be assigned due to line broadening.
7
2
Poly[(1E,3Z,5Z,7Z)-1-(4-vinylphenyl)cycloocta-1,3,5,7-tetraene] (P1).
Azobisisobutyronitrile (2.4 mg, 14.6 µmol) was added to a solution of
(1E,3Z,5Z,7Z)-1-(4-vinylphenyl)cycloocta-1,3,5,7-tetraene (11, 95.5 mg,
463 µmol) in dry and degassed toluene (0.1 mL) in an argon-filled
glovebox. The resulting solution was immersed in an oil bath preheated to
60 °C and stirred at this temperature for 24 h. MeOH (5 mL) was added,
and the reaction was evaporated to dryness under reduced pressure. The
added, and the organic layer was separated. The aqueous layer was
extracted with cyclohexane (3 x 50 mL). The combined organic layers
were dried (MgSO
pressure. Column chromatography (silica gel, cyclohexane/Et
afforded 4 (86.8 mg, 66%) as a yellow oil. R = 0.85 (cyclohexane/EtOAc:
): δ 5.91-5.75 (m, 7H), 4.49 (s, 2H), 2.07
s, 3H); C NMR (101 MHz, CDCl ): δ 170.9, 138.7, 133.3, 132.3, 132.1,
31.9, 131.3, 131.2, 130.2, 67.3, 21.1.
4
), filtered, and the solvent was removed under reduced
2
O: 10/1)
f
1
2
/1); H NMR (400 MHz, CDCl
3
1
3
(
3
residue was dissolved in CHCl
3
, and the polymer purified by successive
1
precipitation from MeOH and n-pentane. P1 (36 mg, 38%) was isolated as
1
a yellow powder. H NMR (400 MHz, CDCl
3
): 7.09 (br s), 6.46 (br s), 6.36
(
br s), 6.01 (br s), 5.86 (br s), 1.93-0.85 (m); GPC (eluent THF, polystyrene
(
(1E,3Z,5Z,7Z)-Cycloocta-1,3,5,7-tetraen-1-yl)methyl benzoate (5).
4
–1
–1
standard): M
n
1.09 × 10 g mol , M
w
/M
n 2
1.90; DSC (10 °C min , N ): Texo
Benzoyl chloride (170 µL, 1.49 mmol), triethylamine (260 µL, 1.86 mmol)
and 4-dimethylaminopyridine (4.91 mg, 40.2 µmol) were sequentially
–
1
2
58 °C; TGA (10 °C min , N ): Td10% 438 °C.
2
added to
a
solution of ((1E,3Z,5Z,7Z)-cycloocta-1,3,5,7-tetraen-1-
Cl (3 mL) at 0 °C. After
yl)methanol (9, 100 mg, 745 µmol) in dry CH
2
2
(1Z,3Z,5Z,7Z)-1-(4-Vinylphenethyl)cycloocta-1,3,5,7-tetraene (12). 9-
Borabicyclo(3.3.1)nonane (5.5 mL, 2.75 mmol, 0.5 M in THF) and dry THF
(15 mL) were added to potassium vinyltrifluoroborate (8, 300 mg,
2.24 mmol). After stirring at room temperature for 4 h the mixture was
stirring at room temperature for 3 h, the reaction mixture was quenched
with aq. 1 M HCl (3 mL), and the organic layer was separated. The
aqueous layer was extracted with CH
organic layers were dried (MgSO ), and the solvent was removed under
reduced pressure. Column chromatography (silica gel, cyclohexane/Et
2 2
Cl (6 x 25 mL). The combined
4
added to Pd(OAc)
2
(11 mg, 49 µmol), RuPhos (52 mg, 111 µmol) and
(323 mg, 6.72 mmol). (1E,3Z,5Z,7Z)-1-
2
2
O:
O:
potassium fluoride
2
2
0/1) afforded 5 (157 mg, 88%) as a yellow oil. R
f
0.49 (cyclohexane/ Et
bromocycloocta-1,3,5,7-tetraene (6, 446 mg, 2.44 mmol) was added, and
1
0/1); H NMR (300 MHz, CDCl
3
): δ 8.07-8.04 (m, 2H), 7.56 (tt, J = 7.5,
the resulting mixture was stirred at room temperature for 24 h. The solvent
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ChemPlusChem
10.1002/cplu.201700356
FULL PAPER
was removed under reduced pressure, and a degassed mixture of toluene
Keywords: Organic batteries • Redox polymers •
Electrochemistry • Redox chemistry • Valence isomerization
(
12 mL), H
was added to a mixture of Pd(OAc)
01 µmol) and K CO (930 mg, 6.73 mmol). 1-Bromo-4-vinylbenzene
520 mg, 0.29 mL, 2.84 mmol) was added dropwise, and the mixture was
stirred at 60 °C for 41 h. H O (20 mL) was added, and the mixture was
extracted with CH Cl . The organic extracts were dried (MgSO ), filtered,
2
O (3 mL) and acetone (2 mL) was added. The resulting mixture
2
(12 mg, 54 µmol), RuPhos (47 mg,
1
2
3
[
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2
4
[
[
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chromatography (silica gel, cyclohexane) afforded 12 (231 mg, 44%) as a
1
slightly yellow oil. R
f
0.34 (cyclohexane); H NMR (400 MHz, CDCl
3
): δ
7
.33 (d, J = 8.1 Hz, 2H), 7.16 (d, J = 8.1 Hz, 2H), 6.69 (dd, J = 17.6, 10.9
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1
1
7
C
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1
3
3
H); C NMR (101 MHz, CDCl ): δ* 143.9, 141.8, 136.8, 135.4, 134.3,
[
7]
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+
•
+•
0 eV), m/z (%): 234 (24) [M] , 117 (100) [M–C
9
H
9
] , 115 (40) [M–
+
•
+
9
H
11] ; HRMS (APCI+): calculated for C18
H
18: 234.1409 [M] , found:
[
[
[
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(
P2). Azobisisobutyronitrile (3.0 mg, 18.3 µmol) was added to a degassed
solution of (1E,3Z,5Z,7Z)-1-(4-vinylphenethyl)cycloocta-1,3,5,7-tetraene
12, 53.2 mg, 227 µmol) in dry toluene (70 µL). The resulting solution was
1
402034.
(
[11]
G. Schröder, Cyclooctatetraen, Verlag Chemie, GmbH,
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immersed in an oil bath preheated to 60 °C and stirred at this temperature
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evaporated to dryness under reduced pressure. The residue was
[
[
12]
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1
a yellow powder. H NMR (400 MHz, CDCl
3
): δ 7.03-6.25 (m, 4H), 5.78 (br
s, 6H), 5.51 (br s, 1H), 2.63 (br s, 2H), 2.27 (br s, 2H), 1.84-1.06 (m, 3H);
[
15]
M. J. Marsella, Acc. Chem. Res. 2002, 35, 944–951.
4
–1
n w n
GPC (eluent THF, polystyrene standard): M 1.28 × 10 g mol , M /M
–
1
–1
[16]
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Electrochemical Cells, 2010, WO2011142777 A1.
2
4
.90; DSC (10 °C min , N
19 °C.
2 2
): Texo 286 °C; TGA (10 °C min , N ): Td10%
[
17]
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98.
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37,38]
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with
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[
41]
[42]
conducted at the TPSS -D3/def2-TZVP
level of theory, the latter in
order to characterize the nature of stationary points (no imaginary
frequencies for local minima and one imaginary frequency for transition
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calculations at the PW6B95 -D3/def2-QZVP
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692–5694.
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45]
model was used to compute the solvation energies with benzene as the
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molecule, and the solvation contribution was added to the gas-phase
enthalpies. The final enthalpies in solution were calculated as the sum of
the gas-phase single point electronic energies, the gas-phase thermal
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Entry for the Table of Contents
FULL PAPER
COT battery? Two novel aliphatic
polymers, side-group functionalized
with cyclooctatetraene (COT) units,
and four COT model compounds
were synthesized and investigated
towards their ability to serve as
electrode material in organic
Martin E. Speer, Christopher
Sterzenbach and Birgit Esser*
Page No. – Page No.
Evaluation of cyclooctatetraene-
based aliphatic polymers as battery
materials: Synthesis,
batteries. While the model
electrochemical and thermal
characterization, supported by DFT-
calculations
compounds showed promising
electrochemical reversibility, the
polymers suffered from thermal
dimerization and cross-linking
reactions between the COT units.
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