Naphthyridine derivatives as a model system for potential lithium-sulfur energy-storage applications

Article abstract of DOI:10.1002/ejoc.201403542

Naphthyridines have been identified as structural elements in sulfurized polyacrylonitrile, which is a common electrode material in lithium-sulfur batteries. Some dibenzonaphthyridine derivatives with a fused dithiolo moiety were prepared as model compounds for battery studies. These heterocyclic systems were prepared via the corresponding diphenyldicarbamide intermediate. Followed by naphthyridione formation, stepwise installation of the dithiolane subunit occurred in a straightforward manner. In the solid state, the heteroaromatic system is completely planar and was thoroughly characterized. Initial battery cycling tests indicated a potential use of such structural motifs in sulfur-lithium systems.

Full text of DOI:10.1002/ejoc.201403542

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SHORT COMMUNICATION
DOI: 10.1002/ejoc.201403542
Naphthyridine Derivatives as a Model System for Potential Lithium–Sulfur
Energy-Storage Applications
[
a]
[a]
[a]
[b]
Sebastian Resch, Anna-Rebekka Schneider, Ronja Beichler, Marcelle B. M. Spera,
[b]
[a]
[a]
Jean Fanous, Dieter Schollmeyer, and Siegfried R. Waldvogel*
Keywords: Electrochemistry / Energy storage / Batteries / Lithium / Sulfur / Heterocycles
Naphthyridines have been identified as structural elements
in sulfurized polyacrylonitrile, which is a common electrode
material in lithium–sulfur batteries. Some dibenzonaphthyr-
idine derivatives with a fused dithiolo moiety were prepared
as model compounds for battery studies. These heterocyclic
systems were prepared via the corresponding diphenyldi-
carbamide intermediate. Followed by naphthyridione forma-
tion, stepwise installation of the dithiolane subunit occurred
in a straightforward manner. In the solid state, the heteroaro-
matic system is completely planar and was thoroughly char-
acterized. Initial battery cycling tests indicated a potential
use of such structural motifs in sulfur–lithium systems.
Introduction
In the past decade, great efforts went into the develop-
[
1]
ment of high-density lithium battery storage systems. To
increase the battery capacity compared to commercially
available lithium-ion batteries, a suitable cathode material
needs to be developed.[ A promising candidate for a high-
density cathode material is sulfur, because of its high theo-
2]
–
1
retical energy density of 2600 Whkg and its general abun-
[
3,4]
dance.
The major drawback of elemental sulfur for the
application in energy-storage systems lays in its insulating
nature, which makes conductive additives necessary, but
this also lowers the energy density of the final device.
Figure 1. Postulated polymeric structure of SPAN.[10]
[
5]
Several concepts were elaborated over the past years to
overcome this drawback.[ The elegant concept published
by Wang et al. in 2002 embedded sulfur inside a conducting
polymeric matrix by pyrolizing polyacrylonitrile (PAN)
with elemental sulfur.[ The resulting composite, referred
to as sulfurized polyacrylonitrile (SPAN, Figure 1), was
analyzed over the past years, and a covalent bond between
pound exhibiting this structural feature (Scheme 1). The an-
alytical data of 1a allow structural and electronic compari-
son of SPAN with the model compound.
4,6]
7]
sulfur and
found.
a polymeric, conducting backbone was
[
8,9]
Scheme 1. Elaborated structure for the model compound.
Owing to the insoluble nature of the polymer, only frag-
ments of the polymeric structure could be elucidated. To
obtain further insight into that structure, we identified the
Results and Discussion
9,10-dithiolonaphthyridine moiety as a structural feature of
the polymer and elaborated the synthesis of a model com-
As the starting compound for our synthesis towards di-
thiolo dibenzonaphthyridine derivative 1, we selected di-
benzonaphthyridione 2, as through benzannulation better
solubility properties and less potential side reactions were
anticipated. The naphthyridine moiety of 2 was constructed
within three steps by following modified procedures known
in the literature. We decided to construct parent compound
[
[
a] Institute for Organic Chemistry, Johannes Gutenberg
University,
Duesbergweg 10–14, 55128 Mainz, Germany
E-mail: waldvogel@uni-mainz.de
http://www.chemie.uni-mainz.de/OC/AK-Waldvogel/
b] Corporate Sector Research and Advanced Engineering
(
CR/ARC1), Robert Bosch GmbH,
Postfach 106050, 70049 Stuttgart, Germany
2a (Figure 2) and dibromo derivative 2b, which opened up
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201403542.
potential applications.
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S. R. Waldvogel et al.
SHORT COMMUNICATION
direct transformation towards desired compound
Scheme 3).
1
(
Figure 2. Selected compound as central intermediate for our syn-
thesis.
Scheme 3. Direct transformation of naphthyridione 2 into disulfide
derivative 1.
Phenyl isothiocyanate derivative 3 was converted into
symmetric N,NЈ-diphenylthiourea derivative 4 in up to 90%
yield by simple heating with substituted or unsubstituted
To overcome the poor reactivity of 2, we chlorinated the
molecule in the 9-position by using an excess amount of
[
11]
aniline derivative 5 in ethyl acetate for 1 h (Scheme 2).
The formation of N,NЈ-diphenylcarbodiimide derivatives 6 PCl in boiling POCl . Resulting chloronaphthyridone de-
5
3
was performed by following the protocol of Ali, and this rivative 8 was isolated in excellent yields up to 96%.
[
12]
provided the desired products in good yields up to 75%.
The slightly improved solubility of 2 in nonpolar solvents
The addition of diethyl malonate at the central carbon atom offered us the possibility for further transformations. We
yielded condensation product malonate derivative 7 in good installed the first sulfur atom for the target molecule by
yields up to 73%. The twofold Conrad–Limpach synthesis nucleophilic substitution by using benzylthiol, which re-
in diphenyl ether resulted in the formation of 5H,6H- sulted in 6H-12-(benzylsulfanyl)dibenzo[b,g]-1,8-naphthyr-
dibenzo[b,g]-1,8-naphthyrine-11,12-dione derivative 2 in idin-11-one (9) in good yields up to 77%. The final product,
[
13]
yields up to 89%.
dibenzo[b,g]-1,2-dithiolo[3,4,5-d,e]-1,8-naphthyridine (1),
was synthesized by a thionation reaction under reflux con-
ditions in chlorobenzene by using a mixture of P4S10 and
Na CO .
2
3
After the successful synthesis of desired model com-
pound 1a, we extended our synthetic approach towards di-
bromo-substituted naphthyridione derivative 1b. For fur-
ther use of the target structure, for example, polymeric en-
ergy-storage structures, the halide substituent offers the
possibility for additional functionalization mostly on the
[
14]
basis of transition-metal catalysis.
pound even more similar to SPAN, it is possible to subject
b to polymerizing coupling reactions such as the Yamam-
To generate a com-
1
oto reaction or Suzuki-type reactions.
Model compound 1a was investigated by UV/Vis, IR,
and NMR spectroscopy, and a suitable single crystal was
analyzed by X-ray diffraction. The electrochemical proper-
ties of 1a were investigated by cyclic voltammetry as well as
by application of the material in a prototype Li-battery cell
system.
The diffraction study of a suitable single crystal by using
X-ray diffraction offered us the possibility to determine the
length of the S–S bond at 2.07 Å, which is in the range of
an average disulfide bond. The polycyclic core of the mol-
ecule is flat, with a small distortion of 2° towards the plane
(Figure 3). The average C–C bond inside the molecule has
a length of 1.40 Å, which fits the average of a typical aro-
matic C–C bond.
Scheme 2. Synthetic pathway for the synthesis of dithiolo naphthyr-
idines 1.
Owing to the low solubility and reactivity of naphthyri-
dione derivatives 2, it was not possible to accomplish the of a suitable single crystal: Top view (left) and side view (right).
Figure 3. Molecular structure of 1a by X-ray diffraction analysis
2
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Naphthyridines for Potential Li–S Energy-Storage Applications
Naphthyridine derivatives 1a, 8a, and 9a were analyzed
The electrochemical properties of naphthyridine deriva-
by UV/Vis absorption spectroscopy (Figure 4). All three de- tive 1a were investigated by cyclic voltammetry (CV, Fig-
rivatives show their strongest absorption band at around ure 5). The experiments were conducted at room tempera-
300 nm. Naphthyridone derivatives 8a and 9a show a lower ture in DMF solutions containing tetra-n-butylammonium
degree of resonance stabilization, owing to a blueshift in tetrafluoroborate (0.1 m) as a supporting electrolyte. A
the absorption band at 450 nm. Dithiolo naphthyridine de- glassy carbon electrode tip (d = 2 mm) was used as the
rivative 1a displays a fully conjugated polycyclic aromatic working electrode and a glassy carbon rod was employed
system, which appears in the UV/Vis spectrum as four dif- as the counter electrode. The data was measured against
ferent absorption bands in the 500–620 nm range. The same Ag/AgCl in a saturated LiCl/EtOH solution and was re-
–1
additional absorption behavior in the visible spectrum can corded at a scan rate of 200 mVs . Additionally, peak po-
be found in the absorption spectrum of SPAN, which is tentials were referenced against ferrocene. As expected, di-
indicative of the striking similarity of the fully conjugated thiolo derivative 1a shows two reversible reduction/oxid-
backbone structure.[
15]
ation waves at –354 and –594 mV versus Ag/AgCl.
Figure 4. UV/Vis absorption spectra of naphthyridine derivatives
1a, 8a, and 9a.
Figure 5. Cyclic voltammogram of 1a in 0.1 m Bu NBF /DMF vs.
4
4
–
1
satd. Ag/AgCl, sweep rate 200 mVs .
Analysis of final compound 1a by IR transmission spec-
troscopy shows two characteristic absorption bands for the
Naphthyridine derivative 1a was applied to a battery test
disulfide structure at ν˜ = 514.1 for ν(S–S) and 672.7 cm–1 cell setup. The cathode consisted of 70% 1a, 15% carbon
for ν(C–S). Three absorption bands at ν˜ = 1514.1; 1536.5, black, and 15% binder. LiPF (1 m) was dissolved in a mix-
6
–
1
and 1552.1 cm correspond to a thioamide moiety, in ture of ethylene carbonate, diethyl carbonate, and dimethyl
which the sulfur atom has the same oxidation state as that carbonate (2:2:1) as supporting electrolyte. As anode mate-
in sulfides. Compared to SPAN, it is plausible that inside a rial, lithium metal was chosen. The setup was charged and
statistical polymeric structure, these bands superimpose and discharged with a C rate of C/10 for 20 cycles. Figures 6
form a broad intense absorption band, as observed by sev- and 7 show the charge and discharge profiles of the first
[
9,10,15,16]
eral other groups.
five charging/discharging cycles. The reversible redox reac-
Owing to the sufficient solubility of 1a in DMSO, it was tion of the disulfide bond can be found at a cell potential
possible to record and analyze the solution NMR spectra of 2.25 V, which is consistent with CV analysis.[
17]
The
of the product by using 1D and 2D NMR techniques. The decreasing cell capacity can be rationalized with the low,
1
3
C NMR spectroscopy data of the product revealed a sig- but still existing, solubility of the active material in the sup-
nal at δ = 152.3 ppm, which was assigned to carbon atoms porting electrolyte.
in positions 4a and 6a of the aromatic structure. The carbon
Moreover, upon reduction of 1, dramatically enhanced
atoms in positions 11 and 12 were equivocally assigned only solubility in the electrolyte system was expected. With every
by 1H– C HMBC spectroscopy at δ = 161.1 ppm. By cycle, a little amount of the active material migrates and
comparing these data with the magic-angle solid-state cannot be used for subsequent cycles. Although the cell ca-
13
1
3
C NMR spectroscopy data of SPAN, a broad peak at δ = pacity fades, it is possible to charge and discharge a battery
150 ppm with a shoulder at a higher chemical shift repre- setup consisting of the model system for several cycles,
sent the consistent equivalent. The quaternary carbon which proves its similarity to SPAN (Figure 8). One of the
atoms at 5a and 11a could not be resolved within the spec- future projects to overcome the capacity fading due to solu-
tra, owing to the relative low solubility of sulfanyl derivative bility is the polymerization of substituted naphthyridine de-
1a and the poor signal intensity for these atoms.
rivative 1b.
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S. R. Waldvogel et al.
SHORT COMMUNICATION
Conclusions
We developed a synthetic strategy for the synthesis of
4,5-dithiolo-1,8-naphthyridine derivatives 1 by using di-
benzonaphthyridione-based compounds 2 as starting mate-
rials. Resulting compound 1a was fully characterized and
investigated for its electrochemical properties. The cell po-
tential during charge and discharge cycles was comparable
to that of SPAN. As a potential building block for polymer
synthesis, we extended our synthetic approach towards sub-
stituted dibenzonaphthyridone derivatives, which resulted
in compound 1b. This molecule can be applied to Suzuki
cross-coupling and Yamamoto coupling reactions to over-
come the solubility drawback of the single naphthyridine
moiety.
Figure 6. Charging profile of the first five charging cycles.
Experimental Section
Supporting Information (see footnote on the first page of this arti-
cle): General procedures, characterization data, and copies of the
1
13
H NMR and C NMR spectra
Acknowledgments
This work was generously supported by the Federal Ministry of
Education and Research (BMBF, HE-Lion, 03X4612B) and the
German Research Foundation (DFG) in the frame of the research
unit FOR1616.
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Received: November 27, 2014
1
Published Online: ᭿
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S. R. Waldvogel et al.
SHORT COMMUNICATION
Energy Storage
S. Resch, A.-R. Schneider, R. Beichler,
M. B. M. Spera, J. Fanous,
D. Schollmeyer, S. R. Waldvogel* ..... 1–6
Naphthyridine Derivatives as a Model Sys-
tem for Potential Lithium–Sulfur Energy-
Storage Applications
The structure of a polyacrylonitrile-derived
sulfur composite is elucidated by a bottom-
up approach. New naphthyridine deriva-
tives are synthesized as model systems for
analytical comparison. The IR, NMR, and
UV/Vis spectroscopy data indicate a strong
correlation between this simple model com-
pound and sulfurized polyacrylonitrile
polymer.
Keywords: Electrochemistry / Energy stor-
age / Batteries / Lithium / Sulfur / Hetero-
cycles
6
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