Synthesis and catalytic performance of ferrocene-based compounds as burning rate catalysts

Article abstract of DOI:10.1002/aoc.3754

To overcome migration problems of ferrocene-based burning rate catalysts and to enhance burning rate of ammonium perchlorate (AP)-based propellants, eleven ferrocene-based compounds (1–11) were synthesized by the condensation reaction of ferrocenecarbonyl chloride with corresponding amines and alcohols. The synthesis of 1–11 was confirmed using ¹H NMR, Fourier transform infrared and UV–visible spectroscopy. Their electrochemical properties were analyzed using cyclic voltammetry. The compounds showed redox behavior due to the presence of ferrocene. Their catalytic behavior in the thermal decomposition of AP was investigated using thermogravimetry (TG) and differential TG (DTG). In the presence of 5?wt% 1–11, the thermal decomposition temperature of AP was significantly decreased. TG and DTG analyses showed that 1–11 had a good catalytic effect in the thermal decomposition of AP. Anti-migration studies showed that migration of 1–11 was slower than that of 2,2-bis(ethylferrocenyl)propane (catocene) and ferrocene. The effect of the presence of polar elements like oxygen and nitrogen on anti-migration behavior of small ferrocene-based compounds was also investigated. Oxygen-containing compounds showed better anti-migration behavior than nitrogen-containing compounds.

Full text of DOI:10.1002/aoc.3754

Received: 28 November 2016
DOI 10.1002/aoc.3754
Revised: 9 January 2017
Accepted: 9 January 2017
F U L L PA P E R
Synthesis and catalytic performance of ferrocene‐based
compounds as burning rate catalysts
Zain‐ul‐Abdin | Li Wang
| Haojie Yu
| Muhammad Saleem | Muhammad Akram |
Hamad Khalid | Nasir M. Abbasi | Rizwan Ullah Khan
State Key Laboratory of Chemical
To overcome migration problems of ferrocene‐based burning rate catalysts and to
Engineering, College of Chemical and
Biological Engineering, Zhejiang University,
Hangzhou 310027, China
enhance burning rate of ammonium perchlorate (AP)‐based propellants, eleven
ferrocene‐based compounds (1–11) were synthesized by the condensation reaction
of ferrocenecarbonyl chloride with corresponding amines and alcohols. The synthesis
of 1–11 was confirmed using 1H NMR, Fourier transform infrared and UV–visible
spectroscopy. Their electrochemical properties were analyzed using cyclic voltamm-
etry. The compounds showed redox behavior due to the presence of ferrocene. Their
catalytic behavior in the thermal decomposition of AP was investigated using
thermogravimetry (TG) and differential TG (DTG). In the presence of 5 wt% 1–11,
the thermal decomposition temperature of AP was significantly decreased. TG and
DTG analyses showed that 1–11 had a good catalytic effect in the thermal decompo-
sition of AP. Anti‐migration studies showed that migration of 1–11 was slower than
that of 2,2‐bis(ethylferrocenyl)propane (catocene) and ferrocene. The effect of the
presence of polar elements like oxygen and nitrogen on anti‐migration behavior of
small ferrocene‐based compounds was also investigated. Oxygen‐containing com-
pounds showed better anti‐migration behavior than nitrogen‐containing compounds.
Correspondence
Li Wang and Haojie Yu, State Key Laboratory
of Chemical Engineering, College of
Chemical and Biological Engineering,
Zhejiang University, Hangzhou 310027,
China.
Email: opl_wl@dial.zju.edu.cn; hjyu@zju.
edu.cn
Funding Information
Natural Science Foundation of China, Grant/
Award Number: 21272210, 21372200,
21472168, 21411130187; International Sci-
ence and Technology Cooperation Project of
Ministry of Science and Technology of
China, Grant/Award Number: 2009 DFR
40640; Science and Technology Program of
Zhejiang Province, Grant/Award Number:
2013C24001; Science and Technology
Innovation Team of Ningbo, Grant/Award
Number: 2011B82002; Fundamental
Research Funds for the Central Universities,
Grant/Award Number: 2016FZA4018.
KEYWORDS
anti‐migration behavior, burning rate catalyst, electrochemical properties, ferrocene‐based compounds,
synthesis
1 | INTRODUCTION
rate of solid propellants. Among all BRCs, ferrocene‐based
BRCs are considered as excellent BRCs due to their good
Ferrocene‐based compounds and numerous derivatives are
well known not only due to their potential application as burn-
ing rate catalysts (BRCs),[1–4] but also due to their increasing
applications in various fields like catalysis,[5–9] medicine,[10]
memory storage devices,[11] nanomaterials,[12,13] electro-
chemical sensors,[3,14–16] biologically active compounds,[17]
ion recognition and material science.[18–20] The high thermal
stability, reversible redox behavior and modification
possibilities of ferrocene‐based compounds make these com-
pounds an important class of organometallic compounds.[21]
Several kinds of BRCs have been used to increase burning
ignitability in solid propellants and compatibility with
organic binders.[1–4] Although ferrocene‐based BRCs are
capable of increasing the burning rate of ammonium per-
chlorate (AP)‐based propellants but on long‐time storage,
simple ferrocene‐based compounds show intrinsic draw-
backs, such as their migration to the interface of the solid
propellant.[22–24] These drawbacks result in poor aging and
irreproducible properties of solid propellants,[25–27] which
change the designed burning parameters of AP‐based pro-
pellants and may cause serious unexpected explosions.[28]
The burning rate catalytic effect of ferrocene‐based
Appl Organometal Chem. 2017;e3754.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3754

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ZAIN‐UL‐ABDIN ET AL.
compounds fluctuates with their chemical structure, solubil-
ity, molecular mobility and effective iron content.[23]
mechanism of AP catalyzed by ferrocene‐based BRCs. So,
the electrochemical properties of the synthesized ferrocene‐
based compounds were analyzed using cyclic voltammetry
(CV). Thermal behavior and catalytic performance of ferro-
cene‐based compounds in the thermal decomposition of AP
were investigated using thermogravimetry (TG) and differen-
tial TG (DTG). Anti‐migration behavior of 1, 3, 6–9 in AP‐
based propellant was investigated at 50 °C and atmospheric
pressure in comparison with catocene and ferrocene. In our
previous work, we found that ferrocene‐based branched
polymers containing large number of polar elements show
excellent anti‐migration properties in AP‐based propellant
due to the formation of attractive forces between ferrocene‐
based branched polymers and the propellant.[42] In continua-
tion of our interest in the field of BRCs, we investigated the
effect of the presence of polar elements (oxygen and nitrogen)
on anti‐migration behavior of small ferrocene‐based
compounds.
In order to reduce migration problems of ferrocene‐based
BRCs and to enhance the burning rate of AP‐based propel-
lants, n‐butylferrocene (NBF), tert‐butylferrocene (TBF)
and binuclear 2,2‐bis(ethylferrocenyl)propane (catocene)
have been synthesized.[23,29] Due to shorter carbon chains
on ferrocenyl ring and lower molecular weight, NBF and
TBF show obvious migration into insulation layer during
curing and storage and evaporation loss during processing.
In order to overcome migration problems, catocene was then
developed.[30] However, migration problems have not been
significantly overcome and on long‐time storage, migration
of catocene to the surface of a solid propellant was still
observed obviously.[23,29] Many efforts have been made to
synthesize new ferrocene‐based BRCs to overcome migration
problems and to enhance the burning rate of AP‐based pro-
pellants.[31] Liu and co‐workers synthesized ionic ferrocenyl
derivatives bearing methylimidazolium and methyltriazolium
substituents with nitrate and picrate anions.[28] Cheng and
co‐workers synthesized ionic ferrocenyl compounds contain-
ing nitrate and picrate ions.[7] Gao and co‐workers synthe-
sized two poly(ferrocenylsilane)s one of which showed
good catalytic activity.[32] Xiao and co‐workers synthesized
ferrocene‐functionalized polyester dendrimers.[33] Yuan and
co‐worker prepared a few nitrogen‐rich binuclear ferrocene
derivatives.[34] Zhou and co‐workers synthesized ferrocene‐
based sulfonyl dihydropyrazole derivatives.[35] Li and co‐
workers grafted ferrocenyl moieties on mesoporous silica
SBA‐15.[36] Luo and co‐workers synthesized a few ferrocene
end‐cap hyperbranched poly(amine‐ester) and hyper‐
branched poly(amine‐ester).[37] All these synthesized ferro-
cene‐based BRCs showed burning rate catalytic activity in
AP‐based propellants, but on prolonged storage, these
ferrocene‐based BRCs still showed obvious migration to the
interface of the solid propellant.
AP is the most commonly used oxidizer in AP‐based
propellants due to its excellent burning characteristics, good
processability and storability.[38–40] It has been found that
the combustion performance of AP‐based propellants is
directly influenced by the thermal decomposition of
AP.[33,41] Thermal decomposition of AP can be accelerated
by the addition of ferrocene‐based BRCs in AP‐based propel-
lants. So, the catalytic activity of BRCs can be assessed from
the thermal decomposition of AP.[39]
In the study reported here, to overcome migration
problems of ferrocene‐based BRCs and to enhance burning
rate of AP‐based propellants, we synthesized eleven
ferrocene‐based compounds (1–11). Synthesis of 1–11 was
confirmed using 1H NMR, Fourier transform infrared
(FT‐IR) and ultraviolet–visible (UV‐Vis) spectroscopy. The
electrochemical properties of ferrocene‐based BRCs are
important for investigating electron transfer catalytic
2 | EXPERIMENTAL
2.1 | Materials
Ethylene glycol, glycerol, diethanolamine, ethylene diamine,
methanol, pyridine, chloroform and petroleum ether were pur-
chased from Sinopharm Chemical Reagent Co. Ltd and were
used after drying with 4 Å‐type molecular sieves. Dichloro-
methane (DCM), tetrahydrofuran (THF) and triethylamine
(TEA) were also purchased from Sinopharm Chemical
Reagent Co. Ltd and were used after drying with 4 Å‐type
molecular sieves followed by reflux. Phloroglucinol,
tris(2‐aminoethyl)amine, pentaerythritol, oxalyl chloride,
ferrocenecarboxylic acid and NaHCO3 were purchased from
Sinopharm Chemical Reagent Co. Ltd and were used with-
out further purification. Tetrabutylammonium tetrafluorobo-
rate (Bu4NBF4) was purchased from J & K Co. Ltd and
was used as received.
2.2 | Synthesis
2.2.1 | Ferrocenecarbonyl chloride
Ferrocenecarbonyl chloride was synthesized from
ferrocenecarboxylic acid in freshly distilled DCM employing
oxalyl chloride as a chlorinating agent and pyridine as a cat-
alyst. In a typical synthetic procedure, ferrocenecarboxylic
acid (20.7140 g, 83.92 mmol) was dried at 40 °C under
vacuum for about 4 h. Then freshly dried ferrocenecarboxylic
acid was dissolved in 150 ml of DCM and the resulting
solution was stirred under argon atmosphere at room temper-
ature (25 °C). Pyridine (14.5 ml) was added to the
ferrocenecarboxylic acid solution. The resulting reaction
mixture was stirred for about 15 min at room temperature.

ZAIN‐UL‐ABDIN ET AL.
3 of 10
Oxalyl chloride (15.5 ml, 180.72 mmol) was added dropwise
to this solution at room temperature. The obtained reaction
mixture was stirred for 30 min at room temperature and
then it was refluxed for 6 h. Solvent and excess amount of
pyridine and oxalyl chloride were evaporated under
reduced pressure and then remaining residue was extracted
with petroleum ether (150 ml) at 90 °C. The obtained
product (ferrocenecarbonyl chloride) was stored under argon
atmosphere.
The synthetic procedure for 9 and 10 was the same.
Therefore, synthesis of 9 is taken as an example. In a typical
procedure, triethanolamine (0.62 ml, 4.69 mmol) was dried
under vacuum and then was dissolved in 25 ml of freshly
distilled THF. A suspension of NaH (0.34 g, 14.17 mmol) in
25 ml of THF was prepared. The solution of triethanolamine
was added to the NaH suspension. The resulting mixture was
stirred for 8 h at 25 °C. Afterward, a solution of
ferrocenecarbonyl chloride (3.5000 g, 14.08 mmol) prepared
in 40 ml of freshly distilled THF was added dropwise to the
solution. The resulting solution was then refluxed for 16 h.
Solvent was evaporated using a rotary evaporator. The
obtained residue was dissolved in 200 ml of CHCl3. The
resulting solution was washed (four times) with 1% NaHCO3
solution prepared in distilled water and then it was further
washed (three times) with distilled water. The organic layer
was separated, anhydrous Na2SO4 (2.0000 g) was added and
the resulting mixture was left overnight. The mixture was
filtered to separate Na2SO4 and then resulting filtrate was
dried using a rotatory evaporator to afford the product. The
experimental details are given in Table S1.
2.2.2 | Ferrocene‐based compounds
Ferrocene‐based compounds (1–11) were synthesized by the
condensation reaction of ferrocenecarbonyl chloride with
corresponding amines and alcohols. The synthetic procedure
for 1, 2, 6 and 8 was the same. Therefore, synthesis of 1 is
taken as an example. In a typical procedure, ethylene diamine
(17.73 ml, 265.55 mmol) was dried under vacuum and then
was dissolved in 65 ml of freshly distilled DCM. Afterward,
a
solution of ferrocenecarbonyl chloride (6.0000 g,
24.14 mmol) prepared in 35 ml of DCM was added dropwise
to the ethylene diamine solution. The resulting solution was
then stirred for 12 h at room temperature. Solvent was evap-
orated using a rotary evaporator. The obtained residue was
dissolved in 200 ml of CHCl3. The resulting solution was
washed (four times) with 1% NaHCO3 solution prepared in
distilled water and then it was further washed (three times)
with distilled water. The organic layer was separated,
anhydrous Na2SO4 (2.0000 g) was added and then resulting
mixture was left overnight. The mixture was filtered to sepa-
rate Na2SO4 and the resulting filtrate was dried on rotatory
evaporator to afford the product.
The synthetic procedure for 3, 4, 5, 7 and 11 was the
same. Therefore, the synthesis of 3 is taken as an example.
In a typical procedure, ethylene glycol (0.50 ml, 8.97 mmol)
was dried under vacuum and then was dissolved in 35 ml
of freshly distilled THF. TEA (2.5 ml, 17.94 mmol) was
added to ethylene glycol solution. The resulting solution
was stirred for 15 min at room temperature. Afterward, a
solution of ferrocenecarbonyl chloride (5.0100 g,
20.18 mmol) prepared in 35 ml of THF was added
dropwise to the solution. The resulting solution was then
refluxed for 16 h. Solvent was evaporated using a rotary
evaporator. The obtained residue was dissolved in 200 ml
of CHCl3. The resulting solution was washed (four times)
with 1% NaHCO3 solution prepared in distilled water and
then it was further washed (three times) with distilled
water. The organic layer was separated, anhydrous Na2SO4
(2.0000 g) was added and the resulting mixture was left
overnight. The mixture was filtered to separate Na2SO4
and then the resulting filtrate was dried using a rotatory
evaporator to afford the product.
Crude products 3, 4, 5, 9, 10 and 11 were purified by
column chromatography using CHCl3 as an eluent, while
crude products 6 and 7 were purified by column chromatog-
raphy using DCM as an eluent. The pure products were dried
in a vacuum oven at 40 °C for two days.
2.3 | Characterization
1H NMR spectra of 1–11 were recorded with an AVANCE
NMR spectrometer (600 MHz, model DMX‐400). In the case
of 2–4 and 6–11, the chemical shifts were related to
tetramethylsilane at δ = 0 ppm using CDCl3 as a solvent,
while for 1 and 5, 1H NMR spectra were reordered in D2O.
FT‐IR spectra of 1–11 were recorded with a Nicolet 5700
infrared spectrometer using the KBr pellet technique. Sample
(2%) and KBr were crushed to a powder and mixed together
and then KBr pellet was prepared. UV‐Vis spectra of 1–11
were recorded with a 3802 UV‐Vis Unico spectrophotometer.
The details of sample preparation for UV‐Vis studies are
given in Table S2.
CV was carried out with a CHI‐630A electrochemical
analyzer (CH Instruments Inc., Austin, TX) in an undivided
three‐electrode cell. All the electrodes were from CH Instru-
ments. A Teflon‐shrouded platinum disc electrode with a
diameter of 2 mm was used as a working electrode for the
solution test. The working electrode was polished to a mirror
finish with 0.05 μm Al2O3 paste on felt, cleaned using
ultrasonication successively in 0.1 M NaOH, 1:1 HNO3,
anhydrous ethyl alcohol and doubly distilled water, then
dried and used for electrochemical measurements of the test
solution. A platinum wire electrode was used as a counter
electrode and a silver wire electrode was used as a reference

4 of 10
ZAIN‐UL‐ABDIN ET AL.
electrode for the solution test. Every CV experiment was
performed two times to get an average result. In every
experiment, the concentration of the electrolyte (Bu4NBF4)
was 0.1 M, the potential scan rates were 0.1 to 0.5 V s−1
and concentration of 1–11 was 0.5 mM. The details of sample
preparation for CV studies are given in Table S3.
The samples for anti‐migration studies consisted of
three adjacent parts: unloaded part (blank), interface and
loaded part. These three constituents represent insulation,
liner and propellant, respectively. The unloaded part
consisted of AP (7.0535 g, 71.93%), hydroxyl‐terminated
polybutadiene (HTPB; 2.0873 g, 21.28%) and isophorone
diisocyanate (IPDI; 0.6657 g, 6.79%) and it was prepared
by mixing AP, HTPB and IPDI for 30 min to obtain a
homogeneous slurry. The ratio of NCO groups in IPDI
was according to ─OH groups of HTPB. The resulting
mixture was cast into a mold and cured at 25 °C for three
days before undergoing accelerated aging. The loaded part
was prepared by mixing AP, HTPB, IPDI and a BRC (1,
3, 6, 7, 8, 9, catocene and ferrocene). Typically, sample
containing 1 was prepared by mixing AP (1.9050 g,
69.744%), HTPB (0.5710 g, 20.91%), IPDI (0.1740 g,
6.37%) and 1 (0.0814 g, 2.98%) for approximately 1 h.
The resulting mixture was subsequently cast on unloaded
layer that had been cured for three days. After curing for
three days at room temperature, the prepared sample was
aged in an oven at 50 °C and atmospheric pressure for
30 days. The details of sample preparation for anti‐migra-
tion studies are given in Table S4.
Burning rate catalytic performance of 1–11 was
investigated with a PerkinElmer Pyris 1 thermogravimetric
instrument at a heating rate of 5 °C min−1 under nitrogen in
the range 50–600 °C. The required amount (5 wt%) of 1–11
and AP was mixed and ground. The details of sample
preparation for catalytic performance of 1–11 via thermal
decomposition of AP are given in Table S5.
O
O
Oxalyl Chloride, Pyridine
Cl
OH
Fe
Fe
DCM
O
NH2
O
O
O
HN
Fe
O
O
N
Fe
O
NH
Fe
Fe
H
Fe
1
2
O
O
O
O
Fe
O
Fe
O
O
Fe
O
Fe
11
3
NH2
HO
HO
OH
H2N
O
O
H
OH
O
N
HO
O
O
O
O
OH
Fe
O
Fe
OH
HO
HO
HN
4
Fe
O
O
HO
OH
O
Fe
HO
HO
OH
OH
10
Cl
Fe
HO
O
HO
Fe
O
O
OH
N
Fe
O
OH
NH2
O
HO
N
H2N
5
O
N
N
Fe
O
O
NH2
NH2
OH
N
H2N
N
O
O
HO
OH
H2N
O
Fe
HN
O
N
N
O
N
N
NH
O
9
Fe
H
O
O
Fe
HN
Fe
6
Fe
O
N
O
O
N
H
O
O
O
N
Fe
Fe
H
8
Fe
7
SCHEME 1 Reaction pathways for synthesis of ferrocene‐based compounds 1–11

ZAIN‐UL‐ABDIN ET AL.
5 of 10
compounds were increased, more intense charge transfer
absorption band was observed.
3 | RESULTS AND DISCUSSION
3.1 | Synthesis of ferrocene‐based compounds
3.2 | Electrochemical behavior of 1–11
Ferrocenecarbonyl chloride was synthesized from
ferrocenecarboxylic acid by following a reported literature
procedure (Scheme 1).[42]
The electrochemical properties of ferrocene‐based com-
pounds are important for investigating electron transfer burn-
ing rate catalytic mechanism. Among various methods for
determining electrochemical properties, CV is considered as
one of the best methods.[45] The electrochemical properties
of 1–11 (0.5 mM) were studied in DCM, CHCl3 and
dimethylsulfoxide (DMSO) containing Bu4NBF4 (0.10 M)
as a supporting electrolyte at 20 °C. CV curves of 1–11 at var-
ious potential scan rates (0.1, 0.2, 0.3, 0.4 and 0.5 V s−1) and in
different organic solvents are shown in Figs S4–S14, respec-
tively. The results showed that CV curves were affected by
polarity of solvent and potential scan rate.[46–50] The change
in polarity of the solvent affected the shapes of CV curves.
Peak shapes of CV curves were deformed with an increase
in the polarity of solvent. For 1–11, the shapes of CV curves
were distorted in DMSO. Oxidation peak potential was
increased with an increase in solvent polarity, which showed
that oxidation of 1–11 was inversely proportional to solvent
polarity, while reduction of 1–11 was proportional to solvent
polarity.[51] In DCM, sharp CV curves with high current were
obtained. A large peak‐to‐peak potential separation (ΔEp) was
obtained in CHCl3 and small ΔEp values were obtained in
DCM. It was found that from DCM to CHCl3, the rate of elec-
trode reaction decreased. The resistance of the solution was
smaller and diffusion rate of the charge was faster in DCM
than CHCl3, which showed that redox reactions occurred more
easily in DCM in comparison with CHCl3. The electrochemi-
cal data of 1–11 in DCM, CHCl3 and DMSO at 0.1 V s−1 scan
rate are summarized in Table S6.
The electrochemical properties of 1–11 were also studied
at various potential scan rates in DCM, CHCl3 and DMSO. It
was found that the shapes of the CV curves of 1–11 were also
affected by the potential scan rate. Additionally, the peak cur-
rent values of 1–11 increased with an increase in the potential
scan rate. According to CV theory,[52] these results show that
at room temperature, the charge transport of the electrode
processes obeyed Fick's law and also the electrode processes
were diffusion controlled over the scan rate range investi-
gated. The electrochemical data of 1–11 at various potential
scan rates and in different organic solvents are summarized
in Tables S7–S17.
Ferrocene‐based compounds 1–11 were synthesized by
the condensation reaction of ferrocenecarbonyl chloride with
corresponding amines and alcohols in freshly distilled THF
or DCM. The reaction pathways for the synthesis of 1–11
are shown in Scheme 1 and experimental details are given in
Table S1.
The structures of 1–11 were characterized using 1H NMR
1
spectroscopy. The H NMR spectra of 1–11 are shown in
Figure S1. On comparing 1H NMR spectra of 1–11 with corre-
sponding amine or alcohol, three new peaks (4.00–5.00 ppm)
attributed to ferrocene protons appeared. The appearance of
methylene (─CH2─) protons adjacent to N─H groups of
amide around 3.3 ppm,[43] methylene (─CH2─) protons adja-
cent to N atom around 3.0 ppm,[43] methylene (─CH2─)
protons adjacent to oxygen of ester around 4.5 ppm[44] and
aromatic ─CH─ protons of benzene ring of the aromatic
ferrocene‐based compound around 7.0 ppm[15] confirmed
the successful synthesis of these ferrocene‐based compounds.
The integration of all the peaks including peaks of ferrocene
was according to the structures, which further supported the
successful synthesis of 1–11. The spectroscopic data for
1–11 are given in the supporting information.
The structures of 1–11 were further confirmed using FT‐
IR spectroscopy. The FT‐IR spectra of 1–11 are shown in
Fig. S2. The amide (N─H) stretching and bending vibrations
of 1, 2, 6 and 8 were observed around 3100 and 1550 cm−1
and stretching vibrations of amide carbonyls of 1, 2, 6 and
8 were observed around 1645 cm−1. The stretching vibrations
of ester carbonyls of 3, 4, 5, 7, 9, 10 and 11 were observed
around 1718 cm−1. The stretching vibrations of esters
(C─O) of 3, 4, 5, 7, 9, 10 and 11 were observed around
1135 cm−1. The (C─H) bending vibrations of 1–11 were
observed around 1460 cm−1 [37]
mational bands of ferrocene of 1–11 were observed around
1015, 832 and 485 cm−1 [39]
.
The vibrational and defor-
.
UV‐Vis absorption spectra of 1–11 (c = 0.025 mM) in
DCM showed absorption bands with λmax around 260 and
240 nm which can be assigned to π–π* transitions, while
absorption bands with λmax around 310 and 450 nm can be
assigned to the charge transfer band and d–d transitions,
respectively.[9] UV‐Vis absorption spectra of 1–11 are shown
in Fig. S3. Intense absorption bands corresponding to π–π*
transitions were observed. In the case of 1, no d–d transition
and charge transfer were observed, while for 2–11 significant
bands of d–d transitions, charge transfer and π–π* transitions
were observed. As ferrocene moieties in the synthesized
3.3 | Anti‐migration studies
Compounds 1, 3, 6, 7, 8 and 9 were used for anti‐migration
studies in comparison with catocene and ferrocene. The
results are shown in Figure 1 and photos are shown in
Fig. S15. It was found that migration of 1, 3, 6, 7, 8 and 9

6 of 10
ZAIN‐UL‐ABDIN ET AL.
FIGURE 1 Anti‐migration studies of compounds 1, 3, 6, 7, 8 and 9,
catocene and ferrocene on days 7, 15 and 30 at 50 °C and atmospheric
pressure
was slower than that of catocene and ferrocene. The slower
migration of 1, 3, 6, 7, 8 and 9 was due to the presence of
polar elements (oxygen and nitrogen). The presence of polar
elements in 1, 3, 6, 7, 8 and 9 resulted in dipole–dipole inter-
actions and hydrogen bonding between these synthesized
compounds and AP‐based propellant. Therefore, the migra-
tion tendency of 1, 3, 6, 7, 8 and 9 was significantly
decreased. It was also found that with an increase in ferrocene
moieties in ferrocene‐based compounds, migration tendency
was increased.[42] Among 1–11, compound 1 showed least
migration. This might be due to the presence of a small num-
ber of ferrocene moieties in 1.
The migration mechanisms of 1 and ferrocene are shown
in Figure 2. On comparing the effect of incorporation of polar
elements (oxygen and nitrogen), it was found that oxygen‐
containing ferrocene‐based compounds showed least migra-
tion in comparison with nitrogen‐containing ferrocene‐based
compounds. The presence of oxygen and nitrogen in ferro-
cene‐based compounds resulted in dipole–dipole
interactions and hydrogen bonding of these compounds with
the propellant, which reduced migration tendency of the
ferrocene‐based compounds in the propellant. So, by incor-
poration of a large number of polar elements (oxygen and
nitrogen) in ferrocene‐based BRCs, migration problems can
significantly be decreased. In our previous study, we found
that a branched ferrocene‐based polymer containing a large
number of N─H groups showed excellent anti‐migration
behavior in AP‐based propellant.[42] In small ferrocene‐based
compounds, few binding sites are available. One N─H group
can form one hydrogen bond, while one oxygen atom can
form two hydrogen bonds with binding agent. So, oxygen‐
containing small ferrocene‐based compounds showed better
anti‐migration behavior in AP‐based propellant.
FIGURE 2 Migration mechanisms of (a) compound 1 and (b)
ferrocene; migration models of (c) compound 1 and (d) ferrocene

ZAIN‐UL‐ABDIN ET AL.
7 of 10
3.4 | Catalytic performance and possible
burning rate catalytic mechanism
Thermal stability is important for BRCs. It was found that all
the synthesized ferrocene‐based compounds (1–11) were
thermally stable up to 230 °C. AP is the main component
of AP‐based propellants. The combustion behavior of AP‐
based propellant can be assessed by the thermal decomposi-
tion of AP. The addition of BRCs as additives results in a
shift (towards the left) in the peak decomposition temperature
of AP as well as accelerating the decomposition of AP.[53]
The catalytic behavior of 1–11 (5 wt%) was investigated for
thermal decomposition of AP using TG and DTG techniques,
as shown in Figure 3. It was found that in the case of pure AP,
decomposition was observed at 406.42 °C, but on the addi-
tion of 5 wt% of 1–11, thermal decomposition temperature
of AP was significantly decreased. As ferrocene moieties in
ferrocene‐based compounds were increased, thermal decom-
position temperature of AP was decreased.
On comparing the effect of incorporation of polar
elements (oxygen and nitrogen), it was found that oxygen‐
containing ferrocene‐based compounds showed better
catalytic behavior on lowering thermal decomposition tem-
perature of AP than nitrogen‐containing ferrocene‐based
compounds. Among 1–11, compound 11 showed excellent
catalytic activity for thermal decomposition of AP and
thermal decomposition temperature of AP was decreased to
317.16 °C, as shown in Figure 3(a) and (b). Thermal decom-
position of pure AP and AP with 5 wt% 1–11 occurred in two
stages. The first stage is low‐temperature decomposition
(LTD), while the second stage is high‐temperature decom-
position (HTD). In the case of pure AP, LTD was observed
at 302.94 °C and HTD was observed at 398.35 °C, while
in the case of 1–11, LTD was observed around 270 °C
and HTD was observed around 340 °C. With an increase
in ferrocene moieties in the ferrocene‐based compounds,
first stage weight loss was increased and thermal decompo-
sition temperature was decreased, as shown in Figure 3(c)
and (d). In the case of 11, maximum first stage weight loss
and lower shift were observed. The addition of 1–11 in AP
affected both LTD and HTD stages of AP. In the case of
oxygen‐containing ferrocene‐based compounds, better
results were observed. These results show that 1–11 have
a good catalytic effect on lowering thermal decomposition
temperature of AP.
In the burning rate catalytic mechanism of AP‐based
propellant, decomposition of AP is considered as the first
step.[54] Various possible mechanisms (proton transfer,
electron transfer, formation of transition metal materials,
acid–base interaction mechanism, etc.) for the thermal
decomposition of AP have been proposed. On combustion
of AP‐based propellant containing ferrocene‐based BRCs,
iron atoms of ferrocene change into iron oxides. When
FIGURE 3 (a) TG curves of pure AP and AP with 5 wt% 1–5, (b)
TG curves of pure AP and AP with 5 wt% 6–11, (c) DTG curves of
pure AP and AP with 5 wt% 1–5 and (d) DTG curves of pure AP and AP
with 5 wt% 6–11

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ZAIN‐UL‐ABDIN ET AL.
FIGURE 4 Possible mechanisms for decomposition of AP catalyzed by (a) mono‐nuclear ferrocene‐based compounds, (b) bi‐nuclear ferrocene‐
based compounds and (c) tetra‐nuclear ferrocene‐based compounds

ZAIN‐UL‐ABDIN ET AL.
9 of 10
ferrocene‐based compounds are heated, the distance between
Cp rings and iron atom increases and then ferrocene unit
begins to decompose, which results in the oxidation of Cp
rings of Fc to produce CO2. Meanwhile, iron atoms of
ferrocene react with oxygen to form nanoscale hematite.
These nanoscale hematite particles show excellent burning
rate catalytic activity in thermal decomposition of AP. These
nanoscale particles accelerate thermal decomposition of AP
by proton/electron transfer (N─H bond cleavage) from
NH4ClO4 to NH3 and HClO4, which further involve a redox
process to produce gaseous products. The possible burning
rate catalytic mechanisms for thermal decomposition of AP
catalyzed by Fc‐based BRCs are shown in Figure 4.
LTD of AP continues through dissociative sublimation
followed by multiphase reactions, which leads to porous
AP.[55] The reactions of the gaseous products compete with
dissociative sublimation during HTD.[56] The preference of
one process over the other depends on the reaction condi-
tions. Confined conditions favor gas‐phase reaction to
proceed in the condensed phase.
of China (2009 DFR 40640), Science and Technology Pro-
gram of Zhejiang Province (2013C24001), Science and
Technology Innovation Team of Ningbo (2011B82002) and
the Fundamental Research Funds for the Central Universities
(2016FZA4018) is gratefully acknowledged.
REFERENCES
[1] H. D. Li, Z. H. Ma, K. Yang, L. L. Xie, Y. F. Yuan, J. Mol. Struct.
2012, 1024, 40.
[2] B. Wei, Y. Gao, C. X. Lin, H. D. Li, L. L. Xie, Y. F. Yuan,
J. Organometal. Chem. 2011, 696, 1574.
[3] M. Drusan, R. Sebesta, Tetrahedron 2014, 70, 759.
[4] D. J. Young, S. W. Chien, T. S. A. Hor, Dalton Trans. 2012, 41,
12655.
[5] D. Schaarschmidt, H. Lang, Organometallics 2013, 32, 5668.
[6] V. H. Purecha, N. S. Nandurkar, B. M. Bhanage, J. M. Nagarkar,
Tetrahedron Lett. 2008, 49, 5252.
[7] Z. Cheng, G. Zhang, X. Fan, F. Bi, F. Zhao, W. Zhang, Z. Gao,
191–199, Inorg. Chim. Acta 2014, 421.
[8] R. Kurane, V. Gaikwad, J. Jadhav, R. Salunkhe, G. Rashinkar,
Tetrahedron Lett. 2012, 53, 6361.
[9] Z. M. Lai, H. M. Ye, Q. Wan, L. L. Xie, S. Bai, Y. F. Yuan, J. Mol.
Struct. 2014, 1059, 33.
4 | CONCLUSIONS
[10] A. W. Orbaek, N. Aggarwal, A. R. Barron, J. Mater. Chem. 2013,
1, 14122.
In the work reported in this paper, eleven ferrocene‐based
compounds (1–11) were successfully synthesized to over-
come migration problems of ferrocene‐based BRCs and to
enhance the burning rate of AP‐based propellant. UV‐Vis
spectra indicated that 1–11 show a photo‐induced charge
transfer effect. CV results indicated that 1–11 show redox
behavior due to the presence of ferrocene and redox behavior
of these ferrocene‐based compounds was diffusion regulated.
Burning rate catalytic investigation indicated that addition of
1–11 in AP resulted in a decrease in its thermal decomposi-
tion temperature. Oxygen‐containing ferrocene‐based com-
pounds showed better anti‐migration behavior in AP‐based
propellant than nitrogen‐containing compounds. TG and
DTG results confirmed the catalytic activity in lowering
thermal decomposition temperature of AP. On the basis of
the results obtained, we concluded that these ferrocene‐based
compounds have potential catalytic effect in thermal decom-
position of AP. The presence of polar elements in 1–11
resulted in the hydrogen bonding of these compounds with
propellant, which resulted in excellent anti‐migration
behavior.
[11] G. Huang, J. Weng, Curr. Org. Chem. 2011, 15, 3653.
[12] S. S. Braga, A. M. S. Silva, Organometallics 2013, 32, 5626.
[13] H. Khalid, H. Yu, L. Wang, W. A. Amer, M. Akram, N. M. Abbasi,
Zain‐ul‐Abdin, M. Saleem, Polym. Chem. 2014, 5, 6879.
[14] P. Li, Z. Liu, Eur. J. Med. Chem. 2011, 46, 1821.
[15] M. Saleem, H. Yu, L. Wang, Zain‐ul‐Abdin, H. Khalid, M. Akram,
N. M. Abbasi, Y. Chen, J. Electroanal. Chem. 2016, 763, 71.
[16] M. Saleem, H. Yu, L. Wang, H. Zain‐ul‐Abdin, M. Khalid,
N. Akram, M. Abbasi, J. Huang, Anal. Chim. Acta 2015, 876, 9.
[17] P. Molina, A. Tarraga, M. Alfonso, Dalton Trans. 2014, 43, 18.
[18] M. Alfonso, A. Espinosa, A. Tarraga, P. Molina, Chem. Commun.
2012, 48, 6848.
[19] S. R. Beeren, J. K. M. Sanders, J. Am. Chem. Soc. 2011, 133, 3804.
[20] J. Gao, L. Wang, H. Yu, A. Xiao, W. Ding, Propell. Explos. Pyrot.
2011, 36, 404.
[21] N. Dilsiz, A. Unver, J. Appl. Polym. Sci. 2006, 101, 2538.
[22] P. J. Swarts, M. Immelman, G. J. Lamprecht, S. E. Greyling,
J. C. Swarts, S. Afr. J. Chem. 1997, 50, 208.
[23] H. Yu, L. Wang, J. Huo, J. Ding, Q. Tan, J. Appl. Polym. Sci. 2008,
110, 1594.
[24] W. Zhou, L. Wang, H. Yu, Zain‐ul‐Abdin, X. Yang, Q. Chen, J.
Wang, RSC Adv. 2016, 6, 53679.
ACKNOWLEDGMENTS
[25] K. F. Grythe, F. K. Hansen, J. Appl. Polym. Sci. 2007, 103, 1529.
[26] L. Gottlieb, S. Bar, Propell. Explos. Pyrot. 2003, 28, 12.
Financial support by the National Natural Science
Foundation of China (21272210, 21372200, 21472168,
21411130187), International Science and Technology
Cooperation Project of Ministry of Science and Technology
[27] F. Xiao, X. Yu, F. Feng, X. Sun, X. Wu, Y. Luo, J. Inorg.
Organometal. Polym. Mater. 2012, 23, 315.

10 of 10
ZAIN‐UL‐ABDIN ET AL.
[28] X. Liu, W. Zhang, G. Zhang, Z. Gao, New J. Chem. 2015, 39, 155.
[29] K. Subramanian, K. S. Sastri, J. Appl. Polym. Sci. 2003, 90, 2813.
[45] N. G. Tsierkezos, J. Solution Chem. 2007, 36, 289.
[46] L. Ma, L. Wang, Q. Tan, H. Yu, J. Huo, Z. Ma, H. Hu, Z. Chen,
Electrochim. Acta 2009, 54, 5413.
[30] X. Liu, D. Zhao, F. Bi, X. Fan, F. Zhao, G. Zhang, W. Zhang,
Z. Gao, J. Organometal. Chem. 2014, 762, 1.
[47] Q. Tan, L. Wang, L. Ma, H. Yu, Q. Liu, A. Xiao, Macromolecules
2009, 42, 4500.
[31] Zain‐ul‐Abdin, L. Wang, H. Yu, M. Wang, M. Saleem, N. M.
Abbasi, H. Khalid, M. Akram, Appl. Organometal. Chem. 2014,
28, 567.
[48] C. Li, L. Wang, L. Deng, H. Yu, J. Huo, L. Ma, J. Wang, J. Phys.
Chem. B 2009, 113, 15141.
[32] J. Gao, L. Wang, Y. Tai, J. Wang, J. Huo, A. M. Amin, H. Yu,
[49] Q. Tan, L. Wang, L. Ma, H. Yu, J. Ding, Q. Liu, A. Xiao, G. Ren,
W. Ding, J. Propul. Power 2011, 27, 1143.
J. Phys. Chem. B 2008, 112, 11171.
[33] F. Xiao, X. Sun, X. Wu, J. Zhao, Y. Luo, J. Organometal. Chem.
2012, 713, 96.
[50] H. Yu, L. Wang, J. Huo, C. Li, Q. Tan, Des. Monom. Polym. 2009,
12, 305.
[34] W. X. Liao, Y. J. Dou, J. Wang, L. L. Xie, F. Lin, Y. F. Yuan,
[51] T. Chen, L. Wang, G. Jiang, J. Wang, X. J. Wang, J. Zhou, J. Wang,
Chem. J. Chinese Univ. 2012, 33, 2244.
C. Chen, W. Wang, H. Gao, J. Electroanal. Chem. 2006, 586, 122.
[35] J. B. Zhuo, H. D. Li, C. X. Lin, L. L. Xie, S. Bai, Y. F. Yuan,
[52] A. Bard, L. Faulkner, Electrochemical Methods: Fundamentals and
Applications, John Wiley, New York 2001.
J. Mol. Struct. 2014, 1067, 112.
[36] T. Fu, L. Liu, Z. Gu, Y. Yang, F. Li, J. Solid Rocket Technol. 2008,
31, 612.
[53] Q. Yang, S. Chen, G. Xie, S. Gao, J. Hazard. Mater. 2011,
197, 199.
[37] F. Xiao, M. Shi, L. Peng, Y. Luo, J. Zhao, J. Inorg. Organometal.
Polym. Mater. 2011, 21, 175.
[54] K. Fujimura, A. Miyake, J. Therm. Anal. Calorim. 2010, 99, 27.
[55] V. V. Boldyrev, Thermochim. Acta 2006, 443, 1.
[38] M. Kohga, K. Okamoto, Combust. Flame 2011, 158, 573.
[56] S. Vyazovkin, C. A. Wight, Chem. Mater. 1999, 11, 3386.
[39] R. Sun, L. Wang, H. Yu, Zain‐ul‐Abdin, Y. Chen, H. Khalid,
N. Abbasi, M. Akram, J. Inorg. Organometal. Polym. Mater.
2014, 24, 1063.
SUPPORTING INFORMATION
Additional Supporting Information may be found online in
the supporting information tab for this article.
[40] J. K. Sharma, P. Srivastava, G. Singh, M. S. Akhtar, S. Ameen,
Ceram. Int. 2015, 41, 1573.
[41] H. Zhao, M. Chen, X. Zhu, S. Chen, Z. Bian, Res. Chem. Intermed.
2015, 41, 3971.
How to cite this article: Zain‐ul‐Abdin, Wang L, Yu
H, et al. Synthesis and catalytic performance of
ferrocene‐based compounds as burning rate catalysts.
Appl Organometal Chem. 2017;e3754. https://doi.org/
10.1002/aoc.3754
[42] Zain‐ul‐Abdin, H. Wang, M. Yu, M. Saleem, N. Akram,
M. Abbasi, H. Khalid, R. Sun, Y. Chen, New J. Chem. 2016,
40, 3155.
[43] Zain‐ul‐Abdin, H. Wang, M. Yu, M. Saleem, H. Akram, N. Khalid,
M. Abbasi, X. Yang, J. Colloid Interface Sci. 2017, 487, 38.
[44] Zain‐ul‐Abdin, H. Wang, M. Yu, N. Saleem, M. Abbasi,
R. U. Khan, R. Summe, M. Haroon, RSC Adv. 2016, 6, 97469.