Synthesis, complexation of 1,2,3-(NH)-triazolylferrocene derivatives and their catalytic effect on thermal decomposition of ammonium perchlorate

Article abstract of DOI:10.1039/c3ra43117g

Ferrocenyl 1,2,3-triazoles 3a-3f and their Cu(ii) or Zn(ii) complexes have been synthesized and characterized. Compound 3d was structurally determined by X-ray crystallography. The DTA and TG measurements confirm the obvious catalytic effect of the representative compounds 3a and 3b on the decreasing of the decomposition temperature of ammonium perchlorate (AP) (by 32.3 and 36.2 °C respectively), whereas the Cu or Zn complexes of 3a lowers the thermal decomposition temperature of AP more dramatically, by 60.6 and 61.9 °C respectively. So ferrocenyl 1,2,3-triazoles 3a-3f and their Cu(ii) or Zn(ii) complexes are a kind of potentially high-burning-rate catalyst. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3ra43117g

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Synthesis, complexation of 1,2,3-(NH)-triazolylferrocene
derivatives and their catalytic effect on thermal
decomposition of ammonium perchlorate†
Cite this: DOI: 10.1039/c3ra43117g
Received 21st June 2013
*
Haiying Zhao, Le Guo, Shufeng Chen and Zhanxi Bian
Accepted 3rd September 2013
DOI: 10.1039/c3ra43117g
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Ferrocenyl 1,2,3-triazoles 3a–3f and their Cu(II) or Zn(II) complexes have the hyper-branched structures13 are effective ways to augment
been synthesized and characterized. Compound 3d was structurally burning rates and to reduce the migration tendency. However,
determined by X-ray crystallography. The DTA and TG measurements study on the migration problem is still being continued to nd a
confirm the obvious catalytic effect of the representative compounds 3a lower cost and a more efficient way to avoid this problem.
and 3b on the decreasing of the decomposition temperature of
The transition metal complexes based on the heterocyclic
ammonium perchlorate (AP) (by 32.3 and 36.2 ꢀC respectively), whereas ligand have been reported as potentially burning-rate catalysts.14
the Cu or Zn complexes of 3a lowers the thermal decomposition The van der Waals force between the propellant and ferrocene
temperature of AP more dramatically, by 60.6 and 61.9 ꢀC respectively. burning-rate catalysts may be enhanced as a result of the intro-
So ferrocenyl 1,2,3-triazoles 3a–3f and their Cu(II) or Zn(II) complexes are duction of heteroatoms to ferrocene compounds, which is
a kind of potentially high-burning-rate catalyst.
anticipated to hinder the migration in composite propellants.15,16
As an important heterocyclic compound 1,2,3-triazole makes up
the core structure of numerous compounds, and ferrocene–tri-
azole conjugates have been applied in various elds such as
conjugate chemistry, asymmetric catalysis, medicinal chemistry,
host–guest interactions, and materials chemistry,17–19 but so far
ferrocene derivatives of 1,2,3-triazole as potentially high-burning-
rate catalysts have been rarely reported. In these compounds, the
big polarity and bulky substituent is expected to preclude effec-
tively the migration of ferrocene.20 AP is the common oxidizer in
composite propellants, and the thermal decomposition charac-
teristics of AP directly inuence the burning velocity and energy
features of propellants.21,22 In the present paper, we report the
synthesis of 1,2,3-(NH)-triazolylferrocene derivatives and their
Cu(II) or Zn(II) complexes (Scheme 1), and their catalytic effect on
the thermal decomposition of AP was researched in order to
conrm the potentially burning rate catalytic activity.
Introduction
Ferrocene derivatives have attracted wide attention not only from
the viewpoint of their high thermal stability, reversible redox
behavior, and their chemical modication possibilities but also
from their increasing applications in many elds of chemistry
such as biologically active compounds,1 asymmetric catalysis2
and material science.3 Ferrocene derivatives are also known as
high-burning-rate catalysts for composite propellants containing
oxidizer AP and aluminum powder,4–6 but they have some draw-
backs, such as their migration to insulation composition during
storage, evaporation, or sublimation loss during processing, and
phase separation by crystallization.7,8 To preclude these problems
and also to enhance the efficiency of ferrocene-based burn-rate
catalysts, much endeavor was made to prepare ferrocene deriva-
tives with relatively high molecular weight, such as 2,2-bis
(ethylferrocenyl)propane, (trade name: catocene) and n-butyl
ferrocene.9 Some later studies indicated that linking ferrocenes to
the propellant binder via graing or introducing ferrocenes into
the binder backbone during curing10–12 or graing ferrocene on
Results and discussion
Synthesis and characterization
The carbonylative coupling reaction of acyl chloride with fer-
rocenylethyne using PdCl2(PPh3)2 (2%)/CuI (5%) as catalyst and
Et3N as base provided aryl ferrocenylethynyl ketones23 in
toluene. The ynones then underwent the Cu(I)-catalyzed 1,3-
dipolar cycloaddition with NaN3 in DMSO at room temperature
to form ferrocenyl 1,2,3-(NH)-triazoles 3 in excellent yields
(Scheme 1).24 The structures of 3a–3f were fully characterized by
College of Chemistry and Chemical Engineering, Inner Mongolia University, Huhhot
010021, China. E-mail: bzx1957@sina.com
† Electronic supplementary information (ESI) available: Crystal data and structure
renement for 3d, selected bond distances (A) and angles (ꢀ) of 3d, full
˚
instrumentation details, experimental procedures, characterization. CCDC
922174. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3ra43117g
a combination of analytical techniques such as IR, 1H NMR, 13
C
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Scheme 1 Synthesis of compounds 3 and the complexes.
NMR, MS spectral data and elemental analyses. The medium coordination with metal indicated the deprotonation of the
intensity absorption in the 3087–3012 cmÀ1 region revealed the ferrocenyl 1,2,3-triazole ligand. In addition, the characteristic
existence of ferrocenyl groups. The strong bands at 1620–1715 peaks of Cu–N and Zn–N were enhanced at around 505 and 487
cmÀ1 in the IR spectra of all the compounds may be assigned to cmÀ1 respectively upon complexation. The possible formula of
the carbonyl group stretching vibrations. The formation of tri- complexes was (L)M(OAc)$nH2O presumed by elemental anal-
azole ring was supported by the medium intensity absorption at yses data. Preliminary results for the complexation show that
916–945 and 1025–1069 cmÀ1 25 In 1H NMR spectra, it is worth complex formation does take place at the carbonyl oxygen, 1N of
.
pointing out that the signals of NH proton of the triazole ring the triazole groups and two oxygen atoms from one acetate
shied downeld at the d 14.45–16.06 ppm region. In 13C NMR group. The possible structures of complexes were given in
spectra, the ferrocenyl group and the carbonyl group C atoms Scheme 1. Similar coordination complexes, where 1N of a tri-
resonated in the region of 68.97–70.38 and 173.06–187.47 ppm, azole moiety and carbonyl group of the chelating ligand form-
respectively.
ing a 7-member ring is involved, have been reported recently.27
The 1,2,3-(NH)-triazole 3d was also characterized by X-ray However, no crystals suitable for X-ray could be obtained from
methods. The molecular structure of 3d is shown in Fig. 1. The any of the complexes by us so far. Thus, structures of the
X-ray structure reveals that 3d exists in the crystal as the 2H complexes are preliminary.
isomer form, however 1,2-diH tautomers equilibrium exists in
neutral solution within these kinds of compounds.26 The 1,2,3-
Catalytic effect on the decomposition of ammonium
triazole ring locates almost in the same plane of furan ring,
whereas is slightly twisted from substituted Cp ring plane with a
dihedral angle of 10.112(6)ꢀ. The distances of N(1)–N(2)
(1.330(2)) and N(2)–N(3) (1.310(2)) in the 1,2,3-triazole ring are
not equal, just like the distances of O(2)–C(14) (1.375(2)) and
O(2)–C(17) (1.359(2))in the furan ring. The distance of C(13)–
perchlorate
In order to probe the catalytic performance of ferrocenyl 1,2,3-
triazoles and their complexes to the thermal decomposition of
AP, the thermal decomposition characteristics of pure AP and
mixtures of AP and a 5% of 3a, 3b, the Cu or Zn complexes of 3a
were studied using DTA (Fig. 2) and TG (Fig. 3). From Fig. 2, it
can be seen that the DTA curve for thermal decomposition of
pure AP shows two endothermic peaks and one exothermic
peak. The rst endothermic peak at 244.8 ꢀC, without weight
loss according to the TG curve in Fig. 3, corresponds to the
morphological transition from an orthorhombic to a cubic
phase of AP.28,29 The second peak at 305.5 ꢀC is exothermic,
which is corresponding to the low-temperature decomposition
˚
O(1) double bond is 1.229(2) A.
Ferrocenyl 1,2,3-triazoles 3a–3d, which is able to form a 5-
member chelate ring, were then converted to the Cu(II) or Zn(II)
complexes by reaction with copper(II)/zinc(II) acetate in anhy-
drous ethanol (Scheme 1). In the IR spectroscopy, the disap-
pearance of n(N–H) at around 3150–3250 cmÀ1 in 3a–3d aer
(LTD).22 The third peak at 413.8 C following the LTD instantly
ꢀ
is an endothermic peak which is assigned to the high-temper-
ature decomposition (HTD). The HTD is either exothermic or
endothermic process, depending on the competition between
sublimation and thermal decomposition. The endothermic
process suggests that the HTD of pure AP occurs predominantly
via the sublimation channel.30
As shown in Fig. 2, aer adding 5% of 3a, 3b, or the Cu or Zn
complexes of 3a, the peaks near 244 ꢀC and 305 ꢀC appearing in
Fig. 1 X-ray structure of 3d.
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45.2 ꢀC respectively. Therefore, both ligands and complexes can
advance the decomposition temperature of AP and make the
exothermic more concentration, but the Cu or Zn complexes are
more effective catalysts than the ligands.
The additives lowering the thermal decomposition temper-
ature of AP is further proved by the TG experiments. In Fig. 3 the
TG curves exhibit that all samples start to decompose at about
ꢀ
286 C, while the nal decompose temperatures advance obvi-
ously compared with pure AP, and are about 386.2, 388.5, 370.5
ꢀ
and 369.6 C for the addition of 3a, 3b, Cu or Zn complexes of
3a, respectively. In addition, the TG curve of pure AP exhibits
two obvious weight-loss steps, while the TG curves of AP in the
presence of Cu or Zn complexes of 3a tend to merge into one
weight-loss step, in agreement with the decomposition trend of
the DTA curves.
Fig. 2 DTA curves of AP, AP + 5% 3a, AP + 5% 3b, AP + 5% (3a)Cu(OAc) and AP +
5% (3a)Zn(OAc).
Conclusions
In summary, 1,2,3-(NH)-triazolylferrocene derivatives 3a–3f and
their Cu(II) or Zn(II) complexes have been synthesized and
characterized. The DTA and TG measurements conrm the
obvious catalytic effect of the representative compounds 3a and
3b on the decreasing of the decomposition temperature of AP
(by 32.3 and 36.2 ꢀC respectively), whereas the Cu or Zn
complexes lowers the thermal decompꢀosition temperature of AP
more dramatically, by 60.6 and 61.9 C respectively. Although
the effect of burning rate catalysts can not only be focused on
the inuence on the thermal decomposition of AP, the results
conrm ferrocenyl 1,2,3-triazoles 3a–3f and their Cu(II) or Zn(II)
complexes are a kind of potentially high-burning-rate catalyst.
Acknowledgements
Fig. 3 TG curves of AP, AP + 5% 3a, AP + 5% 3b, AP + 5% (3a)Cu(OAc) and AP +
5% (3a)Zn(OAc).
We thank the National Natural Science Foundation of China
(NSFC, no. 21102068, 21262023) and Natural Science Founda-
tion of Inner Mongolia of China (no. 20080404ZD04,
2013MS0207) for their generous nancial support.
all samples exhibit no signicant changes compared with pure
AP, indicating that additives have little effect on the crystallo-
graphic transition and LTD of AP. However, dramatic changes
have been observed at the stage of HTD. The last endothermic
peak at 413.8 for pure AP disappears, whereas new exothermic
peaks appear in the region of 353–380 ꢀC. This implies that the
additives have a greater catalytic effect on the HTD of AP. The
exothermic process suggests that the HTD of the AP with the
additives occurs predominantly via the thermal decomposition
channel. Aer adding 3a and 3b, the highest thermal decom-
position temperature is 381.5 and 377.6 ꢀC respectively,
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