Novel ferrocene-based 1,2,3-triazolyl compounds: Synthesis, anti-migration properties and catalytic effects on oxidizers during combustion

Article abstract of DOI:10.1016/j.ica.2019.119374

To tackle high-migratory and high-volatility problem of marketed neutral ferrocene-based burning rate catalysts, twenty-one ferrocene-based 1,2,3-triazolyl compounds (Fc-TAZs) were synthesized by click reaction and characterized completely by NMR, FT-IR,

Full text of DOI:10.1016/j.ica.2019.119374

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Research paper
Novel ferrocene-based 1,2,3-triazolyl compounds: Synthesis, anti-migration
properties and catalytic effects on oxidizers during combustion
Wenqian Cheng, Xiaoling Shi, Yu Zhang, Yajun Jian, Guofang Zhang
PII:
S0020-1693(19)31769-4
https://doi.org/10.1016/j.ica.2019.119374
ICA 119374
DOI:
Reference:
Inorganica Chimica Acta
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14 November 2019
15 December 2019
15 December 2019
Please cite this article as: W. Cheng, X. Shi, Y. Zhang, Y. Jian, G. Zhang, Novel ferrocene-based 1,2,3-triazolyl
compounds: Synthesis, anti-migration properties and catalytic effects on oxidizers during combustion, Inorganica
Chimica Acta (2019), doi: https://doi.org/10.1016/j.ica.2019.119374
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Novel ferrocene-based 1,2,3-triazolyl compounds: Synthesis,
anti-migration properties and catalytic effects on oxidizers
during combustion
Wenqian Cheng, Xiaoling Shi, Yu Zhang, Yajun Jian and Guofang Zhang*
Key Laboratory of Applied Surface and Colloid Chemistry, School of Chemistry and
Chemical Engineering, Shaanxi Normal University, Xi’an, 710119, China
Abstract: To tackle high-migratory and high-volatility problem of marketed neutral
ferrocene-based burning rate catalysts, twenty-one ferrocene-based 1,2,3-triazolyl compounds
(Fc-TAZs) were synthesized by click reaction and characterized completely by NMR, FT-IR,
UV−Vis and elemental analysis. In addition, four compounds were structurally confirmed by
single crystal X-ray diffraction. TG and DSC analysis showed that the new Fc-TAZs are of high
thermal stability. Cyclic voltammetry investigations suggested that more than half of the Fc-TAZs
are reversible redox systems. Anti-migration and anti-volatility tests revealed that all the Fc-TAZs
display, on comparison with Catocene, extremely low volatility and migration tendency due to the
appearance of polar oxygen and nitrogen atoms in their molecules. Catalytic activity tests of the
novel Fc-TAZs towards the thermal decomposition of oxidizers, evaluated by TG and DSC
techniques, indicated that all Fc-TAZs exert great effects on the thermal disintegration of AP and
compounds 5, 7 and 11 can promote the thermal decomposition of HMX during combustion.
Keywords: ferrocene-based 1,2,3-triazolyl compounds; click reaction; thermal stability;
anti-migration property; combustion catalysis
1. Introduction
Composite solid propellants are heterogeneous propellants consisting mainly of oxidizers and
polymeric binders (metal powder is also usually added). In an aluminized ammonium perchlorate
(AP)-based solid propellant a ferrocene derivative is commonly added to enhance burning rate and

Corresponding authors. G. F. Zhang: Tel:+86-29-81530830; Fax: +86-29-81530727; E-mail
address: gfzhang@snnu.edu.cn
1

decrease pressure exponent of the propellant [1-4]
.
Although the commercialized ferrocene-based burning rate catalysts (BRCs), such as
tert-butylferrocene (TBF), n-butylferrocene (NBF) and 2,2-Bis(ethylferrocenyl)propane
(Catocene), have shown highly catalytic efficiency in the composite solid propellants, they bear
some unavoidable problems due to their lower molecular weights and neutral nature. They could
sublime during fabrication of the propellants and move gradually to the surface and interface of
the propellant columns after long-time storage [3,4]. This type of high-migratory deficiency can
lead to non-uniform distribution of BRCs in the propellants. During combustion process of the
propellants this defect will enlarge burning area and increase pressure in the chamber of the rocket
engine due to rapid decomposition of the migrated BRCs, and finally increase explosion danger of
the propellants. Therefore, in order to extend service life of the propellants and decrease military
expenses, it is necessary to develop low and even non-migratory ferrocene derivatives as BRCs.
In recent decades great efforts have been devoted to design and synthesize ferrocene
derivatives as BRC candidates with low migration tendency and high catalytic activity. A few
effective methods have been adopted to deal with the issues of the neutral BRCs, for examples,
increasing molecular weight or molecular polarity of the small neutral ferrocene derivatives,
grafting ferrocenyl groups on the polymer or dendrimer chains, introducing concepts of ionic
liquid and coordination compound into ferrocene derivatives [5-26]. D. Saranvannakumar, T. Jana,
et al developed low- and even non-migratory ferrocenyl-functionalized polymers or dendrimers
[5-9]. H. Y. Zhao, Y. F. Yuan and our group prepared a large number of metal complexes derived
from ferrocenyl ligands [15-20]. C. Morales-Verdejo and coworkers evaluated anti-migratory
ability and combustion catalytic performance of some homo- and hetero-nuclear conjugated
metallocenes with Fe (II), Co (II), Ni(II) or Mn (II) as central metals and found that all
metallocenes show low migration trends and high combustion catalytic performance in the thermal
decomposition of AP [11,12]. L. Wang group used ferrocenecarbonyl chloride as a precursor and
synthesized a series of ferrocenyl esters, amides and hydroquinones by condensation reactions
[21,22]. Our group designed and synthesized hundreds of energetic ionic ferrocenyl compounds to
enhance anti-migration ability and catalytic activity of the neutral BRCs [23-26]. Although
hundreds of novel ferrocene derivatives have been reported to tackle the high-migration issues and
2

enhance catalytic activity of the neutral ferrocene-based BRCs, the existing problems have not
been well solved yet.
Copper-catalyzed azide alkyne cycloaddition (CuAAC), also known as "click reaction", has
been developed for many years [27-29]. Ferrocene-based 1,2,3-triazolyl compounds have been
reported mainly as ionic recognition sensors, antifungal and anticancer medicines, etc. [30-33].
Their application in composite solid propellants as BRCs is limited, however [34]. Herein, based
on straightforward construction and nitrogen-rich feature of 1,2,3-triazolyl groups, we have
designed and synthesized a series of ferrocenyl 1,2,3-triazolyl compounds (Fc-TAZs) (Scheme 1)
by CuAAC method to enhance anti-migratory property and to ameliorate catalytic activity of the
marketed ferrocene-based BRCs in composite solid propellants. The molecular structures of the
novel Fc-TAZs were characterized completely by 1H NMR, 13C NMR, FT-IR, UV-Vis
spectroscopes, elemental analysis and some of them additionally by single-crystal X-ray
diffraction. Their thermal stability were investigated by TG and DSC. Electrochemical properties
were measured by cyclic voltammetry (CV). Anti-migration and anti-volatility performances were
determined with Catocene and ferrocene (Fc) as references. Their catalytic activities towards the
thermal degradation of AP, RDX and HMX were measured by DSC and TG techniques.
(Please insert Scheme 1 here)
2. Experimental
2.1. Materials and equipment
Hydroxymethylferrocene was purchased from Xuzhou Guanrong Pharmaceutical &
Chemical Co., Ltd, China. AP, RDX and HMX were gained from Xi’an Modern Chemistry
Research Institute. Azidomethylferrocene was prepared according to the synthetic procedure as
1
described [35]. H and 13C NMR spectra were performed on a Bruker Avance 400 MHz
spectrometer. UV-Vis absorption spectra were recorded on a UV-2450 spectrophotometer.
Elemental analyses were conducted with a Vario EL III Elemental Analyzer. DSC and TG studies
were achieved on HS-1 and Q50 models, respectively, under nitrogen atmosphere (50 mL min-1)
at 5°C·min-1 with sample mass around 3.0 mg. Cyclic voltammetry (CV) studies were executed on
a CHI660C analyzer with a platinum electrode for working and an Ag/Ag+ electrode as the
3

reference. In the CV determination experiments the compounds were solved in 0.1 mol L-1
n-Bu4PF6-DMSO supporting electrolyte.
2.2. Synthesis
Since the synthetic procedures of the new Fc-TAZs 121 are identical,
1-ferrocenylmethyl-1H-1,2,3-triazol-4-yl-methyl phenyl ether (1) was taken as an example [36,37]:
To a 20 mL DMF solution of phenol 1.14 g (15.0 mmol), 5.18 g (37.5 mmol) K2CO3 was added
and stirred at 60 ºC for 1 h and then 1.42 ml (18.1 mmol) propargyl bromide was added dropwise
and the reaction mixture was kept stirring and heating at 60 ºC for 8 h until completion of the
reaction, the reaction mixture was then cooled to room temperature and filtered. The filtrate was
evaporated to dryness. The crude 2-propargyl phenyl ether was purified by column
chromatography using petroleum ether/ethyl acetate (v:v) 5:1 as eluent to collect the purified
intermediate 2-propargyl phenyl ether. To a 100 mL round-bottom flask containing 0.41 g (3.12
mmol) 2-propargyl phenyl ether and 0.75 g (3.12 mmol) azidomethylferrocene in 30 ml methanol
was added a solution of 0.23 g (0.94 mmol) CuSO4 5H2O in 15 ml water. A freshly prepared
solution of 0.19 g (0.94 mmol) sodium ascorbate in 15 ml water was added and the reaction
solution was stirred at room temperature for 24 h. After the solvents were removed under vacuum,
the residue was eluted from a chromatographic column using dichloromethane/methanol (v:v)
50:1. The solvents were evaporated to dryness and the residue was dried to collect the desired
product 1.
1-Ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl phenyl ether (1). Yellow powder. Yield:
1.024 g (88%). M. p.: 110 °C (DSC). FT-IR (KBr): ν = 3434 m, 3087 m, 2894 w, 2859 w, 1598 s,
1
1494 s, 1452 w, 1314 w, 1251 vs, 1168 m, 1050 s, 1002 w, 822 s, 760 s, 691 m, 490 m cm-1. H
NMR (400 MHz, DMSO-d6): δ 8.20 (s, 1H), 7.28 (t, J = 7.6 Hz, 2H), 7.01 (d, J = 8.4 Hz, 2H),
6.94 (t, J = 7.6 Hz, 1H), 5.32 (s, 2H), 5.10 (s, 2H), 4.34 (s, 2H), 4.19 (s, 7H). 13C NMR (101 MHz,
DMSO-d6): δ 159.65 (OC), 145.53 (NCCH), 130.95 (NCCH), 123.45, 122.64, 116.19 (C6H5),
82.13, 70.53, 70.36 (C5H4), 70.35 (C5H5), 63.45 (C5H4CH2), 51.57 (OCH2). Calcd.
C20H19FeN3O(373.09):C, 64.36; H, 5.13; N, 11.26 %; Anal. Found: C, 64.30; H, 5.19; N, 11.23%.
Bis(ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl) hydroquinone ether (2). Yellow
powder. Yield: 1.751 g (84%). M. p.: 207.3 °C (DSC). FT-IR (KBr): ν = 3441 m, 3149 w, 3073 w,
4

2921 w, 2866 w, 1626 m, 1501 vs, 1460 m, 1335 m,1231 vs, 1106 m, 1037 s, 815 s, 732 w, 503 m
cm-1. 1H NMR (400 MHz, DMSO-d6): δ 8.16 (s, 2H), 6.93 (s, 4H), 5.31 (s, 4H), 5.03 (s, 4H), 4.34
(s, 4H), 4.18 (s, 14H). 13C NMR (101 MHz, DMSO-d6) δ 153.67 (OC), 145.08 (NCCH), 122.89
(NCCH), 116.73 (C6H4), 81.59, 70.01, 69.84 (C5H4), 69.82 (C5H5), 63.62 (C5H4CH2), 51.03
(OCH2). Calcd. C34H32Fe2N6O2 (668.13):C, 61.10; H, 4.83; N, 12.57 %; Anal. Found: C, 61.02; H,
4.88; N, 12.52%.
Bis(ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl) resorcinol ether (3). Yellow powder.
Yield: 1.688 g (81%). M. p.: 150.1 °C (DSC). FT-IR (KBr): ν = 3441 m, 3087 w, 2935 w, 2866 w,
1591 vs, 1487 m, 1460 m, 1383 m, 1341 m, 1279 s, 1182 vs, 1147 vs, 1106 m, 1009 s, 815 s, 725
1
m, 490 s cm-1. H NMR (400 MHz, DMSO-d6): δ 8.19 (s, 2H), 7.16 (t, J = 8.0 Hz,1H), 6.68 (s,
1H), 6.60 (d, J = 6.0 Hz, 2H), 5.32 (s, 4H), 5.07 (s, 4H), 4.34 (s, 4H), 4.19 (s, 14H). 13C NMR
(101 MHz, CDCl3): δ 160.86 (OC), 145.31 (NCCH), 131.46 (NCCH), 123.52, 109.00, 103.55
(C6H4), 82.13, 70.54, 70.38 (C5H4), 70.35 (C5H5), 63.53 (C5H4CH2), 51.56 (OCH2). Calcd.
C34H32Fe2N6O2 (668.13):C, 61.10; H, 4.83; N, 12.57 %; Anal. Found: C, 61.01; H, 4.90; N,
12.51%.
Bis(ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl) catechol ether (4). Yellow powder.
Yield: 1.918 g (92%). M. p.: 153.2 °C (DSC). FT-IR (KBr): ν = 3441 m, 3087 w, 2935 w, 2866 w,
1591 vs, 1487 m, 1460 m, 1383 m, 1341 m, 1279 s, 1182 vs, 1147 vs, 1106 m, 1009 s, 815 s, 725
1
m, 490 s cm-1. H NMR (400 MHz, CDCl3): δ 7.55 (s, 2H), 7.02 (m, 2H), 6.90 (m, 2H), 5.25 (s,
4H), 5.19 (s, 4H), 4.25 (t, J = 1.6 Hz, 4H), 4.19 (t, J = 1.6 Hz, 4H), 4.16 (s, 10H). 13C NMR (101
MHz, CDCl3): δ 148.44 (OC), 144.11 (NCCH), 122.51 (NCCH), 122.13, 115.47 (C6H4), 80.98,
69.02 (C5H4), 68.90 (C5H5), 63.55 (C5H4CH2), 50.04 (OCH2). Calcd. C34H32Fe2N6O2 (668.13):
C, 61.10; H, 4.83; N, 12.57 %. Anal. Found: C, 61.00; H, 4.89; N, 12.52 %.
O,O',O"-Tris(ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl) phloroglucinol ether (5).
Yellow powder. Yield: 2.404 g (80%). M. p.: 298.2 °C (dec, DSC). FT-IR (KBr): ν = 3441 m,
3094 w, 2928 w, 1591 vs, 1452 m, 1328 w, 1217 w, 1147 vs, 1113 m, 1044 vs, 1002 m, 822 s, 718
w, 490 s cm-1. 1H NMR (400 MHz, CDCl3): δ 7.50 (s, 3H), 6.21 (s, 3H), 5.29 (s, 6H), 5.06 (s, 6H),
4.27 (s, 6H), 4.21 (s, 6H), 4.17 (s, 15H). 13C NMR (101 MHz, CDCl3): δ 160.95 (OC), 144.56
(NCCH), 123.08 (NCCH), 95.96 (C6H3), 81.61, 70.02, 69.86 (C5H4), 69.82 (C5H5), 63.00
5

(C5H4CH2), 51.03 (OCH2). Calcd. C48H45Fe3N9O3 (963.17): C, 59.84; H, 4.71; N, 13.08 %. Anal.
Found: C, 59.68; H, 4.79; N, 13.02 %.
O,O',O"-Tris(ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl) pyrogallol ether (6).
Yellow powder. Yield: 2.284 g (76%). M. p.: 198.2 °C (DSC). FT-IR (KBr): ν = 3441 w, 3094 w,
2921 w, 2353 w, 1591 s, 1473 s, 1300 m, 1244 s, 1091 vs, 1037 vs, 1002 s, 815 s, 732 w, 490 s
1
cm-1. H NMR (400 MHz, CDCl3): δ 7.65-7.55 (d, 3H), 6.89 (t, 1H), 6.63 (d, 2H), 5.24 (s, 4H),
5.19 (s, 2H), 5.10 (s, 6H), 4.27 (s, 4H), 4.20 (s, 2H), 4.18-4.10 (d, 21H). 13C NMR (101 MHz,
CDCl3): δ 153.28 (OC), 145.49, 144.86 (NCCH), 138.46 (OC), 124.99, 124.02 (NCCH), 123.49,
108.94 (C6H3), 82.22, 81.96, 69.92, 69.85 (C5H4), 69.79 (C5H5), 67.57, 64.15 (C5H4CH2), 50.98,
50.78 (OCH2). Calcd. C48H45Fe3N9O3 (963.17): C, 59.84; H, 4.71; N, 13.08 %. Anal. Found: C,
59.72; H, 4.82; N, 13.12 %.
Ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl p-tert-butylphenol ether (7). Yellow
powder. Yield: 1.218 g (91%). M. p.: 120.3 °C (DSC). FT-IR (KBr): ν = 3434 w, 3087 w, 2963 m,
2866 w, 1605 m, 1508 s, 1460 m, 1397 w, 1300 w, 1244 vs, 1182 s, 1106 m, 1044 s, 822 s, 753 w,
490 s cm-1. 1H NMR (400 MHz, CDCl3): δ 7.51 (s, 1H), 7.30 (d, J = 8.4 Hz, 2H), 6.90 (d, J = 8.4
Hz, 2H), 5.29 (s, 2H), 5.15 (s, 2H), 4.42–3.98 (m, 9H), 1.28 (s, 9H). 13C NMR (101 MHz,
CDCl3): δ 156.89 (OC), 145.22 (NCCH), 144.80 (NCCH), 127.20, 122.91, 115.14 (C6H4), 81.67,
69.90 (C5H4), 69.82 (C5H5), 63.12 (C5H4CH2), 51.11 (OCH2), 34.99 (CCH3), 32.41 (CH3). Calcd.
C24H27FeN3O3 (429.15): C, 67.14; H, 6.34; N, 9.79 %. Anal. Found: C, 67.10; H, 6.38; N, 9.78 %.
Ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl 2-nitrophenol ether (8) Yellow powder.
Yield: 1.030 g (79%). M. p.: 107.5 °C (DSC). FT-IR (KBr): ν = 3427 w, 3087 w, 2921 m, 2866 w,
1612 m, 1522 vs, 1452 m, 1356 s, 1287 vs, 1251 m, 1050 s, 995 m, 822 s, 746 s, 691 w, 497 s
cm-1. 1H NMR (400 MHz, CDCl3): δ 7.83 (d, J = 15.2 Hz, 1H), 7.64 (s, 1H), 7.53 (t, J = 7.6 Hz,
1H), 7.31 (d, J = 8.4 Hz, 1H), 7.05 (t, J = 7.6 Hz, 1H), 5.34 (s, 2H), 5.30 (s, 2H), 4.28 (s, 2H), 4.22
(s, 2H), 4.17 (s, 5H). 13C NMR (101 MHz, CDCl3): δ 151.56 (OC), 143.07 (NCCH), 140.10
(NO2C), 134.31 (NCCH), 125.69, 122.59, 121.03, 115.44 (C6H4), 80.74, 69.13 (C5H4), 68.90
(C5H5), 63.79 (C5H4CH2), 50.23 (OCH2). Calcd. C20H18FeN4O3 (418.07): C, 57.44; H, 4.34; N,
13.40 %. Anal. Found: C, 57.38; H, 4.30; N, 13.42 %.
6

Ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl 4-nitrophenol ether (9) Yellow powder.
Yield: 1.017 g (78%). M. p.: 153.8 °C (DSC). FT-IR (KBr): ν = 3434 w, 3101 w, 2942 m, 2838 w,
1598 s 1508 vs, 1425 m, 1390 m, 1335 vs, 1265 s, 1113 s, 1009 m, 849 s, 801 s, 746 m, 691 w,
497 m cm-1. 1H NMR (400 MHz, CDCl3): δ 8.19 (d, J = 8.8 Hz, 2H), 7.53 (s, 1H), 7.06 (d, J = 8.8
Hz, 2H), 5.32 (s, 2H), 5.25 (s, 2H), 4.28 (s, 2H), 4.23 (s, 2H), 4.19 (s, 5H). 13C NMR (101 MHz,
CDCl3): δ 163.14 (OC), 142.54 (NCCH), 141.82 (NO2C), 125.92 (NCCH), 122.41, 114.86 (C6H4),
80.36, 69.23, 69.00 (C5H4), 68.97 (C5H5), 62.46 (C5H4CH2), 50.29 (OCH2). Calcd. C20H18FeN4O3
(418.07): C, 57.44; H, 4.34; N, 13.40 %. Anal. Found: C, 57.38; H, 4.31; N, 13.43 %.
Bis(ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl) 4,6-dinitrocatechol ether (10). Light
brown powder. Yield: 2.105 g (89%). M. p.: 192.8 °C (dec, DSC). FT-IR (KBr): ν = 3419 w, 3094
w, 2935 w, 1605 vs, 1522 s, 1404 m, 1341 m, 1293 s, 1224 m, 1030 m, 815 s, 746 w, 490 s cm-1.
1H NMR (400 MHz, CDCl3): δ 8.68 (s, 1H), 7.70 (s, 2 H), 7.64 (s, 1H), 5.46 (s, 4H), 5.31 (s, 4H),
4.29 (s, 4H), 4.23 (s, 4H), 4.19 (s, 10H). 13C NMR (101 MHz, CDCl3): δ 156.80 (OC), 141.56
(NCCH), 131.47, 125.57 (NO2C), 123.30 (NCCH), 101.98 (C6H2), 80.37, 69.25, 68.97 (C5H4),
68.94 (C5H5), 64.13 (C5H4CH2), 50.36 (OCH2). Calcd. C34H30Fe2N8O6 (758.10): C, 53.85; H,
3.99; N, 14.78 %. Anal. Found: C, 53.80; H, 3.95; N, 14.81 %.
1-Ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl benzoate (11) Yellow powder. Yield:
1.026 g (82%). M. p.: 153.7 °C (DSC). FT-IR (KBr): ν = 3108 m, 2955 w, 1709 vs, 1605 m, 1438
m, 1328 m, 1265 vs, 1099 s, 1037 m, 815 m, 704 m, 497 s cm-1.1H NMR (400 MHz, CDCl3): δ
8.02 (d, J = 7.5 Hz, 2H), 7.59 (s, 1H), 7.54 (d, J = 14.8 Hz, 1H), 7.41 (d, J = 15.4 Hz, 2H), 5.43 (s,
2H), 5.29 (s, 2H), 4.28 (d, J = 3.4 Hz, 2H), 4.22 (d, J = 3.4 Hz, 2H), 4.17 (s, 5H).13C NMR (101
MHz, CDCl3): δ 166.46 (OOC), 142.78 (NCCH), 133.17 (NCCH), 129.75, 128.37, 123.29 (C6H5),
80.65 (C5H5), 69.13, 68.98, 68.91 (C5H4), 58.11 (C5H4CH2), 50.14 (OCH2). Calcd. C21H19FeN3O2
(401.08): C, 62.86; H, 4.77; N, 10.47 %. Anal. Found: C, 62.74; H, 4.80; N, 10.42 %.
1-Ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl p-nitrobenzoate (12) Light brown
powder. Yield: 1.197 g (86%). M. p.: 145.6 °C (DSC). FT-IR (KBr): ν = 3094 m, 2963 w, 1723 vs,
1605 m, 1529 s, 1348 m, 1265 vs, 1099 s, 1044 m, 815 m, 718 s, 497 s cm-1. 1H NMR (400 MHz,
CDCl3): δ 8.26 (d, J = 8.8 Hz, 2H), 8.19 (d, J = 8.8 Hz, 2H), 7.60 (s, 1H), 5.46 (s, 2H), 5.31 (s,
2H), 4.30 (s, 2H), 4.23 (s, 2H), 4.18 (s, 5H). 13C NMR (101 MHz, CDCl3): δ 165.45 (OOC),
7

151.52 (CNO2), 142.85 (NCCH), 136.04 (NCCH), 131.79, 124.43, 124.32 (C6H4), 81.38, 70.09,
69.91 (C5H4), 69.84 (C5H5), 59.68 (C5H4CH2), 51.12 (OCH2). Calcd. C21H18FeN4O4 (446.07): C,
56.52; H, 4.07; N, 12.56 %. Anal. Found: C, 56.57; H, 4.00; N, 12.64 %.
1-Ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl o-nitrobenzoate (13) Orange yellow
powder. Yield: 1.072 g (77%). M. p.: 222.6 °C (dec, DSC). FT-IR (KBr): ν = 3094 m, 2942 w,
1
1730 vs, 1605 m, 1529 vs, 1348 s, 1272 vs, 1127 s, 1050 s, 926 m, 829 s, 725 s, 490 s cm-1. H
NMR (400 MHz, CDCl3): δ 7.90 (d, J = 7.9 Hz, 1H), 7.72 (d, J = 7.2 Hz, 1H), 7.64 (m, 3H), 5.45
(s, 2H), 5.31 (s, 2H), 4.30 (s, 2H), 4.23 (s, 2H), 4.18 (s, 5H). 13C NMR (101 MHz, CDCl3): δ
165.17 (OOC), 148.12 (CNO2),141.74 (NCCH), 132.99 (NCCH), 131.92, 129.97, 127.19, 123.94,
123.43 (C6H4), 80.70, 69.12 (C5H4), 68.92 (C5H5), 59.58 (C5H4CH2), 50.19 (OCH2). Calcd.
C21H18FeN4O4 (446.07):C, 56.52; H, 4.07; N, 12.56 %; Anal. Found: C, 56.47; H, 4.03; N,
12.55%.
1-Ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl 3,5-dinitrobenzoate (14) Dark brown
powder. Yield: 1.088 g (71%). M. p.: 196.6 °C (DSC). FT-IR (KBr): ν = 3115 m, 2921 w, 1730 vs,
1626 m, 1557 vs, 1348 vs, 1272 vs, 1162 s, 1044 m, 954 m, 822 m, 711 m, 490 m cm-1. 1H NMR
(400 MHz, DMSO-d6): δ 9.03 (d, J = 2.0 Hz, 1H), 8.86 (s, 2H), 8.30 (s, 1H), 5.51 (s, 2H), 5.34 (s,
2H), 4.36 (s, 2H), 4.19 (s, 7H). 13C NMR (101 MHz, DMSO-d6): δ 163.65 (OOC), 149.78 (CNO2),
142.38 (NCCH), 133.61 (NCCH), 130.24, 126.21, 124.02 (C6H3), 83.65, 70.11, 70.00 (C5H4),
69.76 (C5H5), 60.67 (C5H4CH2), 50.35 (OCH2). Calcd. C21H17FeN5O6 (491.05):C, 51.35; H, 3.49;
N, 14.26 %; Anal. Found: C, 51.43; H, 3.56; N, 14.23%.
1-Ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl terephthalate (15) Yellow powder. Yield:
2.033g (90%). M. p.: 222.6 °C (DSC). FT-IR (KBr): ν = 3155 m, 2955 w, 1715 vs, 1626 m, 1383
m, 1335 m, 1265 vs, 1106 vs, 1044 m, 801 m, 718 m, 490 s cm-1. 1H NMR (400 MHz, CDCl3): δ
8.04 (s, 4H), 7.59 (s, 2H), 5.43 (s, 4H), 5.30 (s, 4H), 4.01 (s, 4H), 4.23 (s, 4H), 4.18 (s, 10H). 13
C
NMR (101 MHz, CDCl3): δ 166.47 (OOC), 143.27 (NCCH), 134.62 (NCCH), 130.59, 124.24
(C6H4), 81.47, 70.05, 69.88 (C5H4), 69.81 (C5H5), 59.45 (C5H4CH2), 51.07 (OCH2). Calcd.
C36H32Fe2N6O4 (724.12):C, 59.69; H, 4.45; N, 11.60 %; Anal. Found: C, 59.62; H, 4.52; N,
11.55%.
8

1-Ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl phthalate (16) Yellow powder. Yield:
1.875 g (83%). M. p.: 135.8 °C (DSC). FT-IR (KBr): ν = 3094 m, 2955 w, 1723 vs, 1445 m, 1383
1
m, 1272 vs, 1120 vs, 1058 s, 940 m, 822 s, 753 m, 490 s cm-1. H NMR (400 MHz, CDCl3): δ
7.67 (m, 2H), 7.60 (s, 2H), 7.50 (m, 2H), 5.30 (s, 4H), 5.29 (s, 4H), 4.30 (m, 4H), 4.18 (m, 14H).
13C NMR (101 MHz, CDCl3): δ 167.20 (OOC), 142.19 (NCCH), 131.56 (NCCH), 131.28, 129.07,
123.61 (C6H4), 80.81, 69.10, 69.01 (C5H4), 68.92 (C5H5), 58.83 (C5H4CH2), 50.13 (OCH2). Calcd.
C36H32Fe2N6O4 (724.12):C, 59.69; H, 4.45; N, 11.60 %; Anal. Found: C, 59.74; H, 4.48; N,
11.53%.
1-Ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl isophthalate (17) Yellow powder. Yield:
1.943 g (86%). M. p.: 193.1 °C (DSC). FT-IR (KBr): ν = 3087 m, 2921 w, 1715 vs, 1438 m, 1397
1
m, 1341 m, 1307 vs, 1231 vs, 1102 s, 1078 s, 961 m, 822 m, 732 s, 482 s cm-1. H NMR (400
MHz, CDCl3): δ 8.63 (s, 1H), 8.18 (d, 2H), 7.59 (s, 2H), 7.47 (s, 1H), 5.43 (s, 4H), 5.30 (s, 4H),
4.29 (s, 4H), 4.22 (s, 4H), 4.18 (s, 10H). Calcd. C36H32Fe2N6O4 (724.12):C, 59.69; H, 4.45; N,
11.60 %; Anal. Found: C, 59.63; H, 4.39; N, 11.68%.
Bis(ferrocenylmethyl-1H-1,2,3-triazol-4-ylmethyl) 3-nitrophthalate (18). Dark brown
powder. Yield: 1.799 g (75%). M. p.: 226.2 °C (dec, DSC). FT-IR (KBr): ν = 3087 w, 2914 w,
1730 vs, 1612 m, 1536 vs, 1460 m, 1356 s, 1265 vs, 1141 s, 1106 s, 1044 s, 822 m, 711 m, 482 s
cm-1. 1H NMR (400 MHz, CDCl3): δ (d, J = 15.0 Hz, 2H), 7.69 (s, 1H), 7.63 (d, J = 19.0 Hz, 2H),
5.43 (s, 2H), 5.34(s, 2H), 5.32 (s, 4H), 4.33 (s, 2H), 4.30 (s, 2H), 4.19 (s, 14H). 13C NMR (101
MHz, CDCl3): δ 165.90, 164.25 (OOC), 147.12 (CNO2), 142.49, 142.46 (NCCH), 136.80
(NCCH), 131.51, 131.19, 130.66, 129.33, 124.80 (C6H3), 81.71, 70.05, 69.97 (C5H4), 69.82
(C5H5), 60.63, 60.22 (C5H4CH2), 51.07 (OCH2). Calcd. C36H31Fe2N7O6 (769.10):C, 56.20; H,
4.06; N, 12.74 %; Anal. Found: C, 56.15; H, 4.02; N, 12.73%.
Bis(ferrocenylmethyl-1H-1,2,3-triazolyl-4-ylmethyl) 4-nitrophthalate (19). Dark brown
powder. Yield: 1.987 g (80%). M. p.: 237.8 °C (dec, DSC). FT-IR (KBr): ν = 3087 w, 2921 w,
1730 vs, 1605 m, 1529 s, 1356 s, 1272 vs, 1134 s,1050 s, 822 s, 732 m, 490 s cm-1. 1H NMR (400
MHz, CDCl3): δ 8.56 (s, 1H), 8.34 (d, J = 8.5 Hz, 1H), 7.80 (d, J = 8.5 Hz, 1H), 7.64 (s, 1H), 7.61
(s, 1H), 5.32 (s, 8H), 4.31 (s, 4H), 4.20 (s, 14H). 13C NMR (101 MHz, CDCl3): δ 166.65, 165.57
(OOC), 149.76 (CNO2), 142.40, 142.40 (NCCH), 138.43 (NCCH), 133.37, 131.12, 127.07, 125.39,
9

124.69 (C6H3), 81.61, 70.07, 69.91 (C5H4), 69.84 (C5H5), 60.30 (C5H4CH2), 51.11 (OCH2). Calcd.
C36H31Fe2N7O6 (796.10):C, 56.20; H, 4.06; N, 12.74 %; Anal. Found: C, 56.06; H, 4.15; N,
12.70%.
O,O',O"-Tris(ferrocenylmethyl-1H-1,2,3-triazolyl-4-ylmethyl) 1,3,5-benzenetricarboxy
late (20). Yellow powder. Yield: 2.777 g (85%). M. p.: 184.1 °C (DSC). FT-IR (KBr): ν = 3087 w,
2942 w, 1730 vs, 1612 w, 1452 m, 1321 m, 1231 vs, 1113 s, 1058 s, 1002 s 995 s, 739 s, 497 s
cm-1. 1H NMR (400 MHz, CDCl3): δ 8.77 (s, 3H), 7.59 (s, 3H), 5.43 (s, 6H), 5.31 (s, 6H), 4.30 (s,
6H), 4.23 (s, 6H), 4.18 (s, 15H). Calcd. C51H45Fe3N9O6 (1047.15):C, 58.48; H, 4.33; N, 12.03 %;
Anal. Found: C, 58.42; H, 4.39; N, 12.00%.
O,O',O"-Tris(ferrocenylmethyl-1H-1,2,3-triazolyl-4-ylmethyl) 1,2,4-benzenetricarboxy
late (21). Yellow powder. Yield: 2.810 g (86%). M. p.: 278.1 °C (dec, DSC). FT-IR (KBr): ν =
3087 w, 2948 w, 1723 vs, 1633 w, 1445 w, 1231 vs, 1113 s, 1044 s, 995 m, 822 m, 760 w, 495 s
1
cm-1. H NMR (400 MHz, CDCl3) δ 8.32 (s, 1H), 8.12 (d, J = 8.1 Hz, 1H), 7.68 (d, J = 8.0 Hz,
1H), 7.63–7.56 (m, 3H), 5.42 (s, 2H), 5.33–5.27 (m, 10H), 4.30 (s, 6H), 4.23 (s, 2H), 4.18 (s, 19H).
13C NMR (101 MHz, CDCl3): δ 167.51, 166.93, 165.50 (OOC), 142.99, 142.81, 142.75 (NCCH),
136.73 (NCCH), 133.39, 133.14, 132.36, 131.33, 130.01, 124.60, 124.34 (C6H3), 81.68, 81.41,
70.09, 70.02 (C5H4), 69.91, 69.82 (C5H5), 60.01, 59.93, 59.56 (C5H4CH2), 51.09, 51.06 (OCH2).
Calcd. C51H49Fe3N9 O6 (1047.15):C, 58.48; H, 4.33; N, 12.03 %; Anal. Found: C, 58.41; H, 4.39;
N, 12.00 %.
2.3. X-ray crystallography
Suitable X-ray quality crystals of 1, 9, 13 and 16·CH2Cl2 were grown by slow diffusion of
n-pentane into dichloromethane solution of the above compounds in sealed bottles at 0-5 °C.
Single crystal X-ray diffraction studies were conducted on a Bruker D8 QUEST diffractionmeter,
which equipped with a Photo 100 CMOS detector. The data were collected using graphite
monochromated MoK radiation. The crystals were kept at 153 K for 1, 9, 16·CH2Cl2 and 293 K
for 13 during data collection. Their molecular structures were constructed by direct method using
SHELXS-2014 and refined by full-matrix least-squares techniques using SHELX-2014/7 [38].
Their crystallographic data and structure refinement parameters are listed in Table 1. Their
10

selected bond lengths and angles are given in Table S1. Their hydrogen bonds can be found in
Table S2.
(Please insert Table 1 here)
Their crystallographic data (excluding structure factors) have been deposited with the
Cambridge Crystallographic Data Centre, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK.
Copies of the data can be obtained free of charge through the depository numbers CCDC-1956243
(1), CCDC-1956257 (9), CCDC-1961098 (13), CCDC-1961100 (16·CH2Cl2) (Fax: (+44)
1223-336-033; or E-mail: deposit@ccdc.cam.ac.uk)
.
2.4. Computational details
For determining iron-iron distances in the molecules of 15-17 and Catocene (for comparison),
the DFT method with the Becke's three parameter hybrid functional and Lee Yang Parr's gradient
corrected correlation functional (B3LYP) was used to calculate their optimized geometry and
ground state electronic structure [39]. The calculations were performed with the GAUSSIAN-09
program [40]. The LanL2DZ basis set and effective core potential were used for iron atoms and
the 6-31G basis sets were used for all other atoms [41].The nature of all stationary points was
confirmed by performing a normal-mode analysis.
3. Results and Discussion
3.1. Syntheses and characterization
The new ferrocene-based 1,2,3-triazolyl compounds 1-21 were synthesized using the classic
CuAAC method with high yields. The crude products can be purified rapidly by column
chromatography on silicone gel. The new compounds are mostly yellow solid and soluble in
CH2Cl2, CHCl3, etc, but the solubility of 17 and 20 is very low and their 13C NMR spectra were
hardly to be measured. The DSC curves of the new Fc-TAZs 1-21 were shown in Figures S1 and
S2, which exhibited that their thermal decomposition peaks are higher than 200 ºC (except 10 with
192 ºC), indicative of their high thermal stability and further confirmed by their TG curves
(Figures S3 and S4). The formation of 1,2,3-triazolyl rings in the new ferrocenes was evidenced
by the medium intensity absorptions ranged between 923 and 937 cm-1 and the strong intensity
absorptions in the range of 1037–1052 cm-1 (Figures S5–S8). The absorption bands in the FT-IR
11

spectra of the novel compounds in the regions of 3109–3087, 1113–1097, 827–816, 502–485 cm-1
verified the appearance of ferrocenyl groups in the new compounds. The strong bands around
1730 and 1250 cm-1 in their FT-IR spectra can be assigned to the stretching vibrations of carbonyl
1
groups. In their H NMR spectra, it is found that chemical shifts of the proton atoms of
1,2,3-triazolyl groups located in the regions of 8.16-8.20 or 7.55-7.65 ppm depending on the
substituents and their positions on the phenyl rings. In their 13C NMR spectra, carbon atoms of the
ferrocenyl and the carbonyl groups resonated in the ranges of 68–81 and 160–167 ppm,
respectively.
The UV/Vis absorption spectra of the ferrocene-functionalized 1,2,3-triazolyl compounds
1-21 in DMSO (Figures S7–S8) showed strong absorption bands between 290 and 300 nm, which
can be ascribed to the π-π* transitions of cyclopentadienyl and phenyl groups, and the shoulders
between 318 and 330 nm could be assigned to charge transfer bands of the ferrocenyl groups.
Meanwhile, the wide and strong absorption bands spanning from 360 nm to 530 nm with peaks
around ca. 430 nm, are appointed to the π-π* transitions of the ferrocenyl chromophores. The
presence of strong electron-withdrawing nitro groups in the phenyl rings weaken absorption bands
of the ferrocenyl groups. The usual weak absorptions, due to the d-d transitions of the Fe2+ ions
peaked in the range of 440-450 nm, are completely covered by the strong π-π* transitions of the
ferrocenyl units [42-45].
3.2 Crystal structures
We grew single crystals of 1, 9, 13 and 16·CH2Cl2 successfully to confirm the molecular
structures of the new compounds. Their crystal structures are shown in Figure 1. Compounds 1, 9
and 13 crystallize in the monoclinic space group P21/c (1 and 9) and P21/n (13), respectively.
Compound 16·CH Cl crystallizes in the triclinic space group P . The wR2 of 13 (all data) is
1
2
2
0.43, higher than 0.25, due to bad quality of the single crystals of 13, which have been grew
several times and unfortunately no high-quality single crystals were collected. The distances of Cp
rings and the sandwiched Fe atoms are in the range of 1.6443(7) Å to 1.6591(5) Å. The dihedral
angles between the planar rings in the molecules are of striking difference owing to the
appearance of methylene spacers between phenyl, triazolyl and ferrocenyl groups. For examples,
the dihedral angles are 63.179(90)° (1) and 80.711(56)° (9) between the substituted Cp rings and
12

the 1,2,3-triazolyl rings, 24.795(76)° (1) and 59.514(61)° (9) between the 1,2,3-triazolyl rings and
the phenyl rings. The molecules are linked by weak inter- and intramolecular CHN and
CHO hydrogen bonds into three-dimensional networks, but no classical hydrogen bonds exist
in the molecules (Table S2).
(Please insert Figure 1 here)
3.3 Electrochemical behavior
Each catalytic reaction should has at least an electron gain and loss procedure during its
catalysis. Therefore, it is necessary to investigate electrochemical behavior of the novel Fc-TAZs,
including determining their redox reversibility and comparing their oxidation potentials with those
of TBF, NBF and Catocene, to estimate their possibility as potential BRCs in solid propellants.
Generally, CV is employed to analyze redox properties of ferrocene-based BRC candidates
[15-26]. CV curves of the new ferrocenyl compounds in DMSO in the presence of 0.10 M
Bu4NBF4 as the supporting electrolyte are illustrated in Figure S11 and their numerical
information is listed in Table S3. The appearance of only one pair of redox peak for each bis- or
trisferrocenyl compound indicated that there is a simultaneous transfer of more electrons in the
multinuclear ferrocenyl compounds, due to no considerable electron transport between their
a
c
ferrocenyl groups. The measured Ep1/2, ∆Ep and Ip /Ip in the ranges of 538-551 mV, 75-105 mV
a
c
and 1.14-1.43 (except Ip /Ip = 1.82 for 1), respectively, suggested that more than half of them
exhibit reversible Fc/Fc+ waves. It is also observed that the oxidation potentials of the new
Fc-TAZs are higher by ca 150 mV than those of TBF, NBF and Catocene, indicative of their
higher anti-oxidative ability on comparison with those neutral ferrocenes in DMSO. Effects of the
strong electron-withdrawing nitro groups on the redox potentials of the new Fc-TAZs are
negligible. Moreover, the redox properties of the new compounds may give us useful information
in better understanding catalytic activity and the prevalent electron-transfer mechanism of the
ferrocene-based BRCs for AP thermal decomposition.
(Please insert Figure 2 here)
3.4 Anti-migratory and anti-volatility studies
Neutral ferrocene derivatives with lower molecular weights such as ferrocene (Fc) and NBF
migrate obviously when the composite solid propellants using them as ingredients stored for a
long time and thus give rise to a series of problems that affect combustion properties of the
13

propellants. For dealing with the high-migration problem of the neutral alkyl-substituted
ferrocenes, we synthesized a series of ferrocene-based 1,2,3-triazolyl compounds. Anti-migration
property of the Fc-TAZs 1-4, 6, 7, 9-12, 16, 18 and 21 were tested with Fc and Catocene as
references under similar conditions. Anti-migration sample preparation details and the
measurement procedures are similar to that described previously [16], except the migration
temperature was kept at 50 ºC to accelerate their migration rates. From the photos shown in
Figures S10‒S24 it is noticed that both Fc and Catocene migrated considerably even after one
week aging, whilst all tested Fc-TAZs exhibited no obvious diffusion after four weeks storage.
The negligible migration of the new compounds has probably a strong correlation with the
non-classic weak hydrogen bonding interactions and van de Waals forces between the propellant
components and the novel ferrocenes [22]. These weak interactions are caused by the presence of
polar oxygen and nitrogen atoms in the molecules of the tested ferrocene derivatives, AP and
(Please insert Figures 3 and 4 here)
cross-linked HTPB. The migration distances versus storage time are illustrated in Figure 3. It is
observed that both Fc and Catocene migrated longer distances (2.5 cm and 1.7 cm, respectively)
after four weeks aging. Meanwhile, the tested Fc-TAZs moved much slowly after aging over a
four-week period (< 0.2 cm), indicating that they show high anti-migration property than Fc and
Catocene.
The neutral alkylferrocene-based BRCs show noticeable volatility during fabrication of
composite propellants and leads probably to their non-uniform distribution issues in the propellant
columns. Additionally, the vaporization and sublimation behavior of the BRCs may give rise to
other unanticipated danger [5-9]. Therefore, low-volatility is a necessary property for
ferrocene-based BRCs. Increasing polarity of the alkylferrocenes through inserting polar atoms
such as O and/or N atoms into their alkyl chains, is a favorable method to improve their
anti-volatility property. TG analysis of the new Fc-TAZs at 70 °C for 24 h has been carried out to
estimate their anti-volatility performance. The results are displayed in Figure 4 and S27. It is noted
that Catocene shows ca. 4.39% weight-loss after 24h, revealing that Catocene is a relatively
high-volatile ferrocene derivative. In contrast, the as-synthesized Fc-TAZs displayed negligible
weight loss under similar conditions, except 18, which lost about 1.5% weight after 24 hours,
revealing that the new compounds is mostly non-volatile. The consistent-temperature TG analysis
confirmed again that functionalization of the alkylferrocenes via insertion of polar O and/or N
atoms can tackle their high-migration and high-volatility problems effectively.
3.5 Catalytic performances
14

In formula of a typical AP-based composite propellant the percentage of the main oxidizer
AP is very high and combustion property of AP has intimate correlation with combustion behavior
of a classic AP-based propellant. Researchers generally perform TG and DSC studies on thermal
decomposition behavior of pure AP and its mixture with a BRC to figure out catalytic effect of the
BRC on AP thermal degradation and the results can be used as a pre-estimation for its catalytic
activity towards combustion process of a AP-based propellant [46-49].
In these years the traditional AP-based composite propellants are usually modified by
addition of other oxidizers such as RDX or HMX to partly substitute AP to lower smoke released
by AP and Al powder during propellant combustion and thus increase signal receiving abilities of
their IR sensors and reduce detecting possibilities by opposite radars. Thermal degradation
performances of RDX and HMX with the as-synthesized ferrocenyl compounds as additives were
measured, too.
Concentrations of the new Fc-TAZs in the oxidizers were optimized firstly with compounds
1 and 11 as references, based on molecular structural difference between compounds 1-10 and
11-21. The test results, shown in Figures S28-S33, indicated that the optimal addition amounts in
three oxidizers are: 5 wt% in AP and 2 wt% in HMX for both compounds, 4 wt% and 5 wt% in
RDX for 1 and 11, respectively. Therefore, in AP and HMX all compounds were added in 5 wt%
and 2 wt%, respectively, but in RDX 1-10 and 11-21 were added in 4 wt% and 5 wt%,
respectively.
From Figures 5 and S34, it is found that pure AP started to lose weight at 268 °C and ceased
to decomposition at 395 °C. When the Fc-TAZs (5 wt%) were mixed with AP, the initial
weight-loss temperatures for the mixtures shifted towards left by 3-23 °C to the range of
245–265 °C, indicative of the decomposition of AP in advance in the presence of the new
ferrocenes. Meanwhile, the ceased decomposition temperatures of the mixtures, ranging from
337 °C to 353°C, were much lower by 42-58 °C than that of the pure AP. The TG analysis results
implied that the Fc-TAZs show positive effect on the thermal disintegration of AP.
(Please insert Figure 5 and 6 here)
DSC analysis of the pure AP and its mixtures were additionally performed and their DSC
curves were illustrated in Figures 6 and S35. It is noted that the thermal decomposition process of
the pure AP has three steps: phase-transition stage, low-temperature stage (LTD) and
high-temperature stage (HTD). It is observed that the DSC curves of the mixtures each exhibits
three stages, too. The phase-transition temperature of AP (243.6 °C) moved a few degree in the
mixtures except its mixture with compound 2 (8.7 °C delay), implying that the additives did not
affect the phase transition of AP distinctly. It is observed that most of the mixtures show
exothermic peaks in the range of 184-202 °C, which can be assigned to the heat release peaks
formed by the catalytic effects of the nano iron oxides on the AP thermal decomposition [46-49].
The nano iron oxides are produced in-situ by the heterogeneous redox interaction of ferrocene
derivatives with AP, as observed by other researchers when they studied combustion processes of
15

AP with ferrocene and other liquid ferrocene derivatives [49-51]. The exothermic peaks appeared
around 305 °C and in the range of 341.8-363.3 °C for the mixtures suggested that the LTD stage
of AP (peaked at 292.5 °C) shifts right slightly to ca. 305 °C and the HTD stage moves
dramatically forwards from 406.6 °C by 43.3-64.8 °C. The opposite movement of two stages
narrows the temperature span of AP drastically (from 151°C to 75-92 °C), revealing that the AP
thermal degradation rate is enhanced with compounds 1-21 as additives and thus demonstrating
that the new ferrocenyl compounds exert great effects on the thermal decomposition of AP. The
heats released by the mixtures are between -1013 to -1478 J·g-1, with 5 wt.% 6 +AP being the
highest, which is almost twice higher than that of AP itself (-746 J·g-1) and higher than that of the
mixture of 5 wt.% Catocene +AP (-1303.0 J·g-1). The increment of the released heat of AP
verified again that the thermal disintegration of AP is accelerated by addition of the new
Fc-TAZs.
It is noted that compounds 10, 15-17, 18 and 19 are dinuclear ferrocenyl derivatives and 5, 6,
20 and 21 are trinuclear ferrocenyl compounds. For studying influence of Fe-Fe distances in these
compounds on their catalytic activities towards AP thermal degradation, we calculated Fe-Fe
distances in 15-17. The calculation results exhibited that the Fe-Fe distances in the molecules of
15-17 are 17.38 Å, 18.33 Å and 14.15 Å in gas phase. On comparison, the Fe-Fe distance in
Catocene is 6.63 Å in gas phase. The HTD temperature peaks of AP in the mixtures of AP with
15-17 and Catocene are 345.2, 349.3, 345.9 and 342.2 °C, respectively, and the released heats of
AP in the mixtures with 15-17 and Catocene are 1189.7, 1361.9, 1271.9 and 1303.0 J·g-1,
respectively. From these data we can't give a correlation between the Fe-Fe distance in the
binuclear ferrocenyl compounds and their catalytic activities for AP thermal decomposition. In
addition, the oxidation potentials of 15-17 in DMSO are 580, 586 and 587 mV, which increase
with the increase of the iron-iron distance in their molecules, indicating that with the increase of
the Fe-Fe distance the compounds display high anti-oxidation ability, but no imitate correlation
between their oxidation potentials and catalytic activities towards AP thermal decomposition was
found.
DCS curves of RDX and its mixtures with 1-21, HMX and its mixtures with 1-21 were
shown in Figures S36S39. Each DSC curve in both Figures S36 and S37 is composed of two or
three exothermic peaks, which have never been observed in our previously reported DSC curves
of mixtures of RDX and a ferrocene derivative, implying that these new ferrocenyl compounds
probably exhibit a different catalytic mechanism during catalyzing RDX thermal degradation
[19,20,23-26]. The peak temperature of RDX (231.2 °C) moved right and the released heat of
RDX increased (from -827.9 J·g-1 to -862.7 to -1590.0 J·g-1), implying that the as-prepared
triazolyl ferrocenyl compounds make no distinct effects on the thermal degradation of RDX. As
shown in both Figures S38 and S39, most of the mixtures showed slightly lower peak
temperatures than that of pure HMX, suggesting that the new compounds exert positive effect on
the thermal decomposition of HMX during combustion. The mixture containing HMX and 1, 5, 7,
16

8, 11 or 14 releases more heat than that of pure HMX. Taking both peak temperature and released
heat into account, compounds 5, 7 and 11 exhibit considerably positive effect on the thermal
degradation of HMX. RDX and HMX are typical nitramines, which are unable to oxidize
ferrocenes to form iron oxides at low temperatures, the exothermic peaks are absent on their
mixtures' DSC curves up to the main decomposition peaks of RDX and HMX. Therefore, the
decomposition peak temperatures of RDX and HMX showed no significant movement to left in
the presence of the as-synthesized Fc-TAZs, indicating that the new compounds exert
unpronounced effects on the thermal decomposition of RDX and HMX on comparison with that of
AP.
4. Conclusions
In summary, twenty-one ferrocene-based 1,2,3-triazolyl derivatives were synthesized to
tackle the high-migratory problem of the neutral alkylferrocene-based BRCs. The results showed
that the newly synthesized ferrocenyl compounds are of high thermal stability and more than half
of them show excellent electrochemical reversibility. The tested compounds display much high
anti-migration and anti-volatility abilities on comparison with ferrocene and Catocene because of
the appearance of polar oxygen and nitrogen atoms in their molecules. TG and DSC results
revealed that the new ferrocenyl compounds exhibit high catalytic activity in the thermal
degradation of AP during their combustion. Compounds 5, 7 and 11 as additives can promote
thermal decomposition of HMX. It is also concluded that the iron-iron distances and oxidation
potentials of the polyferrocenyl compounds have no distinct relationship with their catalytic effect
on the thermal decomposition of AP.
Author statement
Wenqian Cheng: Investigation, Methodology, Data curation; Xiaoling Shi.: Writing-
Original draft preparation. Yu Zhang: Software, Visualization; Yajun Jian:
Writing-Reviewing and Editing,; Guofang Zhang: Conceptualization, Supervision.
Declaration of interests
The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.
17

Acknowledgements
This work is supported by National Natural Science Foundation of China (21401124,
21602129), Fundamental Research Funds for Central Universities (GK201803027).
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Scheme, Figure captions and Table title
Scheme 1. Molecular structures of the novel ferrocene-based 1,2,3-triazolyl compounds 1-21.
Figure 1. Crystal structures of 1, 9, 13 and 16·CH2Cl2. (solvents are omitted for clearity).
Figure 2. Cyclic voltammograms of 11–21 in 0.1 M n-Bu4PF6-DMSO with a scanning rate of
0.1 V/s.
Figure 3. Migration distances of the simulated composite propellant samples containing 1-4,
6, 7, 9-12, 16, 18, 21 after 1-4 weeks migration at 50 ºC. (Fc (ferrocene) and Cat (Catocene) were
used as references).
Figure 4. TG curves of 11, 13, 16, 18, 21 and Cat at 70 ºC for 24 h.
Figure 5. TG curves of AP and of the mixtures AP + 5 wt.% 1121.
Figure 6. DSC curves of AP and of the mixtures AP + 5 wt.% 11–21.
Table 1. Summary of the crystallographic data of 1, 9, 13 and 16·CH2Cl2.
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Table 1. Summary of the crystallographic data of 1, 9, 13 and 16·CH2Cl2.
Compound
formula
Fw(g mol-1)
T (K)
1
9
13
16·CH2Cl2
C37H34Cl2Fe2N6O4
809.30
C20H19FeN3O
373.23
153(2)
C20H18FeN4O3
418.23
153(2)
Monoclinic
P21/c
C21H18FeN4O4
446.24
293(2)
153(2)
crystal system
space group
a (Å)
monoclinic
P21/c
Monoclinic
P21/n
Triclinic
P
1
5.7232(11)
23.191(5)
13.045(3)
90
21.858(4)
7.8241(14)
10.398(2)
90
5.5889(14)
31.929(9)
10.698(4)
90
12.137(3)
12.766(2)
13.384(3)
98.257(7)
114.876(7)
104.537(7)
1746.2(6)
2
b (Å)
c (Å)
α(°)
β(°)
102.583(7)
90
94.015(7)
90
90.976(10)
90
γ (°)
V /Å3
1689.8(6)
4
1773.8(6)
4
1908.7(9)
4
Z
Dc (Mg m-3)
1.467
0.905
1.566
0.881
1.553
6.666
1.539
1.034
μ (mm-1)
Crystal sizes (mm)
reflns collected
Independent reflns
Rint
0.17×0.13×0.11 0.14×0.12×0.10 0.10×0.08×0.06 0.14×0.12×0.10
11933
2061
20177
12805
20255
3469
2942
6796
0.0387
1.064
0.0385
0.1499
0.0282
GOF on F2
1.072
1.799
1.028
R1, wR2 [I ≥2σ(I)] 0.0304, 0.0702
R1, wR2 (all data) 0.0372, 0.0725
0.0295, 0.0734
0.0330, 0.0755
0.1514, 0.3704
0.2407, 0.4328
0.0560, 0.1512
0.0606, 0.1560
22

Highlights
·Ferrocene-based triazolyl compounds (Fc-TAZs) were synthesized by click
reaction
·Fc-TAZs show excellent anti-migratory and anti-volatility properties
·Fc-TAZs are highly thermal stable and accelerate thermal degradation of AP
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