The synthesis, property and reduction of high-nitrogen compound 3,3′,5,5′-tetraazido-4,4′-bis(1,2,4-triazole)

Article abstract of DOI:10.1016/j.poly.2016.06.025

High-nitrogen compound, 3,3′,5,5′-tetraazido-4,4′-bis(1,2,4-triazole) (TABT, 83.99% N), is synthesized from sodium azide and 3,3′,5,5′-tetrabromo-4,4′-bis(1,2,4-triazole) (TBBT) which is prepared by the bromination of 4,4′-bis(1,2,4-triazole) (BTz). It is fully characterized by IR, HRMS, NMR, and single crystal X-ray diffraction showing two triazole rings of TABT perpendicular to each other. DSC and TGA are employed to study TABT's thermal stability with a decomposition temperature at 125.39?°C (onset). The calculated detonation heat of TABT and the predicted detonation velocity are 6449?kJ·kg^?1and 8649?m·s^?1, respectively. The reduction of TABT with hydrogen and Pd/C gave the stabilized 3,3′,5,5′-tetra(t-butyloxycarbamido)-4,4′-bis(1,2,4-triazole) (11) in the presence of (Boc)₂O, providing an alternative path to the high energy density material (HDEM) TNBT [3,3′,5,5′-tetranitro-4,4′-bis(1,2,4-triazole)].

Full text of DOI:10.1016/j.poly.2016.06.025

Polyhedron 117 (2016) 445–452
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
The synthesis, property and reduction of high-nitrogen compound
3,30,5,50-tetraazido-4,40-bis(1,2,4-triazole)
Feipeng Lu a,1, Engyu Wang a,1, Jinglun Huang b, Ming Huang b, Fude Nie b, Fu-Xue Chen a,
⇑
a School of Chemical Engineering and the Environment, Beijing Institute of Technology, Beijing 100081, China
b Research Center of Energetic Material Genome Science, Institute of Chemical Materials, China Academy of Engineering Physics, Mianyang 621050, Sichuan, China
a r t i c l e i n f o
a b s t r a c t
High-nitrogen compound, 3,30,5,50-tetraazido-4,40-bis(1,2,4-triazole) (TABT, 83.99% N), is synthesized
from sodium azide and 3,30,5,50-tetrabromo-4,40-bis(1,2,4-triazole) (TBBT) which is prepared by the
bromination of 4,40-bis(1,2,4-triazole) (BTz). It is fully characterized by IR, HRMS, NMR, and single crystal
X-ray diffraction showing two triazole rings of TABT perpendicular to each other. DSC and TGA are
employed to study TABT’s thermal stability with a decomposition temperature at 125.39 °C (onset). The
Article history:
Received 23 March 2016
Accepted 14 June 2016
Available online 23 June 2016
calculated detonation heat of TABT and the predicted detonation velocity are 6449 kJꢀkgꢁ1 and 8649 mꢀsꢁ1
,
Keywords:
Azidation
respectively. The reduction of TABT with hydrogen and Pd/C gave the stabilized 3,30,5,50-tetra(t-butyloxy-
carbamido)-4,40-bis(1,2,4-triazole) (11) in the presence of (Boc)2O, providing an alternative path to the
high energy density material (HDEM) TNBT [3,30,5,50-tetranitro-4,40-bis(1,2,4-triazole)].
Ó 2016 Elsevier Ltd. All rights reserved.
High-nitrogen compound
3,30,5,50-Tetraazido-4,40-bis(1,2,4-triazole)
(TABT)
Explosives
Synthesis
1. Introduction
was proposed to solve this problem. And 1,10-(ethane-1,2-diyl)-
bis(3-nitro-1H-1,2,4-triazol-5-nitroamine) (3) and its energetic
Energetic materials have been widely used in the fields of both
propellant and gunpowder for civil and military use [1a–e]. Among
them, heterocycle-based nitrogen-rich energetic compounds
[2a–i], featuring in the release of environment-friendly by-product
N2 after explosive decomposition, have attracted more and more
attention in the context of high energy density materials (HDEMs)
research [3a,b].
Triazole ring is a frequently utilized energetic moiety in the
design of energetic molecules [4a]. Further, bistriazole motif has
promising capability to increase both energy and safety by incor-
poration of other energetic groups on each triazole ring (Fig. 1)
[4b–e]. Thus, azo (N = N) linkage was introduced to give the birth
of 1,10-dinitro-3,30-azo-bis(1,2,4-triazole) (N-DNAT) but failure to
be converted into more stable 5,50-dinitro-3,30-azo-bis(1,2,4-tria-
zole) (DNAT) via thermal rearrangement [5a]. When the azo linker
anchored to N instead of C, a stable N8 chain was constructed in
the case of 1,10-azo-bis(1,2,3-triazole) (1) [5b]. Thereafter, more
energetic high-nitrogen compounds were synthesized as 3,30,5,50-
tretraazido-4,40-azo-bis(1,2,4-triazole) (2) [5c,d]. Unfortunately,
all these azo-linked high-nitrogen compounds encountered the
same safety concern of high mechanic sensitivity. Ethylene linker
ionic salts were prepared with promising low sensitivity and
generally good detonation performance [5e]. However, a few direct
CAC bond linked bistriazoles have been investigated. Recently,
Shreeve disclosed the synthesis of 3,30-bis(1H,4H-5-nitroimino-
1,2,4-triazole) (4) [6a]. Klapotke demonstrated the preparation of
5,50-diazido-3,30-bis(1H-1,2,4-triazole) (5) [6b], and its insensitive
oxidized isomer 5,50-bis(3-nitro-1,2,4-triazol)-1,10-diol (6) [6c].
The most recent progress in this field were reported by Thomas
and Chavez accomplishing the new energetics tricyclic nitramine
moiety (7) [7a] and tricyclic hexaazene moiety (8) [7b]. On the
hand, the direct N-N bond linked bis-(1,2,4-triazole) was extremely
scarcely explored. We noticed that 4,40-bis(1,2,4-triazole) (BTz)
skeleton in the pursuing for high-energy low-sensitivity energetic
materials [8a–d], as the excellent thermal stability of BTz (on-set
decomposition temperature 274.6 °C) [9a]. It’s nitration compound
3,30,5,50-tetranitro-4,40-bis(1,2,4-triazole) (TNBT, Fig. 1) was just
theoretically studied decades ago [5a], declaring TNBT superior
to cyclotetramethylene tetranitramine (HMX), e.g., with density
of 1.99 gꢀcmꢁ3, detonation velocity of 9500 mꢀsꢁ1, and detonation
pressure 42 GPa.
Herein, we report our progress in pursue of the terminal target
TNBT. Here was disclosed the synthesis and property of
a
high-nitrogen 3,30,5,50-tetraazido-4,40-bis(1,2,4-triazole) (TABT),
and the subsequent reduction achieving a highly hindered 3,30,5,50-
tetraazayliden-4,40-bis(1,2,4-triazole) (9) through Staudinger
⇑
Corresponding author.
E-mail address: fuxue.chen@bit.edu.cn (F.-X. Chen).
These authors contributed equally.
1
http://dx.doi.org/10.1016/j.poly.2016.06.025
0277-5387/Ó 2016 Elsevier Ltd. All rights reserved.

446
F. Lu et al. / Polyhedron 117 (2016) 445–452
azo or ethylene-linked bis-triazoles
O2N
N
N
N
N
NO2
NO2
N
HN
NH
NO2
N
N
N
N
N
N
N
N
N
N
O2N
N
DNAT [5a]
N3
N-DNAT [5a]
N
N3
N
NO2
HN
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
O2N
NH
NO2
3 [5e]
N
N
N3
N3
1 [5b]
2 [5c, 5d]
direct bis-triazoles
H
O2NN
N
N
N
N
N
N
HN
NH
OH
NH
NNO2
NO2
N
N
N
HN
N
N
N
H
N3
N3
N
4 [6a]
NHNO2
5 [6b]
N
O2N
HO
N
N
H2N
6 [6c]
N
N
N
N
N
N
N
N
N
N
N
N
8 [7b]
NH2
NO2
O2NHN
7 [7a]
NO2
N
NO2
R
N
R
R
N
N
N
N
N
N
N
N
N
N
BTz R= H
TIBT R= I
NO2
NO2
TNBT [5a]
R
[8b, 8c]
Fig. 1. Different bis-triazoles in the literature.
process, and 3,30,5,50-tetra(t-butyloxycarbamido)-4,40-bis(1,2,4-tri-
azole) (11) via hydrogenation of TABT on Pd/C incorporated with
in situ amino protection with Boc2O as possible intermediates for
the synthesis of TNBT (Scheme 1).
10 °C/30 min and kept for 10 h at 90 °C. The excessive DMF was
filtered off after the reaction cooled down, and the white residue
was washed with diethyl ether (20 mL). The pure product of BTz
was obtained in white crystal after recrystallization from MeOH
with 90% yield.
Tm ¼ 275 ꢂ C; Tdec ¼ 288 ꢂ C; 1H NMR ð400 MHz; D2OÞ :
2. Experimental
d ¼ 9:02 ppm; 13C NMR ð100 MHz; D2OÞ : d ¼ 141 ppm:
2.1. Physical measurements
2.2.2. The synthesis of 3,30,5,50-tetraiodo-4,40-bis(1,2,4-triazole) (TIBT)
A solution of I2 (12.7 g, 50 mmol, 5 equiv), and KI (9.96 g,
60 mmol, 6 equiv) in distilled water (100 mL) was added dropwise
to a stirred solution of BTz (1.36 g, 10 mmol) in potassium
hydroxide solution (2 M, 50 mL, 100 mmol, 10 equiv). The resulting
mixture was stirred at room temperature for 48 h. The white
precipitate was collected by filtration, washed with acetone
(2 ꢃ 3 mL) and dried under vacuum. It was dissolved in the mini-
mum volume of DMSO at 60 °C, and the solution was poured into
cold water. The canary precipitate was filtered, washed with water
(2 ꢃ 3 mL) and dried under vacuum. In this way, we obtained the
pure TIBT in a good reproducibility of 85% yield.
The IR spectra was measured on a Perkin Elmer 480 FTIR
spectrophotometer (KBr pellet). Mass spectrum and HRMS spectra
were recorded at a Bruker Apex IV FTMS mass spectrometer with
ESI as the ionization method. Single-crystal X-ray diffraction data
of TABT was collected on a Rigaku AFC10/Saturn724+. DSC and
TGA were carried out on Mettler DSC-1 and Mettler TGA/DSC-1
respectively.
2.2. Synthetic procedures
2.2.1. The synthesis of 4,40-bis(1,2,4-triazole) (BTz)
SOCl2 (9 mL, 6 mmol) was add to DMF slowly on ice-salt bath,
and the mixture was stirred at the same temperature for least
4 h. Allowing warm up to room temperature freely and stirring
for 24 h, a solution of hydrazine hydrate (80%, 1.5 mL, 30 mmol)
in DMF (6 mL) was added dropwise. And this solution was stirred
for another 36 h. Then, the precipitate was filtered, and washed
with DMF (10 mL) and diethyl ether (10 mL) respectively. The
white solid was obtained after dried in 89% yield.
1H NMR (400 MHz, CDCl3): ppm; 13C NMR (100 MHz, DMSO):
d = 107.8 ppm; IR (KBr)
m: 1442, 1424, 1261, 1223, 949, 937,
637 cmꢁ1; HRMS (ESI) calcd for C4HI4N6 640.6436 [M+H], found
640.6440.
2.2.3. The synthesis of 3,30,5,50-tetrabromo-4,40-bis(1,2,4-triazole)
(TBBT)
The above solid (5.16 g, 24 mmol) was added to a round-bottom
flask with toluene (45 mL), and the solution was heated to 60 °C.
4-Amino-1,2,4-triazole (2.419 g, 28.8 mmol) was added. The
reaction was then heated from 60 °C to 90 °C at a rate of
BTz (680 mg, 5 mmol) was added to bromine (3 mL), and the
mixture was stirred for 2 days at room temperature. An aqueous
solution of potassium hydroxide (2 M) was added to the reaction
dropwise, until the color of the reaction changed into yellow. The

F. Lu et al. / Polyhedron 117 (2016) 445–452
447
N
N NH2
O
H
N
N
N
N
N
1. SOCl2
BTz
Yield: 90%
N N
N
N N
Yield: 89%
N
2HCl
N
Toluene, 90 o
C
2. N2H4 H2O
NPPh3
Br
NPPh3
Br
N
N
N
N
N
N
N
N
N
N N
N
r
2
B
N
a
N3
D
h 3
P
Br Br
TBBT
NPPh3NPPh3
M
N3 N3
N N
P
O
S
9
S
O
M
N
N
N
N
D
N
N
N N
BTz
N
Hydrolysis
I
2
N
,
H2
K
,
I
P
K
C
d
N3 N3
TABT
(83.99% N)
H2
O
/
C
I
I
H
C
NH2
NH2
NHBoc
NHBoc
l2
,
M
N
N
N
N
e
N
N
Boc2O, Et3N
N
N
NH2
O
N
N
N N
N
N
N N
H
N
N
I
I
NH2
10
NHBoc
NHBoc
TIBT
11
Scheme 1. Synthesis and reduction of TABT.
Table 1
yellow precipitates were filtered, washed with distilled water
(2 ꢃ 3 mL) and dried under vacuum. Similarly, the pure TBBT was
obtained in a good yield of 77%.
The halogenation reaction of BTz.
Entry
Reagent
Solvent
Product
Yield (%)
1a
2b
3c
4d
I2/KI
Br2
NBS
Br2
H2O
H2O
THF
–
TIBT
85
trace
28
1H NMR (400 MHz, CDCl3): ppm; 13C NMR (100 MHz, DMSO):
TBBT
TBBT
TBBT
d = 133.2 ppm; IR (KBr)
m: 1456, 1301, 1286, 1258, 943,
644 cmꢁ1; HRMS (ESI, m/z) calcd for C4HBr4N6 452.6950 [M+H],
found 452.6948; calcd for C4NaBr4N6 474.6918 [M+Na], found
474.6766.
77
a
BTz (10 mmol), solution of I2 (50 mmol, 5 equiv) and KI (60 mmol, 6 equiv) in
H2O (100 mL), KOH (2 M, 50 mL, 6 equiv), r. t., 48 h.
b
BTz (5 mmol), bromine (3 mL), H2O (3 mL), r. t., 2 d.
BTz (5 mmol), NBS (20 equiv) in THF (3 mL), r. t., 2 d.
BTz (5 mmol), bromine (3 mL), r. t., 2 d.
c
2.2.4. The synthesis of 3,30,5,50-tetraazido-4,40-bis(1,2,4-triazole)
(TABT)
d
NaN3 (94 mg, 1.2 mmol, 6 equiv) was added into the solution of
TBBT (90 mg, 0.2 mmol) in DMSO (2 mL) and distilled water
(0.2 mL), and then, the mixture was stirred for 10 h. After that,
distilled water (4 mL) was added to the reaction for the purpose
of finishing the reaction, and stirring for another 2 h to dissolve
out all of the precipitates. The precipitates were filtered carefully,
washed with petroleum ether, and dried in the air. At last, 37 mg
of TABT was obtained in the yield of 68%. A colorless single crystal
of TABT was obtained in the mixture of dichloromethane and
petroleum ether (1:1, V:V) in the condition of 0 °C.
Table 2
The synthesis of TABT with NaN3 in different solvents.
Entrya
Solvent
Yield (%)b
1
2
3
4
5
THF
DMF
trace
20
60
68
60
DMSO
DMSO/H2O (10:1, V:V)
DMSO/H2O (8:1, V:V)
a
TBBT (0.2 mmol), NaN3 (1.2 mmol, 6 equiv), solvent (2 mL), r. t., 10 h.
Yield after recrystallization.
b
Tdec = 125.39 °C (onset); 1H NMR (400 MHz, CDCl3): ppm; 13C
NMR (100 MHz, CDCl3): d = 146.6 ppm; IR (KBr)
m: 2143, 1530,
1394, 1237, 797, 700, 522 cmꢁ1; HRMS (ESI, m/z) calcd for
Table 3
The hydrogenation of TABT.a
C4HN18 301.0626 [M+H], found 301.0628.
Entry Catalyst Solvent
Conversion (%)d Yield (%)
0
1
PtO2
Pd/C
Pd/C
Pd/C
Pd/C
MeOH/CH2Cl2 (10 mL, 1:1)
MeOH/CH2Cl2 (10 mL, 1:1)
2.2.5. The synthesis of 3,30,5,50-tetraazayliden-4,40-bis(1,2,4-triazole)
(9)
2
trace
0
3
MeOH/CH2Cl2 (100 mL, 1:1) 100
MeOH/CH2Cl2 (100 mL, 1:1) 100
MeOH/CH2Cl2 (100 mL, 1:1) 100
0e
69f
0g
4b
5c
NaN3 (94 mg, 1.2 mmol, 6 equiv) was added into the solution of
TBBT (90 mg, 0.2 mmol) in DMSO (2 mL) and distilled water
(0.2 mL), and then, the mixture was stirred at room temperature
for 10 h. Then, triphenyl phosphine (419 mg, 1.6 mmol) was added,
and the reaction was stirred for additional 10 h. The precipitates
were filtered, washed with a small amount of distilled water
(10 mL) and a large number of diethyl ether. Then, the precipitates
were dried under vacuum, the yellow crude product was
recrystallized from methanol giving 9 in 71% yield.
a
b
c
d
e
f
TABT (0.5 mmol), catalyst (8 mol%), r. t., 12 h.
Boc2O (3 mmol) and trimethylamine (2 mmol) were added.
FmocCl (3 mmol) and trimethylamine (2 mmol) were added.
Conversion of TABT.
Yield of 10.
Yield of 11.
g
Yield of Fmoc-protected reduced product.
1H NMR (400 MHz, CDCl3): d = 7.73 (dd, J = 12.4, 8 Hz, 24H),
7.31 (t, J = 7.2 Hz, 12H), 7.09 (td, J = 7.6, 2 Hz, 24H) ppm; 13C
NMR (100 MHz, CDCl3): d = 152.7, 133.4, 131.2, 131.2,
128.2 ppm; 31P NMR (162 MHz, CDCl3, 85% H3PO4): d = 9.7 ppm;
2.2.6. The synthesis of 3,30,5,50-tetra(tert-butyloxycarbamido)-4,40-bis
(1,2,4-triazole) (11)
TABT (90 mg, 0.3 mmol) was dissolved in the mixed solution of
CH2Cl2 (30 mL) and MeOH (30 mL). Pd/C (40 mg, 0.03 mmol),
Boc2O (392 mg, 1.8 mmol) and trimethylamine (183 mg, 1.8 mmol)
were added to the solution. The reduction was performed under H2
IR (KBr)
751, 716, 691, 528, 492.5 cmꢁ1
76H61N10P4 1237.4026 [M+H], found 1237.4023.
m: 3050, 1521, 1482, 1435, 1373, 1328, 1186, 1111, 948,
;
HRMS (ESI, m/z) calcd for
C

448
F. Lu et al. / Polyhedron 117 (2016) 445–452
Table 5
The single crystal and structure modification data of TABT.
Entry
Data
Empirical formula
C4N18
Formula weight
300.22
T (K)
153
k (Å)
0.71073
monoclinic, P2(1)/c
Crystal system, space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
11.948(3)
8.7210(17)
12.495(3)
a
(°)
90
b (°)
116.249(2)
c
(°)
90
1167.7(4)
4, 1.708
0.137
V (Å3)
Z, Dcalc (g/cm3)
Absorption coefficient (mmꢁ1
F(000)
)
600
Crystal size (mm)
h (°)
0.30 ꢃ 0.23 ꢃ 0.13
2.96–29.15
Limiting indices
ꢁ15 6 h 6 16, ꢁ11 6 k 6 11,
ꢁ17 6 l 6 13
Reflections collected/unique
Completeness to h = 29.15
Absorption correction
11871/3132 [R(int) = 0.0336]
99.7%
none
full-matrix least-squares on F2
3132/0/199
Fig. 2. The single crystal structure of TABT.
Refinement method
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
1.004
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0448, wR2 = 0.1227
R1 = 0.0609, wR2 = 0.1310
0.570 and ꢁ0.257
Largest difference in peak and hole
(e Åꢁ3
)
atmosphere at room temperature for 24 h. The solid was strained,
then, the filtrate was concentrated into sticky residues. Faint
yellow solids were obtained with diethyl ether (8 mL) washing
the sticky materials, then, the crude product was washed three
times with diethyl ether to reach the pure product. The yield of
compound 11 is 69%.
Tdec = 268 °C. 1H NMR (400 MHz, DMSO): d = 6.73 (s, 4H), 1.51
(s, 36H) ppm; 13C NMR (100 MHz, DMSO): d = 147.7, 145.3, 82.7,
27.8 ppm; IR (KBr) m: 3357, 2994, 2922, 1770, 1757, 1667, 1383,
1245, 1057 cmꢁ1; HRMS (ESI) calcd for C24H41N10O8 597.3103
[M+H]; found 597.3106.
3. Results and discussion
3.1. Synthesis
Initially, we modified the process of Garcia [9b] and Li [9c] by
using toluene as the solvent and elevating the reaction
temperature stepwise from 60 °C to 90 °C over a period of 1.5 h,
thus the yield was improved up to 90%. Direct nitration of BTz turn
out to be failure as either the formation of mononitrate salt in
Fig. 3. The crystal packing of TABT.
Table 4
Selected bond lengths (Å), bond angles (o) and torsion angles (o) for TABT.
Bond
Length/Å
Bond
Length/Å
Bond
Length/Å
N(1)–N(2)
N(3)–N(4)
Angle
1.423(2)
1.3729(17)
/ °
N(1)–C(1)
N(3)–C(1)
Angle
1.294(2)
1.373(2)
/ °
N(5)–N(6)
C(1)–N(7)
Angle
1.4178(19)
1.396(2)
/ °
C(2)–N(3)–C(1)
104.74(12)
171.81(17)
106.68(19)
ꢁ87.3(2)
N(2)–C(2)–N(3)
111.03(14)
115.62(14)
ꢁ0.59(19)
1.35(18)
1.72(18)
–0.26(18)
C(2)–N(2)–N(1)
N(2)–C(2)–N(10)
N(1)–N(2)–C(2)–N(10)
N(2)–N(1)–C(1)–N(7)
N(5)–N(6)–C(4)–N(16)
N(6)–N(5)–C(3)–N(13)
106.66(13)
131.26(15)
179.70(17)
ꢁ177.00(16)
ꢁ179.76(16)
177.53(16)
N(12)–N(11)–N(10)
C(1)–N(3)–N(4)–C(3)
C(1)–N(3)–N(4)–C(4)
C(2)–N(3)–N(4)–C(3)
C(2)–N(3)–N(4)–C(4)
N(11)–N(10)–C(2)
N(1)–N(2)–C(2)–N(3)
N(2)–N(1)–C(1)–N(3)
N(5)-N(6)-C(4)-N(4)
N(6)–N(5)–C(3)–N(4)
ꢁ62.5(2)
103.5(2)

F. Lu et al. / Polyhedron 117 (2016) 445–452
449
Table 6
Subsequently, iodo and bromo-BTz were prepared (Scheme 1).
Treatment of BTz with I2/KI in aqueous KOH produced the desired
3,30,5,50-tetraiodo-4,40-bis(1,2,4-triazole) (TIBT) in 85% yield
(Table 1, entry 1) [10a], which is higher than that with ICl [11].
Similarly, 3,30,5,50-tetrabromo-4,40-bis(1,2,4-triazole) (TBBT) was
obtained in 77% yield by treatment of BTz in liquid bromine (entry
4) while the yield was only 28% in THF (entry 3), and even less in
aqueous bromine (entry 2). The effort to synthesize the chloro-BTz
was declared unsuccessful after screening a few normal chloro
reagents such as NCS. However, nitration of TIBT and TBBT was
turn out to be failure again.
The single crystal and structure modification data of 9 2MeOHꢀ2H2O.
Entry
Data
Empirical formula
Formula weight
T (K)
k (Å)
Crystal system, space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
C
78H72N10O4P4
1337.34
163(2)
0.71073
monoclinic, C2/c
27.840(6)
14.094(2)
20.900(4)
90
a
(°)
Then, another strategy of transformation of amino into nitro
group by oxidation was explored. Considering the electron density
on triazole rings of BTz was decreased by halogenation, nucleophilic
substitution of TBBT and TIBT with sodium azide was investigated. It
was found that only TBBT was converted to a high-nitrogen
energetic compound 3,30,5,50-tetraazido-4,40-bis(1,2,4-triazole)
(TABT) with NaN3 in DMSO, while TIBT gave no conversion
(Scheme 1). Solvent affected the yield greatly. As shown in Table 2,
DMSO gave higher yield than DMF and THF as the low solubility of
NaN3 in them (Table 2, entry 3 versus entries 1–2). Small volume of
water in DMSO (DMSO/H2O, 10:1, V/V) increased the yield of TABT
to 68% after recrystallization from CH2Cl2 (entry 4) while more
water in DMSO (DMSO/H2O, 8:1, V/V) reduced the yield to 60%
(entry 5).
b (°)
122.302(2)
90
6932(2)
8, 1.281
0.168
2808
c
(°)
V (Å3)
Z, Dcalc (g/cm3)
Absorption coefficient (mmꢁ1
F(000)
)
Crystal size (mm)
h (°)
Limiting indices
0.64 ꢃ 0.36 ꢃ 0.29
2.31–29.15
ꢁ30 6 h 6 38, ꢁ19 6 k 6 19,
ꢁ28 6 l 6 28
Reflections collected/unique
Completeness to h = 29.15
Absorption correction
30278/9232 [R(int) = 0.0347]
98.6%
semi-empirical from equivalents
full-matrix least-squares on F2
9232/0/447
Refinement method
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
0.999
Final R indices [I > 2
R indices (all data)
Extinction coefficient
Largest difference in peak and hole
(e Åꢁ3
r(I)]
R1 = 0.0636, wR2 = 0.1727
R1 = 0.0679, wR2 = 0.1769
0.0008(2)
0.749 and ꢁ0.581
The Staudinger process [10b] with triphenyl phosphine was
chosen to reduce TABT. Unfortunately, the highly hindered
3,30,5,50-tetraazaylide-4,40-bis(1,2,4-triazole) (9) was isolated
quantitatively instead of the desired tetraamino product 10 while
the N = N linker analogue 2 was readily reduced to the tetraamino
)
derivative [5]. Effort to hydrolysis
hydrochloride, trifluoroacetic acid and aqueous ammonia.
9 was unsuccessful with
acidic medium, the same result with Shreeve [9d] or no conversion
with neutral nitrating reagent. Further effort to dehydrate the
bis-1,2,4-triazolium mononitrate salt was unsuccessful. Consider-
ing the readily complexation with metals of the electron-rich
N1-N2 in BTz thus avoiding the formation of nitrate salt, nitration
of the formed copper(II) complex [9e] with fuming HNO3/Ac2O but
resulted in the collapse of the bistriazole skeleton without any
desired TNBT. Therefore, nitronium halogen exchange strategy
was then conducted toward the synthesis of TNBT.
Next, hydrogenation of TABT was studied. As shown in Table 3,
Pd/C catalyzed the reduction effectively while the isolation was
problematic probably because of either the strong absorption of
ammine on the surface of carbon or the bad open-to-air stability
of 10, or both (entry 3 versus 2). At last, TABT was successfully
transferred into N-Boc-protected 11 in 69% yield under H2 atmo-
sphere in the mixture solvent of MeOH and CH2Cl2 (entry 4) while
the N-protection was unsuccessful in the case of FmocCl (entry 5).
Fig. 4. The crystal packing of 9ꢀ2MeOHꢀ2H2O.

450
F. Lu et al. / Polyhedron 117 (2016) 445–452
Fig. 5. The single crystal structure of 9ꢀ2MeOHꢀ2H2O.
Table 7
Selected bond lengths (Å), bond angles (°) and torsion angles (°) for 9ꢀ2MeOHꢀ2H2O.
Bond
Length/Å
Bond
Length/Å
Bond
Length/Å
1.354(2)
N(1)–N(2)
N(3)–N(3)#1
Angle
1.429(2)
1.364(3)
/ °
N(1)–C(1)
N(3)–C(1)
Angle
1.307(2)
1.381(2)
/ °
C(1)–N(7)
Angle
/ °
C(2)–N(3)–C(1)
N(2)–C(2)–N(10)
N(2)–N(1)–C(1)–N(3)
C(2)–N(3)–C(1)–N(4)
107.49(14)
133.03(17)
0.1(2)
ꢁ179.52(16)
N(2)–C(2)–N(3)
108.17(14)
178.61(19)
ꢁ162.64(18)
1.2(2)
C(2)–N(2)–N(1)
C(1)–N(1)–N(2)–C(2)
C(2)–N(3)–C(1)–N(1)
108.25(15)
0.6(2)
ꢁ0.8(2)
N(2)–N(1)–C(1)–N(4)
N(3)#1–N(3)–C(1)–N(1)
C(1)–N(3)–C(2)–N(2)
3.2. X-ray crystallography
the theoretical value (1.29 Å versus 1.28 Å) [13] suggesting the
electron delocalization to some extent in the triazole rings. More-
over, the linkage N3–N4 bond length (1.3729 Å), close to the short-
ened CAN single bond length (1.37 Å) of the triazole ring, is much
shorter than both the theoretical N–N (1.45 Å) and the N1–N2 or
N5–N6 bond length (1.423 Å or 1.418 Å) in the triazole ring.
Therefore, the electron delocalization within two triazole rings
and the perpendicular configuration between them stabilize such
high-nitrogen compound TABT.
The single crystal of TABT suitable for X-ray analysis was
cultivated by freely evaporation of solvent in the solution of
dichloromethane and petroleum ether (1:1, V/V) at 0 °C.
Figs. 2 and 3 showed the single crystal structure and the crystal
packing of TABT. Table 5 showed that TABT crystalizes in the mon-
oclinic space group P21/n. Table 4 listed some selected bond
lengths and dihedral angles [12].
From the small torsion angles within each triazole ring it is con-
cluded that both triazole rings adapt nearly planar configuration.
The orthogonality of the two azido groups on each ring is benefit
to minimize the steric hindrance between and within two triazole
rings. Comparing with the structure of BTz [9c], the dihedral angles
of C1–N3–N4–C4, C1–N3–N4–C3, C2–N3–N4–C4 and C2–N3–N4–
C3 are ꢁ87.3°, 106.7°, 103.5°, and ꢁ62.5°, respectively, which indi-
cate that four azido groups in TABT caused a slight deviation from
the perpendicular configuration in BTz. The CAN single bonds are
much shorter than the standard (1.37 Å versus 1.47 Å) while the
C@N double bonds length in the two triazole rings are close to
The single crystal of 9 suitable for X-ray analysis was obtained
from a solution of MeOH/H2O at 0 °C while the single crystal of
compound 11 wasn’t successfully cultivated with variety of
methods.
Table
6
shows that 9ꢀ2MeOHꢀ2H2O crystallizes in the
monoclinic space group C2/c. It’s crystal packing and molecular
structure are shown in Figs. 4 and 5 [12]. The crowded hydropho-
bic ylide outsphere may be attributed to the failure hydrolysis of
the Staudinger intermediate 9.
The torsion angles of C(1)–N(1)–N(2)–C(2), N(2)–N(1)–C(1)–N
(3), C(2)–N(3)–C(1)–N(1) and C(1)–N(3)–C(2)–N(2) are 0.6°, 0.1°,

F. Lu et al. / Polyhedron 117 (2016) 445–452
451
Fig. 6. DSC curve of TABT.
Fig. 7. TGA curve of TABT.
ꢁ0.8°, and 1.2°, respectively (Table 7), which indicate triazole rings
within the triazole rings of 9ꢀ2MeOHꢀ2H2O adapt nearly planar
configuration.
The CAN single bonds within trizole rings are longer than the
bands in TABT (1.38 Å versus 1.37 Å) while the C@N double bonds
length in the two triazole rings are longer than the bands in TABT
(1.30 Å versus 1.29 Å) suggesting that the electron delocalization of
9ꢀ2MeOHꢀ2H2O is stronger than TABT. Moreover, the linkage
N3–N3#1 bond length is 1.364 Å, which is shorter than the band
length in TABT (N3–N4, 1.37 Å) and the theoretical bands length

452
F. Lu et al. / Polyhedron 117 (2016) 445–452
(N–N, 1.45 Å). Meanwhile, the linkage N3–N3#1 bond length is
shorter than the band length of N1–N2 (1.364 Å versus 1.429 Å)
in the triazole ring.
be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223
336 033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.poly.2016.06.025.
3.3. Thermal stability of TABT
The thermal stability of TABT was measured by differential
scanning calorimeter (DSC) and thermogravimetric analysis (TGA).
DSC was carried out from 50 °C to 400 °C at a heating rate of
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This research is financially supported by NSFC (21372027,
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Appendix A. Supplementary data
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CCDC 1434592 and 1443122 contains the supplementary
crystallographic data for TABT and 9, respectively. These data can