5-(1,2,3-Triazol-l-yl)tetrazole derivatives of an azidotetrazole via click chemistry

Article abstract of DOI:10.1002/chem.200901029

N-C bonded (non-bridged) 5-(l,2,3-triazol-1-yl)tetrazoles were synthesized by the Cu-catalyzed 1,3-dipolar azide-alkyne cycloaddition click reaction using 5-azido-N-(propan-2-ylidene)-1H-tetrazole (1). For example, the click reaction of 1 in the presence

Full text of DOI:10.1002/chem.200901029

FULL PAPER
DOI: 10.1002/chem.200901029
5-(1,2,3-Triazol-1-yl)tetrazole Derivatives of an Azidotetrazole via Click
Chemistry
Takashi Abe,[a] Guo-Hong Tao,[a] Young-Hyuk Joo,[a] Rolf W. Winter,[b]
Gary L. Gard,[b] and Jean’ne M. Shreeve*[a]
ꢀ
ꢁ
Abstract: N C bonded (non-bridged)
and SF5C CH (2b), giving rise to iso-
propylidene-[5-(4-trifluoromethyl-1,2,3-
conditions using CuI and 2,6-lutidine as
catalysts at 08C for 13 h in CHCl3, the
click reaction was versatile toward al-
kynes even those having electron-do-
nating groups. Properties of new prod-
ucts were determined and compared
with those of 1. Heats of formation,
detonation pressures, detonation veloc-
ities and impact sensitivities are report-
ed for these new 5-(1,2,3-triazol-1-yl)-
tetrazoles.
5-(1,2,3-triazol-1-yl)tetrazoles were syn-
thesized by the CuI-catalyzed 1,3-dipo-
lar azide–alkyne cycloaddition click re-
action using 5-azido-N-(propan-2-yli-
dene)-1H-tetrazole (1). For example,
the click reaction of 1 in the presence
of CuSO4·5H2O and Na ascorbate at
65–708C for 48 h in CH3CN/H2O co-
solvent was found to be limited to only
terminal alkynes that have electron-
triazol-1-yl)tetrazol-1-yl]amine
(3a)
and isopropylidene-[5-(4-pentafluoro-
sulfanyl-1,2,3-triazol-1-yl)tetrazol-1-yl]-
amine (3b) in 47% and 66% yields, re-
spectively. When carried out under
Keywords: azoles · click chemistry ·
energetic materials · heterocyclic
compounds · tetrazoles
ꢁ
withdrawing groups, CF3C CH (2a)
Introduction
azoles or bicyclic azolium salts is the reaction using precur-
sor rings substituted with a halogen, nitro, or methylsulfonyl
moiety as a leaving group.[3] For example, the reactions of
sodium 1,2,4-triazolate with the methylsulfonyl-substituted
azoles, 2-methyl-5-(methylsulfonyl)-2H-tetrazole and 1-
methyl-5-(methylsulfonyl)-2H-tetrazole, the corresponding
The synthesis of energetic heterocyclic compounds has at-
tracted considerable interest in recent years, especially for
the syntheses and applications of new members of heterocy-
clic-based energetic materials.[1] Therefore, the development
of versatile synthetic methods is of great importance for ex-
ploration of energetic materials. High-nitrogen compounds
constitute a unique class of energetic materials. Five-mem-
bered nitrogen-containing heterocycles are traditional sour-
ces of energetic materials, and much attention is currently
focused on bicyclic azoles in this role.[2] Many papers have
ꢀ
2- and 1-methyl-5-(1,2,4-triazol-1-yl)tetrazole, which are N
C bonded (nonbridged) triazolyltetrazoles, are obtained, re-
spectively,[3c] (Scheme 1).
ꢀ
dealt with the preparation of bridged and/or N C bonded
(non-bridged) bicyclic azoles. One of the fundamental meth-
ꢀ
Scheme 1. Several N C bonded (nonbridged) and/or bridged triazolylme-
thyltetrazoles.
ꢀ
ods known for the preparation of N C bonded bicyclic
Earlier, we reported that 5-[(4-pentafluorosulfanyl)-1,2,3-
triazol-1-yl]methyl-1H-tetrazole, which is a bridged 1,2,3-tri-
azolyltetrazole, was formed by the CuI-catalyzed 1,3-dipolar
[a] Dr. T. Abe, Dr. G.-H. Tao, Dr. Y.-H. Joo, Prof. Dr. J. M. Shreeve
Department of Chemistry, University of Idaho
Moscow, ID 83844-2343 (USA)
Fax : (+1)208-885-9146
E-mail: jshreeve@uidaho.edu
cycloaddition of 5-[(4-pentafluorosulfanyl)-1,2,3-triazol-1-
[4]
ꢁ
yl]azidomethane with SF5C CH (Scheme 1). Similarly, bi-
[b] Dr. R. W. Winter, Prof. G. L. Gard
Department of Chemistry, Portland State University
Portland, OR 97207 (USA)
ꢀ
cyclic azoles consisting of two N C bonded (nonbridged)
triazoles have been prepared by click reactions of azidetri-
AHCTUNGTRENNUNG
azoles with alkynes.[5] Although a considerable number of
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200901029.
ꢀ
N C bonded (nonbridged) triazolyltetrazoles have been
Chem. Eur. J. 2009, 15, 9897 – 9904
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
9897

synthesized by several synthetic methods, we believe that bi-
CuSO4·5H2O and sodium ascorbate at 60–708C for 48 h in a
CH3CN/H2O co-solvent system, the outcome of the reaction
varied drastically depending on the alkyne (Table 1).
ꢀ
cyclic azoles in the form of N C bonded (nonbridged) 5-
(1,2,3-triazol-1-yl)tetrazoles have not been reported.
We are interested in using 5-azido-N-(propan-2-ylidene)-
1H-tetrazole (1),[6a] as a starting material for the synthesis of
ꢀ
Table 1. CuI catalyzed 1,3-dipolar cycloaddition of alkyne and azide.
N C bonded (nonbridged) 1,2,3-triazolyltetrazoles (3) with
ꢁ
various terminal alkynes (2) including CF3C CH (2a) and
ꢁ
SF5C CH (2b) via click reactions; then, subsequently, to
evaluate 3 as energetic materials comparing the properties
with those of 1. Structural differences have an impact on the
heat of formation for which 5-(1,2,3-triazolyl)tetrazole, as
the product of a click reaction rather than the 5-(1,2,4-tri-
ACHTUNGTRENNUNGazolyl)tetrazole isomer, has the higher heat of formation
Entry
Alkyne
Product
Method A[a]
yield [%]
Method B[b,c]
yield [%]
(270 kJmolꢀ1 vs. 193 kJmolꢀ1 based on G3 calculation).[4]
We report the straightforward synthesis of several new
1
2
3
4
5
6
7
8
2a
2a
2b
2c
2d
2e
2 f
2g
3a
3a
3b
3c
3d
3e
3 f
3g
47[c]
20[d]
66[c]
0[e]
0[e]
0[e]
0[e]
–
53
–
ꢀ
N C bonded (nonbridged) 5-(1,2,3-triazol-1-yl)tetrazoles via
CuI-catalyzed 1,3-dipolar azide–alkyne cycloaddition click
reactions of 5-azido-N-(propan-2-ylidene)-1H-tetrazole (1).
Their thermal, physical, and energetic properties were stud-
ied in detail.
48
34
62
67
14[f]
40
[a] A solution of alkyne (2–3 mmol), azide (1.3–1.5 mmol), CuSO4·5H2O
(10 mol%), Na ascorbate (5 mol%) in CH3CN/H2O was stirred for 48 h
at 708C. [b] A solution of alkyne (1.3–1.5 mmol), azide (1.5–2.5 mmol),
2,6-lutidine (1.5–2.5 mmol), and CuI (10 mol%) in CHCl3 stirred for 13 h
at 08C. [c] Yield of isolated product after chromatography. [d] Yield of
isolated product after recrystallization. [e] Azide recovered (10–48%) to-
gether with the formation of N1-isopropylidenetetrazole-1,5-diamine (4)
(Yield: 5–32%). [f] Isolated as a mixture with N1-isopropylidenetetra-
zole-1,5-diamine (4) (1:0.4).
Results and Discussion
Recently, we reported that the trifluoromethylazo group
(CF3-N=N-) is transformed into the (5-azido-1H-tetrazol-1-
yl)imino moiety by taking advantage of the activation of the
C F bond by the reaction with sodium azide. For example,
from the reaction of isopropyl(trifluoromethyl)diazene with
sodium azide, 5-azido-N-(propan-2-ylidene)-1H-tetrazole (1)
is formed in good yield. This compound was used as the
starting azide for click reactions with alkynes (2a–g) to
obtain new 1,2,3-triazolyltetrazoles (3a–g) (Scheme 2). 1,3-
[6]
ꢀ
Method A: Except for 2a and 2b, in which electron-with-
drawing substituents (CF3- and SF5-) are attached to the
triple bond, alkynes, 2c--f, did not react with 1 under the
same reaction conditions applied for 2a and 2b. From the
reactions of 1 with 2a and 2b, the corresponding isopropyli-
dene-[5-(4-trifluoromethyl-1,2,3-triazol-1-yl)tetrazol-1-yl]am-
AHCTUNGERTGiNNUN ne, 3a, and isopropylidene-[5-(4-pentafluorosulfanyl-1,2,3-
triazol-1-yl)tetrazol-1-yl]amine, 3b, were formed in 47%
and 66% yield, respectively (Entries 1 and 3). Whereas, in
the reactions with 2c–f, starting material 1 was recovered
(10–48%) together with N1-isopropylidenetetrazole-1,5-di-
Scheme 2. Preparation of 5-(1,2,3-triazol-1-yl)tetrazoles (3a–g) from 1 by
CuI catalyzed 1,3-dipolar cycloaddition.
AHCTUNGTRENNUNG
amine, 4,[9] which was formed as a byproduct (5–32%). In a
separate experiment, which was carried out in the absence
of alkyne under the same reaction conditions, the azido
group of 1 was found to decompose into an amino group to
yield 4 (yield 20%).
Dipolar cycloaddition via click reactions has been estab-
lished as one of the most reliable methods for the covalent
assembly of complex molecules. It has enabled a number of
applications in synthesis, medicinal chemistry, molecular
biology, and material science.[7]
We find that 1 reacts with several terminal alkynes, 2a–g,
yielding 1,4-disubstituted 1,2,3-triazole products regioselec-
tively. No 1,5-disubstituted 1,2,3-triazole products were
formed.[8] However, the formation and the yield of the click
products are strongly dependent on the reaction conditions
and the alkynes employed. When the reactions of 1 with al-
kynes, 2a–f, were carried out in the presence of
It is known that the more electron-withdrawing substitu-
ents on the alkyne, the easier that cycloaddition occurs, and
strong electron-donating substituents on the azides favor
that reaction. Bulky substituents on the acetylene sterically
hinders the cycloaddition lowering the reaction rate.[10] As
CF3- and SF5- groups are typical electron-withdrawing sub-
stituents, the alkynes 2a and 2b, which have these groups,
exhibit enhanced reactivity. In addition, it has been reported
that 1,3-dipolar cycloadditions with electron-rich dipolaro-
philes are accelerated in water and protic co-solvents,
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Chem. Eur. J. 2009, 15, 9897 – 9904

Tetrazole Derivatives of an Azidotetrazole
FULL PAPER
whereas an aqueous medium has no specified effects when
electron-poor dipolarophiles are involved.[11] The beneficial
effect of an CH3CN/H2O co-solvent system in this case is at-
tributable to the enhanced hydrophobic interactions occur-
ring between the substrates during the activation process,
which favors the reaction. As CF3- and SF5- groups are typi-
cal electron poor substituents, hydrophobic interactions in
the CH3CN/H2O co-solvent system were considered to be
the prime accelerating factor for the rate enhancement in
the reactions using 2a and 2b. Therefore, these factors fa-
vored the reaction of 1 with 2a and 2b under these reaction
conditions (Entries 1, 2 and 3 in Table 1).
1584–1590 cmꢀ1, owing to asymmetric stretching of -N=C-
AHCTUNGTRENNG(UN CH3)2. Their physicochemical properties (melting point, de-
composition temperature, and density) are shown in Table 2.
Table 2. Melting points (M.p.), decomposition points (Td), density, heats
of formation (DH8f), and detonation pressure (P), and detonation veloci-
ty (D) of the energetic materials.
[a]
M.p. Td
d[b]
[gcmꢀ3
DHof [c]
[kJmolꢀ1
DHof [c]
[kJgꢀ1
P[d]
[GPa]
D[d]
[msꢀ1
IS[e]
[J]
[8C] [8C]
N
]
G
]
E
]
G
N
]
1
67
149 1.36
162 1.44
162 1.64
168 1.43
177 1.45
164 1.27
169 1.17
730.5
4.39
16.5
11.8
16.2
13.3
12.4
10.5
10.4
7251
6160
6777
6543
6315
5995
6184
–
3a 64
3b 76
3c 125
3d 172
3e 122
ꢀ37.9
ꢀ0.15
ꢀ0.99
2.61
1.75
1.79
40
35
35
35
40
–
ꢀ315.9
699.4
499.7
581.1
512.1
Method B: After several attempts to optimize the click reac-
ꢁ
tion of 1 with other alkynes, 2c–f, and n-C4H9C CH, 2g, it
3g
–
2.06
[a] DSC under nitrogen, 108C minꢀ1
. [b] Gas pycnometer (258C).
was found that the application of similar reaction conditions
as described earlier, i.e., using CuI and 2,6-lutidine as the
catalyst at 08C for 13 h in CHCl3, enabled the reactions to
occur with alkynes, 3c–g, giving rise to the corresponding
products in low to moderate yields[12] (Table 1). Among the
click products, 3a–g, isopropylidene-[5-(4-hydroxymethyl-
1,2,3-triazol-1-yl)tetrazol-1-yl]amine, 3 f, was obtained as a
mixture with 4 (1:0.4). Purification using column chromatog-
raphy was not successful (Entry 6).The click products were
[c] Heats of formation. [d] Calculated using Cheetah 5.0. [e] Impact sensi-
tivity.
Compounds 3a and 3b have lower melting points (64 and
768C, respectively) compared with those of 3c–e (122–
1728C). Decomposition temperatures, Td, of 3a–e, 3g are in
the range of 162–1788C. The Td for 3a and 3b are the same
(1628C), which implies that in this case Td is independent of
the perfluoroalkyl substituent (CF3- and SF5-).
1
characterized by H, and 13C NMR, and IR spectra, and ele-
mental analysis, and those of 3b–e were unambiguously con-
firmed by single crystal X-ray diffraction analysis. Thermal
ellipsoid plots of 3b–e are given in Figures 1–4, respectively.
Compounds 3a–e are solids, while 3 f and 3g are liquids.
In the IR spectra, typical strong bands were observed at n˜ =
It is known that the incorporation of perfluoroalkyl moi-
eties into organic compounds increases density considerably.
ꢁ
ꢁ
By the introduction of CF3C CH and SF5C CH group into
1, the densities of 3a (1.44 gcmꢀ3) and 3b (1.64 gcmꢀ3) were
increased by 0.08 gcmꢀ3 and 0.28 gcmꢀ3, respectively, when
compared with 1 (1.36 gcmꢀ3)[6a] showing the impact of the
SF5- group is nearly 0.2 gcmꢀ3 greater than that of the CF3-
group. This result was in agreement with our finding that
the SF5- group influences density more than CF3- by the
order of ꢂ0.3 gcmꢀ3.[4] Density is one of the most important
properties of energetic materials, since density is a critical
factor that, according to a semi-empirical equation suggest-
ed by Kamlet and Jacobs, affects detonation performance;
detonation pressure (P) is dependent on the square of the
density, and the detonation velocity (D) is proportional to
the density.[13] However, since
1 has a low density
(1.36 gcmꢀ3),[6a] densities of the products including 3a and
3b are low with values in the range of 1.17–1.64 gcmꢀ3, lead-
ing to low detonation performances as energetic materials.
Impact sensitivity tests were carried out using a BAM
Fallhammer method.[14] 5-Azido-N-(propan-2-ylidene)-1H-
tetrazole, 1, is a very impact sensitive material which explo-
des at ꢃ1 J.[6a] However, after the introduction of the termi-
nal alkynes into 1, the impact sensitivities of products 3a–e
are reduced (IS=35–40 J).[15]
Structure: Compounds 3b–e were characterized by single
crystal X-ray structure analysis. Single crystals were grown
either in CHCl3 or in CH3OH. The crystallographic data of
3b–e are summarized in Table 3. The structure of compound
3b was solved in the space group Pbca by analysis of sys-
Figure 1. Top: Molecular structure of 3b (thermal displacement at 30%
probability). Hydrogen atoms are unlabelled for clarity. Bottom: Packing
diagram of 3b with hydrogen atoms omitted for clarity.
Chem. Eur. J. 2009, 15, 9897 – 9904
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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9899

J. M. Shreeve et al.
Table 3. Crystallographic data and structure refinement parameters.
mean plane of the ring
(Figure 3). The bond length of
the tetrazole linked to the
newly formed triazole was
ꢀ
3b
3c
3d
3e
formula
Mr
C6 H7F5N8S
318.26
C12H12N8
268.30
C12H11FN8
286.29
monoclinic
P21/c
10.4825(17)
11.904(2)
10.5344(18)
105.653(2)
1265.8(4)
4
93(2)
0.71073
1.502
0.112
0.42ꢂ0.21ꢂ0.03
ꢀ13ꢃhꢃ13
ꢀ15ꢃkꢃ15
ꢀ13ꢃlꢃ14
1.036
C16H20N8
324.40
triclinic
¯
P1
5.6911(17)
12.278(4)
12.889(4)
80.216(5)
865.3(4)
2
93(2)
0.71073
1.245
crystal system
space group
a [ꢁ]
b [ꢁ]
c [ꢁ]
orthorhombic
Pbca
10.1922(7)
8.7940(6)
27.1500(18)
90
monoclinic
P21/c
found
to
be
C6 N1=
1.3932(14) ꢁ which is longer
than the bond length (1.3881 ꢁ)
10.496(2)
12.299(3)
10.502(2)
100.409(3)
1333.4(5)
4
ꢀ
of the C N3 bond of 1.
b [ꢁ]
The molecular structural data
and the packing of 3e[20]
(Figure 4) are very similar to
that of 3d. The space group is
V [ꢁ3]
Z
2433.5(3)
8
T [K]
293(2)
296(2)
l [ꢁ]
0.71073
1.737
0.335
0.71073
1.336
0.091
1calcd [Mgm3]
P1. The imino group of tetra-
¯
m [mmꢀ1
]
0.082
zole and the hydrogen of the
triazole ring are on opposite
sides from each other forming a
dihedral angle of ꢂ208 to the
mean plane of the tetrazole
crystal size [mm]
index ranges
0.28ꢂ0.25ꢂ0.19
ꢀ13ꢃhꢃ13
ꢀ11ꢃkꢃ11
ꢀ36ꢃlꢃ33
1.047
0.26ꢂ0.20ꢂ0.04
ꢀ12ꢃhꢃ12
ꢀ14ꢃkꢃ14
ꢀ12ꢃlꢃ12
1.028
0.27ꢂ0.12ꢂ0.08
ꢀ7ꢃhꢃ7
ꢀ16ꢃkꢃ16
ꢀ15ꢃlꢃ17
1.005
GOF
R1[a] [I>2s(I)]
0.0396
0.1071
0.0464
0.1154
0.0353
0.0897
0.0506
0.1254
ꢀ
ring with N10 C5=1.386(2) ꢁ
[a]
wR2 [I>2s (I)]
(Figure 4). The extended struc-
ture, Figure 4 (bottom), shows
that the triazolyl tetrazole rings
[a] R1 =SjjFo jꢀjFc jj/SjFo j ; wR2 ={S[w(F2oꢀFc2)2]/S[w(Fo2)2]}1/2
.
tematic absences.[16] In 3b, the tetrazole linked to the newly
stack in the ab plane and the triazolyl tetrazole groups point
ꢀ
ꢀ
formed triazole with a N C bond (C5 N10=1.396(2) ꢁ)
towards each other and are stacked in a stepped fashion.
(Figure 1). Compared with the bond length (1.3881 ꢁ) of
[6a]
ꢀ
the C N3 bond of 1, an elongation of the bond (0.008 ꢁ)
was observed. This bond length is between the typical C N
ꢀ
single bond length (1.475 ꢁ) and the typical C=N double
bond length (1.320 ꢁ).[17] This means that two heterocycle
rings form a conjugated structure. Two rings present in 3b
were found to be almost co-planar with a dihederal angle of
only 0.78. The large bicyclic conjugated structure may de-
crease the energy of the whole molecule. The hydrogen
atom bonded to the triazole ring and the imino group, which
is on the tetrazole ring, are on the same side, but the imino
group is in an anti facial position to it.
The structure of molecule 3c[18] (Figure 2) shows similari-
ties to 3b. The space group is P21/c. The hydrogen atom of
triazole and the imino group of tetrazole are at the same
side, but the imino group is antifacial to it. The tetrazole
linked to the newly formed triazole has a bond length of
ꢀ
C1 N6=1.378(3) ꢁ which is shorter than that (1.3881 ꢁ) of
ꢀ
ꢀ
the C N3 bond of 1. Accordingly, the C1 N6 bond length in
3c strongly suggests a conjugated structure similar to that in
3b. Moreover, the bond between the trizole ring and the
phenyl ring also shows some double bond character. The
ꢀ
ꢀ
C4 C15 bond length (1.453 ꢁ) is between the typical C C
single bond length (1.541 ꢁ) and the typical C=C double
bond length (1.337 ꢁ).[17] Therefore, the crystal structure of
3c is a large tricyclic conjugated one which consists of a tri-
ACHTUNGTRENNUNG
group of 3d is also P21/c. Compared with the structure of
3c, a difference was observed for 3d[19] with respect to the
position of the imino group of tetrazole and the proton of
the triazole ring. The triazole ring is twisted back towards
the tetrazole ring and forms a dihedral angle of ꢂ158 to the
Figure 2. Top: Molecular structure of 3c (thermal displacement at 30%
probability). Hydrogen atoms are unlabelled for clarity. Bottom: Packing
diagram of 3c with hydrogen atoms omitted for clarity.
9900
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Chem. Eur. J. 2009, 15, 9897 – 9904

Tetrazole Derivatives of an Azidotetrazole
FULL PAPER
Figure 4. Top: Molecular structure of 3e (thermal displacement at 30%
probability). Hydrogen atoms are unlabeled for clarity. Bottom: Packing
diagram of 3e with hydrogen atoms omitted for clarity.
presence of the CF3 and SF5 group, respectively. In 3b, the
SF5 group significantly increases the density of the com-
pound, while it also introduces a concomitant decrease of
the heat of formation. Compound 3c exhibits the highest
heat of formation (699.4 kJmolꢀ1). In comparison with 3c,
the heat of formation for 3d is decreased by about
200 kJmolꢀ1 which was suggested to be caused by the pres-
ence of a fluorine atom. Different from the fluorine-contain-
ing groups in 3a, 3b and 3d, the substituent groups such as
phenyl and n-butyl groups in 3c and 3 f contribute to in-
crease the heat of formation inversely.
Figure 3. Top: Molecular structure of 3d (thermal displacement at 30%
probability). Hydrogen atoms are unlabelled for clarity. Bottom: Packing
diagram of 3d with hydrogen atoms omitted for clarity.
Theoretical study: Theoretical computations were per-
formed by using the Gaussian 03 (Revision D.01) suite of
programs.[21] The geometric optimization and the frequency
analyses are carried out at the level of Becke three Lee–
The detonation pressures (P) and velocities (D) of the tri-
azolyltetrazoles were calculated based on traditional Chap-
man–Jouget thermodynamic detonation theory by using
Cheetah 5.0.[25] These new 1,2,3-triazolyltetrazoles exhibit
detonation pressures more than 10 GPa and detonation ve-
locities more than 6000 msꢀ1. Their detonation properties
are very low except for 3b which has better values compara-
tively due to its higher density introduced by the SF5 group.
Yan–Parr (B3LYP) parameters up to 6-31+GACTHNURGTNE(NUG d,p) basis
sets.[22] All of the optimized structures were characterized to
be true local energy minima on the potential energy surface
without imaginary frequencies. The heats of formation of
the products were determined by using the method of iso-
desmic reactions (Scheme 3).[23] The enthalpy of reaction
(DHro298) is obtained by combining the MP2/6-311++G**[24]
energy difference for the reaction, the scaled zero point en-
ergies, and other thermal factors. The heats of formation in
the solid phase were calculated by using 20 kcalmolꢀ1 as the
enthalpy of sublimation for each compound. The data for
3a–f were calculated and are summarized in Table 2.
Conclusions
ꢀ
A straightforward synthesis for new bicyclic azoles, N C
bonded (nonbridged) 5-(1,2,3-triazol-1-yl)tetrazoles via click
reactions is described. The yields of products depend on the
reaction conditions and terminal alkynes used. Reactions of
1 with phenylacetylenes, 2c–e, gave rise to large conjugated
tricyclic compounds (a triazole, a tetrazole and a phenyl
ring), which are found to be almost co-planar. The new 5-
(1,2,3-triazol-1-yl)tetrazoles were fully characterized includ-
ing calculation of their thermal and detonation properties.
The heats of formation of triazolyltetrazoles are clearly
affected by the groups attached on the 1,2,3-triazole ring.
The heats of formation of compounds are greatly reduced if
they have fluorine-containing substituents. For example, 3a
and 3b have negative heats of formation arising from the
Chem. Eur. J. 2009, 15, 9897 – 9904
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9901

J. M. Shreeve et al.
APEX2 [v2.1–0].[26] Data Reduction
was
performed
using
SAINT
[v7.34 A][27] and XPREP [v2005/2].[28]
Corrections were applied for Lorentz
polarization, and absorption effects
using SADABS [v2004/1].[29] The
structure was solved and refined with
the aid of the programs in the
SHELXTL-plus [v6.12] system of pro-
grams.[30] The full-matrix least-squares
refinement on F2 included atomic co-
ordinates and anisotropic thermal pa-
rameters for all non-H atoms. The H
atoms were included using
a riding
model. Details of the data collection
and refinement are given in Table 3
and in the CCDC information.
CuI-catalyzed 1,3-dipolar cycloaddition
of 5-azido-N-(propan-2-ylidene)-1H-
tetrazole (1)
ꢁ
Reaction of
(Method
1
with CF3C CH (2a)
A
in Table 1): Azide (1)
(0.210 g, 1.3 mmol) in CH3CN (6 mL)
was placed in a 50 mL Schlenk tube
equipped with
a Teflon stopcock.
After the temperature was lowered to
ꢀ1958C, CuSO4·5H2O (5 mol%,
16.0 mg) in water (1 mL) and sodium
ascorbate (10 mol%, 25.7 mg) in
water (0.5 mL) were added successive-
ꢁ
ly. Then 3 mmol CF3C CH, 2a, was
added by means of vacuum transfer.
The mixture was allowed to warm to
room temperature and stirred for 2 h
and then at 708C for 48 h. After evap-
oration of the solvent, the residue was
purified by chromatography (n-
hexane/ethyl acetate=4:1) to give iso-
propylidene-[5-(4-trifluoromethyl-
1,2,3-triazol-1-yl)tetrazol-1-yl]amine,
3a: Straw-colored solid; yield: 0.152 g
(0.59 mmol, 47%). Recrystallization of
3a using several solvents gave only
small thin plates which were not suita-
ble for X-ray determination. 1H NMR
Scheme 3. Isodesmic reactions used for the calculation of 5-(1,2,3-triazol-1-yl) tetrazoles.
(300 MHz, CDCl3): d=8.71ACHTGNUTRENNUNG
Experimental Section
Safety precautions: For handling the azidotetrazole, 5-azido-N-(propan-
2-ylidene)-1H-tetrazole (1), use of small scale and best safety practices
(leather gloves, face shield) are strongly encouraged in undertaking prep-
aration of compounds 3a–g.
ꢀ
(KBr): n˜ =1025, 1087, 1139-1180 (s, C F), 1234, 1268, 1366, 1472, 1578,
1593 (ms, -N=C<), 3096 cmꢀ1
;
elemental analysis calcd (%) for
C7H7N8F3 (260.18): C 32.31, H 2.69, N 43.08; found: C 32.09, H 2.59, N
43.00.
General: 1H, 19F and 13C NMR spectra were recorded by using
a
ꢁ
Reaction of 1 with SF5C CH (2b) (Method A in Table 1): Reaction was
300 MHz Bruker Avance nuclear magnetic resonance spectrometer oper-
ating at 300.1, 282.4 and 75.5 MHz, respectively, using CDCl3, CD3CN
and [D6]DMSO as solvent. Chemical shifts for 1H and 13C are reported
relative to Me4Si and 19F relative to CFCl3. The melting and decomposi-
tion points were obtained by using a differential scanning calorimeter at
a scan rate of 108Cminꢀ1. Densities of solid salts were obtained at RT by
carried out similarly as for 2a (vide supra) giving isopropylidene-[5-(4-
pentafluorosulfanyl-1,2,3-triazol-1-yl)tetrazol-1-yl]amine, 3b: Straw-col-
ored solid; yield: 0.291 g (0.92 mmol, 66%). Recrystallization of 3b from
methanol gave a straw-colored crystalline solid, whose structure was de-
termined by X-ray crystallography. 1H NMR (300 MHz, CDCl3) d=8.70
(s, 1H), 2.39
150.2, 1F), 67.0 ppm (d, 2J=150.2 Hz, 4F); 13C NMR (CDCl3): d=183.8,
156.2 (quin, J(C,F)=27.6 Hz), 143.8, 124.0 (quin, J(C,F)=5.1 Hz), 25.9,
22.6 ppm; IR (KBr): n˜ =822–878 (s, S F), 983, 1029, 1269, 1584 (ms; -N=
C<), 1632, 3177 cmꢀ1
elemental analysis calcd (%) for C6H7N8SF5
(s, 3H), 2.26 ppm (s, 3H); 19F NMR: d=75.9 (quin, 2J=
ACHTUNGTRENNUNG
employing
a Micromeritics Accupyc1330 gas pycnometer. Elemental
analyses were determined by using an Exeter CE-440 elemental analyzer.
A
ACHTUNGTRENNUNG
ꢀ
X-ray crystallography: Crystals of compounds 3b–e were removed from
the flask and covered with a layer of hydrocarbon oil. A suitable crystal
was selected, and mounted on a MiteGen MicroMesh using a small
amount of Cargille Immersion Oil. Data were collected by using a
Bruker three-circle platform diffractometer. The crystals were irradiated
using graphite monochromated MoKa radiation (l =0.71073 ꢁ). Data
collection was performed and the unit cell was initially refined using
;
(318.23): C 22.64, H 2.20, N 35.22; found: C 22.53, H 2.12, N 35.18.
Blank experiment in the absence of alkyne (Method A in Table 1): Azide
1 (0.208 g, 1.3 mmol) in CH3CN (6 mL) was placed in 50 mL Schlenk
tube equipped with a Teflon stopcock. After the temperature was low-
ered to 08C, CuSO4·5H2O (5 mol%, 15.5 mg) in water (1 mL) and
9902
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Chem. Eur. J. 2009, 15, 9897 – 9904

Tetrazole Derivatives of an Azidotetrazole
FULL PAPER
sodium ascorbate (10 mol%, 33.3 mg) in water (0.5 mL) were added sim-
ilarly. The mixture was stirred at 708C for 48 h. After evaporation of the
solvent, the residue was purified by chromatography to give unreacted 1
(0.055 g, 0.33 mmol) and N1-isopropylidenetetrazole-1,5-diamine, 4,[10]
(0.036 g, 0.25 mmol). Straw-colored solid; yield: 0.036 g (0.25 mmol,
20%).
brown liquid: yield: 0.149 g (0.63 mmol, 40%). 1H NMR (300 MHz,
CDCl3): d=8.07 (s, 1H), 2.79 (t, 3J=7.6 Hz, 2H), 2.37 (s, 3H), 2.17 (s,
3
3
3
3H), 1.69 (tt, J=7.5 Hz, J=7.5 Hz, 2H), 1.40 (m, 2H), 0.92 ppm (t, J=
7.3 Hz, 3H); 13C NMR ([D6]DMSO): d=184.7, 150.1, 145.2, 122.6, 31.8,
26.7, 25.8, 23.0, 22.3, 14.5 ppm; IR (film): n˜ =974, 1036, 1258, 1374, 1435,
1459, 1536, 1561, 1590 (s, -N=C<), 2863, 1933, 2959 cmꢀ1; MS-FAB (3-ni-
trobenzyl alcohol matrix): m/z: calcd. for C10H17N8 (M+ +H) 249.1576;
found, 249.1574.
ꢁ
Reaction of 1 with CF3C CH (2a) (Method B in Table 1): Azide 1
(0.218 g, 1.3 mmol) in CHCl3 (2 mL) was placed in 50 mL Schlenk tube
equipped with a Teflon stopcock. After the temperature was lowered to
ꢀ1958C, CuI (10 mol%, 25.2 mg) in CHCl3 (1 mL) and 2,6-lutidine
(1.3 mmol, 0.144 g) in CHCl3 (1 mL) were added successively. Then
ꢁ
CF3C CH, 2a (1.6 mmol), was added by means of vacuum transfer. The
mixture was allowed to warm to 08C and held for 13 h. After the addi-
tion of saturated aqueous NH4Cl (4 mL), the organic phase was extracted
with CH2Cl2 (6 mL) and CH2Cl2 (2ꢂ1 mL), and dried over MgSO4. After
filtration, the solvent was removed, then the residue was purified by
chromatography to give 3a (0.180 g (0.69 mmol, 53%).
Acknowledgements
The authors gratefully acknowledge the support of DTRA (HDTRA1-
07-1-0024), NSF (CHE-0315275), and ONR (N00014-06-1-1032).
ꢁ
Reaction of 1 with SF5C CH (2b) (Method B in Table 1): Reaction was
carried out as for 2a giving isopropylidene-[5-(4-pentafluorosulfanyl-
1,2,3-triazol-1-yl)tetrazol-1-yl]amine, 3b: Yield 48%.
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[13] a) M. J. Kamlet, S. J. Jacob, J. Chem. Phys. 1968, 48, 23–35; b) M. J.
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ꢁ
Reaction of 1 with C6H5C CH (2c) (Method B in Table 1): Reaction
was carried out as for 2a except for cooling at 08C when catalysts (CuI
and 2,6-lutidine) and 2c (0.253 g, 2.5 mmol) were added to the solution
of 1 in CHCl3 giving isopropylidene-[5-(4-phenyl-1,2,3-triazol-1-yl)tetra-
zol-1-yl]amine, 3c: Straw-colored solid; yield: 0.198 g (0.74 mmol, 34%).
Recrystallization of the product from methanol gave a straw-colored
crystalline solid, whose structure was determined by X-ray. 1H NMR
(300 MHz, CDCl3): d=8.57
(s, 1H), 7.91 (d, 3J=6.4 Hz, 2H), 7.43–7.52
ACHTUNGTRENNUNG
(m, 3H), 2.44
ACHTUNGTRENNUNG
149.3, 145.2, 130.1, 130.0, 128.5, 121.2, 26.8, 22.0 ppm; IR (KBr): n˜ =690,
763, 1005, 1586 (s, -N=C<), 1627, 2927, 2962, 3160 cmꢀ1; elemental anal-
ysis calcd (%) for C12H12N8 (268.28): C 53.72, H 4.51, N 41.77; found: C
53.43, H 4.92, N 36.35.
ꢁ
Reaction of 1 with p-F-C6H4C CH (2d) (Method B in Table 1): Reaction
was carried out similarly as for 2c to give isopropylidene-[5-(4-fluoro-
phenyl-1,2,3-triazol-1-yl)tetrazol-1-yl]amine, 3d: Straw-colored solid;
yield: 0.134 g (0.47 mmol, 60%). Recrystallization of the product from
methanol gave a straw-colored crystalline solid, the structure of which
was determined by X-ray. 1H NMR (300 MHz, CDCl3): d=8.50
ACTHNUTRGNEU(GN s, 1H),
7.84–7.90 (m, 2H), 7.12ꢂ7.20 (m, 2H), 2.40 (s, 3H), 2.22 ppm (s, 3H);
19F NMR: d=ꢀ111.5 ppm (tt, 4J
(F,H)=6.0 Hz, 3J
ACHUTGTNRENNGU ACHTUNGTNER(NUGN F,H)=9.0 Hz, 1F); IR
(KBr): n˜ =624, 675, 808, 851, 1010, 1217, 1499, 1585 (s, -N=C<), 1630,
2924, 3064, 3148 cmꢀ1
; elemental analysis calcd (%) for C12H11N8F
(286.27): C 50.35, H 3.85, N 39.16; found: C 49.59, H 3.74, N 38.89.
ꢁ
Reaction of 1 with p-tert-butyl-C6H4C CH (2e) (Method B in Table 1):
Reaction was carried out as for 2c to give isopropylidene-[5-(4-tert-butyl-
phenyl-1,2,3-triazol-1-yl)tetrazol-1-yl]amine, 3e: Straw-colored solid;
yield: 0.114 g (0.35 mmol) 67%. Recrystallization of the product from
chloroform gave a straw-colored crystalline solid, whose structure was
determined by X-ray. 1H NMR (300 MHz, CDCl3): d=8.51
ACTHNUGRTENUNG(s, 1H), 7.80–
7.83 (m, 2H), 7.48ꢂ7.51 (m, 2H), 2.41 (s, 3H), 2.21 (s, 3H), 1.34 ppm (s,
9H); 13C NMR (CDCl3): d=183.9, 152.6, 148.5, 126.0, 125.9, 125.8, 119.8,
34.8, 31.3, 31.2, 25.9, 21.5 ppm; IR (KBr): n˜ =816, 995, 1013, 1248, 1366,
1461, 1495, 1590 (s, -N=C<), 2868, 2903, 2949, 2968, 3113 cmꢀ1; elemen-
tal analysis calcd (%) for C16H20N8 (324.38): C 59.26, H 6.17, N 34.54;
found: C 58.94, H 6.13, N 34.41.
ꢁ
Reaction of 1 with OCH2C CH (2 f) (Method B in Table 1): Reaction
was carried out as for 2c and purified by chromatography to give isopro-
pylidene-[5-(4-hydroxymethyl-1,2,3-triazol-1-yl)tetrazol-1-yl]amine, 3 f, as
a mixture with N1-isopropylidenetetrazole-1,5-diamine, 4 (1:0.4). Light
1
brown liquid: 0.065 g, yield of 3 f, 14%. H NMR (300 MHz, [D6]DMSO)
: d=8.66 (s, 1H), 5.46 (t, 3J=5.0 Hz, 1H), 4.66 (d, 3J=5.0 Hz, 2H), 2.34
(s, 3H), 2.20 ppm (s, 3H); 13C NMR ([D6]DMSO): d=184.7, 149.1, 144.5,
124.6, 54.5, 25.7, 21.2 ppm; MS-FAB (3-nitrobenzyl alcohol matrix): m/z:
calcd for C7H11N8O (M+ +H) 223.1056; found, 223.1059.
ꢁ
Reaction of 1 with n-C4H9C CH (2g) (Method B in Table 1): Reaction
was carried out as for 2c and purified by chromatography to give isopro-
pylidene-[5-(4-n-butyl-1,2,3-triazol-1-yl)tetrazol-1-yl]amine, 3g: Light
[14] Reichel and Partner GmbH, http://www.reichel-partner.de/.
Chem. Eur. J. 2009, 15, 9897 – 9904
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9903

J. M. Shreeve et al.
[15] Impact: insensitive >40 J, less sensitive ꢄ35 J, sensitive ꢄ4, very
sensitive ꢃ3 J, according to the UN recommendations on the trans-
port of dangerous goods.
[16] CCDC 724962 contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif
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[18] CCDC 724965 contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[19] CCDC 724964 contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[20] CCDC 724963 contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
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Received: April 19, 2009
Published online: August 13, 2009
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Chem. Eur. J. 2009, 15, 9897 – 9904