Preparation of energetic poly(azolyl)borates as new environmentally benign green-light-emitting species for pyrotechnics

Article abstract of DOI:10.1002/zaac.201300259

Three different energetic poly(azolyl)borates, potassium dihydridobis(4-nitroimidazolyl)borate, sodium dihydridobis(4, 5-dinitroimidazolyl)borate, and sodium dihydridobis(3, 4,5-trinitropyrazolyl) borate, were synthesized as starting materials for metal-f

Full text of DOI:10.1002/zaac.201300259

Job/Unit: Z13259
/KAP1
Date: 16-07-13 12:05:16
Pages: 12
ARTICLE
DOI: 10.1002/zaac.201300259
Preparation of Energetic Poly(azolyl)borates as New Environmentally
Benign Green-Light-Emitting Species for Pyrotechnics
[a]
[a]
[a]
Thomas M. Klapötke,* Magdalena Rusan, and Véronique Sproll
Dedicated to Professor Bernt Krebs on the Occasion of His 75th Birthday
Keywords: Poly(azolyl)borates; Pyrotechnics; Borates; Nitrogen-rich compounds; Energetic materials
Abstract. Three different energetic poly(azolyl)borates, potassium di- man spectroscopy and high mass resolution spectrometry. Moreover,
hydridobis(4-nitroimidazolyl)borate, sodium dihydridobis(4,5-dinitro- the energetic properties regarding physical and thermal stability were
imidazolyl)borate, and sodium dihydridobis(3,4,5-trinitropyrazolyl)- determined. The B NMR chemical shifts were calculated and com-
11
borate, were synthesized as starting materials for metal-free environ-
mentally benign green-light-emitting substitutes for barium salts in py-
rotechnical mixtures. The compounds were analyzed by NMR and Ra-
pared to the experimental values and intense investigations on the for-
mation of poly(4-nitroimidazolyl)borates were performed. Further-
more, the solvolytic stability towards alcohol and water was tested.
Kulshrestra et al.[11] found the barium concentrations in air
increased by more than a factor of 1000 in the course of one
excessive night of fireworks compared to the usual back-
ground. Thus, in terms of green chemistry, the barium nitrate
content makes the green-luminescent pyrotechnics the “dirtiest
Introduction
Fireworks, though spectacular and entertaining, come with
a gammy leg. Due to their vast sphere of action, aerial fire-
works and pyrotechnics are also great environmental polluters,
which disperse several hazardous substances over a large
[1]
bombs of all”.
area.[
1,2]
These toxic compounds are released upon explosion,
An alternative is offered by the usage of boron based
deflagration, or burning of the pyrotechnics, including both
reaction products and unburned constituents of a pyrotechnic
mixture.[ In recent years, the number of scientific articles
focusing on environmental analysis and development of new
energetic compounds increases (see, for example Refs.[1,2,4–6])
thereby emphasizing the importance of this topic.
formulations as barium substitutes for pyrotechnic composi-
[12–14]
tions.
Most of the boron compounds currently tested
3]
have in common that they do not possess any energetic charac-
ter. Especially with regard to the formulation of highly ef-
ficient colorful pyrotechnics, it is of interest to combine the
energetic properties with the coloring agent in the same mole-
cule. Therefore, it is essential to create new energetic boron
compounds, which could reduce the amount of different addi-
tives of pyrotechnics as well as the weight due to a better
performance than the currently tested compositions. Among
the possible energetic boron compounds nitrogen-rich hetero-
cycles combine both thermal and physical stability and are
therefore worthwhile targets for the development of new color-
ing agents. Through the last decades a variety of poly(azolyl)-
One of the major toxic components of pyrotechnics form the
coloring heavy metals, leading to the emission of heavy metal
aerosols.[ A comprehensive investigation of those aerosols
for Beijing in the night of the annual “festival of rows of light”
7]
(
Diwali festival, a five days remaining celebration traditionally
[8]
accompanied by fireworks and firecrackers ) showed not only
a dramatic increase in concentration for sulfur dioxide, nitro-
gen dioxide and PM10 (increase of 57%, 25% and 183%,
[9]
respectively) but also for toxic metals as barium, lead, copper, borates have been reported and become increasingly important,
aluminum, manganese, and strontium (increase of 8200%, especially as so called scorpionate ligands.[ Particularly, pyr-
15]
10]
00%, 600%, 600%, and 400%, respectively).[ Beside lead azolylborates display a versatile class of monoanionic, nitro-
8
aerosols, especially the emission of soluble barium salts and gen-based and multidentate ligands in coordination, organome-
aerosols is a cause of concern due to their toxicity.[
1,2,7d,11]
[15,16,17]
tallic and bioinorganic chemistry.
Another area of ap-
Regarding an exposure caused by the usage of fireworks, plication opens when the relatively unenergetic heterocycle
pyrazole gets substituted by triazoles or tetrazoles. For the lat-
ter, the Naval Air Warfare Center studied, for example, the
transition metal complexes of dihydridobis(5-aminotetrazolyl)-
*
Prof. Dr. T. M. Klapötke
Fax: +49-89-2180-77492
E-Mail: tmk@cup.uni-muenchen.de
[
a] Department of Chemistry
Energetic Materials Research
Ludwig-Maximilian University
Butenandtstr. 5–13 (D)
borate as potential propellant ingredients containing both metal
[18]
and boron centers might act as burn rate modifiers.
Another
interesting example for tetrazole containing poly(azolyl)bor-
[
19]
81377 München, Germany
ates was synthesized recently by Winter et al.
Z. Anorg. Allg. Chem. 0000, ᭿,(᭿), 0–0
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T. M. Klapötke, M. Rusan, V. Sproll
ARTICLE
Commonly, Trofimenko[20] is referred to as the father of po-
ly(azolyl)borate chemistry, especially regarding tetrakis(azo-
lyl)borates. Though Sazanova et al.[21] reported the synthesis
of potassium tetrakis(pyrrolyl)borate already in 1955, it has
been Trofimenko[
20,22]
who provided a synthetic route to afford
tetrakis(azolyl)borates in good yields. His thermolytic ap-
proach has been applied to most of the known poly(azolyl)-
borates bearing insensitive groups as alkyl- or aryl-substitu-
ents, which are typically synthesized at high temperature using
a mixture of the corresponding azole and alkali metal borohyd-
ride (e.g. literature[
15,17b,17c,17d,17s,20,22]
).
In order to increase the energetic character of the borate,
nitrated azoles are used in this work. To date only a small
number of nitrated poly(azolyl)borates is known. Some exam-
ples are given in Figure 1.
Scheme 1. Schematic metathesis reaction to yield nitrogen-rich, metal-
free salts.
sium borohydride (Scheme 2). On the other hand, the ex-
tremely low solubility of this compound in common organic
solvents limited the possible synthetic routes. Nevertheless,
different solvents, stoichiometry, concentrations and tempera-
tures were tested.
Scheme 2. General reaction scheme for potassium poly(4-nitroimid-
azolyl)borates (6).
[
23]
Figure 1. Dihydridobis(3-nitro-1,2,4-triazolyl)borate (1),
dihydri-
[
24]
dobis(3,5-dinitro-1,2,4-triazolyl)borate (2),
dihydridobis (3-nitro-
and hydridotris(3-nitropyrazolyl) borate (3)
The first choice was to go for mild conditions. The reaction
of the azole ring and potassium borohydride can be understood
as some kind of acid-base reaction with the evolving hydrogen
[
25]
[26]
pyrazolyl)borate (3),
anions.
In this work poly(azolyl)borates of potassium and sodium as driving force. Having an electron-withdrawing group at-
are synthesized. For further application in pyrotechnic compo- tached to the imidazole moiety, it was expected to have a more
sitions and to further improve the properties, the herein devel- acidic and therefore mildly activated system where, at least for
oped compounds will be transformed into nitrogen-rich salts bissubstitution, relatively low temperatures should be suf-
by salt metathesis reactions as shown in Scheme 1. The metal- ficient.
free salts are generally known to show a more brilliant green
color performance and will then be tested for pyrotechnic mix-
tures.
Synthesis of Potassium Dihydridobis(4-nitroimidazolyl)-
borate (8)
Acetonitrile was chosen as solvent owing to its b.p. of 82 °C
Results and Discussion
and thus also easy removability afterwards as well as its polar
as well as tris(imidazolyl)- character. In order to obtain potassium dihydridobis(4-nitro-
Tetrakis(imidazolyl)borates[
27]
borates[ have been of interest in the construction of new imidazolyl)borate (8), 5 was reacted with potassium boro-
metal-organic framework structures. Nevertheless, to the best hydride in freshly distilled acetonitrile at reflux conditions
of our knowledge there have been no substituted imidazole (Scheme 3). Immediate gas evolution was observed after add-
derivatives reported, especially with regards to the more ener- ing 5 to the suspension of potassium borohydride in acetoni-
getic nitrated compounds. Therefore, it has been of interest trile even at room temperature. During the reaction, the sus-
to study the properties of the nitrated derivatives as energetic pension discolored and turned from colorless over beige-brown
28]
materials.
to completely black.
I. Poly(4-nitroimidazolyl)borates
4
-Nitroimidazole (5) is commercially available and provided
therefore an easily accessible starting material in order to study
different reaction conditions for nitrated imidazoles and potas- Scheme 3. Synthesis of 8.
2
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Energetic Poly(azolyl)borates as New Environmentally Benign Green-Light-Emitting Species for Pyrotechnics
The reaction procedure was monitored by 11B NMR (Fig- ligands[33]
or
22,24,25,29,34,35]
hydridopoly(azolyl)borates
In the region between 3141 cm
in
gene-
and
ure 2). After 3.5 h the obtained data showed already a com- ral.[
–1
plete consumption of potassium borohydride (–38 to –43 ppm) 3084 cm–1 the C–H stretching vibration of the nitroimidazole
and the formation of two new compounds with signals at moiety is clearly visible, as well as the NO asymmetric and
2
–
20.1 ppm and –9.8 ppm. Earlier observations on this topic as symmetric valence vibrations found in the range between
[18,29–32]
–1
–1
[25,26,34,35]
well as consulted literature
allowed an assignment of 1490–1545 cm and 1315–1375 cm , respectively.
these signals to the monosubstituted (–20.1 ppm) and bissub- As expected from the obtained NMR spectroscopic data no
stituted (–9.8 ppm) borate. This first assignment was affirmed traces of boric acid can be found.
1
1
by the proton coupled B NMR spectra, which showed the
Due to the asymmetric character of 5 with its two feasible
1
expected multiplets, a quartet ( J
= 89 Hz) at –20.1 ppm bonding positions for boron (N1 and N3), the formation of
B–H
1
and a triplet ( J
= 100 Hz) at –9.8 ppm (Figure 2) as well three isomeric compounds was regarded possible (Figure 3).
B–H
as by calculations (see Table 2).
Figure 3. Illustration of the isomeric compounds of 8 due to B–N
bonding via position 1 (8a), position 3 (8c), or 1 and 3 (8b).
This assumption was corroborated by NMR spectroscopic
data. Though there is only one boron signal in the 11B NMR
at –10.7 ppm (in [D ]DMSO), there are, despite of the men-
6
tioned three possible structures, only two sets of ligand-signals
1
13
to be found in the H NMR and C NMR spectra. These sets
can probably be explained by N1 and N3 bound imidazole
rings.
The main compound is most reasonably 8a due to the crystal
structure of 5 with the proton bound to N1 and a possible steric
Figure 2. Monitored reaction procedure by 11B{H} NMR measure-
ments. Due to a better clarity the left part of the spectra with the repulsion by the nitro group.[36,37] It shows proton shifts in
[
37]
growing signal at –9.8 ppm (product signal, 8) was darker colored than [D ]DMSO at δ = 8.01 ppm (5-CH) and 7.50 ppm (2-CH)
6
the right handed one with the decreasing signal at –20.1 ppm (7). The
corresponding reaction times are listed at the right edge of the respec-
tive spectrum. (solvent: non-deuterated MeCN).
and a broad signal of the BH group centered at δ = 3.30 ppm.
2
It was possible to extract the boron hydrogen coupling and
thereby assign this signal unambiguously to the BH group
2
During the reaction procedure further 11B NMR spectra (Figure 4). This was achieved by a measurement at elevated
were measured, which show the continuous decline of the sig- temperature (85 °C) as under these conditions the quadrupole
nal of trihydridomono(4-nitroimidazolyl)borate (7) in favor of relaxation of the boron core is minored.
the signal of (the higher substituted) compound 8 until after
4
0 h under reflux conditions the reaction was completed and
only the signal of 8 was visible in the NMR spectrum.
To isolate 8 the reaction mixture was simply diluted with
further freshly distilled acetonitrile and the insoluble mixture
of remaining starting material and impurities was filtered off.
Compound 8 was obtained after removal of the solvent as be-
ige solid with a yield of 80%. The applied procedure capti-
vates with its simplicity and easy work up. This pathway can
be easily upscaled and opens access to a possible industrial
application of this compound.
1
Figure 4. Extract of the H NMR spectrum in [D
6
]DMSO to visualize
1
Characterization
the quartet splitting of the BH
2
group ( JB–H = 123 Hz, T = 85 °C).
The product was fully characterized by H, 13C, and 11
1
B
The 13C NMR signals are located at δ = 148.1 ppm (4-C–
NMR as well as elemental analysis, Raman spectroscopy, and NO ), 141.1 ppm and 124.9 ppm and thereby show, as ex-
2
–
high resolution mass spectrometry ([C H O N B] calcd.: pected when bound to boron, a clear downfield shift compared
6
6 4 6
2
37.0545; found: 237.0530).
The Raman spectrum exhibits bands attributable to the
to the signals of 5 (δ =147.6 ppm, 135.9 ppm and 119.0 ppm).
The second compound is slightly downfield shifted com-
–1
boron-hydrogen stretching vibration at 2409 cm , which is pared to the first one with signals at δ = 8.05 ppm (5-CH),
38]
similar to values in complexes containing bis(pyrazolyl)borate 7.52 ppm (2-CH)[ and a very broad one for the correspond-
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T. M. Klapötke, M. Rusan, V. Sproll
ARTICLE
ing BH group centered around 6.30 ppm (T = 85 °C). The pact sensitivity Ն 40 J, friction sensitivity Ն 360 N and ESD
2
relatively large difference in the chemical shifts of the two Ն 0.85 J. The decomposition point was found to be at 189 °C.
BH groups can be rationalized by a possible intramolecular
2
hydrogen bonding between the BH protons and the adjacent
2
nitro group (Figure 5). The assumption of an intramolecular Investigation of Reaction Conditions in Search for a Higher
interaction is also supported by a possible formation of the Substitution
favored structural motif of a six-membered ring as shown in
1
3
As previously mentioned, different reaction conditions were
investigated especially with a regard to possible higher substi-
tution of the poly(4-nitroimidazolyl)borate (6). Some of these
conditions are compiled in Table 1. For the bissubstituted com-
pound 8 a higher dilution deteriorates the reaction conditions
and leads to a prolonged reaction time that could not be
counteracted by the usage of 4.5 equivalents instead of 2
equivalents 4-nitroimidazole (Table 1, entry 1 and 2).
Figure 5. The C NMR chemical shifts of 4-C–NO , 2- and
2
3
1
-CH carbon atoms appear at δ = 147.9 ppm, 140.5 ppm, and
24.8 ppm, respectively.
Concerning a higher substitution, high-boiling solvents as
diglyme (b.p. 162 °C) and benzonitrile (b.p. 191 °C) were in-
vestigated. These solvents showed at elevated temperatures a
rising solubility towards 5, which was expected to facilitate
the reaction. However, reactions in these solvents showed right
Figure 5. Schematic view of possible intramolecular hydrogen bond-
ing for compound 8b/c.
Whether all three isomers are present or only two isomers from the beginning the formation of several different boron
were formed cannot be clearly determined by the obtained ana- compounds.
lytical data. As the proton shifts of the BH fragment display
The reaction of 3 equiv. 5 at 103 °C (Table 1, entry 3) did
2
the greatest sensitivity towards isomeric structure, three dif- only yield the bissubstituted compound 8 contaminated with
11
ferent signals for this group would be expected. Whereas the minor signals at 0.9 ppm and 5.3 ppm ( B NMR spectra re-
NMR spectrum at 25 °C only shows one signal for a BH2 corded of the reaction mixture). Even a prolonged reaction
group (δ = 3.3 ppm), the signal of the second BH group at time and an increase of temperature (22.5 h, 121 °C and 4 h,
2
6
.3 ppm slowly appears with rising temperature until the spec- 200 °C) did not change the signal ratio and proved therefore
trum at 65 °C clearly shows the second BH group. The ques- these conditions not to be sufficient for a higher substitution.
2
tion, whether all three isomers were formed and the NMR
Due to these results, the reaction was tried with a great ex-
shifts of the protons of imidazole rings are independent from cess of 5 in diglyme (Table 1, entry 4) and the temperature
the bonding situation of the second imidazole moiety at the was raised to 156 °C right from the beginning. This led to a
boron atom, along with a still missing third BH group that significantly shortened formation time of compound 8
2
could appear at even higher temperatures, or only two isomers (–10.4 ppm), which was after 1 h already completed but again
were formed could currently not be solved.
also accompanied by the formation of side-products (δ =
Regarding an ensuing investigation and possible application 0.3 ppm, 4.7 ppm). After 26.75 h the signal of 8 was strongly
in pyrotechnical mixtures the insensitive character of com- diminished in favor of the signal at 1.2 ppm whereas the inten-
pound 8 was confirmed according to BAM standards:[ im- sity of the third signal (δ = 5.3 ppm) remained the same. With
39]
Table 1. Different reaction conditions for the 4-nitroimidazole (5) / potassium borohydride system.
Entry
Stoichiometry
:KBH
Solvent
Temperature /°C
Concentration
mmol(5):mL(solvent)
Reaction time /h
δ 11Ba) /ppm
5
4
1
2
3
2:1
4.5:1
3:1
MeCN
MeCN
diglyme
reflux (ca. 90)
reflux (ca. 90)
103
0.918
0.575
0.463
40
164
20
–9.84
–10.0
–10.0
(
5.3; 0.9)
–10.4
0.3; 4.7)
1.2
4
8:1
5:1
diglyme
156
1.405
1
(
2
4
6.75
5
(–9.2; 5.3)
1.1
(–4.4; 5.2; 7.6)
5
benzonitrile
163
0.451
0.451
0.451
5
1
9
–10.1
–10.1
–9.7
9.5
187
(
–4.6)
reflux (ca. 195)
15
3
–4.2
dec.
8
a) Shifts given in parentheses are minor impurities.
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Energetic Poly(azolyl)borates as New Environmentally Benign Green-Light-Emitting Species for Pyrotechnics
regards to the 11B NMR shifts of other tetrakis(azolyl)bor- ther nitrated according to a procedure devised by Katritzky et
ates[
40,41]
the signal at 1.2 ppm can reasonably be assigned to al.
[43]
to afford 4,5-dinitroimidazole (11). Regarding the higher
the tetrakisubstituted compound, in this case tetrakis(4-nitro- activation due to the presence of two nitro moieties as well as
imidazolyl)borate (9) (see also Table 2 for calculations of the the related possible lower decomposition temperatures, a non-
NMR chemical shifts). During this reaction the trissubstituted thermolytic approach was chosen to afford the bissubstituted
intermediate was not observed.
borate. It was expected, that when in solution, the dinitrated
A further reaction attempt was conducted in benzonitrile, imidazole would react with sodium borohydride even at room
using an excess of 5 (Table 1, entry 5). The reaction mixture temperature (Scheme 4). In the first approach a slight excess
was heated to 163 °C, during which time it discolored. Starting of 11 was used, but proved difficult to be removed afterwards.
from a colorless suspension it turned over a yellow-brown Therefore, the reaction was conducted stoichiometric, which
solution with white solid to completely black. After 5 h com- led to a prolonged reaction time at ambient temperature. This
pound 8 was exclusively formed and remained the only signal can be overcome by mildly heating to 45–50 °C.
11
in the recorded B NMR spectra until the temperature was
raised to 187 °C. After 9 h at this temperature a second signal
at –4.1 ppm emerged (together with a minor impurity at
0
.7 ppm). This signal (most probably assignable to hydri-
dotris(4-nitroimidazolyl)borate 10, for calculations see also
Table 2) was afforded as single boron compound by a further
raise of temperature (15 h, 195 °C), yet maintenance of this
temperature did not lead to the formation of a higher substi-
tuted compound but to complete decomposition.
Scheme 4. Synthesis of 12.
The reaction procedure was monitored by 11B NMR mea-
surements of the crude reaction mixture and showed a smooth
transition from the initially formed monosubstituted compound
Investigation of Solvolytic Stability
1
(
with a signal at –21.3 ppm, q, J
= 102 Hz) to the bissub-
B–H
1
Sodium tetrakis(imidazolyl)borate is set to be completely stituted 12 (–11.3 ppm, t, J
= 102 Hz) (Figure 6).
B–H
stable towards hydrolyses as it was even investigated as gravi-
metric reagent for proton.[
42]
Nevertheless, it is commonly
known that the general stability of these complexes decrease
with the increase of hydrogen atoms attached to the central
[
22]
boron atom.
In order to investigate the stability of 8 towards solvolysis
by alcohols, experiments with deuterated methanol were car-
ried out in the scale of NMR-tubes. The results show the rather
high stability of 8 against solvolysis in methanol solution.
Even after keeping 8 in the system methanol/acetonitrile
(
[
(
0.6:1.0) for 2 d only a slight decomposition could be observed
decomposition product: 11.6 (0.13) ppm; product signal: –9.7
1.00) ppm].
Carrying out the same experiment in the mixture of meth-
anol/diglyme/DMSO (0.4:0.6:0.2) a faster hydrolysis of 8 [sig-
nal at –9.8 (1.00) ppm, decomposition product: 16.6 (1.11)
ppm, after 1 d] was observed.
The investigation of the stability of the main compound of
entry 4 in Table 1 (shift at 1.2 ppm) under the same conditions
Figure 6. Monitored reaction procedure by 11B{H} ⁿmr measurements.
Due to a better clarity the left part of the spectra with the growing
signal at –11.3 ppm (product signal, 12) was darker colored than the
right handed one with the decreasing signal at –21.3 ppm (intermediate
showed a much higher sensitivity against solvolysis of this product). The corresponding reaction times are listed at the right edge
compound. After keeping the compound in the methanol solu- of the respective spectrum. (solvent: undeuterated MeCN).
tion for 1 d, the chemical shift at 1.2 ppm nearly disappeared
After removal of the solvent, compound 12 was obtained as
completely and a new signal at δ = 15.2 ppm, probably tri-
pale yellow solid in almost quantitative yield. Despite drying
methyl borate, rose as main compound.
under high vacuum at elevated temperature, a small amount of
acetonitrile remained in the solid product. It was assumed that
II. Poly(4,5-dinitroimidazolyl)borates
the acetonitrile is part of the solid structure.
Synthesis of Sodium Dihydridobis(4,5-dinitroimidazolyl)-
borate (12)
Characterization
The product was fully characterized by H, 13C, 14N, and
1
In order to further increase the energetic character the ni-
tration level of the borate was enhanced. Therefore, 5 was fur-
11
B NMR as well as elemental analysis, vibrational spec-
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troscopy, and high resolution mass spectrometry These results point out that compound 12 is mostly stable
–
(
[C H O N B] calcd.: 327.0246; found: 327.0254).
towards hydrolysis. Nevertheless, longer times of storage in
aqueous solution will lead to a degradation of the compound.
In conclusion, the novel borate 12 is a pale yellow solid,
6
4 8 8
The Raman spectrum shows the clear evidence of the BH
fragment by exhibiting a band at 2449 cm which is character-
2
–
1
istic for boron–hydrogen stretching vibrations in comparable soluble in water, methanol, DMSO, acetonitrile, and THF. It
complexes.[
22,24,25,29,33–35]
At 3140 cm the band correspond- can be kept in aqueous and methanol solutions without signifi-
–1
ing to the C–H stretching vibration of the imidazole moiety is cant hydrolysis to boronic acids and trimethyl borate, respec-
visible as well as the NO asymmetric and symmetric valence tively. Moreover, the synthesis was optimized and could be up-
2
–
1
vibrations found in the range between 1490–1564 cm and scaled without further problems.
301–1375 cm , respectively.
–
1
[25,26,34,35]
1
As already men-
tioned, small residues of acetonitrile remained in the solid
product and the corresponding bands are displayed in the Ra-
man spectrum [pure acetonitrile: 2943 (100), 2253 (73), 921
III. Poly(3,4,5-trinitropyrazolyl)borates
Among the numerous known poly(azolyl)borates the group
of pyrazole based borates display the greatest variety. Though,
electron withdrawing substituents on the pyrazolyl moiety are
relatively less common compared to the scorpionate ligands
with electron donating substituents like methyl or isopropyl on
–
1 [44]
(
(
26), 382 (20) cm ;
4), 955 (3), 388 (2) cm ]. As expected from the obtained
acetonitrile residues: 2944 (10), 2266
–
1
NMR spectroscopic data no traces of boric acid can be found.
1
The H NMR chemical shift of the 2-CH protons (in CD CN
3
solution) is observed at δ = 7.40 ppm and the BH protons
[16]
2
the pyrazolyl rings. The groups of Santini and Dias reported
appear as a broad signal at δ = 3.29 ppm, while the 13C chemi-
a view of these rare compounds, e.g. trihydrido(5-CF -pyrazo-
3
cal shifts of 2-CH and 4/5-C–NO carbon atoms are at δ =
2
lyl) borate as well as the mono-, bis-, and tris-substituted 3-
1
4
1
39.6 ppm and 138.7 ppm. N NMR shows the signal of the
[17b,25,45]
nitropyrazolyl-borates.
imidazolyl moiety at a shift of –185.3 ppm and the signals of
the two nitro groups at a shift of –17.3 ppm and –20.6 ppm. In
11
the B NMR spectrum the signal appears at a shift of Synthesis of Sodium Dihydridobis(3,4,5-trinitropyrazolyl)-
12.2 ppm with a coupling constant J(B–H) between the boron borate (14)
–
and the hydrogen atoms of 98 Hz.
NMR spectroscopic data of compound 12 was also mea-
sured in deuterated acetone with the only major difference that
2
,4,5-Trinitropyrazole (13) was synthesized via a multi-step
reaction sequence of nitrations and ensuing rearrangements
starting from commercially available 1H-pyrazol. After the ex-
periences with 12 similar mild reaction conditions were chosen
for the synthesis of sodium dihydridobis(3,4,5-trinitropyrazo-
lyl)borate (14) (Scheme 5). As the trinitrated pyrazole is well
soluble in organic solvents the reaction was performed in
freshly distilled diethyl ether at ambient temperature.
the protons of the BH fragment spread over the range of
2
1
.39 ppm (3.89–2.50 ppm).
Regarding an ensuing investigation and possible application
in pyrotechnical mixtures the sensitivities of compound 12
were determined according to BAM standards:[ impact sen-
sitivity Ն 10 J and friction sensitivity Ն 240 N. These results
show that compound 12 is, in contrast to the complete insensi-
tive compound 8, sensitive towards impact and friction. This
behavior of 12 is in accordance with the expected tendency
that more nitro groups at the imidazole ring will lead to a
higher energetic character along with a higher sensitivity. This
trend is also supported by the drop of the decomposition point
from 189 °C (8) to 127 °C of compound 12.
39]
Scheme 5. Synthesis of 14.
Investigation of Solvolytic Stability of Compound 12
An excess of 13 was reacted with sodium borohydride for
1
6 h, during which time a pale yellow precipitate was formed.
Experiments regarding the stability of 12 towards solvolysis
were conducted in aqueous and methanol solutions. In the sys-
tem water/acetone (0.6:1.0) compound 12 showed only a minor
decomposition to boric acid [boric acid signal: 18.5 (0.085)
ppm; product signal: –12.5 (1.00) ppm] after 2 h. The inten-
sities of the boric acid were corrected by the intensity of the
signal of boric acid resulting from hydrolysis by the water im-
purities of deuterated acetone (measured after several days of
storage in deuterated acetone).
The reaction solid was filtered off and washed with diethyl
ether to obtain 14 in a good yield of 83%.
Characterization
The product was fully characterized by H, 13C, 14N, and
1
11
B NMR as well as elemental analysis, vibrational spec-
troscopy, and high resolution mass spectrometry
–
In the system methanol/acetonitrile (0.6:1.0) compound 12 ([C H O N B] calcd.: 416.9948; found: 416.9916).
6
2 12 10
has a comparable sensitivity towards solvolysis. After 3.5 h
The Raman spectrum shows the clear evidence of the BH2
the decomposition signal (δ = 17.9 ppm) showed an intensity fragment by exhibiting a band at 2476 cm–1 which is character-
of 0.19 compared to the signal of 12 at –11.9 ppm (1.00). istic for boron-hydrogen stretching vibrations in comparable
6
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Energetic Poly(azolyl)borates as New Environmentally Benign Green-Light-Emitting Species for Pyrotechnics
complexes.[22,24,25,29,33–35] The asymmetric and symmetric val- substituted before the final hydrogen atom, indicating that this
–
1
ence vibrations of the NO group appear at 1567 cm and moiety is bound to boron less strong than the hydrogen atom.
2
–
1
1
408 cm , respectively, in accordance with the values gen-
[
46,47]
erally found for polynitropyrazolyl moieties.
Furthermore, small diethyl ether residues remained in the
solid product and the typical “triplet” centered at 2945 cm–1
can be found in the Raman spectrum. These small residues can
be reduced by prolonged storage under high vacuum at ele-
vated temperature of 75–80 °C. However, these diethyl ether
residues are assumed to stabilize the structure of compound 14
as after removal some kind of decomposition is detected in
NMR spectroscopic data. This decomposition led not only to
the formation of some boric acid or presumably triethyl borate
when resolved in deuterated acetone or acetonitrile (signal at
δ = 18.5 ppm and 18.6 ppm, respectively) but also to the for-
mation of a second set of signals for the ethoxy moiety in
1
the H NMR (4.70, 1.54 ppm, diethyl ether, 3.45, 1.14 ppm,
CD CN).
3
Scheme 6. Proposed degradation pathway of compound 14.
1
The H chemical shift of the BH group was observed at
2
δ = 3.80 ppm as broad signal (in CD CN solution). In addition,
the C spectrum of 14 showed two signals for the C–NO2 27.9 ppm cannot correspond to the scaffold L BH with L
This is corroborated by the fact that the signal at δ =
3
1
3
2
carbon atoms at δ = 146.6 ppm and 144.6 ppm, while standing for the trinitropyrazolyl moiety. For such a species the
1
4
N NMR displayed the signals of the three nitro groups at a B–H coupling ranges between 126–131 Hz [HB(NR ) : 26–
2
2
1
[30]
shift of –23.7 ppm, –25.5 ppm, and –27.3 ppm. In the 29 ppm, J
= 126–131 Hz]
instead of the found 162 Hz.
B–H
11
B NMR spectrum the signal appears at a shift of –7.4 ppm.
Furthermore, it has to be the original hydrogen, as only deuter-
The analysis of the energetic properties of 14 was performed ated solvents were used and no coupling of a BD fragment
39]
according to BAM standards:[ impact sensitivity Ն 10 J and could be observed, as for this fragment a triplet with a coupling
friction sensitivity Ն 120 N. These results show only a small constant of 24 Hz would be expected.[
30]
increase of sensitivity for compound 14 compared to the dini-
trated imidazolyl derivative 12, which is in accordance with verted to trimethyl borate, which remained the only signal.
the already observed tendency that more nitro groups at the
Experiments regarding the stability of 14 towards solvolysis
After 4 d the signal at δ = 27.9 ppm was completely con-
azole moiety will lead to a higher energetic character along were not only conducted in methanol solution but in aqueous
with a higher sensitivity. In contrast to this finding, the decom- solution as well. In the system water/acetonitrile (0.6:1.0) com-
position temperature raises from 127 °C (12) to 170 °C of pound 14 showed noticeable decomposition to boric acid [bo-
compound 14. Of course, compound 12 is based on an imid- ric acid signal: 18.6 (0.66) ppm; product signal: –12.5 (1.00)
azole scaffold, whereas 14 has two pyrazole moieties, never- ppm] after 3.5 h, as well as the intermediate formation of a
theless, this raise of decomposition temperature is noteworthy. third compound with a shift at δ = 26.3 ppm.
IV Calculation of 11B Chemical Shifts
Investigation of Solvolytic Stability of Compound 14
As additional verification of the analytical data, the 11B
As well as for the other synthesized borates, the solvolytic NMR chemical shifts were calculated and compared to the ex-
stability of compound 14 was also investigated. But in this perimental data.
case the obtained data does not only show the relative stability
In order to compute the 11B NMR chemical shifts for vari-
towards solvolysis but also allows an assumption of the degra- ous high-nitrogen boron compounds, the isotropic magnetic
dation process. In the system methanol/acetonitrile (0.6:1.0) shielding was computed using the GIAO (Gauge-Independent
[
48,49]
compound 14 showed after 3.5 h the formation of two new Atomic Orbital) method implemented in G03.
The struc-
compounds with signals at δ = 27.9 ppm and 18.3 ppm. The tures were fully optimized and the frequencies calculated
latter can be clearly assigned to the expected solvolysis to tri- (NIMAG = 0) at MPW1PW91/aug-cc-pVDZ level of theory.
methyl borate,[ whereas the former signal refers to the inter- Subsequently, the NMR shielding tensors were calculated at
30]
[
49]
mediate formation of dimethyl boronate [HB(OMe) ]. This the same level of theory using the GIAO method.
Table 2
2
11
signal displays in the proton coupled B NMR a doublet with summarizes the computed isotropic magnetic shielding and rel-
a coupling constant of 162 Hz, in accordance with the values ative 11B NMR chemical shifts (ppm) referenced to BF ·Et O.
3
2
generally found for B–H coupling in the HB(OR) scaffold
The comparison of the calculated values with the experi-
2
1
[30]
[
HB(OR) : 26–28 ppm, J
= 160–168 Hz].
B–H
Therefore, mentally determined shifts shows a good accordance thereof.
2
the solvolysis of 14 could reasonably follow the pathway sug- In case of the mono- and bissubstituted nitroimidazolyl, dini-
gested in Scheme 6 where the trinitropyrazolyl moiety gets troimidazolyl and trinitropyrazolyl borates, all compounds
Z. Anorg. Allg. Chem. 0000, 0–0
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
7

Job/Unit: Z13259
/KAP1
Date: 16-07-13 12:05:16
Pages: 12
T. M. Klapötke, M. Rusan, V. Sproll
ARTICLE
Table 2. Computed isotropic magnetic shieldings (GIAO method[48,49] MPW1PW91/aug-cc-pVDZ) and relative 11B chemical shifts /ppm refer-
3 2
enced to BF ·Et O.
Compound
–E/ a.u.
NIMAG
p.g.
δ 11B /ppm,
calcd. isotr.
shielding
δ 11B /ppm, calcd.
δ 11B /ppm, exptl.,
(ref. to BF ·Et O)
3 2
(ref. to BF
3
·Et
2
O)
BF
BH
3
·Et
4
2
O
558.164166
27.246888
0
0
C
1
+110.0
+159.0
0.0
–49.0
0.0
–41.6 [50]
–
T
d
B(OH)
B(OH)
3
252.468079
328.333947
0
0
C
3h
92.4
107.9
+17.6
+2.1
18.4–19.6 [30]
+1.1 [30]
–
4
S
4
c)
BH
BH
3
(DNT)–
677.334541
1327.389843
0
0
C
C
1
+130.2
+117.5
–20.2
–7.5
–17.2 [24]
–6.2 [24]
–
c)
2
(DNT)
2
1
–
a)
BH
BH
BH(NIM)
3
(NIM) (7)
456.829447
886.389580
1315.931096
1745.446360
0
0
0
0
C
C
C
C
s
133.0
121.8
115.8
112.8
–23.0
–11.8
–5.8
–20.1
–9.8
–4.1
+1.1
–
a)
2
(NIM)
2
–
(8)
1
1
1
b)
3
–
(9)
b)
B(NIM)
BH
4
(10)
–2.8
–
–12.2a)
2
(DNIM)
2
(12)
1295.333327
0
C
1
122.5
–12.5
a) Compounds verified by high resolution mass spectrometry. b) Compounds not isolated and fully verified up to now. c) DNT stands for 3,5-
dinitro-1,2,4-triazole.
were unambiguously proven by high-resolution mass spec- Experimental Section
trometry and can therefore be used as control for the calculated
All manipulations were carried out in an atmosphere of dry argon using
values. The calculated chemical shifts of the trissubstituted and
standard vacuum line techniques. Experimental reaction procedures to
tetrakissubstituted imidazolyl borates reveal a good accordance
11
yield boron compounds were monitored by B NMR measurements
and every reaction setting thereof was equipped with a bubble counter
to track gas evolution. Solvents were dried by standard procedures.
Deuterated NMR solvents were purchased from Eurisotop. 4,5-Dini-
to in the course of the investigations obtained NMR shifts
Table 1, entry 4 and 5). Therefore, two systems were found
(
that most likely open access to higher substituted 4-nitroimid-
azolyl borates and consequently will be further investigated.
[43]
[51–53]
troimidazole (11)
and 3,4,5-trinitropyrazole (13)
were pre-
pared as stated in the corresponding references. All other chemicals
were commercially available and used as received. The NMR spectra
were recorded with a JEOL Eclipse 400, JEOL Eclipse 270 or JEOL
EX400 instrument at an ambient temperature of 25 °C if not stated
Conclusions
1
3
1
4
-Nitroimidazole was used for the investigation of various otherwise. All C NMR spectra were recorded { H}-decoupled.
reaction conditions leading to mono-, bis-, tris- or tetrakissub- Chemical shifts (δ) were calibrated using the residual undeuterated
solvent as an internal reference and are according to the common con-
stituted borates. These experiments showed that the formation
vention reported in parts per million (ppm) downfield relative to
of the bissubstituted compound potassium dihydridobis(4-ni-
1
3
1
tetramethylsilane (TMS,
C, 100.6 MHz resp. 67.9 MHz; H,
troimidazolyl)borate (8) proceeds smoothly in acetonitrile and
can easily be upscaled. In order to increase the oxygen content,
the higher nitrated derivative 3,4-dinitroimidazole (11) was
used. The increased reactivity of 11 due to the second nitro
group facilitates milder reaction conditions for the formation
of sodium dihydridobis(4,5-dinitroimidazolyl)borate (12).
1
4
3
99.8 MHz resp. 270.2 MHz), nitromethane ( N) or boron trifluoro
11
etherate ( B) as external standards. The chemical shifts of the refer-
ence solvents were defined concurrent with the data from Nudel-
[54]
man.
For the designation of multiplicities the following abbrevi-
ations were used: s (singlet), d (doublet), t (triplet), q (quartet), br
(
broad) and m (multiplet) or combinations thereof; coupling constants
Furthermore, sodium dihydridobis(3,4,5-trinitropyrazolyl)bor- (J) are given in Hertz (Hz). Raman spectra were recorded with a
ate (14) was synthesized as fully nitrated compound in high Bruker FT-Raman-MultiRAM Spectrometer instrument equipped with
yields and could easily be upscaled. The energetic properties a Klaastech DENICAFC LC-3/40 laser device. The intensities are re-
ported in percentages relative to the most intense peak and are given
in parentheses. High resolution (HRMS) and low resolution (LRMS)
mass spectra were recorded by the mass spectrometry facility of the
Department of Chemistry and Pharmacy of the Ludwig Maximilian
University Munich on a JEOL MS station JMS 700 instrument. Ioniza-
tion of the samples was achieved using fast atom bombardment (FAB)
were determined, whereas two compounds, potassium dihydri-
dobis(4-nitroimidazolyl)borate (8) and sodium dihydri-
dobis(3,4,5-trinitropyrazolyl)borate (14), showed very promis-
ing properties regarding an application in pyrotechnics (de-
composition points of 189 °C and 170 °C, respectively).
Furthermore, the compounds exhibit a moderate stability
as indicated in the experimental section. Elemental analyses were per-
towards solvolysis. Especially when subjected to metathesis
formed with an Elementar Vario EL or an Elementar Vario EL micro
reactions these compounds are very promising candidates as
coloring agents in pyrotechnic formulations. Moreover, the
cube. DSC-measurements were performed with a Perkin-Elmer Pyris
–1
6
DSC- instrument at a heating rate of 5 °C min in closed aluminum
high oxygen content of compound 14 can influence the oxygen containers with a hole (1 μm) on the top for gas release and a nitrogen
–
1
balance of the whole pyrotechnic mixture positively.
flow of 5 mL·min . The reference sample was an empty closed alumi-
8
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Z. Anorg. Allg. Chem. 0000, 0–0

Job/Unit: Z13259
/KAP1
Date: 16-07-13 12:05:16
Pages: 12
Energetic Poly(azolyl)borates as New Environmentally Benign Green-Light-Emitting Species for Pyrotechnics
num container. The impact and friction sensitivity was determined 2848 (3), 2449 (6), 1563 (40), 1528 (11), 1473 (11), 1398 (19), 1363
[
39]
using a BAM drophammer and a BAM friction tester. The sensitivi-
ties of the compounds are indicated according to the UN Recommen-
dations on the Transport of Dangerous Goods (+):[ impact: insensi-
tive Ͼ 40 J, less sensitive Ͼ 35 J, sensitive Ͼ 4 J, very sensitive Ͻ
(26), 1336 (5), 1308 (100), 1280 (13), 1251 (7), 1216 (13), 1182 (16),
1127 (2), 1016 (7), 900 (2), 855 (22), 817 (4), 763 (8), 725 (2), 654 (3),
39]
–1
–
–
512 (3), 423 (3), 267 (4) cm . HRMS (FAB ): m/z for C
6 4 8 8
H O N B :
calcd. 327.0246, found 327.0254. IS (grain Ͻ 100 μm): Ͼ 10 J.
4
3
J; friction: insensitive Ͼ 360 N, less sensitive = 360 N, sensitive Ͻ FS(grain Ͻ 100 μm): Ͼ 240 N.
60 N and Ͼ 80 N, very sensitive Ͻ 80 N, extreme sensitive Ͻ 10 N.
Sodium Dihydridobis(3,4,5-trinitropyrazol-1-yl)borate (14): So-
dium borohydride (167 mg, 4.40 mmol) was suspended in diethyl ether
(25 mL) before 3,4,5-trinitropyrazole (13) (2.69 g, 13.2 mmol) was
CAUTION! The compounds described in this work are potential ex-
plosives, which are sensitive to environmental stimuli such as impact,
friction, heat or electrostatic discharge. While we encountered no is- added in small portions. Immediate gas evolution was visible and the
sues in the handling of these materials, appropriate precautions, and yellow reaction solution was stirred for 16 h at ambient temperature,
proper protective measures (safety glasses, face shields, leather coat,
during which time a pale yellow precipitate was formed. The reaction
Kevlar gloves, and ear protectors) should be taken when preparing and solid was filtered off and washed with diethyl ether to obtain 14 in
manipulating these materials.
6 2 10 12
high yields (1.61 g, 83%). DSC: Tdec = 170 °C. C H BN NaO ·4/
1
2
13
1Et
2
O: calcd. C 19.18,H 1.22, N 30.00%, found C 19.07, H 1.17, N
CN): δ = 3.80 (br. s, 2 H, BH ) ppm.
CN): δ = 146.6, 144.6 ppm. 14N NMR (CD
CN): δ =
) ppm. 11B NMR (CD
), –27.3 (NO CN): δ
–7.4 ppm. Raman (500 mW): ν˜ = 2476 (8), 1567 (17), 1478 (12),
Potassium Dihydridobis(4-nitroimidazolyl)borate (8): 4-Nitroimid-
azole (5) 4.15 g, 36.7 mmol) was added in portions to a suspension of
potassium borohydride (990 mg, 18.4 mmol) in acetonitrile (40 mL).
The obtained colorless suspension was stirred under reflux conditions
for 40 h, during this period the suspension discolored and turned from
colorless over beige-brown to completely black. After cooling to ambi-
ent temperature the reaction mixture was strongly diluted with further
acetonitrile and the insoluble impurities were filtered off. After re-
moval of the solvent in vacuo compound 8 was obtained as off-white
solid in high yields (4.06 g, 80%). Isomer 1 and isomer 2 were ob-
9.55%. 1H NMR (CD
3
2
C NMR(CD
3
3
–23.7 (NO
2
), –25.5 (NO
2
2
3
=
1457 (3), 1409 (100), 1331 (18), 1302 (4), 1223 (7), 1181 (22), 1135
(
2), 1066 (3), 850 (46), 808 (5), 769 (3), 750 (10), 561 (4), 503 (2),
–1
–
430 (2), 390 (3), 328 (6), 293 (2) cm . HRMS (FAB ): m/z for
–
C
1
6
H
2
O
12
N
10B : calcd. 416.9948, found 416.9916. IS (grain Ͻ
00 μm): Ͼ 10 J. FS (grain Ͻ 100 μm): Ͼ 120 N.
tained in the ratio of 2 to 1. DSC: Tdec = 189 °C. C
6
H
6
BKN
6 4
O ·1/
2
2
(
(
(
(
MeCN: calcd. C 28.35, H 2.55, N 30.70%, found C 28.80, H 2.59, N Acknowledgments
9.39%. 11B NMR ([D
]DMSO): δ = –10.7 ppm. Isomer 1: H NMR
1
6
4
[D
d,
6
4
]DMSO, 25 °C): δ = 8.01 (d, JC,H, C–H = 1.4 Hz, 2 H, C–H), 7.50
Financial support of this work by the Ludwig-Maximilian University
) ppm. of Munich (LMU), the U.S. Army Research Laboratory (ARL) under
]DMSO, 85 °C): δ = 7.86 (d, JC,H, C–H = 1.1 Hz, 2 H, C–H), 7.42
grant no. W911NF-09–2-0018, the Armament Research, Development,
JC,H, C–H = 1.4 Hz, 2 H, C–H), 3.30 (br. s, 2 H, BH
2
4
[D
6
d, JC,H, C–H = 1.1 Hz, 2 H, C–H), 3.34 (br. q, 1JB– H = 123 Hz, 2 H, and Engineering Center (ARDEC) under grant no. W911NF-12–1-
4
BH
2
) ppm. 13C NMR ([D
C–H), 124.9 (C–H) ppm. Isomer 2: H NMR ([D
6
]DMSO, 25 °C): δ = 148.1 (C–NO
2
), 141.1
]DMSO, 25 °C): δ
0467, and the Office of Naval Research (ONR) under grant nos.
ONR.N00014–10–1-0535 and ONR.N00014–12–1-0538 is gratefully
acknowledged. The authors acknowledge collaborations with Dr. Mila
1
(
6
4
4
=
2
8.05 (d, JC,H, C–H = 1.1 Hz, 2 H, C–H), 7.52 (d, JC,H, C–H = 1.1 Hz,
H, C–H) ppm. ([D
]DMSO, 85 °C): δ = 7.97 (br. s, 2 H, C–H), 7.46 Krupka (OZM Research, Czech Republic) in the development of new
) ppm. 13C NMR ([D
]DMSO, testing and evaluation methods for energetic materials and with Dr.
), 140.5 (C–H), 124.8 (C–H) ppm. Raman
6
(
2
br. s, 2 H, C–H), 6.30 (br. s, 2 H, BH
5 °C): δ = 147.9 (C–NO
2
6
Muhamed Suceska (Brodarski Institute, Croatia) in the development
of new computational codes to predict the detonation and propulsion
parameters of novel explosives. We are indebted to and thank Drs.
2
(
(
(
(
(
(
(
300 mW): ν˜ = 3141 (10), 3124 (3), 3117 (5), 3106 (3), 3084 (2), 2409
8), 1544 (6), 1519 (36), 1510 (3), 1474 (23), 1467 (5), 1434 (3), 1404
96), 1379 (21), 1340 (18), 1288 (21), 1279 (100), 1261 (23), 1219 Betsy M. Rice and Brad Forch (ARL, Aberdeen, Proving Ground, MD)
72), 1152 (43), 1112 (10), 1033 (13), 991 (62), 915 (3), 877 (4), 829
for many inspired discussions. The authors want to thank St. Huber
for measuring the sensitivities. The Cusanuswerk is gratefully ac-
knowledged for the award of a PhD scholarship (M. Rusan).
–
1
7), 811 (19), 705 (8), 640 (6), 551 (8), 342 (3), 314 (11) cm . HRMS
–
–
FAB ): m/z for C
6 6 4 6
H O N B : calcd. 237.0545, found 237.0530. IS
grain Ͻ 100 μm): Ͼ 40 J. FS (grain Ͻ 100 μm): Ͼ 360 N. ESD (grain
Ͻ 100 μm): Ͼ 0.85 J.
References
Sodium Dihydridobis(4,5-dinitroimidazol-1-yl)borate (12): Sodium
borohydride (265 mg, 7.00 mmol) was suspended in acetonitrile
[
1] T. M. Klapötke, G. Steinhauser, Angew. Chem. Int. Ed. 2008, 47,
330.
3
(
60 mL) before 4,5-dinitroimidazole (11) (2.21 g, 14.0 mmol) was
[
[
2] T. M. Klapötke, G. Steinhauser, J. Chem. Educ. 2010, 87, 150.
3] K. R. Tarantik, Dissertation, Ludwig Maximilian University Mu-
nich, 2010.
added in small portions. Immediate strong gas evolution was visible
and the reaction mixture was stirred at ambient temperature for 12 h,
followed by additional 15 h at 45 °C. After removal of the solvent,
compound 12 was obtained as pale yellow solid in almost quantitative
yield (2.51 g, 97%). Despite drying under high vacuum at elevated
temperature, a small amount of acetonitrile remained in the solid prod-
uct. It was assumed that the acetonitrile is part of the solid structure.
[4] R. P. Singh, R. D. Verma, D. T. Meshri, J. M. Shreeve, Angew.
Chem. Int. Ed. 2006, 45, 3584.
[5] a) O. P. Murty, J. Forensic Med. Toxicol. 2000, 17, 23; b) T. M.
Klapötke, G. Holl, Green Chem. 2001, 3, G75.
[
6] a) G. Steinhauser, K. Tarantik, T. M. Klapötke, J. Pyrotech. 2008,
7, 3; b) T. M. Klapötke, K. R. Tarantik, 11th Conference New
2
DSC: Tdec = 127 °C. C
.50, N 32.14%, found C 22.72, H 1.95, N 30.50%. H NMR
CD CN): δ = 7.40 (s, 2 H, C–H), 3.29 (br. s, 2 H, BH ) ppm.
CN): δ =
), –185.3 (ring) ppm. 11B NMR (CD
CN): δ
–12.2 ppm. Raman (300 mW): ν˜ = 3172 (2), 3137 (6), 2985 (2),
6 4 8 8
H BN NaO ·1/2MeCN: calcd. C 22.69, H
Trends in Research of Energetic Materials, Pardubice, Czech Re-
public, Apr. 9–11, 2008, Part 2, pp. 586; c) T. M. Klapötke, J.
Stierstorfer, K. R. Tarantik, 12th Conference New Trends in Re-
search of Energetic Materials, Pardubice, Czech Republic, Apr.
1–3, 2009, Part 2, pp. 647; d) T. M. Klapötke, J. Stierstorfer,
K. R. Tarantik, J. Pyrotech. 2009, 28, 61.
1
1
(
1
3
2
3
14
C NMR (CD
3 3
CN): δ = 139.6, 138.7 ppm. N NMR (CD
–
17.3 (NO ), –20.6 (NO
2
2
3
=
Z. Anorg. Allg. Chem. 0000, 0–0
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
9

Job/Unit: Z13259
/KAP1
Date: 16-07-13 12:05:16
Pages: 12
T. M. Klapötke, M. Rusan, V. Sproll
ARTICLE
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www.zaac.wiley-vch.de
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 0000, 0–0

Job/Unit: Z13259
/KAP1
Date: 16-07-13 12:05:16
Pages: 12
Energetic Poly(azolyl)borates as New Environmentally Benign Green-Light-Emitting Species for Pyrotechnics
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Received: May 21, 2013
Published Online: ᭿
Z. Anorg. Allg. Chem. 0000, 0–0
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
11

Job/Unit: Z13259
/KAP1
Date: 16-07-13 12:05:16
Pages: 12
T. M. Klapötke, M. Rusan, V. Sproll
ARTICLE
T. M. Klapötke,* M. Rusan, V. Sproll ............................. 1–12
Preparation of Energetic Poly(azolyl)borates as New Environ-
mentally Benign Green-Light-Emitting Species for Pyro-
technics
12
www.zaac.wiley-vch.de
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 0000, 0–0