Microwave alkylation of lithium tetrazolate

Article abstract of DOI:10.1007/s00706-016-1867-7

Abstract: N1-substituted tetrazoles are interesting ligands in transition metal coordination chemistry, especially in the field of spin crossover. Their synthesis is performed in most cases according to the Franke-synthesis, using a primary amine as reagent introducing the substitution pattern. To enhance flexibility in means of substrate scope, we developed a new protocol based on alkylation of lithium tetrazolate with alkyl bromides. The N1–N2 isomerism of the tetrazole during the alkylation was successfully suppressed by use of highly pure lithium tetrazolate and 30?vol.% aqueous ethanol as solvent, leading to pure N1-substituted products. The feasibility of this reaction was demonstrated by a selection of different substrates. Graphical abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s00706-016-1867-7

Monatsh Chem (2017) 148:131–137
DOI 10.1007/s00706-016-1867-7
ORIGINAL PAPER
Microwave alkylation of lithium tetrazolate
1
1
1
Danny M u¨ ller
•
Christian Knoll
•
Peter Weinberger
Received: 29 September 2016 / Accepted: 25 October 2016 / Published online: 30 November 2016
Ó The Author(s) 2016. This article is published with open access at Springerlink.com
Abstract N1-substituted tetrazoles are interesting ligands
in transition metal coordination chemistry, especially in the
field of spin crossover. Their synthesis is performed in
most cases according to the Franke-synthesis, using a pri-
mary amine as reagent introducing the substitution pattern.
To enhance flexibility in means of substrate scope, we
developed a new protocol based on alkylation of lithium
tetrazolate with alkyl bromides. The N1–N2 isomerism of
the tetrazole during the alkylation was successfully sup-
pressed by use of highly pure lithium tetrazolate and
Introduction
Tetrazoles are five-membered 6p-aromatic heterocyclic
compounds and, in the case of the unsubstituted form, with
the notably high nitrogen content of 79.98%. Tetrazoles
allow for three different isomers (Scheme 1), among which
only the 5H–tetrazole being non-aromatic [1].
Depending on the substituent, substituted tetrazoles can
undergo several forms of tautomerism: apart from the ring-
opening within the azido-imine-tautomerism, C5-alkyl or
unsubstituted rings undergo changes in the substitution
pattern via annular-tautomerism [2], whereas an elec-
tronegative substituent in the C5-position favours amino-
imino-tautomerism [3].
3
0 vol.% aqueous ethanol as solvent, leading to pure N1-
substituted products. The feasibility of this reaction was
demonstrated by a selection of different substrates.
Graphical abstract
The very first reported employments of tetrazoles were
as colorants, photographical chemicals, explosives, pro-
pellants, and agrochemicals [4–6]. Since the 1960s,
tetrazoles witnessed a renaissance but now with their
application strongly depending on their isomeric form. In
the medicinal chemistry, N2- and especially C5-substituted
tetrazoles are used as carboxylic acid bioisosteres [7], as
structural motif for angiotensin blockers [8–10], as acti-
vator in oligonucleotide synthesis [11] or in the MTT-
assay, determining the metabolic cell activity by reduction
of a tetrazole-dye to a formazan by living cells [12].
In contrast, N1-substituted tetrazoles are mainly used as
ligands in inorganic coordination chemistry for transition
metal complexes. One major application there is the field of
spin-crossover materials. The spin crossover effect is known,
since over 80 years [13, 14], but with the discovery of the
light-induced excited spin state trapping effect (LIESST-
effect) [15, 16] in 1984, spin crossover complexes arouse
nearly overnight notable interest as switchable components
for data storage [17, 18], sensor materials [19], and minia-
turization of magneto-optical devices [20, 21].
Keywords N1-Tetrazole Á Heterocycles Á Basicity Á
Solvent effect Á N-Heterocyclic ligands Á Spin crossover
&
Danny M u¨ ller
danny.mueller@tuwien.ac.at
1
Institute of Applied Synthetic Chemistry, TU Wien,
Getreidemarkt 9/163-AC, 1060 Vienna, Austria
123

1
32
D. M u¨ ller et al.
Scheme 1
is known that a mixture of the N1–N2 isomeric products is
obtained [1].
To gain a first impression on the feasibility of the
attempted alkylation reaction in a first screening series,
1-chlorobutane, 1-bromobutane, and 1-iodobutane were
reacted for 6 h at 25, 75, and 150 °C with the lithium,
sodium, and potassium salts of 1H-tetrazole. For the
reaction, sealed vessels with THF as solvent were used
Two of the earliest publications about spin-transition in
N1-tetrazole-complexes were the reports on 1-alkyltetra-
zole-complexes by Franke [22, 23]. Since these first
publications, tetrazoles were used in many investigations,
as variation of crystallization [24, 25], solvent [25], the
anion and its size [26], spacer-substitution [27, 28] and
length [28], or the number of coordinating sites [27, 28]
provides independent different access–points allowing for
rational design of the ligand system.
(Scheme 2). The tetrazolate salts were prepared according
to the literature. The isomer ratio is easily determined by
1
H NMR, as the tetrazolic CH and the signals of the
adjacent CH -groups are significantly shifted to low field in
x
the case of the N2-isomer.
Whereas for room temperature no reaction was evi-
denced, for the samples at elevated temperatures, 1-butyl-
1
H-tetrazole as alkylation product was isolated. Indepen-
dent from the used tetrazolate, for all reactions at 150 °C,
:1 mixtures of the N1 and N2 isomer were identified. The
Different synthetic approaches towards N1-substituted
tetrazoles were established so far. They are based on
1
best results were achieved at 75 °C, where for the first
time, a clear tendency towards the desired N1 isomer was
observed: LiTz yielded a 3:1 mixture of N1 and N2 isomer
[
2 ? 3]-cycloaddition of isonitriles and azides [4–6],
functionalization of 1H-tetrazole using tosylates [29], or a
cycloaddition of sodium azide, triethyl orthoformate, and a
primary amine known as the Franke-synthesis [23].
Although the Franke-synthesis is by far the most common,
all approaches have, in common, moderate yields. A more
challenging weakness of these approaches is the reagent
introducing the substitution pattern: only a few isonitriles
and tosylates are commercially available. Regarding the
primary amines, the spectrum of commercial materials is
notably larger, but many substrates need to be purified in
advanced or—in the case of a non-available amine pre-
cursor—synthesized in the lab. Therefore, an approach
using alternative substrates was attempted. Main focus
points for this purpose were first, a larger commercial
spectrum of available substitution patterns which are, in
best case, also cheaper than amines. Second, the use of
bench-stable and, if necessary, easily prepared precursors,
and third, shorter reaction times and possibly higher yields
in the tetrazole formation.
(NaTz and KTz both 1:1). It should be mentioned that in all
experiments, the 1-iodobutane behaved worse than the
corresponding chloride and bromide, as coloured products
along untraceable by-products were isolated.
In a second series of experiments, LiTz was reacted with
1-bromobutane in methanol for 6 h at 130 °C in a sealed
vessel in presence of 10 mol% LiOH as additional base and
once as control experiment without. The presence of base
turned out to be disadvantageous, as a 1:1.5 ratio of N1/N2
isomers was found. In contrast, the use of MeOH led to
49% isolated yield of 1-butyl-1H-tetrazole, contaminated
by only 11% N2-isomer.
For a detailed screening of temperature, reaction time,
and stoichiometry on basis of these first results, the com-
bination of LiTz and 1–bromobutane in methanol was
chosen. To decrease the reaction time and enlarge the
temperature window, all further reactions were performed
using a laboratory microwave oven.
For this purpose, we decided to focus on the reaction of
alkali tetrazolates (Tz) with alkyl halides.
As the amount of pure N1-alkylation was irreproducible
under all investigated circumstances, the quality of the
lithium tetrazolate was identified to be the only variable
among these experiments. By determination of the pH-
value and use of powder X-ray diffraction (P–XRD)
Results and discussion
The complete series of alkali-tetrazolate salts was reported
in 2008 by Klap o¨ tke et al. [30]. All of these salts are rel-
atively stable compounds and easily prepared in good
yields by neutralization of a 1H-tetrazole solution with the
corresponding base.
Scheme 2
Regarding the alkylation reaction of tetrazoles, a non-
negligible difficulty is found in its tendency towards iso-
merization: For many substitution reactions of tetrazoles, it
1
23

Microwave alkylation of lithium tetrazolate
133
Scheme 3
analysis, for the so far used batches of LiTz, varying
amounts of contamination with LiOHÁH O and Li CO
2
2
3
were found. As the used anhydrous LiOH is very sensitive
towards moisture and atmospheric CO , an alternative
2
procedure for the LiTz-synthesis was developed. By the
use of a freshly prepared LiOMe-solution in MeOH and
subsequent removal of unreacted 1H-tetrazole by extrac-
tion with hot anhydrous isopropanol, a reproducibly pure
LiTz could be obtained (Scheme 3).
Fig. 1 Correlation between N2-isomer concentration and ethanol–
water ratio
The use of high temperatures (varying conditions
between 140 and 200 °C) and the use of methanol yielded
rather irreproducible results, leading to a systematic opti-
mization regarding reaction temperature and polarity of the
solvent. To enhance reactivity and reduce reaction time, the
addition of 10 mol% of lithium iodide hydrate was found
to be advantageous. With constant yield and isomer ratio,
the reaction temperature could be decreased to 100 °C and
reaction times of 45 min. Samples reacted for longer times
in the microwave showed increasing N2-isomer fractions.
Very promising results were obtained due to the varia-
tion of the solvent polarity. The use of anhydrous ethanol
yielded reproducible mixtures with N2 contents between
commonly used Franke-synthesis, the yields could not be
notably enhanced for all investigated cases. Moreover, the
main advantages of the alkylation protocol are shorter
reaction times and, especially, the use of bromides as cheap
commercially available starting materials with a broader
structural variety than for amines. The alkylation protocol
cannot be seen as replacement for the Franke reaction, but
notably enhances the flexibility regarding synthetic
approaches to desired target structures.
Conclusion
2
0 and 43%. The use of water instead of methanol led to a
negligible product formation, promoting the formation of
intractable products. By the use of water–ethanol mixtures,
finally, the desired selectivity could be obtained. As shown
in Fig. 1, the amount of N2-isomer decreases with
increasing water content. Using 30% v/v ethanol–water
mixtures led, reproducibly, to pure N1-isomeric products.
By means of NMR and IR spectroscopy, no N2-isomer
formation was detected.
Based on the alkylation of alkali tetrazolates, within this
work, a novel approach to N1-functionalized tetrazoles was
developed. The aim was to establish a protocol using
bench-stable commercial substrates, which are cheaper and
available for a broader scope of substrates than amines are.
These demands were satisfied by the alkylation of lithium
tetrazolate with alkyl bromides.
The major difficulty for alkylation of the tetrazole was
the N1–N2 isomerism. Within several screening steps, the
purity of the lithium tetrazolate, as well as the polarity of
the solvent were identified as crucial parameters. A mod-
ified protocol using lithium methanolate guarantees for a
reproducibly high quality of the LiTz. In combination with
30 vol.% aqueous ethanol as solvent, this protocol allows
for quantitative suppression of N2-isomer formation. The
reaction was optimized using microwave conditions,
leading finally to a protocol, which allows for good yields
after 45-min reaction time at 100 °C. Whereas longer
reaction times do not significantly increase the yield, they
promote side reactions.
Summarizing the optimization procedure, the best
results were achieved using a mixture of fresh lithium
3
tetrazolate and R-Br substrate (1–3 mmol per cm of sol-
vent) in a solution of 30 vol.% ethanol–water mixture,
reacted for 45 min under microwave conditions at 100 °C.
Once proper conditions were found, the reaction was
repeated with different substrates. Yields and structure of
the investigated materials are given in Table 1.
For the selection of substrates presented in Table 1, the
conditions developed during the screening-process at hand
of the reaction of 1–bromobutane with LiTz were suc-
cessfully applied. The formation of the corresponding N2-
isomer was not evidenced in any case. Contrasting the
newly developed substitution protocol with the so far
The alkylation reaction leads in a very short time to a
broad spectrum of interesting ligands, as could be shown
123

1
34
D. M u¨ ller et al.
Table 1 Target structures and
isolated yields used in the
substrate screening (conditions
and used substrates are given in
the ‘‘Experimental section’’)
3
6
(61.3%)
(48.1%)
4 (56.4%)
7 (57.3%)
5 (64.8%)
8 (55.2%)
9
(56.7%)
10 (64.6%)
13 (48.4%)
11 (52.4%)
12 (44.1%)
14 (41.7%)
15 (64%)
16 (33.6%)
by several examples within this work. In summary, it was
possible to modify, through this new approach, the ligand
synthesis for N1-substituted tetrazoles in an effective way.
This allows, in the future, for significantly higher
throughput and an optimized design of interesting target
structures for spin-crossover materials based on N1-sub-
stituted tetrazoles.
with an UATR accessory attached. If not otherwise stated,
the background was measured with opened anvil versus
ambient air. The powder X–ray diffraction measurements
were carried out on a PANalytical X’Pert diffractometer in
Bragg–Brentano geometry using Cu Ka1,2 radiation, an
X’Celerator linear detector with a Ni–filter, sample spin-
ning with back loading zero background sample holders
and 2h = 4°–90°, T = 297 K at the X–ray Center at TU
Wien. The diffractograms were evaluated using the PAN-
alytical program suite HighScore Plus v3.0d. A background
correction and a Ka2 strip were performed.
Experimental
For all experiments, reagents and solvents were commer-
cially obtained from Sigma-Aldrich and used as supplied.
Unless otherwise stated, all reactions were performed
under normal aerobic conditions.
Warning: Tetrazoles and its derivatives are potential
explosive and shock sensitive compounds; therefore
handle with care. Proper protective measures should
be taken [31, 32].
1
13
H and C{1H} NMR spectra were recorded on a
Bruker Avance UltraShield 400 spectrometer with broad-
band probe head. All NMR chemical shifts are reported in
1H-tetrazole (1)
NH Cl (53.49 g, 1 mol, 1 eq.) and 97.51 g NaN (1.5 mol,
4
3
1
13
3
1.5 eq.) were suspended in 258 cm triethyl orthoformate
ppm; H and C shifts are referenced to the residual sol-
vent resonance. Mid-range infrared spectra were recorded
3
(1.55 mol, 1.55 eq.) and 500 cm acetic acid. The reaction
-
1
in ATR technique within the range of 4000–450 cm
using a PerkinElmer Spectrum Two FTIR spectrometer
mixture was stirred for 18 h at 95 °C and filtrated after
cooling. After evaporation to dryness, the solid residue was
1
23

Microwave alkylation of lithium tetrazolate
135
3
extracted with 450 cm of boiling isopropanol. This step
1
13
( H NMR, C{1H} NMR, and MIR) were found to be
identical with the ones described in Ref. [28].
was repeated once. The off-white residue after evaporation
of the combined isopropanol fractions was recrystallized
from ethanol. Yield: 42.4 g (60.5%). The spectroscopic
1-Butyl-1H-tetrazole (5)
Lithium tetrazolate and 1-bromobutane were used as
reagents. Workup A, product obtained as colourless oil.
Yield: 245.26 mg (64. %). The spectroscopic properties
1
13
properties ( H NMR, C{1H} NMR, and MIR) were
found to be identical with the ones described in Ref. [30].
1
13
Lithium tetrazolate (2)
Lithium granulate (2 g, 0.29 mol, 1 eq.) was dissolved
3
under cooling in 250 cm dry methanol. To the lithium
( H NMR, C{1H} NMR, and MIR) were found to be
identical with the ones described in Ref. [28].
1-Pentyl-1H-tetrazole (6)
methoxide solution, slowly, 22.2 g of 1H-tetrazole
Lithium tetrazolate and 1-bromopentane were used as
reagents. Workup A, product obtained as colourless oil.
Yield: 202.29 mg (48.1%). The spectroscopic properties
(
0.32 mol, 1.1 eq.) was added. The suspension was stirred
for 1 h at room temperature. After filtration, the lithium
tetrazolate was dried in vacuum and stored under inert gas.
1
13
(
H NMR, C{1H} NMR, and MIR) were found to be
1
Yield: 18.3 g (83.6%). The spectroscopic properties ( H
identical with the ones described in Ref. [33].
1
3
NMR, C{1H} NMR, and MIR) were found to be
identical with the ones described in Ref. [30].
1-Hexyl-1H-tetrazole (7)
Lithium tetrazolate and 1-bromohexane were used as
reagents. Workup A, product obtained as colourless oil.
Yield: 265.11 mg (57.3%). The spectroscopic properties
General procedure for microwave alkylations
1
13
Freshly prepared lithium tetrazolate (228 mg, 3 mmol,
( H NMR, C{1H} NMR, and MIR) were found to be
identical with the ones described in Ref. [33].
1
3
eq.) and 3 mmol of the alkyl bromide were dissolved in
3
cm of 30% v/v ethanol in a microwave vial. Lithium
1,2-Bis(tetrazol-1-yl)ethane (8)
iodide hydrate (45.5 mg, 0.3 mmol, 0.1 eq.) was added.
The mixture was immediately reacted in the microwave at
Lithium tetrazolate and 1,2-dibromoethane were used as
reagents. Workup B, product obtained as white solid.
Yield: 275.14 mg (55.2%). The spectroscopic properties
100 °C for 45 min. Two different workup strategies were
used:
1
13
(
H NMR, C{1H} NMR, and MIR) were found to be
3
Workup A The reaction mixture was diluted with 5 cm
3
water and, afterwards, extracted twice with 10 cm of
hexane to remove the eventually formed N2-isomer.
identical with the ones described in Ref. [34].
1,4-Bis(tetrazol-1-yl)butane (9)
Lithium tetrazolate and 1,4-dibromobutane were used as
reagents. Workup B, product obtained as off-white solid.
Yield: 330.33 mg (56.7%). The spectroscopic properties
Afterwards, the extraction was repeated three times with
3
0 cm of ethyl acetate each. The combined organic phases
1
were dried over MgSO4 and evaporated to yield the
product.
1
13
(
H NMR, C{1H} NMR, and MIR) were found to be
identical with the ones described in Ref. [35].
Workup B The reaction mixture was filtered through a thin
1
,5-Bis(tetrazol-1-yl)pentane (10)
layer of silica gel and evaporated. The solid residue was
3
triturated with 30 cm ethyl acetate and evaporated,
Lithium tetrazolate and 1,5-dibromopentane were used as
reagents. Workup B, product obtained as white solid.
Yield: 403.55 mg (64.6%). The spectroscopic properties
yielding the product.
1
13
(
H NMR, C{1H} NMR, and MIR) were found to be
Indicated yields refer to isolated yields
identical with the ones described in Ref. [36].
1
-Ethyl-1H-tetrazole (3)
1,6-Bis(tetrazol-1-yl)hexane (11)
Lithium tetrazolate and 1-bromoethane were used as
reagents. Workup A, product obtained as colourless oil.
Yield: 180.43 mg (61.3%). The spectroscopic properties
Lithium tetrazolate and 1,6-dibromohexane were used as
reagents. Workup B, product obtained as beige solid.
Yield: 349.39 mg (52.4%). The spectroscopic properties
1
13
(
H NMR, C{1H} NMR, and MIR) were found to be
1
13
(
H NMR, C{1H} NMR, and MIR) were found to be
identical with the ones described in Ref. [28].
identical with the ones described in Ref. [24].
1
-Propyl-1H-tetrazole (4)
1-Isopropyl-1H-tetrazole (12)
Lithium tetrazolate and 1-bromopropane were used as
reagents. Workup A, product obtained as colourless oil.
Yield: 189.74 mg (56.4%). The spectroscopic properties
Lithium tetrazolate and 2-bromopropane were used as
reagents. Workup A, product obtained as colourless oil.
Yield: 148.36 mg (44.1%). The spectroscopic properties
123

1
36
D. M u¨ ller et al.
1
13
H NMR, C{1H} NMR, and MIR) were found to be
(
3. Lieber E, Rao CNR, Pillai CN, Ramachandran J, Hites RD (1958)
Can J Chem 36:801
identical with the ones described in Ref. [37].
4
5
6
7
8
9
. Benson FR (1967) In: Elderfield RC (ed) Heterocyclic com-
pounds. Wiley, New York
. Butler R (1997) In: Boulton AR (ed) Advances in heterocyclic
chemistry. Academic Press, New York
. Rathsburg H (1921) Explosives. GB 185555, Sep 14, 1922;
(1923) Chem Abstr 17:6365
. Malik MA, Wani MY, Al-Thabaiti SA, Shiekh RA (2013) J Incl
Phenom Macro 78:15
. Kawata T, Hashimoto S, Koike T (1996) J Pharmacol Exp Ther
1
-Isobutyl-1H-tetrazole (13)
Lithium tetrazolate and 1-bromo-2-methylpropane were
used as reagents. Workup A, product obtained as colourless
oil. Yield: 183.18 mg (48.4%). The spectroscopic proper-
1
13
ties ( H NMR, C{1H} NMR, and MIR) were found to be
identical with the ones described in Ref. [37].
2
77:572
1
-Benzyl-1H-tetrazole (14)
. Kim JH, Lee JH, Paik SH, Kim JH, Chi YH (2012) Arch Pharm
Res 35:1123
Lithium tetrazolate and (bromomethyl)benzene were used
as reagents. Workup B, product obtained as white solid.
Yield: 200.39 mg (41.7%). The spectroscopic properties
10. Velasquez MT (1996) Arch Fam Med 5:351
11. Berner S, M u¯ hlegger K, Seliger H (1989) Nucleic Acids Res
17:853
1
13
(
H NMR, C{1H} NMR, and MIR) were found to be
1
2. Berridge MV, Herst PM, Tan AS (2005) Biotechnol Annu Rev
1:127
identical with the ones described in Ref. [38].
1
1
1
1
3. Cambi L, Szeg o¨ L (1931) Ber Dtsch Chem Ges 64:2591
4. Cambi L, Szeg o¨ L (1933) Ber Dtsch Chem Ges 66:656
5. Decurtins S, Gutlich P, Hasselbach KM, Hauser A, Spiering H
(1985) Inorg Chem 24:2174
6. Decurtins S, Gutlich P, Kohler CP, Spiering H, Hauser A (1984)
Chem Phys Lett 105:1
7. Kahn O, Martinez CJ (1998) Science 279:44
1
-(1H-Tetrazol-1-yl)propan-2-ol (15)
Lithium tetrazolate and 1-bromopropan-2-ol were used as
reagents. Workup A, product obtained as colourless oil.
1
Yield: 219.09 mg (64%). The spectroscopic properties ( H
1
1
3
NMR, C{1H} NMR, and MIR) were found to be
identical with the ones described in Ref. [1, 4].
1
1
8. G u¨ tlich P, Goodwin HA (2004) Spin Crossover in Transition
Metal Compounds I-III. Topics in Current Chemistry, vol
2
-(1H-Tetrazol-1-yl)acetic acid (16)
2
33–235. Springer, Berlin
Lithium tetrazolate and 2-bromoacetic acid were used as
reagents. Workup B, product obtained as white solid.
Before evaporation of the crude reaction mixture, the
solution was acidified using hydrochloric acid. For the final
extraction, isopropanol instead of ethyl acetate was used.
Yield: 129.11 mg (33.6%). The spectroscopic properties
19. Linares J, Codjovi E, Garcia Y (2012) Sensors 12:4479
20. Dugay J, Gimenez-Marques M, Kozlova T, Zandbergen HW,
Coronado E, van der Zant HSJ (2015) Adv Mater 27:1288
2
1. Zhu L, Zou F, Gao JH, Fu YS, Gao GY, Fu HH, Wu MH, Lu JT,
Yao KL (2015) Nanotechnology 26:315201
22. Franke PL, Groeneveld WL (1981) Transit Metal Chem 6:54
23. Franke PL, Haasnoot JG, Zuur AP (1982) Inorg Chim Acta 5
24. Grunert CM, Weinberger P, Schweifer J, Hampel C, Stassen AF,
Mereiter K, Linert W (2005) J Mol Struct 733:41
1
13
(
H NMR, C{1H} NMR, and MIR) were found to be
identical with the ones described in Ref. [39].
2
2
2
2
5. Stassen AF, Grunert M, Dova E, M u¨ ller M, Weinberger P,
Wiesinger G, Schenk H, Linert W, Haasnoot JG, Reedijk J (2003)
Eur J Inorg Chem 12:2273–2282
6. Absmeier A, Bartel M, Carbonera C, Jameson GNL, Werner F,
Reissner M, Caneschi A, Letard JF, Linert W (2007) Eur J Inorg
Chem 19:3047–3054
7. Quesada M, Kooijman H, Gamez P, Costa JS, van Konings-
bruggen PJ, Weinberger P, Reissner M, Spek AL, Haasnoot JG,
Reedijk J (2007) Dalton Trans 46:5434–5440
8. Hassan N, Weinberger P, Mereiter K, Werner F, Molnar G,
Bousseksou A, Valtiner M, Linert W (2008) Inorg Chim Acta
Acknowledgements Open access funding provided by Austrian
Science Fund (FWF). We acknowledge financial support of the
Austrian Science Fund (FWF Der Wissenschaftsfond) Project
P24955-N28. This work was performed in the framework of the
Corporation in Science and Technology (COST) action CM1305
Explicit Control Over Spin-states in Technology and Biochemistry
(ECOSTBio). The X-ray center (XRC) of TU Wien (head: Klaudia
Hradil) provided access to the powder X-ray diffractometer.
Open Access This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://
creativecommons.org/licenses/by/4.0/), which permits unrestricted
use, distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were
made.
3
61:1291
2
3
3
3
9. Koren AO, Gaponik PN, Ivashkevich OA, Kovalyova TB (1995)
Mendeleev Commun 5:10
0. Klapotke TM, Stein M, Stierstorfer J (2008) Z Anorg Allg Chem
¨
634:1711
1. Klapotke TM, Krumm B, Steemann FX, Steinhauser G (2010)
¨
Safety Sci 48:28
2. Steinhauser G, Evers J, Jakob S, Klap o¨ tke TM, Oehlinger G
(
2008) Gold Bull 41:305
3. Weinberger P, Grunert M (2004) Vib Spec 34:175
4. Schweifer J, Weinberger P, Mereiter K, Boca M, Reichl C,
Wiesinger G, Hilscher G, van Koningsbruggen PJ, Kooijinan H,
Grunert M, Linert W (2002) Inorg Chim Acta 339:297
3
3
References
1
2
. Meier H (1994) Tetrazole. Houben Weyl, Methods of organic
chemistry, E-series, vol E8d. Thieme Chemistry, Stuttgart
. Moore DW, Whittaker AG (1960) J Am Chem Soc 82:5007
3
5. Grunert CM, Schweifer J, Weinberger P, Linert W, Mereiter K,
Hilscher G, M u¨ ller M, Wiesinger G, van Koningsbruggen PJ
(
2004) Inorg Chem 43:155
1
23

Microwave alkylation of lithium tetrazolate
137
3
3
6. Absmeier A, Bartel M, Carbonera C, Jameson GNL, Weinberger
P, Caneschi A, Mereiter K, Letard JF, Linert W (2006) Chem Eur
J 12:2235
7. Hassan N, Stelzl J, Weinberger P, Molnar G, Bousseksou A,
Kubel F, Mereiter K, Boca R, Linert W (2013) Inorg Chim Acta
38. Bahari S (2013) Lett Org Chem 10:527
39. Heppekausen J, Klap o¨ tke TM, Sproll SM (2009) J Org Chem
74:2460
3
96:92
123