Synthesis of linear and hyperbranched tetrazine-based polyhetarylene assemblies with high nitrogen content

Article abstract of DOI:10.1016/j.tet.2007.07.097

The synthesis of polyhetarylenes containing exclusively s-tetrazine and another nitrogen heterocycle (pyridine or s-triazine) is described. The key step involved the polymerization of a suitable di- or triamidrazone, leading to a linear or hyperbranched dihydrotetrazine-based assembly, respectively. The triazinylenetetrazinylene material stands as one of the most nitrogenated polymers ever described.

Full text of DOI:10.1016/j.tet.2007.07.097

Tetrahedron 63 (2007) 11189–11194
Synthesis of linear and hyperbranched tetrazine-based
polyhetarylene assemblies with high nitrogen content
*
E. Sagot, A. Le Roux, C. Soulivet, E. Pasquinet, D. Poullain, E. Girard and P. Palmas
CEA Le Ripault, BP 16, 37260 Monts, France
Received 21 June 2007; revised 24 July 2007; accepted 26 July 2007
Available online 1 August 2007
Abstract—The synthesis of polyhetarylenes containing exclusively s-tetrazine and another nitrogen heterocycle (pyridine or s-triazine) is
described. The key step involved the polymerization of a suitable di- or triamidrazone, leading to a linear or hyperbranched dihydro-
tetrazine-based assembly, respectively. The triazinylenetetrazinylene material stands as one of the most nitrogenated polymers ever
described.
Ó 2007 Elsevier Ltd. All rights reserved.
1
. Introduction
to a pyridine ring and (ii) a hyperbranched assembly of
s-tetrazine and s-triazine units. Such polymers could ben-
efit from several advantages over monomeric compounds,
including long-term stability and chemical resistance.
Moreover, these targets should exhibit modular solubil-
ities, ranging from soluble (linear oligomers) for use as en-
ergetic binders to insoluble (hyperbranched polymer) for
specific applications.
Poly(azahetarylene)s have been the subject of numerous
studies, particularly owing to their luminescent and electron
1
–3
4
transport properties.
pound of this class, but polypyrimidine and pyridine oligo-
Polypyridine is a reference com-
5
6
mers have also been described and sometimes used as
complexants or as building blocks for metallosupramole-
cular chemistry. The transition metal complexes of aza-
heterocyclic-based molecular architectures are also widely
known as luminescent and redox-active materials.
7
8
In the literature, only a few tetrazine-containing polymers
have been mentioned. One of the known pathways to-
9
22
wards tetrazine polymers arises from the well-known reac-
tion of hydrazine with nitriles to build the dihydrotetrazine
ring. This has been used with polyacrylonitrile as a start-
Due to the large scope of applications of tetrazine-based
1
0
23
compounds, the introduction of tetrazine units would
give such materials new valuable properties. As a matter
of fact, tetrazines exhibit dye, insecticide, optical,
2
2c
ing material.
However, the incorporation of tetrazine
1
1
12
13,14
rings remained weak by this method and it was not clear
whether tetrazine or aminotriazole was the actual pendant
nucleus formed during the process. More than 30 years
ago, Romanian and Japanese authors demonstrated the syn-
thesis of polymers containing tetrazine rings in the main
1
5
16,17
electrochemical, biomedical
properties, and readily
1
8
react in inverse demand Diels–Alder reactions. Some tet-
razine compounds are also known for their use in explo-
1
9
sives and propellants. Focusing on the latter feature,
our aim was to synthesize polymers with a high nitrogen
content, in order to optimize their use as energetic compo-
nents. Indeed, the high density, heat of formation and ther-
mal stability of high-nitrogen compounds make them
2
2d–f
chain.
The key step was the polycondensation of a dini-
trile or of the corresponding diimidate with hydrazine to
obtain a polydihydrotetrazine polymer of type 1 (Scheme
1). Even though this reaction was restricted to non-hetero-
cyclic precursors, we anticipated that this polycondensation
strategy could be extended further in order to synthesize
our target architectures.
2
0
attractive materials as pyrotechnic fuels or gas genera-
2
1
tors. In this paper, we will describe our efforts towards
the synthesis of unprecedented all-heterocyclic, tetrazine-
based architectures. Two structures were addressed: (i)
a polymer bearing an s-tetrazine ring directly connected
HN
NH
HN NH
NH2NH2
NC
A
CN or
A
A
EtO
OEt
N
N
n
1
Keywords: Nitrogen heterocycles; Tetrazine; Polymerization; Microwaves.
*
A = (CH2)m, CH2-p-C6H4, OCH2-p-C6H4, OCH2CH2-p-C6H4, p-C6H4
Corresponding author. Tel.: +33 2 47 34 56 94; fax: +33 2 47 34 51 42;
e-mail: eric.pasquinet@cea.fr
Scheme 1. Polycondensatescontaininga dihydrotetrazine ring (Refs. 22d–f).
0
040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.07.097

11190
E. Sagot et al. / Tetrahedron 63 (2007) 11189–11194
2
. Results and discussion
Table 1. Optimization of the polycondensation reaction leading to 4
Entry Solvent Power of Temperature Time Isolated
ꢀ
a
(min) yield (%)
2.1. Linear polymer 5 constituted of s-tetrazine and
pyridine units
irradiation (W)
(
C)
1
2
3
4
5
6
DMF
DMF
DMF
DMF
DMSO 50
NMP 50
40
150
150
150
150
180
195
20
60
60
30
20
20
47
45
16
0
40
42
40
50
60
The synthesis of 5 is outlined in Scheme 2.
2
4
Following the work of Korshak et al., pyridine-2,6-diimi-
date dihydrochloride was synthesized by bubbling gaseous
HCl into a dioxane solution of pyridine-2,6-dicarbonitrile
containing ethanol. The isolated crude dihydrochloride
was not suitable for polycondensation due to low purity. In-
stead the free diimidate 2 was obtained in pure form in a 46%
yield after neutralization of this crude product with saturated
aqueous sodium carbonate. The reaction with hydrazine hy-
a
Weight of polymer 4/weight of 3.
work at higher temperatures, however, yields were slightly
lower than in DMF (entries 5 and 6). The high resolution
C and N solid state NMR spectra of 4 showed the ex-
1
3
15
pected lines for the polymer structure, especially regarding
the dihydrotetrazine moiety. An extra signal representing a
minor contribution (see Section 4) was also observed in
2
2d,e
drate (proposed by Stoicescu-Crivetz et al.
) was used in
a second step to produce the poly(2,6-pyridinediyl-dihydro-
s-tetrazinylene). As a result, we did not observe the forma-
tion of the polymer but diamidrazone 3 quickly separated
from the reaction mixture and was isolated in high yield. It
is likely that the insolubility of 3 in THF is responsible for
the ineffective polycondensation reaction. Further attempts
to produce the polymer from 3 in DMF (in which it was
found sparingly soluble) using classical heating conditions
failed. Activation of the polycondensation step by micro-
wave irradiation was then investigated. A first experiment,
using an irradiation power of 50 W and DMF as solvent,
yielded after precipitation in MeOH a yellow solid, which
turned orange upon standing in ambient air. This was attrib-
uted to a partial oxidation of the dihydrotetrazine moieties
into tetrazines. The reaction conditions were then optimized,
by varying experimental parameters including irradiation
power, time and temperature (Table 1).
1
5
the N spectrum at ꢁ310 ppm, indicative of an NH group,
2
which was assigned to a partial rearrangement of the dihy-
drotetrazine moiety to a 4-amino-1,2,4-triazole moiety.
This is a known process that was further evidenced in
recent microwave experiments. Actually, elemental analy-
ses revealed the presence of oxygen due to water inclusion,
as already observed for polypyrimidine. Steric exclusion
2
5
2
6
5
chromatographic analysis could not be performed due to
the high insolubility of 4.
Having established that pyridine-2,6-diamidrazone 3 would
be a more useful intermediate than the corresponding diimi-
2
7
date dihydrochloride, the known 3 was synthesized di-
rectly from pyridine-2,6-dicarbonitrile. The reaction with
hydrazine hydrate produced the expected diamidrazone in
good yield and purity. However, the microwave treatment
led to the polycondensate 4 with only a 10% yield. This
drop in yield when changing the conditions of synthesis of
ꢀ
The application of an irradiation power of 40 W at 150 C
for 20 min led to the maximum yield of 47%, this value de-
creasing with higher power and longer irradiation time. At
0 W, a treatment with methanol did not produce any precip-
itate at all, indicating a possible degradation of the polymer
entry 4). Using other similar polar solvents allowed us to
1
the diamidrazone is still unexplained, since H NMR spectra
and elemental analyses were very similar regardless of the
origin of the diamidrazone. A probable reason could be the
generation of a side product in minute amount, which would
interfere with the polycondensation process. From a
6
(
NH2NH2.H2O/EtOH/55 °C/4 h
7%
8
NH2NH2
(
1M in THF)
1
) HClg/EtOH/dioxane
THF/80 °C/4 h
93%
0
°C/5 h
H2NHN
NHNH2
NH
EtO
OEt
NH
N
N
NC
N
CN 2) aq. Na2CO3
6%
NH
NH
4
2
3
MW (40W)/DMF
50 °C/20 min
7%
1
4
N
H
N
NaNO2/aq. AcOH/0 °C/15 min
63%
N
N
N
NH
N
N
N
n
N
n
5
4
Scheme 2. Synthesis of polymer 5.

E. Sagot et al. / Tetrahedron 63 (2007) 11189–11194
11191
mechanistic point of view, these results clearly evidenced
that a diamidrazone is the key intermediate in the process
of hydrazine-mediated polycondensation of diimidates to
polydihydrotetrazines (Scheme 3), as anticipated from the
The successful synthesis of the pyridyltetrazine-based poly-
mer prompted us to challenge an ever more nitrogenated
structure, consisting of alternating 1,3,5-triazine and
2
9–31
1,2,4,5-tetrazine rings. The known
2,4,6-tricyano-
2
3
known dimerization of amidrazones.
1,3,5-triazine (TCT) was used as the starting material to
achieve this goal, using the general methodology described
above for polymer 5. TCTwas prepared using a modification
HN
NH
HN
H2NHN
NH
NH2NH2
30
of the patent of Beck, using strictly anhydrous conditions
in order to limit hydrolysis of TCT to hydroxydicyano-
A
A
NC
A CN
or
EtO
OEt
NHNH2
3
1
s-triazine. The synthesis of the corresponding imidate
was attempted using the HCl /EtOH method, nevertheless
dimerization of
amidrazone
g
the hydrochloride was found to be very prone to hydrolysis.
The triamidrazone was therefore directly synthesized from
TCT with hydrazine (1 M in THF) yielding an orange solid.
Although its high insolubility made purification and charac-
terization difficult, this new product was identified as the
HN NH
HN
H2NHN
HN NH
NH
A
A
A
N
N
n
N
N
NHNH2
1
3
15
wanted s-triazine-triamidrazone by C and N solid state
CP/MAS NMR, elemental and IR analyses.
Scheme 3. Mechanism of hydrazine-mediated polycondensation of dini-
triles or diimidates to polydihydrotetrazines.
The polycondensation could be carried out using classical
experimental conditions in DMSO at high temperature le-
ading to an optimal yield of 44%. This implies that the
s-triazine-triamidrazone is more reactive than the related
pyridine-2,6-diamidrazone, certainly resulting from the
more pronounced electron-deficient character of the triazine
nucleus. The use of microwave irradiation was also investi-
gated but did not yield any improvement. The highly insol-
The poly(2,6-pyridinediyl-dihydro-s-tetrazinylene) 4 was
subjected to the usual sodium nitrite/aq AcOH oxidation
2
8
conditions. The suspension immediately turned to pink,
while a red solid separated. The oxidation of the tetrazine nu-
1
5
cleus was confirmed, in the N CP/MAS spectrum, by both
the presence of a new signal at 8 ppm (tetrazine nitrogen) and
the disappearance of the NH signal at ꢁ250 ppm. As for 4,
elemental analyses of the tetrazine polymer 5 showed the
presence of oxygen, which was attributed to the hygroscopic
character of the product. This was confirmed by the loss of
13
15
uble material was analyzed by C and N CP/MAS NMR
spectroscopies. The expected lines for structure 7 were
observed, but were also accompanied by an extra NH signal
2
ꢁ
1
the large absorption band centred at 3300 cm in the IR
spectrum (assigned to OH bonds) when the sample was dried
(
shoulder at ꢁ310 ppm) assigned to a partial rearrangement
of dihydrotetrazine moieties into 4-amino-1,2,4-triazole
units. This product was found hygroscopic, the elemental
composition being consistent with two water molecules
per unit.
ꢀ
utes upon air exposure.
at 80 C invacuum. This signal reappeared within a few min-
2.2. Hyperbranched polymer 8 consisting of s-tetrazine
and s-triazine units
Polymer 7 stands as one of the most nitrogenated polymers
described (theoretical N content: 62.7%), comparing well
with other high-nitrogen polymers based on triazine
3
2
33–35
The synthesis of 8 is outlined in Scheme 4.
HN
N
NHNH2
CN
NH2NH2 (1M in THF)
N
THF/0 °C/2 h
N
N
H2NHN
NHNH2
NH
93%
N
NC
N
CN
NH
6
DMSO/180 °C/5 h
45%
N
N
N
N
HN
HN
N
N
N
N
N
N
oxidation
oxidation
N
N
N
N
H
N
H
N
N
N
N
N
H
N
N
N
N
N
N
HN
N
NH
N
N
NH
N
N
N
N
N
N
N
N
N
N
N
8
7
(only partial oxidation)
Scheme 4. Synthesis of polymer 8.

11192
E. Sagot et al. / Tetrahedron 63 (2007) 11189–11194
3
6
1
or tetrazole monomers. A density of 1.56 was measured for
, a value, which is significantly higher than the one reported
used a standard Bruker 5 mm QNP probe for H measure-
ments and an H-X broadband probe for 10 mm sample tubes
7
3
7
13
15
1
13
for amorphous poly(p-phenylene) (1.11 ). This clearly
shows how the introduction of nitrogen heterocycles in
polyarylene structures is valuable in the field of energetic
materials, by increasing this crucial parameter.
for C and N measurements. H and C chemical shifts
were calibrated according to DMSO signal ( H: 2.5 ppm;
1
1
3
1
13
C: 39.5 ppm) or acetone signal ( H: 2.05 ppm; C:
29.92 ppm with respect to TMS, 0 ppm) used as secondary
internal references. The N signal of a 90% formamide so-
1
5
The NaNO /aq AcOH oxidation method was ineffective in
2
lution in DMSO (ꢁ269.5 ppm with respect to CH NO ,
3
2
the case of polymer 7, presumably for insolubility reasons.
Several other oxidants were tested without success except
0 ppm) was used as an external secondary reference for
N chemical shifts. High resolution solid state spectra
1
5
3
8
N O . Liquid N O was introduced directly in a small re-
2
were acquired with a Bruker broadband X-H CP/MAS probe
(7 and 4 mm outer diameter rotors). Using the CP/MAS
(Cross-Polarization/Magic Angle Spinning) experiment the
intensity of the NMR lines is primarily related to the effi-
ciency of the cross-polarization transfer, which depends on
the number of hydrogen atoms and their distance from nitro-
gen. Hence, amine protons appeared more intense than ring
4
2 4
actor containing the solid dihydrotetrazine polymer 7. After
elimination of the excess N O under a nitrogen stream, the
2
4
1
3
15
resulting solid was analyzed by C and N solid state CP/
MAS NMR. New lines assignable to the expected tetrazine
polymer were observed (especially at ꢁ5 and ꢁ239 ppm
1
5
in the N spectrum), however, remaining contributions
from dihydrotetrazine moieties were still detected even after
using harsh oxidation conditions (excess N O , 6 h at
1
13
15
pyridine-like nitrogen atoms. H, C and N chemical shifts
were calibrated according to external secondary references:
water (4.8 ppm with respect to TMS, 0 ppm), adamantane
2
4
ꢀ
1
5 C). Presumably, the highly reticulated structure of 7 gen-
1
3
erates inaccessible sites for the oxidant, leading to a structure
constituted of both dihydrotetrazine and tetrazine moieties.
(up-field C transition at 38.46 ppm with respect to TMS,
0 ppm) and NH NO (down-field transition at ꢁ358.4 ppm
4
3
with respect to CH NO , 0 ppm). For a more detailed de-
3
2
scription of NMR experimental conditions and assignments
of products 3–7, see also Ref. 39. Multiplicity is indicated
using the following abbreviations: d for a doublet, t for a trip-
let, q for a quadruplet, and br s for a broad singlet. Infrared
spectra were recorded with an attenuated total reflectance
Perkin–Elmer SpectrumOne spectrometer. Melting points
were determined on a Kofler apparatus and are uncorrected.
Elemental analyses were performed on a ThermoFisher
Scientific Flash EA 1112CHNS/O apparatus. Microwave-
assisted reactions were performed with a CEM Discover
apparatus. Reagent-grade dioxane and THF were distilled
from sodium–benzophenone ketyl. Acetonitrile was distilled
3
. Conclusion
In this work, original molecular architectures have been de-
scribed, constituted exclusively of aza-heterocycles: (dihy-
dro)-s-tetrazine and pyridine or s-triazine. In the pyridine
series, we showed that pyridine-2,6-diamidrazone can be
converted in two steps into a polymer bearing alternating
pyridine and tetrazine units. The key polycondensation
step to the dihydrotetrazine polymer was achieved using mi-
crowave activation. These results are in contrast with already
published syntheses of tetrazine polymers containing ali-
phatic and/or phenyl residues. In those cases, polymers
were obtained directly from the reaction of hydrazine with
dinitriles or diimidates. Present results clearly established
that the diamidrazone is the actual intermediate in the poly-
merization process.
over CaH . Anhydrous ethanol was obtained by distillation
2
over magnesium ethoxide. All other reagents were purchased
from Sigma–Aldrich and were used as such.
4.2. Pyridine-2,6-diimidate 2
ꢀ
In the s-triazine series, microwave activation was useless to
obtain the hyperbranched dihydrotetrazine polymer 7. This
product exhibits a high nitrogen content, comparing well
with the reference nitrogenated polymers from the literature.
Nevertheless the final oxidation step was incomplete, leav-
ing a polymer containing both dihydro-s-tetrazine and s-tet-
razine moieties. These all-aza-heterocyclic assemblies
containing tetrazine units could be of great interest in
many fields, taking advantage of the unique properties of
the tetrazine nucleus. In particular, the high density of 7
makes it a potential candidate in energetic applications.
Gaseous HCl was bubbled at 0 C over 5 h in a solution of
pyridine-2,6-dicarbonitrile (2 g, 15.5 mmol) in freshly dis-
tilled dioxane (40 mL) containing anhydrous ethanol
(2.3 mL, 40 mmol). The reaction mixture was stored at
ꢀ
5 C for 3 days. The white solid was then filtered and washed
with diethylether. The resulting crude dihydrochloride was
dissolved in water and neutralized by adding saturated aque-
ous Na CO . The precipitate was filtered and washed with
2
3
ꢀ
water to give pure 2 as a white solid, mp 72 C. Yield
1.47 g (46%). IR: n¼3261, 3239, 2979, 2934, 2899,
ꢁ
3
1
1
ꢀ
1660 cm . H NMR (200 MHz, DMSO-d , 21 C): d¼
6
3
8
.13 (t, J ¼7.2 Hz, 1H, 4-H), 7.95 (d, J ¼7.5 Hz,
H,H
H,H
3
2
H, 3-H+5-H), 4.34 (q, J ¼7.0 Hz, 2H, CH ), 1.36 (t,
H,H
2
3
13
4. Experimental
JH,H¼7.0 Hz, 3H, CH ) ppm.
C
NMR (50 MHz,
3
ꢀ
14.1 ppm. Anal. Calcd for C H O N : C 59.71, H 6.83,
N 18.99. Found: C 59.53, H 6.79, N 18.53.
DMSO-d , 21 C): d¼163.6, 146.6, 140.0, 122.3, 61.7,
6
4
.1. General
1
1 15 2 3
Solutions in (CD ) SO, with concentrations in the range of
3
2
3
0–100 mg/mL were prepared for solution-state NMR anal-
4.3. Pyridine-2,6-diamidrazone 3
yses. All NMR measurements were performed at room tem-
perature on Bruker Avance 200, Avance 300 WB and Avance
This product was obtained from pyridine-2,6-dicarbonitrile
as described, or from diimidate 2: pyridine-2,6-diimidate
2
7
4
00 WB spectrometers. For solution-state experiments, we

E. Sagot et al. / Tetrahedron 63 (2007) 11189–11194
11193
2
1
8
(0.9 g, 4.1 mmol) was dissolved in hydrazine (1 M in THF,
6 mL, 16 mmol) and the reaction mixture was heated at
0 C for 4 h. The precipitate was filtered and washed with
Anal. Calcd for C N : C 46.16, N 53.84. Found: C 45.90,
6 6
N 53.69.
ꢀ
THF to give 3 as a yellow solid. Yield 0.73 g (93%). IR:
n¼3450, 3292, 3190, 1664, 1621, 1585, 1568, 1460,
4.7. s-Triazine-triamidrazone 6
ꢁ
1
1
ꢀ
1
7
6
425 cm . H NMR (200 MHz, DMSO-d , 21 C): d¼
2,4,6-Tricyano-1,3,5-triazine (700 mg, 4.49 mmol) was in-
troduced in a 50 mL three-necked flask and anhydrous
THF (5 mL) was added under nitrogen. The mixture was
6
3
.82 (d, J ¼7.1 Hz, 2H, 3-H+5-H), 7.64 (m, 1H, 4-H),
H,H
1
3
.05 (br s, 4H), 5.25 (br s, 4H) ppm. C NMR (50 MHz,
N
ꢀ
15
ꢀ
DMSO-d , 21 C): d¼150.2, 143.6, 136.0, 118.0 ppm.
cooled to 0 C and hydrazine (1 M in THF, 35 mL,
35 mmol) was added dropwise. An orange precipitate sepa-
6
ꢀ
NMR (30 MHz, DMSO-d , 21 C): d¼ꢁ97.7, ꢁ130.2,
6
ꢀ
ꢁ
287.1, ꢁ320.4 ppm.
rated. The reaction mixture was stirred for 2 h at 0 C, then
filtrated and washed with hot THF to give 6 as an orange
solid. Yield: 1.05 g (93%). IR: n¼3421, 3299, 3183, 1653,
4
.4. Poly(2,6-pyridinediyl-dihydro-s-tetrazinylene) 4
ꢁ
1 13
1
620, 1538, 1343 cm
ꢀ
.
C solid state NMR (100 MHz,
15
A suspension of diamidrazone 3 in the appropriate solvent
100 g/L) was heated under microwave irradiation for
21 C): d¼166.3, 146.8 ppm. N solid state NMR (40 MHz,
ꢀ
Calcd for C H N : C 28.57, H 4.79, N 66.63. Found:
C 26.92, H 4.41, N 66.67.
(
21 C): d¼ꢁ132, ꢁ181, ꢁ272, ꢁ285, ꢁ325 ppm. Anal.
specified time (see Table 1). After cooling, the polymer
was precipitated by adding methanol into the reaction mix-
ture. The solid was filtered and washed with methanol to
6
12 12
give 4 as a yellow solid. Optimal conditions: DMF, 40 W,
4.8. Hyperbranched polydihydrotetrazine 7
ꢀ
1
1
2
50 C, 20 min. Yield 46%. IR: n¼3335, 1615, 1584,
ꢁ
1 13
560,1461, 1387 cm
.
C solid state NMR (100 MHz,
Triamidrazone 6 (1.2 g, 4.7 mmol) was heated in DMSO
ꢀ
ꢀ
15
1 C): d¼150.2, 146.3, 137.4, 122.4 ppm. N solid state
(12 mL) at 180 C for 5 h. The precipitate was filtered and
ꢀ
NMR (40 MHz, 21 C): d¼ꢁ94, ꢁ118, ꢁ254 ppm. Anal.
placed in a Soxhlet apparatus. The solid was extracted
with acetone for 24 h and dried in vacuo to give 7 as a
brownish powder. Yield: 540 mg (45%). IR: n¼3202,
Calcd for (C H N $0.3H O) : C 51.09, H 3.43, N 42.56.
7
5
5
2
n
Found: C 51.61, H 3.85, N 40.51 (the nitrogen content was
consistently lower than expected; this had been observed
before in other tetrazine-based compounds ).
ꢁ
1
13
1698, 1625, 1532, 1369 cm
.
C solid state NMR
1
9e
ꢀ
15
(100 MHz, 21 C): d¼166, 156 ppm. N solid state NMR
ꢀ
(
40 MHz, 21 C): d¼ꢁ150/ꢁ180, ꢁ268 ppm. Anal.
4
.5. Poly(2,6-pyridinediyl-s-tetrazinylene) 5
Calcd for (C H N $2H O) : C 30.38, H 2.97, N 53.15.
6 3 9 2 n
Found: C 30.61, H 3.00, N 53.39.
ꢀ
Saturated aqueous NaNO was added dropwise at 0 C into
2
a solution of polydihydrotetrazine 4 (93 mg) in water/acetic
acid 1:3 (6 mL). The pink reaction mixture was neutralized
with 30% aqueous ammonium hydroxide and filtered.
The solid was placed in a Soxhlet apparatus and extracted
with water (24 h) and then with acetone (24 h) to give 5 as
a red solid. Yield 58 mg (63%). IR: n¼3350,1614, 1440,
Acknowledgements
The SPOT laboratory (University of Tours) is acknowledged
for microwave experiments in the triazinyltetrazine series.
ꢁ
1
13
ꢀ
C solid state NMR (75 MHz, 21 C):
9
22 cm
.
1
5
d¼162.4, 148.4, 140.7, 125.8 ppm. N solid state NMR
References and notes
ꢀ
(
(
30 MHz, 21 C): d¼8, ꢁ170 ppm. Anal. Calcd for
C H N $0.6H O) : C 50.06, H 2.52, N 41.70. Found: C
n
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7
3
5
2
50.07, H 3.06, N 38.47 (the nitrogen content was consis-
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1
9e
3
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4
.6. 2,4,6-Tricyano-1,3,5-triazine
4
Calcined sodium cyanide was introduced under argon in
a 500 mL three-necked flask, followed by the addition of dry
ꢀ
acetonitrile (300 mL). The mixture was cooled to ꢁ35 C
and 2,4,6-trifluoro-1,3,5-triazine (12.7 mL, 0.148 mol) was
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ꢀ
ꢀ
and stirred at 0 C for 8 h, and then at 15 C for 13 h. The
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ꢁ
4
at 5ꢂ10 mbar). The 2,4,6-tricyano-1,3,5-triazine was
ꢀ
obtained as a white solid, mp 120 C. Yield: 10.62 g
C
ꢁ
1 13
(
46%). IR: n¼2276, 2255, 1510, 1333, 937, 819 cm
.
ꢀ
NMR (200 MHz, acetone-d , 21 C): d¼155.1, 113.7 ppm.
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