C6N7Cl[N(C6H5) 2]2·p-C6H4(CH 3)2 - A mono-chloro-tri-s-triazine adduct

Article abstract of DOI:10.1039/b924428j

We report the synthesis and comprehensive characterization including the first crystal structure of a disubstituted tri-s-triazine. The molecule bears one chlorine atom as a reactive site for further derivatisation.

Full text of DOI:10.1039/b924428j

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C6N7Cl[N(C6H5)2]2ꢀp-C6H4(CH3)2—a mono-chloro-tri-s-triazine adductw
Anke Schwarzer and Edwin Kroke*
Received (in Cambridge, UK) 23rd November 2009, Accepted 9th February 2010
First published as an Advance Article on the web 25th February 2010
DOI: 10.1039/b924428j
We report the synthesis and comprehensive characterization
including the first crystal structure of a disubstituted tri-s-
triazine. The molecule bears one chlorine atom as a reactive site
for further derivatisation.
In 2, diphenylamine seems to neutralize this reactivity for
the last Cl atom. While diphenylamine replaces the first and
second Cl atoms under mild conditions, stronger conditions
have to be used to substitute the third Cl atom. At least,
several hours under reflux are necessary (see Notes and
references).
Tri-s-triazine derivatives (compounds based on the tricyclic
C6N7 unit) have recently gained considerable attention.1–7 In
the patent literature numerous claims for uses as flame
retardants are reported.1 Several authors have used them as
precursors for carbon(IV)nitrides (with sp3-hybridised
C-atoms) which have been predicted to be harder than
diamond.2 Nitrogen rich derivatives such as C6N7(N3)3 or
C6N7(NHNH2)3 have been suggested to be useful blowing
agents and/or propellants.3 While C6N7(NEt2)3 shows NLO
properties4 the polymer melon [C6N7(NH2NH)]n has recently
been reported to be a semiconductor.5 Related derivatives
were used as metal-free catalysts for CO2-fixation (artificial
photosynthesis)6 or photocatalysis, e.g. for H2 formation from
water.5,7 Despite these interesting potential applications of
compounds containing the C6N7-unit, there are no reports
on asymmetric molecular derivatives, which have been
structurally analysed.
Schroeder and Kober8 described the synthesis of 1,5,8-
tris-(diphenylamino)-tri-s-triazine from diphenylamine and
cyameluric chloride (C6N7Cl3, 1)9 in p-xylene using a molar
ratio of 9 : 1.z On performing this synthesis in boiling THF
instead of xylene we were not able to isolate the trisubstituted
compound but the disubstituted title compound 2 and the
respective amine hydrochloride as by-product.
The thermal stability of the host–guest-compound
2ꢀp-C6H4Me2 was investigated by TG/DTA (Fig. 1). It shows
an onset of desorption of the guest molecule at 149.7 1C while
p-xylene itself boils at 138 1C.
The mass loss reached at 200 1C indicated one guest
molecule per C6N7Cl[N(C6H5)2]-host. The crystal structure
reveals the same situation: one xylene per heptazine.
C6N7Cl[N(C6H5)2]2ꢀp-C6H4Me2 crystallizes in the monoclinic
space group P21/n (no. 14).y All bond lengths and angles of all
four phenyl rings are within the range of the expected values.
For a detailed discussion of differences in bond lengths and
angles on the one hand, and intermolecular interactions on the
other hand, it is essential to compare the disubstituted hepta-
zine 2 to cyameluric chloride solvate 1ꢀ(CH3)2COꢀ(C2H5)2O,9
110 and the tri-amino-substituted heptazine C6N7(NEt2)3 3.4
1,5,8-Tris-(diethylamino-tri-s-triazine), 3, is the only structu-
rally characterised NR2-substituted tri-s-triazine with R not
being hydrogen. Table 1 represents the average bond lengths
and angles, and reveals significant differences resulting from
either the chlorine or the amine substitution at the C6N7 core.
While 2 comprises phenyl rings, in 3 aliphatic ethyl moieties
are substituted at the amino N atom. This leads to an
elongation of the C3–N3 bonds in 3 (Fig. 2). The planarity
of the host molecule 2 is not reduced by the asymmetric
substitution of the C6N7 core. The fit of the 13-membered
ring system to a plane leads to a RMS deviation of 0.0451 A2
indicating nearly perfect planarity.
In a modified approach diphenylamine and 1 were used in a
2 : 1 ratio, dissolved in THF. After refluxing and stirring for
two days THF was removed, p-xylene added and HN(C6H5)2ꢀ
HCl separated. Reducing the volume leads to the pale yellow
target inclusion compound. Single crystals were obtained by
evaporation of the solvent at B20 1C. Surprisingly, the
p-xylene-adduct turned out to be air stable, even in solution.
This stability is unexpected since C6N7Cl3 is extremely
sensitive towards hydrolysis. In contrast to cyanuric chloride
C3N3Cl3 it has to be handled under inert conditions. The
very high reactivity at the C–Cl bonds in C6N7Cl3 leads to
trisubstitution in most cases.
Technische Universitat Freiberg, Institut fur Anorganische Chemie,
¨
Leipziger Strasse 29, 09596 Freiberg, Germany.
¨
E-mail: Edwin.Kroke@chemie.tu-freiberg.de;
Fax: +49 (0)3731 394058; Tel: +49 (0)3731 393174
w Electronic supplementary information (ESI) available: Raman-, IR-,
1H- and 13C-NMR spectra and two figures displaying the crystal
structure. CCDC 753726. For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/b924428j
Fig. 1 TG and DTA curves of the title compound 2ꢀp-C6H4Me2.
Chem. Commun., 2010, 46, 2829–2831 | 2829
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Table 1 Average bond lengths (A) and angles (1) for 1,10 1ꢀ(CH3)2COꢀ(C2H5)2O,9 2ꢀp-C6H4Me2 and 34 (for atom numbering see Scheme 1)
Bond length in A (s/A)
1ꢀ(CH3)2COꢀ(C2H5)2O9
110
2ꢀp-C6H4Me2
34
N1–C1
C1–N2
1.397(4)
1.334(4)
1.328(8)
1.390(8)
1.330(8)
1.321(8)
1.3977(14)
1.3285(15)
1.3178(15)
1.3499(15)
1.4428(15)
1.7417(11)
1.3553(15)
2ꢀp-C6H4Me2
1.402(3)
1.330(3)
C2–N20
C2–N2
C2–N3
1.352(3)
1.348(3)
C20–Cl
N3–C3
1.716(4)
1.715(6)
1.466(3)
3
Bond angle in degrees (s/1)
1ꢀ(CH3)2COꢀ(C2H5)2O
1
C1–N1–C10
N20–C20–N20
N2–C2–N2
Cl–C20–N2
N2–C2–N3
C2–N3–C3
120.0(6)
130.2(4)
119.99(5)
130.2(5)
120.00(9)
131.90(10)
127.02(10)
114.05(9)
116.49(10)
121.17(9)
119.99(1)
127.19(1)
114.9(4)
114.9(4)
116.43(2)
120.96(2)
coplanar arrangement of the C6N7-units has been observed
in related derivatives such as C6N7(OSiMe3)3,11 alkali cyamelurates
13
M3[C6N7O3],11,12 C6N7(N3)3 or melonates.14
Although the peripheral N-atoms of the tri-s-triazine
tricycle are very suitable as acceptors for H-bridges,15–17 only
weak hydrogen bonds occur since no typical hydrogen donor
is present. The guest molecule is an aprotic solvent not having
even a potential hydrogen acceptor site such as nitrogen,
oxygen or sulfur nor a hydrogen donor site. Therefore, the
most significant interactions are one C–Hꢀ ꢀ ꢀN and several
C–Hꢀ ꢀ ꢀp contacts (Table 2).
The C24–H24ꢀ ꢀ ꢀN1 (d = 2.51 A, y = 157.81) interaction
leads to dimerisation of two host molecules while the other
two weak C–Hꢀ ꢀ ꢀN interactions form an intermolecular four-
membered ring consisting of two host and two guest molecules
(C38–H38ꢀ ꢀ ꢀN4 with d = 2.71 A, y = 135.51). The C–Hꢀ ꢀ ꢀp
contacts lead to zigzag chains in the ac plane connecting two
host molecules.
Scheme 1 Molecular structure of 2 with the used numbering.
The FTIR spectra of 2ꢀp-C6H4Me2 show the typical
absorption of the tri-s-triazine moiety at 809 cmꢂ1. Further
vibrations of the heptazine unit at about 1649 and 1426 cmꢂ1
interfere with the vibrations of phenyl rings and the p-xylene.
The guest shows the typical phenylene ring signals. At 690 and
701 cmꢂ1 the characteristic bands of a monosubstitution for
the phenyl groups can be found. The C–Cl vibration appears
at 1226 cmꢂ1. In contrast to cyameluric chloride, where the
C–Cl group shows a signal at 1205 cmꢂ1, a shift to higher
wavenumbers is observed. The complex Raman spectrum
below 1700 cmꢂ1 is due to the aromatic vibrations of the
diphenylamine moiety and p-xylene.
Fig. 2 ORTEP-plot of 2ꢀp-C6H4Me2. Hydrogen atoms are omitted
Table 2 Intermolecular hydrogen bond (C–Hꢀ ꢀ ꢀN and C–Hꢀ ꢀ ꢀp)
lengths (A) and angles (1) for 2ꢀp-C6H4Me2
for clarity, thermal ellipsoids are at 50% probability level.
The phenyl rings are not coplanar with the C6N7 core. While
the aromatic moieties orientated to the chlorine atom reveal a
twisting towards the C6N7-plane of 53.95(3)1 and 57.42(3)1,
respectively, the other two phenyl rings are almost perpendi-
cular to the C6N7-unit [83.80(3)1 and 87.69(3)1].
Another point of interest is the intermolecular arrangement
of the host molecule and the guest p-xylene which exhibits an
angle of 11.52(5)1 with a centre-to-centre distance of 3.42 A
indicating p-stacking. The latter type of interaction and a
Interaction
d/A D/A
y/1
Symmetry
C24–H24ꢀ ꢀ ꢀN1
C33–H33ꢀ ꢀ ꢀN6
C37–H37Cꢀ ꢀ ꢀN4
C17–H17ꢀ ꢀ ꢀCg4a
C21–H21ꢀ ꢀ ꢀCg4a
2.51 3.4121(16) 157.8 1 ꢂ x, ꢂy, ꢂz
2.69 3.5955(18) 158.8 1 ꢂ x, 1 ꢂ y, ꢂz
2.71 3.4765(19) 135.5 x, y, z
2.62 3.5118(15) 157
2.85 3.7434(15) 157
1
2
1
2
1
2
ꢂ x, + y, ꢂ z
1 1 1
2
ꢂ + x, ꢂ y, ꢂ + z
2
2
C38–H38Cꢀ ꢀ ꢀCg6a 2.94 3.6550(17) 131
1 ꢂ x, 1 ꢂ y, ꢂz
a
Cg4 is defined as the centre of gravity of the ring C7–C12; Cg6 is
defined as the centre of gravity of the ring C19–C24.
ꢁc
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In summary, we present here the first disubstituted
cyameluric chloride. The three Cl-atoms of cyameluric
chloride 1 have been considered to be of similar reactivity.
Due to the relatively large distance between these chlorine
Dc = 1.352 Mg mꢂ3, T = 100(2) K, 47 117 collected reflections, 9271
unique reflections, Rint = 0.0386, 435 parameters, R(all) = 0.0633, wR(all
data) = 0.1107, S = 1.068. CCDC 753726.
1 See e.g.: (a) S. Hoerold, O. Schacker, H. Bauer, W. Krause and
D. Eisenhauer, PCT Int. Appl., WO 2009109318 A1, 2009;
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atoms
a weak influence of successive substitution was
expected. Contrarily, the two N(C6H5)2-groups in 2 decrease
the reactivity of the remaining Cl-atom significantly.
Nevertheless, the latter chlorine substituent is a useful reactive
site for further synthesis of novel asymmetric tri-s-
triazine derivatives. As mentioned in the introduction,1–7
molecular3,4,8–12,14 and polymeric5–7,20 tri-s-triazines have
recently proved to possess numerous interesting properties,
which may also be relevant for asymmetric derivatives.
We acknowledge the German Research Foundation
(DFG, project # KR1739/9-2) for financial support.
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Notes and references
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z All manipulations were performed under argon atmosphere using
standard Schlenk techniques. The solvents THF and p-xylene were
distilled from a sodium–benzophenone mixture. Cyameluric chloride,
1, was obtained as described in ref. 9 and characterised compre-
hensively. Synthesis of 2 was performed by mixing 0.66 g (3.91 mmol)
diphenylamine in 15 ml THF with a solution of 0.54 g (1.95 mmol)
cyameluric chloride in 50 ml THF at B20 1C. Additional stirring over
night leads to a pale yellow solution with a slight white precipitate. The
solvent was completely evaporated under vacuum. Addition of
p-xylene and separation of the white by-product HN(C6H5)2ꢀHCl lead
to a yellow solution. Crystals were obtained by slow evaporation of the
solvent at room temperature. Yield: 0.21 g (16.6%). Anal calcd. for
C30H20ClN9ꢀC8H10 (648.16): C 70.42, H 4.67, Cl 5.47, N 19.45%;
found C 70.72, H 4.47, N 19.56%; C/N ratio: calcd. 3.62, found 3.62.
13C NMR (101 MHz, d6-DMSO):
d = 163.0 (CClN2); 156.4
(CN(Ph)2N2); 154.1/152.2 (CN3); 142.5 (aryl); 134.2 (xylen); 129.5
(CCH3); 128.9 (aryl); 127.9/127.5 (aryl); 20.6 (CH3) ppm. 1H NMR
(500 MHz, d6-DMSO): d = 7.4–7.2 (m, 20H, Ar-H); 7.1 (s, 4H, xylen);
2.3 (s, 6H, CH3). IR (KBr): 3057 (n CAr-H), 1649, 1426 (nass heptazine
ring), 1601, 1497 (n CAr = CAr), 809 (heptazine ring), 690, 701
(d CHoop, phenyl rings), 802 (d CHoop, p-xylene). Refluxing of an
equimolar solution of 2 and diethylamine in THF under argon for
4 hours and stirring at 20 1C for an additional hour leads to a
colourless solution with a white precipitate. The hydrochloride was
separated via filtration and the solvent was removed under vacuum.
p-Xylene was added, and small portions of solid hydrochloride
were removed again. Finally xylene was distilled off to give 1,5-
bis(diphenylamino)-8-diethylamino-tri-s-triazin. The resulting solid
contains small amounts of HN(C2H5)2ꢀHCl as indicated in the
NMR and IR data (see ESIw). X-Ray diffraction data were recorded
on a BRUKER-NONIUS-X8 APEXII-CCD-diffractometer (Mo-Ka
radiation). The structure was solved by direct methods18 and
refined with full-matrix least-squares methods against F2 using
SHELXL-97.18,19 Non-hydrogen atoms were refined anisotropically.
NMR spectra (BRUKER DPX 400) were recorded at 20 1C in
d6-DMSO. Chemical shifts are reported relative to TMS. FTIR
spectra (Nicolet 510-FTIR) were recorded in a range from 400 to
4000 cmꢂ1 at 20 1C. The Raman spectra were obtained with a Bruker
RFS 100/S, Nd YAG Laser instrument (l = 1064 nm). TG/DTA
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29, 693–699.
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Heidelberg, vol. 108 and 111, 2004; (b) D. N. Chin, J. A. Zerkovski,
J. C. MacDonald and G. M. Whitesides, in Organised Molecular
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19 SMART and SAINT, Bruker AXS Inc., Madison, Wisconsin,
USA, 2007.
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Chem. Commun., 2006, 4741–4743; (b) B. V. Lotsch, M. Doblinger,
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(Seiko Instruments) was performed with a heating rate of 5 K minꢂ1
,
argon flow of 400 ml minꢂ1, max. temperature 600 1C. Elemental
analyses were determined with a Heraeus CHN rapid analyser.
y Crystal structure data for 2ꢀp-C6H4Me2 [C30H20ClN9, C8H10]:
M = 648.16, monoclinic, P21/n, a = 14.2050(5), b = 9.4560(4),
c = 24.7016(10) A, b = 106.356(2)1, Z = 4, V = 3183.7(2) A3,
ꢁc
This journal is The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 2829–2831 | 2831