Microwave-assisted solvent-free synthesis and spectral and structural characterization of cyclotriphosphazene hexakis(o-tolylamide)

Article abstract of DOI:10.1515/znb-2018-0136

A new cyclotriphosphazene, 2,2,4,4,6,6-hexakis (o-tolylamono)-1,3,5,2λ⁵,4λ⁵,6λ⁵-triazatriphosphinine (MPAP), was prepared using microwave irradiation and identified by elemental analysis, FT-IR, Raman, ³¹P NMR s

Full text of DOI:10.1515/znb-2018-0136

Z. Naturforsch. 2018; aop
Mohammad Hakimi*, Homeyra Rezaei, Keyvan Moeini, Heidar Raissi, Vaclav Eigner
aMndiMcirchoalwDuaševke-assisted solvent-free synthesis
and spectral and structural characterization of
cyclotriphosphazene hexakis(o-tolylamide)
https://doi.org/10.1515/znb-2018-0136
gas membranes [7], ionic conductors [8], flame retardants
[9], and optical materials [7, 10], and in ion separation [11].
In order to extend the chemistry of the cyclotriphos-
phazene, in this work we describe the synthesis of
a new derivative, 2,2,4,4,6,6-hexakis(o-tolylamino)-1,3,5,
2λ5,4λ5,6λ5-triazatriphosphinine (MPAP, Scheme 1), along
with its characterization including elemental analysis,
FT-IR, Raman, and 31P NMR spectroscopy.
Received June 29, 2018; accepted October 2, 2018
Abstract: A new cyclotriphosphazene, 2,2,4,4,6,6-hexakis
(o-tolylamono)-1,3,5,2λ5,4λ5,6λ5-triazatriphosphinine
(MPAP), was prepared using microwave irradiation and
31
identified by elemental analysis, FT-IR, Raman, P NMR
spectroscopy, and single-crystal X-ray diffraction. In the
crystal, in addition to hydrogen bonds, the network is fur-
ther stabilized by inter- and intramolecular π–π stacking
interactions between aromatic rings.
2 Results and discussion
Keywords: crystal structure; cyclotriphosphazene; micro-
wave; 31P NMR.
The reaction between hexachlorocyclotriphosphazene
and an excess of o-toluidine under microwave irradiation
[12–15] and solvent-free conditions gave MPAP in good
yields. This compound is air-stable and soluble in ethanol
and DMSO.
1 Introduction
Phosphazenes are compounds containing a phosphorus–
nitrogen double bond in their skeleton. They are well
known as iminophosphoranes and phosphine imides. 2.1 Spectroscopic studies
Phosphazenes fall into three categories: cyclo-, poly-,
and monophosphazenes. Cyclo- and polyphosphazenes In the IR spectrum of the compound, frequencies below
are very well known and have been intensively studied and above 3000 cm−1 and also at 3300 cm−1 can be
because they are more stable than monophosphazenes assigned to the stretching vibrations of the C–H and N–H
[1]. The properties of phosphazenes can be changed over a bonds, confirming the presence of the aliphatic, aromatic,
wide range by attaching different substituents to the main and amine moieties, respectively, in MPAP. These vibra-
backbone [2]. The synthesis of phosphazene compounds tions confirm the successful substitution of o-toluidine on
has become important because these compounds have hexachlorocyclotriphosphazene. The FT-IR and Raman
many potential applications, including as biomaterials spectra of MPAP show two intense absorption signals at
[3], drug delivery systems [4], fuel cell membranes [5, 6], 1157 and 937 cm−1, which are attributed to the asymmetric
and symmetric stretching vibrations of the P=N bonds in
the phosphazene ring, respectively [16, 17]. In the low-fre-
quency region, the phosphazene ring exhibits four other
types of vibrations, namely bending, wagging, twisting,
and rocking, in the order (δbend PN)ringꢀ>ꢀ(δwag PN)ringꢀ>ꢀ(δrock
PN)ringꢀ>ꢀ(δbend NPN)ꢀ>ꢀ(δtwist NPN) [16].
*Corresponding author: Mohammad Hakimi, Chemistry Department,
Payame Noor University, Tehran 19395-4697, I. R. Iran,
Fax: +98 44 32768825, E-mail: mohakimi@yahoo.com
The 31P NMR spectrum of MPAP shows an intense
single peak at δꢀ=ꢀ5.12 ppm. This shows that the three
phosphorus atoms in the compound have the same chem-
ical environment, which can happen only with the sym-
metric substitution of all the chlorine atoms. Comparing
Homeyra Rezaei and Keyvan Moeini: Chemistry Department,
Payame Noor University, Tehran 19395-4697, I. R. Iran
Heidar Raissi: Chemistry Department, Birjand University, Shokat
Abad-Pardis-e-Daneshgag, Birjand, South Khorasan 13179, I. R. Iran
Vaclav Eigner and Michal Dušek: Institute of Physic of the Czech
Academy of Sciences, Na Slovance 2, Prague 182 21, Czech Republic
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ꢀꢀꢀꢁ
2ꢀ ꢀM. Hakimi et al.: Synthesis and spectral and structural characterization of MPAP
Table 1:ꢀSelected bond lengths (Å) and angles (deg) for MPAP with
estimated standard deviations in parentheses.
Bond lengths
Angles
NH
N1–P1
N1e–P3
N2–P2
N3–P3
N2–P1
N1a–P1
N1b–P1
N3–P2
N1c–P2
N1d–P2
N1–P3
N1f–P3
1.5897(9)
1.661(1)
1.5937(8)
1.6054(9)
1.6118(9)
1.654(1)
1.664(1)
1.5918(9)
1.676(1)
1.6629(9)
1.5833(8)
1.666(1)
N1–P3–N3
N1b–P1–N1a
N1d–P2–N1c
N1f–P3–N1e
N2–P1–N1
N3–P2–N2
P1–N1–P3
P2–N2–P1
P3–N3–P2
116.64(5)
103.11(5)
100.02(5)
102.11(5)
116.77(4)
117.59(5)
123.67(5)
121.75(5)
121.51(6)
H
N
P
N
N
NH
N
P
N
H
P
HN
HN
The suffixes a, b, c, d, e, f denote crystallographically distinct
o-toluidine groups.
Scheme 1:ꢀStructure of the MPAP molecule.
The core of the molecule is a six-membered ring N1–P1–
the 31P NMR spectra of hexachlorocyclotriphosphazene N2–P2–N3–P3 with the bond lengths averaging 1.596 Å,
(δꢀ=ꢀ0.60 ppm) and MPAP (δꢀ=ꢀ5.12 ppm), the latter shows which is smaller than the average length of the newly
a shift of Δδꢀ=ꢀ4.52 ppm to lower magnetic field.
created P–N single bonds (1.664 Å). The average of the
P–N–P bond angles of the ring in MPAP is 122.3°, i.e.
smaller than the average N–P–N bond angles of the same
ring (117.0°). On the other hand, the average N–P–N bond
angles between the o-toluidine groups are smaller (101.8°)
than the endocyclic angles. The average bond angles
around the phosphorus atoms reveal distorted tetrahedral
geometries (Table 1). The rms value from the mean plane
through the cyclotriphosphazene ring shows that the ring
slightly deviates from planarity (0.092 Å for the N3 atom).
In the crystal network of MPAP, there are weak inter-
molecular C–Hꢀ·ꢀ·ꢀ·ꢀN and N–Hꢀ·ꢀ·ꢀ·ꢀN hydrogen bonds
between adjacent molecules (Fig. 2) in which the carbon
atoms act as proton donors while the nitrogen atoms
are both proton donors and acceptors. Among the
intermolecular contacts, the aromatic rings of the o-tolu-
idine moieties appear to play a significant role by par-
ticipating in the formation of the C–Hꢀ·ꢀ·ꢀ·ꢀπ (Table 2) and
π–π stacking (Table 3) interactions [18, 19]. Based on the
centroid–centroid distances between the aromatic rings,
these intermolecular π–π stacking interactions (Fig. 2) are
stronger than the intramolecular ones.
2.2 Crystal structure of MPAP
The single-crystal X-ray diffraction analysis of the MPAP
(Fig. 1)confirmedthefullsubstitutionofthechlorineatoms
on the cyclotriphosphazene ring by o-toluidine groups.
3 Conclusion
A new cyclotriphosphazene, MPAP, was prepared and
31
its spectral (IR, Raman, P NMR) and structural (single-
Fig. 1:ꢀOrtep-III diagram of the molecular structure of MPAP.
The ellipsoids are drawn at the 35% probability level.
crystal X-ray diffraction) properties were investigated.
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M. Hakimi et al.: Synthesis and spectral and structural characterization of MPAPꢂ
ꢂ3
Fig. 2:ꢀPacking of MPAP molecules in the crystal, showing the hydrogen bonds and π–π stacking interactions. Only the hydrogen atoms
involved in hydrogen bonding are shown.
Table 2:ꢀHydrogen bond dimensions (Å and deg) in MPAP.
contents were determined using a Thermo Finnigan Flash
Elemental Analyzer 1112 EA. Infrared spectra (as KBr
pellets) were recorded from 400 to 4000 cm−1 using an
FT-IR 8400 Shimadzu spectrometer. Melting point was
determined using a Barnsted Electrothermal 9200 electri-
cally heated apparatus. 31P NMR spectrum was recorded on
a Bruker Aspect 3000 instrument operating at 300 MHz,
and chemical shifts are given in parts per million with
reference to an internal standard of phosphoric acid.
The microwave-assisted synthesis of the title compound
was carried out using a Microwave Laboratory Systems
MicroSYNTH (Milestone s.r.l.)
D–Hꢁ·ꢁ·ꢁ·ꢁA
ꢂ d(D–H) ꢂ d(Hꢁ·ꢁ·ꢁ·ꢁA) ꢂ d(Dꢁ·ꢁ·ꢁ·ꢁA) ꢂ ꢁ<(DHA)ꢂ Symmetry
code of A
C5c–H1c5cꢁ·ꢁ·ꢁ·ꢁN3ꢃ 0.960 ꢃ 2.7282 ꢃ 3.479(1) ꢃ 135.54ꢃ 1ꢁ+ꢁx, y, z
C7f–H2c7fꢁ·ꢁ·ꢁ·ꢁN2 ꢃ 0.960 ꢃ 2.7387 ꢃ 3.657(1) ꢃ 160.38ꢃ −1ꢁ+ꢁx, y, z
N1f–H1n1fꢁ·ꢁ·ꢁ·ꢁN2 ꢃ 0.86 ꢃ 2.612 ꢃ 3.424(1) ꢃ
158ꢃ −1ꢁ+ꢁx, y, z
C7f–H3c7fꢁ·ꢁ·ꢁ·ꢁπ 0.960 ꢃ 3.098 ꢃ 3.592 ꢃ 113.63ꢃ
ꢃ
C7b–H1c7bꢁ·ꢁ·ꢁ·ꢁπ ꢃ 0.960 ꢃ 2.595 ꢃ 3.536 ꢃ 166.57ꢃ
C5b–H1c5bꢁ·ꢁ·ꢁ·ꢁπ ꢃ 0.960 ꢃ 2.868 ꢃ 3.694 ꢃ 144.84ꢃ
Table 3:ꢀπ–π stacking interactions (Å and deg) in MPAP.
Centroid–centroidꢂ
distance
Angle betweenꢂ
the planes
Type of interaction
4.2 Preparation of MPAP
3.899
3.851
ꢃ
ꢃ
7.22ꢃ
7.22ꢃ
Intramolecular
Intermolecular
Dry and pure hexachlorocyclotriphosphazene (0.35 g,
1 mmol) was added to 3.00 g (28 mmol) of o-toluidine and
In the crystal structure of the MPAP, the bond angles of irradiated in the synthetic microwave oven under reflux
the phosphorus atoms revealed a distorted tetrahedral and under solvent-free conditions for 2 h with a power
geometry around these atoms. In addition to the C–Hꢀ·ꢀ·ꢀ·ꢀN 200 W. Then the reaction mixture was allowed to cool
and N–Hꢀ·ꢀ·ꢀ·ꢀN hydrogen bonds in the crystal network, the down to room temperature. The product was extracted
structure features both inter- and intramolecular interac- with chloroform and water three times. The reaction
tions between aromatic rings in a form of π–π stacking product was in the phase of chloroform and the amine
and C–Hꢀ·ꢀ·ꢀ·ꢀπ interactions.
salt by-product in the water phase. After evaporation of
chloroform at ambient temperature, the desired product
was obtained. Finally, the product was recrystallized
from methanol to produce colorless crystals. Yield 0.46 g,
60%; m. p. 150°C. Anal. calcd. for C42H48N9P3 (771.83): C
65.36, H 6.27, N 16.33; found C 65.84, H 6.36, N 16.43%. IR
(KBr): νꢀ=ꢀ3310 m (N–H), 3007 w (C–H)ar, νasꢀ=ꢀ2950 w (CH3),
νꢀ=ꢀ1497 m (C=C)ar, δasꢀ=ꢀ1465 w (CH3), δsꢀ=ꢀ1369 m (CH3),
4 Experimental
4.1 Materials and measurements
All chemicals and solvents were used as received without νasꢀ=ꢀ1157 s (P=N)ring, νꢀ=ꢀ1107 m (C–N), νsꢀ=ꢀ937 m (P=N)ring
,
further purification. Carbon, hydrogen, and nitrogen δbendꢀ=ꢀ714 m (P=N)ring, 617 w δwagꢀ=ꢀ(PN)ring, δrockꢀ=ꢀ536 w
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ꢀꢀꢀꢁ
4ꢀ ꢀM. Hakimi et al.: Synthesis and spectral and structural characterization of MPAP
(P=N)ring, δbendꢀ=ꢀ465 w (N–P–N) cm−1. Raman: δasꢀ=ꢀ1415 m 0.86 Å with s.u. of the constraintꢀ=ꢀ0.001 and Uisoꢀ=ꢀ1.2 Ueq of
(CH2), νasꢀ=ꢀ1172 m (PN)ring, νꢀ=ꢀ1049 s (C–N), νsꢀ=ꢀ894 m the corresponding parent atom. Diagrams of the molecu-
(P=N)ring, δbendꢀ=ꢀ712 m (P=N)ring, δrockꢀ=ꢀ588 s (P=N)ring
,
lar structure and unit cell were created using the programs
31
δbendꢀ=ꢀ432 m (N–P–N), δtwistꢀ=ꢀ154 s (N–P–N) cm−1. P NMR Ortep [23, 24] and Diamond [25]. Crystal data and details
(250 MHz, CDCl3): δꢀ=ꢀ5.12 ppm.
of the data collection and refinement are given in Table 4.
Selected bond lengths and angles of the compound are
listed in Table 1 and the hydrogen bond geometries in
Table 2.
4.3 Crystal structure determination
CCDC 1842613 (MPAP) contains the supplemen-
A suitable crystal of MPAP was chosen, and its X-ray dif- tary crystallographic data for this paper. These data
fraction analysis was performed at Tꢀ=ꢀ95 K using a Super- can be obtained free of charge from The Cambridge
Nova diffractometer equipped with a micro-focus sealed Crystallographic Data Centre via www.ccdc.cam.ac.uk/
tube, mirror-collimated Cu Kα radiation (λꢀ=ꢀ1.54184 Å), data_request/cif.
and a CCD detector (Atlas S2). The data was processed
with CrysAlis [20]. The structure was solved with the
charge flipping algorithm Superflip [21] and refined
5 Supporting information
by full-matrix least-squares on F2 using the program
Jana2006 [22]. Anisotropic displacement parameters
31P NMR, FT-IR, and Raman spectra of MPAP and the
were used for all non-hydrogen atoms. Hydrogen atoms
31P NMR spectrum of hexachlorocyclotriphosphazene
on carbon were kept at geometrically expected positions
are given as supplementary material available online
and refined as riding atoms with Uisoꢀ=ꢀ1.2 Ueq of the cor-
(DOI: 10.1515/znb-2018-0136).
responding parent atom. Positions of hydrogen atoms on
nitrogen were refined using the N–H bond length restraint
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Supplementary Material: The online version of this article offers
supplementary material (https://doi.org/10.1515/znb-2018-0136).
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Z. Naturforsch.ꢂ
ꢂ2018 | Volume x | Issue x(b)
Graphical synopsis
Mohammad Hakimi, Homeyra Rezaei,
Keyvan Moeini, Heidar Raissi,
Vaclav Eigner and Michal Dušek
Microwave-assisted solvent-free
synthesis and spectral and structural
characterization of cyclotriphosphazene
hexakis(o-tolylamide)
https://doi.org/10.1515/znb-2018-0136
Z. Naturforsch. 2018; x(x)b: xxx–xxx
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