Phosphorus-nitrogen compounds: Synthesis and spectral investigations on new spiro-cyclic phosphazene derivatives

Article abstract of DOI:10.1016/j.saa.2006.10.029

The condensation reaction of {N-[(2-hydroxyphenylmethyl)amino]-4,6-dimethylpyridine} (2), which is a reduction product of 1, with trimer N₃P₃Cl₆ affords partially a substituted spiro-cyclic phosphazene derivative (3). The

Full text of DOI:10.1016/j.saa.2006.10.029

Spectrochimica Acta Part A 67 (2007) 1392–1397
Phosphorus–nitrogen compounds: Synthesis and spectral investigations
on new spiro-cyclic phosphazene derivatives
∗
¨
Hakan Dal , Yasemin Suzen
Department of Chemistry, Faculty of Science, Anadolu University, 26470 Yenibag˘lar, Eskis¸ehir, Turkey
Received 27 May 2006; received in revised form 7 October 2006; accepted 18 October 2006
Abstract
The condensation reaction of {N-[(2-hydroxyphenylmethyl)amino]-4,6-dimethylpyridine} (2), which is a reduction product of 1, with trimer
N3P3Cl6 affords partially a substituted spiro-cyclic phosphazene derivative (3). The fully substituted phosphazenes (4 and 5) have also been obtained
fromthereactionsof 3withtheexcessofpyrrolidineandmorpholine. Thecharacterizationsandspectralinvestigationsofthesecompoundshavebeen
made by elemental analyses, FTIR, 1H-, 13C-, 31P NMR, correlation spectroscopy (COSY), heteronuclear chemical shift correlation (HETCOR),
heteronuclear multiple-bond correlation (HMBC) and mass spectroscopy (MS). The salient features of spectral data of these compounds have been
discussed.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Synthesis of phosphazene derivatives; spiro-Phosphazenes; Spectroscopic studies of phosphazenes; HETCOR; HMBC
1H-, 13C- and 31P NMR spectra for the structures were made
with help of H–H correlation spectroscopy (H–H COSY), as
well as heteronuclear chemical shift correlation (HETCOR) and
heteronuclear multiple-bond correlation (HMBC).
1. Introduction
Cyclophosphazenes are an important family of inorganic ring
systems, which traditionally have received attention for two
main reasons: (i) to obtain small molecules of phosphazene
derivatives [1,2] and (ii) to produce polymeric phosphazene
derivatives [3]. They also play an important role in the chem-
istry of heteroatom compounds. In recent years, phosphazene
polymers have attracted considerable attention because they can
be tailored to possess a wide variety of physical and chemical
properties by changing the side groups [4,5]. The coordina-
tion chemistry of the various multi-site ligands derived from
cyclophosphazenes is extremely interesting new area. Phosp-
hazenes have been proposed for a broader array of applications
including flame-retardants [6,7], rechargeable lithium batteries
[8,9], microencapsulant membranes, high performance fluids
and ionic conductors [10], the further design of the highly
selective anticancer [11], antibacterial [12], anti-HIV [13] and
artificial bone [14] agents.
2. Experimental
2.1. Reagents and materials
Hexachlorocyclotriphosphazatriene, N3P3Cl6, was pur-
chased from Aldrich and recrystallized from dry
hexane followed by sublimation twice before use. 2-
Hydroxybenzaldehyde, triethylamine (99.5%), aminopyridines
and sodium borohydride were purchased from Fluka and
used as received. All experimental manipulations were car-
ried out under argon atmosphere. Solvents tetrahydrofuran
(98%), dichloromethane (98%), acetonitrile (99.5%) and light
petroleum were dried by standard methods prior to use. Melting
points were measured on a Gallenkamp apparatus using a
capillary tube. 1H-, 13C-, 31P NMR, HETCOR and HMBC
spectra were obtained on a Bruker DPX FT NMR (500 MHz)
spectrometer (SiMe4 as internal standard and 85% H3PO4 as
an external standard). Spectrometer equipped with a 5 mm
PABBO BB-inverse gradient probe. The concentration of solute
molecules was 150 mg in 1.0 mL CDCl3. Standard Bruker pulse
In this study, the novel spiro-cyclic phosphazene derivatives
(4,5) have been obtained (Scheme 1) and their spectroscopic
characterizations have been carried out. Total assignments of
∗
Corresponding author. Tel.: +90 222 335 05 80; fax: +90 222 320 49 10.
E-mail address: hakandal@anadolu.edu.tr (H. Dal).
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.10.029

H. Dal, Y. Su¨zen / Spectrochimica Acta Part A 67 (2007) 1392–1397
1393
Scheme 1.
programs [15] were used throughout the entire experiment.
2.3. Synthesis of phosphazene derivatives
FTIR spectra were recorded on a Jasco 300E FTIR spectrometer
in KBr discs and were reported in cm−1 units. Microanalyses
were carried out by Medicinal Plants and Medicine Research
Center of Anadolu University Eskis¸ehir (Turkey). Electro-
spray ionization mass spectrometric (ESI-MS) analyses were
performed on the AGILEND 1100 MSD spectrometer.
4,4ꢀ,6,6ꢀ-Tetrachloro-3,4-dihydro-3-(4,6-dimethylpyridin-2-
yl)spiro-[1,3,2-benzoxazaphosphinine-2,2ꢀ-(2␭5,4␭5,6␭5-cycl-
otriphosphazene)] (3), the synthesis and solid state structure
of 3 have been published and it was prepared accord-
ing to the published procedure [17]. 4,4ꢀ,6,6ꢀ-Tetrapyrroli-
dine-3,4-dihydro-3-(4,6-dimethylpyridin-2-yl)spiro-[1,3,2-ben-
zoxazaphosphinine-2,2ꢀ-(2␭5,4␭5,6␭5-cyclotriphosphazene)]
(4), 4,4ꢀ,6,6ꢀ-tetrachloro-3,4-dihydro-3-(4,6-dimethylpyridin-2-
yl)spiro-[1,3,2-benzoxazaphosphinine-2,2ꢀ-(2␭5, 4␭5, 6␭5-cyc-
lotriphosphazene)] (3) (2.17 g, 3.38 mmol) and pyrrolidine
(1.92 g, 2.24 mL, 27.04 mmol) in acetonitrile (150 mL) were
allowed to react by refluxing 62 h. After work-up it was done
as in synthesis of compound 3 crystallized from THF/n-
hexane (2:1), Rf = 0.57 [n-hexane/THF (2:1)]. 4,4ꢀ,6,6ꢀ-Tetra-
morpholine-3,4-dihydro-3-(4,6-dimethylpyridin-2-yl)spiro-[1,
3,2-benzoxazaphosphinine-2,2ꢀ-(2␭5,4␭5,6␭5-cyclotriphospha-
zene)] (5), the work-up procedure of this compound was as
in the preparation of 4. It was recrystallized from THF/light
petroleum (bp 40–60) (2:1) Rf = 0.76 [THF/n-hexane (2:1)].
Experimental and analytical data are listed in Table 1. The
ESI-MS spectra of compounds (1, 3–5) show the protonated
[M + H]+ and deprotonated [M − H]+molecular ion peaks. The
elemental analyses results are in agreement with the proposed
structures.
2.2. Synthesis of ligands
Preparation of compounds (1–3) were carried out as in
Scheme 1, adapting a reported procedure [16]. 2-[(1E)-2-
aza-2-(4,6-dimethyl(2-pyridyl))vinyl] (1) has been obtained
using a method in which salicylaldehyde (4.87 g, 3.99 mmol)
and 4,6-dimethyl-2-aminopyridines (4.88 g, 3.99 mmol)
were refluxed in MeOH (50 mL). The resulting solid
was crystallized from MeOH. For the synthesis of N-[2-
hydroxy(phenylmethyl)amino]-4,6-dimethylpyridine
(2),
2-[(1E)-2-aza-2-(4,6-dimethyl(2-pyridyl))vinyl] (1) (7.64 g,
33.9 mmol) was refluxed in MeOH (50 mL) for 1 h and then
equimolar amount of sodium borohydride (1.28 g, 33.9 mmol)
was partially added to the reaction mixture. The reduction
was completed after 2 h. Then, the solvent was evaporated in
reduced pressure, the residue was dissolved in dichloromethane
and washed with water. Compound (2) was crystallized from
MeOH.

1394
H. Dal, Y. Su¨zen / Spectrochimica Acta Part A 67 (2007) 1392–1397
Table 1
Experimental and analytical data
Calculated (found) (%)
Compound
Empirical formula
MW
Yield (%)
mp (◦C)
C
H
N
1
2
3
4
5
C14H14N2O
226.27
228.29
500.92
641.30
705.67
85
90
72
59
51
94
109
228
153
234
74.31 (73.89)
73.66 (73.42)
33.43 (34.32)
56.15 (56.54)
51.06 (51.62)
6.24 (5.32)
7.06 (6.41)
2.81 (2.67)
7.23 (7.10)
6.57 (6.26)
12.38 (13.51)
12.27 (13.05)
13.92 (13.83)
19.65 (19.41)
17.86 (18.51)
C14H16N2O
C14H14Cl4N5OP3
C30H46N9OP3
C30H46N9O5P3
Table 2
Selected IR bands
Compound
ν(N–H)
ν(C–H) arom
ν(C–H) alip
2918 m
2958; 2924 m
2950; 2853 m
2962; 2860 s
2964; 2962 vs
ν(C
ν(P
ν(P–Cl)
C)
N)
1
2
3
4
5
–
3061 m
3049 m
3089 m
3093 m
3087 m
1544 vs
1587 s
1577 s
1560 s
1570
–
–
–
–
3421 vs
–
–
–
1189; 1228 vs
1170; 1225 vs
1188; 1256 vs
516; 578 s
–
–
Abbreviations: s, strong; m, medium; v, very.
3. Results and discussion
5.58 ppm, respectively, while the signals of the tetrapyrrolidinyl-
substituted and tetramorpholine-substituted PX atoms of 4 and
5 are upfield-shifted with respect to corresponding PX atom of
3 by 11.94 and 9.99 ppm, respectively, probably due to the lone
electron pairs of the pyrrolidine or morpholine N-atoms of elec-
tron releasing to the PX atoms. On the other hand, the chemical
shifts are highly sensitive to the changes in the exocyclic NPN
angles [18,19], thus the small variations in the angles possi-
bly can deviate chemical shifts, significantly as observed in 3
(Table 3).
Proton magnetic resonance spectroscopy is a helpful tool
for the identification of organic compounds in conjunction with
other spectrometric informations. Table 4 lists complete 1H- and
13C NMR assignments for all of the compounds (1–5). The 1H
signals were assigned on the basis of chemical shifts, multi-
plicities and coupling constants. The two CH3 protons of 3–5
are easily distinguishable, and they are observed at 2.68 and
2.46 ppm for 3; 2.41 and 2.18 ppm for 4; 2.42 and 2.90 ppm for
5 as singlets. In addition, in pyrrolidine and morpholine NCH2
(Hg and Hgꢀ) and NCH2CH2 (Hh and Hhꢀ) protons of the rings
Table 1 lists the empirical formulae, yields, molecular
weights, melting points and partial elemental analyses for the
compounds (1–5). Selected FTIR frequencies of various diag-
nostic bands of 1–5 are given in Table 2. In the FTIR spectra of
the compounds characteristic νN–H and νC–H stretching bands
are observed between 3421 cm−1 for 2 and 3093–3049 cm−1
for 1–5. The absorption bands assignable to the stretching of
the –P N– for compounds (3–5) and P–Cl bands for 3 were ca.
1200 cm−1 and 516 and 578 cm−1. These data are in accordance
with the reported values for the similar phosphazene derivatives
[16].
The proton decoupled (for 3) and coupled for (4 and 5) 31
P
NMR spectral data of spiro-phosphazenes are given in Table 3
and Fig. 1. 31P NMR spectra show AX2 spin system and they
were critical for monitoring the degree to which the chlorine
atoms in hexachlorocyclotriphosphazene had been substituted
with bulky spiro-cyclo-N-methylpyridine groups. According to
the pattern of proton coupled 31P NMR spectra of 3, it is
concluded that the only spiro-architectures are possible. It is
observed that 2J(P,P) values (48.6 and 49.9 Hz) of the fully sub-
stituted phosphazene derivatives (4 and 5) are smaller than the
value (62.8 Hz) of spiro-phosphazene 3. The δ(PA) signal of 4
and 5 are downfield-shifted with respect to δ(PA) of 3 by 6.79 and
Table 3
31P(1H) NMR spectral data in CDCl3
Compound
δ (A)a
δ (X)a
2JPNP (Hz)
3
4
5
6.43 (t)b
13.22 (tt)
12.01 (tt)
29.89 (d)
17.95 (d)
19.90 (d)
62.8
48.6
49.9
d: doublet, t: triplet.
a
Fig. 1. 31P(1H) NMR spectrum in δ 11–30 ppm for: (a) compound 4 and (b)
compound 5.
A and X are shown in Scheme 1.
31P NMR spectrum is decoupled.
b

Table 4
1H- and 13C NMR spectral data in CDCl3
Compounds
1
2
3
4
5
Ha
6.93 (s)
6.03 (s)
6.57 (s)
6.53 (s)
6.62 (s)
Hb
Hc
Hd
He
6.94–6.98 (m)
6.30 (s)
6.70 (s)
6.25 (m)
7.33 (s)
7.16 (s)
7.04 (d) [3JHc–Hd = 8.35]
6.98 (d) [3JHc–Hd = 8.03]
6.95 (d) [3JHc–Hd = 7.98]
6.96 (d) [3JHc–Hd = 8.23]
7.40 (t, d) [3JHd–Hc,e = 6.78] [4JHd–Hf = 1.69]
6.94–6.98 (m)
7.52 [3JHf–He = 7.65] [4JHf–Hd = 1.54]
–
–
–
–
2.60
2.40
164.27
118.09
157.72
117.22
149.82
157.07
119.04
133.34
119.12
133.52
161.93
–
7.23 (t,d) [3JHd–Hc,e = 8.03] [4JHd–Hf = 1.66]
7.25 (m)
7.23 (m)
7.03 (t) [3JHe–Hd,f = 7.41]
7.23 (m)
3.20 (m)
1.82 (s)
1.73 (m)
5.11 (d) [3JP–H = 12.45]
7.25 (m)
7.07 (t) [3JHe–Hd,f = 7.49]
7.25 (m)
3.05 (m) and 3.15 (d, m)
3.55 (m)
3.69 (m)
5.05 (d) [3JP–H = 12.94]
6.86 (t) [3JHe–Hd,f = 7.34]
7.20 (t) [3JHe–Hd,f = 7.53]
Hf
7.18 (d) [3JHf–He = 7.48] [4JHf–Hd = 1.61]
7.38 (d) [3JHf–He = 7.38]
Hg, gꢀ
Hh
–
–
–
–
–
–
Hhꢀ
CH2
4.45 (d) [3JHNCH = 6.64]
4.75 (d) [3JP–H = 12.96]
14
CH3
CH3
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12, 12ꢀ
C13, 13ꢀ
C14
C15
CH2
2.49
2.15
2.68
2.46
157.3
119.1
2.41
2.18
155.7
117.3
146.8
112.0
2.42
2.90
156.5
118.5
147.4
112.9
128.5
15
154.8
106.8
149.4
113.5
126.6
1563.4
118.3
129.4
119.4
131.0
156.7
–
149.7
107.1 [3JP–C4 = 6.32]
124.9 [2JP–C5 = 7.57]
128.0 [2JP–C5 = 6.30]
149.2 [3JP–C6 = 8.30]
151.7 [3JP–C6 = 8.90]
151.2 [3JP–C6 = 8.90]
117.9 [4JP–C7 = 6.44]
119.2
126.8
125.1
129.7
154.7
–
117.6 [4JP–C7 = 5.92]
127.0
123.2
128.1
155.1
127.2
123.6
128.5
154.8 [2JP–C11 = 8.2]
46.1 (d) [2JPNC12 = 15.4]
44.7 (d) [2JPNC12 = 12.4]
–
–
22.6
20.9
42.6
–
26.4
24.3
20.9
46.5
67.1
24.2
21.4
47.2
24.21
20.83
–
24.2
21.4
47.7

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H. Dal, Y. Su¨zen / Spectrochimica Acta Part A 67 (2007) 1392–1397
Fig. 2. 1H NMR spectrum in δ 1–8 ppm for: (a) compound 4 and (b) compound
5.
are distinguishable from each other and resonate at 3.20 ppm
for 4; 3.05 and 3.15 ppm for 5 and 1.82 and 1.73 ppm for 4;
3.55 and 3.69 ppm for 5. The Ar–CH2–N– protons of (3–5)
δ = 4.75, 5.11 and 5.05 ppm as doublets, in which those have
three bond-coupling constants, ca. 3JPH = 12.78 Hz (Fig. 2).
Fig. 4. HETCOR spectrum of 5.
All of the possible carbon peaks are observed from the 13
C
NMRspectraldata, asexpected. Theaveragefourbond-coupling
constant, 4JPC, of Ar–CH2–N is found 6.18 Hz. It is interesting
that the two bond-coupling constants, 2JPC, of C5 carbons of 3–5
areobservedintherangeof6.30–7.57 Hz, whicharesmallerthan
those of the C6 carbons (Fig. 3 and Table 4).
C8, C9, C10, C12 and C13 carbon atoms. In 5, the absence of
any contours at δ = 156.5, 147.4, 128.5, 151.2 (2JPNC = 8.9 Hz)
and 154.8 (2JPNC = 8.2 Hz) ppm assign them to the C1, C3, C5,
C6 and C11 carbon atoms, respectively. They belong to non-
protonated atoms on the pyridine ring, C1, C3, C5 and on the
phenyl ring carbons, respectively, all of which are unable to show
any direct 1H–13C coupling interactions. C1 carbon atom adja-
cent to the more electronegative nitrogen atom of pyridine ring
is shifted further downfield when compared to the neighboring
and C5 carbon atoms. In addition, the carbon atom at para
Assignments of the protonated carbons were made by two-
dimensional heteronuclear-correlated experiments (HETCOR,
1
Fig. 4) using delay values which correspond to J(C,H). As
an example, only the HETCOR spectrum of 5 is depicted in
Fig. 4. The peaks at δ = 118.5, 112.9, 117.9, 127.2, 123.6, 128.5,
44.7 and 67.1 ppm have been assigned them to C2, C4, C7,
Fig. 3. 13C NMR spectrum in 10–160 ppm for 5.

H. Dal, Y. Su¨zen / Spectrochimica Acta Part A 67 (2007) 1392–1397
1397
position to heteroatom, viz. C3 resonates at lower field value
when compared to the meta positioned carbons, C2 and C4.
However, the non-protonated carbon C5 is more shielded than
C1 and C3 carbon atoms in the pyridine ring. On the other
hand, the non-protonated carbons C1, C3, C5, C6 and C11 of
compound (5) were also determined using delays in the two-
dimensional HMBC experiment to emphasize the long range
2
3
coupling, either J(C,H) or J(C,H) between the carbons and
protons (Fig. 5 and Table 5). Consequently, according to the
NMR results (HETCOR and HMBC) the probable conforma-
tion of compound 5 in CDCl3 solution is depicted in Fig. 6, as
an example.
Acknowledgements
Fig. 5. HMBC correlations for 5.
The authors wish to acknowledge financial support of this
work under grants Commission of Scientific Research Projects
(grant no. 061037). We also thank Anadolu University and
Medicinal Plants and Medicine Research Center of Anadolu
University, Eskis¸ehir, for allowing us to use the NMR facility.
Table 5
2D 1H–13C HETCOR and HMBC correlations for 5
Atom
HETCOR
HMBC [J(C,H)]
1J
2J
3J
4J
intraJ
References
Ha
Hb
Hc
Hd
He
Hf
Hg, gꢀ
Hh, hꢀ
CH2
C2
C4
C7
C8
C1, C3
–
C6, C8
–
C8, C10
–
C13
C12
C6
C14, C15
C15
C9, CH2
C6
C7
C6
–
–
C5
–
–
–
–
–
C6
–
–
–
C10
–
C13, 13ꢀ
C7, C11, C14
C14
C14, CH2
C14
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Fig. 6. The possible stereoisomer structure of compound 5 at ambient temper-
ature in CDCl3.