Synthesis of cyclotriphosphazenes containing cyanostilbenes with different terminal substituents

Article abstract of DOI:10.1080/00397911.2010.542861

The synthesis and mesomorphic properties of a class of cyclotriphosphazenes containing cyanostilbene groups with different terminal substituents (-H, -CH₃, -OCH₃,-CN) are described. All the resulting compounds are characterized by ¹H, ¹³C, and ³¹P NMR, matrix-assisted laser desorption/ionization time of flight, and elemental analysis. The thermal behaviors of cyclotriphosphazene derivatives are studied by the means of differential scanning calorimetry and polarizing optical microscopy. Nematic phases are observed in cyclotriphosphazenes with terminal substituents (-CH₃, -OCH₃, -CN). Copyright Taylor & Francis Group, LLC.

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Synthesis of Cyclotriphosphazenes
Containing Cyanostilbenes with Different
Terminal Substituents
Rui Bao a , Min Pan a , Yun Zhou b , Jin-Jun Qiu a , He-Qing Tang a
Cheng-Mei Liu a
&
a School of Chemistry and Chemical Engineering , Huazhong
University of Science and Technology , Wuhan , China
b Institute of Marine Materials Science and Engineering , Shanghai
Maritime University , Shanghai , China
Accepted author version posted online: 28 Nov 2011.Published
online: 03 Feb 2012.
To cite this article: Rui Bao , Min Pan , Yun Zhou , Jin-Jun Qiu , He-Qing Tang & Cheng-Mei Liu (2012)
Synthesis of Cyclotriphosphazenes Containing Cyanostilbenes with Different Terminal Substituents,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 42:11, 1661-1668, DOI: 10.1080/00397911.2010.542861
To link to this article: http://dx.doi.org/10.1080/00397911.2010.542861
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Synthetic Communications1, 42: 1661–1668, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.542861
SYNTHESIS OF CYCLOTRIPHOSPHAZENES
CONTAINING CYANOSTILBENES WITH
DIFFERENT TERMINAL SUBSTITUENTS
Rui Bao,1 Min Pan,1 Yun Zhou,2 Jin-Jun Qiu,1
He-Qing Tang,1 and Cheng-Mei Liu1
1School of Chemistry and Chemical Engineering, Huazhong University
of Science and Technology, Wuhan, China
2Institute of Marine Materials Science and Engineering, Shanghai
Maritime University, Shanghai, China
GRAPHICAL ABSTRACT
Abstract The synthesis and mesomorphic properties of a class of cyclotriphosphazenes
containing cyanostilbene groups with different terminal substituents (-H, -CH3, -OCH3,
-CN) are described. All the resulting compounds are characterized by 1H, 13C, and 31P
NMR, matrix-assisted laser desorption/ionization time of flight, and elemental analysis.
The thermal behaviors of cyclotriphosphazene derivatives are studied by the means of
differential scanning calorimetry and polarizing optical microscopy. Nematic phases are
observed in cyclotriphosphazenes with terminal substituents (-CH3, -OCH3, -CN).
Keywords Cyanostilbene; cyclotriphosphazene; Knoevenagel condensation; liquid
crystal; star-shaped molecule
INTRODUCTION
Cyclotriphosphazene is a broad class of molecules with six arms at the
periphery and an alternating nitrogen–phosphorus six-atom ring as the core group.
Received January 6, 2010.
Address correspondence to Cheng-Mei Liu, School of Chemistry and Chemical Engineering,
Huazhong University of Science and Technology, Wuhan, China. E-mail: liukui@mail.hust.edu.cn
1661

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R. BAO ET AL.
Scheme 1. Synthetic routes leading to compounds 5a–d. (i) t-BuOK, n-Bu4NOH=t-BuOH; (ii) TsOH=
methanol; and (iii) NaH=THF.
Hexachlorocyclotriphosphazene (HCCP) is usually the starting molecule for the
synthesis of cyclotriphosphazene derivatives.[1] Because of the high reactivity of
the P-Cl bond, the corresponding substitution method allows the introduction of a
wide range of substituents and hence provides cyclotriphosphazene derivatives with
different chemical and physical properties.[2] For examples, the cyclotriphosphazenes
with different substituents have applications as fire-retardant materials,[3,4] biomedi-
cal materials,[5] liquid crystals,[1,6] and optical material.[7]
a-Cyanostilbene is a rigid, conjugated organic group with a strong electron-
withdrawing cyano group on the vinyl group. Cyano-poly(p-phenylene vinylenes)
(CN-PPV) and low-molecular compounds with a-cyanostilbene groups have been
extensively synthesized for semiconductor device applications.[8–10] CN-PPV and its
derivatives show high photoluminescence (PL) efficiencies and electroluminescence
(EL) efficiencies, which are attributed to the electron-withdrawing cyano groups that
can facilitate electron injection.[11] The conjugated and rigid structure of a-cyanostil-
bene also provides it with another important application as the main chain (or side
chain) in liquid-crystalline polymers.[12] a-Cyanostilbene derivatives were also found
to possess a strong gelation power at room temperature.[13]
In this study, a class of cyclotriphosphazenes bearing six a-cyanostilbene
groups with different terminal substituents was synthesized through the nucleophilic
reaction. The synthetic routes leading to the compounds 5a–d are shown in Scheme 1.
RESULTS AND DISCUSSION
Compounds 4a–d were synthesized by Knoevenagel-type condensation with t-
BuOH as solvent in the presence of t-BuOK and n-Bu4NOH. The terminal substituent

CYCLOTRIPHOSPHAZENES CONTAINING CYANOSTILBENES
1663
has the effect on the condensation reaction. The terminal electron-withdrawing cyano
group facilitated the condensation reaction and reduced the reaction temperature and
the reaction time. Comparing to the reaction time for compounds 3a–c, a shorter
reaction time of 15 s was used for the preparation of compound 3d. Besides the
reaction time, the reaction temperature was also reduced from 80 ꢀC to 30 ꢀC. The
cyano group also simplified the purification procedure of compound 3d. Upon the
completion of this reaction, a yellow precipitate was formed and readily collected
by filtration. In contrast to compound 4a with no terminal substituent, compound
4d with electron-withdrawing terminal substituent showed relatively higher melting
points of 226–228 ꢀC. Meanwhile, compounds 4b and 4c with electron-releasing
terminal substituents showed lower melting points than that of compound 4a.
The nucleophilic reaction was used to prepare compounds 5a–d. HCCP was
reacted with an excess of corresponding compound 4a–d in the presence of NaH in
dry tetrahydrofuran (THF) to yield compounds 5a–d with isolated yields of
87–92%. The products of compounds 5a–c were readily purified by reprecipitating
the corresponding crude product into methanol to remove the excess compound
1
4a–c. All the compounds 5a–d were characterized by H NMR, 13C NMR and 31P
NMR spectroscopy, mass spectrometry (MALDI-TOF), and elemental analysis.
The 1H and 13C NMR spectra of compounds 5a–d were consistent with the formulas
indicated. The 31P spectra of compounds 5a–d consisted of one sharp peak with sig-
nals at positions similar to those observed for other (phenoxy)cyclotriphosphazenes,[1]
indicating the completion of the substituted reaction. The MALDI-TOF mass spectra
further identified the predicted structures of compounds 5a–d. Compounds 5a–c
showed good solubilities in common solvents such as CHCl3 and THF. Compound
5d could not dissolve in low polar solvents even at elevated temperature but exhibited
good solubility in high polar solvents at elevated temperature, such as N,N-dimethyl-
formamide (DMF), dimethyl sulfoxide (DMSO), and pyridine. The melting points of
compounds 5b–d with terminal substituents were higher than those of corresponding
compounds 4b–d; however, the melting point of compound 5a with no terminal
substituent was lower than that of compound 4a.
The thermal behaviors of compounds 5a–d were studied by differential scanning
calorimetry (DSC). The transition temperatures and associated enthalpy changes of
transition are summarized in Table 1. The representative polarized optical micro-
graphs (POM) of compounds 5a–d are shown in Figure 1.
Table 1. Thermal behavior of compounds 5a–d
Phase-transition behaviora
Compounds
Heating
Cooling
5a
5b
5c
5d
Cr 209(73.60) I
Cr 220(87.24) I
I 124(41.00) Cr0 78(3.55) Cr
I 143(13.84)N 132(44.02) Cr
Cr 108(ꢁ44.79) Cr0 189(61.28) N 199(3.25) I
I 196(1.85) N 114(2.50) Cr
I 249(1.16) N 204(1.93) Cr0 130(5.47) Cr
Cr 154(ꢁ17.67) Cr0 270(47.81) I
aTransition temperatures (ꢀC) are taken from the second run. Enthalpies (DH) of transition (kJ=mol, in
parentheses). Cr, crystalline; N, nematic phase; I, isotropic state.

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R. BAO ET AL.
Figure 1. Representative polarized optical micrographs of 5a–d: (a) 5a at 110 ꢀC, on cooling; (b) 5b at
140 ꢀC, on cooling; (c) 5c at 150 ꢀC, on cooling; and (d) 5d at 230 ꢀC, on cooling. (Figure is provided in color
online.)
The results indicated that compounds 5b–d exhibited nematic phases while
compound 5a exhibited only crystal phase both on heating and cooling. For 5a, typi-
cal texture of crystal was observed as shown in Figure 1a. For 5b, threadlike text was
observed, which is a typical texture for nematic phase as shown in Figure 1b. For 5c
and 5d, characteristic schlieren textures, which contribute to nematic phase, were
observed as shown in Fig. 1c and 1d.
CONCLUSION
In conclusion, we have synthesized a class of a-cyanostilbene-containing
cyclotriphosphazenes with different terminal substituents. All the studied cyclotri-
phosphazenes with terminal substituents could exhibit nematic phases.
EXPERIMENTAL
HCCP was synthesized according to the literature method.[14] 3,4-Dihydroxy-
pyran, t-BuOK, n-Bu4NOH, and 4-cyanobenzaldehyde were purchased from Alfa
Aesar. All other chemicals and solvents were purchased from Sinopharm Chemical
Reagent Co., Ltd. All solvents were dried by standard techniques before use. 1H, 13C,
and 31P NMR spectra were measured on a Bruker AV 400-MHz spectrometer in

CYCLOTRIPHOSPHAZENES CONTAINING CYANOSTILBENES
1665
deuterated solvent with tetramethylsilane (TMS) as an internal standard (1H and
13C) and with 85% H3PO4 as an external reference (31P). High-resolution mass spec-
tra (HRMS) were recorded on the Applied Biosystems API-3000 LC=MS TOF mass
spectrometer. MALDI-TOF mass spectrometry was carried out on the Applied
Biosystems Voyager-DE-STR MALDI-TOF mass spectrometer. Elemental analyses
were performed using a Vario Micro cube analyzer. Thermal behaviors of the trimer
derivatives were studied on a Perkin-Elmer Diamond DSC under a heating and
cooling rate of 10 ꢀC=min in nitrogen. The peak temperature of the endotherms
and exotherms were taken as the phase transition temperatures. Polarized optical
microscopy was carried out on Olympus BX51 equipped with a hot stage system.
Synthesis of 4-(Tetrahydro-2-pyranoxy)phenylacetonitrile (1)
Compound 1 was prepared according to the literature method.[15]
General Procedure for the Preparation of Compounds 4a–c
t-BuOK (0.13 g, 1.2 mmol) and n-Bu4NOH (6.91 g, 40% in methanol,
10.6 mmol) were added quickly to a solution of 4-(tetrahydro-2-pyranoxy)phenylace-
tonitrile (3.85 g, 17.7 mmol) and the corresponding benzaldehyde derivative
(16.1 mmol) in t-BuOH (40 mL) at 80 ꢀC under nitrogen. After stirring at 80 ꢀC for
30 min, the mixture was poured into water and extracted with ethyl acetate. The
organic layer was then washed with water and dried. The solvent was removed under
reduced pressure. The crude products of compounds 3a–c were used in the deprotec-
tion reaction without further purification. p-Toluenesulfonic acid (TsOH) (0.84 g,
4.9 mmol) was added to the solution of compound 3 in methanol (100 mL), and the
mixture was stirred for 1.5 h under reflux. Most of the solvent was removed under
reduced pressure. The resulting solid was collected by filtration and then recrystal-
lized from methanol to give compounds 4a–c.
Synthesis of (Z)-2-(4-Hydroxyphenyl)-3-(4-cyanophenyl)
acrylonitrile (4d)
In a procedure similar to the synthetic method of compounds 4a–c with little
modification, t-BuOK and n-Bu4NOH were added quickly to the t-BuOH solution
at 30 ꢀC under nitrogen. The mixture was stirred at 30 ꢀC for 15 s, and then poured
quickly into water (200 mL). The resulting solid was collected by filtration and
washed with methanol to give compound 3d. The deprotection reaction was the same
as those for compounds 4a–c.
General Procedure for the Preparation of Compounds 5a–d
A mixture of HCCP (0.30 g, 0.9 mmol), with 20% in excess of compound 4
(6.2 mmol) and NaH [0.25 g, 60% (w=w) dispersed in mineral oil, 6.3 mmol] in dry
THF (100 mL), was refluxed for 48 h. Upon completion of the reaction, the mixture
was poured into methanol=water (v=v: 1=1, 300 mL) and reprecipitated twice from
THF into methanol to give compounds 5a–c (for compound 5d, the crude product
was recrystallized from DMF).

1666
R. BAO ET AL.
Data
(Z)-2-(4-Hydroxyphenyl)-3-phenylacrylonitrile (4a). Yield 69%; mp 219–
1
221 ꢀC; white crystal; H NMR (DMSO-d6) d: 9.92 (s, 1H, OH), 7.88 (d, J ¼ 7.6 Hz,
2H, Ar-H), 7.83 [s, 1H, C(CN)¼CH], 7.59 (d, J ¼ 8.4 Hz, 2H, Ar-H), 7.54–7.44 (m,
3H, Ar-H), 6.89 (d, J ¼ 8.8 Hz, 2H, Ar-H). 13C NMR (DMSO-d6) d: 159.10, 140.08,
134.58, 130.46, 129.33, 129.26, 127.76, 125.04, 118.56, 116.42, 110.91. HRMS:
C15H10NOþ calculated: 220.0762. Found: 220.0786 [M ꢁ H]þ.
(Z)-2-(4-Hydroxyphenyl)-3-(4-methylphenyl)acrylonitrile (4b). Yield 65%;
1
mp 172–174 ꢀC; yellow crystal; H NMR (DMSO-d6) d: 9.93 (s, 1H, OH), 7.79 [t,
J ¼ 8.0 Hz, 3H, Ar-H and C(CN)¼CH], 7.58 (d, J ¼ 8.8 Hz, 2H, Ar-H), 7.31 (d,
J ¼ 8.0 Hz, 2H, Ar-H), 6.90 (d, J ¼ 8.8 Hz, 2H, Ar-H), 2.36 (s, 3H, CH3). 13C
NMR (DMSO-d6) d: 158.94, 140.50, 140.06, 131.82, 129.91, 129.27, 127.61,
125.20, 118.75, 116.40, 109.73, 21.50. HRMS: C16H12NOþ calculated: 234.0919.
Found: 234.0944 [M ꢁ H]þ.
(Z)-2-(4-Hydroxyphenyl)-3-(4-methoxyphenyl)acrylonitrile
(4c). Yield
1
72%; mp 159–161 ꢀC; yellowish crystal; H NMR (DMSO-d6) d: 9.84 (s, 1H, OH),
7.88 (d, J ¼ 8.8 Hz, 2H, Ar-H), 7.74 [s, 1H, C(CN)¼CH], 7.54 (d, J ¼ 6.8 Hz, 2H,
Ar-H), 7.08 (d, J ¼ 8.8 Hz, 2H, Ar-H), 6.87 (d, J ¼ 6.8 Hz, 2H, Ar-H), 3.83 (s, 3H,
OCH3). 13C NMR (DMSO-d6) d: 161.14, 158.69, 139.88, 131.13, 127.42, 127.11,
125.42, 119.05, 116.37, 114.87, 107.84, 55.86. HRMS: C16H12NOþ2 calculated:
250.0868. Found: 250.0893 [M ꢁ H]þ.
(Z)-2-(4-Hydroxyphenyl)-3-(4-cyanophenyl)acrylonitrile (4d). Yield 74%;
1
mp 226–228 ꢀC; yellow crystal; H NMR (DMSO-d6) d: 10.05 (s, 1H, OH), 8.01
(q, J ¼ 8.8 Hz, 4H, Ar-H), 7.93 [s, 1H, C(CN) ¼ CH], 7.63 (d, J ¼ 8.8 Hz, 2H,
Ar-H), 6.91 (d, J ¼ 8.8 Hz, 2H, Ar-H). 13C NMR (DMSO-d6) d: 159.70, 139.06,
137.79, 133.17, 129.84, 128.16, 124.49, 118.99, 117.94, 116.53, 113.95, 112.20.
HRMS: C16H9N2Oþ calculated: 245.0715. Found: 245.0750 [M ꢁ H]þ.
2,2,4,4,6,6-Hexakis[4-((Z)-1-cyano-2-phenylvinyl)phenoxy]cyclotriphos-
phazene (5a). Yield 90%; mp 209–211 ꢀC; white powder; 1H NMR (CDCl3) d: 7.78
(dd, J ¼ 2.0, 8.0 Hz, 2H, Ar-H), 7.55 (d, J ¼ 8.8 Hz, 2H, Ar-H), 7.48 [s, 1H,
C(CN)¼CH], 7.39–7.34 (m, 3H, Ar-H), 7.08 [d, J ¼ 8.4 Hz, 2H, Ar-H]. 13C NMR
(CDCl3) d: 150.86, 142.57, 133.35, 131.77, 130.66, 129.34, 128.92, 127.28, 121.53,
117.90, 110.18. 31P NMR (CDCl3) d: 8.53. MS (MALDI-TOF) m=z: 1456.3
[M þ H]þ, 1478.3 [M þ Na]þ, 1495.2 [M þ K]þ. Anal. calcd. for C90H60N9O6P3: C,
74.22; H, 4.15; N, 8.66. Found C, 74.21; H, 4.09; N, 8.85.
2,2,4,4,6,6-Hexakis[4-((Z)-1-cyano-2-p-tolylvinyl)phenoxy]cyclotriphosp-
1
hazene (5b). Yield 92%; mp 217–219 ꢀC; white powder; H NMR (CDCl3) d: 7.68
(d, J ¼ 8.4 Hz, 2H, Ar-H), 7.53 (d, J ¼ 8.8 Hz, 2H, Ar-H), 7.42 [s, 1H, C(CN)¼CH],
7.15 (d, J ¼ 8.4 Hz, 2H, Ar-H), 7.06 (d, J ¼ 8.4 Hz, 2H, Ar-H), 2.38 (s, 3H, CH3). 13
C
NMR (CDCl3) d: 150.65, 142.54, 141.15, 131.91, 130.69, 129.57, 129.40, 127.12,
121.48, 118.12, 108.90, 21.56. 31P NMR (CDCl3) d: 8.59. MS (MALDI-TOF) m=z:
1540.3 [M þ H]þ, 1562.2 [M þ Na]þ. Anal. calcd. for C96H72N9O6P3: C, 74.84; H,
4.71; N, 8.18. Found C, 74.68; H, 4.61; N, 8.29.

CYCLOTRIPHOSPHAZENES CONTAINING CYANOSTILBENES
1667
2,2,4,4,6,6-Hexakisf4-[(Z)-1-cyano-2-(4-methoxyphenyl)vinyl] phenoxyg
cyclotriphosphazene (5c). Yield 91%; mp 186–193 ꢀC; yellowish crystal; 1H NMR
(CDCl3) d: 7.75 (d, J ¼ 9.2 Hz, 2H, Ar-H), 7.49 (d, J ¼ 8.8 Hz, 2H, Ar-H), 7.37 [s, 1H,
C(CN)¼CH], 7.04 (d, J ¼ 8.4 Hz, 2H, Ar-H), 6.84 (d, J ¼ 8.8 Hz, 2H, Ar-H), 3.84 (s,
3H, OCH3). 13C NMR (CDCl3) d: 161.44, 150.51, 142.08, 132.05, 131.32, 126.94,
126.20, 121.51, 118.47, 114.30, 107.11, 55.34. 31P NMR (CDCl3) d: 8.72. MS
(MALDI-TOF) m=z: 1637.2 [M þ H]þ, 1658.2 [M þ Na]þ. Anal. calcd. for
C96H72N9O12P3: C, 70.45; H, 4.43; N, 7.70. Found C, 70.68; H, 4.38; N, 7.79.
2,2,4,4,6,6-Hexakisf4-[(Z)-1-cyano-2-(4-cyanophenyl)vinyl]
phenoxyg
1
cyclotriphosphazene (5d). Yield 87%; mp 269–279 ꢀC; white crystal; H NMR
(DMSO-d6) d: 7.97 (s, 1H, C(CN)¼CH), 7.88 (q, J ¼ 8.8 Hz, 4H, Ar-H), 7.67 (d,
J ¼ 8.8 Hz, 2H, Ar-H), 7.17 (d, J ¼ 8.8 Hz, 2H, Ar-H). 13C NMR (DMSO-d6) d:
150.98, 141.18, 138.09, 133.02, 130.95, 129.99, 128.12, 121.68, 118.73, 117.48,
112.82, 112.68. 31P NMR (DMSO-d6) d: 8.52. MS (MALDI-TOF) m=z: 1607.1
[M þ H]þ. Anal. calcd. for C96H54N15O6P3: C, 71.77; H, 3.39; N, 13.08. Found C,
71.29; H, 3.30; N, 13.44.
ACKNOWLEDGMENTS
The authors are grateful to the Natural Science Foundation of China (No.
50703013) and Independent Innovative Position of Hubei Province for financial
support of this work.
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