Liquid crystalline N-aryl-β-aminovinyl ketones and their complexes with lanthanides

Article abstract of DOI:10.1134/S1070363206070152

Liquid crystalline lanthanide complexes with N-aryl-substituted β-aminovinyl ketones were synthesized for the first time. The complexes give rise to smectic A mesophase and are stable only in the solid state; in going to solution, they dissociate with for

Full text of DOI:10.1134/S1070363206070152

ISSN 1070-3632, Russian Journal of General Chemistry, 2006, Vol. 76, No. 7, pp. 1095 1099.
Pleiades Publishing, Inc., 2006.
Original Russian Text O.A. Turanova, Yu.G. Galyametdinov, 2006, published in Zhurnal Obshchei Khimii, 2006, Vol. 76, No. 7, pp. 1143 1147.
Liquid Crystalline N-Aryl- -aminovinyl Ketones
and Their Complexes with Lanthanides
O. A. Turanovaa and Yu. G. Galyametdinova, b
a Zavoiskii Kazan Physical and Technical Institute, Kazan Research Center,
Russian Academy of Sciences, Sibirskii trakt 10/7, Kazan, 420029 Tatarstan, Russia
fax: (8432) 765075; e-mail: turanova@mail.knc.ru
b Kazan State Technological University, Kazan, Tatarstan, Russia
Received July 26, 2005
Abstract Liquid crystalline lanthanide complexes with N-aryl-substituted -aminovinyl ketones were
synthesized for the first time. The complexes give rise to smectic A mesophase and are stable only in the solid
state; in going to solution, they dissociate with formation of the initial ligand.
DOI: 10.1134/S1070363206070152
Studies in the field of liquid crystalline coordina-
tion compounds (metallomesogens) constitute an int-
erdisciplinary line appearing at the junction of co-
ordination chemistry and physics of liquid crystals.
The series of available metallomesogens has been
extended considerably due to diversity of ligands
(uni-, bi-, and multidentate) and variation of metals
(s, p, d, and f) used in complex formation. The pre-
sence of a metal ion in coordination liquid crystals
endows them with unique electric and magnetic pro-
perties [1, 2]. Therefore, metallomesogens together
with organic liquid crystals are widely used in modern
technics (displays, optical trsnducers, etc.). Lantha-
nide-containing liquid crystals are advantageous due
to their strong magnetic anisotropy and easy control
by weak magnetic fields [3]. Apart from liquid crys-
talline properties, lanthanide adducts exhibit efficient
luminescence [4]. A drawback of such systems is dif-
ficult generation of geometric anisotropy (anisometry)
of their molecules owing to high coordination
numbers of lanthanides. It is known that anisometry is
a necessary condition for the appearance of liquid
crystalline properties: smectic, nematic, discotic, etc.
Up to now, liquid crystalline coordination com-
pounds of some lanthanides with Schiff bases have
been studied in detail [1], and adducts of lanthanide
-diketonates with Schiff bases [5], bipyridine, and
phenanthroline [4] have been obtained. Previously,
only N-alkyl-substituted ligands were involved in
complex formation with f elements. Coordination of
lanthanides to N-aryl-substituted ligands was ques-
tioned [6]. Only a few publications are available on
related compounds with Schiff bases [7, 8].
In the present article we describe our successful
attempt to synthesize liquid crystalline N-aryl-sub-
stituted -aminovinyl ketones and their complexes
with lanthanum and dysprosium. The ligands were
obtained in several steps according to Scheme 1. The
first step was alkylation of phenol with alkyl bromides.
The reactions were carried out following the Claisen
procedure, in anhydrous acetone in the presence of
potassium carbonate. The resulting alkoxybenzenes
were acetylated with acetic anhydride using 60%
perchloric acid as catalyst.
Intermediately formed acetyl perchlorate is an
Scheme 1.
RBr
HBr
(CH3CO)2, HClO4
HO
RO
RO
RO
C CH3
O
CH3COOH
CH CH=O
ONa
CH=CH
Na, HCOOEt
p-R OC6H4NH2 HCl
RO
C
C
N
OR
NaCl, H2O
O
H
LH
R = C9H19, C12H25, C14H29; R = C4H9, C8H17, C10H21, C11H23.
1095

1096
Table 1. Elemental analyses of -aminovinyl ketones LH and their complexes with lanthanides Ln(LH)3(NO3)3
Found, % Calculated, %
TURANOVA et al.
R
R
Ln
Formula
C
H
Ln
N
C
H
Ln
N
C9H19
C9H19
C9H19
C9H19
C9H19
C9H19
C9H19
C12H25
C12H25
C14H29
C14H29
C4H9
C4H9
76.89
60.85
78.32
64.12
64.49
78.49
65.72
78.59
64.12
8.92
6.94
9.87
8.16
8.45
9.99
8.37
9.83
8.35
3.48 C84H117N6O18
4.99 C84H117DyN6O18 60.73
2.58 C102H153N6O18 78.27
4.59 C102H153DyN6O18 64.01
4.56 C102H153LaN6O18 64.81
2.89 C105H159N6O18
4.40 C105H159LaN6O18 65.26
2.39 C105H159N6O18 78.46
4.48 C105H159DyN6O18 64.48
2.32 C111H171N6O18
4.33 C111H171DyN6O18 65.35
76.85
8.98
7.10
9.85
8.06
8.16
9.97
8.29
9.97
8.19
3.20
5.06
2.68
4.39
4.45
2.61
4.35
2.61
4.30
2.48
4.12
Dy
9.93
9.78
C10H21
C10H21
C10H21
C11H23
C11H23
C8H17
C8H17
C8H17
C8H17
Dy
La
8.63
7.89
8.49
7.35
78.46
La
Dy
Dy
7.01
8.57
8.12
7.19
8.31
7.97
78.93 10.21
65.47 8.63
78.81 10.19
8.45
acetylating agent which ensures higher yield of the
acetylation product and considerably shortens the
reaction time [9]. The use of aluminum chloride as
a catalyst in such reactions also provides good results.
The next stage was the synthesis of -hydroxymethyl-
ideneacetophenone sodium salt. The reaction was
carried out by heating the reactants in anhydrous
benzene. The product was a yellow powder which was
recrystallized from benzene. The use of a large excess
of ethyl formate allowed us to raise the yield to 90%
and reduce the reaction temperature.
pose under these conditions. After heating, the solvent
was immediately and completely removed from the
reaction mixture. If the mixture was allowed to cool
down before removal of the solvent or even traces of
the latter were present in the residue, the complex
formation equilibrium was displaced completely
toward the initial components. The products were
isolated as yellow powders. The complexes can not be
purified
by
recrystallization
or
reprecipita-
tion; in both cases their decomposition occurred. Such
instability in solution is inherent in the complexes
derived from both N-aryl- and N-alkyl-substituted
ligands. Analogous results were discussed previously
while studying coordination compounds of lanthani-
des with Schiff bases [11, 12].
Substituted
-hydroxymethylideneacetophenone
sodium salts were then brought into reaction with
palkoxyaniline hydrochlorides to obtain the desired
-aminovinyl ketones LH as ligands (Scheme 1). The
reactions were performed by heating the reactants in
boiling ethanol. After cooling, the precipitate was
filtered off and recrystallized from alcohol, or repre-
cipitated from chloroform with ethanol. -Aminovinyl
ketones thus obtained were stable in air, as well as
on heating to isotropic melt and subsequent cooling.
Scheme 2.
3LH + Ln(NO3)3 6H2O
Ln(LH)3(NO3)3.
Since no single crystal could be grown, the struc-
ture of the ligands and their complexes was deter-
mined on the basis of their elemental analyses (Tab-
We previously reported on liquid crystalline lan-
thanide complexes with nonmesogenic N-alkyl-sub-
stituted -aminovinyl ketones [10]. Surprisingly, our
attempt to obtain coordination compounds with meso-
genic N-aryl-substituted ligands, following an
analogous procedure, was unsuccessful. Presumably,
complex formation was hampered for steric reasons
owing to the presence of an additional benzene ring
on the nitrogen atom. We found that more severe
conditions are necessary to obtain the desired com-
plexes (heating of the reactants in boiling ethanol at
80 C for 4 5 h, Scheme 2). It should be noted that
complexes with N-alkyl-substituted ligands decom-
1
le 1) and H NMR and IR spectra. According to the
1H NMR and IR data, most of the synthesized
-aminovinyl ketones have ketoenamine structure
which is favored by formation of stable quasiaromatic
ring via intramolecular O H hydrogen bonding. The
presence of an H-chelate ring with conjugated double
bonds is confirmed by displacement of the IR bands
belonging to the stretching vibrations of the N H
1
(3310 and 3435 cm ), C O, and C C bonds (1640
1
and 1602 cm , respectively) toward lower frequencies.
The chemical shift of the NH proton ( 12 ppm) and
splitting of its signal due to coupling with the vinyl
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LIQUID CRYSTALLINE N-ARYL- -AMINOVINYL KETONES
1097
1
proton (J 12 Hz) in the H NMR spectra also suggest
the presence of a strong intramolecular hydrogen bond
in the ligand.
Table 2. Phase transition temperatures and mesophase
temperature ranges T of ligands LH and their complexes
with lanthanides with the composition Ln(LH)3(NO3)3
CH=CH
Phase transition
R
C
N R
temperatures,a
C
T,
C
O
H
R
R
Ln
Cr SA
SA(N) I
It is known that biphenyl rod-like structures are
prone to form mesophases [13, 14]. Introduction of
an N-aryl substituent into aminovinyl ketone molecule
gives rise to conjugation between the aromatic rings
and enaminoketone moiety, which stabilizes a rigid
rod-like structure and leads to appearance of the
desired liquid crystalline properties.
b
b
b
C9H19
C9H19
C9H19
C9H19
C9H19
C9H19
C9H19
C4H9
C4H9
129
178
118
173
175
106
178
140
177
139
169
195
217
189
216
210
184
218
180
212
182
208
66
39
71
43
35
78
40
40
35
43
40
Dy
C10H21
C10H21
C10H21
C11H23
C11H23
C8H17
C8H17
C8H17
C8H17
Dy
La
In the IR spectra of the complexes (in mineral oil)
we observed a slight narrowing of absorption bands
due to stretching vibrations of the NH group (3304,
La
Dy
Dy
C12H25
C12H25
C14H29
C14H29
1
3442 cm ) involved in the intramolecular hydrogen
bond; this pattern indicates that the ligand structure
remained essentially the same on complex formation
{the proton on the nitrogen atom is retained, though
it is usually replaced upon complex formation with d
elements, e.g., in copper(II) complexes [15]}. In addi-
tion, displacement of the C O and C C stretching
vibration bands toward higher frequencies (1653 and
a
Cr stands for crystalline, S for smectic A, N for nematic,
A
b
and I for isotropic.
S
N phase transition temperature 186 C.
A
compounds are thermally stable: they did not change
after several heating cooling cycles. The phase transi-
tion temperatures and temperature ranges of meso-
phases formed by -aminovinyl ketones and their
complexes with lanthanides are given in Table 2.
1
1605 cm , respectively) was observed. Analogous IR
spectra were reported for coordination compounds of
dioxomolybdenum(VI) dichloride with -aminovinyl
ketones [16]. Four bands in the IR spectra, in parti-
1
Increase in the number of benzene rings in the
cular at 1465, 1261, 1106, and 847 cm for the
ligand favors additional
-electron interactions
lanthanum complex, were assigned to stretching vibra-
between the phenyl fragments; as a result, the phase
transition temperature increases. On the average, it
becomes by 50 60 C hygher than the corresponding
parameter found for N-alkyl-substituted analogs [17].
The phase transition temperatures also increase in
going from the ligands to their lanthanide complexes;
their ability to form smectic phase increases in parallel.
tions of the nitro group ( ,
,
2, and 6, respect-
and frequencies
1
ively). The difference in t4he
4
1
1
(204 cm ) is typical for bidentane nitrate groups.
Analysis of the 1H NMR spectrum of the dia-
magnetic lanthanum complex showed that in solution
it undergoes dissociation to the initial components.
1
The H NMR spectrum contained a dublet of dublets
Insofar as the behavior and liquid crystalline
properties of lanthanide complexes with Schiff bases
and -aminovinyl ketones are very similar, we pre-
sume that these compounds have similar structures
and that their molecules in the mesophase are packed
in the same mode [18]. The data of elemental analysis
and spectral and liquid crystalline properties of the
synthesized compounds suggest that the complexes
have the composition Ln(LH)3(NO3)3 where the
nearest environment of the rare-earth metal ion in-
cludes three oxygen atoms of the ligands and six
oxygen atoms of the bidentate nitrate groups to form
a one-cap square antiprism.
at 7.44 ppm, which belongs to the CHN proton. The
position of the NH doublet ( 12.15 ppm) corresponds
to the free ligand. Complexes with N-alkyl-substituted
ligands, which are stable in solution, are characterized
by splitting of the NH signal into a multiplet and its
displacement to a stronger field ( 10.38 ppm) [17].
Thus the H NMR spectra confirm that liquid crystal-
line lanthanide complexes with N-aryl-substituted
ligands are stable only in the absence of a solvent.
1
Mesogenic properties of the synthesized com-
pounds (phase transition temperatures and types of
mesophases) were studied by polarizing microscopy.
Both initial ligands and the complexes are thermo-
tropic liquid crystals giving rise to a fan texture
typical of smectic A mesophase on heating. All
Thus we were the first to synthesize liquid crystal-
line lanthanide complexes with N-aryl-substituted
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 7 2006

1098
TURANOVA et al.
-aminovinyl ketones, whose phase transition tem-
Sodium 1-(4-nonyloxyphenyl)-3-oxoprop-1-en-
1-olate. A mixture of 0.01 mol of 1-(4-nonyloxy-
phenyl)ethanone, 0.01 mol of ethyl formate, and
0.01 mol of metallic sodium in anhydrous benzene
was heated for 5 h under reflux. The precipitate was
filtered off, washed with hot diethyl ether, and recrys-
tallized from benzene. Yield 3.39 g (72%), mp 221 C
(decomp.). The reaction occurred under milder condi-
tions and the yield was greater in the presence of
excess ethyl formate.
peratures (or thermal stability) exceed by 50 60 C
those typical of N-alkyl-substituted analogs. The
complexes are stable only as neat substances, and they
undergo dissociation into the initial ligand and metal
salt on dissolution.
EXPERIMENTAL
The textures and phase transition temperatures
were determined using a Boetius polarizing micro-
scope equipped with a computer-guided temperature-
control unit. The temperatures were measured with an
accuracy of 0.1 C. The IR spectra were recorded in
1-(4-Nonyloxyphenyl)-3-(4-undecyloxyphenyl-
amino)prop-2-en-1-one. A solution of 0.35 mmol of
sodium 1-(4-nonyloxyphenyl)-3-oxo-1-propen-1-olate
in ethanol was mixed with a solution of 0.35 mmol of
4-undecyloxyphenylamine hydrochloride in the same
solvent, and the mixture was heated for 10 min. After
cooling, the yellow precipitate was filtered off and
1
mineral oil on a Specord IR-75 spectrometer. The H
NMR spectra were obtained on a Varian Unity-300
spectrometer from solutions in CDCl3 using TMS as
reference.
1
recrystallized from ethanol. Yield 0.09 g (64%). H
NMR spectrum (CDCl3), , ppm (J, Hz): 0.90 0.94 m
(6H, CH3), 1.31 1.48 m (14H, CH2), 1.65 1.90 m
(4H, CH2CH2O), 4.01 d.t (4H, CH2O, J 6.8, 24.6),
5.97 d [1H, C(O)CH, J 7.9], 6.90 6.98 m (4H,
OC6H4C), 7.07 d and 7.96 d (2H each, NC6H4O, J
9.01), 7.44 d. d (1H, CHN, J 12.4, 7.8), 12.15 d (1H,
NH, J 12.1).
The ligands and complexes were synthesized ac-
cording to the general procedure described below. All
initial reagents and solvents were preliminarily puri-
fied by recrystallization or distillation until their
physical constants coincided with reference values.
Nonyloxybenzene. A mixture of 0.53 mol of
phenol, 0.53 mol of nonyl bromide, and 0.53 mol of
finely powdered potassium carbonate in 100 ml of
anhydrous acetone was heated for 8 h under reflux on
a water bath. During the reaction, KBr precipitated.
The mixture was cooled, 300 ml of water was added,
and the product was extracted into diethyl ether. The
extract was washed with a 10% solution of sodium
hydroxide and dried over K2CO3. The solvent was
distilled off, and the residue was distilled under
reduced pressure, a fraction boiling in the temperature
range from 100 to 110 C (3 mm) being collected.
Yield 43.3 g (40%), n2D0 = 1.4857.
Tris[1-(4-nonyloxyphenyl)-3-(4-undecyloxy-
phenylamino)-2-propen-1-one]trinitrolantha-
num(III). Lanthanum(III) nitrate hexahydrate,
0.07 mmol, was added to a solution of 0.20 mmol of
1-(4-nonyloxyphenyl)-3-(4-undecyloxyphenylamino)-
prop-2-en-1-one in ethanol, and the mixture was
heated for 5 h under reflux. The solvent was removed
under reduced pressure to obtain a yellow finely
1
crystalline powder. IR spectrum (mineral oil), , cm :
1
3304, 3342 (NH); 1653 (CO); 1605 (C=C). H NMR
spectrum (CDCl3), , ppm (J, Hz): 0.90 0.94 m (6H,
CH3), 1.31 1.48 m (14H, CH2), 1.65 1.90 m (4H,
CH2CH2O), 4.01 d.t (4H, CH2O, J 6.8, 24.6), 5.97 d
[1H, C(O)CH, J 7.9], 6.90 6.98 m (4H, OC6H4C),
7.07 d and 7.96 d (2H each, NC6H4O, J 9.01),
7.44 d.d (1H, CHN, J 12.4, 7.8), 12.15 d (1H, NH,
J 12.1).
1-(4-Nonyloxyphenyl)ethanone.
Nonyloxyben-
zene, 0.1 mol, was mixed with 0.1 mol of acetic an-
hydride, and 60 drops of 60% perchloric acid were
added. The solution warmed up and turned dark red.
It was heated for 30 min on a boiling water bath and
poured into 100 ml of cold water, and the mixture was
left to stand for 1 h to remove excess of acetic an-
hydride. In order to accelerate this process, 8 g of
sodium carbonate can be added, followed by heating
to the boiling point. The organic layer was separated,
and the aqueous layer was extracted with diethyl
ether. The extract was combined with the organic
phase, treated with a solution of sodium carbonate to
neutral reaction, washed with water, and dried over
K2CO3. The solvent was distilled off, and the residue
was distilled under reduced pressure. Yield 8.71 g
(33%), bp 150 160 C (3 mm), n2D0 = 1.4890.
ACKNOWLEDGMENTS
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 04-03-32923).
REFERENCES
1. Metallomesogens. Synthesis, Properties, and Applica-
tions, Serrano, J.L., Ed., Weinheim: VCH, 1996.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 7 2006

LIQUID CRYSTALLINE N-ARYL- -AMINOVINYL KETONES
1099
2. Hudson, S.A. and Maitlis, P.M., Chem. Rev., 1993,
12. Berg, D.J., Retting, S.J., and Orvig, C., J. Am. Chem.
Soc., 1991, vol. 113, no. 7, p. 2528.
vol. 93, no. 3, p. 861.
3. Donnio, B., Guillon, D., Deschenaux, R., and Bru-
ce, D., Comprehensive Coordination Chemistry II,
Amsterdam: Elsevier, 2004, vol. 7, p. 357.
13. Handbook of Liquid Crystals, Demus, D., Goodby, J.,
Gray, G.W., Spiess, H.-W., and Vill, V., Eds.,
Weinheim: VCH, 1998.
4. Galyametdinov, Yu.G., Turanova, O.A., Ven Van,
Knyazev, A.A., and Haase, W., Dokl. Ross. Akad.
Nauk, 2002, vol. 384, no. 2, p. 206.
14. Amerik, Yu.B. and Krentsel’, B.A., Khimiya zhidkikh
kristallov i mezomorfnykh polimernykh sistem (Chem-
istry of Liquid Crysals and Mesomorphic Polyneric
Systems), Moscow: Nauka, 1981.
5. Binnemans, K. and Lodewyckx, K., Angew. Chem.,
Int. Ed., 2001, vol. 40, no. 1, p. 242.
15. Turanova, O.A., Galyametdinov, Yu.G., and Ovchin-
nikov, I.V., Izv. Ross. Akad. Nauk, Ser. Khim., 2001,
no. 5, p. 771.
6. Binnemans, K., Bruce, D., Collinson, S., Deun, R.,
Galyametdinov, Yu., and Martin, F., Phil. Trans. Roy.
Soc. Lond. A, 1999, vol. 357, no. 1765, p. 3063.
16. Sergienko, V.S., Garnovskii, A.D., Porai-Ko-
shits, M.A., and Abramenko, V.L., Koord. Khim.,
1985, vol. 11, no. 10, p. 1407.
7. Guofa, L., Chongwu, N., Bin, L., and Kunyuan, M.,
Polyhedron, 1990, vol. 9, no. 17, p. 2019.
8. Nandiraju, V.S., Manoj, K.P., Thatavarthi, R.R., and
17. Kharitonova, O.A., Prosvirin, A.V., Galyametdi-
nov, Yu.G., and Ovchinnikov, I.V., Izv. Ross. Akad.
Nauk, Ser. Khim., 1996, no. 9, p. 2331.
Archana, P., Liq. Cryst., 2002, vol. 29, no. 9, p. 1243.
9. Dorofeenko, G.I. and Polishchuk, L.V., Zh. Obshch.
Khim., 1962, vol. 32, no. 2, p. 364.
18. Binnemans, K., Galyametdinov, Yu., Haase, W., Pro-
svirin, A., Tinchurina, L., Litvinov, I., Deun, R.,
Bruce, D., Collinson, S., Polishchuk, A., Bikchanta-
ev, I., Rakhmatullin, A., Uytterhoeven, K., and Me-
ervelt, L., J. Am. Chem. Soc., 2000, vol. 122, no. 18,
p. 4335.
10. Galyametdinov, Yu.G., Kharitonova, O.A., Kad-
kin, O.N., and Ovchinnikov, I.V., Izv. Ross. Akad.
Nauk, Ser. Khim., 1994, no. 9, p. 1685.
11. Smith, A., Rettig, S.J., and Orvig, C., Inorg. Chem.,
1988, vol. 27, no. 22, p. 3929.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 7 2006