Calamitic metallomesogens derived from unsymmetric pyrazoles

Article abstract of DOI:10.1016/j.tet.2009.08.062

Three series of copper(II) complexes 1a-1c derived from unsymmetric pyrazoles 2a-2c were prepared and their mesomorphic properties investigated. The mesomorphic behavior of compounds was studied by differential scanning calorimetry, polarizing optical mic

Full text of DOI:10.1016/j.tet.2009.08.062

Tetrahedron 65 (2009) 9460–9467
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Calamitic metallomesogens derived from unsymmetric pyrazoles
Min-Chou Chen c, Shih-Chieh Lee c, Chia-Chung Ho a, Tarng-Shiang Hu a,
,
Gene-Hsiang Lee b, Chung K. Lai c
*
a Industrial Technology Research Institute, HsinChu 300, Taiwan, ROC
b Instrumentation Center, National Taiwan University, Taipei 10660, Taiwan, ROC
c Department of Chemistry, National Central University, Chung-Li 32001, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 July 2009
Received in revised form 19 August 2009
Accepted 25 August 2009
Available online 29 August 2009
Three series of copper(II) complexes 1a–1c derived from unsymmetric pyrazoles 2a–2c were prepared
and their mesomorphic properties investigated. The mesomorphic behavior of compounds was studied
by differential scanning calorimetry, polarizing optical microscopy, and powder X-ray diffractometry. The
crystal and molecular structures of mesogenic copper complex (2a; n¼10) of 3-[4-decyloxyphenyl]-1H-
pyrazole were determined by means of X-ray structural analysis. It crystallizes in the triclinic space group
P-1, with a¼4.0890(1) Å, b¼18.0167(2) Å, c¼25.5015(5) Å, and Z¼2. The geometry at copper center was
not perfectly square planar. A weak intermolecular H-bond (d¼2.36 Å) between Cl1 and H2 atoms and
p–p interaction (ca. 3.45–3.55 Å) was also observed. All their precursors 2a–2c were not mesogenic. In
contrast, copper complexes 1a formed nematic or smectic C phases and complexes 1b–1c formed
crystalline phases. Powder X-ray diffraction experiments confirmed the presence of SmC phase.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
possible structures can be various and diverse. A trinuclear Au(I)
pyrazole-based complex6 bearing long alkyl chains has been pre-
Pyrazoles,1 classified as heterocyclic compounds, and their metal
pyrazolate2 have been widely applied in inorganic, organometallic,
and bioinorganic chemistry. As with most other heterocyclic com-
pounds they are often considered as electron-deficient or electron
acceptors, therefore, a local dipole of donor-to-acceptor (D–A) in-
teraction was possibly induced within molecules or between mol-
ecules. This type of weak intermolecular interaction was often
applied to generate useful materials with preferred molecular ori-
entation in a particular state. Liquid crystalline material is such an
example. In addition, intramolecular or intermolecular hydrogen
bondings (–NH/N) can be also possibly induced in such systems if
molecules designed properly. In fact hydrogen bonded liquid crys-
tals3 or H-bond-stabilized LCs have been widely observed in meso-
genic materials, as well as in a few pyrazole derivatives.4 X-ray
crystallographic analysis indicated that H-bonds can be either inter-
molecularly3c or/and intra-molecularly induced. Interest in such
systems stems from their diverse structures and known chemistry.
More and more examples of mesogenic pyrazoles4 were reported
since the first symmetric mesogenic pyrazoles5 Ia prepared and
investigated in 1992. On the other hand, two nitrogen atoms on the
pyrazole ring are potentially capable of binding to metal ions. Their
pared and its solution in hexane was found to form a red-lumines-
cent organogel (lem¼640, lext¼284 nm) for an application of
reversible RGB color switching. In contrast, known metal-
lomesogens derived from pyrazoles were relatively scarce, some of
the complexes incorporated with Ir/Rh(I/II),7 Ni(II),8 and Pd(II),9
Cu(I/II),10 Ag/Au(I),11 and Zn(II)12 ions were already reported. Co-
lumnar or smectic phases were obtained by rhodium(I) complexes
derived from symmetrical or unsymmetric pyrazoles. A few novel
samples of trimetallomesogens constructed by use of Ag(I) and Au(I)
with a coordination number equal to two were also prepared, and
columnar phases observed. On the other hand, mesogenic Pd(II) and
Ni(II) complexes were also obtained bysymmetric or unsymmetrical
pyrazole. The geometry at metal center was mostly square planar or
distorted tetrahedral. Metallomesogens with a square planar ge-
ometry often facilitated the molecular arrangements in solid or LC
states. These reported mesogens or metallomesogens formed layer
smectic or columnar phases. Some of structurally similar symmet-
rical Ib or unsymmetric pyrazoles13 II–IV and their derived metal-
lomesogens V,10 VI8 were previously prepared in this group.
Here we wish to report the preparation, characterization, and
mesomorphic studies of three series of rod-like copper(II) com-
plexes 1a–1c derived from unsymmetric pyrazoles 2a–2c. The
crystal and molecular structures of mesogenic copper complex (1a;
n¼10) of 3-[4-decyloxyphenyl]-1H-pyrazole were determined by
means of X-ray structural analysis, and geometry at copper center
was perfectly square planar. All pyrazoles 2a–2c were not
* Corresponding author.
E-mail address: cklai@cc.ncu.edu.tw (C.K. Lai).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.08.062

M.-C. Chen et al. / Tetrahedron 65 (2009) 9460–9467
9461
mesogenic. Coppercomplexes 1a formed nematic or smectic phases,
however, copper complexes 1b–1c were not mesogenic. The pre-
ferred mesophase formation of compound 1a over 1b–1c might
probably be attributed to a better aspect ratio. XRD experiments
were also performed to confirm the presence of SmC phase. EPR
studies indicated the presence of anisotropic behavior at para-
magnetic copper(II) center. The relationship between molecular
structures and mesomorphic behavior was also discussed. This is the
second example of copper pyrazolate complexes exhibiting meso-
morphic behavior.
of pyrazoles 2a–2c with copper(II) chloride in refluxing THF/
C2H5OH produced the copper complexes 1a–1c as bright yellowish
green solids. The similar reactions with ZnCl2 to prepare zinc
complexes were not successful for an unknown reason. Similar
palladium(II) complexes9e–g has been prepared and studied.
X
H2n+1CnO
Y
N
NH
Cl Cu Cl
HN
N
Y
OCnH2n+1
X
1a X = Y = H; n = 8, 10, 12, 14, 16
1b X = OC16H33 Y = H
1c X = H; Y = CH3; n = 16
RO
O
RO
X
OR
X
N
NH
HN
N
Ia; X = H,
II
Ib; X = OR
OR
Fe
O
O
OR
Fe
N
NH
IV
N
NH
III
RO
OR
OR
+
O
Cu
N
N
N
N
RO
O
N
NH
O
Cl Ni Cl
HN
N
RO
RO
OR
OR
OR
RO
-
BF4
OR
OR
V
VI
2. Results and discussion
2.1. Synthesis and characterization
X
X
H2n+1CnO
H2n+1CnO
a
The synthetic pathways14 followed to prepare compounds
1a–1c are summarized in Schemes 1 and 2. All precursors 3a–3c
were prepared according to the literature procedures. The further
condensation reactions of 1-(4-alkoxyphenyl)-3-hydroxy-2-
propen-1-ones 3a, 1-(3,4-alkoxy phenyl)-3-hydroxy-2-propen-1-
ones 3b, and 4-hexadecoxyphenylbutane-1,3-dione 3c with
hydrazine monohydrate in refluxing absolute ethanol produced
the pyrazole derivatives 2a–2c as off-white solids with a yield of ca.
61–83%. All compounds were characterized by 1H and 13C NMR
spectroscopy. The formation for compound 2c was easily moni-
O
OH
O
3a X = H
3b X = OC16H33
X
b
H2n+1CnO
X
H2n+1CnO
c
N NH
Cl Cu Cl
HN
N
tored by the disappearance of a singlet at
d 16.30 assigned for
NH
N
–CHCOH of 3c on 1H NMR spectroscopy. Similarly, the formation for
compound 2a was also monitored by the disappearance of a singlet
2a X = H
2b X = OC16H33
OCnH2n+1
at
d
9.93–8.11 assigned for –COH of 3a on 1H NMR spectroscopy.
X
Two tautomers for pyrazoles 2a–2b are spectroscopically
1a X = H; n = 8, 10, 12, 14, 16
1b X = OC16H33
observed. On the 1H NMR spectra, only two characteristic peaks at
d
6.50–6.55 and 7.57–7.63, assigned to keto-H(–CHCN) pyrazole-
H(]CHNH) were observed, however, the pyrazole-H(–NH) often
occurred at 11.60–12.60 was not observed. The further reactions
Scheme 1. Reagents and conditions. (a) NaOMe, ethyl formate, stirring at rt in dry THF,
24 h. (b) Hydrazine monohydrate, refluxing in THF/C2H5OH, 24 h. (c)CuCl2, refluxing in
THF/C2H5OH, 1 h.
d

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M.-C. Chen et al. / Tetrahedron 65 (2009) 9460–9467
C16H33
O
C16H33
O
C16H33
O
N NH
Cl Cu Cl
HN N
a
b
N
O
OH
NH
2c
3c
1c
OC16H33
Scheme 2. Reagents and conditions. (a) Hydrazine monohydrate, refluxing in THF/C2H5OH, 24 h. (b) CuCl2, refluxing in THF/C2H5OH, 1 h.
Figure 1. An ORTEP drawing for 1a (n¼10) with the numbering scheme. The thermal ellipsoids of the non-hydrogen atoms are drawn at the 50% probability level.
2.2. X-ray crystallographic analysis of copper complex
of 3-[4-decyloxyphenyl]-1H-pyrazole (1a; n[10)
Table 1
Crystal and refinement data for compound 1a (n¼10)
Compound
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
a/Å
1a (n¼10)
C38H56Cl2CuN4O2
735.31
200(2) K
0.71073 Å
Triclinic
A needle-like single crystal 1a (n ¼ 10) grown slowly from CH2Cl2
solution suitable for X-ray crystallography was obtained by diffusion
technique at room temperature and the structure resolved. The
molecular structure with numbering scheme is shown in Figure 1.
Table 1 lists its crystallographic and structural refinement data for
the molecule. The unit cell is triclinic and the molecular geometry is
fully extended with two molecules per unit cell. The overall molec-
ular shape is considered as a nearly linear structure, and the mo-
lecular length (C19–C190 atoms) and width were measured as
w40.59 Å and w4.41 Å, respectively, resulting in a rod-like molecule
with an aspect ratio of w0.11 (4.41/40.59 Å). The geometry at copper
center was perfectly square planar, and copper atom was trans-co-
ordinated to the two chlorine atoms. The two angles of N(1)–Cu–
Cl(1A) and N(1)–Cu–N(2) were of 90.09ꢀ and 89.91ꢀ, which were
close to an ideal angle of 90ꢀ expected for a square planar geometry.
Two bond distances of Cu–N(1) and Cu–Cl(1) were 1.9815(1) Å and
2.3093(5) Å. Two chlorines, two nitrogens, and copper atom were in
fact coplanar, however, this defined plane was not coplanar with the
neighboring pyrazole ring, having a dihedral angle of w9.96ꢀ. On the
P-1
4.0890(1)
18.0167(3)
25.5015(5)
89.925(1)
88.968(1)
84.413(1)
1869.47(7)
2
b/Å
c/Å
ꢀ
ꢀ
a
/
b
/
ꢀ
/
g
U/Å3
Z
Dc/Mg/m3
1.306
782
F(000)
Crystal size/mmꢁ3
Reflections collected
Independent reflections
Data/restraints/parameters
Final R1, wR2
0.35ꢂ0.15ꢂ0.12
18,944
8543 [R(int)¼0.0338]
8543/0/429
0.0382, 0.1110
Figure 2. A weak intramolecular H-bond (w2.36 Å) and an
p–p
interaction (w3.45 Å) were observed in crystal 1a (n¼10).

M.-C. Chen et al. / Tetrahedron 65 (2009) 9460–9467
9463
other hand, both pyrazole and benzene rings were also not coplanar
with a dihedral angle of w6.63ꢀ. Surprisingly, a weak intramolecular
H-bond (w2.36 Å) between Cu atom and the H(2) of the pyrazole
fact interdigitated, and arranged parallel to each other in an ex-
tended fashion.
ring and
p–p interaction (w3.45 Å) are observed in crystal 1a
(n¼10), shown in Figure 2. This H-bonding kept two chlorines,
copper, and two pyrazole rings nearly coplanar, which probably
better facilitated the molecular packing both in the solid and/or
liquid crystalline state. However, no intermolecular H-bonding was
observed. Some selected bond distances and angles for compound
1a (n¼10) are summarized in Table 2. Aview of the crystal packing in
the unit cell is presented in Figure 3 and reveals that the molecules
were all tilted by ca. w53ꢀ within the layers. This was quite consis-
tent for the SmC phases observed. All terminal alkoxy chains were in
Table 2
Selected bond distances and angles in crystal 1a (n¼10)
Figure 3. Molecular arrangements viewed from b axis in the unit cell.
Bond distances
Cu–N(1)
1.9815(18)
1.356(3)
1.349(3)
1.371(3)
Cu–Cl(1)
N(1)–C(1)
C(1)–C(2)
2.3093(5)
1.329(3)
1.386(3)
N1(1)–N(2)
N(2)–C(3)
C(2)–C(3)
2.3. Mesomorphic properties
The thermal behavior of compounds 1a–1c and 2a–2c were
investigated by polarized optical microscopy (POM) and differential
scanning calorimetry (DSC). The transition temperatures and en-
thalpies of the compounds are listed in Table 3. All pyrazole
derivatives 2a, 2b were not mesogenic. A transition of crystal-to-
isotropic was observed at 89.5 ꢀC and 80.6 ꢀC, respectively, for
compound 2a (n¼12) and 2b (n¼16) on heating process. A slightly
Bond angles
N(1)–Cu–N(1A)
N(1)–Cu–Cl(1A)
N(2)–N(1)–Cu
C(1)–N(1)–N(2)
N(1)–C(1)–C(2)
C(3)–C(2)–C(1)
180.00(15)
90.09(6)
121.98(14)
104.86(18)
110.4(2)
Cl(1)–Cu–Cl(1A)
Cl(1)–Cu–Cl(1A)
C(1)–N(1)–Cu
C(3)–N(2)–N(1)
N(2)–C(3)–C(2)
180.00(3)
180.00(3)
133.07(17)
112.58(19)
105.2(2)
107.0(2)
Table 3
The transition temperaturesa and enthalpies of compounds 1–2
89.5 (45.3)
I
Cr
2a; n = 12
63.1 (44.9)
80.6 (55.0)
57.6 (27.4)
60.8 (-43.6)
30.2 (2.52)
Cr3
Cr2
I
I
I
2b; n = 16
Cr1
49.0 (50.0)
101.0 (58.1)
Cr2
N
2c; n = 16
1a; n = 8
Cr1
Cr2
80.0 (57.8)
92.7 (29.2)
34.3 (21.0)
120.9 (29.1)
124.6 (1.32)
Cr1
108.3 (30.2)
122.0 (26.6)
121.5 (3.68)
130.1 (10.7)
I
I
I
Cr
SmC
SmC
10
12
125.8 (11.0)
137.7 (10.0)
108.4 (26.1)
122.8 (20.4)
104.6 (9.72)
106.1 (27.4)
Cr2
Cr1
106.9 (19.6)
114.7 (19.1)
130.0 (9.71)
136.1 (14.9)
Cr2
SmC
Cr1
Cr1
14
133.6 (13.6)
138.5 (12.7)
105.2 (27.4)
113.3 (99.9)
I
I
SmC
Cr2
16
Cr2
Cr1
131.5 (12.3)
125.7 (44.5)
101.3 (20.5)
106.8 (11.8)
72.8 (69.9)
1b; n = 16
119.8 (43.6)
108.7 (40.2)
74.1 (8.39)
50.4 (23.9)
84.4 (1.43)
78.7 (1.00)
Cr3
Cr1
I
1c; n = 16
Cr2
a
n¼The carbon numbers in the alkoxy chains, Cr¼crystal, N¼nematic, SmC¼smectic C, I¼isotropic phase. The phase transition temperatures (ꢀC) and enthalpies (in pa-
rentheses, kJ/mol) were determined by DSC at a scan rate of 10 ꢀC/min.

9464
M.-C. Chen et al. / Tetrahedron 65 (2009) 9460–9467
bent shape and more lath-like shape generated by 2a and 2b, re-
spectively, might be attributed to the lack of mesophase. A similar
compound 2c (n¼16) with one methyl group added on the terminal
core moiety did not improve the mesophase, and a higher clearing
temperature at Tcl¼101.0 ꢀC was only observed. The same structural
effect on the formation of mesophases induced by the presence of
a terminal methyl group extended to the core has been previously
observed in other metallomesogens.15 On the other hand, the me-
somorphic properties were better improved upon complexation to
copper ion. All compounds 1a with two alkoxy chains displayed
enantiotropic liquid crystalline behavior, however, other com-
pounds 1b with four alkoxy chains formed crystalline phase. The
clearing temperatures of copper complexes 1a–1c were all higher
than those of their precursor compounds 2a–2c, which were at-
tributed to the larger molecular size or/and core rigidity. They
exhibited nematic or smectic C phases, as expected for rod-like and
linear molecules. These mesophases were identified by polarized
optical microscope. Compound 1a (n¼8) with shorter terminal
alkoxy chains formed N phase, whereas, all other compounds 1a
with longer terminal alkoxy chains (n¼10, 12, 14, 16) formed SmC
phase. A nematic schlieren texture (Fig. 4) with homeotropic do-
mains under polarizing microscopy was observed when cooled
from isotropic liquid. The phases of compounds 1a (n¼10, 12,14,16)
were identified as smectic C phases, and typical textures described
as schlieren domains (Fig. 4) were easily observed under optical
polarized microscope when cooling from isotropic liquid. The
preferred formation of SmC phase over N phase in rod-like meso-
gens appended with longer terminal chains was attributed to the
stronger van der Waals interaction. These textures were not
homeotropic, which were often observed in SmA phases. A rea-
sonable enthalpy (i.e.,
H¼10.7–14.9 kJ/mol on heating cycle) for
D
the transition of SmC/I phase was obtained. On heating they all
showed only one transition from mesophase-to-isotropic, however,
a few extra transitions of crystal-to-crystal were also observed in
this system. The clearing temperatures slightly increased with
carbon length of terminal alkoxy chains, i.e., Tcl¼138.5 ꢀC
(n¼16)>137.7 ꢀC (n¼12)>124.6 ꢀC (n¼8). The temperature range of
mesophase also increased with carbon length, i.e.,
D
T¼30.2 ꢀC
(n¼16)>23.1 ꢀC (n¼12)>13.2 ꢀC (n¼8) on cooling process. Both
compounds 1b and 1c were also not mesogenic as their ligands 2b
and 2c. Trying to improve the formation of mesophase by adding
a methyl group on the core in compound 1c was in fact un-
successful. A tetrahedral methyl group might have increased the
interlayer distances, thus destroying the mesophase.
2.4. XRD diffraction data and EPR study
Variable-temperaturepowder XRD experiments were conducted
to confirm the structure of the mesophases. For compound 1a
(n¼10) measured at 126.0 ꢀC one strong diffraction peak and a rel-
atively weak peak at lower angle was observed, shown in Figure 5.
These two diffractionpeaks corresponded to a layer structure of SmC
phase with a spacing of d001 w42.34 Å and d002 w21.13 Å. The ob-
served d-spacing was slightly longer than that of molecular length
(w40.59 Å) obtained from single crystallographic data. This implied
that the molecules were probably not interdigitated between the
molten alkoxy chains in the mesophase. Also a very road diffuse halo
peak (w4.45 Å) at wide-angle region was observed.
Rpc (n=10) - 126
d001= 42.34 Å
4000
d002= 21.13 Å
3000
2000
1000
0
10
20
30
2 Theta
Figure 5. The XRD diffraction plot for compound 1a (n¼10) measured at 126.0 ꢀC.
Electron paramagnetic resonance spectroscopy has been
a valuable technique for investigating the mesomorphic behavior of
paramagnetic metallomesogenic materials.16 Figure 6 shows the
X-band EPR spectra of copper complex 1a (n¼10) measured at 77 K
and at 298 K. Two spectra were only slightly different in peak
shape, which might be attributed to preferred molecular orienta-
tion or arrangement at two lower temperatures. The spectra consist
of broad lines, not expected as a resolved three-line hyperfine band
(
63.5Cu, I¼1/2) of the characteristic d9-Cu2þ center and the hyper-
fine structure was not observed. The spectra consist of two features,
one shoulder barely observed in the low-field region and the other
in the high-field region. The lack of the hyperfine structures was
probably due to the strong exchange interaction among the para-
magnetic copper centers. The EPR data also indicated that the
spectra were independent of the aliphatic chain length. However,
more useful spectrum measured at mesophase temperature was
not possible due to the instrument’s limitation.
Figure 4. The optical textures. (a) Top plate: nematic phase observed by 1a
(n¼8) at 118 ꢀC and (b) bottom plate: smectic C phase observed by 1a (n¼10) at
120.0 ꢀC.

M.-C. Chen et al. / Tetrahedron 65 (2009) 9460–9467
9465
Intensity
6000
capillary tubes (80 mm long and 0.01 mm thick) from Charles
Supper Co. with an inner diameter of 1.0 mm.
Rpc-10 - 77K
4000
2000
0
4.2. 4-Dodecyloxyacetophenone (n[12)
White solids. 1H NMR (300 MHz, CDCl3):
d 0.86 (t, 3H, –CH3,
J¼6.5 Hz), 1.18–1.63 (m, 18H, –CH2), 1.73–1.82 (m, 2H, –CH2), 3.99 (t,
2H, –OCH2, J¼6.6 Hz), 6.88 (d, 4H, Ar–H, J¼8.7 Hz), 7.89 (d, 4, Ar–H
H, J¼8.7 Hz). 13C NMR (75 MHz, CDCl3):
d 14.09, 22.67, 25.95, 26.29,
29.08, 29.33, 29.56, 29.62, 31.90, 68.25, 114.11, 130.09, 130.55,
163.12, 196.74.
-2000
-4000
-6000
-8000
4.3. 1-(4-Dodecyloxyphenyl)-3-hydroxy-2-
propen-1-one (3a; n[12)
The solution of 4-dodecyloxyacetophenone (3.00 g, 9.85 mmol)
dissolved in 30 mL of THF and NaOMe (0.74 g, 14.78 mmol) was
stirred for 30 min. To the solution was dropwise added ethyl for-
mate (0.95 g, 12.81 mmol). The solution was stirred at room tem-
perature for 24 h to give yellow cloudy solution of sodium salts. The
solids were filtered, and the solution was extracted with H2O/
CH2Cl2 (1/1). The organic layers were then collected and dried over
NaSO4. The solution was concentrated to give yellow solids. The
product isolated as light yellow solids were obtained after re-
crystallization from THF. Yield 72%. 1H NMR (300 MHz, CDCl3):
2500
3000
3500
[G]
4000
4500
Intensity
2000
Rpc-10 - RT
1000
0
d
0.86 (t, 3H, –CH3, J¼6.52 Hz), 1.24–1.82 (m, 20H, –CH2), 3.99 (t, 2H,
–OCH2, J¼6.46 Hz), 6.12 (d, 1H, CH, J¼4.47 Hz), 6.91 (d, 2H, Ar–H,
J¼8.72 Hz), 7.85 (d, 2H, Ar–H, J¼8.80 Hz), 8.10 (d, 1H, –COCH,
J¼3.65 Hz), 9.93 (s, 1H, –COH). 13C NMR (75 MHz, CDCl3):
d 14.05,
-1000
-2000
-3000
22.63, 25.91, 29.03, 29.29, 29.50, 29.52, 29.58, 31.86, 68.25, 97.62,
114.41, 127.37, 129.53, 130.76, 163.16, 176.46, 188.09.
4.4. 1-(4-Octyloxyphenyl)-3-hydroxy-2-propen-
1-one (3a; n[8)
2000
2500
3000
3500
4000
4500
Light yellow solids. 1H NMR (300 MHz, CDCl3):
d 0.85 (t, 3H,
[G]
–CH3, J¼6.00 Hz), 1.24–1.81 (m, 12H, –CH2), 3.98 (t, 2H, –OCH2,
J¼6.60 Hz), 6.12 (d, 1H, –COHCH, J¼4.40 Hz), 6.90 (d, 2H, Ar–H,
J¼7.04 Hz), 7.84 (d, 2H, Ar–H, J¼7.04 Hz), 8.10 (d, 1H, –(CO)CH,
Figure 6. The EPR spectra of copper complex 1a (n¼10) measured at 77 K (top) and at
298 K (bottom).
J¼4.44 Hz), 9.93 (s, 1H, –COH). 13C NMR (75 MHz, CDCl3):
d 14.04,
3. Conclusions
22.60, 25.93, 29.04, 29.16, 29.26, 31.75, 68.18, 68.27, 68.35, 97.65,
114.34, 114.43, 129.56, 163.18, 176.50, 188.11.
A new series of rod-like metallomesogens exhibiting nematic
or smectic phases was prepared and studied. X-ray single crys-
tallographic results indicated that the geometry at copper center
was perfectly square planar. These copper complexes 1a exhibited
N or SmC phase. A methyl group added close to rigid core in-
creased the interlayer distances, hence losing liquid crystallinity.
4.5. 1-(4-Decyloxyphenyl)-3-hydroxy-2-propen-
1-one (3a; n[10)
Light yellow solids. 1H NMR (300 MHz, CDCl3):
d 0.85 (t, 3H,
–CH3, J¼6.00 Hz), 1.25–1.83 (m, 16H, –CH2), 3.99 (t, 2H, –OCH2,
J¼6.54 Hz), 6.13 (d, 1H, CH, J¼4.47 Hz), 6.91 (d, 2H, Ar–H,
J¼8.98 Hz), 7.85 (d, 2H, Ar–H, J¼8.95 Hz), 8.11 (d, 1H, –COCH,
4. Experimental
4.1. General
J¼4.47 Hz), 9.93 (s, 1H, –COH). 13C NMR (75 MHz, CDCl3):
d 14.07,
22.64, 25.94, 29.06, 29.28, 29.31, 29.51, 31.86, 68.29, 97.66, 114.00,
114.44, 127.41, 129.56, 130.80, 163.19, 176.50, 188.13.
All chemicals and solvents were reagent grade from Aldrich
Chemical Co., and all solvents were dried by standard techniques.
1H and 13C NMR spectra were measured on a Bruker DRS-200. DSC
thermographs were carried out on a Mettler DSC 822 and calibrated
with a pure indium sample. All phase transitions are determined by
a scan rate of 10.0 ꢀ/min. Optical polarized microscopy was carried
out on Zeiss Axioplan 2 equipped with a hot stage system of Mettler
FP90/FP82HT. Elemental analyses were performed on a Heraeus
CHN-O-Rapid elemental analyzer. The powder diffraction data were
collected from the Wiggler-A beam line of the National Synchrotron
Radiation Research Center (NSRRC) with the wavelength of
1.3263 Å. The powder samples were charged in Lindemann
4.6. 1-(4-Tetradecyloxyphenyl)-3-hydroxy-2-
propen-1-one (3a; n[14)
Light yellow solids. 1H NMR (300 MHz, CDCl3):
d 0.86 (t, 3H,
–CH3, J¼6.58 Hz), 1.24–1.83 (m, 24H, –CH2), 3.99 (t, 2H, –OCH2,
J¼6.60 Hz), 6.13 (d, 1H, CH, J¼4.50 Hz), 6.91 (d, 2H, Ar–H,
J¼8.80 Hz), 7.85 (d, 2H, Ar–H, J¼9.10 Hz), 8.11 (d, 1H, –COCH,
J¼4.44 Hz), 9.93 (s, 1H, –COH). 13C NMR (75 MHz, CDCl3):
d 14.06,
22.66, 25.94, 29.06, 29.32, 29.53, 29.55, 29.63, 31.89, 68.28, 97.66,
114.44, 127.41, 129.56, 130.79, 163.19, 176.49, 188.13.

9466
M.-C. Chen et al. / Tetrahedron 65 (2009) 9460–9467
4.7. 1-(4-Hexadecyloxyphenyl)-3-hydroxy-2-
propen-1-one (3a; n[16)
4.13. 3-[4-Hexadecyloxyphenyl]-1H-pyrazole (2a; n[16)
White solid. 1H NMR (300 MHz, CDCl3):
d
0.86 (t, 3H, –CH3,
Light yellow solids. 1H NMR (300 MHz, CDCl3):
d
0.86 (t, 3H,
J¼6.69 Hz), 1.24–1.83 (m, 28H, –CH2), 3.97 (t, 2H, –OCH2,
J¼6.65 Hz), 6.54 (s, 1H, –CH]C), 6.93 (d, 2H, Ar–H, J¼8.74 Hz), 7.62
(s, 1H, –C]CH), 7.67 (d, 2H, Ar–H, J¼8.47 Hz). 13C NMR (75 MHz,
–CH3, J¼6.65 Hz), 1.24–1.83 (m, 28H, –CH2), 3.99 (t, 2H, –OCH2,
J¼6.60 Hz), 6.13 (d, 1H, CH, J¼4.40 Hz), 6.91 (d, 2H, Ar–H,
J¼8.80 Hz), 7.85 (d, 2H, Ar–H, J¼8.80 Hz), 8.11 (d, 1H, –COCH,
CDCl3): d 14.08, 22.66, 26.03, 29.25, 29.33, 29.29, 29.58, 29.67, 31.90,
J¼4.40 Hz), 9.93 (s, 1H, –COH). 13C NMR (75 MHz, CDCl3):
d
14.09,
68.11, 102.14, 114.82, 123.85, 127.15, 133.85, 148.36, 159.36.
22.67, 25.95, 29.07, 29.34, 29.54, 29.56, 29.67, 31.91, 68.30, 97.67,
114.45, 127.42, 129.58, 130.81, 162.92, 163.20, 176.51, 188.14.
4.14. 3-[3,4-Dihexadecyloxyphenyl]-1H-pyrazole (2b; n[16)
White solid. 1H NMR (300 MHz, CDCl3):
d 0.86 (t, 3H, –CH3,
4.8. 4-Hexadecoxyphenyl butane-1,3-dione (3c; n[16)
J¼6.71 Hz),1.17–1.85 (m, 56H, –CH2), 4.01 (t, 2H, –OCH2, J¼6.63 Hz),
6.50 (d, 1H, –CH]C–N, J¼2.04 Hz), 6.87 (d, 1H, Ar–H, J¼8.31 Hz),
7.20 (d, 1H, Ar–H, J¼1.98 Hz), 7.29 (d, 1H, Ar–H, J¼1.98 Hz), 7.56 (d,
Light yellow solid, yield 70%. 1H NMR (CDCl3):
d 0.84 (t, –CH3,
3H), 1.22–1.80 (m, –CH2, 28H), 2.13 (s, –COCH3, 3H), 3.97 (t, –OCH2,
2H), 6.10 (s, –CCHCO, 1H), 6.92 (d, –C6H4, 2H), 7.81 (d, –C6H4, 2H),
1H, ]CHN, J¼2.01 Hz). 13C NMR (75 MHz, CDCl3):
d 14.08, 22.67,
26.04, 29.35, 29.44, 29.65, 29.70, 31.91, 69.37, 102.21, 111.57, 113.97,
118.53, 124.96, 133.26, 148.94, 149.36, 149.43.
16.30 (s, –OH, 1H). 13C NMR (CDCl3):
d 14.07, 22.65, 25.24, 25.98,
29.37, 29.59, 29.69, 31.90, 68.05, 95.71, 114.58, 129.00, 130.18,
162.30, 183.97, 191.62.
4.15. 3-(4-(Hexadecyloxy)phenyl)-5-methyl-1H-pyrazole
(2c; n[16)
4.9. 3-[4-Dodecyloxyphenyl]-1H-pyrazole (2a; n[12)
White solid, yield 83%. 1H NMR (300 MHz, CDCl3):
d 0.84 (t,
–CH3, 3H), 1.19–1.79 (m, CH2, 28H), 2.37 (s, –CNCH3, 3H), 3.96 (t,
–OCH2, 2H), 6.33 (s, –CNCH, 1H), 6.86 (d, –C6H4, 2H), 7.66 (d, –C6H4,
d 12.04, 14.15, 22.72, 26.05, 29.29, 29.46,
29.63, 31.82, 68.10, 102.89, 114.96, 125.08, 126.98, 142.96, 149.68,
159.62.
To he solution of 1-(4-dodecyloxyphenyl)-3-hydroxy-2-propen-
1-one (3.00 g, 9.02 mmol) dissolved in 25 mL of THF/EtOH (1/1)
was added 1.0 mL of dilute hydrochloric acid (3.0 M), and the so-
lution was stirred for 5 min. To the solution was added hydrazine
monohydrate (0.91 g) and the solution was refluxed for 12 h.
The solids were filtered, and the products isolated as white solids
were obtained after recrystallization from THF/EtOH. Yield 70–75%.
2H). 13C NMR (CDCl3):
4.16. Copper complexes 3-[4-alkoxyphenyl]-1H-
pyrazoles (1a; n[8, 10, 12, 14, 16)
White solid. 1H NMR (300 MHz, CDCl3):
d 0.86 (t, 3H, –CH3,
J¼6.72 Hz), 1.26–1.83 (m, 20H, –CH2), 3.98 (t, 2H, –OCH2,
J¼6.53 Hz), 6.55 (s, 1H, –CH]C), 6.96 (d, 2H, Ar–H, J¼6.66 Hz), 7.63
(s, 1H, –C]CH), 7.68 (d, 2H, –C6H4, J¼8.77 Hz). 13C NMR (75 MHz,
The mixture of 3-[4-(dodecyloxy)phenyl]-1H-pyrazole (0.3 g,
0.304 mmol) and copper(II) chloride dehydrate (0.052 g,
0.304 mmol) was refluxed in ethanol for 3 h. The solids were filtered.
The products isolated as bright yellow-greenish solids were obtained
after recrystallization from THF/ethyl acetate. Yield 87–90%. Anal.
Calcd. for 1a (n ¼ 8) C34H48O2N4CuCl2: C, 60.12; H, 7.12. Found:
C, 60.06; H, 7.11. 1a (n ¼ 10) C38H56O2N4CuCl2: C, 62.07; H, 7.68.
Found: C, 62.19; H, 7.76. 1a (n ¼ 12) C42H64O2N4CuCl2: C, 63.74;
H, 8.15. Found: C, 63.80 H, 8.33. 1a (n ¼ 14): C46H72O2N4CuCl2:
CDCl3): d 14.09, 22.66, 26.03, 29.25, 29.33, 29.39, 29.58, 31.90, 68.12,
102.15, 114.86, 123.61, 127.21, 133.72, 148.23, 159.47.
4.10. 3-[4-Octyloxyphenyl]-1H-pyrazole (2a; n[8)
White solid. 1H NMR (300 MHz, CDCl3):
d 0.89 (t, 3H, –CH3,
J¼6.78 Hz),1.28–1.82 (m,12H, –CH2), 3.96 (t, 2H, –OCH2, J¼6.57 Hz),
6.51 (d, 1H, –CH]C, J¼2.19 Hz), 6.91 (d, 2H, Ar–H, J¼8.77 Hz), 7.58
(d, 1H, –C]CH, J¼2.22 Hz), 7.64 (d, 2H, Ar–H, J¼8.80 Hz). 13C NMR
C, 65.19; H, 8.56. Found: C, 64.87; H, 8.44. 1a (n ¼ 16) C50H80O2N4
-
CuCl2: C, 66.46; H, 8.92. Found: C, 66.41; H, 8.91.
(75 MHz, CDCl3):
d 14.06, 22.63, 26.02, 29.22, 29.35, 68.01, 102.07,
Acknowledgements
114.81, 123.86, 127.15, 133.74, 148.28, 159.34.
We thank the National Science Council of Taiwan (NSC 97-2738-
M-008-001 and NSC 98-2752-M-008-001-PAE) and also Display
Technology Center and Active Device Technology Dept., EOL/In-
dustrial Technology Research Institute of Taiwan, ROC (ITRI 98-B-08-
8351AA5140) in generous support of this work.
4.11. 3-[4-Decyloxyphenyl]-1H-pyrazole (2a; n[10)
White solid. 1H NMR (300 MHz, CDCl3):
d 0.87 (t, 3H, –CH3,
J¼6.66 Hz), 1.26–1.82 (m, 16H, –CH2), 3.96 (t, 2H, –OCH2,
J¼6.56 Hz), 6.50 (s, 1H, –CH]C), 6.91 (d, 2H, Ar–H, J¼8.74 Hz), 7.57
(s, 1H, –C]CH), 7.64 (d, 2H, Ar–H, J¼8.71 Hz). 13C NMR (75 MHz,
References and notes
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