Novel metallomesogens derived from heterocyclic benzoxazoles

Article abstract of DOI:10.1016/j.tet.2008.03.101

The synthesis, mesomorphic behavior, and optical properties of a new series of transition metal complexes 1a and 1b derived from benzoxazoles 2 are reported. The crystal and molecular structure of copper complex of 6-dodecyloxynaphthalene-2-carboxylic acid 4-(6-hexyloxybenzooxazol-2-yl)-3-hydroxyphenyl ester 1a (n=6; m=12) was determined by means of X-ray structural analysis, and it crystallizes in the triclinic space group P-1. The geometry at copper center is perfectly square-planar, and the overall molecular shape is considered as rod-shape. All precursors 2 with shorter chains (n=0, 1, 4) exhibited nematic, and all others with longer chains (n=6, 7, 8, 10, 12) formed N/SmC phases. In contrast, all copper(II) complexes 1a and palladium complexes 1b formed N phase. On the other hand, the temperature range of mesophase in compound 1a was wider than those in compound 1b. The difference of the mesomorphic properties in compounds 1a and 1b was attributed to the geometry or/and the size of the metal center. The fluorescent properties of these compounds were also examined.

Full text of DOI:10.1016/j.tet.2008.03.101

Tetrahedron 64 (2008) 4939–4948
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Tetrahedron
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Novel metallomesogens derived from heterocyclic benzoxazoles
,
Hsiang-Cheng Wang a, Yueh-Ju Wang a, Hui-Mei Hu a, Gene-Hsiang Lee b, Chung K. Lai a
*
a Department of Chemistry, National Central University and Center for Nano Science Technology, UST, Chung-Li 32054, Taiwan, ROC
b Instrumentation Center, National Taiwan University, Taipei 10660, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis, mesomorphic behavior, and optical properties of a new series of transition metal com-
plexes 1a and 1b derived from benzoxazoles 2 are reported. The crystal and molecular structure of
copper complex of 6-dodecyloxynaphthalene-2-carboxylic acid 4-(6-hexyloxybenzooxazol-2-yl)-3-
hydroxyphenyl ester 1a (n¼6; m¼12) was determined by means of X-ray structural analysis, and it
crystallizes in the triclinic space group P-1. The geometry at copper center is perfectly square-planar, and
the overall molecular shape is considered as rod-shape. All precursors 2 with shorter chains (n¼0, 1, 4)
exhibited nematic, and all others with longer chains (n¼6, 7, 8, 10, 12) formed N/SmC phases. In contrast,
all copper(II) complexes 1a and palladium complexes 1b formed N phase. On the other hand, the tem-
perature range of mesophase in compound 1a was wider than those in compound 1b. The difference of
the mesomorphic properties in compounds 1a and 1b was attributed to the geometry or/and the size of
the metal center. The fluorescent properties of these compounds were also examined.
Received 7 January 2008
Received in revised form 25 March 2008
Accepted 28 March 2008
Available online 3 April 2008
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
past decade. Numerous transition metal complexes with a variety
of geometric structures were thus generated, and their mesomor-
The incorporation of heterocyclic rings1 used as core center to
generate mesogenic materials has been widely investigated during
the past decades. Numerous novel compounds exhibiting unique
mesophases were prepared and studied. Among them five- or six-
membered rings have been studied mostly due to their varieties in
structures and/or known chemistry. Better mesomorphic behavior
formed by such structures was often accomplished, which was
attributed to their electronic unsaturation and/or more polarizable
ability.2 On the other hand, many heterocyclic molecules3–7 with
a lower symmetry and/or non-planar structure caused by nitrogen,
oxygen, sulfur or other heteroatoms incorporated would be easily
obtained, leading to practical materials with a lower clearing or/
and melting temperature useful in device applications. Benzox-
azole derivatives, considered as an important class of heterocyclic
compounds, have been studied in a variety of materials research
during the past years. Most of the studies were focused on, such as
non-linear optics,8 organic light-emitting diodes,9 and polymeric
materials. However, mesogenic examples derived from benzox-
azoles10 or benzothiazoles11 were relatively rare. Common phases,
for example, nematic, smectic A or/and smectic C phases were often
observed, as expected for rod-like molecules.
phic properties investigated as well. Many atoms incorporated
within a heterocyclic structure, such as nitrogen, oxygen, sulfur or
others might provide electron lone pairs for potential coordination
site to the transition metals. Depending on the structure of the
heterocyclic derivatives, a variety of metal ions, particularly metals
with a 3d-orbital were structurally possible in generating this type
of metallomesogenic materials. Metal complexes12–14 with cop-
per(II) and palladium(II) incorporated were all known the most.
Cu2þ ion is d9-electronic and paramagnetic, whereas, Pd2þ ion is d8
and diamagnetic configuration. A variety of coordination com-
pounds with tetrahedral (Td), twisted tetrahedral or square-planar
geometry (SP) have been reported and investigated. The difference
in electronic configuration or/and coordinative geometry inherent
from metal ions often reflected to the formation of the observed
mesophases in this type of metallomesogenic materials. A similar
compound 5, benzothiazole was reported,15 and all free ligands,
copper and oxovanadium complexes15 were found non-mesogenic.
A loss of linearity, strong intermolecular dipolar repulsion caused
by the presence of lateral hydroxyl group was attributed for the lack
of mesomorphic behavior. A palladium complex 1c with a similar
structure has been previously prepared11 in this group, however, it
was in fact non-mesogenic. A transition of crystal-to-isotropic
(Cr/I) at 194.6 ꢀC was observed. In this work, as part of our con-
tinuing research in metallomesogens11,16–19 we report the prepa-
ration, mesomorphic, and optical studies of a new series of
copper(II) and palladium(II) complexes 1a and 1b derived from
benzoxazole. All copper and palladium complexes exhibit nematic
On the other hand, metal-containing liquid crystals, or so-called
metallomesogens,12–14 have been paid much attention during the
* Corresponding author. Tel.: þ886 03 4259207; fax: þ886 03 4277972.
E-mail address: cklai@cc.ncu.edu.tw (C.K. Lai).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.03.101

4940
H.-C. Wang et al. / Tetrahedron 64 (2008) 4939–4948
or/and smectic C phases. To our knowledge, this is the first metallo-
mesogens derived from heterocyclic benzoxazoles.
shows the two molecular structures with the atomic numbering
schemes. Table 1 lists their crystallographic and structural re-
finement data for the two molecules. The overall molecular shape
of crystal 2 (n¼0, m¼4) was considered as a slightly bent structure.
The benzoxazole and central phenolic rings were nearly coplanar
(dihedral angle<1ꢀ), however, they were not coplanar with the
naphthalene ring. A dihedral angle of 75.64ꢀ was measured. Un-
surprisingly, an intramolecular H-bond between phenolic O(2)–H2A
and N1 atom was observed, and the distance was measured by ca.
1.811 Å. The H-bonding kept the two rings (i.e., benzoxazole and
phenolic rings) nearly coplanar, and the coplanar structure was
attributed to a preferred better packing both in the solid or/and the
liquid crystal state. In the unit cell, all molecules were arranged by
antiparallel and head-to-tail arrangements when viewed down
b axis. The phenolic –OH groups between the neighboring mole-
cules were outwardly pointed each other, therefore, intermolecular
H-bonding was not possibly formed. The distances measured for all
other possible H-bonds were all longer than 3.0 Å. On the other
hand, all perpendicular distances between the molecules were
OCmH2m+1
O
H2n+1CnO
O
O
N
M O
O
O
O
N
OCnH2n+1
O
H2m+1CmO
m = 8, 12;
n = 0, 1, 4, 6, 7, 8, 10, 12
1a; M = Cu
1b; M = Pd
O
O
OC12H25
C12H25
O
O
N
Cl Pd Cl
N
O
O
measured larger than 4.80 Å, therefore, a
existent.
p–p interaction was not
O
OC12H25
C12H25
O
1c
The single crystal structure of copper complex 1a (n¼6, m¼12)
was also resolved. An overall rod-shaped molecule with a length L
(w41.2 Å) and width d (w3.5 Å) was in fact obtained. The geometry
at copper center was a perfect square-planar. The two angles of
N(1)–Cu–O(1) and N(1)–Cu–O(1A) were of 90.51(8)ꢀ and 89.49(8)ꢀ,
which showed almost an ideal angle of 90ꢀ expected for a square-
planar geometry. Two benzoxazole and two phenol rings were
coplanar, however, they were not coplanar with two naphthalene
rings. The dihedral angle of naphthalene (C2–C7) and benzoxazole
rings was measured as 13.315ꢀ, however, the dihedral angle of
naphthalene (C9–C18) and benzene ring (C2–C7) was measured as
73.489ꢀ. The closest perpendicular distance between the two
naphthalene rings in neighboring molecules is measured ca.
3.682 Å (Fig. 2). Some selected bond distances and angles for
compound 1a are also summarized in Table 2.
194.6 (30.8)
174.7 (16.2)
Cr
I
S
N
C10H21
O
O
M O
N
OC10H21
S
5; M = Cu, VO
2. Results and discussion
2.1. Synthesis and characterization
2.3. Mesomorphic properties of benzoxazoles 2
The synthetic routes10a used in this work for benzoxazole de-
rivatives2andtheircopperandpalladiumcomplexes1aand1bwere
summarized in Scheme 1. The reactions of 2-amino-5-alkylphenols
and 6-alkoxylnaphthalene-2-carboxylic acid 4-formyl-3-hydroxy-
phenyl esters 4 in refluxing absolute ethanol gave 6-alkoxynaph-
thalene-2-carboxylic acid 4-[(4-alkyl-2-hydroxylphenylimino)-
methyl]-3-hydroxyphenyl esters 3. The final compounds 2;
6-alkoxynaphthalene-2-carboxylic acid 4-(6-alkylbenzooxazol-2-
yl)-3-hydroxyphenyl esters was then obtained by intracyclic re-
action of 3 in CHCl3 using lead acetate Pb(OAc)4. The copper(II) and
palladium(II) complexes were prepared by the reaction of appro-
priate benzoxazoles 2 and copper(II) acetate or palladium(II) acetate
in refluxing ethanol. 1H and 13C NMR spectroscopy were used to
characterize all intermediates, and the elemental analysis was used
to confirm the purity of the metal complexes.
The liquid crystalline behavior of benzoxazole derivatives 2 and
their copper and palladium complexes 1a and 1b was investigated
and studied by differential scanning calorimeter (DSC) and polar-
izing optical microscope. In order to understand the relationship
between the structure and the mesomorphic properties in the type
of rod-like benzoxazole derivatives, a variety of compounds 2 with
carbon chain’s length systematically changed on naphthyl ring
(n¼0–12) while another side chain of the benzoxazole ring fixed at
m¼8 or 12 was investigated.
The phase transitions and thermodynamic data of compounds 2
were summarized in Table 3. All compounds 2 formed liquid
crystalline phases regardless of the carbon length on the alkoxy
side chains, and the formation of mesophases was dependent on
the carbon length of terminal chains. Totally five derivatives 2 with
a shorter carbon chain (m¼8, n¼0, 1; m¼12; n¼0, 1, 4) exhibited
only nematic (N) phase, however, all other derivatives with a longer
carbon length (m¼12, n¼6, 7, 8, 10, 12) formed N phase at higher
temperature and smectic C (SmC) phases at lower temperature. The
mesophase was characterized by optical textures, as shown in
Figure 3. This type of mesophase dependence on the carbon length
is quite common in rod-like mesogens. Interestingly, compounds 2
with no polar substituent (n¼0) or a methoxy group (n¼1) on
naphthyl ring were truly mesogenic, which indicated that the ter-
minal 40-alkoxyl chain (m¼8, 12) on the benzoxazole ring was
crucially required for the formation of mesophases. These two
compounds have a relatively short temperature range of meso-
2.2. Single crystal structures of 6-naphthalene-2-carboxylic
acid 4-(6-butyloxy benzooxazol-2-yl)-3-hydroxyphenyl
ester (2; n[0, m[4) and copper complex of
6-hexyloxynaphthalene-2-carboxylic acid
4-(6-dodecyloxybenzooxazol-2-yl)-3-hydroxyphenyl
ester (1a; n[6, m[12)
Two single crystals of the non-mesogenic benzoxazole 2 (n¼0;
m¼4) and mesogenic copper complex 1a (n¼6, m¼12) suitable for
crystallographic analysis were obtained by slow vaporization from
CH3Cl at room temperature and their structures resolved. Figure 1
phase,
D
T¼6.40 ꢀC (n¼0; m¼8)–15.5 ꢀC (n¼0, m¼12). The

H.-C. Wang et al. / Tetrahedron 64 (2008) 4939–4948
4941
HO
HO
HO
b
H2n+1CnO
OH
O
OH
OCmH2m+1
c
a
HO
d
H2n+1CnO
O
O
O2N
OCmH2m+1
H2N
OCmH2m+1
O
OH
4
e
HO
H2n+1CnO
O
O
N
OCmH2m+1
OH
OH
3
f
OCmH2m+1
O
N
H2n+1CnO
O
O
2
g
OCmH2m+1
O
N
H2n+1CnO
O
O
O
M O
N
O
O
OCnH2n+1
O
H2m+1CmO
1a; M = Cu
1b: M = Pd
Scheme 1. Reactions and conditions: (a) 2,4-dihydroxybenzaldehyde (1.0 equiv), DCC (1.2 equiv), DMAP (1.2 equiv) in dried CH2Cl2, 24 h, 62%; (b) n-alkylbromides (1.1 equiv),
KHCO3 (1.3 equiv), KI, refluxed in CH3COCH3, 24 h, 35%; (c) NaNO2 (0.1 equiv), HNO3 (1.2 equiv), in CH2Cl2, 6 h, 42%; (d) H2NNH2 (1.2 equiv), Pd/C (10%, 0.1 equiv), refluxed in
C2H5OH, 4 h, 86%; (e) 2-amino-5-alkylphenols (1.0 equiv), CH3COOH (drops) in absolute C2H5OH, 24 h, 88%; (f) Pb(OAc)4 (1.2 equiv), refluxed in CHCl3, 2 h, 70%; (g) Cu(OAc)2 or
Pd(OAc)2 (1.0 equiv), refluxed in absolute C2H5OH, 24 h, 73–87%.
benzoxazole was relatively considered as a large core, and generally
more or longer terminal chains were required to induce the
mesophases. The induction of the observed mesophases might be
attributed to the better molecular arrangement and the enhanced
van der Waals interaction. On the other hand, the single bond of the
ester group (–OC]O) on the naphthyl ring might also play an
important role in forming the mesophase. The higher flexibility or
conformation caused by free rotation of the –OC bond covering
a large volume might be considered as a terminal chain at meso-
genic temperature. This result was also supported by crystallo-
graphic data discussed later. The crystallographic data indicated
that all molecules were in fact antiparallel arranged (head-to-tail
arrangement) between the neighboring layers, therefore, com-
pounds with no or only methoxy substituent would not drastically
alter the overall molecular length.
narrowest range (
D
T¼6.40 ꢀC) of the nematic mesophase. The
clearing temperatures were drastically increased by ca. 85.0 ꢀC
(Tcl¼122.4 ꢀC/207.4 ꢀC; m¼8) and 75.6 ꢀC (Tcl¼107.7 ꢀC/
183.3 ꢀC; m¼12) when one more methoxy group was substituted.
This increase in both clearing temperature and temperature range
was probably attributed to the enhanced dipole–dipole interaction.
The clearing temperature of all other m¼12 derivatives was slightly
decreased with carbon length, i.e., Tcl¼183.3 ꢀC (n¼1)>173.7 ꢀC
(n¼7), 164.6 ꢀC (n¼12), and this trend indicated that the dispersive
force induced by alkoxy chains played an important role on the
formation of the mesophases. The enthalpies for the phase transi-
tion of the nematic-to-isotropic were ranged from
DH¼0.30 kJ/mol
(n¼0, m¼8)–1.35 kJ/mol (n¼12, m¼12) on the heating process.
When compounds are substituted with a longer chain (n¼6, 7, 8, 10,
12), a second phase, SmC, appeared on the DSC analysis. However,
the SmC phase was monotropic and observed for two derivatives
with shorter chains (n¼6, 7; m¼12). However, the SmC phase was
enantiotropic and observed at higher temperature for the higher
homologues (n¼8, 10, 12). The temperature range of the SmC phase
The mesophase was better improved when a longer chain was
attached. The two derivatives (n¼1; m¼8, 12) with a methoxy
group attached have a temperature range, much wider than those
of two derivatives without a polar group, i.e.,
D
T¼106.6 ꢀC (n¼
1, m¼8)–78.7 ꢀC (n¼1, m¼12)>
D
T¼6.40 ꢀC (n¼0; m¼8)–15.5 ꢀC
was increased with the carbon length, i.e.,
D
T¼10.9 ꢀC
(n¼0, m¼12) on heating process. On the other hand, the derivative
(n¼1, m¼8) in this series has the highest isotropic temperature
(Tcl¼207.4 ꢀC), whereas the derivative (n¼0, m¼8) has the
(n¼6)>38.2 ꢀC (n¼8)>66.0 ꢀC (n¼12) on cooling process, however,
the temperature range of the N phase was decreased with carbon
lengths, i.e., 103.8 ꢀC (n¼1)>101.9 ꢀC (n¼6)>67.1 ꢀC (n¼8)>25.0 ꢀC

4942
H.-C. Wang et al. / Tetrahedron 64 (2008) 4939–4948
Figure 1. Two ORTEP drawings for compound 2 (n¼0; m¼4) and 1a (n¼6; m¼12) with the numbering scheme, and the thermal ellipsoids of the non-hydrogen atoms are drawn at
the 50% probability level.
Table 1
Table 2
Crystallographic and experimental data for compounds 2 and 1a
Selected bond distances (Å) and angles (ꢀ) for 1a
Compound
2 (n¼4, m¼0)
28H23NO5
453.47
150(1)
Monoclinic
P2(1)/c
7.1202(5)
16.8522(11)
18.1847(12)
90.0
97.433(2)
90.0
2163.7(3)
4
1a (n¼6, m¼12)
C84H100CuN2O12
1393.20
150(1)
Triclinic
P-1
4.8037(2)
14.7194(6)
25.4589(10)
91.431(1)
91.461(1)
95.785(1)
1789.70(13)
1
Cu–O(1)
Cu–O(1A)
Cu–N(1A)
Cu–N(1)
O(1)–Cu-O(1A)
O(1)–Cu–N(1A)
O(1A)–Cu–N(1A)
O(1)–Cu–N(1)
O(1A)–Cu–N(1)
N(1A)–Cu–N(1)
1.8758(17)
1.8758(17)
2.018(2)
Empirical formula
Formula weight
T/K
Crystal system
Space group
a/Å
C
2.018(2)
180.00(17)
89.49(8)
90.51(8)
90.51(8)
89.49(8)
180.00(12)
b/Å
c/Å
ꢀ
ꢀ
a
/
b/
ꢀ
g
/
(n¼12) on the cooling process. On the other hand, the overall
U/Å3
temperature range of mesophases were not quite correlated well
Z
with carbon chain length, which were all ranged from
D
T¼90.8 ꢀC
F(000)
952
1.392
743
1.293
Dc/Mg/m3
(n¼4)–112.8 ꢀC (n¼6). Elongation of overall molecule by increasing
the carbon length on the other side of terminal chains led to the
formation of more ordered phases, SmC. This is generally attributed
to an enhanced dipole–dipole interaction between the terminal
chains. The N phase and SmC phase were identified by polarized
optical microscope, and under the optical microscope typical
Schlieren textures (Fig. 3) for the N and SmC phase was observed
upon cooling from the isotropic state. Powder X-ray diffraction
experiment for compound 2 (n¼12, m¼12) was performed to
confirm the SmC phase. A diffraction plot at 95.0 ꢀC with three
peaks at 31.98 Å, 16.17 Å, and 11.37 Å were observed, which were
indexed as 001, 002, and 003 showing a layered structure of SmC
phase. The layer spacing of 31.98 Å was much smaller than 48.18 Å,
which was the overall molecular length obtained by MM2 molec-
ular calculation, indicating that the molecules were either tilted or
interdigitated in the mesophases.
Crystal size/mm3
Range for data collection/Å
Reflection collected
Data, restraints, parameters
Independent reflection
Final R1, wR2
0.60ꢁ0.33ꢁ0.25
1.65–27.5
21,438
4973/0/311
4973[Rint¼0.0308]
0.0475, 0.1146
0.50ꢁ0.10ꢁ0.03
0.80–27.5
23,880
8210/0/496
8210[Rint¼0.0503]
0.0680, 0.1608
2.4. Mesomorphic properties of compounds 1a and 1b
The phase transitions and thermodynamic data of metal com-
Figure 2. A
p–p
interaction of 3.682 Å is observed in crystal 1a (n¼6, m¼12).
plexes 1a and 1b were summarized in Table 4. The melting

H.-C. Wang et al. / Tetrahedron 64 (2008) 4939–4948
4943
Table 3
The phase transitions and the enthalpiesa of compounds 2
n
m
Compound 2
116.0 (35.3)
122.4 (0.30)
0
1
8
8
Cr
N
I
I
69.9 (33.4)
100.8 (20.1)
52.3 (8.30)
92.2 (37.8)
69.9 (33.4)
104.6 (31.6)
77.9 (23.1)
119.7 (51.7)
89.1 (49.6)
120.4 (0.29)
207.4 (0.64)
205.6 (0.58)
107.7 (0.55)
N
Cr
Cr
0
1
4
12
12
12
N
N
N
I
I
I
105.7 (0.53)
183.3 (0.57)
Cr
Cr
181.7 (0.52)
182.9 (0.48)
179.9 (0.46)
96.9 (40.9)
178.8 (0.89)
176.5 (0.86)
173.7 (1.15)
171.8 (1.06)
170.3 (0.95)
6
7
8
12
12
12
N
I
Cr
Cr
SmC
63.7 (31.6)
74.6 (0.35)
97.9 (39.7)
88.6 (0.52)
103.8 (0.47)
100.4 (0.55)
127.2 (1.10)
125.2 (0.90)
139.8 (1.69)
N
I
SmC
SmC
66.3 (36.3)
92.2 (15.1)
62.2 (25.1)
86.4 (26.4)
64.7 (26.3)
91.9 (33.7)
N
N
I
I
Cr
Cr
167.5 (0.94)
167.7 (1.00)
10 12
SmC
SmC
166.2 (0.94)
164.6 (1.35)
163.0 (1.33)
12 12
N
I
Cr
72.0 (31.1)
138.0 (1.63)
a
n represents the carbon numbers in the alkoxy chain. Cr¼crystal; SmC¼smectic
C; N¼nematic; I¼isotropic phases. The transition temperatures (ꢀC) and enthalpies
(in parenthesis, kJ/mol) are determined by DSC.
temperatures and clearing temperatures of copper complexes 1a
and palladium complexes 1b were all higher than their precursor
compounds 2, as expected, which were attributed to the larger
molecular size or/and coral rigidity. All copper complexes 1a except
for one derivative (n¼0, m¼8) exhibited mesomorphic behavior;
the complexes with terminal chains from n¼4–10 exhibited
nematic phase and complex with n¼12 formed smectic C phase at
lower temperature and nematic phase at higher temperature. The
complex with the shortest chain (1a; n¼0, m¼8) was not meso-
genic due to the insufficient chain flexibility. The lack of meso-
morphic properties in this series of copper complexes was better
improved, and their mesophase were induced upon addition of
a methoxy group (n¼1, m¼8) on the naphthyl ring. In contrast, the
complex with n¼1/m¼12 was truly mesogenic, which has a tem-
Figure 3. Optical textures observed by compound 2 (n¼10, m¼12); N phase at 160 ꢀ
C
(top plate) and SmC phase at 120 ꢀC (bottom plate).
complex should have a similar square-planar structure with copper
complexes. Palladium complexes 1b have a higher clearing tem-
perature than copper complex 1a by ca. 19.5 ꢀC (n¼4)>14.7 ꢀC
(n¼6)>46.9 ꢀC (n¼0). An increase in clearing temperature was
probably attributed to a stronger intermolecular attraction caused
by a larger Pd2þ core. The too stronger interaction in the Pd com-
plexes 1b might also be responsible for the lack of liquid crystal-
linity for the longer chain derivatives (n¼6 or higher homologues).
On the other hand, the benzoxazole is often considered as an
electron deficient heterocycle, therefore, the electronic configura-
tion of the central ions, d9-Cu and d8-Pd might be another impor-
tant factor in determining the mesophase.
perature range of
D
T¼66.9 ꢀC. The clearing temperatures of com-
plexes 1a were slightly decreased with the carbon chain length,
249.7 ꢀC (n¼0, m¼12)>241.6 ꢀC (n¼7, m¼12)>220.1 ꢀC (n¼12,
m¼12). The transition enthalpies of nematic-to-isotropic phases
ranged from 0.91 kJ/mol (n¼1, m¼8) to 1.05 kJ/mol (n¼7, m¼12)
were not sensitive to the terminal carbon length. The temperature
range of nematic phase was decreased with carbon length, 67.2 ꢀC
(n¼1)>15.5 ꢀC (n¼8)>9.4 ꢀC (n¼12) on the heating process. For the
complex with n¼12 a SmC phase was also observed at lower
temperature, however, the temperature range of the SmC phase
was only 3.80 ꢀC. The phases were identified and confirmed as
nematic and smectic C phases by polarized microscope, and typical
optical textures, shown in Figure 4, were observed. Palladium
compounds 1b were also prepared and studied in order to un-
derstand the influence of incorporated metal on the mesogenic
behavior upon formation of the complexes.
2.5. Optical properties
Benzoxazole derivatives have been considered as potential
light-emitting materials due to their photophysical and fluorescent
properties.20–22 The luminescent properties observed by such
compounds were often affected by substituent and/or conjugation
length. The UV–vis absorption and the photoluminescence spectra
of the compounds 2 in CH2Cl2 solution are shown in Figure 5. The
absorption and emission spectra were very similar in shape. The
highest absorption peaks of all compounds 2 were found to be in-
sensitive to the carbon length, and they all occurred at ca. 330.5–
331.0 nm. On the other hand, a similar trend was also observed in
the photoluminescence spectra. The emission peaks were much
broader, which occurred at 467.0–470.0 nm for compounds 2.
However, the quantum yields measured in CH2Cl2 estimated with
Palladium complex 1b with a terminal chain n¼1 and n¼4
exhibited nematic phases, and all other complexes 1b with n¼0 and
n¼6 formed crystalline states. A single crystal structure of Pd2þ
complexes was not possible for a comparison for the relative geo-
metric difference with Cu2þ center. However, the palladium

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H.-C. Wang et al. / Tetrahedron 64 (2008) 4939–4948
Table 4
The phase transitions and the enthalpiesa of compounds 1a and 1b
n
m
Compound 1a
218.0 (51.5)
181.1 (49.5)
0
1
0
8
8
Cr
N
I
201.2 (33.9)
173.5 (20.2)
268.1 (0.91)
267.3 (0.93)
170.2 (45.8)
I
Cr
Cr
12
I
N
N
160.8 (0.68)
249.7 (0.84)
148.3 (42.3)
182.5 (38.7)
1
4
12
12
I
I
Cr
Cr
162.9 (25.0)
224.3 (53.1)
245.6 (0.56)
247.0 (0.58)
N
216.0 (53.1)
223.1 (53.5)
215.3 (51.8)
224.4 (66.2)
241.0 (0.64)
245.6 (0.68)
241.7 (0.74)
241.6 (1.05)
6
12
N
N
N
I
I
I
Cr
Cr
Cr
7
8
12
12
213.6 (49.8)
215.5 (30.0)
238.2 (0.94)
231.0 (0.62)
205.7 (24.1)
215.5 (49.1)
229.7 (0.74)
228.1 (0.74)
10 12
N
N
I
Cr
225.3 (0.71)
220.1 (1.02)
210.8 (48.5)
210.7 (43.3)
12 12 Cr
I
SmC
203.4 (36.3)
207.2 (2.26)
218.4 (1.00)
Compound 1b
217.1 (47.0)
0
12
Cr
N
I
I
I
200.0 (44.2)
259.7 (1.31)
248.4 (39.6)
1
4
12
12
Cr
Cr
212.7 (8.81)
260.4 (51.8)
252.5 (1.46)
266.5 (0.29)
N
244.1 (42.8)
255.4 (0.25)
260.3 (55.6)
254.7 (39.3)
6
12
I
Cr
a
n represents the carbon numbers in the alkoxy chain. Cr¼crystal; N¼nematic;
SmC¼smectic C; I¼isotropic phases. The transition temperatures (ꢀC) and enthalpies
(in parenthesis, kJ/mol) are determined by DSC.
anthracene as a standard (4f¼0.27 in hexane) were ranged from
8.5–11.4%.
3. Conclusions
In conclusion, the first series of metallomesogenic materials
derived from benzoxazoles exhibiting mesophases was prepared
and investigated. Their precursor derivatives 2 were truly meso-
genic, and their fluorescent properties were also examined
as potential lighting materials. All copper exhibited nematic and/
or smectic C phase, however, palladium complexes formed ne-
matic phases. The preparation of metal complexes with other
metal ions incorporated is needed in order to understand the ef-
fect or the role of metal ion in this type of metallomesogenic
materials.
Figure 4. Optical textures observed by 1a (n¼12, m¼12); N phase at 215 ꢀC (top plate);
N/SmC transition at 209 ꢀC (central plate), and by 1b (n¼4, m¼12); N phase at 250 ꢀ
C
(bottom plate).
821 and calibrated with a pure indium sample and all phase tran-
sitions are determined by a scan rate of 10.0ꢀ/min. Optical polarized
microscopy was carried out on an Zeiss AxiaPlan equipped with
a hot stage system of Mettler FP90/FP82HT. The UV–vis absorption
and fluorescence spectra were obtained using HITACHI F-4500 or
JASCO V-530 spectrometer. Elemental analysis for carbon, hydro-
gen, and nitrogen were conducted on a Heraeus Vario EL-III ele-
mental analyzer at National Taiwan University. The preparation of
3-alkoxyphenols 5-alkoxy-2-nitrophenols and 2-amino-5-alkoxy-
phenols was followed by literature procedures.
4. Experimental
4.1. General
All chemicals and solvents were reagent grades from Aldrich or
Lancaster Co. Solvents used were dried by standard techniques. 1H
and 13C NMR spectra were measured on a Bruker AM-300 or Bruker
Avance-500. FTIR spectra were performed on Nicolet Magna-IR 550
spectrometer. DSC thermographs were carried out on a Mettler DSC

H.-C. Wang et al. / Tetrahedron 64 (2008) 4939–4948
4945
0.6
0.5
0.4
0.3
0.2
0.1
0.0
6.0. The white solids were collected, and then recrystallized from
CH2Cl2/CH3OH. White solid, yield 88%. 1H NMR (CDCl3):
0.85–0.90
C4
d
C6
(t, J¼6.6 Hz, –CH3, 3H),1.29–1.50 (m, –CH2,12H),1.83–1.85 (m, –CH2,
2H), 4.08–4.11 (t, J¼6.5 Hz, –OCH2, 2H), 7.14 (s, –C10H6,1H), 7.18–7.20
(d, J¼8.9 Hz, –C10H6,1H), 7.23 (s, –C10H6,1H), 7.73–7.75 (d, J¼8.6 Hz,
–C10H6, 1H), 7.83–7.85 (d, J¼8.9 Hz, –C10H6, 1H), 8.04–8.06 (d,
C7
C8
C10
C12
J¼8.8 Hz, –C10H6, 1H), 8.59 (s, –C10H6, 1H). 13C NMR (CDCl3):
d 13.91,
22.55, 26.05, 29.15, 29.28, 29.35, 31.75, 68.30, 106.72, 119.97, 121.29,
124.16, 126.05, 126.85, 127.85, 130.95, 131.80, 137.75, 159.51.
4.5. 6-Dodecyloxynaphthalene-2-carboxylic acid 4-formyl-3-
hydroxyphenyl ester (4, n[12)
The mixture of 6-dodecyloxynaphthalene-2-carboxylic acid
(2.00 g, 0.006 mol), 4-dimethyl-aminopyridine (DMAP; 0.89 g,
0.007 mol), and 2,4-dihydroxybenzoaldehyde (0.84 g, 0.006 mol)
dissolved in 100 ml of dried CH2Cl2 was stirred at ice bath tem-
perature for 30 min under nitrogen atmosphere. To the solution
was then added N,N0-dicyclohexyl carbodiimide (DCC; 1.51 g,
0.007 mol) and the solution was stirred at room temperature for
24 h. The solids were filtered off and the filtrate was concentrated
to dryness. The product was purified by passage to a short column
of silica gel eluting with hexane/CH2Cl2 (1:1). White solid, yield
250
30
0
3
50
400
wavelength (nm)
450
500
700
600
500
400
300
200
100
0
C4
C6
C7
C8
62%. 1H NMR (CDCl3):
d
0.86–0.90 (t, J¼6.7 Hz, –CH3, 3H), 1.27–1.56
C10
C12
(m, –CH2, 18H), 1.83–1.86 (m, –CH2, 2H), 4.08–4.10 (t, J¼6.5 Hz,
–OCH2, 2H), 6.91 (s, –C6H3, 1H), 6.93–6.96 (d, J¼8.4 Hz, –C6H3, 1H),
7.15 (s, –C10H6,1H), 7.20–7.22 (d, J¼8.9 Hz, –C10H6,1H), 7.60–7.62 (d,
J¼8.4 Hz, –C6H3, 1H), 7.77–7.79 (d, J¼8.6 Hz, –C10H6, 1H), 7.85–7.87
(d, J¼8.9 Hz, –C10H6, 1H), 8.08–8.10 (d, J¼8.6 Hz, –C10H6, 1H), 8.65
(s, –C10H6, 1H). 13C NMR (CDCl3):
d 14.11, 22.67, 26.10, 29.15, 29.25,
29.37, 31.83, 68.28, 106.48, 110.94, 114.18, 118.68, 120.33, 123.51,
126.00, 127.16, 127.75, 131.04, 132.06, 134.98, 137.86, 157.93, 159.70,
163.25, 164.48, 195.50.
4.6. 6-Dodecyloxynaphthalene-2-carboxylic acid 4-
[(4-dodecyloxy-2-hydroxyphenylimino) methyl]-3-
hydroxyphenyl ester (3; n[12, m[12)
350
400
450
wavelength (nm)
500
550
600
Figure 5. Normalized UV absorption and PL spectra of compounds 2 in CH2Cl2.
To the solution of 6-dodecyloxynaphthalene-2-carboxylic acid
4-formyl-3-hydroxy-phenyl ester (0.35 g, 0.78 mmol) dissolved in
30 ml of hot absolute ethanol with five drops acetic acid added was
added dropwise hot ethanolic solution of 2-amino-5-dodecyloxy-
phenol (0.23 g, 0.78 mmol) under nitrogen atmosphere. The solu-
tion was gently refluxed for 24 h. The solution was cooled and the
yellow solids were collected by suction. The products isolated as
light yellow solids were obtained after recrystallization from THF/
4.2. 5-Dodecyloxy-2-nitrophenol
Yellow solid, yield 42%. 1H NMR (CDCl3):
d
0.86 (t, J¼6.7 Hz,
–CH3, 3H), 1.24–1.38 (m, –CH2, 18H), 1.74–1.82 (m, –OCH2CH2, 2H),
3.99 (t, J¼6.4 Hz, –OCH2, 2H), 6.45–6.51 (m, –C6H3, 2H), 8.00 (d,
J¼10.02 Hz, –C6H3, 1H), 11.03 (s, –C6H3, 1H). 13C NMR (CDCl3):
d
14.10, 22.66, 28.81, 29.25, 29.26, 29.32, 29.49, 29.54, 29.6, 31.90,
CH3OH. Yield 88%. 1H NMR (CDCl3):
d
0.87–0.89 (t, J¼4.2 Hz, –CH3,
69.12, 101.76, 109.82, 126.89, 127.51, 157.98, 166.72.
6H),1.27–1.51 (m, –CH2, 36H), 1.75–1.86 (m, –CH2, 4H), 3.94–3.97 (t,
J¼6.6 Hz, –OCH2, 2H), 4.10–4.13 (t, J¼6.7 Hz, –OCH2, 2H), 6.50–6.51
(d, J¼8.4 Hz, –C6H3, 1H), 6.95 (s, –C6H3, 1H), 7.10–7.11 (d, J¼8.7 Hz,
–C6H3, 1H), 7.20 (s, –C10H6, 1H), 7.21–7.23 (d, J¼9.1 Hz, –C6H3, 1H),
7.42–7.44 (d, J¼8.4 Hz, –C10H6, 1H), 7.77–7.79 (d, J¼8.6 Hz, –C10H6,
1H), 7.84–7.86 (d, J¼9.0 Hz, –C10H6, 1H), 8.11–8.12 (d, J¼8.3 Hz,
–C10H6, 1H), 8.64 (s, –C10H6, 1H), 8.66 (s, –CHN, 1H). 13C NMR
4.3. 2-Amino-5-dodecyloxyphenol
White solid, yield 86%. 1H NMR (CDCl3):
3H), 1.24–1.38 (m, –CH2, 18H), 1.67–1.71 (m, –CH2, 2H), 3.84 (t,
d
0.86 (t, J¼6.7 Hz, –CH3,
J¼6.5 Hz, –OCH2, 2H), 6.42–6.45 (d, J¼7.6 Hz, –C6H3, 2H), 6.74 (d,
J¼7.6 Hz, –C6H3, 1H), 11.03 (s, –OH, 1H). 13C NMR (CDCl3):
d 14.10,
(CDCl3):
d 13.93, 22.58, 26.00, 26.05, 26.16, 29.16, 29.20, 29.25,
23.12, 28.81, 29.25, 29.26, 29.32, 29.49, 29.61, 31.91, 72.28, 102.17,
107.60, 117.23, 125.64, 144.53, 162.17.
29.33, 29.52, 29.56, 29.58, 29.65, 29.96, 30.02, 31.85, 68.34, 68.43,
101.98, 105.56, 106.72, 107.95, 110.54, 118.37, 118.91, 120.14, 120.40,
123.79, 126.04, 127.02, 127.90, 128.05, 130.97, 131.82, 133.11, 136.81,
151.26, 159.22, 160.22, 161.75, 166.98.
4.4. 6-Dodecyloxynaphthalene-2-carboxylic acids
The mixture of 6-hydroxy-2-naphthoic acid (5.0 g, 0.027 mol)
and KOH pellets (3.0 g, 0.053 mol) dissolved in 100 ml of ethanol/
H2O (10/1) was gently refluxed for 30 min under nitrogen atmo-
sphere. To this solution was then added 1-bromododecane (13.92 g,
0.056 mol), and the solution was refluxed for 24 h. The solution was
neutralized with dilute hydrochloric acid until the pH value reached
4.7. 6-Dodecyloxynaphthalene-2-carboxylic acid 4-
(6-dodecyloxybenzooxazol-2-yl)-3-hydroxyphenyl ester
(2; n[12, m[12)
The white solids of 6-dodecyloxynaphthalene-2-carboxylic acid
4-[(4-dodecyloxy-2-hydroxyphenylimino)methyl]-3-hydroxyphenyl

4946
H.-C. Wang et al. / Tetrahedron 64 (2008) 4939–4948
ester (0.45 g, 0.622 mmol) was dissolved in 150 ml of hot CHCl3, and
the solution was slowly added to lead acetate (0.33 g, 0.746 mmol).
The mixture was gently refluxed for 2 h. The solution was filtered off,
and concentrated to dryness. The solids were then redissolved in
CH2Cl2 and then extracted twice with water. The organic layers were
collected and dried with anhydrous MgSO4. The product was purified
by flash chromatography with hexane/CH2Cl2 (1:1). White solids
were isolated after recrystallization from CH2Cl2/CH3OH. Yield 70%.
4.10. 6-Hexyloxynaphthalene-2-carboxylic acid 4-(6-dode-
cyloxybenzooxazol-2-yl)-3-hydroxylphenyl ester (2;n[6, m[12)
White solid, yield 43%. 1H NMR (CDCl3):
d 0.85–0.93 (m, –CH3,
6H), 1.26–1.38 (m, –CH2, 24H), 1.49–1.55 (m, –CH2, 2H), 1.84–1.85
(m, –OCH2CH2–, 2H), 3.99–4.02 (t, –OCH2–, 2H, J¼6.6 Hz), 4.09–4.11
(t, –OCH, 2H, J¼6.5 Hz), 6.93 (s, –C6H3, 1H), 6.94–6.96 (d, –C6H3, 1H,
J¼6.1 Hz), 6.97 (s, –C6H3,1H), 7.03–7.03 (d, –C6H3,1H, J¼2.2 Hz), 7.11
(s, –C6H3,1H), 7.16–7.16 (d, –C6H3,1H, J¼2.2 Hz), 7.56–7.57 (d, –C10H6,
1H, J¼8.7 Hz), 7.78–7.79 (d, –C10H6, 1H, J¼8.7 Hz), 7.86–7.88 (d,
–C10H6, 1H, J¼9.0 Hz), 8.01–8.02 (d, –C10H6, 1H, J¼8.6 Hz), 8.10–8.11
1H NMR (CDCl3):
d 0.86–0.88 (t, –CH3, 6H), 1.25–1.56 (m, –CH2, 36H),
1.82–1.85(m, –CH2, 4H), 3.99–4.02 (t, –OCH2, 2H),4.08–4.11(t, –OCH2,
2H), 6.94 (s, –C6H3, 1H), 6.95–6.96 (d, J¼5 Hz, –C10H6, 1H), 6.97
(s, –C6H3, 1H), 7.03–7.03 (d, J¼2.2 Hz, –C6H3, 1H), 7.10–7.10
(d, J¼2.2 Hz, –C6H3, 1H), 7.15–7.16 (d, J¼2.0 Hz, –C6H3, 1H), 7.24
(s, –C10H6, 1H), 7.55–7.57 (d, J¼8.5 Hz, –C10H6, 1H), 7.77–7.79 (d,
J¼8.5 Hz, –C10H6, 1H), 7.86–7.87 (d, J¼9.0 Hz, –C10H6, 1H), 8.00–8.02
(d, J¼8.5 Hz, –C10H6, 1H), 8.12–8.13 (d, J¼2.2 Hz, –C6H3, 1H), 8.68
(d, –C10H6, 1H, J¼8.6 Hz), 8.78 (s, –C10H6, 1H), 11.59 (s, –OH, 1H). 13
C
NMR (CDCl3): d 14.05, 14.13, 22.62, 22.70, 25.78, 26.06, 29.14, 29.22,
29.36, 29.41, 29.59, 29.61, 29.65, 29.67, 31.60, 31.93, 68.26, 68.97,
96.22, 106.47, 108.83, 110.77, 113.61, 113.75, 119.18, 120.22, 123.98,
126.10, 127.07, 127.61, 127.80, 131.03, 131.90, 133.49, 137.74, 150.09,
154.73, 158.06, 159.42, 159.56, 161.54, 164.95. Anal. Calcd for
(s, –C10H6, 1H), 11.59 (s, –OH, 1H). 13C NMR (CDCl3):
d 14.11, 22.68,
26.04, 26.08, 29.15, 29.20, 29.35, 29.39, 29.58, 29.60, 29.63, 29.66,
31.92, 68.24, 68.95, 96.19,106.45,108.80,110.75,113.59,113.73,119.15,
120.20, 123.95, 126.08, 127.05, 127.59, 127.77, 131.00, 131.88,
133.46, 137.71, 150.07, 154.71, 158.04, 159.40, 159.54, 161.52, 164.93.
Anal. CalcdforC48H63NO6:C,76.87;H, 8.47;N,1.87. Found:C,76.89;H,
8.68; N, 1.68. MS (FAB): calcd for MHþ C48H63NO6: 750.0; found:
750.0.
C42H51NO6: C, 75.76; H, 7.72; N, 2.10. Found: C, 75.63; H, 7.90; N,1.92.
MS (FAB): calcd for MHþ C42H51NO6: 665.9; found: 666.0.
4.11. 6-Heptyloxynaphthalene-2-carboxylic acid 4-
(6-dodecyloxybenzooxazol-2-yl)-3-hydroxylphenyl ester
(2; n[7, m[12)
White solids, yield 64%. 1H NMR (CDCl3):
d 0.85–0.91 (m, –CH3,
6H),1.26–1.37 (m, –CH2, 26H), 1.48–1.55 (m, –CH2, 2H),1.84–1.86 (m,
–CH2, 2H), 3.99–4.02(t, –OCH2, 2H, J¼6.5 Hz),4.08–4.11(t, –OCH2, 2H,
J¼6.6 Hz), 6.94–6.94 (d, –C6H3,1H, J¼2.2 Hz), 6.97–6.97 (d, –C6H3,1H,
J¼2.3 Hz), 7.03 (s, –C6H3, 1H), 7.11 (s, –C6H3, 1H), 7.16 (s, –C6H3, 1H),
7.22–7.23 (d, –C6H3,1H, J¼6.5 Hz), 7.56–7.57 (d, –C10H6,1H, J¼8.7 Hz),
7.78–7.79(d, –C6H3,1H,J¼8.7 Hz), 8.01–8.02(d, –C10H6,1H,J¼8.6 Hz),
8.10–8.11 (d, –C10H6, 1H, J¼8.6 Hz), 8.68 (s, –C10H6,1H),11.59 (s, –OH,
4.8. 6-Methoxynaphthalene-2-carboxylic acid 4-
(6-dodecyloxybenzooxazol-2-yl)-3-hydroxyphenyl ester
(2; n[1, m[12)
White solid, 52%. 1H NMR (CDCl3):
d 0.87–0.89 (t, –CH3, 3H,
J¼4.5 Hz), 1.26–1.46 (m, –CH2, 18H), 1.79–1.81 (d, –CC2, J¼4.7 Hz),
3.90–3.92 (t, –OCH3, 3H, J¼6.6 Hz), 3.94–3.96 (d, –OCH2, 2H,
J¼6.7 Hz), 6.91–6.92 (m, –C6H3, 2H), 7.03 (s, –C6H3, 1H), 7.05 (s,
–C6H3, 1H), 7.11 (s, –C10H6, 1H), 7.17–7.19 (d, –C6H3, 1H, J¼8.2 Hz),
7.51–7.53 (d, –C6H3, 1H, J¼8.3 Hz), 7.74–7.76 (d, –C10H6, 1H,
J¼8.0 Hz), 7.82–7.83 (d, –C10H6, 1H, J¼8.5 Hz), 7.93–7.95 (d, –C10H6,
1H, J¼8.1 Hz), 8.10–8.11 (d, –C10H6, 1H, J¼8.0 Hz), 8.64 (s, –C10H6,
1H). 13C NMR (CDCl3):
d 14.10, 14.13, 22.63, 22.70, 26.07, 29.08, 29.18,
29.22, 29.36, 29.41, 29.59, 29.61, 29.65, 29.67, 31.80, 31.93, 68.26,
68.97, 96.22, 106.47, 108.83, 110.77, 113.61, 113.76, 119.18, 120.22,
123.98, 126.10, 127.07, 127.61, 127.80, 131.03, 131.90, 133.49, 137.73,
150.09, 154.73, 158.06, 159.42, 159.56, 161.54, 167.95. Anal. Calcd
for C43H53NO6: C, 75.96; H, 7.86; N, 2.06. Found: C, 75.67; H, 7.97; N,
1.85. MS (FAB): calcd for MHþ C43H53NO6: 679.9; found: 680.0.
1H), 11.56 (s, –OH, 1H). 13C NMR (CDCl3):
d 14.19, 22.75, 26.11, 29.26,
29.43, 29.48, 29.66, 29.68, 29.74, 29.77, 31.98, 55.39, 68.90, 96.08,
105.70, 108.73, 110.69, 113.54, 113.69, 119.10, 119.88, 124.09, 126.13,
127.10, 127.54, 127.86, 131.05, 131.84, 133.39, 137.62, 150.00, 154.68,
158.03, 159.36, 159.92, 161.44, 164.82. Anal. Calcd for C37H41NO6: C,
74.60; H, 6.94; N, 2.35. Found: C, 74.58; H, 6.96; N, 2.12. MS (FAB):
calcd for MHþ C37H41NO6: 595.7; found: 595.9.
4.12. 6-Heptyloxynaphthalene-2-carboxylic acid 4-
(6-dodecyloxybenzooxazol-2-yl)-3-hydroxylphenyl ester
(2; n[8, m[12)
White solid, yield 58%. 1H NMR (CDCl3):
d 0.87–1.26 (m, –CH3,
6H),1.26–1.49 (m, –CH2, 28H),1.81–1.84 (m, –CH2, 4H), 3.96–3.99 (d,
–OCH2, 2H, J¼6.5 Hz), 4.05–4.07 (d, –OCH2, 2H, J¼6.5 Hz), 6.91–6.94
(m, –C6H3, 2H), 7.03 (s, –C6H3,1H), 7.07 (s, –C6H3,1H), 7.12 (s, –C10H6,
1H), 7.19–7.20 (d, –C6H3, 1H, J¼8.6 Hz), 7.53–7.54 (d, –C10H6, 1H,
J¼8.8 Hz), 7.75–7.76 (d, –C6H3, 1H, J¼8.7 Hz), 7.83–7.85 (d, –C10H6,
1H, J¼9.0 Hz), 7.96–7.97 (d, –C10H6, 1H, J¼8.6 Hz), 8.10–8.11 (d,
–C10H6,1H, J¼8.7 Hz), 8.65 (s, –C10H6,1H),11.57(s, –OH,1H).13CNMR
4.9. 6-Butoxynaphthalene-2-carboxylic acid 4-
(6-dodecyloxybenzooxazol-2-yl)-3-hydroxyphenyl ester
(2; n[4, m[12)
White solid, 74%. 1H NMR (CDCl3):
d 0.85–0.88 (t, –CH3, 3H,
J¼4.5 Hz), 0.99–1.02 (t, –CH3, 3H, J¼4.9 Hz), 1.27–1.57 (m, –CH2,
20H), 1.82–1.86 (m, –CH2, 4H), 4.00–4.02 (t, –OCH2, 2H, J¼6.5 Hz),
4.10–4.12 (t, –OCH2, 2H, J¼6.5 Hz), 6.95–6.97 (m, –C6H3, 2H), 7.03
(s, –C6H3, 1H), 7.11 (s, –C6H3, 1H), 7.16 (s, –C10H6, 1H), 7.22–7.23
(d, –C6H3, 1H, J¼6.5 Hz), 7.56–7.58 (d, –C10H6, 1H, J¼8.7 Hz), 7.79–
7.81 (d, –C10H6, 1H, J¼8.5 Hz), 7.86–7.88 (d, –C10H6, 1H, J¼9.0 Hz),
8.12–8.14 (d, –C10H6, 1H, J¼8.7 Hz), 8.68 (s, –C10H6, 1H), 11.59
(CDCl3): d 14.17, 22.71, 22.74, 26.10, 26.14, 29.20, 29.25, 29.31, 29.41,
29.43, 29.46, 29.64, 29.67, 29.70, 29.72, 31.88, 31.97, 68.23, 68.91,
96.12, 106.40, 108.75, 110.72, 113.57, 113.71, 119.13, 120.18, 123.94,
126.08, 127.05, 127.56, 127.76, 131.00, 131.87, 133.42, 137.71, 150.03,
154.70, 158.03, 159.38, 159.53, 161.48, 164.89. Anal. Calcd for
C
44H55NO6: C, 76.38; H, 7.72; N, 2.02. Found:C, 76.59; H, 8.07; N, 2.71.
(s, –OH, 1H). 13C NMR (CDCl3):
d
13.87, 14.13, 19.31, 22.70, 26.06,
MS (FAB): calcd for MHþ C44H55NO6: 693.9; found: 694.0.
27.24, 29.22, 29.36, 29.40, 29.59, 29.61, 29.65, 29.67, 31.22, 31.93,
67.93, 68.97, 96.23, 106.46, 108.83, 110.78, 113.62, 113.76, 119.18,
120.22, 123.99, 126.11, 127.07, 127.62, 127.80, 131.04, 131.91, 133.49,
137.74, 150.09, 154.73, 158.06, 159.42, 159.56, 161.55, 164.95. Anal.
Calcd for C40H47NO6: C, 75.33; H, 7.43; N, 2.20. Found: C, 74.96; H,
7.43; N, 1.94. MS (FAB): calcd for MHþ C40H47NO6: 637.8; found:
638.0.
4.13. 6-Decyloxynaphthalene-2-carboxylic acid 4-
(6-dodecyloxybenzooxazol-2-yl)-3-hydroxylphenyl ester
(2; n[10, m[12)
White solid, yield 70%. 1H NMR (CDCl3):
6H), 1.26–1.38 (m, –CH2, 30H), 1.48–1.54 (m, –CH2, 2H), 1.84–1.86
d 0.85–0.88 (m, –CH3,

H.-C. Wang et al. / Tetrahedron 64 (2008) 4939–4948
4947
(d, –CH2, 2H, J¼4.0 Hz), 3.99–4.02 (t, –OCH2, 2H, J¼6.5 Hz), 4.08–4.11
(t, –OCH2, 2H, J¼6.5 Hz), 6.92–6.92 (d, –C6H3, 1H, J¼2.2 Hz), 6.93–
6.93 (d, –C6H3, 1H, J¼2.3 Hz), 6.94 (s, –C6H3, 1H), 7.03 (s, –C6H3, 1H),
7.11 (s, –C10H6, 1H), 7.16–7.16 (d, –C6H3, 1H, J¼2.2 Hz), 7.56–7.57
(d, –C10H6, 1H, J¼8.7 Hz), 7.78–7.79 (d, –C6H3, J¼8.7 Hz), 7.86–7.88
(d, –C10H6, 1H, J¼9.0 Hz), 8.01–8.03 (d, –C10H6, 1H, J¼8.6 Hz), 8.10–
8.11 (d, –C10H6,1H, J¼8.5 Hz), 8.68 (s, –C10H6,1H),11.59 (s, –OH,1H).
C33H33NO6: C, 73.45; H, 6.16; N, 2.60. Found: C, 73.55; H, 6.18; N,
2.67. MS (FAB): calcd for MHþ C33H33NO6: 539.6; found: 540.0.
4.17. Naphthalene-2-carboxylic acid 4-
(6-octyloxybenzooxazol-2-yl)-3-hydroxyphenyl ester
(2; n[0, m[8)
13C NMR (CDCl3):
d 14.08, 22.67, 26.05, 26.09, 29.17, 29.22, 29.31,
White solids, yield 72%. 1H NMR (CDCl3):
d 0.88–0.90 (t, –CH3,
29.34, 29.39, 29.57, 29.63, 29.65, 31.89, 31.91, 68.27, 69.00, 96.27,
106.53, 108.82, 110.76, 113.59, 113.76, 119.17, 120.19, 124.02, 126.09,
127.06, 127.60, 127.82, 131.01, 131.88, 133.53, 137.74, 150.11, 154.77,
158.09, 159.44, 159.57, 161.57, 164.91. Anal. Calcd for C46H59NO6: C,
76.53; H, 8.24; N, 1.94. Found: C, 76.22; H, 8.41; N, 1.76. MS (FAB):
calcd for MHþ C46H59NO6: 722.0; found: 722.0.
3H, J¼4.5 Hz), 1.25–1.49 (m, –CH2, 10H), 1.79–1.84 (m, –CH2, 2H),
3.98–4.00 (d, –OCH2, 2H, J¼6.5 Hz), 6.93–6.96 (m, –C6H3, 2H), 7.04
(s, –C6H3, 1H), 7.09 (s, –C6H3, 1H), 7.54–7.56 (d, –C10H7, 2H,
J¼4.4 Hz), 7.61–7.62 (d, –C6H3, 1H, J¼8.5 Hz), 7.88–7.90 (d, –C6H3,
1H, J¼8.2 Hz), 7.92–7.93 (d, –C10H7, 1H, J¼8.6 Hz), 7.97–8.01
(t, –C10H7, 2H, J¼8.2 Hz), 8.16–8.17 (d, –C10H, 1H, J¼8.4 Hz), 8.77
(s, –C10H7, 1H), 11.60 (s, –OH, 1H). 13C NMR (CDCl3):
d 14.15, 22.70,
4.14. Naphthalene-2-carboxylic acid 4-
(6-butyloxybenzooxazol-2-yl)-3-hydroxylphenyl ester
(2; n[0, m[4)
26.09, 29.24, 29.29, 31.86, 68.94, 96.15, 108.92, 110.73, 113.53,
113.76, 114.59, 119.18, 125.43, 126.41, 126.92, 127.64, 127.86, 128.49,
128.77, 129.54, 132.13, 132.49, 133.42, 135.91, 150.06, 154.58, 159.40,
161.45, 164.80. Anal. Calcd for C32H31NO5: C, 75.42; H, 6.13; N, 2.75.
Found: C, 75.11; H, 5.87; N, 2.64. MS (FAB): calcd for MHþ
C32H31NO5: 509.6; found: 509.9.
White solid, yield 65%. 1H NMR (CDCl3):
d 0.98–1.01 (t, –CH3, 3H,
J¼4.9 Hz), 1.50–1.54 (m, –CH2, 2H), 1.77–1.83 (t, –CH2, 2H, J¼7.5 Hz),
3.98–4.01 (d, –OCH2, 2H, J¼6.5 Hz), 6.93–6.96 (m, –C6H3, 2H), 7.05
(s, –C6H3, 1H), 7.08 (s, –C6H3, 1H), 7.54–7.55 (d, –C10H7, 2H,
J¼4.4 Hz), 7.88–7.90 (d, –C6H3, 1H, J¼8.2 Hz), 7.91–7.93 (d, –C10H7,
1H, J¼8.6 Hz), 7.97–8.00 (t, –C10H7, 2H, J¼7.7 Hz), 8.15–8.17 (d,
–C10H7, 1H, J¼8.5 Hz), 8.76 (s, –C10H7, 1H), 11.60 (s, –OH, 1H). 13C
4.18. Copper complex of 6-dodecyloxynaphthalene-2-
carboxylic acid 4-(6-dodecyloxybenzooxazol-2-yl)-3-
hydroxyphenyl ester (1a; n[12, m[12)
NMR (CDCl3):
d 14.10, 19.29, 31.27, 68.60, 96.14, 108.91, 110.72,
The mixture of 6-dodecyloxy-naphthalene-2-carboxylic acid 4-
(6-dodecyloxybenzooxazol-2-yl)-3-hydroxyphenyl ester (0.10 g,
0.138 mmol) and copper(II) acetate (0.014 g, 0.0693 mmol) was
refluxed in 50 ml of ethanol for 24 h. The solids were collected. The
product isolated as brown solids was obtained after recrystallization
from THF/CH3OH. Yield 87%. Anal. Calcd for C96H124N2O12Cu: C,
73.84; H, 8.00; N, 1.79. Found: C, 73.90; H, 8.04; N, 1.70.
113.53, 113.74, 119.7, 125.42, 126.40, 126.92, 127.64, 127.86, 128.48,
128.77, 128.83, 130.92, 132.12, 132.48, 133.42, 135.90, 150.48, 154.58,
158.06, 159.40, 161.45, 164.79.
4.15. Naphthalene-2-carboxylic acid 4-
(6-dodecyloxybenzooxazol-2-yl)-3-hydroxyphenyl
ester (2; n[0, m[12)
4.19. Palladium complex of 6-dodecyloxynaphthalene-2-
carboxylic acid 4-(6-dodecyloxybenzooxazol-2-yl)-3-
hydroxyphenyl ester (1b; n[12, m[12)
White solids, yield 56%. 1H NMR (CDCl3):
d 0.87–0.89 (t, –CH3,
3H, J¼4.5 Hz), 1.34–1.50 (m, –CH2, 18H), 1.78–1.84 (m, –CH2, 2H),
3.97–3.99 (d, –OCH2, 2H, J¼6.5 Hz), 6.93–6.95 (m, –C6H3, 2H), 7.05
(s, –C6H3,1H), 7.08 (s, –C6H3,1H), 7.53–7.55 (d, –C6H3, 2H, J¼8.9 Hz),
7.60–7.61 (d, –C10H7, 1H, J¼8.6 Hz), 7.88–7.89 (d, –C10H7, 1H,
J¼8.1 Hz), 7.91–7.92 (d, –C10H7, 1H, J¼8.6 Hz), 7.98–7.99 (t, –C10H7,
2H, J¼4.2 Hz), 8.15–8.16 (d, –C10H7, 1H, J¼8.7 Hz), 8.76 (s, –C10H7,
The synthetic procedures were similar to copper complex as
described above except palladium(II) acetate was used. Yellow to
light orange solids, yield 73%. Anal. Calcd for C96H124N2O12Pd: C,
71.86; H, 7.79; N, 1.75. Found: C, 71.78; H, 7.82; N, 1.52.
1H), 11.60 (s, –OH, 1H). 13C NMR (CDCl3):
d 14.18, 22.75, 26.10, 29.25,
29.42, 29.47, 29.65, 29.67, 29.73, 29.76, 31.98, 68.93, 96.13, 108.89,
110.71, 113.52, 113.74, 119.16, 125.42, 126.41, 126.91, 127.62, 127.86,
128.48, 128.76, 129.53, 132.11, 132.49, 133.41, 135.90, 150.04, 154.58,
159.40, 161.44, 164.77. Anal. Calcd for C36H39NO6: C, 76.43; H, 6.95;
N, 2.48. Found: C, 76.93; H, 7.26; N, 2.18. MS (FAB): calcd for MHþ
C36H39NO5: 565.7; found: 565.9.
Acknowledgements
We thank the National Science Council of Taiwan, ROC for
funding (NSC 95-2752-M-008-010-PAE & NSC 95-2113-M-008-010)
generously in support of this work.
References and notes
4.16. 6-Methoxynaphthalene-2-carboxylic acid 4-
(6-octyloxybenzooxazol-2-yl)-3-hydroxyphenyl ester
(2; n[1, m[8)
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