Metallomesogens derived from benzoxazoles-salicylaldimine conjugates

Article abstract of DOI:10.1016/j.tet.2011.08.048

The synthesis, characterization, and mesomorphic properties of a new series of Schiff bases 2a-h and metal complexes 1a-h-M are prepared and their mesomorphic properties studied. Two single crystallographic structures of 2d (n=12, m=1) and 1g-Pd (n=m=12) were determined by X-ray analysis. Both compounds crystallize in a triclinic space group P-1. A dimeric structure formed by intermolecular H-bonds in 2d was observed, giving nematic phase due to a better aspect ratio. The central geometry at Pd²⁺ ion is nearly perfect square plane. All Schiff bases 2a-h formed N or/and SmC phases. The formation of mesophases of complexes 1a-h-M was strongly dependent on metal ions incorporated. All Cu²⁺, Ni²⁺ and Pd²⁺ complexes exhibited N or/and SmC phase, respectively. However, Zn²⁺ and Co²⁺ complexes were not mesogenic. The lack of mesomorphism was probably attributed to a preferred tetrahedral geometry at Zn²⁺ and Co²⁺ over a square-planar geometry at Cu²⁺ and Pd ²⁺.

Full text of DOI:10.1016/j.tet.2011.08.048

Tetrahedron 67 (2011) 8120e8130
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Metallomesogens derived from benzoxazolesesalicylaldimine conjugates
,
Chun-Jung Chen a, I-Wen Wang a, Hwo-Shuenn Sheu b, Gene-Hsiang Lee c, Chung K. Lai a
*
a Department of Chemistry and Center for Nano Science Technology, National Central University, Chung-Li 32001, Taiwan, ROC
b National Synchrotron Radiation Research Center, Hsinchu 30077, Taiwan, ROC
c 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:
Received 6 June 2011
Received in revised form 13 August 2011
Accepted 19 August 2011
Available online 25 August 2011
The synthesis, characterization, and mesomorphic properties of a new series of Schiff bases 2aeh and
metal complexes 1aeheM are prepared and their mesomorphic properties studied. Two single crys-
tallographic structures of 2d (n¼12, m¼1) and 1gePd (n¼m¼12) were determined by X-ray analysis.
Both compounds crystallize in a triclinic space group Pꢀ1. A dimeric structure formed by intermolecular
H-bonds in 2d was observed, giving nematic phase due to a better aspect ratio. The central geometry at
Pd2þ ion is nearly perfect square plane. All Schiff bases 2aeh formed N or/and SmC phases. The formation
of mesophases of complexes 1aeheM was strongly dependent on metal ions incorporated. All Cu2þ, Ni2þ
and Pd2þ complexes exhibited N or/and SmC phase, respectively. However, Zn2þ and Co2þ complexes
were not mesogenic. The lack of mesomorphism was probably attributed to a preferred tetrahedral
geometry at Zn2þ and Co2þ over a square-planar geometry at Cu2þ and Pd2þ
.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
other hand, paramagnetic d9-Cu2þ ions, depending on the organic
moiety can be either tetrahedral, twisted square planar or perfectly
square planar at central geometry.
The coordination geometry of metal ions as core center in-
corporated in metallomesogenic materials1 has been demonstrated
to play a key element in controlling or inducing the formation of
mesophases. Coordination complexes1 constitute the largest cate-
gory among the known metallomesogens, in which numerous
metallomesogens with unique geometric structures and novel
mesomorphic behavior were thus generated by incorporating ap-
propriate metal ions. In general, the overall molecular shape1f,g,i of
a particular compound was closely determined by the geometry of
central metals and/or also surrounding organic moieties. The co-
ordination numbers (CN) of metal ions are virtually diverse, which
are often correlated with their oxidation states/electronic states.
For example, M2þ ions have a CN¼4, while M3þ ions have a CN¼6.
Metallomesogens with a CN¼4 are mostly known, of which a ge-
ometry of either tetrahedral or square-planar geometry is all pos-
sible. Complexes with a square-planar geometry give preferably
rise to liquid crystallinity, whereas complexes with a tetrahedral
geometry are usually not mesogenic due to their unfavorable
packing. However, a few tetrahedral complexes1a were in fact
mesogenic, giving columnar or nematic structures in LC states.
Metal ions, such as diamagnetic d8-Ni2þ and d8-Pd2þ/Pt2þ ions
generate square planar complexes, while paramagnetic d7-Co2þ
and d10-Zn2þ ions preferably give tetrahedral complexes. On the
Benzoxales or 2-(o-hydroxylphenyl)-2-benzoxales (HPBs),
grouped as a member of heterocyclic derivatives have been applied
to construct a variety of novel mesophases previously in this group2
and others.3 The formation of liquid crystallinity was found to be
favored by
pep interactions and/or H-bonds induced in such
structures. Higher polarization was induced by incorporation of
heteroatoms, such as N, S, and O atoms, which often facilitate the
formation of mesophases. Intramolecular or/and intermolecular H-
bonds might be possibly induced by H/N, H/S or H/O atoms. An
intramolecular or/and intermolecular force polarized by donor and
acceptor interaction (D/A) between the electron-deficient five-
membered ring and neighboring electron-rich phenyl or aromatic
rings was often observed. In addition, nonplanar core structures can
lead to lower symmetries, giving lower melting and/or clearing
temperatures required for potential device applications. Most of
known mesogenic benzoxales2,3 exhibited nematic and/or smectic
A/C phases, as expected for linear-shaped molecules. The formation
of mesophases in such electron-deficient benzoxales was found to
be greatly affected by polar substituents.2 Like oxadiazoles,
they have been studied due to their interesting spectroscopic
and photophysical properties. The HPB molecules showed lumi-
nescent properties,4 which were useful in organic light-emitting
diodes (OLEDs). A few metal complexes5 derived from HPBs,
such as iridium(III),5a vanadyl(IV),5b zinc(II),5c and ruthenium(II)/
osmium(II)5def were known and their structures characterized.
However, only one metallomesogen6 (i.e., Cu2þ, Pd2þ) derived from
* Corresponding author. Tel.: þ886 3 4259207; fax: þ886 3 4277972; e-mail
address: cklai@cc.ncu.edu.tw (C.K. Lai).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.08.048

C.-J. Chen et al. / Tetrahedron 67 (2011) 8120e8130
8121
benzoxales was reported by this group.6a Both complexes exhibited
N or/and SmC phases over a wide range of mesophases.
mesogenic 2d (n¼12, m¼1) and mesogenic 1gePd (n¼m¼12)
suitable for crystallographic analysis were obtained by slow diffu-
sion from CH2Cl2/MeOH at room temperature and their structures
resolved. Fig. 1 shows the two molecular structures with the atomic
numbering schemes.
Transition metal complexes derived from salicylaldimines7 were
among one of the most known complexes that exhibited mesogenic
properties in metallomesogens. Almost all 3d transition metal
complexes derived from salicylaldimines1h exhibited mesomorphic
properties. A tetrahedral or square-planar geometry in [O2,N2]-
chelating fashions of salicylaldimines is often found for complexes
with a CN¼4. Pd2þ/Pt2þ ions prefer square-planar geometries,
while Co2þ and Zn2þ ions form tetrahedral geometries. Cu2þ ions
can coordinate by either tetrahedral or square-planar geometries.
Most of reported metallomesogens with a CN¼4 were more likely
rod-shaped molecules, exhibiting nematic and/or layered smectic
phases, while few complexes7a,7t with more disc-shaped molecules
formed columnar phases. Known metallomesogens with octahe-
Table 1 lists their crystallographic and structural refinement
data for the two molecules. Compound 2d crystallizes in a triclinic
space group Pꢀ1 with a Z¼2. The overall molecular shape of 2d was
considered as linear-shaped with an overall molecular length of
ꢀ
w33.438 (32) A. As expected, an intramolecular H-bond between
phenolic H2A/N2 atoms was observed, and the distance was
ꢀ
measured by ca. 1.745 (7) A. Also a few intermolecular H-bonds were
observed in the crystal lattice. A dimeric structure with a length of
ꢀ
ca. 53.28 A in a head-to-head fashion was thus formed by H-bonds,
and these H-bonds were relatively weak (Fig. 2). The H-bond
dral geometries1b,8 obtained by incorporating Mn3þ/Cr3þ/Co3þ
/
lengths were ranged from d¼2.541e2.669 A. These weak H-bonds
ꢀ
Fe3þ ions or others exhibiting columnar phases were relatively
limited. In this work, as part of our continuing research on ex-
were consistent with nematic phase observed in 2d. The formation
of the dimeric structure was probably two-fold; a larger core in-
duced and an elongated molecule were generated, leading to
a better aspect ratio, as often required for mesogens. The induced
conformation was believed to facilitate molecular packing both in
the solid or/and the liquid crystal state. The benzoxazole, phenolic,
and lateral phenyl rings were in fact not coplanar, with a small
dihedral angle; 2.833 (164)e4.416 (157)ꢁ. The intramolecular H-
bonding kept all three rings roughly coplanar, and the planar
structure was responsible for a better packing. In the unit cell, all
molecules were arranged by antiparallel and head-to-tail ar-
ploring new metallomesogens,
a
new series of benzox-
azoleesalicylaldimine conjugates 2aeh and their transition metal
complexes 1aeheM were prepared. In order to comprehend the
effect of the geometry of metal ions incorporated, cobalt, nickel,
palladium, zinc, and copper complexes were prepared. Results
showed that Cu2þ, Ni2þ, and Pd2þ complexes exhibited N or/and
SmC phase. However, Zn2þ and Co2þ complexes were all crystalline.
The lack of mesomorphism was attributed to a preferred tetrahe-
dral geometry at Zn2þ and Co2þ
.
rangements (Fig. 3). No
pep interaction, consistent with only ne-
2. Results and discussion
matic phase was observed in 2d. Some selected bond lengths and
bond angles are listed in Table 2. A layered structure was observed
and the molecular arrangement in unit cell was shown in Fig. 3.
The complex 1gePd (n¼m¼12) also crystallizes in triclinic space
group Pꢀ1 with a Z¼1. The geometry at palladium was coordinated
as perfect square planar. The two angles of N1(#)ePdeO1 and
N1(#)1ePdeO1(#) atoms were of 88.60 (9)ꢁ and 91.42 (9)ꢁ, which
were close to an angle of 90ꢁ expected for a square-planar geom-
etry. The overall molecular shape was considered as chair-shaped
2.1. Synthesis and characterization
The synthetic pathways9 to benzoxazoles 2aeh and their metal
complexes 1aeheM (M¼Co, Ni, Cu, Zn, Pd) are summarized in
Scheme 1. Most benzoxazoles were prepared by the condensation
of 2-aminophenols with benzaldehydes or benzoic acid and sub-
sequent intramolecular cyclization. In this work, 2-(4-
alkoxyphenyl)benzoxazol-5-ylamines 3 were similarly prepared
by our previous procedures.6a The Schiff bases 2aeh were obtained
by reactions of amines 3 and 4-alkoxy-2-hydroxy benzaldehydes in
refluxing absolute ethanol for 12 h. The yields were slightly in-
creased with carbon lengths. 1H and 13C NMR spectroscopy were
used to characterize all intermediates 2e4. A singlet appeared at
ꢀ
with a length of ca. 47.29 A [i.e., C44eC44(#)]. The two central
planes defined by N1eO1ePdeO1eN1 atoms were coplanar. The
benzoxazole ring and central Pd plane (by N1eO1ePdeO1eN1)
were not coplanar, with a dihedral angle of 70.692ꢁ. In the lattice,
two molecules were attracted by a weak
tance of ca. w2.863 A as point-to-face alignment between the H17A
pep interaction. A dis-
ꢀ
d
8.53e8.55 ppm, characteristic of imine (eN]CH) was observed
of phenyl ring and central Pd plane was obtained. Two other
for the formation of compounds 2aeh. The solvent-dependent
ground-state conformational equilibrium and excited dynamic of
2-(20-hydroxyphenyl)benzoxazole have been characterized in sev-
eral solvents.10 The only observable ground-state tautomers is the
enol form, which exists in equilibrium between the syn- and anti-
rotational isomers.
weaker pep interactions were also observed between the neigh-
boring up-and-down molecules, and the distances were measured
ꢀ
as 3.048 and 3.732 A (Fig. 4). All alkoxy chains were interdigitated
and the Van der Waal interaction between the alkoxy chains was
observed. A layered structure observed in 1gePd and the molecular
arrangement in unit cell were shown in Fig. 5.
The metal complexes were prepared by the reaction of ben-
zoxazoleeimines 2aeh and M(OAc)2 (M¼Co, Ni, Cu, Zn, Pd) in
refluxing abs ethanol/THF for 2 h. Metal complexes, isolated as
gray-green (Cu), yellow (Ni), light orange (Pd), pale-yellow (Zn),
2.3. Mesomorphic properties
The liquid crystalline behavior of compounds 2aeh and
1aeheM was characterized and studied by differential scanning
calorimetry and polarized optical microscope. The phase transi-
tions and thermodynamic data are summarized in Tables 3 and 4.
All derivatives 2aeh exhibited enantiotropic nematic or/and
smectic C phases. Four derivatives 2aed appended with two
shorter alkoxy chains formed nematic phases, while other three
derivatives 2eeg with two longer alkoxy chains formed nematic
phase at higher temperature and smectic C phase at lower tem-
perature. The derivative 2h (n¼12, m¼16) showed SmC phase. This
type of mesophase-dependence on the lateral carbon length is of-
ten observed in rod-like mesogens. Interestingly, the derivative 2a
with two eOCH3 chains were truly mesogenic, which has been
and brown (Co) solids were purified by
a few times re-
crystallizations from THF/CH3OH at room temperature. The yields
were modestly ranged from 58 to 81%. Cobalt complexes were
slightly sensitive to air, especially when dissolved in the solution.
The elemental analysis was used to confirm the purity of Schiff
bases 2aeh and metal complexes 1aeheM.
2.2. Single crystal structures of 2d (n[12, m[1) and 1gePd (n
[m[12)
In order to understand the correlation between the molecular
structures and mesomorphic behavior, two single crystals of the

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C.-J. Chen et al. / Tetrahedron 67 (2011) 8120e8130
R1O
OH
HO
a
b
X = H
O2N
N
5
X
O
O
OR1
X = H or OH
c
a
X = OH
R2O
H2N
O2N
O
O
d
N
N
4
OR1
OR1
OH
O
3
e
R2O
R1O
R2O
N
O
N
O
N
f
O
M
N
O
OH
O
N
N
OR1
OR2
OR1
2a-h
1a-h-M; R1 = (CH2)nH; R2 = (CH2)m
M = Cu, Ni, Pd, Co, Zn
H
Scheme 1. Reaction and Reagents. (a) RBr (1.0 equiv), K2CO3 (1.5 equiv), KI (cat.), refluxing in dry CH3COCH3, 48 h; (b) 2-amino-4-nitrophenol (1.0 equiv), CH3COOH (drops),
refluxing in abs C2H5OH, 12 h; (c) Pb(OAc)4 (1.3 equiv), refluxing in CHCl3, 4 h; (d) N2H4 (1.1 equiv), Pd/C (0.1 equiv), refluxing in C2H5OH, 6 h; (e) CH3COOH (drops), refluxing in dry
C2H5OH, 12 h; (f) M(OAc)2 M¼Cu, Ni, Pd, Co (0.5 equiv), refluxing in abs C2H5OH/THF, 2 h.
Fig. 1. Two ORTEP plots for compound 2d (n¼12, m¼1) and 1gePd (n¼12, m¼12) with the numbering scheme, and the thermal ellipsoids of the non-hydrogen atoms are drawn at
the 50% probability level.
observed in other similar benzoxazoles.6a A higher clearing tem-
perature of 2a at Tcl¼293.7 ꢁC was observed due to its more rigid
core and/or less flexible chains. 2a showed slight decomposition at
temperature higher than its isotropic point. Methoxy group is
usually not considered as a flexible chain. The formation of nematic
phases might be attributed to the more hindered conformation
caused by two lateral phenyl rings. Its lesser coplanar core resulted
from the tetrahedral methyl and also a free rotation between car-
bonecarbon single bond between the central and two lateral
phenyl rings might induce the formation of ne2matic phase. The
clearing temperatures decreased with increasing carbon lengths,
Tcl¼224.6 (2c)>200.6 (2d)>197.9 (2e)>185.2 (2f)>179.0 (2g)>
164.9 ꢁC (2h). Single crystallographic analysis of 2d showed that
a dimeric structure was induced by H-bonds in a head-to-head
fashion, indicating that the lower alkoxy chains (i.e., m value)
merged into the two lateral alkoxy chains (i.e., n value) will not alter
or affect much the overall molecular length. The temperature range
of mesophase in 2 increased from a
D
TLC¼56.2 (2h)e110.0 ꢁC (2c)
on the heating process. Both derivatives 2b (n¼1, m¼12) and 2d
(n¼12, m¼1) showed similar mesomorphic behavior due to their

C.-J. Chen et al. / Tetrahedron 67 (2011) 8120e8130
8123
Pd2þ complexes exhibited N or/and SmC phase, respectively. Both
Co2þ and Zn2þ complexes were crystalline. All complexes (except
complex 1geNi) have higher clearing temperatures than those of
free Schiff bases 2aeh due to their larger core sizes or molecules.
The clearing temperatures of all complexes formed, for example,
with same derivative 2g decreased in the order of Tcl¼224.4 (Pd)>
200.2 (Zn)>198.8 (Co)>197.2 (Cu)>174.2 ꢁC (Ni). The transition
temperatures for some derivatives 1eM are not observed on DSC
analysis, therefore they were obtained by optical microscope. Sur-
prisingly, complex 1aeCu (n¼m¼1) was also mesogenic, exhibiting
a nematic phase at Tmp¼284.6 ꢁC and Tcl¼304.2 ꢁC. This complex
showed slightly decomposition at temperature higher than
Table 1
Crystallographic and experimental data for compounds 2d and 1gePd
Compds.
2d (n¼12, m¼1)
C33H40N2O4
528.67
150 (2)
Triclinic
1gePd (n¼12, m¼12)
C88H122N4O8Pd
1470.30
150 (2)
Triclinic
Empirical formula
Formula weight
T/K
Crystal system
Space group
Pꢀ1
Pꢀ1
ꢀ
a/A
8.6607 (11)
12.7815 (15)
14.3162 (16)
66.610 (5)
75.484 (7)
78.191 (7)
1935.0 (2)
2
8.3188 (3)
10.1646 (3)
23.2657 (7)
93.3681 (18)
93.407 (2)
93.1423 (15)
1957.06 (11)
1
ꢀ
b/A
ꢀ
c/A
ꢁ
ꢁ
a
/
b
/
ꢁ
/
g
Tcl>304.2 ꢁC. The temperature range of N phase,
D
TN¼19.6 ꢁC was
3
ꢀ
U/A
Z
relatively short on heating process. The clearing temperatures of
complexes 1aeheCu in this series decreased with increasing car-
bon length, i.e., Tcl¼304.2 (1aeCu)>255.6 (1ceCu)>223.1
(1eeCu)>192.6 ꢁC (1heCu). Both two complexes 1geCu and
1heCu formed only smectic C phases. The nematic and smectic C
phases were identified by microscope. A typical texture described
as focal-conic or Schlieren domains (Fig. 6) were observed under
POM when cooling from isotropic liquid. Nickel and palladium
formed similar mesomorphic behavior as copper complexes.
F(000)
568
1.256
788
1.248
Dc/Mg mꢀ3
Crystal size/mm3
Range for data collection/ꢁ
Reflection collected
Data, restraints, parameters
Independent reflection
Final R1, wR2
0.70ꢂ0.06ꢂ0.03
1.58e25.00
14,454
4892/0/355
4892 [R(int)¼0.1217]
0.1047, 0.2749
0.25ꢂ0.17ꢂ0.02
1.76e25.00
25,339
6860/0/457
6860 [R(int)¼0.0763]
0.0525, 0.1082
Fig. 2. A dimeric structure formed by intermolecular H-bonds in 2d (n¼12, m¼1).
Fig. 3. The molecular arrangements in 2d when viewed from a-axes.
approximately equal overall molecular lengths. The temperature
range of N phase decreased with increasing carbon lengths, for
Complexes 1ePd have higher clearing temperatures then those of
1eNi, which might be attributed to the stronger coordinative in-
teraction between the neighboring molecules in Pd over than in Ni
complexes. All Zn2þ and Co2þ complexes were not mesogenic.
example,
D
TN¼122.6 (2c)>95.1 (2d)>32.0 (2e)>211.3 (2f)>2.6 ꢁC
(2g), whereas, the temperature range of smectic C phase remained
from
D
TSmC¼94.6 (2f)e69.7 ꢁC (2h). The phases were identified as
A
transition from crystal-to-isotropic at Tm¼200.2 ꢁC and
N and smectic C phase by POM. A typical texture as Schlieren do-
mains for N phase, or fan-shaped or Schlieren for SmC phase were
observed under optical polarized microscope when cooling from
isotropic states (Fig. 6). Optical textures of SmC phase were not
homeotropic, which were often observed in SmA and N phases. A
Tm¼198.8 ꢁC, for 1geZn and 1geCo, respectively, was observed.
Both Zn2þ and Co2þ ions often prefer tetrahedral coordinations. The
lack of mesomorphism was probably attributed to the tetrahedral
geometry, in which molecules were unfavorable to pack in a more
regular arrangement required for mesogens.
lower enthalpy, i.e.,
D
H¼0.26e2.26 kJ/mol for the transition of N/I
phase was obtained. The formation of N phases was also quite
consistent with molecular packing, as seen from single crystal
analysis.
2.4. Variable-temperature powder XRD diffraction data
The powder X-ray diffraction experiments for two compounds
2geh and three complexes 1geCu (n¼m¼12), 1heCu (n¼12,
m¼16), and 1gePd (n¼12, m¼12) were performed to confirm the
structures of the smectic C phases. The X-ray diffraction data were
On the other hand, complexes 1aeheM showed a strong de-
pendence of metal ions incorporated on the formation of meso-
phases. Cu2þcomplexes formed N or/and SmC phases, and Ni2þ and

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C.-J. Chen et al. / Tetrahedron 67 (2011) 8120e8130
Table 2
assigned to the molten alkoxy chains. The d-spacings of compounds
ꢁ
ꢀ
Selected bond distances [A] and angles [ ] for 2d and 1gePd
2g and 2h were quite close due to their similar structures in overall
length. Powder XRD diffraction data of complexes 1geCu
(n¼m¼12), 1heCu (n¼12, m¼16) and 1gePd (n¼12, m¼12)
showed similar diffraction patterns as SmC phases compounds
2d (n¼12, m¼1)
Bond distances
O(2)eC(13)
N(2)eC(7)
N(2)eC(4)
Bond angles
1.369 (6)
1.287 (6)
1.405 (6)
C(8)eC(9)
C(8)eC(13)
1.414 (7)
1.423 (7)
ꢀ
2geh. Both complexes have two diffraction peaks at 34.3 A and
ꢀ
ꢀ
ꢀ
17.2 A, and 36.9 A and 18.5 A assigned as index 001 and 002 for
C(7)eN(2)eC(4)
N(2)eC(4)eC(3)
N(2)eC(7)eC(8)
C(9)eC(8)eC(13)
1gePd (n¼12, m¼12)
Bond distances
PdeO(1)
PdeN(1)
O(1)eC(1)
N(1)eC(7)
N(1)eC(8)
122.9 (4)
125.1 (4)
122.1 (5)
116.6 (5)
C(9)eC(8)eC(7)
C(13)eC(8)eC(7)
O(2)eC(13)eC(8)
120.5 (4)
122.9 (4)
119.6 (4)
1geCu (n¼m¼12), 1heCu (n¼12, m¼16), respectively. Complex
ꢀ
1gePd (n¼12, m¼12) showed a similar d-spacing of 34.8 A as that
ꢀ
(w34.3 A) of 1geCu (n¼12, m¼12).
3. Conclusions
1.954 (2)
2.033 (3)
1.323 (4)
1.301 (4)
1.445 (4)
C(1)eC(2)
C(1)eC(6)
C(6)eC(7)
C(8)eC(9)
1.410 (4)
1.411 (4)
1.422 (4)
1.391 (4)
A new metallomesogens based on NiII, CoII, CuII, PdII, and ZnII
centers coordinated to benzoxazolesesalicylaldimine conjugates
were prepared and their mesomorphic properties studied. An in-
duced dimeric structure by H-bonds formed in single crystal 2d
(n¼12, m¼1) facilitates the formation of mesophases. Metal com-
plexes derived from bidentate salicylaldimines adopted a preferred
bonding fashion of [O2,N2]-donor atoms. Single crystal X-ray
structural analysis of 1gePd (n¼m¼1) confirmed a trans-square
planar arrangement for palladium complex. A strong dependence
of geometries of metal ions incorporated on the formation of
mesophase was demonstrated. Metal ions, such as Cu2þ, Ni2þ, and
Bond angles
O(1)ePdeO(1)#1
O(1)ePdeN(1)#1
O(1)#1ePdeN(1)#1
C(7)eN(1)eC(8)
C(8)eN(1)ePd
O(1)eC(1)eC(6)
C(3)eC(2)eC(1)
180.00 (10)
88.60 (9)
91.40 (9)
117.8 (3)
117.86 (19)
123.6 (3)
119.8 (3)
N(1)eC(7)eC(6)
C(9)eC(8)eN(1)
C(1)eO(1)ePd
C(7)eN(1)ePd
O(1)eC(1)eC(2)
C(2)eC(1)eC(6)
C(1)eC(6)eC(7)
127.6 (3)
120.7 (3)
128.5 (2)
123.4 (2)
115.9 (3)
120.5 (3)
123.8 (3)
Fig. 4. The
p
ep
interactions observed in 1gePd (m¼n¼12).
summarized in Table 5. As indicated, they all displayed a similar
diffraction pattern with one strong peak and/or one very weak at
lower angle region, and also a very weak and broad diffraction peak
at wider angle. The first two diffraction peaks appeared at lower
angle were assigned as 001 and 002. This diffraction pattern was
typically characteristic of a layer structure observed for SmC pha-
Pd2þ coordinated by a square-planar geometry formed N or/and
SmC phases. In contrast, Zn2þ and Co2þ complexes with a tetrahe-
dral geometry were not mesogenic.
4. Experimental section
ꢀ
ses. For example, compound 2h showed a strong peak at 39.8 A and
4.1. General
ꢀ
ꢀ
a weak peak at 19.9 A, shown in Fig. 7. A d-spacing of 38.2 A at
ꢁ
ꢀ
150 C obtained for 2g was much smaller than 47.1 A obtained from
calculated molecular length, which indicated the molecules were
tilted and also the alkoxy chains were highly interdigitated. A very
All chemicals and solvents were reagent grades from Lancaster
or Aldrich. Solvents were dried by standard techniques. 1H and 13
C
NMR spectra were measured on a Bruker AM-300. FT-IR spectra
were performed on Nicolet Magna-IR 550 spectrometer. DSC
ꢀ
broad and weak peak at w4.60 A was observed, and this peak was

C.-J. Chen et al. / Tetrahedron 67 (2011) 8120e8130
8125
Fig. 5. Molecular arrangements in 1gePd when viewed from a- and b-axes.
Table 3
Phase transitions and enthalpiesa of compounds 2aeh
217.3 (51.4)
293.7 (0.44)
N
2a
2b
n = 1, m = 1
Cr
Cr
Id
287.0b
164.0b
123.0 (39.0)
202.8 (0.30)
1
12
I
N
N
N
N
109.5 (39.0)
114.6 (23.8)
200.0 (0.29)
224.6 (2.26)
Cr
I
2c
2d
2e
2f
8
1
1
223.1 (0.26)
200.6 (0.45)
100.5 (23.6)
115.6 (39.8)
I
Cr
12
12
12
12
12
103.7 (39.5)
166.9 (0.24)
198.8 (0.43)
197.9 (0.83)
103.1 (23.3)
Cr
Cr
Cr
SmC
SmC
SmC
Cr
I
I
4
84.1 (23.0)
163.4 (0.23)
174.1 (0.93)
195.4 (0.72)
185.2 (1.00)
100.0 (30.2)
N
N
8
169.8 (0.85)
176.4 (2.25)
75.2 (30.0)
181.1 (0.98)
179.0 (1.60)
105.4 (47.8)
2g
2h
I
I
12
16
83.4 (46.8)
177.9 (1.44)
164.9 (7.91)
175.3 (1.89)
108.7 (69.8)
SmC
163.3 (7.26)
93.6 (71.5)
a
Cr¼crystalline, SmC¼smectic C and N¼nematic phase, I¼isotropics.
b
Observed by microscope.
thermographs were carried out on a Mettler DSC 821 and calibrated
with a pure indium sample. All phase transitions are determined
by a scan rate of 10.0ꢁ/min. Optical polarized microscopy was car-
ried out on a Zeiss AxiaPlan equipped with a hot stage system of
Mettler FP90/FP82HT. Elemental analysis for carbon, hydrogen,
and nitrogen were conducted on a Heraeus Vario EL-III elemental
analyzer at National Taiwan University. All compounds of
4-alkoxybenzaldehydes, 4-alkoxy-2-hydroxy benzaldehydes, 2-
{[1-(4-alkoxy phenyl)-methylidene]amino}-4-nitrophenols, 2-(4-
alkoxyxyphenyl)-5-nitro-benzoxazoles, and 2-(4-alkoxyphenyl)
benzoxazol-5-ylamines were prepared by similar procedures.6a
1H). 13C NMR (CDCl3):
d 14.04, 22.61, 25.88, 28.97, 29.27, 29.48,
29.51, 29.57, 31.84, 68.32, 114.64, 129.63, 131.88, 164.18, 190.68.
4.1.2. 2-{[1-(4-Dodecyloxyphenyl)-methylidene]amino}-4-
nitrophenol (5; n¼12). The solution of 4-dodecyloxybenzaldehyde
(5.0 g, 0.017 mol) dissolved in 100 mL dry C2H5OH with a few
drops CH3COOH added was added 2-amino-4-nitrophenol (2.66 g,
0.017 mol), and the solution was refluxed for 12 h under nitrogen
atmosphere. The solution was cooled and the solids were collected.
The products isolated as yellow solids were obtained by re-
crystallization from C2H5OH. Yield 90%. 1H NMR (CDCl3):
d 0.86 (t,
J¼6.71 Hz, eCH3, 3H), 1.25 (m, eCH2, 18H), 1.73e1.84 (m,
eOCH2CH2, 2H), 4.03 (t, J¼6.48 Hz, eOCH2, 2H), 6.96e7.07 (m,
AreH, 3H), 7.87 (d, J¼8.73 Hz, AreH, 2H), 8.09 (dd, J¼2.54 Hz,
8.89 Hz, AreH, 1H), 8.19 (d, J¼2.55 Hz, AreH, 1H), 8.69 (s, Ar-CHN,
4.1.1. 4-Dodecyloxybenzaldehyde (n¼12). White solids; yield 65%.
1H NMR (CDCl3):
d
0.84 (t, J¼5.93 Hz, eCH3, 3H), 1.23 (m, eCH2,
18H), 1.70e1.84 (m, eOCH2CH2, 2H), 4.00 (t, J¼6.51 Hz, eOCH2, 2H),
6.92e6.97 (m, AreH, 2H), 7.75e7.80 (m, AreH, 2H), 9.83 (s, eCHO,
1H). 13C NMR (CDCl3):
d 14.11, 22.68, 25.97, 29.09, 29.34, 29.56,

8126
C.-J. Chen et al. / Tetrahedron 67 (2011) 8120e8130
Table 4
Phase transitions and ehthalpiesa of compounds 1aeheM (M¼Cu, Ni, Pd, Zn, Co)
284.6 (20.5)
304.2 (0.42)
N
1a-Cu n = 1, m = 1
Cr
Cr
Cr
Cr
Cr
Id
144.2b
275.8b
208.3 (37.0)
255.5 (0.40)
I
1b-Cu
1c-Cu
1d-Cu
1e-Cu
1f-Cu
1g-Cu
1h-Cu
1f-Ni
1
8
12
1
N
N
N
N
156.4b
221.7 (0.32)
255.6 (1.03)
185.1 (68.1)
I
85.3b
236.4 (0.34)
227.3 (0.97)
176.8 (63.0)
I
12
12
12
1
80.1b
222.1 (0.78)
223.1 (1.00)
154.4 (59.0)
I
I
4
83.3 (8.01)
219.8 (0.94)
212.6 (1.66)
193.4 (53.4)
N
Cr
8
SmC
Cr
190.7 (1.55)
162.3 (56.1)
145.4 (37.8)
209.3 (1.62)
197.2 (10.6)
I
I
SmC
SmC
N
12
12
12
12
12
12
12
16
8
124.3 (48.1)
151.6 (65.9)
195.6 (10.3)
192.6 (13.2)
Cr
114.0 (54.0)
184.8 (5.57)
191.5 (11.4)
197.3b
126.5 (12.1)
85.7b
SmC
Cr
I
I
I
I
Cr
193.5b
177.0 (5.48)
104.1 (57.0)
174.2 (8.08)
SmC
1g-Ni
12
8
86.1b
165.5 (4.72)
228.8 (1.25)
200.0 (1.90)
161.3 (4.24)
Cr
Cr
SmC
SmC
N
1f-Pd
144.5 (11.2)
160.2 (7.12)
198.7 (1.62)
214.6 (2.82)
228.0 (1.07)
224.4 (0.47)
N
1g-Pd
12
102.5 (32.0)
209.2 (2.60)
218.5 (0.46)
200.2 (48.9)
1g-Zn
1g-Co
12
12
12
12
I
I
Cr
Cr
189.9 (48.7)
198.8 (37.1)
182.7 (36.3)
a
Cr¼crystalline, SmC¼smectic C and N¼nematic phase, I¼isotropics.
b
Observed by microscope
Fig. 6. The optical textures. N phase at 176.0 ꢁC (top left)and SmC phase at 160.0 ꢁC (top right) by 2g, and N phase at 220 ꢁC (bottom left) and SmCphase at 200 ꢁC (bottom right)by 1gePd.

C.-J. Chen et al. / Tetrahedron 67 (2011) 8120e8130
8127
Table 5
Powder XRD diffraction data for compounds 2geh and 1geheM
Compds
Mesophase
(temp/ꢁC)
d-Spacing
(A)
Miller
index
Molecular
length (A)
ꢀ
ꢀ
2g (n¼12, m¼12)
2h (n¼12, m¼16)
SmC at 150 ꢁC
38.2
4.60
39.8
19.9
4.60
34.3
17.2
4.60
36.9
18.5
4.60
34.8
17.4
4.60
001
Halo
001
002
Halo
001
002
Halo
001
002
Halo
001
002
Halo
47.1
SmC at 148 ꢁC
52.0
1geCu (n¼12, m¼12)
1heCu (n¼12, m¼16)
1gePd (n¼12, m¼12)
SmC at 182 ꢁC
SmC at 188 ꢁC
SmC at 206 ꢁC
52.9
53.2
54.0
29.63, 31.90, 68.38, 111.77, 114.63, 115.01, 123.98, 127.64, 131.29,
135.97, 141.18, 157.62, 159.72, 163.06.
4.1.3. 2-(4-Dodecyloxyphenyl)-5-nitrobenzoxazole (4; n¼12). The
mixture of 2-{[1-(4-dodecyloxy-phenyl)-methylidene]-amino}-4-
nitrophenol (7.0 g, 0.016 mol) dissolved in 200 mL of CHCl3 and
Pb(OAc)4 (9.74 g, 0.021 mol) was refluxed for 4 h. The solution was
extracted with 100 mL of CH2Cl2/H2O, and the organic layers were
combined and dried over MgSO4. The solution was concentrated
and the brown solids. The residue was purified by column chro-
matography (silica gel) eluting with hexane/EA (20/1). The prod-
ucts isolated as pale solids were obtained by recrystallization from
CH2Cl2/CH3OH. Yield 83%. 1H NMR (CDCl3):
d
0.86 (t, J¼5.84 Hz,
eCH3, 3H), 1.25 (m, eCH2, 18H), 1.74e1.88 (m, eOCH2CH2, 2H), 4.03
(t, J¼6.48 Hz, eOCH2, 2H), 6.99e7.04 (m, AreH, 2H), 7.61 (d,
J¼8.90 Hz, AreH, 1H), 8.15e8.19 (m, AreH, 2H), 8.26 (dd, J¼2.30 Hz,
8.92 Hz, AreH, 1H), 8.57 (d, J¼2.22 Hz, AreH, 1H). 13C NMR (CDCl3):
d
14.11, 22.67, 25.96, 29.07, 29.34, 29.56, 29.62, 31.90, 68.35, 110.35,
115.02, 115.68, 117.97, 120.60, 129.87, 142.81, 145.26, 154.24, 162.80,
166.17.
4.1.4. 2-(4-Dodecyloxyphenyl)benzoxazol-5-ylamine (3; n¼12). The
mixture of 2-(4-dodecyloxy-phenyl)-5-nitro-benzoxazole (5.0 g,
0.012 mol) and Pd/C (0.125 g, 0.001 mol) dissolved in 100 mL abs
C2H5OH was refluxed for 20 min. To this solution, N2H4 (0.649 g,
0.013 mol) was added and then refluxed for 6 h. The solids were
filtered off and the solution was concentrated to dryness. The
product isolated as white solids was obtained after re-
crystallization from C2H5OH. Yield 80%. 1H NMR (CDCl3):
d 0.86 (t,
J¼5.84 Hz, eCH3, 3H), 1.24 (m, eCH2, 18H), 1.75e1.82 (m,
eOCH2CH2, 2H), 3.69 (br, eNH2, 2H), 4.00 (t, J¼6.06 Hz, eOCH2,
2H), 6.64 (dd, J¼2.20 Hz, 8.52 Hz, AreH, 1H), 6.95e6.99 (m, AreH,
3H), 7.29 (d, J¼8.46 Hz, AreH, 1H), 8.09e8.13 (m, AreH, 2H). 13C
NMR (CDCl3):
d 14.09, 22.66, 25.97, 29.13, 29.33, 29.56, 29.62,
Fig. 7. Powder XRD diffraction plots of 2h at 148 ꢁC (top left), 1heCu at 188 ꢁC and
1gePd at 200 ꢁC (bottom).
31.89, 68.19, 104.83, 110.35, 113.04, 114.73, 119.64, 129.14, 143.30,
143.68, 144.66, 161.74, 163.67.
4.1.5. 4-Dodecyloxy-2-hydroxybenzaldehyde (m¼12). White solid;
yield 65%. 1H NMR (CDCl3):
d
0.86 (t, J¼5.84 Hz, eCH3, 3H), 1.25 (m,
eCH2, 18H), 1.77 (m, eOCH2CH2, 2H), 3.98 (t, J¼6.00 Hz, eOCH2,
2H), 6.39 (m, AreH, 1H), 6.48e6.53 (m, AreH, 1H), 7.39 (d,
J¼8.46 Hz, AreH, 1H), 9.68 (s, eCHO, 1H), 11.47 (s, AreOH, 1H). 13C
dodecyloxy-phenyl)-benzoxazol-5-ylamine (1.287 g, 0.003 mol),
and acetic acid (0.5 mL) was gently refluxed for 12 h. The solution was
cooled and the solids were collected. The product isolated as yellow
solids were obtained after recrystallization from CH2Cl2/MeOH. Yield
NMR (CDCl3): d 14.11, 22.67, 25.89, 28.89, 29.32, 29.61, 31.89, 68.58,
101.00, 108.77, 114.96, 135.18, 164.50, 166.45, 194.29.
79%. 1H NMR (CDCl3):
d
0.88 (t, J¼6.56 Hz, eCH3, 6H), 1.27 (m, eCH2,
36H), 1.78e1.83 (m, eOCH2CH2, 4H), 4.00 (t, J¼6.58 Hz, eOCH2, 2H),
4.04 (t, J¼6.51 Hz, eOCH2, 2H), 6.49e6.53 (m, AreH, 2H), 7.02 (d,
J¼8.73 Hz, AreH, 2H), 7.24 (d, J¼8.53 Hz, AreH, 1H), 7.29 (d,
J¼8.44 Hz, AreH, 1H), 7.54 (d, J¼8.51 Hz, AreH, 1H), 7.58 (s, AreH,
4.1.6. 5-Dodecyloxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-ylimino]
methyl}phenol 2g. Under the nitrogen atmosphere, the mixture of 4-
dodecyloxy-2-hydroxybenzaldehyde (1.0 g, 0.003 mol), 2-(4-

8128
C.-J. Chen et al. / Tetrahedron 67 (2011) 8120e8130
1H), 8.17 (d, J¼8.71 Hz, AreH, 2H), 8.56 (s, eNCH, 1H). 13C NMR
N, 5.27. IR (KBr): 3064, 2917, 2850, 1631, 1609, 1502, 1254, 826,
808 cmꢀ1
(CDCl3):
d
14.46, 23.04, 26.34, 29.43, 29.50, 29.70, 29.72, 29.91, 29.94,
.
29.99, 30.01, 32.27, 68.64, 101.94, 108.06, 110.94, 110.97, 113.27, 115.24,
119.38, 119.52, 129.80, 133.94, 143.68, 145.99, 149.71, 161.78, 162.50,
164.05, 164.76. MS (FAB): calcd for MHþ C44H63N2O4: 684.0. Found:
684.5. Anal. Calcd for C44H62N2O4: C, 77.38; H, 9.15; N, 4.10. Found: C,
77.03; H, 9.09; N, 4.11. IR (KBr): 3066, 2919, 2850, 1631, 1603, 1500,
4.1.11. 5-Butoxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-ylimino]
methyl}phenol 2e. Yellow solid; yield 86%. 1H NMR (CDCl3):
0.89
d
(t, J¼6.69 Hz, eCH3, 3H), 0.99 (t, J¼7.37 Hz, eCH3, 3H), 1.27 (m,
eCH2, 20H), 1.77e1.82 (m, eOCH2CH2, 4H), 3.98e4.02 (m,
eOCH2, 4H), 6.48e6.50 (m, AreH, 2H), 7.00 (d, J¼8.76 Hz, AreH,
2H), 7.21 (d, J¼7.02 Hz, AreH, 1H), 7.26 (d, J¼7.85 Hz, AreH, 1H),
7.50 (d, J¼8.52 Hz, AreH, 1H), 7.56 (s, AreH, 1H), 8.15 (d,
J¼8.70 Hz, AreH, 2H), 8.53 (s, eNCH, 1H). 13C NMR (CDCl3):
1470, 1248, 827, 807 cmꢀ1
.
4.1.7. 5-Methoxy-2-{[2-(4-methoxyphenyl)benzoxazol-5-ylimino]
methyl}phenol 2a. Yellow solid; 81%. 1H NMR (CDCl3):
3.83 (s,
d
eCH3, 3H), 3.88 (s, eCH3, 3H), 6.48e6.51 (m, AreH, 2H), 7.01 (d,
J¼8.87 Hz, AreH, 2H), 7.22 (dd, J¼1.99 Hz, 8.51 Hz, AreH, 1H), 7.28
(d, J¼8.40 Hz, AreH, 1H), 7.54 (d, J¼8.51 Hz, AreH, 1H), 7.58 (s,
AreH, 1H), 8.17 (d, J¼8.71 Hz, AreH, 2H), 8.56 (s, N]CH, 1H).13C
d 14.14, 14.44, 19.53, 23.01, 26.33, 29.49, 29.68, 29.72, 29.90,
29.93, 29.97, 29.99, 30.65, 31.46, 32.25, 68.25, 68.59, 101.89,
107.87, 110.87, 110.92, 113.33, 115.17, 119.32, 119.50, 129.74, 133.83,
143.63, 146.07, 149.64, 161.69, 162.43, 163.89, 164.00, 164.65. MS
(FAB): calcd for MHþ C36H47N2O4: 571.8. Found: 571.4. Anal.
Calcd for C36H46N2O4: C, 75.76; H, 8.12; N, 4.91. Found: C, 75.57;
H, 8.16; N, 4.88. IR (KBr): 3064, 2918, 2851, 1632, 1605, 1503,
NMR (CDCl3):
d 55.47, 101.06, 107.15, 110.63, 113.14, 114.39, 119.11,
119.44, 129.46, 133.56, 143.26, 145.77, 149.34, 161.51, 162.47, 163.67,
163.94, 164.29. MS (FAB): calcd for MHþ C22H19N2O4: 375.4. Found:
375.2. Anal. Calcd for C22H18N2O4: C, 70.58; H, 4.85; N, 7.48. Found:
C, 70.47; H, 4.79; N, 7.46. IR (KBr): 1628,1605,1505,1259,1167,1142,
1474, 1250, 829, 807 cmꢀ1
.
1026, 831, 805 cmꢀ1
.
4.1.12. 5-Octyloxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-
ylimino]methyl}phenol 2f. Yellow solid; yield 84%. 1H NMR (CDCl3):
4.1.8. 5-Dodecyloxy-2-{[2-(4-methoxyphenyl)benzoxazol-5-ylimino]
methyl}phenol 2b. Yellow solid; 83%. 1H NMR (CDCl3):
0.86 (t,
d
0.88 (t, J¼5.89 Hz, eCH3, 6H), 1.27 (m, eCH2, 28H), 1.77e1.82 (m,
d
eOCH2CH2, 4H), 3.97e4.02 (m, eOCH2, 4H), 6.47e6.49 (m, AreH,
2H), 6.99 (d, J¼8.80 Hz, AreH, 2H), 7.21 (d, J¼8.51 Hz, AreH, 1H),
7.26 (d, J¼8.41 Hz, AreH, 1H), 7.50 (d, J¼8.55 Hz, AreH, 1H), 7.55 (d,
J¼1.80 Hz, AreH, 1H), 8.15 (d, J¼8.76 Hz, AreH, 2H), 8.53 (s, eNCH,
J¼6.69 Hz, eCH3, 3H), 1.24 (m, eCH2, 18H), 1.76e1.79 (m,
eOCH2CH2, 2H), 3.87 (s, eOCH3, 3H), 3.97 (s, eOCH2, 2H),
6.47e6.52 (m, AreH, 2H), 7.01 (d, J¼8.81 Hz, AreH, 2H), 7.23 (s,
AreH, 1H), 7.27 (s, AreH, 1H), 7.51 (d, J¼8.29 Hz, AreH, 1H), 7.56 (s,
AreH, 1H), 8.15 (d, J¼2.05 Hz, AreH, 1H), 8.17 (s, AreH, 1H), 8.53 (s,
1H). 13C NMR (CDCl3):
d 14.43, 14.44, 22.99, 23.02, 26.33, 29.42,
29.49, 29.56, 29.68, 29.72, 29.90, 29.93, 29.97, 30.00, 32.14, 32.25,
68.58, 101.89, 107.88, 110.88, 110.91, 113.32, 115.17, 119.34, 119.49,
129.75, 133.83, 143.62, 146.07,149.63, 161.70, 162.44,163.89, 164.00,
164.66. MS (FAB): calcd for MHþ C40H55N2O4: 627.9. Found: 627.5.
Anal. Calcd for C40H54N2O4: C, 76.64; H, 8.68; N, 4.47. Found: C,
76.56; H, 8.72; N, 4.42. IR (KBr): 3064, 2919, 2851, 1631, 1604, 1502,
eNCH, 1H). 13C NMR (CDCl3):
d 14.12, 22.68, 25.96, 29.05, 29.35,
29.55, 29.58, 29.62, 29.65, 31.90, 55.45, 68.30, 101.53, 107.74, 110.58,
110.65, 112.75, 114.38, 119.01, 119.39, 129.46, 133.65, 143.26, 149.34,
161.36, 162.47, 163.76, 164.29. MS (FAB): calcd for MHþ C33H41N2O4:
529.7. Found: 529.5. Anal. Calcd for C33H40N2O4: C, 74.97; H, 7.63; N,
5.30. Found: C, 74.80; H, 7.65; N, 5.27. IR (KBr): 3607, 2918, 2851,
1474, 1252, 828, 808 cmꢀ1
.
1630, 1607, 1503, 1253, 829, 805 cmꢀ1
.
4.1.13. 5-Hexadecyloxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-
4.1.9. 5-Methoxy-2-{[2-(4-octyloxyphenyl)benzoxazol-5-ylimino]
methyl}phenol 2c. Yellow solid; 88%. 1H NMR (CDCl3):
0.89 (t,
ylimino]methyl}phenol 2h. Yellow solid; yield 88%. 1H NMR (CDCl3):
d
d
0.89 (t, J¼6.29 Hz, eCH3, 6H), 1.27 (m, eCH2, 44H), 1.80e1.83 (m,
J¼6.76 Hz, eCH3, 3H), 1.30e1.34 (m, eCH2, 10H), 1.78e1.83 (m,
eOCH2CH2, 2H), 3.84 (s, eOCH3, 3H), 4.02 (t, J¼6.53 Hz, eOCH2,
2H), 6.49e6.52 (m, AreH, 2H), 7.00 (d, J¼8.82 Hz, AreH, 2H), 7.22
(dd, J¼2.05 Hz, 8.53 Hz, AreH, 1H), 7.29 (d, J¼8.49 Hz, AreH, 1H),
7.52 (d, J¼8.50 Hz, AreH, 1H), 7.57 (d, J¼1.92 Hz, AreH, 1H), 8.16 (d,
eOCH2CH2, 4H), 3.99e4.05 (m, eOCH2, 4H), 6.49 (m, AreH, 2H),
6.98 (m, AreH, 2H), 7.23 (s, AreH, 1H), 7.29 (s, AreH, 1H), 7.52 (d,
J¼7.99 Hz, AreH, 1H), 7.58 (s, AreH, 1H), 8.17 (d, J¼8.52 Hz, AreH,
2H), 8.56 (s, eNCH, 1H). 13C NMR (CDCl3):
d 14.46, 21.56, 23.07,
26.41, 29.52, 29.58, 29.74, 29.77, 29.96, 29.99, 30.03, 30.05, 30.09,
30.76, 32.32, 34.63, 68.71, 68.73, 108.04, 110.95, 111.07, 115.21,
115.32, 119.44, 119.70, 125.89, 129.86, 133.95, 136.29, 143.80, 146.30,
149.80, 161.84, 162.58, 164.00, 164.79. MS (FAB): calcd for MHþ
C48H71N2O4: 740.1. Found: 740.5. Anal. Calcd for C48H70N2O4: C,
78.00; H, 9.55; N, 3.79. Found: C, 77.99; H, 9.62; N, 3.73. IR (KBr):
J¼8.80 Hz, AreH, 2H), 8.55 (s, eNCH, 1H). 13C NMR(CDCl3):
d 14.42,
22.98, 26.34, 29.49, 29.56, 29.67, 32.14, 55.79, 68.63, 101.46, 107.46,
110.92, 110.96, 113.53, 115.22, 119.36, 119.52, 129.78, 133.90, 143.67,
146.09, 149.70, 161.77, 162.48, 164.05, 164.30, 164.72. MS (FAB):
calcd for MHþ C29H33N2O4: 473.6. Found: 473.3. Anal. Calcd for
C33H40N2O4: C, 73.70; H, 6.83; N, 5.93. Found: C, 73.66; H, 6.89; N,
5.91. IR (KBr): 3062, 2929, 2855, 1629, 1601, 1500, 1254, 1172,
3064, 2918, 2850, 1633, 1605, 1505, 1472, 1254, 829 cmꢀ1
.
1136 cmꢀ1
.
4.1.14. Bis[5-dodecyloxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-
ylimino]methyl}phenol] copper (1geCu; n¼12, m¼12). The mixture of
5-dodecyloxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-ylimino]
methyl}phenol (0.1 g, 0.01 mmol) and copper(II) acetate hydrate
(0.015 g, 0.007 mmol) was dissolved in 20 mL of C2H5OH, and the
solution was gently refluxed for 2 h. The solution was cooled and the
solids were collected. The products isolated as gray to green solid
were obtained by recrystallization from CH2Cl2/CH3OH. IR (KBr):
2923, 2852,1612,1501,1469,1252, 835, 812 cmꢀ1. MS (FAB): calcd for
MHþ C88H123N4O8Cu: 1428.5. Found: 1428.6. Anal. Calcd for
C88H122N4O8Cu: C, 74.04; H, 8.61; N, 3.92. Found: C, 73.60; H, 8.72;
N, 3.75.
4.1.10. 5-Methoxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-
ylimino]methyl}phenol 2d. Yellow solid; 80%. 1H NMR (CDCl3):
d
0.86 (t, J¼6.69 Hz, eCH3, 3H), 1.24 (m, eCH2, 18H), 1.76e1.79
(m, eOCH2CH2, 2H), 3.87 (s, eOCH3, 3H), 3.97 (t, J¼6.54 Hz,
eOCH2, 2H), 6.47e6.52 (m, AreH, 2H), 7.01 (d, J¼8.81 Hz, AreH,
2H), 7.23 (s, AreH, 2H), 7.27 (s, AreH, 2H), 7.51 (d, J¼8.29 Hz,
AreH, 2H), 8.15e8.17 (m, AreH, 2H), 8.53 (s, eNCH, 1H). 13C NMR
(CDCl3):
d 14.43, 23.01, 26.34, 29.50, 29.68, 29.72, 29.90, 29.93,
29.97, 29.99, 32.25, 55.77, 68.62, 101.46, 107.44, 110.90, 110.97,
113.53, 115.21, 119.34, 119.53, 129.77, 133.89, 143.67, 146.07,
149.70, 161.73, 162.47, 164.05, 164.30, 164.71. MS (FAB): calcd for
MHþ C33H41N2O4: 529.7. Found: 529.4. Anal. Calcd for
C33H40N2O4: C, 74.97; H, 7.63; N, 5.30. Found: C, 74.80; H, 7.77;
4.1.15. Bis[5-methoxy-2-{[2-(4-methoxyphenyl)benzoxazol-5-
ylimino]methyl}phenol]copper (1aeCu; n¼1, m¼1). Green solid, IR

C.-J. Chen et al. / Tetrahedron 67 (2011) 8120e8130
8129
(KBr): 1611, 1504, 1259, 1228, 1168, 1139, 1025, 829 cmꢀ1. MS (FAB):
calcd for MHþ C44H35N4O8Cu: 811.3. Found: 811.2.
solid, IR (KBr): 2925, 2854, 1606, 1523, 1499, 1469, 1253, 833,
811 cmꢀ1. MS (FAB): calcd for MHþ C88H123N4O8Pd: 1471.4. Found:
1471.2. Anal. Calcd for C88H122N4O8Pd: C, 71.88; H, 8.36; N, 3.81.
Found: C, 71.89; H, 8.51; N, 3.72.
4.1.16. Bis[5-dodecyloxy-2-{[2-(4-methoxyphenyl)benzoxazol-5-
ylimino]methyl}phenol]copper (1beCu; n¼1, m¼12). Green solid, IR
(KBr): 2924, 2853,1610,1502,1468, 1253, 836 cmꢀ1. MS (FAB): calcd
for MHþ C66H79N4O8Cu: 1119.9. Found: 1119.8. Anal. Calcd for
C66H78N4O8Cu: C, 70.85; H, 7.03; N, 5.01. Found: C, 70.39; H, 7.06; N,
4.96.
4.1.26. Bis[5-dodecyloxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-
ylimino]methyl}phenol]zinc (1geZn; n¼12, m¼12). Pale-yellow
solid, IR (KBr): 2922, 2851, 1612, 1500, 1430, 1253, 1222, 834,
804 cmꢀ1. MS (FAB): calcd for MHþ C88H123N4O8Zn: 1430.3. Found:
1430.8. Anal. Calcd for C88H122N4O8Zn: C, 73.95; H, 8.60; N, 3.92.
Found: C, 73.59; H, 8.67; N, 3.97.
4.1.17. Bis[5-methoxy-2-{[2-(4-octyloxyphenyl)benzoxazol-5-
ylimino]methyl}phenol]copper (1ceCu; n¼8, m¼1). Green solid, IR
(KBr): 2925, 2853,1607,1500,1466,1254, 1221, 835 cmꢀ1. MS (FAB):
calcd for MHþ C58H63N4O8Cu: 1007.7. Found: 1007.3. Anal. Calcd for
C58H62N4O8Cu: C, 69.20; H, 6.21; N, 5.57. Found: C, 68.79; H, 6.19; N,
5.41.
4.1.27. Bis[5-dodecyloxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-
ylimino]methyl}phenol]cobalt (1geCo; n¼12, m¼12). Brown solid,
IR (KBr): 2925, 2853, 1606, 1500, 1469, 1423, 1250, 837, 808 cmꢀ1
.
MS (FAB): calcd for MHþ C88H123N4O8Co: 1423.9. Found: 1423.8.
Anal. Calcd for C88H122CoN4O8: C, 74.28; H, 8.64; N, 3.94. Found: C,
74.17; H, 8.75; N, 3.96.
4.1.18. Bis[5-methoxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-
ylimino]methyl}phenol]copper (1deCu; n¼12, m¼1). Green solid, IR
(KBr): 2922, 2852, 1610, 1594, 1499, 1468, 1254, 1221, 836 cmꢀ1. MS
(FAB): calcd for MHþ C66H79N4O8Cu: 1119.9. Found: 1119.8. Anal.
Calcd for C66H78N4O8Cu: C, 70.85; H, 7.03; N, 5.01. Found: C, 70.39;
H, 7.06; N, 4.96.
Acknowledgements
We thank the National Science Council of Taiwan, ROC (NSC98-
2815-C-008-021-M).
4.1.19. Bis[5-butoxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-
ylimino]methyl}phenol]copper (1eeCu; n¼12, m¼4). Green solid, IR
(KBr): 2921, 2852, 1593, 1499, 1471, 1429, 1254, 1222 cmꢀ1. MS
(FAB): calcd for MHþ C72H91N4O8Cu: 1204.1. Found: 1204.5. Anal.
Calcd for C72H90N4O8Cu: C, 71.88; H, 7.54; N, 4.66. Found: C, 71.46;
H, 7.42; N, 4.43.
References and notes
1. (a) Porta, B.; Klamsi, J.; Noveron, J. Curr. Org. Chem. 2008, 12, 1e24; (b) Date, R.
W.; Iglesias, E. F.; Rowe, K. E.; Elliott, J. M.; Bruce, D. W. Dalton Trans. 2003,
1914e1931; (c) Gimenez, R.; Lydon, D. P.; Serrano, J. L. Currr. Opin. Solid State
Mater. Sci. 2002, 6, 527e535; (d) Donnio, B.; Bruce, D. W. Struct. Bonding 1999,
95, 194e242; (e) Hoshino, N. Coord. Chem. Rev. 1998, 77e108; (f) Inorganic
Materials; Bruce, D. W., Ed.; John Wiley: New York, NY, 1997; (g) Bruce, D. R.;
O’Hare, D. Inorganic Materials, 2nd ed.; Wiley: New York, NY, 1996; (h) Serrano,
J. L. Metallomesogens: Synthesis, Properties, and Applications; VCH: Weinheim,
1996; (i) Hudson, S. A.; Maltlis, P. M. Chem. Rev. 1993, 93, 861e885.
2. (a) Chen, C.-J.; Wu, Y.-C.; Sheu, H.-S.; Lee, G.-H.; Lai, C. K. Tetrahedron 2011, 67,
114e124; (b) Liao, C. C.; Wang, C. S.; Shen, H. S.; Lai, C. K. Tetrahedron 2008, 64,
7977e7985; (c) Wang, C. S.; Wang, I. W.; Lai, C. K. Tetrahedron 2006, 62,
9383e9392; (d) Lai, C. K.; Liu, H. C.; Li, F. J.; Cheng, K. L.; Sheu, H. S. Liq. Cryst.
2005, 32, 85e94.
4.1.20. Bis[5-octyloxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-
ylimino]methyl}phenol]copper (1feCu; n¼12, m¼8). Green solid, IR
(KBr): 2926, 2853, 1611, 1500, 1469, 1253, 835, 812 cmꢀ1. MS (FAB):
calcd for MHþ C80H107N4O8Cu: 1316.3. Found: 1316.6. Anal. Calcd
for C80H106N4O8Cu: C, 73.05; H, 8.12; N, 4.26. Found: C, 72.98; H,
8.08; N, 4.17.
3. Gimenez, R.; Oriol, L.; Pinol, M.; Serrano, J. L.; Vinuales, A. I.; Fisher, T.; Stumpe,
J. Helv. Chim. Acta 2006, 89, 304e319.
4.1.21. Bis[5-hexadecyloxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-
5-ylimino]methyl}phenol] copper (1heCu; n¼12, m¼16). Green
solid, IR (KBr): 2921, 2851, 1612, 1501, 1469, 1254 cmꢀ1. MS (FAB):
calcd for MHþ C96H139N4O8Cu: 1539.7. Found: 1539.9. Anal. Calcd
for C96H138N4O8Cu: C, 74.89; H, 9.03; N, 3.64. Found: C, 73.78; H,
9.04; N, 3.54.
4. (a) Xu, Y.; Pang, Y. Dalton Trans. 2011, 40, 1503e1509; (b) Xu, Y.; Pang, Y. Chem.
Commun. 2011, 4070e4072; (c) Kim, T. H.; Kim, D. G.; Lee, M.; Lee, T. S. Tetra-
hedron 2010, 66, 1667e1672; (d) Shavaleev, N. M.; Scopelliti, R.; Gumy, F.;
Bunzli, J. C. G. Inorg. Chem. 2009, 48, 2908e2918; (e) Shavaleev, N. M.; Scopelliti,
R.; Gumy, F.; Bunzli, J. C. G. Inorg. Chem. 2009, 48, 6178e6191; (f) Tian, Y.; Chen,
C. Y.; Yang, C. C.; Young, A. C.; Jang, S. H.; Chen, W. C.; Jen, A. K. Y. Chem. Mater.
2008, 20, 1977e1987; (g) Klare, J. E.; Tulevski, G. S.; Sugo, K.; Picciotto, A. D.;
White, K. A.; Nuckolls, C. J. Am. Chem. Soc. 2003, 125, 6030e6031; (h) Costa, T.
M. H.; Stefani, V.; Gallas, M. R.; Balzaretti, N. M.; Da Jornada, J. A. H. J. Mater.
Chem. 2001, 11, 3377e3381; (i) Ko, C. W.; Tao, Y. T. Chem. Mater. 2001, 13,
2441e2446; (j) Tanaka, K.; Kumagai, T.; Aoki, H.; Deguchi, M.; Iwata, S. J. Org.
Chem. 2001, 66, 7328e7333.
5. (a) Chen, T. R.; Lee, H. P.; Chen, J. D. Inorg. Chem. 2011, 50, 3645e3650; (b) Back,
D. F.; Oliveira, G. M. d; Ballin, M. A.; Corbellini, V. A. Inorg. Chim. Acta 2010, 363,
807e812; (c) Chu, Q.; Medvetz, D. A.; Panzner, M. J.; Yang, P. Dalton Trans. 2010,
39, 5254e5259; (d) Ma1ecki, J. G.; Kruszynski, R.; Jaworska, M.; Lodowski, P.;
Mazurak, Z. J. Organom. Chem. 2008, 693, 1096e1108; (e) Keyes, T. E.; Leane, D.;
Forster, R. J.; Coates, C. G.; McGarvey, J. J.; Nieuwenhuyzen, M. N.; Figgemeier,
E.; Vos, J. G. Inorg. Chem. 2002, 41, 5721e5732; (f) Chen, X.; Femia, F. J.; Babich,
J. W.; Zubieta, J. Inorg. Chim. Acta 2001, 316, 33e40.
4.1.22. Bis[5-octyloxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-
ylimino]methyl}phenol]nickel (1feNi; n¼12, m¼8). Yellow solid, IR
(KBr): 2922, 2852, 1604, 1500, 1468, 1253, 1211, 1135, 836 cmꢀ1. MS
(FAB): calcd for MHþ C80H107N4O8Ni: 1359.1. Found: 1359.7. Anal.
Calcd for C80H106N4NiO8: C, 73.32; H, 8.15; N, 4.28. Found: C, 72.99;
H, 8.30; N, 4.02.
4.1.23. Bis[5-dodecyloxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-
ylimino]methyl}phenol] nickel (1geNi; n¼12, m¼12). Yellow solid,
IR (KBr): 2919, 2851, 1607, 1503, 1472, 1253, 831, 807 cmꢀ1. MS
(FAB): calcd for MHþ C88H123N4O8Ni: 1423.6. Found: 1423.7.
6. (a) Wang, H. C.; Wang, Y. J.; Hu, H. M.; Lee, G. H.; Lai, C. K. Tetrahedron 2008, 64,
4939e4948; (b) Caruso, U.; Panunzi, B.; Roviello, A.; Tingoli, M.; Tuzi, A. Inorg.
Chem. Commun. 2011, 14, 46e48.
7. (a) Bhattacharjee, C. R.; Das, G.; Mondal, P.; Prasad, S. K.; Rao, D. S. S. Inorg.
Chem. Commun. 2011, 14, 606e612; (b) Bhattacharjee, C. R.; Das, G.; Goswami,
P.; Mondal, P.; Prasad, S. K.; Rao, D. S. S. Polyhedron 2011, 30, 1040e1047; (c)
Binnemans, K. J. Mater. Chem. 2009, 19, 448e453; (d) Pucci, D.; Aiello, I. ,;
Bellusci, A.; Crispini, A.; Ghedini, M.; Deda, M. L. Eur. J. Inorg. Chem. 2009,
4274e4281; (e) Pucci, D.; Aiello, I.; Bellusci, A.; Callipari, G.; Crispini, A.; Ghe-
dini, M. Mol. Cryst. Liq. Cryst. 2009, 500, 144e154; (f) Ocak, H.; Bilgin-Eran, B.;
Tschierske, C.; Baumeisterc, U.; Pelzlc, G. J. Mater. Chem. 2009, 19, 6995e7001;
(g) Rezvani, Z.; Ghanea, M. A.; Nejati, K.; Baghaei, S. A. Polyhedron 2009, 28,
2913e2918; (h) Kadkin, O. N.; An, J.; Han, H.; Galyametdino, Y. G. Eur. J. Inorg.
Chem. 2008, 1682e1688; (i) Yelamaggad, C. Y.; Shashikala, I. S.; Tamilenthi, V. P.;
Rao, D. S. S.; Nair, G. G.; Prasad, S. K. J. Mater. Chem. 2008, 18, 2096e2103; (j)
Singh, A. K.; Kumari, S.; Kumar, K. R.; Sridhar, B.; Rao, T. R. Polyhedron 2008, 27,
4.1.24. Bis[5-octyloxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-
ylimino]methyl}phenol]palladium (1fePd; n¼12, m¼8). Light or-
ange solid, IR (KBr): 2922, 2852, 1604, 1500, 1468, 1253, 1211, 1135,
836 cmꢀ1. MS (FAB): calcd for MHþ C80H107N4O8Pd: 1359.1. Found:
1359.7. Anal. Calcd for C80H106N4O8Pd: C, 70.75; H, 7.87; N, 4.13.
Found: C, 71.15; H, 8.13; N, 4.11.
4.1.25. Bis[5-dodecyloxy-2-{[2-(4-dodecyloxyphenyl)benzoxazol-5-
ylimino]methyl}phenol] palladium (1gePd; n¼12, m¼12). Orange

8130
C.-J. Chen et al. / Tetrahedron 67 (2011) 8120e8130
181e186; (k) Aiello, I.; Bellusci, A.; Crispini, A.; Ghedini, M.; Pucci, D.; Spataro, T.
K.; Cahng, C. H.; Tai, C. H. J. Mater. Chem. 1998, 8, 599e602; (u) Lai, C. K.; Lin, R.;
Lu, M. Y.; Kao, K. C. J. Chem. Soc., Dalton Trans. 1998, 1857e1862.
8. (a) Kakegawa, N.; Hoshino, N.; Matsuoka, Y.; Wakabayashi, N.; Nishimura, S.;
Yamagishi, A. Chem. Commun. 2005, 2375e2377; (b) Trazska, S. T.; Hsu, H. F.;
Swager, T. M. J. Am. Chem. Soc. 1999, 121, 4518e4519.
9. (a) Siracusa, M. A.; Salerno, L.; Modica, M. N.; Pittala, V.; Romeo, G.; Amato, M.
E.; Nowak, M.; Bojarski, A. J.; Mereghetti, I.; Cagnotto, A.; Mennini, T. J. Med.
Chem. 2008, 51, 4529e4538; (b) Hart, A.; Karan, C.; Rodrigues, W.; Miller, B. L. J.
Org. Chem. 2001, 66, 881e996; (c) So, Y. H.; Zaleski, J. M.; Murlick, C.; Ellaboudy,
A. Macromolecules 1996, 29, 2783e2796.
Mol. Cryst. Liq. Cryst. 2008, 481, 1e13; (l) Yang, Y.; Driesen, K.; Nockemann, P.;
Hecke, K. V.; Meervelt, L. V.; Binnemans, K. Chem. Mater. 2006, 18, 3698e3704;
(m) Rezvani, Z.; Divband, B.; Abbasi, A. R.; Nejati, K. Polyhedron 2006, 25,
1915e1929; (n) Abe, Y.; Nakabayashi, K.; Matsukawa, N.; Takashima, H.; Iida,
M.; Tanase, T.; Sugibayashi, M.; Mukai, H.; Ohta, K. Inorg. Chim. Acta 2006, 359,
3934e3946; (o) Binnemans, K.; Lodewyckx, K.; Donnio, B.; Guillon, D. Eur. J.
Inorg. Chem. 2005, 1506e1513; (p) Paschke, R.; Liebsch, S.; Tschierske, C.;
Oakley, M. A.; Sinn, E. Inorg. Chem. 2003, 42, 8230e8240; (q) Nejati, K.; Rezvani,
ꢁ
Z. New J. Chem. 2003, 27, 1665e1669; (r) Barbera, J.; Gimenez, R.; Marcos, M.;
Serrano, J. L.; Alonso, P. J.; Martínez, J. I. Chem. Mater. 2003, 15, 958e964; (s) Ku,
S. M.; Wu, C. Y.; Lai, C. K. J. Chem. Soc., Dalton Trans. 2000, 3491e3492; (t) Lai, C.
10. Abou-Zied, O. K.; Jimenez, R.; Thompson, E. H. Z.; Millar, D. P.; Romesberg, F. E. J.
Phys. Chem. A 2002, 106, 3665e3672.