Synthesis of alkynylated photo-luminescent Zn(ii) and Mg(ii) Schiff base complexes

Article abstract of DOI:10.1039/b615380a

A new series of photo-luminescent Zn(ii) and Mg(ii) Schiff base complexes were prepared by treatment of the arylethynyl-substituted salicylaldehydes obtained from the Sonogashira reaction with the metal salt followed by addition of the different diamines.

Full text of DOI:10.1039/b615380a

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Synthesis of alkynylated photo-luminescent Zn(II) and Mg(II) Schiff base
complexes
Hung-Chih Lin, Chiung-Cheng Huang, Chih-Hau Shi, Yong-Hong Liao, Chien-Chih Chen, Ying-Chih Lin* and
Yi-Hong Liu
Received 24th October 2006, Accepted 3rd January 2007
First published as an Advance Article on the web 17th January 2007
DOI: 10.1039/b615380a
A new series of photo-luminescent Zn(II) and Mg(II) Schiff base complexes were prepared by treatment
of the arylethynyl-substituted salicylaldehydes obtained from the Sonogashira reaction with the metal
salt followed by addition of the different diamines. Most square-planar Zn(II) complexes exhibited good
quantum efficiencies. The Mg(II) complexes displayed even higher quantum yields than the
corresponding Zn-complexes. Unsymmetrical Zn(II) Schiff base complexes were also successfully
prepared from organic monoimines obtained as intermediates in the formation of the Mg metal Schiff
base complex. The monoimine can also be prepared from the reaction of salicylaldehydes with excess
diaminoarene. Two crystal structures featuring the zinc atom are reported, one with a rare
four-coordinate square planar geometry and the other with a five-coordinate square pyramidal
geometry.
type ligands to serve as building blocks for cyclic supramolecular
Introduction
structures.12 The free-base salen-linked molecular loops can be
Transition metal complexes with salen-type ligands have been
quantitatively converted to molecular squares by reducing the
extensively studied mainly due to their ability to catalyze an
extremely broad range of chemical transformations, including the
asymmetric ring-opening of epoxides, aziridination, cyclopropa-
flexibility of the ligand via Zn(II) metalation. Alternatively, the
square framework could be obtained by the direct assembly of
square planar complex cis-(PEt3)2Pt(OTf)2 and bis(4-pyridyl)-
nation, epoxidation of olefins and formation of cyclic and linear
functionalized Zn(II)–salen-type ligands. Recently, the application
polycarbonates.1 Moreover, applications in materials science, such
of “pyridine–Zn” coordination in Zn(II)–salphen complexes has
as their nonlinear optical (NLO) properties, have been explored
also been demonstrated as an excellent building block for the
in recent years.2 Nevertheless, application studies on metal–salen
derivatives in materials science remain sparse in the literature,3–5
even if these compounds are known to be photoluminescent
for a long time.6 A recent paper by Che et al. described the
utilization of vapor deposited Pt–salen complexes as efficient
electrophosphorescent dyes in multilayer organic light emitting
diode (OLED) devices with a maximum luminous efficiency of 31
Cd A−1.7 Recent work has suggested that high OLED efficiencies
can be achieved when the phosphorescent chromophore is molec-
ularly dispersed within the composite material. Scherf et al.8 have
designed OLED devices based on novel fluorene-type copolymers
with on-chain Pt–salen units giving promising performances.
However, there are only a few reports of metal–salen complexes in
which one or both aryl rings are alkynylated.4–5,9–12a Gothelf and
his co-workers have recently described the synthesis of thiolated
phenylacetylene linked porphyrin molecules10 using Sonogashira
coupling for the immobilization of chiral Mn–salen complexes on
gold surfaces. Alkynylated Schiff base metal complexes have also
been applied in the macromolecules. The salen moiety was utilized
to establish a simple, general approach to build new, large, shape-
persistent conjugated macrocycles with tunable pore diameters
in the nanometer regime. These macrocycles can bind multiple
metals, forming soluble, luminescent complexes. Moreover, Hupp
and his coworkers have developed a series of bifunctional salen
construction of catalytically active supramolecular assemblies.13a,b
In addition, some unsymmetrical and ethynyl-free metallo(II)–
salphen complexes have been prepared from monoimine.13c,14 Pre-
viously, we have developed an efficient method for the preparation
of a series of alkynylated zinc–salen complexes.15 Introduction of a
pyridyl group as a bridging unit as well as incorporation of ethynyl
and electron-donating groups into the salicylidene moiety of these
complexes enhances the quantum yield of photoluminescence. It is
also known that the Mg(II)–salen-type complex displayed excellent
photoluminescent properties.16 However in the past Mg(II) salen
complexes were mostly synthesized by the reaction of the salen
ligand with highly reactive n-Bu2Mg in THF. We report here that
our one-pot strategy for the synthesis of the Zn(II) Schiff base
complex can be successfully applied for the preparation of Mg(II)
Schiff base complexes. Furthermore, the ethynyl monoimine is
used as a good precursor for the synthesis of unsymmetrical Zn(II)
Schiff base complexes. Photophysical properties of alkynylated
Schiff base complexes of Zn(II) and Mg(II) with different bridging
groups are also reported.
Results and discussion
Synthesis of 5-substituted ethynylsalicylaldehyde
Salicylaldehydes containing alkynyl substituent used in this
study are prepared by the Pd(II)/Cu(II) catalyzed Sonogashira
cross-coupling reaction17 of either 5-bromosalicylaldehyde with
Department of Chemistry, National Taiwan University, Taipei, Taiwan.
E-mail: yclin@ntu.edu.tw; Fax: +(886)-2-23636359
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Synthesis of Zn(II) Schiff base complexes
The synthesis of the Zn(II) Schiff base complex 2a was achieved
by treatment of zinc acetate with substituted salicylaldehyde 1a
in a mixture of MeOH–THF for 30 min at room temperature,
followed by addition of 2,3-diaminopyridine to yield precipitate
which was collected by filtration to produce the product. Orange
complexes 2d and 2e were synthesized at room temperature from
1d and 1e, respectively, using the same method (Scheme 2). The
resulting products were isolated in high yield. In general, two 1H
=
NMR absorptions of non-equivalent imine N CH protons are
observed for these complexes.
To explore the influence of a bridging group on the photo-
physical properties of these salen complexes, various diamines
were used as bridging units. Complexes 3a and 3d were prepared
1
using furazan group as a bridging unit. Both H NMR spectra
of 3a and 3d are expected to display one resonance for the imine
protons due to the symmetrical structure of the bridge. For 3a,
imine protons indeed give one singlet resonance at d 9.12 in d8-
THF in the 1H NMR spectrum. Complex 3d is not soluble in THF,
therefore, d5-pyridine is used for NMR spectroscopy. Interestingly,
two resonances of the imine protons of 3d with a ratio of 1.8 : 1
are observed at d 9.58 and 9.45 at 298 K. At 328 K, the ratio
of the two imine protons changes to 1.3 : 1 indicating that in
d5-pyridine the four-coordinate square planar Zn(II) complex and
the five-coordinate complex with pyridine at the apical position
are probably in equilibrium.18
Single crystals of the pyridine adduct of complex 3d suitable
for single-crystal X-ray diffraction analysis were obtained by
recrystallization from a mixture of THF–pyridine–MeOH. Five-
coordinated Zn(salen)(L) complexes are known to form single
crystals relatively easily.12b,15,18 Pyridine was thus added to induce
the formation of single crystals of the adduct of 3d. The structure
of this adduct was determined by X-ray diffraction analysis. An
ORTEP24b drawing is shown in Fig. 1 and selected bond distances
and angles are listed in Table 1. The molecular structure of the
pyridine adduct of 3d highlights the zinc atom in a five-coordinate
square pyramidal geometry. The salophen ligand occupies the
basal plane while the pyridine ligand occupies the apical position.
Scheme 1
ethynylarene (pathway A of Scheme 1) or haloarene with 5-
ethynylsalicylaldehyde15 (pathway B). We prepared seven alkyny-
lated salicylaldehydes 1a–1g shown in Scheme 1. Using the
standard conditions for Sonogashira coupling, compounds 1a,
1b and 1c were synthesized from 5-bromosalicylaldehyde with
1-dodecyne, 1-ethynyl-4-pentylbenzene and ethynylferrocene, re-
spectively, via pathway A. Synthetic pathway B utilizes the
reaction of 5-ethynylsalicylaldehyde with haloarene such as 1-
alkoxyl-4-iodobenzene, 1,2,3,4,5-pentafluoro-6-iodobenzene and
2-iodothiophene to give 1d–1g by the same catalyst. These
salicylaldehydes readily purified by silica gel packed column
chromatography were isolated in 46–97% yields. Compounds 1a–
1g are stable towards light and air at ambient temperature. In
the 1H NMR spectra of these salicylaldehydes, resonances of the
hydroxyl proton are observed at around d 11.0 and resonances near
d 9.9 are assigned to the aldehyde group. In 13C NMR spectra,
resonances of carbonyl carbon are located at around d 196 and
resonances of two alkynyl carbons are found in the range of d
85–90. Other spectroscopic data are consistent with the proposed
structure.
˚
The Zn–N(5) distance (2.075(3) A) of the pyridine ligand, similar
Scheme 2
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Fig. 1 An ORTEP drawing of complex 3d·pyridine (30% probability ellipsoids).
◦
◦
˚
˚
Table 2 Selected bond distances (A) and angles ( ) of 4e
Table 1 Selected bond distances (A) and angles ( ) of 3d·pyridine
Zn(1)–O(1)
Zn(1)–N(1)
1.963(3)
2.135(3)
Zn(1)–O(2)
Zn(1)–N(2)
1.970(3)
2.124(3)
Zn(1)–O(1)
Zn(1)–N(1)
1.898(3)
1.953(4)
Zn(1)–O(2)
Zn(1)–N(2)
1.889(3)
1.954(4)
Zn(1)–N(5)
2.075(3)
O(1)–Zn(1)–O(2)
O(1)–Zn(1)–N(1)
O(1)–Zn(1)–N(2)
87.87(15)
92.79(16)
178.04(17)
O(2)–Zn(1)–N(1)
O(2)–Zn(1)–N(2)
N(1)–Zn(1)–N(2)
178.84(16)
93.24(16)
86.08(16)
O(1)–Zn(1)–O(2)
O(2)–Zn(1)–N(5)
O(2)–Zn(1)–N(2)
O(1)–Zn(1)–N(1)
N(5)–Zn(1)–N(1)
96.73(12)
101.87(13)
85.44(12)
86.40(12)
111.46(12)
O(1)–Zn(1)–N(5)
O(1)–Zn(1)–N(2)
N(1)–Zn(1)–N(2)
O(2)–Zn(1)–N(1)
N(2)–Zn(1)–N(1)
99.65(12)
158.98(12)
100.35(12)
145.53(13)
80.33(12)
d 8.88 and two thiophene protons at d 7.62 and 7.17. Interestingly
a broad singlet resonance at d 5.19 is observed and is assigned
to the amine proton. In the FAB mass spectrum, the parent peak
is observed at m/z 565.2. According to these spectroscopic data,
4eꢀ is neither an organic monoimine nor a complete Schiff base
Zn(II) complex. Although the structure of 4eꢀ was not completely
identified, the subsequent reaction of 4eꢀ with one equivalent of 1e
giving complex 4e seems to indicate that complex 4eꢀ could be a
three-coordinated complex serving as a precursor for forming the
complete Schiff base metal complex 4e.
to that observed in other complexes,12b,15,18 is slightly shorter than
˚
other Zn–N(imine) (2.135(3), 2.124(3) A) distances.
Preparation of complex 4e with the thiophene bridging unit
was achieved by a similar one-pot reaction. Namely, compound
1e, 3,4-diaminothiophene dihydrochloride and Zn(OAc)2 were
reacted in a mixed solvent of THF and MeOH at 65 ◦C for
1
3 days to yield 4e. In the H NMR spectrum of 4e, resonance
of the imine proton is located at d 9.59, shifted slightly downfield
relative to that of complex 2e. The FAB mass spectrum of 3e
shows the parent peak at m/z 953.5 (M + 1). Single crystals of
complex 4e suitable for X-ray diffraction were obtained by slow
evaporation of the solvent from a mixture of THF–EtOH, and
the structure of 4e was determined. An ORTEP presentation is
shown in Fig. 2 and selected bond distances and angles are listed
in Table 2. The molecular structure of 4e shows the zinc atom
in a rare four-coordinate square planar geometry with no solvent
molecule at the apical position. The distances of Zn–N (imine)
Recently, Reddinger and Reynolds19 also utilized 3,4-
diaminothiophene as a bridging unit to synthesize salicylidene-
based Co(II), Cu(II), Ni(II) and Zn(II) complexes. They opted to
prepare these metal complexes by the direct route of first com-
bining the salicylaldehyde and metal acetate and then condensing
the resulting species with the corresponding diamine giving higher
yields in comparison with the conventional step-by-step method.
Similarly, we modified our previous one-pot methodology slightly
by prolonging the reaction time for 3 days and raising temperature
to 80 ◦C to give the thiophene-bridged complex 4e with 92% yield.
Additionally, diaminomaleonitrile, a nonaromatic diamine con-
sisting of electron-withdrawing CN groups was also introduced
into the Zn(II) Schiff base complex to give 5a as a dark blue powder.
In the 1H NMR spectrum of 5a in d8-THF, the resonance at d 8.62
is assigned to the characteristic imine proton, which shifts slightly
upfield compared with those of the Zn(II) Schiff base with aromatic
˚
(1.953(4), 1.954(4) A) in 4e are significantly shorter than that in
˚
the five-coordinate complex 3d·pyridine (2.135(3), 2.124(3) A).
˚
Additionally, the distances of Zn–O (1.889(3), 1.898(3) A) in 4e
˚
are also shorter than those (1.963(3), 1.970(3) A) in 3d·pyridine.
If the same reaction was carried out at room temperature for
1 day, a green solid 4eꢀ was obtained. The 1H NMR spectrum of
4eꢀ in d6-DMSO displays characteristic imine proton resonance at
Fig. 2 An ORTEP drawing of complex 4e (30% probability ellipsoids).
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bridging units. However, only very weak fluorescence is observed
for 5a either in solution or in solid state under UV irradiation.
resonances of imine protons are located at d 9.51 and 8.84. The
parent peak found in the FAB mass spectrum is at m/z 552.1 (M+
+ 1). Following the same procedures, monoimines 6b and 6g and
their corresponding Mg complexes 7b and 7g were also prepared.
Recently,16 the 1,2-cyclohexane-diamino-(S,S)-N,Nꢀꢀ-bis(3,5-di-
tert-butylsalicyl-aldehyde)Mg(II), an excellent photoluminescent
compound, was synthesized by reaction of the salen ligand with
highly reactive n-Bu2Mg, instead of Mg(OAc)2. Our one-pot
preparation provides a possible alternative for such a synthesis.
Synthesis of Mg(II) Schiff base complexes
In order to investigate if our synthetic strategy for the preparation
of Zn(II) Schiff base complexes could be applied to the synthesis of
Mg(II) Schiff base complex, the direct and one-pot methodology is
used for the preparation of Mg(II) analogues. Magnesium acetate
was first treated with the alkynyl-substituted salicylaldehyde 1a
in a mixture of THF–methanol for 30 min at room temperature.
2,3-Diaminopyridine was added to the resulting solution, and the
mixture was heated to 65 ◦C for 24 h. After removal of the solvent,
yellow organic monoimine 6a in 20% yield was first extracted by
CH2Cl2. From the remaining residue, dark brown Mg(II) Schiff
base complex 7a in 62% yield was obtained by THF extraction.
Subsequent treatment of monoimine 6a with 1 equivalent of 1a
and magnesium acetate at refluxing temperature for 1 day gave the
Schiff base complex 7a. Hence, monoimine 6a could serve as an
intermediate of this reaction (Scheme 3).
Synthesis of unsymmetrical Zn(II) Schiff base complexes
Organic monoimines are considered to be good precursors for the
synthesis of unsymmetrical Zn(II) Schiff base complexes. As 6a
containing an alkylethynyl group is significantly more soluble than
the corresponding monoimine, we use 6a as the starting material
in order to increase the solubility of the subsequent unsymmetrical
Zn(II) Schiff base complex. Compound 6a could also be synthe-
sized more efficiently20 by the treatment of compound 1a with
excess 2,3-diaminopyridine in THF–MeOH solution for 18 h in
53% yield.
1
In the H NMR spectrum of 6a, the resonance at d 12.65 is
assigned to the hydroxyl proton. The resonance of the imine proton
appears at d 8.56. Additionally, the singlet at d 4.77 is assigned to
the amine proton. In the FAB mass spectrum, the parent peak is
observed at m/z 378.3 (M+ + 1). The aforementioned spectroscopic
data reveal the structure of 6a to be a monoimine. In the 1H NMR
spectrum of 7a, due to the unsymmetrical pyridine bridge, two
The unsymmetrical Zn(II) Schiff base complex 8a was synthe-
sized by the reaction of compound 6a with 1 equivalent of 1f
and zinc acetate in MeOH–THF at room temperature (Scheme 4).
The resulting yellow precipitate was isolated as complex 8a in
62% yield. Similarly, complexes 8b and 8c each containing one
ferrocenyl moiety could be prepared by the same procedure. In
Scheme 3
Scheme 4
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1
=
general, two H absorptions of non-equivalent imine N CH pro-
keeping the absorbance at around 0.2 to avoid the interference of
reabsorption.
tons are observed, and triplet resonances at around d 2.3 (3JH–H
6 Hz) are assigned to the CH2 proton next to the alkynyl group
(C≡CCH2) in the H NMR spectra of 8a, 8b and 8c. Although
≈
In general, introduction of the pyridyl group as a bridging unit
or incorporation of ethynyl groups into the salicylidene moiety
of these complexes enhance the luminescence of Schiff base
Zn(II) complexes. These structural modifications could effect
a larger p charge delocalization over the salicylidene and the
aromatic bridging rings than that reported previously in regular
Zn(salophen) complexes.15 It seems to reveal that the rigidity of the
structure and the dipole moment of the complex possibly increase.
In addition, both absorption and emission peaks of the alkynylated
Zn(II) complexes are expected to red shifted in comparison with
that of the Zn(salophen) complex which is also observed in our
experiments.
1
the alkyl chain (C10H21) is incorporated into the Schiff base
moiety, unfortunately, all these unsymmetrical Zn(II) Schiff base
complexes exhibit poor solubility, thus no 13C NMR spectrum is
obtained. Recently, unsymmetrical and ethynyl-free Zn(II) salen
complexes have also been prepared from monoimine by a similar
preparation method.13c,14 In addition, a few other unsymmetrical
metal salen complexes of Co(II), Cu(II), Mn(II), Ni(II) and Pd(II)
have been reported.14
Photophysical properties of Schiff base complexes
The photophysical data of 2d and 2e show almost the same
absorption and emission peaks at around 442 and 550 nm,
respectively. In addition, the quantum yields are both around
0.30. This indicates that variation of the alkoxyl chains in the
ethynyl substituents does not seem to influence the absorption
and emission properties very much.
Replacement of the pyridyl bridge by the thiophene bridge in
the Schiff base resulted in significant enhancement of the emission
quantum yield of zinc salen complexes. Therefore complex 4e
shows higher quantum efficiency (0.72). The absorption and
emission peaks of 4e are slightly blue shifted contrasting with
that of complexes 2d and 2e which have pyridine bridging units.
Compared with ethynyl-free analogues reported in the literature,19
the absorption peaks of 4e are red shifted by 25 nm. The presence
of two electron-withdrawing C≡N groups in 5a results in a
bathochromic shift in absorption spectra relative to other Zn Schiff
base complexes.21 However, the fluorescence is almost completely
quenched in the presence of a C≡N group.
Table 3 summarizes the photophysical data of these Schiff base
metal complexes, the emission spectra of which are obtained by
excitation at the longest wavelength of their absorption peak. Fig. 3
gives typical examples of emission spectra of some Zn(II) Schiff
base complexes. The wavelength at the intersection point of the
absorption spectra between the sample and the reference is taken as
the excitation wavelength in determining the quantum yield while
Table 3 The photophysical properties of Zn(II) Schiff base complexes in
THF
Absorption kmax/ nm
Emission
kmax/nm
Quantum
a
Compounds
(10−3e/ M−1cm−1
)
yield Uem
2a
2c
2d
2e
3a
3d
4e
5a
7a
7b
7g
8a
8b
8c
438 (20.32)
458 (18.94)
444 (18.94)
441 (19.39)
466 (6.91)
453 (18.45)
431 (18.71)
362 (25.18), 599 (16.62)
436 (26.34)
441 (25.71)
435 (28.91)
431 (19.07)
441 (22.23)
444 (21.12)
535.8
—
0.45
—
b
551.6
548.4
567.2
551.8
525.2
664.0c
524.4
532.8
534.8
532.4
534.4
536.4
0.28
0.33
0.06
0.096
0.72
—
0.81
0.88
0.85
0.157
0.016
—
In 2a, 3a and 5a, the side chain of the salen ligand is abridged by
eliminating the aromatic groups and keeping only the simple alkyl
chains (C10H21). Although the absorption spectra of 2a, 2d and
2e are similar, the emission spectra of 2a are slightly blue shifted
relative to that of two others. Moreover, enhanced fluorescence
intensity with quantum yield of 0.45 for 2a is also observed.
However, both absorption and emission peaks of 3a is observed to
red shift slightly comparing with that of 3d, and the quantum yield
of 3a (0.096) was found to be slightly larger than that of 3d (0.06).
Comparison of the photophysical data of 2a, 3a and 5a shows
that use of the maleonitrile bridging unit results in significant
red shift in both absorption and emission spectra possibly due
to additional electron-withdrawing groups (C≡N). Complex 2a,
having a pyridine bridging unit, exhibits higher quantum efficiency
than 3a and 5a.
a Reference to [RuII(bipy)3]Cl2. b No emission. c kex = 599 nm.
It would be interesting to see if the photophysical character
of these complexes could be affected by the asymmetry of
substituents on the Schiff base. Complexes 8a, 8b and 8c were
prepared for this purpose. For the unsymmetrical complexes 8a,
8b and 8c, both the absorption and emission peaks are almost
the same as those of complex 2a, which has two C10H21 alkyl
chains. Upon replacing one electron-donating alkyl group by an
electron-withdrawing C6F5 group or a ferrocenyl group, complexes
8a, 8b and 8c exhibit lower quantum yield. The emission of
complex 8c is completely quenched even though the ferrocenyl
group is far away from the pyridyl group. Complex 2c, which has
a ferrocenyl group as a substituent unit, has an absorption peak
Fig. 3 The emission spectra of Zn(II) and Mg(II) Schiff base complexes
in THF.
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at 548 nm. However, no emission can be observed for 2c due to
the incorporation of the ferrocenyl group. At this moment these
results seem to indicate that there are only small photophysical
differences between symmetrical and unsymmetrical complexes.
However, in our system the dissimilarities in the substituents are
far away from the chromophore. If the asymmetry was closer to
the chromophore, the photophysical properties could be affected
more significantly.
alkyl group by an electron-withdrawing group or a ferrocenyl
group resulted in lower quantum yields.
Experimental
General procedures
All manipulations were performed under nitrogen using vacuum
line, dry box, and standard Schlenk techniques. CH2Cl2 was
distilled from CaH2 and diethyl ether and THF from Na–ketyl.
All other solvents and reagents were of reagent grade and were
used without further purification. NMR spectra were recorded
on Bruker AC-300, AVANCE-400 and DMX-500SB FT-NMR
spectrometers at room temperature (unless stated otherwise) and
were reported in units of d with residual protons in the solvent as
standard (CDCl3, d 7.24; d6-methyl sulfoxide, d 2.49; d8-THF, d
3.58, 1.73). EI and FAB mass spectra (Zn = 64, Mg = 24) were
recorded on a VG70-250S mass spectrometer and JEOL SX-102A
spectrometers, respectively. Absorption spectra were obtained
using a HP8453, Hewlett-Packard UV-visible spectrophotometer.
Emission spectra were taken using a Hitachi F-4500 luminescence
spectrometer. Luminescence quantum yield (Uem) were calculated
relative to [RuII(bipy)3]Cl2 in air-equilibrated aqueous solution
(Uem = 0.028).22 Elemental analyses were carried on a Perkin-
Elmer 2400 CHN elemental analyzer. Compound 1b was prepared
by method described previously.15
Mg(II) Schiff base complexes. Table 3 summarizes the photo-
physical data for magnesium complexes 7a, 7b and 7g, recorded
in THF. Electronic absorption spectra of these Mg complexes in
THF solution exhibit absorption bands at around 430–440 nm,
which are slightly blue shifted from that of the corresponding
Zn complexes. This blue shifted phenomenon is also observed
in the emission spectra (see Fig. 3). The spectroscopic data of
these complexes also show that changing the substituted group
of the salen ligand in the Mg system does not seem to influence
the absorption or emission properties. General enhancement of
the quantum yield is observed for Mg complexes relative to that
of the corresponding Zn system. Moreover, in comparison with
the ethynyl-free analogue reported in the literature, a similar red
shifting tendency (ca. 65–95 nm) in the emission spectra is ob-
served, possibly due to the elongation of the conjugated backbone
and the presence of the aromatic bridging unit. This phenomenon
is consistent with that observed in the Zn(II) Schiff base system.
As for the quantum yields, Mg(II) Schiff base complexes with
ethynyl substituents show higher quantum efficiency than the
corresponding ethynyl-free analogues.16 Obviously, the Mg metal
Schiff base complexes show much better fluorescence intensity
than the corresponding Zn analogues.
Synthesis of 5-dodec-1-ynyl-2-hydroxy-benzaldehyde (1a). Path-
way A. 30 mL of mixed solvent (THF–Et3N 15 mL : 15 mL)
was added to a mixture of 1-dodecyne (1.61 g, 9.68 mmol), 5-
bromosalicylaldehyde (1.5 g, 7.46 mmol), Pd(PPh3)2Cl2 (261 mg,
0.37 mol) and CuI (15 mg, 0.08 mmol) in a 50 mL flask. The
mixture was heated to 80 ◦C overnight. The ammonium salt
formed during the reaction was filtered off, and the amine solution
was dried under vacuum. The residue was eluted with hexanes–
dichloromethane (9 : 1) as eluent on a silica gel packed column.
The second band was collected. Removal of the solvent afforded
Conclusion
A series of Zn Schiff base complexes bearing alkynyl or alkyl
groups and various bridging units could be readily prepared. The
methodology used for the synthesis of these complexes is simple
and efficient. The crystal structures of 3d and 4e feature the zinc
atom in a five-coordinate square pyramidal geometry and a four-
coordinate square planar geometry, respectively. The variation
of alkoxyl chains does not seem to influence the absorption or
emission properties of metal Schiff base complexes. With different
substituents and bridging units, these Zn(II) Schiff base complexes
display multiform photophysical properties. Use of maleonitrile
as a bridging unit quenches the quantum efficiency of square-
planar Zn(II) Schiff base complexes. The synthetic methodology
used for the Zn complexes could be used in the preparation of
Mg(II) Schiff base derivatives. The organic monoimine 6 was
unexpectedly obtained as an intermediate in the formation of
the metal Schiff base complexes. The electronic absorption and
emission peaks of Mg(II) complexes are slightly blue shifted from
those of Zn complexes. Moreover, the general enhancement of
quantum yield is observed for Mg complexes relative to the
corresponding Zn system. Additionally, the unsymmetrical Zn(II)
Schiff base complexes 8 can be successfully synthesized from the
organic monoimine. Both absorption and emission peaks of these
complexes are found to be slightly blue shifted in comparison with
those of the symmetrical Zn(II) system. The photophysical data of
these complexes reveal that replacement of the electron-donating
1
a brown liquid identified as 1a (2.08 g, 97% yield). H NMR
(CDCl3): d 11.00 (s, 1H, OH), 9.82 (s, 1H, CHO), 7.58 (d, 1H,
ArH, 4JH–H = 2.1 Hz), 7.51 (dd, 1H, ArH, 3JH–H = 8.6 Hz, 4JH–H
=
2.1 Hz), 6.89 (d, 1H, ArH, 3JH–H = 8.7 Hz), 2.36 (t, 2H, C≡CCH2,
3JH–H = 7.1 Hz), 1.61–1.54 (m, 2H, CH2), 1.44–1.38 (m, 2H, CH2),
1.25 (s, 12H, CH2), 0.86 (t, 3H, CH3, 3JH–H = 7.0 Hz). 13C NMR
(CDCl3): d 196.1 (CHO), 160.7, 139.9, 136.6, 120.3, 117.8, 116.0,
89.9 (C≡C), 78.7 (C≡C), 31.8 (C≡CCH2), 29.6, 29.5, 29.3, 29.1,
28.9, 28.6, 22.7, 19.3 (CH2), 14.1 (CH3). MS (FAB): m/z 287.2
(M+ + 1). Anal. Calcd for C19H26O2: C, 79.68; H, 9.15. Found: C,
79.51; H, 9.18%.
Compound 1c was prepared as an orange solid via the pathway
1
A in 63% yield. H NMR (CDCl3): d 11.06 (s, 1H, OH), 9.87
4
(s, 1H, CHO), 7.69 (d, 1H, ArH, JH–H = 2.1 Hz), 7.61 (dd, 1H,
ArH, 3JH–H = 8.6 Hz, 4JH–H = 2.1 Hz), 6.95 (d, 1H, ArH, 3JH–H
=
8.6 Hz), 4.48–4.47 (m, 2H, CpFe), 4.24–4.22 (m, 7H, CpFe). 13C
NMR (CDCl3): d 196.1 (CHO), 161.0, 139.7, 136.5, 120.5, 118.0,
116.0, 87.9 (C≡C), 83.8 (C≡C), 71.4 (CpFe), 70.0 (CpFe), 68.9
(CpFe), 64.9 (CpFe). MS (FAB): m/z 330.0 (M+). Anal. Calcd for
C19H15FeO2: C, 68.91; H, 4.57. Found: C, 69.12; H, 4.51%.
Synthesis of 5-(4-hexyloxy-phenylethynyl)-2-hydroxy-benzal-
dehyde (1d). Pathway B. 30 mL of a mixed solvent (THF–Et3N
786 | Dalton Trans., 2007, 781–791
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©

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15 mL : 15 mL) were added to a 50 mL flask containing 5-ethynyl-
2-hydroxy-benzaldehyde (650 mg, 4.45 mmol), 1-hexyloxy-4-iodo-
benzene (1.42 g, 4.67 mmol), Pd(PPh3)2Cl2 (64 mg, 0.09 mmol) a◦nd
CuI (20 mg, 0.10 mmol). The mixture was then heated to 80 C
overnight. The resulting ammonium salt was filtered off, and the
amine solution was dried under vacuum. The residue was eluted
with hexanes–EA (9 : 1) as the eluent on a silica gel packed column.
The first band identified as product was collected. Removal of
solvent afforded white powder, and the product was identified as
Diaminopyridine (143 mg, 1.308 mmol) was added to the resulting
solution, and the mixture was stirred overnight. Then the solvent
was removed by vacuum. The residue was washed with methanol
and the precipitate was collected by filtration. The yellow-green
product◦was identified as 2a (530 mg, 86% yield). Melting point of
1
=
2a: 224 C (decomp.). H NMR (d8-THF): d 9.55 (s, 1H, N CH),
3
=
8.95 (s, 1H, N CH), 8.35 (d, 1H, PyrH, JH–H = 4.4 Hz), 8.18 (d,
1H, PyrH, 3JH–H = 7.2 Hz), 7.43 (d, 1H, ArH, 4JH–H = 2.3 Hz), 7.36
(d, 1H, ArH, 4JH–H = 2.3 Hz), 7.34–7.31 (m, 1H, ArH), 7.23–7.19
(m, 2H, ArH), 6.74 (s, 1H, ArH), 6.71 (s, 1H, ArH), 2.38–2.35
(m, 4H, C≡CCH2), 1.59–1.55 (m, 4H, CH2), 1.48 (s, 4H, CH2),
1.34–1.31 (m, 24H, CH2), 0.91–0.87 (m, 6H, CH3). 13C NMR
1
1d (850 mg, 60%). H NMR (CDCl3): d 11.06 (s, 1H, OH), 9.87
4
(s, 1H, CHO), 7.71 (d, 1H, ArH, JH–H = 2.1 Hz), 7.63 (dd, 1H,
ArH, 3JH–H = 8.6 Hz, 4JH–H = 2.1 Hz), 7.42 (d, 2H, ArH, 3JH–H
=
3
=
=
8.9 Hz), 6.96 (d, 1H, ArH, JH–H = 8.6 Hz), 6.85 (d, 2H, ArH,
(d8-THF): d 175.4 (Ph), 174.6 (Ph), 164.0 (C N), 163.6 (C N),
151.3, 147.3, 141.0, 140.1, 138.9, 138.4, 135.6 125.3, 125.2, 124.5,
123.4, 120.2, 119.9, 109.9, 109.7, 87.2 (C≡C), 87.1 (C≡C), 81.7
(C≡C), 33.0 (C≡CCH2), 30.8, 30.5, 30.4, 30.3, 30.0, 27.3, 23.7,
3
3JH–H = 8.9 Hz), 3.95 (t, 2H, OCH2, JH–H = 6.6 Hz), 1.79–1.75
(m, 2H, CH2), 1.42 (m, 2H, CH2), 1.35–1.30 (m, 4H, CH2), 0.89
(m, 3H, CH3). 13C NMR (CDCl3): d 196.2 (CHO), 161.1, 159.2,
139.7, 136.6, 132.9, 120.4, 118.0, 115.6, 114.5, 88.9 (C≡C), 86.1
(C≡C), 68.0 (OCH2), 31.6, 29.1, 25.7, 22.6 (CH2), 14.1 (CH3). MS
(FAB): m/z 322.1 (M+). Anal. Calcd for C21H22O3: C, 78.23; H,
6.88. Found: C, 78.31; H, 6.88%.
20.2 (CH2), 14.6 (CH3). IR (cm−1 KBr): 2959, 2923, 2852 m(N C–
=
+
=
H), 2223 m(C≡C), 1616 m(C N). MS (FAB): m/z 708.4 (M + 1).
Anal. Calcd for C43H53N3O2Zn·1.5H2O: C, 70.14; H, 7.67; N, 5.71.
Found: C, 70.33; H, 7.44; N, 5.98%.
Synthesis of 5-(4-dodecyloxy-phenylethynyl)-2-hydroxy-benzal-
dehyde (1e). Compound 1e (yellow solid) was prepared via the
pathway B in 46% yield. 1H NMR (CDCl3): d 11.07 (s, 1H, OH),
9.87 (s, 1H, CHO), 7.71 (d, 1H, ArH, 4JH–H = 2.1 Hz), 7.63 (dd, 1H,
Synthesis of complex 2c. Complex 2c (orange solid, 94% yield)
was prepared using the same synthetic procedure as that for
1
=
complex 2a. H NMR (d8-THF): d 9.61 (s, 1H, N CH), 9.01
3
=
(s, 1H, N CH), 8.38 (d, 1H, PyrH, JH–H = 4.4 Hz), 8.22 (d, 1H,
ArH, 3JH–H = 8.6 Hz, 4JH–H = 2.1 Hz), 7.41 (d, 2H, ArH, 3JH–H
=
PyrH, 3JH–H = 8.4 Hz), 7.57 (s, 1H, ArH), 7.49 (s, 1H, ArH), 7.37–
7.29 (m, 3H, ArH), 6.78 (d, 2H, ArH, 3JH–H = 8.8 Hz), 4.44–4.42
(m, 4H, CpFe), 4.21–4.20 (m, 14, CpFe). MS (FAB): m/z 796.1
(M+ + 1). Anal. Calcd for C43H31Fe2N3O2Zn·1.5H2O: C, 62.54; H,
4.15; N, 5.09. Found: C, 62.87; H, 4.01; N, 5.37%.
3
8.6 Hz), 6.96 (d, 1H, ArH, JH–H = 8.6 Hz), 6.85 (d, 2H, ArH,
3
3JH–H = 8.6 Hz), 3.95 (t, 2H, OCH2, JH–H = 6.6 Hz), 1.80–1.73
(m, 2H, CH2), 1.45–1.40 (m, 2H, CH2), 1.24 (s, 16H, CH2), 0.86
(t, 3H, CH3, 3JH–H = 7.1 Hz). 13C NMR (CDCl3): d 196.1 (CHO),
161.1, 159.3, 139.7, 136.6, 132.9, 120.5, 118.0, 115.6, 114.6, 114.5,
88.9 (C≡C), 86.1 (C≡C), 68.1 (OCH2), 31.9, 29.6, 29.5, 29.3, 29.2,
25.9, 22.7 (CH2), 14.1 (CH3). MS (FAB): m/z 406.2 (M+). Anal.
Calcd for C27H34O3: C, 79.77; H, 8.43. Found: C, 79.86; H, 8.48%.
Synthesis of complex 2d. Complex 2d (yellow-orange solid,
83% yield) was prepared using the same synthetic◦procedure as
1
that for complex 2a. Melting point of 2d: >350 C. H NMR
=
=
(d8-THF): d 9.57 (s, 1H, N CH), 8.98 (s, 1H, N CH), 8.37 (dd,
1H, PyrH, 3JH–H = 4.6 Hz, 4JH–H = 1.5 Hz), 8.21 (dd, 1H, PyrH,
3JH–H = 8.1 Hz, 4JH–H = 1.5 Hz), 7.58 (d, 1H, ArH, 4JH–H = 2.3 Hz),
7.50 (d, 1H, ArH, 4JH–H = 2.3 Hz), 7.38–7.31 (m, 7H, ArH), 6.87
Synthesis of2-hydroxy-5-((perfluorophenyl)ethynyl)benzaldehyde
(1f). Compound 1f (white solid) was prepared via pathway B in
1
48% yield. Spectroscopic data of 1f: H NMR (CDCl3): d 11.21
(s, 1 H, OH), 9.90 (s, 1 H, CHO), 7.81 (s, 1 H, Ph), 7.69 (d, 1H,
3
(d, 4H, ArH, JH–H = 8.8 Hz), 6.79 (s, 1H, ArH), 6.77 (s, 1H,
Ph, 3JH–H = 8.7 Hz), 7.01 (d, 1H, Ph, 3JH–H = 8.7 Hz). 13C NMR
3
ArH), 3.98 (t, 4H, OCH2, JH–H = 6.4 Hz), 1.77 (m, 4H, CH2),
=
(CDCl3): 196.9 (C O), 162.4, 140.0, 137.4, 120.5, 118.5, 114.4,
1.49 (m, 4H, CH2), 1.39–1.35 (m, 8H, CH2), 0.94 − 0.90 (m,
99.7 (C≡C), 72.8 (C≡C). MS (EI): m/z 312.0 (M+). Anal. Calcd
13
=
=
6H, CH3). C NMR (d8-THF): d 164.4 (C N), 163.8 (C N),
151.5, 147.4, 141.1, 140.2, 138.7, 138.2, 133.4, 133.3, 125.5, 125.4,
124.5, 123.5, 120.2, 117.5, 115.5, 89.4 (C≡C), 89.3 (C≡C), 87.6
(C≡C), 87.5 (C≡C), 69.0 (OCH2), 32.7, 30.3, 28.1, 23.6 (CH2),
for C15H5F5O2: C, 57.71; H, 1.61. Found: C, 57.65; H, 1.59%.
Synthesis of 5-thiophen-2-ylethynylsalicylaldehyde (1g). Com-
pound 1g (yellow solid) was prepared via the pathway B in 49%
yield. Spectroscopic data of 1g: 1H NMR (300 MHz, d6-acetone):
14.4 (CH3). IR (cm−1 KBr): 2944 (sh), 2927, 2873 m(N C–H),
=
+
d 11.12 (s, 1 H, OH), 10.08 (s, 1 H, CHO), 7.98 (d, 1 H, Ph, 4JH–H
=
=
2206 m(C≡C), 1616 m(C N). MS (FAB): m/z 780.3 (M + 1).
2.1 Hz), 7.73 (dd, 1 H, Ph, 3JH–H = 8.6 Hz, 4JH–H = 2.1 Hz), 7.55
Anal. Calcd for C47H45N3O4Zn·1.5H2O: C, 69.84; H, 5.99; N, 5.20.
3
4
Found: C, 70.20; H, 5.74; N, 5.38%.
(dd, 1 H, thiophene, JH–H = 3.9 Hz, JH–H = 0.9 Hz), 7.34 (dd,
3
4
1 H, thiophene, JH–H = 2.7 Hz, JH–H = 0.9 Hz), 7.10 (dd, 1 H,
Synthesis of complex 2e. Complex 2e (orange solid, 91% yield)
3
3
thiophene, JH–H = 2.7 Hz, JH–H = 3.9 Hz), 7.04 (d, 1 H, Ph,
was prepared using the same synthetic procedure as that for
3
JH–H = 8.6 Hz). 13C NMR (CDCl3): 196.02 (C O), 161.5, 139.6,
=
◦
1
complex 2a. Melting point of 2e: >350 C. H NMR (d8-THF):
136.7, 132.0, 127.4, 127.1, 122.9, 120.5, 118.2, 114.8, 91.1 (C≡C),
82.1 (C≡C). MS (EI): m/z 228 (M+). Anal. Calcd for C13H8O2S:
C, 68.40; H, 3.53; S, 14.05. Found: C, 68.51; H, 6.58; S, 14.12%.
=
=
d 9.59 (s, 1H, N CH), 8.99 (s, 1H, N CH), 8.38 (d, 1H, PyrH,
3JH–H = 4.5 Hz), 8.21 (d, 1H, PyrH, 3JH–H = 8.1 Hz), 7.58 (d, 1H,
4
4
ArH, JH–H = 2.3 Hz), 7.51 (d, 1H, ArH, JH–H = 2.3 Hz), 7.37–
3
Synthesis of Zn(II) Schiff base complex 2a. Compound 1a
(500 mg, 1.746 mmol) was first treated with Zn(OAc)2·2H2O
(287 mg, 1.308 mmol) and the mixture was stirred in MeOH–
THF (30 mL : 30 mL) for 30 min at room temperature. 2,3-
7.31 (m, 7H, ArH), 6.87 (d, 4H, ArH, JH–H = 8.5 Hz), 6.79 (d,
3
3
2H, ArH, JH–H = 8.9 Hz), 3.97 (t, 2H, OCH2, JH–H = 6.5 Hz),
1.77 (m, 2H, CH2), 1.50–1.45 (m, 2H, CH2), 1.30 (s, 16H, CH2),
0.89 (t, 3H, CH3, JH–H = 6.6 Hz). 13C NMR (d8-THF): d 175.8
3
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=
=
(Ph), 175.0 (Ph), 164.3 (C N), 163.7 (C N), 160.1, 151.4, 147.4,
141.1, 140.2, 138.8, 138.3, 135.7, 133.4, 133.3, 125.6, 125.5, 124.4,
123.5, 120.5, 120.2, 117.6, 117.5, 115.5, 109.6, 109.4, 89.4 (C≡C),
89.3 (C≡C), 87.6 (C≡C), 87.5 (C≡C), 68.9 (OCH2), 33.0, 30.7,
30.6, 30.5, 30.4, 27.1, 26.5, 26.0, 25.8, 25.6, 25.5, 25.3, 25.2, 25.0,
thiophene), 7.43 (s, 2H, ArH), 7.34 (d, 4H, ArH, 3JH–H = 8.6 Hz),
3
3
7.29 (d, 2H, ArH, JH–H = 8.8 Hz), 6.86 (d, 4H, ArH, JH–H
=
3
8.6 Hz), 6.76 (d, 2H, ArH, JH–H = 8.8 Hz), 3.97 (t, 4H, OCH2,
3JH–H = 6.4 Hz), 1.49–1.46 (m, 4H, CH2), 1.31 (s, 32H, CH2), 0.90
13
=
(s, 6H, CH3). C NMR (d8-THF): d 174.3 (Ph), 163.4 (C N),
23.6, 14.5 (CH3). IR (cm−1 KBr): 2959 (sh), 2923, 2853 m(N C–
159.8, 142.4, 139.8, 137.5, 133.2, 125.1, 120.3, 117.3, 115.3, 89.4
(C≡C), 87.2 (C≡C), 68.9 (OCH2), 32.9, 30.7, 30.6, 30.5, 30.4, 30.3,
27.1, 26.8, 24.9, 24.0 (CH2), 14.5 (CH3). IR (cm−1 KBr): 2959 (sh),
=
+
=
H), 2209 m(C≡C), 1615m(C N). MS (FAB): m/z 948.4 (M + 1).
Anal. Calcd for C59H69N3O4Zn·1.5H2O: C, 72.56; H, 7.43; N, 4.30.
=
=
Found: C, 72.43; H, 7.24; N, 4.08%.
2923, 2853 m(N C–H), 2216 m(C≡C), 1614 m(C N). MS (FAB):
m/z 953.5 (M+ + 1). Anal. Calcd for C58H68N2O4SZn: C, 72.97; H,
7.18; N, 2.93; S, 3.36. Found: C, 73.11; H, 7.31; N, 2.71; S, 3.49%.
Synthesis of complex 3a. Complex 3a (orange solid, 47% yield)
was prepared using the same synthetic procedure as that for
complex 2a. Melting point of 3a: >350 ◦C. 1H NMR (d8-THF): d
Synthesis of complex 5a. Complex 5a (deep blue solid, 99%
4
yield) was prepared using the same synth◦etic procedure as that for
=
9.12 (s, 2H, N CH), 7.41 (d, 2H, ArH, JH–H = 2.3 Hz), 7.26 (dd,
1
3
4
complex 2a. Melting point of 5a: >350 C. H NMR (d8-THF):
2H, ArH, JH–H = 8.99 Hz, JH–H = 2.3 Hz), 6.71 (d, 2H, ArH,
4
3JH–H = 9.0 Hz), 2.36 (t, 4H, C≡CCH2, JH–H = 6.9 Hz), 1.59–
3
=
d 8.57 (s, 2H, N CH), 7.44 (d, 2H, ArH, JH–H = 2.1 Hz), 7.29
(dd, 2H, ArH, 3JH–H = 9.0 Hz, 4JH–H = 2.3 Hz), 6.74 (d, 2H, ArH,
3JH–H = 9.0 Hz), 2.37 (t, 4H, C≡CCH2, 3JH–H = 6.8 Hz), 1.59–1.54
(m, 4H, CH2), 1.49–1.46 (m, 4H, CH2), 1.31 (s, 24H, CH2), 0.89 (t,
6H, CH3, 3JH–H = 7.1 Hz). 13C NMR (d8-THF): d176.6 (Ph), 164.3
1.54 (m, 4H, CH2), 1.48–1.46 (m, 4H, CH2), 1.32–1.31 (m, 24H,
CH2), 0.89 (t, 6H, CH3, JH–H = 6.6 Hz). 13C NMR (d8-THF): d
3
=
176.6 (Ph), 168.9 (C N), 154.4, 140.5, 140.2, 125.9, 119.9, 110.6,
87.7 (C≡C), 81.1 (C≡C), 32.9 (C≡CCH2), 30.6, 30.5, 30.3, 30.2,
30.1, 29.9, 23.6, 20.0 (CH2), 14.5 (CH3). IR (cm−1 KBr): 2959 (sh),
=
(C N), 140.6, 140.4, 125.9, 123.3 (C≡N), 119.7, 111.9, 111.5, 88.3
(C≡C), 81.1 (C≡C), 33.0 (C≡CCH2), 30.8, 30.5, 30.4, 30.3, 30.2,
=
=
2923, 2852 m(N C–H), 2210 m(C≡C), 1623 m(C N). MS (FAB):
m/z 699.4 (M+ + 1). Anal. Calcd for C40H50N4O3Zn·H2O: C, 66.89;
H, 7.30; N, 7.80. Found: C, 67.17; H, 7.42; N, 7.68%.
30.0, 23.7, 20.1 (CH2), 14.6 (CH3). IR (cm−1 KBr): 2959 (sh),
=
=
2926, 2853 m(N C–H), 2209 m(C≡C), 1618 m(C N). MS (FAB):
m/z 707.4 (M+ + 1). Anal. Calcd for C42H50N4O2Zn: C, 71.22; H,
7.12; N, 7.91. Found: C, 71.33; H, 7.21; N, 7.99%.
Synthesis of complex 3d. Complex 3d (yellow-orange solid,
84% yield) was prepared using the same synth◦etic procedure as
that for complex 2a. Melting point of 3d: >350 C. 1H NMR (d5-
Pyridine): d 9.58 (br, 1H, N CH), 9.45 (s, 1H, N CH), 7.76 (d,
1H, ArH, 4JH–H = 1.8 Hz), 7.70–7.65 (m, 7H, ArH), 7.12 (d, 2H,
ArH, 3JH–H = 7.2 Hz), 7.06–7.02 (m, 4H, ArH), 3.91–3.86 (m, 4H,
OCH2), 1.69–1.65 (m, 4H, CH2), 1.34 (m, 4H, CH2), 1.21–1.18
(m, 8H, CH2), 0.83–0.80 (m, 6H, CH3). IR (cm−1 KBr): 2959 (sh),
Synthesis of monoimine 6a and Mg(II) Schiff base complex
7a. Compound 1a (200 mg, 0.876 mmol) was first treated with
Mg(OAc)2·4H2O (470 mg, 2.191 mmol) in MeOH–THF (20 mL
: 20 mL) for 30 min at room temperature. 2,3-Diaminopyridine
(239 mg, 2.192 mmol) was added to the resulting solution, and
the mixture was heated to reflux overnight. After cooling to room
temperature, the solvent was removed under vacuum. The residue
was washed with methanol and the precipitate was collected
by filtration. Yellow organic monoimine 6a (130 mg, 31%) was
extracted from the residue using three lots of 10 mL of CH2Cl2.
The dark brown Mg complex 7a (161 mg, 43%) was obtained
from the remaining residue by THF extraction. Melting point
=
=
=
=
2928, 2859 m(N C–H), 2211 m(C≡C), 1617 m(C N). MS (FAB):
m/z 771.3 (M+ + 1). Anal. Calcd for C44H42N4O5Zn·H2O: C, 66.88;
H, 5.61; N, 7.09. Found: C, 67.05; H, 5.40; N, 7.38%.
Synthesis of complexes 4eꢀ and 4e. Compound 1e (150 mg,
0.369 mmol) was first treated with Zn(OAc)2·2H2O (204 mg,
0.929 mmol) in MeOH (5 mL) for 30 min. 3,4-Diaminothiophene
dihydrochloride (54 mg, 0.288 mmol) was added to the resulting
solution, and the mixture was stirred overnight at room tem-
perature. The solvent was removed under vacuum. The residue
was washed with methanol and the precipitate was collected by
filtration. The green product was identified as a mixture of 4eꢀ and
4e (ca. 10 : 1, 97 mg). For 4eꢀ: 1H NMR (d6-DMSO): d 8.88 (s, 1H,
◦
of 6a: 115–120 C. Spectroscopic data of 6a: IR (cm−1 KBr):
=
3471m(OH), 3278.4, 3150 m(NH2), 2954 (sh), 2923, 2848 m(N C–
H), 2217m(C≡C), 1610 m(C N). 1H NMR (CDCl3): 12.65 (s,
=
3
=
1H, OH), 8.52 (s, 1H, N CH), 8.01 (dd, 1H, PyrH, JH–H
=
5.0 Hz,4JH–H = 1.6 Hz), 7.44 (d, 1H, ArH, JH–H = 2.0 Hz), 7.41
(dd, 1H, ArH, 3JH–H = 8.5 Hz, 4JH–H = 2.1 Hz), 7.22 (dd, 1H, PyrH,
3JH–H = 7.6 Hz, 4JH–H = 1.6 Hz), 6.93 (d, 1H, ArH, 3JH–H = 8.5 Hz),
6.71 (dd, 1H, PyrH, 3JH–H = 7.6 Hz, 3JH–H = 5.00 Hz), 4.77 (s, 2H,
NH2), 2.37 (t, 2H, C≡CCH2, 3JH–H = 7.1 Hz), 1.60 (m, 2H, CH2),
4
=
N CH), 7.62 (s, 1H, thiophene), 7.56 (s, 1H, ArH), 7.38 (d, 2H,
ArH, 3JH–H = 8.6 Hz), 7.29 (d, 1H, ArH, 3JH–H = 8.2 Hz), 7.16 (s,
3
1H, thiophene), 6.92 (d, 2H, ArH, JH–H = 8.6 Hz), 6.59 (d, 1H,
1.42 (m, 2H, CH2), 1.25 (s, 12H, CH2), 0.86 (t, 3H, CH3, 3JH–H
=
13
ArH, 3JH–H = 8.2 Hz), 5.19 (s, 1H, NH), 3.97 (t, 2H, OCH2, 3JH–H
=
7.12 Hz). C NMR (CDCl3): 163.0 (Ph), 160.1 (C N), 153.2,
146.9, 136.7, 135.4, 130.1, 125.0, 118.9, 117.4, 115.4, 114.4, 89.3
(C≡C), 79.3 (C≡C), 31.9 (C≡CCH2), 29.6, 29.5, 29.3, 29.1, 28.9,
28.8, 22.7, 19.3, 14.1 (CH3). MS (FAB): m/z 378.3 (M+ + 1). Anal.
Calcd for C24H31N3O: C, 76.36; H, 8.28; N, 11.13. Found: C, 76.38;
=
6.3 Hz), 1.73–1.66 (m, 2H, CH2), 1.39–1.37 (m, 2H, CH2), 1.23 (s,
3
18H, CH2), 0.84 (t, 3H, CH3, JH–H = 6.9 Hz). MS (FAB): m/z
565.2. A mixture of complex 4eꢀ and 4e (ca. 10 : 1, 97 mg) and 1e
(70 mg, 0.17 mmol) in 20 mL of THF was refluxed for 3 days, then
the solvent was removed under vacuum. The residue was washed
with methanol and the precipitate was collected by filtration. The
yellow-green product was identified as 4e (150 mg, 42% yield).
Complex 4e can also be synthesized in a one pot reaction after
refluxing the solution for 3 days (92% yield). Melting point of 4e:
H, 8.38; N, 11.18%. Melting point of 7a: >350 ◦C. Spectroscopic
data of 7a: H NMR (d8-THF): d 9.51 (s, 1H, N CH), 8.84 (s,
1
=
3
=
1H, N CH), 8.29 (d, 1H, PyrH, JH–H = 4.4 Hz), 8.15 (d, 1H,
3
4
PyrH, JH–H = 8.3 Hz), 7.40 (d, 1H, ArH, JH–H = 2.1 Hz), 7.35
(d, 1H, ArH, 4JH–H = 2.1 Hz), 7.27–7.24 (m, 1H, ArH), 7.19–7.15
(m, 2H, ArH), 6.61 (s, 1H, ArH), 6.58 (s, 1H, ArH), 2.36 (t, 4H,
◦
1
=
>350 C. H NMR (d8-THF): d 8.91 (s, 2H, N CH), 7.65 (s, 2H,
788 | Dalton Trans., 2007, 781–791
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C≡CCH2, 3JH–H = 6.2 Hz), 1.59–1.54 (m, 4H, CH2), 1.48 (m, 4H,
ArH, 4JH–H = 2.3 Hz), 7.34–7.29 (m, 5H, thiophene + ArH), 7.16
(m, 2H, thiophene), 6.99–6.97 (m, 1H, thiophene), 6.69 (s, 1H,
ArH), 6.67 (d, 1H, ArH). 13C NMR (d8-THF): 174.4 (Ph), 173.8
CH2), 1.33–1.31 (m, 24H, CH2), 0.89 (t, 6H, CH3, 3JH–H = 6.7 Hz).
13
=
C NMR (d8-THF): d 174.0 (Ph), 173.4 (Ph), 164.0 (C N), 163.1
=
=
=
(C N), 153.7, 147.0, 141.3, 140.5, 139.1, 138.8, 137.9 124.9, 124.8,
(Ph), 163.9 (C N), 163.1 (C N), 153.5, 147.2, 141.9, 141.0, 138.4,
138.1, 137.9, 131.3, 131.2, 127.8, 127.0, 126.9, 126.0, 125.6, 125.1,
125.0, 124.7, 123.3, 122.4, 122.1, 107.1, 106.8, 95.1 (C≡C), 95.0
124.6, 123.2, 122.0, 121.7, 108.9, 108.6, 86.6 (C≡C), 86.5 (C≡C),
82.1 (C≡C), 33.1 (C≡CCH2), 30.8, 30.5, 30.4, 30.0, 26.5, 23.7,
20.2 (CH2), 14.6 (CH3). IR (cm−1 KBr): 2952 (sh), 2925, 2853
(C≡C), 80.2 (C≡C), 80.1 (C≡C). MS (FAB): m/z 552.1 (M+
+
=
=
m(N C–H), 2190 m(C≡C), 1593 m(C N). MS (FAB): m/z 668.4
(M+). Anal. Calcd for C43H53MgN3O2·2H2O: C, 73.34; H, 8.16; N,
5.97. Found: C, 73.62; H, 8.30; N, 5.78%.
1). Anal. Calcd for C31H17MgN3O2S2·2H2O: C, 63.33; H, 3.60; N,
7.15; S, 10.91. Found: C, 63.61; H, 3.60; N, 6.78; S, 10.90%.
Synthesis of complex 8a. To compound 6a (16.6 mg,
0.044 mmol) in MeOH–THF (10 mL/10 mL) was added
Zn(OAc)2·2H2O (9.7 mg, 0.044 mmol) and compound 1f (13.8 mg,
0.044 mmol). The mixture was stirred for 20 h, and then the
solvent was removed under vacuum. The residue was washed with
methanol and the precipitate was collected by filtration. The yellow
solid (62% yield, 20 mg) was identified as 8a. Melting point of
Synthesis of monoimine 6b and Mg(II) Schiff base complex 7b.
Monoimine 6b (yellow solid, 20% yield) was prepared using the
same synthetic procedure as that for 6a. Spectroscopic data of 6b:
1
=
H NMR (CDCl3): d 12.75 (s, 1H, OH), 8.57 (s, 1H, N CH), 8.02
(d, 1H, PyrH,3JH–H = 4.8 Hz), 7.58 (d, 1H, ArH, 4JH–H = 1.9 Hz),
7.54 (dd, 1H, ArH, 3JH–H = 8.5 Hz, 4JH–H = 2.4 Hz), 7.41 (d, 2H,
ArH, 3JH–H = 8.2 Hz), 7.21 (d, 1H, PyrH, 3JH–H = 7.6 Hz), 7.14 (d,
2H, ArH, 3JH–H = 8.2 Hz), 7.00 (d, 1H, ArH, 3JH–H = 8.5 Hz), 6.73
(dd, 1H, PyrH, 3JH–H = 7.6 Hz, 3JH–H = 4.8 Hz), 4.81 (s, 2H, NH2),
2.59 (t, 2H, CH2, 3JH–H = 7.4 Hz), 1.63 − 1.58 (m, 2H, CH2), 1.31 −
1.29 (m, 4H, CH2), 0.87 (t, 3H, CH3, 3JH–H = 6.4 Hz). 13C NMR
◦
1
=
8a: >350 C. H NMR (d8-THF): d 9.63 (s, 1H, N CH), 8.96
3
4
=
(s, 1H, N CH), 8.37 (dd, 1H, PyrH, JH–H = 4.6 Hz, JH–H
=
3
4
1.5 Hz), 8.22 (dd, 1H, PyrH, JH–H = 8.3 Hz, JH–H = 1.5 Hz),
4
3
7.76 (d, 1H, ArH, JH–H = 2.4 Hz), 7.42 (dd, 1H, ArH, JH–H
=
4
8.9 Hz, JH–H = 2.4 Hz), 7.38–7.35 (m, 2H, ArH), 7.21 (dd, 1H,
=
(CDCl3) 163.0 (Ph), 160.7 (C N), 153.2, 147.1, 143.4, 136.7, 135.5,
ArH, 3JH–H = 8.9 Hz, 4JH–H = 2.3 Hz), 6.63 (d, 1H, ArH, 3JH–H
=
131.4, 130.1, 128.5, 125.1, 120.3, 119.2, 117.7, 114.8, 114.5 (Ph),
89.3 (C≡C), 79.3 (C≡C), 35.9, 31.4, 30.9, 22.5 (CH2), 14.0 (CH3).
MS (FAB): m/z 384.2 (M+ + 1). Anal. Calcd for C25H25N3O: C,
78.30; H, 6.57; N, 10.96. Found: C, 78.37; H, 6.51; N, 10.86%.
8.9 Hz), 6.73 (d, 1H, ArH, 3JH–H = 8.9 Hz), 2.37 (t, 2H, C≡CCH2,
3JH–H = 6.8 Hz), 1.60–1.57 (m, 2H, CH2), 1.50–1.45 (m, 2H, CH2),
3
1.34–1.29 (m, 12H, CH2), 0.89 (t, 3H, CH3, JH–H = 7.2 Hz).
IR (cm−1 KBr): 2959 (sh), 2926, 2854 m(N C–H), 2209 m(C≡C),
=
Complex 7b: Light yellow solid with 62% yield. Spectroscopic
+
=
1618 m(C N). MS (FAB): m/z 734.1 (M + 1). Anal. Calcd for
1
=
data of 7b: H NMR (d8-THF): d 9.57 (s, 1H, N CH), 8.91 (s,
C39H32F5N3O2Zn·H2O: C, 62.20; H, 4.55; N, 5.58. Found: C, 62.58;
3
=
1H, N CH), 8.33 (d, 1H, PyrH, JH–H = 4.5 Hz), 8.19 (d, 1H,
H, 4.71; N, 5.38%.
3
4
PyrH, JH–H = 8.4 Hz), 7.59 (d, 1H, ArH, JH–H = 2.3 Hz), 7.52
4
(d, 1H, ArH, JH–H = 2.3 Hz), 7.36–7.29 (m, 7H, ArH), 7.14 (d,
Synthesis of complex 8b. Complex 8b (yellow solid, 49% yield)
was prepared using the same synthetic procedure as that for 8a.
3
3
4H, ArH, JH–H = 8.0 Hz), 6.68 (d, 2H, ArH, JH–H = 8.0 Hz),
2.61 (t, 4H, PhCH2, 3JH–H = 6.4 Hz), 1.61 (m, 4H, CH2), 1.35–1.33
1
=
=
H NMR (d8-THF): d 9.59 (s, 1H, N CH), 8.95 (s, 1H, N CH),
(m, 8H, CH2), 0.91 (t, 6H, CH3, JH–H = 6.6 Hz). 13C NMR (d8-
3
3
4
8.36 (dd, 1H, PyrH, JH–H = 4.73 Hz, JH–H = 1.2 Hz), 8.19 (dd,
=
=
THF): d 174.3 (Ph), 173.7 (Ph), 163.9 (C N), 163.1 (C N), 153.5,
147.1, 143.1, 143.0, 141.7, 140.9, 138.7, 138.4, 137.9, 131.8, 129.2,
125.9, 125.0, 124.7, 123.2, 122.9, 122.2, 121.9, 107.8, 107.5, 90.8
(C≡C), 87.2 (C≡C), 87.1 (C≡C), 36.6 (CH2), 32.5, 32.0, 30.8, 23.5
(CH2), 14.4 (CH3). MS (FAB): m/z 680.4 (M+ + 1). Anal. Calcd
for C45H41MgN3O2·2H2O: C, 75.47; H, 6.33; N, 5.87. Found: C,
75.79; H, 6.51; N, 5.94%.
3
4
1H, PyrH, JH–H = 8.3 Hz, JH–H = 1.2 Hz), 7.56 (d, 1H, ArH,
4JH–H = 2.2 Hz), 7.37–7.29 (m, 3H, ArH), 7.21 (d, 1H, ArH, 3JH–H
=
3
8.8 Hz), 6.77 (d, 1H, ArH, JH–H = 8.8 Hz), 6.73 (d, 1H, ArH,
3JH–H = 8.8 Hz), 4.43–4.42 (m, 2H, CpFe), 4.21–4.19 (m, 7H,
CpFe), 2.37 (t, 2H, C≡CCH2, 3JH–H = 6.8 Hz), 1.60–1.58 (m, 2H,
CH2), 1.50–1.48 (m, 2H, CH2), 1.34–1.29 (m, 12H, CH2), 0.89
(t, 3H, CH3, JH–H = 6.8 Hz). MS (FAB): m/z 751.1 (M+ + 1).
3
Synthesis of monoimine 6g and Mg(II) Schiff base complex 7g.
Anal. Calcd for C43H42FeN3O2Zn·H2O: C, 66.89; H, 5.74; N, 5.44.
Complex 6g (yellow solid, 12% yield) was prepared using the same
Found: C, 66.88; H, 5.74; N, 5.64%.
1
synthetic procedure as that for 6a. Spectroscopic data of 6g: H
=
NMR (CDCl3): 12.82 (s, 1H, OH), 8.56 (s, 1H, N CH), 8.03
Synthesis of complex 8c. Complex 8c (yellow solid, 61% yield)
was prepared using the same synthetic procedure as that for 8a.
(dd, 1H, PyrH,3JH–H = 5.0 Hz,4JH–H = 1.6 Hz), 7.58 (d, 1H, ArH,
4JH–H = 2.1 Hz), 7.53 (dd, 1H, ArH, JH–H = 8.6 Hz, JH–H
=
Melting point of 8c: >350 ◦C. 1H NMR (d8-THF): d 9.55 (s, 1H,
3
4
3
=
=
2.1 Hz), 7.28–7.23 (m, 3H, thiophene + PyrH), 7.02–6.99 (m, 2H,
N CH), 8.99 (s, 1H, N CH), 8.36 (d, 1H, PyrH, JH–H = 4.6 Hz),
3
3
3
4
thiophene +ArH), 6.72 (dd, 1H, PyrH, JH–H = 7.6 Hz, JH–H
=
8.20 (d, 1H, PyrH, JH–H = 8.3 Hz), 7.47 (d, 1H, ArH, JH–H
=
5.0 Hz), 4.79 (s, 2H, NH2). 13C NMR (CDCl3): 162.8 (Ph), 160.9
2.3 Hz), 7.43 (d, 1H, ArH, JH–H = 2.3 Hz), 7.35–7.28 (m, 2H,
4
3
4
=
(C N), 153.2, 147.2, 136.5, 135.5, 131.7, 130.0, 127.2, 127.1, 125.1,
ArH), 7.22 (dd, 1H, ArH, JH–H = 8.8 Hz, JH–H = 1.7 Hz), 6.77
(d, 1H, ArH, 3JH–H = 8.8 Hz), 6.73 (d, 1H, ArH, 3JH–H = 8.8 Hz),
4.43–4.41 (m, 2H, CpFe), 4.21–4.19 (m, 7H, CpFe), 2.37 (t, 2H,
123.3, 119.2, 117.7, 114.5, 114.2, 91.9 (C≡C), 81.7 (C≡C). MS
(FAB): m/z 320.0 (M+ + 1). Anal. Calcd for C18H13N3OS: C,
67.69; H, 4.10; N, 13.16. Found: C, 67.76; H, 4.18; N, 13.26%.
Complex 7g: Dark brown solid with 51% yield. Spectroscopic
data of 7g: H NMR (d8-THF): 9.57 (s, 1H, N CH), 8.91 (s, 1H,
C≡CCH2, 3JH–H = 6.9 Hz), 1.60–1.55 (m, 2H, CH2), 1.50–1.48 (m,
3
2H, CH2), 1.34–1.31 (m, 12H, CH2), 0.89 (t, 3H, CH3, JH–H
=
1
6.2 Hz). IR (cm−1 KBr): 2959 (sh), 2924, 2852 m(N C–H), 2210
=
=
3
=
=
N CH), 8.34 (d, 1H, PyrH, JH–H = 3.8 Hz), 8.19 (d, 1H, PyrH,
m(C≡C), 1614m(C N) Anal. Calcd for C43H42FeN3O2Zn·H2O: C,
3JH–H = 8.7 Hz), 7.61 (d, 1H, ArH, 4JH–H = 2.3 Hz), 7.54 (d, 1H,
66.89; H, 5.74; N, 5.44. Found: C, 66.93; H, 5.77; N, 5.66%.
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Table 4 Crystal and intensity data for 3d·pyridine and 4e
3d·pyridine
4e
Mol. formula
Mol. wt
Crystal system
C49H47N5O5Zn
851.29
Monoclinic
¯
P1
9.1749(2)
10.6334(2)
22.2367(5)
87.2140(12)
84.0160(11)
89.0860(11)
2154.92(8)
C62H80N2O6SZn
1046.71
Monoclinic
¯
P1
11.3969(3)
12.1672(3)
12.1672(3)
75.1070(13)
84.4270(15)
80.8510(15)
2972.18(14)
2
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
V/A
Z
3
˚
2
Crystal dimensions/mm
0.25 × 0.20 × 0.15
0.25 × 0.20 × 0.15
˚
Mo Ka radiation: c /A
0.71073
0.71073
h range/◦
1.77–25.00
1.77–25.00
Limiting indices
−10 ≤ h ≤ 10
−12 ≤ k ≤ 12
−26 ≤ l ≤ 26
12579
−13 ≤ h ≤ 13
−13 ≤ k ≤ 14
−23 ≤ l ≤ 26
17844
No. of reflns collected
No. of ind reflns (Rint
)
7582 (0.0355)
0.915 and 0.859
Full-matrix least-squares on F2
7582/0/506
1.048
10399 (0.0422)
0.932 and 0.798
Full-matrix least-squares on F2
10399/0/620
1.048
Max. and min. transmission
Refinement method
No. of data/restraints/params
GOF
Final R indices [I > 2r(I)]
R1
0.0647
0.1650
0.0861
0.2283
wR2
R indices (all data)
R1
0.0984
0.1898
−0.623 and + 0.739
0.1473
0.2844
−0.642 and + 0.791
wR2
−3
˚
Dq (In final map)/e A
Single crystal X-ray diffraction analysis of 3d·pyridine and 4e
Academic Sinica and Prof. Pi-Tai Chou for insightful and helpful
comments about the photophysical properties of these Schiff base
complexes.
Single crystals of the pyridine adduct of 3d suitable for X-ray
diffraction studies were grown as mentioned above. A single crystal
of dimensions 0.25 × 0.20 × 0.15 mm3 was glued to a glass fiber and
mounted on a Nonius KappaCCD diffractometer. The diffraction
data were collected using 3 kW sealed-tube Mo Ka radiation (T =
295 K). Exposure time was 5 s per frame.23 The SADABS (Siemens
area detector absorption) absorption correction24 was applied, and
decay was negligible. Data were processed and the structures was
solved and refined by the SHELXTL program. The structure was
solved using direct methods and confirmed by Patterson methods
refining on F2 using all data.25 Hydrogen atoms were placed
geometrically using the riding model with thermal parameters set
to 1.2 times that for the atoms to which the hydrogen is attached
and 1.5 times that for the methyl hydrogens. The procedures for the
structure determination of 4e were similar. Crystal data of these
complexes are listed in Table 4.
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Acknowledgements
Financial support provided by the National Science Council of
Taiwan is grateful acknowledged. Funding for the Instrumenta-
tion Facility of the Department of Chemistry of NTU has also
been provided in part by the National Science Council of Taiwan.
We also thank Prof. Jiann T. Lin at the Institute of Chemistry in
790 | Dalton Trans., 2007, 781–791
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15 K.-H. Chang, C.-C. Huang, Y.-H. Liu, Y.-H. Hu, P.-T. Chou and Y.-C.
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16 P. G. Cozzi, S. L. Dolci, A. Garelli, M. Montalti, L. Prodi and N.
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17 K. Sonogashira, in Comprehensive Organic Synthesis, ed. B. M. Trost
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18 A. L. Singer and D. A. Atwood, Inorg. Chim. Acta, 1998, 277, 157–162.
24 The SADABS program is based on the method of Blessing; see:(a) R. H.
Blessing, Acta Crystallogr., Sect. A, 1995, 51, 33; (b) SHELXTL: Struc-
ture Analysis Program, version 5.04, Siemens Industrial Automation
Inc., Madison, WI, 1995; L. J. Farrugia, J. Appl. Crystallogr., 1997, 30,
565–566.
25 GOF = [R[w(F2 − F2c)2]/(n − p)]1/2, where n and p denote the
o
number of data and parameters. R1 = (RꢁFo| − |Fcꢁ)/R|Fo|, wR2 =
[R−[w(F2 − F2c)2]/R [w(F2o)2]]1/2 where w = 1/[r2(F2o) + (aP)2 + bP]
o
and P = [(max; 0, F2o) + 2F2c]/3.
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The Royal Society of Chemistry 2007
Dalton Trans., 2007, 781–791 | 791
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