CD spectroscopy as a fingerprint technique for the structural characterization and determination of absolute configurations of unsymmetric chiral Schiff base Ni(II) complexes

Article abstract of DOI:10.1016/j.tetasy.2008.12.009

Unsymmetric Schiff base complexes have attracted more attention in recent years due to their diverse effects in catalytic reactions. Due to their high dissymmetry, unsymmetric metallosalen complexes are harder to prepare than symmetric ones. This means that X-ray crystallographic structural determination is sometimes unavailable, so their absolute configurations are determined by circular dichroism (CD) spectroscopy instead. Herein, some quadridentate unsymmetric metallosalen nickel(II) complexes were synthesized and their structures were characterized by CD spectra. An empirical rule for assignment of the absolute configurations of tetra-coordinated pseudo-planar Ni(II) complexes was put forward. Furthermore, a fingerprint was found to judge whether the metallosalen complexes are symmetric or unsymmetric.

Full text of DOI:10.1016/j.tetasy.2008.12.009

Tetrahedron: Asymmetry 19 (2008) 2653–2658
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
CD spectroscopy as a fingerprint technique for the structural
characterization and determination of absolute configurations
of unsymmetric chiral Schiff base Ni(II) complexes
a,b,
Lei Ding a, Fang Wang a, Leiqi Chen a, Hui Zhang a, , YuFen Zhao
*
*
a Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
b Department of Chemistry, Tsinghua University, Beijing 100084, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Unsymmetric Schiff base complexes have attracted more attention in recent years due to their diverse
effects in catalytic reactions. Due to their high dissymmetry, unsymmetric metallosalen complexes are
harder to prepare than symmetric ones. This means that X-ray crystallographic structural determination
is sometimes unavailable, so their absolute configurations are determined by circular dichroism (CD)
spectroscopy instead. Herein, some quadridentate unsymmetric metallosalen nickel(II) complexes were
synthesized and their structures were characterized by CD spectra. An empirical rule for assignment of
the absolute configurations of tetra-coordinated pseudo-planar Ni(II) complexes was put forward. Fur-
thermore, a fingerprint was found to judge whether the metallosalen complexes are symmetric or
unsymmetric.
Received 5 August 2008
Revised 19 November 2008
Accepted 2 December 2008
Available online 10 January 2009
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
ions.2f Thus, the synthetic unsymmetric metallosalen complexes
may often be contaminated by the symmetric ones. Small changes
Schiff base metal complexes are known to be biologically
important,1 and have been shown to be highly effective catalysts
in various chemical and photochemical reactions such as the enan-
tioselective epoxidation of unfunctionalized olefins by chiral
Mn(III) Schiff base complexes.1a–d Chiral C2-symmetric metallosa-
len complexes, derived from the condensation of optically active
1,2-diamines with 2 equiv of substituted salicylaldehydes (SAL)
or dehydroacetic acids (DHA), have been successfully used in
asymmetric catalytic epoxidations.1d–f
Most of the reported chiral metallosalen complexes are C2-sym-
metric.2a,b However, in recent years, chiral unsymmetric metallos-
alen complexes have attracted more attention. By optimizing the
structure, it is possible to obtain chiral environments inaccessible
for C2 symmetric complexes. Due to their higher dissymmetry,
unsymmetric metallosalen complexes have shown diverse effects
in catalyzed reactions and sometimes enhance the catalytic effec-
tiveness.2c–e Unfortunately, these are much more difficult to
prepare than those of the symmetric ones, as it is harder to obtain
their crystal structures. In addition, the condensations resulting in
unsymmetric products are difficult to be handled.2g,h Furthermore,
unsymmetric metallosalen complexes may sometimes rearrange
to the corresponding symmetric ones in the presence of metal
in their structures generally lead to a remarkable change in cata-
lytic effectiveness; it is necessary to find a convenient method to
distinguish between unsymmetric and symmetric metallosalen
complexes in situ. In addition, X-ray crystallographic structural
determination is frequently unavailable in this case. As a result,
it is important to determine their absolute configuration by other
method such as CD spectroscopy.
The assignment of the absolute configurations of the molecules
requires the knowledge of the molecular structure and an observa-
ble signal that can be assigned to one of the two enantiomers. X-
ray crystallographic structural determination is the first available
method of this sort. Several chiroptical spectroscopic techniques,
such as nonempirical exciton coupled circular dichroism (ECCD),
have been used to assign the absolute configurations of molecules
when their structures have been known.3a,b For the chiral quadrid-
entate metallosalen complexes, CD spectroscopy is useful in deter-
mining their absolute configuration by comparing the CD spectra
in the UV region with similar molecules; their absolute configura-
tions have been determined by X-ray crystallographic structural
determination or ECCD.3c–h These results are in accordance with
predictions of the exciton chirality method.3b,i,j However, because
the bands corresponding to the dipole–dipole interactions between
more than two chromophores may overlap with one another, con-
firming the CD splitting pattern in the UV regions is sometimes
difficult. Thus, some empirical correlations between the CD pattern
in other regions and the absolute configuration for such chiral
metal complexes have been reported.3k
* Corresponding authors. Tel.: +86 592 2183910; fax: +86 592 2089057 (H.Z.),
tel.: +86 592 2185780; fax: +86 592 2185780 (Y.F.Z.).
E-mail addresses: huizhang@xmu.edu.cn (H. Zhang), yfzhao@xmu.edu.cn (Y.
Zhao).
0957-4166/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2008.12.009

2654
L. Ding et al. / Tetrahedron: Asymmetry 19 (2008) 2653–2658
Herein, two series of nickel(II) complexes (Fig. 1) with unsym-
CD pattern (Fig. 3). These results reveal that a chiral unsymmetric
Schiff base will induce a stereoselective synthesis of the corre-
sponding complex with specific stereochemistry.
metric quadridentate Schiff bases prepared from the condensation
of 2-hydroxyacetophenone (HACP), DHA, BuSAL, and bromosalicyl-
aldehyde (BrSAL) with optically active trans-cyclohexane-1,2-dia-
mine (chxn), 1,2-diphenyl-ethylenediamine (dpen) were
synthesized and characterized by EA, IR, UV–vis, and CD spectra.
The absolute configurations of these complexes were assigned by
their CD spectra. An empirical rule was worked out to determine
the absolute configurations of both symmetric and unsymmetric
pseudo-planar Ni(II) metallosalen complexes. A fingerprint was
found to judge whether the metallosalen complexes are symmetric
or unsymmetric.
According to the respective UV–vis spectrum, the bands at
about 230 nm are assigned to the benzene
bands at about 310 nm are the azomethine
p–
p* transitions. The
p–
p* transitions. The
weak bands at 380 nm and 415 nm are considered to be the LMCT
transitions.3g,h,5 The d–d transition bands at 540–560 nm show a
weak Cotton effect (CE), and can be interpreted as the 1A1(F)?1B1
transition.3m
Comparing the CD spectra of the complexes with relevant Schiff
bases, the bands observed in the Schiff bases are still observed in
the relevant complexes, but have shifted more or less. Because of
2. Results and discussion
the distortion of the chelate ring, the two azomethine p–p
* transi-
tions interact with each other and cause an exciton pattern couplet
Enantiomerically pure 1,2-diphenylethylenediamine (dpen) is
commercially available. Diastereomeric trans-cyclo-hexane-1,2-
diamine tartrates were prepared by the reported methods.1d,4
The chiral diamines were set free from the corresponding tartrates
and were used in situ according to the method that was previously
reported by us.4 The free chiral diamines were dissolved in meth-
anol, mixed with 1 equiv. of DHA in dichloromethane solution in
the presence of MgSO4, and stirred at room temperature for
10 h.1f The yellow solution was filtered, evaporated to dryness,
and recrystallized from dichloromethane/methanol (1:1). The
resulting yellow product was dissolved in ethanol, mixed with
1 equiv of HACP or BrSAL in ethanol, and stirred at reflux for 8 h.
The yellow solution was evaporated, recrystallized from dichloro-
methane/methanol (1:1), and dried in vacuum at room
temperature.
around 320 nm (Fig. 3a).
The CD spectra of the complexes prepared from different chiral
diamine show distinct difference. In the CD spectra of DHA–
(SS)(RR)dpen–BrSAL–Ni, the strong band that lies near 310 nm
can be assigned to the absorbance of the benzenes on 1,2-diphen-
ylethylenediamine itself. The stereoeffect of the two benzenes
causes the pseudo-planar coordination environment around the
metal center in the DHA–(SS)(RR)dpen–BrSAL–Ni to contort less
than in the DHA–(SS)(RR)chxn–BrSAL–Ni.3e Thus, the intensity of
the CD band in the d–d region for DHA–(SS)(RR)dpen–BrSAL–Ni
(
D
e
545 = 0.95/ꢂ0.92 L molꢂ1 cmꢂ1
)
is lower than for DHA–
(SS)(RR)chxn–BrSAL–Ni(
D
e
560 = ꢂ4.80/4.36 L molꢂ1 cmꢂ1). Similar
situation is also observed in the corresponding symmetric metal-
losalen complexes.
When comparing the CD spectra of the unsymmetric metallos-
alen complexes with the symmetric ones, the locations of the
main bands are similar. However, more exciton couplets are ob-
served in the UV region of the unsymmetric complexes. This
can be attributed to the fact that the lower symmetry causes
the degenerate energy levels of the transitions to split. Further-
more, a new band, weak but remarkable, can be observed in
the CD spectra of the unsymmetric metallosalen complexes at
about 460–480 nm. It is not found in the corresponding region
of the CD spectra of any symmetric complexes. The existence of
this fingerprint may be attributed to the splitting of the energy
levels of the d–d transitions of the metal located in the coordina-
tion environment with lower symmetry. By examining whether
this fingerprint appears in the CD spectra or not, it is quite easy
to distinguish between most of the symmetric metallosalen com-
plexes and the unsymmetric ones.
An appropriate amount of chiral Schiff base dissolved in meth-
anol was allowed to reflux under an inert atmosphere with
Ni(OAc)2ꢀ4H2O (1 equiv) in the presence of triethylamine (1 equiv)
for 30 min (Scheme 1).1f The solution was filtered and concen-
trated to dryness. The resulting residue was washed in ethanol,
recrystallized from dichloromethane, and dried in vacuum. The
overall yields for the complexes were in the range of 68–78%.
In the UV–vis spectra of unsymmetric Schiff bases, the azome-
thine
and the benzene
= 30,000–45,000). The UV–vis spectra of each complex are
shown in Figure 2. Compared with the spectra of Schiff bases, the
azomethine = 8000–
p* transition bands lie at about 315 nm (
18,000). The benzene
p* transition bands red shift to 230–
250 nm (
p–
p* transition bands lie at 317–328 nm (
p* transition bands lie at 220–233 nm
e = 3500–18,000)
p–
(e
p
–
e
p
–
e
= 30,000–45,000). The d–d transition bands are not ob-
served due to the low concentration, ꢁ10ꢂ4 to 10ꢂ5 mol/L of the
complex solution. There should be low-intensity bands at about
550 nm according to their CD spectra.
The absolute configurations of the metallosalen complexes
prepared from salicylaldehyde and chiral diamine [(S)-1,2-pn,
(S)-1,2-bn, (S)-1,2-dpen, (S)-trans-1,2-chxn, etc.] have been deter-
mined by Pasini using the exciton chirality method.3e However,
for some complexes, such as those prepared from DHA, confirm-
ing the CD splitting pattern in the UV region is sometimes diffi-
The CD spectra of the Schiff bases are approximately mirror
images of those of their respective enantiomers. The complexes
prepared from a Schiff base and its enantiomers give a symmetric
R1
R2
H3C
O
N
O
N
O
Ni
Ph
Ph
Ph
Ph
R1
R3
=
O
1. trans-1,2-chxn
2. 1,2-dpen
H3C
HACP: R2 = CH3 , R3 = H
BrSAL: R2 = H, R3 = BrBuSAL: R2 = H , R3 = t-Bu
Figure 1. Unsymmetric metallosalen complexes.

L. Ding et al. / Tetrahedron: Asymmetry 19 (2008) 2653–2658
2655
R2
R1
O
H3C
H3C
R1
O
O
O
O
O
NH
OH
NH2
R3
HO
H2N
NH2
OH
MgSO4 , CH3OH, rt , 10h
CH3OH, reflux
R1
H3C
H3C
R1
R2
R2
H3C
H3C
HN
NH
OH
O
O
O
N
O
N
O
Ni(OAc)2 . 4H2O
Ni
R3
R3
HO
O
CH3OH, NEt3, reflux
H3C
H3C
Scheme 1. Synthesis of unsymmetric metallosalen complexes.
50000
tween the chiral diamine and the absolute configuration of the
complexes derived from it is the inverse. The reason for this
exception is that the presence of the two fused rings forces the
molecule to distort to the most stable configuration with an in-
verse chirality compared with the corresponding complexes de-
rived from other chiral diamine.
Herein, the exciton chirality method is used to validate the
above-mentioned results. For an exciton couplet pattern, the CD
sign of the band of higher energy is determined by the sign of
the product of the rotational strength (R) and the dipole interac-
tion energy (V12), where R and V12 are given by Eqs. 1 and 2. In
fact, only the angular dependent part of Eqs. 1 and 2 is necessary
for determining the sign of the CD signal.3l For (HACP)2–(RR)-
DHA-chxn-BrSAL-Ni
DHA-chxn-BuSAL-Ni
DHA-chxn-HACP-Ni
DHA-dpen-BrSAL-Ni
DHA-dpen-BuSAL-Ni
DHA-dpen-HACP-Ni
40000
30000
20000
10000
0
300
400
500
λ /nm
Figure 2. UV–vis spectra of unsymmetric metallosalen.
chxn–Ni, whose absolute configuration has been assigned to
by X-ray crystallographic structural determination, angle
the exciton splitting of the azomethine
* transition is obtained
from its crystal structure data,3k,o and b can be estimated,3n and
Dk
c
for
p–p
cult because the bands that correspond to the dipole–dipole
interactions between more than two chromophores may overlap
with one another. A distinctive band of d–d transition can be ob-
served at 500–600 nm in the CD spectra of the tetra-coordinated
pseudo-planar metallosalen complexes. Its CE sign is dependent
on the absolute configuration. We have put forward an empirical
rule to determine the absolute configuration of the symmetric
nickel(II) metallosalen complexes in the past. In the case of tet-
ra-coordinated pseudo-planar Ni(II) symmetric complexes, the
following empirical rule exists: (i) (S)
HACP–(SS)-dpen, DHA–(S)-pn, DHA–(SS)-dpen derivatives, which
is reflected by the positive CE around 550 nm; and (ii) (S) d for
the HACP–(SS)-chxn, DHA–(SS)-chxn derivatives with a concomi-
tant inversion of the CE.3k In the symmetric and unsymmetric
metallosalen complex series, the stereostructures and coordina-
tion environments are all quite similar. Thus, this empirical rule
may also be applicable for unsymmetric metallosalen complexes
(Table 1). For DHA–(SS)-dpen–BrSAL–Ni, DHA–(SS)-dpen–HACP–
Ni, DHA–(SS)-dpen–Bu–SAL–Ni, the sign of the CD pattern around
a
the sign of R ꢀ V12 is positive according to the Eqs. 1 and 2. This
means that the CD sign of the band in longer wavelength of the
exciton couplet pattern of (HACP)2–(RR)-chxn–Ni around
320 nm should be negative. However, the exciton couplet pattern
cannot be observed in this range because the bands of the chro-
mophores in the molecule overlap with one another. On the basis
of the exciton chirality method, the substitution of a ligand with
retention of configuration in the case of degenerate coupling with
a similar chromophore does not change the CD spectra qualita-
tively.3l Thus, the DHA–(RR)-chxn–BrSAL–Ni should have an exci-
ton couplet pattern around 320 nm with negative chirality, whose
Dk for the HACP–(S)-pn,
K
absolute configuration has been assigned to
Dk above. This is con-
sistent with the experimental CD spectra (Fig. 3a). On the other
hand, unlike in the Zn(II) and Cu(II) metallosalens,3d,p the charge
transfer transitions in Ni(II) metallosalens may overlap their exci-
ton split bands sometimes.3d Hence, in most cases, it is difficult to
observe the exciton couplet pattern clearly (Fig. 3b–f).
550 nm is positive. This implies that the chirality is
Dk where
1
l2
r12
lowercase symbols reflect the chirality (or conformation) of the
ethylenediamine chelate ring and the uppercase symbols reflect
that of the tetrahedral distortion of the metal coordination. For
DHA–(RR)-dpen–BrSAL–Ni, DHA-(RR)-dpen-HACP–Ni, DHA–(RR)-
dpen–Bu–SAL–Ni, the sign is negative, which imply the chirality
V12
¼
ðsin
2
a
sin b cos
c
þ 2 cos
a
cos bÞ
ð1Þ
ð2Þ
3
4
p
e0
Rꢃ ¼ ꢃ0:5
p
m sin
a
sin b sin c
~
m
In addition, the solid-state CD spectra of all the unsymmetric
complexes mentioned above were studied. The results, similar to
those of symmetric metallosalens,6 revealed that all chiral com-
K
d. For DHA–(SS)(RR)-chxn–BrSAL–Ni, DHA–(SS)(RR)-chxn–
HACP–Ni, DHA–(SS)(RR)-chxn–Bu–SAL–Ni, the relationship be-

2656
L. Ding et al. / Tetrahedron: Asymmetry 19 (2008) 2653–2658
a
20
10
0
40
d
fingerprint
fingerprint
20
0
-20
-40
-10
-20
200
300
400
500
600
220
330
440
550
λ/nm
λ/nm
20
10
0
30
15
0
e
b
fingerprint
fingerprint
-10
-15
-30
-20
200
300
400
λ/nm
500
600
300
400
500
600
λ/nm
40
20
0
c
f
40
20
0
fingerprint (be partly overlaped)
fingerprint
-20
-20
-40
-40
200
300
400
λ/nm
500
600
330
440
λ/nm
550
Figure 3. CD spectra of complexes DHA–chxn–BrSAL–Ni(II) (a), DHA–chxn–BuSAL–Ni(II) (b), DHA–chxn–HACP–Ni(II) (c), DHA–dpen–BrSAL–Ni(II) (d), DHA–dpen–BuSAL–
Ni(II) (e), DHA–dpen–HACP–Ni(II) (f). Red is (SS), blue is (RR).
Table 1
plexes maintain the same configurations found in solution states.
Furthermore, the solid-state CD spectra are sometimes more
sensitive.
Absolute configuration of the complexes and corresponding CD sign in the 500–
600 nm range
Absolute configuration
CD sign
Symmetric complex3k
(HACP)2–(SS)-dpen–Ni
(HACP)2–(RR)-dpen–Ni
(HACP)2–(SS)-chxn–Ni
(HACP)2–(RR)-chxn–Ni
(DHA)2–(SS)-dpen–Ni
(DHA)2–(RR)-dpen–Ni
(DHA)2–(SS)-chxn–Ni
(DHA)2–(RR)-chxn–Ni
3. Conclusion
D
K
K
D
D
K
K
D
+
ꢂ
ꢂ
+
In conclusion, by comparison of the CD spectra of the unsym-
metric complexes, the CD signal in the d–d transition region is use-
ful as a reference in determining the chiral configurations of the
complexes. In the case of tetra-coordinated pseudo-planar Ni(II)
complexes, we therefore have the following empirical rule: (i) for
both symmetric and unsymmetric complexes prepared from any
chiral diamine, the positive Cotton effects around 550 nm reveal
+
ꢂ
ꢂ
+
Unsymmetric complex
DHA–(SS)-dpen–BrSAL–Ni
DHA–(RR)-dpen–BrSAL–Ni
DHA–(SS)-dpen–HACP–Ni
DHA–(RR)-dpen–HACP–Ni
DHA–(SS)-dpen–BuSAL–Ni
DHA–(RR)-dpen–BuSAL–Ni
DHA–(SS)-chxn–BrSAL–Ni
DHA–(RR)-chxn–BrSAL–Ni
DHA–(SS)-chxn–HACP–Ni
DHA–(RR)-chxn–HACP–Ni
DHA–(SS)-chxn–BuSAL–Ni
DHA–(RR)-chxn–BuSAL–Ni
D
K
D
K
D
K
K
D
K
D
K
D
+
the
D
k chirality, and vice versa; (ii) for both symmetric and unsym-
k chirality corre-
ꢂ
+
metric complexes prepared from dpen, the
D
ꢂ
+
ꢂ
ꢂ
+
sponds to the (SS)-configuration of the chiral diamine, and vice
versa; (iii) for both symmetric and unsymmetric complexes pre-
pared from chxn, the
ration of the chiral diamine, and vice versa. This can be used to
assign the absolute configuration of some tetrahedral or pseudo-
planar metallosalen complexes with similar electronic configura-
tions and coordination spheres. Moreover, it may meet the need
for in situ assignment of absolute configurations and conforma-
Dk chirality corresponds to the (RR)-configu-
ꢂ
+
ꢂ
+

L. Ding et al. / Tetrahedron: Asymmetry 19 (2008) 2653–2658
2657
tions of some chiral diamines by the CD spectra of their metallos-
4.6. N-(1S,2S)-1,2-Diphenylethylene(5-tertbutyl-2-hydrox-
alen complexes. In addition, the existence of the CD fingerprint at
460–480 nm means that the complex is unsymmetric, and vice
versa. This can also lead to an easy method to judge whether the
metallosalen complexes are symmetric or unsymmetric. Further
studies are under investigation.
yformylphenonylideneiminato)-N’-{(4-hydroxy-6-methyl-2-
pyrone)3-acetylidine} nickel(II)
A brick red solid, 76%, mp > 300 °C. IR(KBr): v 2926 (–CH2CH3),
1613 (C@N), 1174 (C–N), 1332 (C–O), 548 (Ni–N), 474 (Ni–O) cmꢂ1
.
Anal. Calcd for C33H32N2O4Ni: requires: C, 68.42; H, 5.57; N, 4.84.
Found: C, 68.23; H, 5.70; N, 4.39.
4. Experimental
4.1. General
4.7. N-(1R,2R)-1,2-Diphenylethylene(5-tertbutyl-2-hydrox
yformylphenonylideneiminato)-N’-{(4-hydroxy-6-methyl-2-
pyrone)3-acetylidine} nickel(II)
Unless otherwise noted, all starting materials and solvents were
obtained from commercial suppliers and used without further
purification. Infrared spectra (KBr pellets) were recorded on a Nico-
let 360 FT-IR spectrometer in the range of 400–4000 cmꢂ1. UV–vis
and CD spectra were performed, respectively, on a Shimadzu UV-
2501 PC spectrophotometer and a JASCO J-810 spectropolarimeter.
Elemental analysis was obtained from an Elementar Vario EL III
elemental analyzer. 1H NMR spectra were measured on a Bruker
DRX400 NMR spectrometer in CDCl3 using tetramethylsilane as
the internal standard. The UV–vis and CD spectra were obtained
at room temperature with the same methanol solutions ranging
from 10ꢂ4 to 10ꢂ5 mol/L using 5 mm quartz cells.
A brick red solid, 79%, mp >300 °C. IR(KBr): v 2926 (–CH2CH3),
1613 (C@N), 1174 (C–N), 1332 (C–O), 548 (Ni–N), 474 (Ni–O)
cmꢂ1. Anal. Calcd for C33H32N2O4Ni: requires: C, 68.42; H, 5.57;
N, 4.84. Found: C, 68.88; H, 5.32; N, 5.01.
4.8. N-(1S,2S)-1,2-Diphenylethylene(2-hydroxyaceto-
phenonylideneiminato)-N0-{(4-hydroxy-6-methyl-2-
pyrone)3-acetylidine} nickel(II)
A brick red solid, 78%, mp >300 °C. IR(KBr): v 2924 (–CH2CH3),
1615 (C@N), 1173 (C–N), 1318 (C–O), 547 (Ni–N), 468 (Ni–O) cmꢂ1
.
1H NMR (CDCl3, TMS, 400 MHz, ppm): 2.07 (3H, s, CH3), 2.10 (3H, s,
CH3), 2.14 (3H, s, CH3), 4.61 (H, m, CH–N), 4.74 (1H, m, CH–N), 5.93
(H, m, CH), 7.02–7.79 (14H, m, Ar). Anal. Calcd for C30H26N2O4Ni: re-
quires: C, 67.07; H, 4.88; N, 5.21. Found: C, 67.22; H, 5.22; N, 5.02.
4.2. N-(1S,2S)-1,2-Cyclohexylene(5-bromo-2-hydroxyformyl-
phenonylideneiminato)-N0-{(4-hydroxy-6-methyl-2-pyrone)3-
acetylidine} nickel(II)
A brick red solid, 73%, mp >300 °C. IR(KBr): v 2934 (–CH2CH3),
4.9. N-(1R,2R)-1,2-Diphenylethylene(2-hydroxyaceto-
phenonylideneiminato)-N0-{(4-hydroxy-6-methyl-2-pyrone)3-
acetylidine} nickel(II)
1621 (C@N), 1183 (C–N), 1322 (C–O), 582 (Ni–N), 448 (Ni–O) cmꢂ1
.
1H NMR (CDCl3, TMS, 400 MHz, ppm): 1.26 (2H, m, CH2), 1.70 (4H,
m, 2ꢄCH2), 1.90 (2H, m, CH2), 2.08 (3H, s, CH3), 2.57 (3H, s, CH3),
3.01 (H, m, CH–N), 3.58 (1H, m, CH–N), 5.87 (H, s, CH), 6.79–7.25
(3H, m, Ar), 7.26 (H, s, CH). Anal. Calcd for C21H21N2O4BrNi: requires:
C, 50.04; H, 4.20; N, 5.56. Found: C, 50.32; H, 4.43; N, 5.18.
A brick red solid, 78%, mp >300 °C. IR(KBr): v 2924 (–CH2CH3),
1615 (C@N), 1173 (C–N), 1318 (C–O), 547 (Ni–N), 468 (Ni–O)
cmꢂ1. Anal. Calcd for C30H26N2O4Ni: requires: C, 67.07; H, 4.88;
N, 5.21. Found: C, 67.46; H, 4.97; N, 5.34.
4.3. N-(1R,2R)-1,2-Cyclohexylene(5-bromo-2-hydroxyformyl-
phenonylideneiminato)-N0-{(4-hydroxy-6-methyl-2-pyrone)3-
acetylidine} nickel(II)
4.10. N-(1S,2S)-1,2-Cyclohexylene(2-hydroxyacetophen-
onylideneiminato)-N’-{(4-hydroxy-6-methyl-2-pyrone)3-
acetylidine} nickel(II)
A brick red solid, 76%, mp >300 °C. IR(KBr): v 2934 (–CH2CH3),
1621 (C@N), 1183 (C–N), 1322 (C–O), 582 (Ni–N), 448 (Ni–O)
cmꢂ1. Anal. Calcd for C21H21N2O4BrNi: requires: C, 50.04; H, 4.20;
N, 5.56. Found: C, 50.35; H, 4.45; N, 5.16.
A brick red solid, 71%, mp >300 °C. IR(KBr): v 2927 (–CH2CH3),
1622 (C@N), 1180 (C–N), 1325 (C–O), 583 (Ni–N), 452 (Ni–O)
cmꢂ1 1H NMR (CDCl3, TMS, 400 MHz, ppm): 1.36 (2H, m, CH2),
.
1.66 (4H, m, 2ꢄCH2), 1.83 (2H, m, CH2), 2.08 (3H, s, CH3), 2.46
(3H, s, CH3), 2.52 (3H, s, CH3), 3.71 (H, m, CH–N), 3.98 (1H, m,
CH–N), 5.84 (H, s, CH), 6.85–7.47 (4H, m, Ar). Anal. Calcd for
C22H24N2O4Ni: requires: C, 60.17; H, 5.51; N, 6.38. Found: C,
59.98; H, 6.66; N, 6.44.
4.4. N-(1S,2S)-1,2-Diphenylethylene(5-bromo-2-hydroxyformyl
phenonylideneiminato)-N0-{(4-hydroxy-6-methyl-2-pyrone)3-
acetylidine} nickel(II)
A brick red solid, 75%, mp >300 °C. IR(KBr): v 2924 (–CH2CH3),
1618 (C@N), 1179 (C–N), 1320 (C–O), 549 (Ni–N), 466 (Ni–O)
4.11. N-(1R,2R)-1,2-Cyclohexylene(2-hydrox-
yacetophenonylideneiminato)-N0-{(4-hydroxy-6-methyl-2-
pyrone)3-acetylidine} nickel(II)
cmꢂ1 1H NMR (CDCl3, TMS, 400 MHz, ppm): 2.15 (3H, s, CH3),
.
2.23 (3H,s, CH3), 4.40 (H, m, CH–N), 4.66 (1H, m, CH–N), 6.04 (H,
m, CH), 6.93–7.59 (10H, m, 2Ph), 7.98–7.99 (2H, m, Ar), 8.44–
8.45(2H, m, Ar, CH). Anal. Calcd for C29H23N2O4BrNi: requires: C,
57.85; H, 3.85; N, 4.65. Found: C, 57.68; H, 3.66; N, 4.74.
A brick red solid, 73%, mp >300 °C. IR(KBr): v 2927 (–CH2CH3),
1622 (C@N), 1180 (C–N), 1325 (C–O), 583 (Ni–N), 452 (Ni–O)
cmꢂ1. Anal. Calcd for C22H24N2O4Ni: requires: C, 60.17; H, 5.51;
N, 6.38. Found: C, 59.89; H, 6.61; N, 6.74.
4.5. N-(1R,2R)-1,2-Diphenylethylene(5-bromo-2-hydroxyformyl
phenonylideneiminato)-N’-{(4-hydroxy-6-methyl-2-pyrone)3-
acetylidine} nickel(II)
4.12. N-(1S,2S)-1,2-Cyclohexylene(5-tertbutyl-2-
hydroxyformylphen onylideneiminato)-N’-{(4-hydroxy-6-methyl-
2-pyrone)3-acetylidine} nickel(II)
A brick red solid, 75%, mp >300 °C. IR(KBr): v 2924 (–CH2CH3),
1618 (C@N), 1179 (C–N), 1320 (C–O), 549 (Ni–N), 466 (Ni–O)
cmꢂ1. Anal. Calcd for C29H23N2O4BrNi: requires: C, 57.85; H, 3.85;
N, 4.65. Found: C, 57.63; H, 3.46; N, 4.88.
A brick red solid, 69%, mp >300 °C. IR(KBr): v 2924 (–CH2CH3),
1619 (C@N), 1182 (C–N), 1327 (C–O), 578 (Ni–N), 447 (Ni–O)

2658
L. Ding et al. / Tetrahedron: Asymmetry 19 (2008) 2653–2658
cmꢂ1
.
1H NMR (CDCl3, TMS, 400 MHz, ppm): 1.26 (9H, s, 3ꢄCH3),
Hong, Y. P.; Nie, X. Y.; Zepp, C. M. J. Org. Chem. 1994, 59, 1939–1942; (e) Kureshy,
R. I.; Khan, N. H.; Abdi, S. H. R.; Patel, S. T.; Iyer, P.; Suresh, E.; Dastidar, P. J. Mol.
Catal. A: Chem. 2000, 160, 217–227; (f) Kureshy, R. I.; Khan, N. H.; Abdi, S. H. R.;
Iyer, P.; Bhatt, A. K. J. Mol. Catal. A: Chem. 1998, 130, 41–50.
1.33 (2H, m, CH2), 1.67 (4H, m, 2ꢄCH2), 1.80 (2H, m, CH2), 2.08
(3H, s, CH3), 2.54 (3H, s, CH3), 2.97 (H, m, CH–N), 3.53 (1H, m,
CH–N), 5.87 (H, s, CH), 6.86–7.17 (3H, m, Ar), 7.27 (H, s, CH). Anal.
Calcd for C25H30N2O4Ni: requires: C, 62.40; H, 6.28; N, 5.82. Found:
C, 61.87; H, 6.36; N, 6.01.
2. (a) Cozzi, P. G. Chem. Soc. Rev. 2004, 33, 410–421; (b) Katsuki, T. Chem. Soc. Rev.
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113; (f) Ray, M. S.; Bhattacharya, R.; Chaudhuri, C.; Righi, L.; Bocelli, G.;
Mukhopadhyay, G.; Ghosh, A. Polyhedron 2003, 22, 617–624; (g) Daly, A. M.;
Dalton, C. T.; Renehan, M. F.; Gilheany, D. G. Tetrahedron Lett. 1999, 40, 3617; (h)
Sasaki, I.; Pujol, D.; Gaudemer, A. Inorg. Chim. Acta 1987, 134, 53.
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4.13. N-(1R,2R)-1,2-Diphenylethylene(5-tertbutyl-2-hydroxy-
formylphenonylideneiminato)-N’-{(4-hydroxy-6-methyl-2-
pyrone)3-acetylidine} nickel(II)
A brick red solid, 74%, mp >300 °C. IR(KBr): v 2924 (–CH2CH3),
1619 (C@N), 1182 (C–N), 1327 (C–O), 578 (Ni–N), 447 (Ni–O)
cmꢂ1. Anal. Calcd for C25H30N2O4Ni: requires: C, 62.40; H, 6.28;
N, 5.82. Found: C, 62.15; H, 5.97; N, 5.78.
Acknowledgments
This work was supported by the Project of Innovation Founda-
tion of Xiamen University (Series 2, No. XDKJCX20061027), the Na-
tional NSF of China (Nos. 20773098 and 20572061), the Projects of
International Cooperation MOST (No. 2006DFA43030), and the Ma-
jor Program of National Natural Science Foundation of China (No.
20732004).
4. Zhang, H.; Li, L.; Chen, G.; Wang, F.; Fang, X. M.; Chen, J. G. Univ. Chem. 2005, 20,
39–43.
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(b) Bella, S. D.; Fragala, I.; Ledoux, I., et al J. Am. Chem. Soc. 1997, 119, 9550–
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6. Zhang, H.; Chen, Y. C.; Wang, F.; Qiu, X. M.; Li, L.; Chen, J. G. Acta Phys. Chim. Sin.
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