Oxime-based salen-type tetradentate ligands with high stability against imine metathesis reaction

Article abstract of DOI:10.1021/jo048030y

(Chemical Equation Presented) Although salen and its analogues are versatile chelate ligands in inorganic and organometallic chemistry, synthesis of unsymmetrical salen derivatives consisting of two different salicylideneimine moieties is difficult becaus

Full text of DOI:10.1021/jo048030y

Oxime-Based Salen-Type Tetradentate Ligands with High Stability
against Imine Metathesis Reaction
†
Shigehisa Akine, Takanori Taniguchi, Wenkui Dong, Sayuri Masubuchi, and
Tatsuya Nabeshima*
Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
nabesima@chem.tsukuba.ac.jp
Received November 5, 2004
Although salen and its analogues are versatile chelate ligands in inorganic and organometallic
chemistry, synthesis of unsymmetrical salen derivatives consisting of two different salicylideneimine
moieties is difficult because of the CdN bond recombination. To develop stable analogues of salen-
type ligands, we synthesized a series of new ligands salamo ()1,2-bis(salicylideneaminooxy)ethane)
on the basis of O-alkyl oxime instead of the imine moiety. Eight salamo ligands 1a-h were prepared
in 64-88% yields as colorless crystals from the corresponding salicylaldehydes 2a-h. The crystal
structure of 1a-c suggests that the oxime-OH form is more predominant than the keto-NH form.
The reaction of 2a-e with excess 1,2-bis(aminooxy)ethane gave monooximes 3a-e in 59-86%,
which further reacted with a different salicylaldehyde to afford unsymmetrical salamo ligands 4-8
as stable crystals in 51-70%. No reaction took place when a mixture of salamo derivatives 1a and
1
b was treated at 40 °C in H
2
O/MeCN (5:95). However, the metathesis reaction of salen derivatives
a and 9b completed in 2 h to give a statistical mixture. Monooxime 3b was much more stable
9
than monoimine 11 which is difficult to be isolated. These results indicate the extremely high
stability of the salamo derivatives 1 and precursors 3.
Introduction
hydrolysis.6 Such reversible CdN bond formation7 is
sometimes useful to synthesize the most thermodynami-
Salen (N,N′-disalicylideneethylenediamine) and its
analogues are most versatile chelate ligands in inorganic
and organometallic chemistry. Some of the metal com-
plexes are used as a catalyst in various organic reactions,
nonlinear optical materials, and metallomesogens or
exhibit interesting magnetic properties and so forth.
Although most of the metal complexes containing salen
8
9
cally stable macrocyclic and interlocked compounds in
high yields. The labile nature of the CdN bonds is also
successfully utilized to generate a dynamic combinatorial
library.10 However, such reversibility of the CdN bond
1
2
3
4
(
5) (a) Koehler, K.; Sandstrom, W.; Cordes, E. H. J. Am. Chem. Soc.
1
964, 86, 2413-2419. (b) T o´ th, G.; Pint e´ r, I.; Messmer, A. Tetrahedron
ligands are stable in solution and in the solid state, Cd
Lett. 1974, 735-738.
N bonds often suffer exchange reaction5 as well as
(6) Cordes, E. H.; Jencks, W. P. J. Am. Chem. Soc. 1962, 84, 832-
8
37.
(
7) For reviews, see: (a) Layer, R. W. Chem. Rev. 1963, 63, 489-
†
Present address: Department of Applied Chemistry, Lanzhou
510. (b) Rowan, S. J.; Cantrill, S. J.; Cousins, G. R. L.; Sanders, J. K.
M.; Stoddart, J. F. Angew. Chem., Int. Ed. 2002, 41, 898-952.
(8) (a) Schmidt, S.; Bauer, W.; Heinemann, F. W.; Lanig, H.;
Grohmann, A. Angew. Chem., Int. Ed. 2000, 39, 913-916. (b) Gawron-
ski, J.; Kolbon, H.; Kwit, M.; Katrusiak, A. J. Org. Chem. 2000, 65,
5768-5773. (c) Akine, S.; Taniguchi, T.; Nabeshima, T. Tetrahedron
Lett. 2001, 42, 8861-8864. (d) Zhao, D.; Moore, J. S. J. Org. Chem.
2002, 67, 3548-3554. (e) Akine, S.; Hashimoto, D.; Saiki, T.;
Nabeshima, T. Tetrahedron Lett. 2004, 45, 4225-4227.
(9) (a) Cantrill, S. J.; Rowan, S. J.; Stoddart, J. F. Org. Lett. 1999,
1, 1363-1366. (b) Rowan, S. J.; Stoddart, J. F. Org. Lett. 1999, 1, 1913-
1916.
Jiaotong University, Lanzhou 730070, China.
(1) (a) Jacobsen, E. N. Catalytic Asymmetric Synthesis; Ojima, I.,
Ed.; VCH: New York, 1993. (b) Katsuki, T. Coord. Chem. Rev. 1995,
40, 189-214.
2) (a) Di Bella, S.; Fragal a` , I. Synth. Met. 2000, 115, 191-196. (b)
1
(
Lacroix, P. G. Eur. J. Inorg. Chem. 2001, 339-348.
(
(
3) Hoshino, N. Coord. Chem. Rev. 1998, 174, 77-108.
4) (a) Bencini, A.; Benelli, C.; Caneschi, A.; Carlin, R. L.; Dei, A.;
Gatteschi, D. J. Am. Chem. Soc. 1985, 107, 8128-8136. (b) Costes,
J.-P.; Dahan, F.; Dupuis, A. Inorg. Chem. 2000, 39, 165-168. (c) Sasaki,
M.; Manseki, K.; Horiuchi, H.; Kumagai, M.; Sakamoto, M.; Sakiyama,
H.; Nishida, Y.; Sakai, M.; Sadaoka, Y.; Ohba, M.; Okawa, H. J. Chem.
Soc., Dalton Trans. 2000, 259-263.
(10) Huc, I.; Lehn, J.-M. Proc. Natl. Acad. Sci. U.S.A. 1997, 94,
2106-2110.
10.1021/jo048030y CCC: $30.25 © 2005 American Chemical Society
1704
J. Org. Chem. 2005, 70, 1704-1711
Published on Web 02/04/2005

Oxime-Based Salen-Type Ligand with High Stability
formation results in unfavorable ring contraction in the
metalation process of some cyclic salen derivatives.11,12
In some cases, macrocyclic imine is formed via CdN bond
recombination of an acyclic diamine.13
CHART 1
Synthesizing unsymmetrical salen derivatives, which
consist of two different salicylideneimine moieties, is
difficult because a statistical mixture of three possible
condensation products is usually obtained.14 Selective
synthesis of these unsymmetrical ligands is important
because electronic and steric effects of the ligands on
salen-metal-assisted catalysis may be controlled by in-
troduction of different substituents into the two benzene
rings. In early works, metal complexes of unsymmetrical
salen and analogues were prepared via the monoimine
complexes without isolation of the unsymmetrical free
SCHEME 1. Synthesis of Salamo Ligands 1
15,16
ligands.
Recently, chiral unsymmetrical salen polymer
complexes which are obtained from a statistical mixture
of symmetrical and unsymmetrical ligands have been
utilized for asymmetric catalysis.17 The unsymmetrical
salen derivatives can be also synthesized by stepwise
condensation. In some cases, however, isolation of the
intermediary monoimine as hydrochloride or (+)-O,O′-
dibenzoyl-D-tartarates is necessary to obtain the unsym-
metrical salens.1 The unsymmetrical ligands thus ob-
tained are sometimes contaminated by a small amount
of symmetrical ligands because of unavoidable dispro-
8
in our preliminary study.22 In this paper, we report
details of the synthesis and structure of the oxime-type
chelate ligands and their stability against exchange
reaction of the CdN bonds, compared with the corre-
sponding salen derivatives. Unsymmetrical salamo de-
rivatives are effectively synthesized because of their
stability.
1
4,18a
portionation.
Rate constants of oxime formation are smaller than
those of imine formation and the equilibrium constants
19
are larger by several orders. Hence, the oxime-type
ligands should be stable enough to resist the metathesis
of the CdN bonds. Thus, we planned synthesis of a new
salen-type chelate ligand salamo ()1,2-bis(salicylidene-
aminooxy)ethane) on the basis of O-alkyl oxime instead
of the imine moiety (Chart 1). Linear derivatives bearing
two salicylaldoxime moieties at both ends have been
Results and Discussion
Synthesis and Characterization of Symmetrical
Salamo Ligands. The oxime ligands 1 were synthesized
according to the procedures shown in Scheme 1. Reaction
2
0
23
reported. A cyclic ligand with a salamo moiety is
of 1,2-bis(aminooxy)ethane with 2 equivalents of sali-
21
isolated as mono- or binuclear complexes. However, the
intrinsic properties of salamo have been described only
cylaldehyde derivatives 2 in ethanol afforded the desired
chelates 1a-h as colorless crystals in 64-88% yields. The
products were easily obtained in pure form by filtering
the precipitates from the reaction mixture or recrystal-
lization. 1
(
11) (a) Dutta, S. K.; Fl o¨ rke, U.; Mohanta, S.; Nag, K. Inorg. Chem.
1
998, 37, 5029-5032. (b) Korupoju, S. R.; Mangayarkarasi, N.;
Ameerunisha, S.; Valente, E. J.; Zacharias, P. S. J. Chem. Soc., Dalton
Trans. 2000, 2845-2852.
In the H NMR spectra of 1a-h, singlets of methylene
protons and oxime protons were observed at 4.3-4.5 and
(12) (a) Nelson, S. M.; Esho, F. S.; Drew, M. G. B.; Bird, P. J. Chem.
Soc., Chem. Commun. 1979, 1035-1037. (b) Drew, M. G. B.; Nelson,
J.; Nelson, S. M. J. Chem. Soc., Dalton Trans. 1981, 1678-1684. (c)
Bailey, N. A.; Fenton, D. E.; Jackson, I. T.; Moody, R.; de Barbarin, C.
R. J. Chem. Soc., Chem. Commun. 1983, 1463-1465.
8
.1-8.4 ppm, respectively, showing the symmetrical
structure of 1 (Table 1). The OH resonance at 9-11 ppm
strongly suggests intramolecular hydrogen bonds be-
tween the oxime nitrogen and the phenolic hydroxyl
groups. In the 13C NMR spectra of 1, the signals of the
CdN carbon atoms were observed at 144-153 ppm. The
IR spectra clearly indicate the CdN group because CdN
stretching absorption bands of the ligands were observed
(
13) Houjou, H.; Nagawa, Y.; Hiratani, K. Tetrahedron Lett. 2001,
2, 3861-3863.
14) Sasaki, I.; Pujol, D.; Gaudemer, A. Inorg. Chim. Acta 1987, 134,
4
(
5
3-57.
(
15) Elder, R. C. Aust. J. Chem. 1978, 31, 35-45.
16) Paschke, R.; Balkow, D.; Sinn, E. Inorg. Chem. 2002, 41, 1949-
(
1
953.
(
17) (a) Konsler, R. G.; Karl, J.; Jacobsen, E. N. J. Am. Chem. Soc.
-1
at 1599-1627 cm . The electronic absorption spectra
1
998, 120, 10780-10781. (b) Annis, D. A.; Jacobsen, E. N. J. Am. Chem.
shows π-π* bands at 303-339 nm. Although the corre-
sponding salen analogues show a band around 400 nm
assigned to their keto-NH form and the π-π* bands (ca.
Soc. 1999, 121, 4147-4154. (c) Smith, K.; Liu, C.-H. Chem. Commun.
2
002, 886-887. (d) Bigi, F.; Moroni, L.; Maggi, R.; Sartori, G. Chem.
Commun. 2002, 716-717. (e) Anyanwu, U. K.; Venkataraman, D.
Tetrahedron Lett. 2003, 44, 6445-6448.
3
15 nm),24 1 showed no absorption around 400 nm. This
(
18) (a) Daly, A. M.; Dalton, C. T.; Renehan, M. F.; Gilheany, D. G.
Tetrahedron Lett. 1999, 40, 3617-3620. (b) Campbell, E. J.; Nguyen,
S.-B. T. Tetrahedron Lett. 2001, 42, 1221-1225.
fact indicates that the population of the keto-NH form
of salamo is negligibly small (Scheme 2).
(
19) Korpela, T. K.; M a¨ kel a¨ , M. J. Anal. Biochem. 1981, 110, 251-
2
57.
20) Rasshofer, W.; M u¨ ller, W. M.; Oepen, G.; V o¨ gtle, F. J. Chem.
Res. Miniprint 1978, 1001-1013.
21) van Veggel, F. C. J. M.; Harkema, S.; Bos, M.; Verboom, W.;
Woolthuis, G. K.; Reinhoudt, D. N. J. Org. Chem. 1989, 54, 2351-
359.
(
(22) (a) Akine, S.; Taniguchi, T.; Nabeshima, T. Chem. Lett. 2001,
682-683. (b) Akine, S.; Taniguchi, T.; Nabeshima, T. Inorg. Chem.
2004, 43, 6142-6144.
(23) Dixon, D. W.; Weiss, R. H. J. Org. Chem. 1984, 49, 4487-4494.
(24) Smith, H. E. Chem. Rev. 1983, 83, 359-377.
(
2
J. Org. Chem, Vol. 70, No. 5, 2005 1705

Akine et al.
TABLE 1. Spectroscopic Data for Salamo Ligands 1
compound
δH (CH2)a
δH (CHdN)a
δH (OH)a
δC (CHdN)a
ν(CdN)b
λ(π-π*)c
1
1
1
1
1
1
1
1
a
b
c
d
e
f
4.49
4.49
4.48
4.47
4.48
4.33d
4.50d
4.43
8.25
8.26
8.26
8.24
8.14
8.31d
8.22d
8.36
9.75
152.3
152.0
153.4
151.9
151.0
1608
1605
1612
1599
1613
1609
1626
1627
310
316
321
327
323
339
317
303
9.74
10.15
10.35
9.74
d
d
9.02, 9.34
5e.56, 9.89
147.3
g
h
152.1
144.7
d
a
In CDCl3. b KBr. c In MeOH (2 × 10-5 M). d In DMSO-d6. e The OH signal was not observed.
SCHEME 2
diamine or cyclohexanediamine are generally unstable
and cannot be isolated.15
By using the stable monooximes 3, we can obtain
unsymmetrical salamo ligands 4-8 bearing two different
salicylaldoxime moieties. The reaction of the monooximes
3
with appropriate salicylaldehyde in ethanol afforded
the unsymmetrical salamo derivatives 4-8 as colorless
crystals in 51-70% yields. The compounds are suf-
ficiently stable in solution as well as in the solid state.
This method has been also applied to the synthesis of a
linear bis(salamo) ligand containing two unsymmetrically
substituted salamo chelate moieties.25
SCHEME 3. Synthesis of Unsymmetrical Salamo
Ligands 4-8
On the other hand, the corresponding unsymmetrical
salen ligands can be obtained after chromatographic
separation of the mixture containing symmetrical and
15
unsymmetrical ligands. Recently, more rational meth-
ods for the reaction have been reported.18 Intermediate
monoimine was isolated as hydrochlorides or (+)-O,O′-
dibenzoyl-D-tartarates, which are further allowed to react
with aldehydes to afford unsymmetrical salen ligands.
However, this method is effective only when the mono-
imine forms a crystalline salt. Although the aromatic
analogues of the monoimine derivatives are much more
stable and can be isolated in high yield, a mixture of the
three possible condensation products is obtained in the
unsymmetrical saloph derivatives.14 This is probably due
to the exchange of the CdN bonds to cause redistribution
of the aldehyde units of the unsymmetrical ligands.
We established a general synthetic method for unsym-
metrical salamo ligands involving stepwise introduction
of two different aldehyde units. Effectiveness of the
method is mainly owing to the stability of the intermedi-
ate monooximes 3, which can be easily isolated. In
addition, greater stability of the unsymmetrical salamo
derivatives 4-8 than that of the imine analogues (vide
infra) also contributes to the higher yields.
Synthesis of Unsymmetrical Salamo Ligands via
Monooxime. To synthesize the unsymmetrical salamo
derivatives, stepwise introduction of the salicylidene
moieties at both ends of 1,2-bis(aminooxy)ethane is
effective (Scheme 3). Thus, we prepared the intermedi-
ates, monooximes 3. The reaction of salicylaldehydes with
excess 1,2-bis(aminooxy)ethane gave a mixture contain-
ing the desired monooximes 3 and a small amount of
dioximes 1. The pure monooximes 3a-e were obtained
in 59-86% yields after silica gel chromatographic sepa-
ration of the crude product. The monooximes 3 were
obtained as stable crystals or an oil. The reaction of
salicylaldehydes with diamines is also reported to give
the corresponding monoimine derivatives. Whereas the
monoimine derivatives obtained from phenylenediamine
Structure of Salamo Ligands. X-ray crystallo-
graphic analysis revealed the crystal structure of the
oxime chelate ligands 1a, 1b, 1c, and 4. A noticeable
conformational difference was observed in the N-O-
CH
2
-CH -O-N linkage between two salicylidene moi-
2
eties of the four molecules, whereas geometries of the
salicylaldoxime moieties are similar.
Parent salamo 1a crystallizes in the triclinic system,
in which two crystallographically independent molecules
exist. The two molecules have similar conformation in
which two salicylidene moieties are apart from each other
(
Figure 1). The torsion angles of the C-C bond and one
C-O bond in the linkage N-O-CH -CH -O-N are in
2
2
(
25) Akine, S.; Taniguchi, T.; Nabeshima, T. Angew. Chem., Int. Ed.
1
4
are isolable, aliphatic analogues containing ethylene-
2002, 41, 4670-4673.
1706 J. Org. Chem., Vol. 70, No. 5, 2005

Oxime-Based Salen-Type Ligand with High Stability
TABLE 2. Selected Torsion Angles (deg) of Salamo Ligands 1a, 1b, 1c, and 4
1
a (Aa)
1a (Ba)
1b
1c (Aa)
1c (Ba)
4
C-CdN-O
CdN-O-C
N-O-C-C
O-C-C-O
C-C-O-N
C-O-NdC
O-NdC-C
-179.63(13)
178.39(13)
-67.09(17)
-59.97(18)
179.50(13)
-175.51(15)
-179.88(14)
-179.44(14)
-179.51(14)
-69.92(18)
-65.12(19)
176.40(13)
178.82(15)
178.96(14)
179.0(5)
178.6(5)
177.6(6)
180
-178.4(2)
176.9(2)
-68.6(3)
65.3(5)
177.4(2)
176.2(2)
168.2(2)
-77.4(5)
177.5(2)
-178.1(2)
70.5(3)
-76.7(3)
-178.6(2)
-174.4(2)
-179.1(2)
a
Crystallographically independent molecules.
FIGURE 1. Crystal structure of 1a. One of the crystallo-
graphically independent molecules is shown. Thermal el-
lipsoids are plotted at 50% probability level.
FIGURE 2. Crystal structure of 1b. Thermal ellipsoids are
plotted at 50% probability level.
FIGURE 3. Crystal structure of 1c. Two crystallographically
independent molecules, A and B, are shown. Thermal ellipsoids
are plotted at 30% probability level.
the range of 60-70°, while those of the N-O bond and
the other C-O bond are around 180° (Table 2). The two
successive bonds in a gauche conformation make the
molecule nonplanar, folded at the center of the molecule.
On the other hand, the methoxy derivative 1b has
almost planar conformation in which two salicylaldoxime
moieties are apart from each other (Figure 2). There is a
crystallographic center of symmetry at the middle point
of the C-C bond. All the torsion angles around the C-C,
C-O, and O-N bonds in the linkage are about 180°,
indicating the all-trans conformation (Table 2).
Compound 1c, which has two tert-butyl groups at each
salicylaldoxime moiety, adopts an extended form (Figure
3
). The unit cell contains two crystallographically in-
dependent molecules with different conformations, al-
though both molecules have a crystallographically im-
posed twofold axis. The linkage of the molecule A
contains three bonds in a gauche conformation (C-C
bond and two C-O bonds), whereas molecule B has only
one (C-C bond).
FIGURE 4. Crystal structure of unsymmetrical ligand 4.
Thermal ellipsoids are plotted at 50% probability level.
The structure of unsymmetrical derivative 4, which has
two different salicylaldoxime moieties, was also deter-
mined by X-ray crystallography (Figure 4). The C-C
bond and one C-O bond have a gauche conformation
O-N distances between the hydroxyl groups and the
oxime nitrogen atoms are in the range of 2.60-2.68 Å
(Table 3), indicating strong O-H‚‚‚N hydrogen bonds.
Observation of OH resonance at 9.7-10.4 ppm in the
1
(torsion angles: 76.7 and 70.5°, respectively), whereas
NMR spectra also supports the hydrogen bonding. The
the other C-O bond has an anti conformation.
hydrogen bonds should stabilize the E geometry of the
oxime bonds. Generally, salicylaldimine derivatives exist
as a mixture of two tautomers, that is, imine-OH and
keto-NH forms, in solution.26 In some cases, the keto-
In all cases, intramolecular hydrogen bonds are found
between the hydroxyl groups and the oxime nitrogen
while there are no intermolecular hydrogen bonds. The
J. Org. Chem, Vol. 70, No. 5, 2005 1707

Akine et al.
TABLE 3. Selected Interatomic Distances (Å) of Salamo Ligands 1a, 1b, 1c, and 4
1
a (Aa)
2.677(2)
.637(2)
1.361(2)
.356(2)
1.402(2)
.405(3)
1.454(3)
.449(2)
1.281(2)
.274(2)
1a (Ba)
1b
1c (Aa)
1c (Ba)
4
SA1b
2.597
SA2c
O-H‚‚‚Nd
C-OH
2.641(2)
2.632(2)
1.352(2)
1.354(2)
1.410(3)
1.401(3)
1.454(2)
1.453(2)
1.277(2)
1.271(2)
2.631(6)
2.650(3)
2.606(3)
2.635(3)
2.642(4)
1.360(3)
1.362(4)
1.398(4)
1.400(4)
1.458(4)
1.454(4)
1.277(4)
1.275(4)
2.514
2
1.367(6)
1.396(7)
1.458(8)
1.284(7)
1.364(3)
1.396(4)
1.454(4)
1.273(3)
1.360(3)
1.396(3)
1.454(3)
1.273(3)
1.350(2)
1.412(3)
1.457(3)
1.291(2)
1.310(1)
1.433(2)
1.425(1)
1.308(1)
1
COH-CArCdN
CAr-CCdN
CdN
1
1
1
a
b
Crystallographically independent molecules. c 4-Chloro-2-(phenyliminomethyl)phenol. This compound exists exclusively as imine-
OH form in the crystalline state at 90 K (ref 27). 4-Chloro-2-((4-hydroxyphenyl)iminomethyl)phenol. This compound exists exclusively
d
as keto-NH form in the crystalline state at 90 K (ref 27). The distances between O and N in the O-H‚‚‚N hydrogen bonds.
FIGURE 6. (a) Metathesis reaction of salen derivatives 9a
FIGURE 5. Chromatograms of HPLC for analysis of stability
of salamo derivatives. (a) Equimolar mixture of 1a and 1b and
2
and 9b in H O/MeCN (5:95) at 40 °C monitored by HPLC. A:
benzamide (internal standard), B: 9b, C: scrambled product
(10), D: 9a. (b) Time dependence of mole fraction of 9a (filled
squares) and 9b (open squares) determined by HPLC.
(
2
b) 4 in H O/MeCN (5:95) at 40 °C monitored by HPLC.
NH form can be also observed in the crystalline state.
However, the bond distances of the C-OH (1.35-1.37 Å)
and CdN (1.27-1.28 Å) of the salamo derivatives are
almost the same as those of 4-chloro-2-(phenyliminom-
ethyl)phenol, which exists exclusively as imine-OH form
1
0 at 4.8 min. The intensity of the new peak increased
as those of 9a and 9b at 5.1 and 4.4 min, respectively,
became smaller (Figure 6, a). After 2 h, the scrambling
reaction reached equilibrium in which the ratio of 9a,
9b, and 10 is nearly 1:1:2 (Figure 6, b). Under these
2
7
(Table 3). The results strongly indicate that the oxime-
28
conditions, the half-life of the reaction is around 30 min.
The scrambling also took place in CDCl containing a
From these results, salamo
ligands are at least 10 times more stable against the
metathesis reaction in H O/MeCN (5:95) at 40 °C than
OH form is more favorable in the crystalline state in the
salamo ligands. The observation is consistent with the
absence of the band at 400 nm in the absorption spectra
of 1.
Stability of Unsymmetrical Salamo Ligands. Ki-
netic stability of the salamo derivatives against the
CdN metathesis reaction was studied by comparison
with the corresponding salen derivatives. An equimolar
3
22a
small amount of water.
4
2
the salen ligands (Scheme 4).
Stability of Monooximes. Since the synthetic dif-
ficulty of unsymmetrical salen derivatives is mainly
attributed to the instability of monoimine derivatives,
1
5
mixture of 1a and 1b was heated at 40 °C in H
2
O/MeCN
investigation of the stability of monooxime derivatives 3
(
5:95) solution (10 mM) and the reaction was monitored
is important.29 The signals of 1,2-bis(aminooxy)ethane
by HPLC (Figure 5, a). The retention times of 1a and 1b
are 4.6 and 3.3 min, respectively. Even after 50 d, no
reaction took place. In addition, unsymmetrical ligand 4
is also stable under similar conditions (Figure 5, b). These
results indicate that the forward and reverse reactions
of the equilibrium involving the CdN exchange of 1a, 1b,
and 4 are slow. Since the conversion of the reaction is
estimated to be less than 5%, the half-life time is
1
and salamo derivative 1b were not observed in the H
NMR spectrum when a solution of the monooxime 3b in
3
CDCl was allowed to stand for 50 d. Similarly, the
reaction of salamo derivative 1b with 1,2-bis(aminooxy)-
ethane did not give monooxime 3b. Thus, the dispropor-
tionation equilibrium of 3b is very slow. These results
indicate that the monooxime 3b is sufficiently stable in
CDCl
ethylenediamine in CDCl
an equilibrated mixture containing 9b, ethylenediamine,
5
3
. On the other hand, the reaction of salen 9b with
calculated to be >7 × 10 min.
3
completed in 1-2 min to give
In contrast, the corresponding salen derivatives are
much less stable. Heating an equimolar mixture of 9a
and 9b resulted in a new peak of the scrambled product
(
28) The rate constants for forward and reverse reactions of the
scrambling cannot be determined because the time dependence of mole
fractions did not obey the ideal second-order kinetics, probably because
of the existence of a small amount of intermediates.
(29) Polyakov, V. A.; Nelen, M. I.; Nazarpack-Kandlousy, N.; Ryabov,
A. D.; Eliseev, A. V. J. Phys. Org. Chem. 1999, 12, 357-363.
(
26) Dudek, G. O.; Dudek, E. P. J. Am. Chem. Soc. 1966, 88, 2407-
412.
27) Ogawa, K.; Kasahara, Y.; Ohtani, Y.; Harada, J. J. Am. Chem.
Soc. 1998, 120, 7107-7108.
2
(
1708 J. Org. Chem., Vol. 70, No. 5, 2005

Oxime-Based Salen-Type Ligand with High Stability
SCHEME 4. Scrambling of Two Chelate Ligands
derivatives. Monooxime derivatives 3 were also synthe-
sized as stable compounds, whereas imine analogues
were difficult to be isolated. The stability of precursors
3
facilitates the synthesis of unsymmetrical salamo
derivatives. Thus, the oxime ligands 1 and unsym-
metrical analogues 4-8, as well as its precursors 3, may
be promising units for the construction of multidentate
ligands containing different kinds of CdN metal-chelate
sites.
Experimental Section
General Procedure for the Synthesis of Symmetrical
Salamo Ligands 1. A solution of 1,2-bis(aminooxy)ethane
(
0.25 mmol) in ethanol (5 mL) was added to a solution of
salicylaldehyde derivative (0.50 mmol) in ethanol (5 mL) and
the mixture was heated at 50-55 °C for 1-2 h. After cooling
to room temperature, white precipitates were collected on a
suction filter to give salamo compound 1.
1
a. Obtained from 2-hydroxybenzaldehyde (491 mg, 4.02
mmol) and 1,2-bis(aminooxy)ethane (185 mg, 2.01 mmol) in
SCHEME 5. Disproportionation Equilibrium of
Monooxime 3b or Monoimine 11
1
8
3% yield as colorless crystals, mp 113-114 °C, H NMR (400
MHz, CDCl ) δ 4.49 (s, 4H), 6.91 (t, J ) 7.6 Hz, 2H), 6.99 (d,
J ) 7.6 Hz, 2H), 7.17 (dd, J ) 7.6, 1.6 Hz, 2H), 7.29 (t, J ) 7.6
Hz, 2H), 8.25 (s, 2H), 9.75 (s, 2H), C NMR (100 MHz, CDCl
δ 73.0 (CH
31.4 (CH), 152.3 (CHdN), 157.4 (C). Anal. calcd for C16H
16
3
13
3
)
2
), 116.2 (C), 116.8 (CH), 119.7 (CH), 130.9 (CH),
1
-
2 4
N O : C, 63.99; H, 5.37; N. 9.33. Found: C, 63.54; H, 5.52; N,
.16.
9
1
b. Obtained from 2-hydroxy-3-methoxybenzaldehyde (199.2
mg, 1.31 mmol) and 1,2-bis(aminooxy)ethane (60.3 mg, 0.655
1
mmol) in 79% yield as colorless crystals, mp 132-134 °C, H
3
NMR (400 MHz, CDCl ) δ 3.91 (s, 6H), 4.49 (s, 4H), 6.83 (dd,
J ) 7.9, 1.9 Hz, 2H), 6.86 (t, J ) 7.9 Hz, 2H), 6.91 (dd, J )
13
7
.9, 1.9 Hz, 2H), 8.26 (s, 2H), 9.74 (s, 2H), C NMR (100 MHz,
CDCl ) δ 56.2 (CH ), 73.0 (CH ), 113.5 (CH), 116.5 (C), 119.4
CH), 122.4 (CH), 147.1 (C), 148.2 (C), 152.0 (CHdN). Anal.
calcd for C18 : C, 59.99; H, 5.59; N, 7.77. Found: C,
9.97; H, 5.87; N, 7.61.
c. Obtained from 3,5-di(tert-butyl)-2-hydroxybenzaldehyde
522.0 mg, 2.23 mmol) and 1,2-bis(aminooxy)ethane (102.6 mg,
.11 mmol) in 74% yield. The sample was purified by recrys-
tallization from chloroform/hexane to give colorless crystals,
3
3
2
(
20 2 6
H N O
5
1
(
1
and monoimine 11. The half-life of the formation of 9b
and ethylenediamine by the CdN exchange of 11 is also
around 1 min. Consequently, the reaction of the dispro-
portionation of monooxime 3b is quite slower than that
of monoimine 11 (Scheme 5).
These results indicate the extremely high stability of
the salamo derivatives 1 and precursors 3. The low
reactivity of monooxime precursors 3 facilitates the
synthesis of unsymmetrical salen ligands bearing two
different salicylidene units at each end of the diimine
bridge. In addition, the resultant salamo ligands that
have two oxime bonds show sufficient stability to avoid
the scrambling reaction. The results contrast sharply
with the labile nature of salen ligands.
1
mp 113-115 °C, H NMR (400 MHz, CDCl
1.43 (s 18H), 4.48 (s, 4H), 6.98 (d, J ) 2.5 Hz, 2H), 7.34 (d, J
) 2.5 Hz, 2H), 8.26 (s, 2H), 10.15 (s, 2H), C NMR (100 MHz,
CDCl ) δ 29.5 (CH ), 31.5 (CH ), 34.1 (C), 35.1 (C), 73.0 (CH ),
15.6 (C), 125.7 (CH), 126.2 (CH), 136.4 (C), 141.2 (C), 153.4
CHdN), 154.3 (C). Anal. calcd for C32 ‚0.25H O: C,
2.62; H, 9.24; N, 5.29. Found: C, 72.41; H, 8.98; N, 5.23.
3
) δ 1.29 (s, 18H),
1
3
3
3
3
2
1
(
H
48
N
O
2 4
2
7
3
0
1
d. Obtained from 2-hydroxy-3-methylthiobenzaldehyde
(
0
84.2 mg, 0.50 mmol) and 1,2-bis(aminooxy)ethane (23.1 mg,
1
.25 mmol) in 74% as colorless crystals, mp 107-108 °C, H
NMR (400 MHz, CDCl ) δ 2.46 (s, 6H), 4.47 (s, 4H), 6.91 (t, J
) 7.7 Hz, 2H), 7.03 (dd, J ) 7.7, 1.4 Hz, 2H), 7.21 (dd, J )
3
13
7.7, 1.4 Hz, 2H), 8.24 (s, 2H), 10.35 (s, 2H), C NMR (100 MHz,
CDCl ) δ 15.1 (CH ), 73.0 (CH ), 115.5 (C), 120.0 (CH), 125.8
C), 127.9 (CH), 128.9 (CH), 151.9 (CHdN), 154.4 (C). Anal.
calcd for C18 : C, 55.08; H, 5.14; N, 7.14. Found: C,
4.92; H, 5.06; N, 7.01.
3
3
2
(
20 2 4 2
H N O S
5
Conclusion
1
e. Obtained from 5-bromo-2-hydroxybenzaldehyde (100.5
mg, 0.50 mmol) and 1,2-bis(aminooxy)ethane (23.0 mg, 0.25
We have designed and synthesized a new series of
salen-type chelate ligands that have two oxime bonds
instead of imine bonds. The ligands are prepared by the
reaction of 1,2-bis(aminooxy)ethane with 2 equivalents
of salicylaldehyde derivatives under mild conditions. The
metathesis of the CdN bonds of the salamo derivatives
1
mmol) in 64% as colorless crystals, mp 144.5-145.5 °C, H
NMR (400 MHz, CDCl
3
) δ 4.48 (s, 4H), 6.87 (d, J ) 8.6 Hz,
2
8
H), 7.26 (d, J ) 2.5 Hz, 2H), 7.36 (dd, J ) 8.6, 2.5 Hz, 2H),
13
3
.14 (s, 2H), 9.74 (s, 2H), C NMR (100 MHz, CDCl ) δ 73.3
(CH ), 111.2 (C), 117.8 (C), 118.7 (CH), 132.9 (CH), 134.0 (CH),
2
did not occur in H
derivatives are at least 10 times more stable than salen
2
O/MeCN (5:95). Hence, the salamo
(
30) Ando, M.; Emoto, S. Bull. Chem. Soc. Jpn. 1978, 51, 2435-
4
2436.
J. Org. Chem, Vol. 70, No. 5, 2005 1709

Akine et al.
1
51.0 (CHdN), 156.4 (C). Anal. calcd for C16
1.95; H, 3.08; N, 6.12. Found: C, 41.78; H, 3.04; N, 6.06.
f. Obtained from 2,5-dihydroxybenzaldehyde (93.0 mg, 0.67
mmol) and 1,2-bis(aminooxy)ethane (30.6 mg, 0.33 mmol) in
H
14Br
2
N
2
O
4
: C,
141.2 (C), 153.2 (CHdN), 154.3 (C). Anal. calcd for C17
0.25H O: C, 65.25; H, 9.18; N, 8.95. Found: C, 65.33; H, 8.91;
N, 8.75.
28 2 3
H N O ‚
4
2
1
3d. Prepared from 2-hydroxy-3-methylthiobenzaldehyde
1
7
7% as colorless crystals, mp 236.5-237.5 °C, H NMR (400
MHz, DMSO-d ) δ 4.33 (s, 4H), 6.67 (dd, J ) 8.8, 2.4 Hz, 2H),
.70 (d, J ) 8.8 Hz, 2H), 6.93 (d, J ) 2.4 Hz, 2H), 8.31 (s, 2H),
.02 (s, 2H), 9.34 (s, 2H), 13C NMR (100 MHz, DMSO-d
) δ
2.5 (CH ), 112.6 (CH), 117.5 (CH), 118.1 (C), 119.3 (CH), 147.3
: C,
7.83; H, 4.85; N, 8.43. Found: C, 57.57; H, 4.86; N, 8.17.
(84.1 mg, 0.50 mmol) and 1,2-bis(aminooxy)ethane (92.1 mg,
1
6
1.0 mmol) in 86% yield as pale yellow oil, H NMR (400 MHz,
6
9
7
3
CDCl ) δ 2.47 (s, 3H), 3.97 (t, J ) 4.5 Hz, 2H), 4.37 (t, J ) 4.5
6
Hz, 2H), 5.52 (brs, 2H), 6.92 (t, J ) 7.6 Hz, 1H), 7.02 (dd, J )
7.6, 1.4 Hz, 1H), 7.22 (dd, J ) 7.6, 1.4 Hz, 1H), 8.21 (s, 1H),
2
1
3
(
CHdN), 149.4 (C), 150.3 (C). Anal. calcd for C16
H
16
N
2
O
6
10.42 (s, 1H). C NMR (100 MHz, CDCl
(CH ), 73.6 (CH
128.8 (CH), 151.5 (CHdN), 154.4 (C). Anal. calcd for C10
S‚0.2H O: C, 48.84; H, 5.90; N, 11.39. Found: C, 48.98;
H, 5.80; N, 10.99.
3
) δ 15.1 (CH
3
), 72.8
5
2
2
), 115.6 (C), 120.0 (CH), 125.9 (C), 127.8 (CH),
3
1
1
g. Obtained from 2,3-dihydroxybenzaldehyde (276.4 mg,
14
H -
2
.0 mmol) and 1,2-bis(aminooxy)ethane (92.0 mg, 1.0 mmol)
N
2
O
3
2
1
in 88% as colorless crystals, mp 111.5-112.5 °C, H NMR (400
MHz, CDCl ) δ 4.50 (s, 4H), 5.56 (s, 2H), 6.74 (dd, J ) 7.8, 1.6
3
3e. Prepared from 5-bromo-2-hydroxybenzaldehyde (100.5
Hz, 2H), 6.83 (t, J ) 7.8 Hz, 2H), 6.97 (dd, J ) 7.8, 1.6 Hz,
mg, 0.50 mmol) and 1,2-bis(aminooxy)ethane (92.1 mg, 1.0
H), 8.22 (s, 2H), 9.89 (s, 2H), 13C NMR (100 MHz, CDCl
) δ
1
2
7
3
mmol) in 59% as colorless crystals, mp 60-61 °C, H NMR
3.1 (CH
2
), 115.9 (C), 116.7 (CH), 120.2 (CH), 121.9 (CH), 144.1
3
(400 MHz, CDCl ) δ 3.97 (t, J ) 4.5 Hz, 2H), 4.38 (t, J ) 4.5
(
C), 144.7 (C), 152.1 (CHdN). Anal. calcd for C16
H
16
N
2
O
6
: C,
Hz, 2H), 5.53 (brs, 2H), 6.88 (d, J ) 9.0 Hz, 1H), 7.27 (d, J )
5
7.83; H, 4.85; N, 8.43. Found: C, 57.75; H, 4.86; N, 8.25.
2.5 Hz, 1H), 7.36 (dd, J ) 9.0, 2.5 Hz, 1H), 8.13 (s, 1H), 9.85
3
2
13
1
h. Obtained from 2-hydroxy-5-nitrobenzaldehyde (83.7
(s, 1H), C NMR (100 MHz, CDCl
3
) δ 72.9 (CH
2
), 73.7 (CH
2
),
mg, 0.50 mmol) and 1,2-bis(aminooxy)ethane (23.0 mg, 0.25
mmol) in 79% as colorless crystals, mp 202-203 °C, H NMR
111.2 (C), 118.0 (C), 118.6 (CH), 132.7 (CH), 133.8 (CH), 150.5
1
9 2 3
(CHdN), 156.4 (C). Anal. calcd for C H11BrN O : C, 39.29; H,
(
400 MHz, DMSO-d
6
) δ 4.43 (s, 4H), 7.01 (d, J ) 9.2 Hz, 2H),
4.03; N, 10.18. Found: C, 39.73; H, 3.97; N, 10.02.
8
.10 (dd, J ) 9.2, 2.6 Hz, 2H), 8.359 (d, J ) 2.6 Hz, 2H), 8.362
General Procedure for the Synthesis of Unsymmetri-
cal Salamo Ligands 4-8. A solution of monooxime 3 (0.10
mmol) in ethanol (2 mL) was added to a solution of salicyla-
ldehyde derivative (0.10 mmol) in ethanol (2 mL) and the
mixture was heated at 50-55 °C for 1 h. After cooling to room
temperature, white precipitates were collected on a suction
filter to give colorless crystals of 4-8.
1
3
(
s, 2H), the OH signal was not observed, C NMR (100 MHz,
) δ 73.1 (CH ), 117.1 (CH), 118.9 (C), 122.7 (CH),
DMSO-d
6
2
1
27.1 (CH), 140.2 (C), 144.7 (CHdN), 162.0 (C). Anal. calcd
for C16
14 4 8
H N O : C, 49.24; H, 3.62; N, 14.35. Found: C, 49.12;
H, 3.69; N, 14.00.
General Procedure for the Synthesis of Monooxime
Ligands 3. A solution of 1,2-bis(aminooxy)ethane (92 mg, 1.0
mmol) in ethanol (2 mL) was added to a solution of salicyl-
aldehyde derivative (0.50 mmol) in ethanol (2 mL) and the
mixture was heated at 50-55 °C for 1 h. The solution was
concentrated in vacuo and the residue was purified by column
4. Prepared from monooxime 3b (90.5 mg, 0.40 mmol) and
2-hydroxybenzaldehyde (48.8 mg, 0.40 mmol) in 56% as
colorless crystals after recrystallization (chloroform/hexane),
1
mp 80-81 °C, H NMR (400 MHz, CDCl ) δ 3.91 (s, 3H), 4.49
3
(s, 4H), 6.82 (dd, J ) 7.6, 1.7 Hz, 1H), 6.86 (t, J ) 7.6 Hz, 1H),
6.90 (t, J ) 7.8 Hz, 1H), 6.92 (dd, J ) 7.6, 1.7 Hz, 1H), 6.98 (d,
J ) 7.8 Hz, 1H), 7.16 (dd, J ) 7.8, 1.7 Hz, 1H), 7.28 (t, J ) 7.8
Hz, 1H), 8.24 (s, 1H), 8.25 (s, 1H), 9.74 (s, 1H), 9.75 (s, 1H).
2
chromatography (SiO , chloroform/ethyl acetate, 50:1) to afford
oil or crystals of 3.
3
a. Prepared from 2-hydroxybenzaldehyde (245 mg, 2.01
1
3
mmol) and 1,2-bis(aminooxy)ethane (368 mg, 4.00 mmol) in
8
4
C NMR (100 MHz, CDCl
2
3 3 2
) δ 56.1 (CH ), 72.9 (CH ), 73.1
1
1% as colorless oil, H NMR (400 MHz, CDCl
3
) δ 3.98 (t, J )
(CH ), 113.5 (CH), 116.1 (C), 116.4 (C), 116.7 (CH), 119.4 (CH),
.6 Hz, 2H), 4.37 (t, J ) 4.6 Hz, 2H), 5.53 (brs, 2H), 6.91 (t, J
7.7 Hz, 1H), 6.98 (d, J ) 7.7 Hz, 1H), 7.16 (dd, J ) 7.7, 1.4
119.6 (CH), 122.4 (CH), 130.9 (CH), 131.3 (CH), 147.1 (C),
)
148.1 (C), 151.9 (CHdN), 152.3 (CHdN), 157.4 (C). Anal. calcd
1
3
Hz, 1H), 7.28 (t, J ) 7.7 Hz, 1H), 8.22 (s, 1H), 9.82 (s, 1H).
C
18 2 5
for C17H N O : C, 61.81; H, 5.49; N, 8.48. Found: C, 61.69;
NMR (100 MHz, CDCl
3
) δ 72.6 (CH
2
), 73.7 (CH
2
), 116.2 (C),
H, 5.56; N, 8.34.
1
16.7 (CH), 119.6 (CH), 130.7 (CH), 131.2 (CH), 151.3 (CHd
N), 157.3 (C). Anal. calcd for C ‚0.2H O: C, 54.10; H,
.26; N, 14.02. Found: C, 54.38; H, 6.10; N, 13.68.
5. Prepared from monooxime 3b (22.6 mg, 0.10 mmol) and
9
H
12 2
N O
3
2
2-hydroxy-3-methylthiobenzaldehyde (16.8 mg, 0.10 mmol) in
1
6
66% as colorless crystals, mp 117-117.5 °C, H NMR (400
3
b. Prepared from 2-hydroxy-3-methoxybenzaldehyde (644
3
MHz, CDCl ) δ 2.46 (s, 3H), 3.90 (s, 3H), 4.48 (s, 4H), 6.82
mg, 4.23 mmol) and 1,2-bis(aminooxy)ethane (774 mg, 8.40
mmol) in 71% yield as colorless crystals after recrystallization
(dd, J ) 7.9, 2.3 Hz, 1H), 6.85 (t, J ) 7.6 Hz, 1H), 6.90 (t, J )
7.6 Hz, 1H), 6.91 (dd, J ) 7.8, 2.3 Hz, 1H), 7.02 (dd, J ) 7.6,
1.3 Hz, 1H), 7.21 (dd, J ) 7.6, 1.3 Hz, 1H), 8.23 (s, 1H), 8.26
1
(
chloroform/hexane), mp 96-97 °C, H NMR (400 MHz, CDCl
3
)
13
δ 3.91 (s, 3H), 3.97 (t, J ) 4.4 Hz, 2H), 4.37 (t, J ) 4.4 Hz,
3
(s, 1H), 9.71 (s, 1H), 10.36 (s, 1H), C NMR (100 MHz, CDCl )
2
H), 5.52 (brs, 2H), 6.81 (dd, J ) 7.7, 1.6 Hz, 1H), 6.86 (t, J )
.7 Hz, 1H), 6.91 (dd, J ) 7.7, 1.6 Hz, 1H), 8.23 (s, 1H), 9.87
3 3 2 2
δ 15.1 (CH ), 56.1 (CH ), 73.0 (CH ), 73.1 (CH ), 113.5 (CH),
7
115.5 (C), 116.4 (C), 119.4 (CH), 119.9 (CH), 122.4 (CH), 125.8
1
3
(
s, 1H); C NMR (75 MHz, CDCl
3.6 (CH
C), 148.0 (C), 151.3 (CHdN). Anal. calcd for C10
3.09; H, 6.24; N, 12.38. Found: C, 52.90; H, 6.26; N, 12.27.
c. Prepared from 3,5-di-tert-butyl-2-hydroxybenzaldehyde
117.2 mg, 0.50 mmol) and 1,2-bis(aminooxy)ethane (92.1 mg,
3
) δ 56.0 (CH
), 113.2 (CH), 116.4 (C), 119.3 (CH), 122.1 (CH), 146.9
: C,
3
), 72.5 (CH
2
),
(C), 127.9 (CH), 128.9 (CH), 147.0 (C), 148.1 (C), 151.8 (CHd
7
2
20 2 5
N), 152.0 (CHdN), 154.4 (C). Anal. calcd for C18H N O S‚
(
H
14
N
2
O
4
0.5H
2
O: C, 56.09; H, 5.49; N, 7.27. Found: C, 55.89; H, 5.24;
5
N, 7.14.
3
6. Prepared from monooxime 3b (22.7 mg, 0.10 mmol) and
(
1
2-hydroxy-5-nitrobenzaldehyde (16.8 mg, 0.10 mmol) in 64%
1
1
.0 mmol) in 82% as pale yellow oil, H NMR (400 MHz, CDCl
δ 1.29 (s, 9H), 1.44 (s, 9H), 3.98 (t, J ) 4.8 Hz, 2H), 4.36 (t, J
4.8 Hz, 2H), 5.52 (brs, 2H), 6.97 (d, J ) 2.0 Hz, 1H), 7.35 (d,
3
)
as colorless crystals, mp 135-136 °C, H NMR (400 MHz,
3
CDCl ) δ 3.90 (s, 3H), 4.49-4.54 (m, 4H), 6.81 (dd, J ) 7.9,
)
1.8 Hz, 1H), 6.85 (t, J ) 7.9 Hz, 1H), 6.91 (dd, J ) 7.9, 1.8 Hz,
1H), 7.04 (d, J ) 8.8 Hz, 1H), 8.12 (d, J ) 2.7 Hz, 1H), 8.16
(dd, J ) 8.8, 2.7 Hz, 1H), 8.24 (s, 1H), 8.28 (s, 1H), 9.66 (s,
1
3
J ) 2.0 Hz, 1H), 8.22 (s, 1H), 10.12 (s, 1H), C NMR (100
MHz, CDCl
3
) δ 29.4 (CH
3 3
), 31.5 (CH ), 34.1 (C), 35.1 (C), 72.5
1
3
(CH
2
), 73.7 (CH ), 115.6 (C), 125.6 (CH), 126.2 (CH), 136.4 (C),
2
3 3
1H), 10.62 (s, 1H), C NMR (100 MHz, CDCl ) δ 56.1 (CH ),
7
2 2
3.1 (CH ), 73.7 (CH ), 113.4 (CH), 116.2 (C), 116.3 (C), 117.5
(
(
(
CH), 119.5 (CH), 122.3 (CH), 126.7 (CH), 126.8 (CH), 140.6
(
31) Dallacker, F.; Holtmann, B.; Coerver, W. Z. Naturforsch. 1983,
8B, 392-397.
32) Dandegaonker, S. H.; Shet, S. G. J. Indian Chem. Soc. 1965,
2, 323-326.
C), 146.9 (C), 148.1 (C), 150.6 (CHdN), 152.0 (CHdN), 162.5
3
4
C). Anal. calcd for C17
17 3 7 2
H N O ‚0.25H O: C, 53.76; H, 4.64;
(
N, 11.06. Found: C, 53.78; H, 4.51; N, 10.97.
1710 J. Org. Chem., Vol. 70, No. 5, 2005

Oxime-Based Salen-Type Ligand with High Stability
TABLE 4. Crystallographic Data for Salamo Ligands 1a, 1b, 1c, and 4a
1a
1b
1c‚0.25H2O
4
formula
temperature (K)
crystal system
space group
a (Å)
C16H16N2O4
180
triclinic
P-1
C18H20N2O6
120
monoclinic
P21/n
4.694(4)
14.616(6)
12.356(4)
C32H48.5N2O4.25
296
monoclinic
C2/c
33.113(5)
16.850(3)
12.654(2)
C17H18N2O5
120
monoclinic
P21/n
15.272(12)
4.628(3)
23.257(18)
4.6416(4)
15.0604(11)
20.9786(14)
92.323(3)
93.095(3)
98.4404(16)
1446.75(19)
4
b (Å)
c (Å)
R (deg)
â (deg)
98.065(3)
110.583(3)
104.485(11)
γ (deg)
3
V (Å )
839.3(9)
2
6609.3(18)
8
1591(2)
Z
4
3
Dcalc (g/cm )
1.379
1.426
1.064
1.379
reflections collected
unique reflections
Rint
11783
5122
21236
11699
5613
1482
6434
3564
0.0411
0.2079
0.0763
0.0527
F000
632
380
2308
696
µMoKR (mm-1)
limiting indices
0.100
0.108
0.070
0.103
-5 e h e 5
-5 e h e 3
-17 e k e 16
-14 e l e 14
0/119
-40 e h e 40
-20 e k e 20
-13 e l e 15
0/384
-18 e h e 19
-6 e k e 6
-27 e l e 30
0/220
-
18 e k e 18
25 e l e 25
-
restraints/parameters
0/401
1.054
2
goodness of fit (F )
0.979
1.009
1.054
R indices (I > 2σ(I))
R1 ) 0.0453
wR2 ) 0.1099
R1 ) 0.0700
wR2 ) 0.1213
R1 ) 0.0816
wR2 ) 0.1696
R1 ) 0.2089
wR2 ) 0.2330
R1 ) 0.0716
wR2 ) 0.1515
R1 ) 0.1138
wR2 ) 0.1747
R1 ) 0.0749
wR2 ) 0.1687
R1 ) 0.1135
wR2 ) 0.1900
R indices (all data)
a
R1 ) Σ||Fo| - |Fc||/Σ|Fo|; wR2 ) [Σ(w(Fo - Fc ) )/Σ(w(Fo ) )]1/2.
2
2 2
2 2
7
. Prepared from monooxime 3c (30.9 mg, 0.10 mmol) and
Metathesis Reaction of 9a and 9b. A mixture of 9a (20
µmol) and 9b (20 µmol) was dissolved in H O/MeCN (5:95, 2
2
-hydroxybenzaldehyde (12.2 mg, 0.10 mmol) in 70%. The
2
sample was purified by column chromatography on silica gel
mL) and the mixture was kept at 40.0 ( 0.1 °C. Aliquots of 2
µL were taken from the reaction mixture, diluted to the volume
of 1 mL with acetonitrile containing benzamide (0.2 mM,
internal standard), and 1 µL of the resulting solution was
injected to HPLC (Shimadzu LC-10A/CLASS-VP system
equipped with a Mightysil RP-18 GP250-4.6 column, eluent,
1
(
chloroform) to give colorless crystals, mp 105-106 °C,
H
NMR (400 MHz, CDCl ) δ 1.29 (s, 9H), 1.43 (s, 9H), 4.48 (s,
3
4
H), 6.90 (td, J ) 7.6, 1.0 Hz, 1H), 6.978 (d, J ) 8.2 Hz, 1H),
.980 (d, J ) 2.3 Hz, 1H), 7.15 (dd, J ) 7.6, 1.5 Hz, 1H), 7.28
6
(
td, J ) 7.8, 1.5 Hz, 1H), 7.35 (d, J ) 2.3 Hz, 1H), 8.24 (s, 1H),
8
.25 (s, 1H), 9.77 (s, 1H), 10.11 (s, 1H), 13C NMR (100 MHz,
CDCl ) δ 29.5 (CH ), 31.5 (CH ), 34.1 (C), 35.1 (C), 72.7 (CH ),
3.2 (CH ), 115.6 (C), 116.2 (C), 116.8 (CH), 119.6 (CH), 125.7
CH), 126.3 (CH), 130.9 (CH), 131.3 (CH), 136.4 (C), 141.3 (C),
52.3 (CHdN), 153.4 (CHdN), 154.3 (C), 157.4 (C). Anal. calcd
for C24 ‚H O: C, 66.95; H, 7.96; N, 6.51. Found: C,
7.41; H, 7.80; N, 6.64.
. Prepared from monooxime 3e (27.5 mg, 0.10 mmol) and
-hydroxybenzaldehyde (12.2 mg, 0.10 mmol) in 51%. The
2
H O/MeCN, 50:50).
X-ray Crystallographic Analysis of 1a, 1b, 1c, and 4.
3
3
3
2
7
2
Intensity data were collected on a Rigaku R-AXIS Rapid or a
Rigaku Mercury CCD diffractometer with MoKR radiation (λ
) 0.71069 Å). Reflection data were corrected for Lorentz and
polarization factors and for absorption using the multiscan
method. Crystal data are collected in Table 4. The structure
(
1
H
32
N
2
O
4
2
6
2
3
3
34
8
was solved by direct methods (SIR-97 or SHELXS 97 ) and
2
35
refined by full-matrix least squares on F using SHELXL 97.
sample was purified by column chromatography on silica gel
The non-hydrogen atoms were refined anisotropically. Hydro-
gen atoms were idealized by using the riding models.
1
(
(
chloroform) to give colorless crystals, mp 88-89 °C, H NMR
400 MHz, CDCl ) δ 4.47-4.50 (m, 4H), 6.87 (d, J ) 8.6 Hz,
H), 6.91 (t, J ) 7.8 Hz, 1H), 6.98 (d, J ) 7.8 Hz, 1H), 7.16
dd, J ) 7.8, 1.5 Hz, 1H), 7.27 (d, J ) 2.5 Hz, 1H), 7.29 (td, J
7.8, 1.5 Hz, 1H), 7.35 (dd, J ) 8.6, 2.5 Hz, 1H), 8.15 (s, 1H),
3
1
Acknowledgment. This work was supported by
Grants-in-Aid for Scientific Research from the Ministry
of Education, Culture, Sports, Science, and Technology,
Japan.
(
)
1
3
8
.23 (s, 1H), 9.72 (s, 1H), 9.77 (s, 1H), C NMR (100 MHz,
CDCl ) δ 73.0 (CH ), 73.3 (CH ), 111.2 (C), 116.1 (C), 116.8
CH), 117.9 (C), 118.7 (CH), 119.7 (CH), 130.9 (CH), 131.5
CH), 132.9 (CH), 134.0 (CH), 151.0 (CHdN), 152.4 (CHdN),
3
2
2
(
(
1
Supporting Information Available: Crystallographic
data for 1a, 1b, 1c, and 4 in CIF format. This material is
available free of charge via the Internet at http://pubs.acs.org.
2 4
56.5 (C), 157.4 (C). Anal. calcd for C16H15BrN O : C, 50.68;
H, 3.99; N, 7.39. Found: C, 50.65; H, 4.08; N, 7.22.
Metathesis Reaction of 1a and 1b. A mixture of 1a (10
JO048030Y
2
µmol) and 1b (10 µmol) was dissolved in H O/MeCN (5:95, 1
mL) at 40 °C and the mixture was kept at 40.0 ( 0.1 °C.
Aliquots of 5 µL were taken from the reaction mixture, diluted
to the volume of 1 mL with acetonitrile, and 1 µL of the
resulting solution was injected to HPLC (Shimadzu LC-10A/
CLASS-VP system equipped with a Mightysil RP-8 GP150-
(33) SIR-97. Program for crystal structure solution. Altomare, A.;
Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo, C.; Guagliardi,
A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl. Crystallogr.
1999, 32, 155-122.
(
34) Sheldrick, G. M. SHELXS 97: Program for Crystal Structure
4
.6 column, eluent, H
µmol) in H O/MeCN (5:95, 0.5 mL) at 40 °C was monitored by
HPLC in a similar manner.
2
O/MeCN, 20:80). The reaction of 4 (10
Determination; University of G o¨ ttingen: G o¨ ttingen, Germany, 1997.
(35) Sheldrick, G. M. SHELXL 97: Program for Crystal Structure
Determination; University of G o¨ ttingen: G o¨ ttingen, Germany, 1997.
2
J. Org. Chem, Vol. 70, No. 5, 2005 1711