Synthesis, structure, and catalytic application of a new (3-methoxy-N-salicylidene)aniline-derived Schiff base complex of methyltrioxorhenium

Article abstract of DOI:10.1134/S1070328410070122

A new (3-methoxy-N-salicylidene)aniline-derived Schiff base complex of methyltrioxorhenium (C₁₄H₁₃NO₂ ? CH ₃ReO₃) (I), displaying a cis-arrangement of the Schiff base ligand to the Re-bonded methyl group, has been synthesized and characterized by elemental analysis, IR, ¹H NMR, and single-crystal X-ray diffraction. The X-ray diffraction analysis reveals that I crystallizes in the triclinic system, space group P, which displays a distorted trigonal-bipyramidal structure in the solid with the O^- moiety binding to the Lewis acidic Re atom. The intermolecular hydrogen bands link the molecules of the complex into a two-dimensional layer structure. The presence of the π-π stacking interactions enhances the stability of the layers, which are further linked via π-π stacking interactions forming a three-dimensional supramolecular network. The unit cell parameters for I: a = 7.0032(14), b = 9.3762(19), c = 11.649(2) A, α = 84.60(3)°, β = 89.08(3)°, γ = 84.45(3)°, V = 757.9(3) A³, Z = 2, F(000) = 456, R ₁ = 0.0591, ωR ₂ = 0.1346. In order to study the catalytic activity of complex I, cis-cyclooctene epoxidation in dichloromethane is examined. The result shows that the electron-donating OCH₃ group on the Schiff base influences the catalytic behavior significantly.

Full text of DOI:10.1134/S1070328410070122

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2010, Vol. 36, No. 7, pp. 547–551. © Pleiades Publishing, Ltd., 2010.
Synthesis, Structure, and Catalytic Application
of a New (3ꢀMethoxyꢀNꢀsalicylidene)aniline—Derived Schiff
Base Complex of Methyltrioxorhenium1
Sh. Yuea, b, J. Lib, Zh. H. Yub, Q. Wanga, c, X. P. Gub, and Sh. L. Zangc
a Department of Chemistry, East China Normal University, Shanghai 200062, P.R. China
b Institute of Rare and Scattered Elements, Liaoning University, Shenyang 110036, P.R. China
c School of Chemistry and Materials Science, Liaoning Shihua University, Fushun 113001, P.R. China
eꢀmail: slzang@lnu.edu.cn
Received November 3, 2009
Abstract—A new (3ꢀmethoxyꢀNꢀsalicylidene)aniline—derived Schiff base complex of methyltrioxorheꢀ
nium (C14H13NO2 · CH3ReO3) (
I
), displaying a cisꢀarrangement of the Schiff base ligand to the Reꢀbonded
NMR, and singleꢀcrystal
crystallizes in the triclinic system, space group
⎯ , which displays a distorted trigonalꢀbipyramidal structure in the solid with the
– moiety binding to the
Lewis acidic Re atom. The intermolecular hydrogen bands link the molecules of the complex into a twoꢀ
dimensional layer structure. The presence of the stacking interactions enhances the stability of the layers,
which are further linked via stacking interactions forming a threeꢀdimensional supramolecular network.
The unit cell parameters for = 7.0032(14), = 9.3762(19), = 11.649(2) = 84.60(3)°, = 89.08(3)°,
84.45(3)°, = 2, (000) = 456, 1= 0.0591, R2 = 0.1346. In order to study the catalytic activity
= 757.9(3) Å3
of complex cisꢀcyclooctene epoxidation in dichloromethane is examined. The result shows that the elecꢀ
methyl group, has been synthesized and characterized by elemental analysis, IR, 1
Xꢀray diffraction. The Xꢀray diffraction analysis reveals that
H
I
P1
O
π–π
π π
–
I:
a
b
c
Å,
α
β
γ
=
V
,
Z
F
R
ω
I,
tronꢀdonating OCH3 group on the Schiff base influences the catalytic behavior significantly.
DOI: 10.1134/S1070328410070122
1
INTRODUCTION
epoxidation of olefins as catalysts [12]. However, only
recently the papers have appeared dealing with Schiff
base complexes of MTO [13–16]. Many of them are
transꢀcoordination, and there are only few cisꢀcomꢀ
plexes. All of them show comparatively good catalytic
activities in cyclooctene epoxidation. An excess of the
ligand is not necessary to achieve high yields in the
process of catalysis. In this work we reported the synꢀ
thesis and structure of the cisꢀMTO complex with the
Methyltrioxorhenium (CH3ReO3 abbreviated as
MTO) has emerged in the last decade, and the discovꢀ
ery of its catalytic activity was made by Herrmann and
coworkers [1]. Since a few years that have passed,
MTO has drawn considerable attention due to its verꢀ
satility as a catalyst [2, 3]. The main areas of its appliꢀ
cation are oxidation catalysis, especially epoxidation
of olefins [4, 5]. Usually, the use of easily available, low
cost, and environmentally friendly oxidants such as
hydrogen peroxide (H2O2) is of particular interest [6,
7], It turned out already nearly two decades ago that
MTO is one of the most active olefin epoxidation catꢀ
alysts. However, Lewis acidity of MTO and the presꢀ
ence of water (formed as a byproduct from hydrogen
peroxide) in organic solvent have a tendency to proꢀ
mote further ringꢀopening reactions of the epoxidaꢀ
tion products to give diols, particularly, when more
sensitive epoxides are formed [8, 9]. Further research
of them revealed that the addition of an excess of
nitrogenous bases, particularly, pyridine as the Lewis
base mediator for the oxidation, is beneficial for both
the product selectivity and catalyst lifetime [10, 11].
Schiff base ligand derived from oꢀvanillin and amine,
as well as its catalytic application in cyclooctene
epoxidation.
EXPERIMENTAL
Materials and methods. All reagents and solvents
employed were commercially available. All preparaꢀ
tions and experimentations were carried out using
standard Schlenk techniques under an argon atmoꢀ
sphere. Solvents were dried by standard procedures (
hexane and Et2O over Na/benzophenone), distilled
under argon, and used immediately or kept over
nꢀ
4
Å
molecular sieves. Elemental analyses were performed
1
with a Flash EA 1112 series elemental analyser. H
To date, many Nꢀbase complexes of MTO have
been isolated, characterized, and applied for the
NMR was measured in DMSO with a MercuryꢀVxꢀ
300 spectrometer. IR spectra were recorded with a
Nicolet 5700 FTꢀIR spectrometer using KBr pellets as
1
The article is published in the original.
547

548
YUE et al.
Table 1. Crystallographic data and experimental details for
structure
SEꢀ54. The Schiff base ligand was prepared according
to the reference [17].
I
Synthesis of C14H13NO2 · CH3ReO3 (I). Complex
I
Parameter
Value
was prepared as follows: MTO (0.10 g, 0.4 mmol) was
dissolved in diethyl ether (5 ml) and added dropwise to
an equally concentrated solution of the ligand
(0.4 mmol) in diethyl ether (5 ml), while stirring at
25°C. After 1.5–2.0 h the yellowꢀorange solution was
concentrated under oilꢀpump vacuum to about 10 ml,
and the precipitate was recrystallized under diethyl
Crystal system
Space group
Triclinic
P1
7.0032(14)
9.3762(19)
11.649(2)
84.60(3)
89.08(3)
84.45(3)
757.9(3)
2
a
,
Å
Å
Å
b,
c,
etherꢀhexane. The salmonꢀpink crystals of
obtained in 30% yield.
I were
α, deg
β, deg
γ, deg
Volume, Å3
For C15H16NO5Re (Mr = 476.49)
anal. calcd., %: C, 37.92;
H, 3.33;
H, 3.36;
N, 3.04.
N, 3.20.
Z
Found, %:
IR (KBr;
C, 38.06;
ρcalcd, mg/cm3
Absorption coefficient, mm–1
2.088
, cm–1): 1638 (CH=N), 1092 νas(Re=O),
934, 922 νs(Re=O), 536 (Re–C). 1H NMR (300 MHz,
DMSO, RT), : 13.212 (s., 1H, NH), 8.268–8.923 (s.,
8.039
ν
F
(000)
Crystal size, mm
range of data collection, deg
Reflections collected
456
0.10 × 0.08 × 0.04
δ
1H, CH=N), 6.861–7.480 (m., 8H, Ph), 3.829–3.847
(s., 3H, OCH3), 1.859 (s., 3H, MTO–CH3).
θ
1.76 to 25.02
4281
Xꢀray structure determination. Preliminary examiꢀ
nation and data collection were performed with a
Bruker Smart 1000 CCD diffractometer operating at
Independent reflections (Rint
Max., min. transmission
Goodnessꢀofꢀfit on F2
)
2614 (0.0506)
0.7392, 0.5003
1.234
50 kV and 30 mA, which was equipped with a Mo
K
α
Data/restraints/parameters
2614/0/201
radiation source (
data of the complex was carried out at 113(2) K with
the diffraction measurement method, and reducꢀ
λ
= 0.71073 Å). A collection of the
Final
R
indices (
I
> 2
σ
(
I
))*
R
1 = 0.0547, wR2 = 0.1338
ω–ϕ
R
indices (all data)*
R1 = 0.0591, wR2 = 0.1346
tion was performed using the SMART and SAINT
software. An empirical absorption correction was
implemented using the ADABS program. The strucꢀ
tures were described by a combination of direct methꢀ
ods. All nonꢀhydrogen atoms were refined with anisoꢀ
tropic displacement parameters by fullꢀmatrix least
squares on F2 using the SHELXLꢀ97 package. All
hydrogen atoms were generated in ideal positions,
appropriate sotropic thermal parameters were calcuꢀ
lated and included in structureꢀfactor calculations at
the final stage of the F2 refinement [18–22]. Crystalꢀ
lographic data are summed up in Table 1. Selected
bond lengths and angles are listed in Table 2. Hydroꢀ
genꢀbonding geometric data are listed in Table 3.
The atomic coordinates and other parameters of
2
2
2 1/2
* R = Σ||F | – |F ||/Σ|F |; wR = Σ[w(F 2 – Fc ) ]/Σ[w(Fo ) ]
.
2
1
o
c
o
2
o
Table 2. Selected bond lengths and angles for
I
Bond
d,
Å
Bond
d, Å
Re(2)–O(1)
Re(2)–O(4)
Re(2)–C(15)
N(1)–C(7)
Angle
2.230(8) Re(2)–O(3)
1.714(8) Re(2)–O(5)
2.119(12) O(1)–C(1)
1.317(14)
1.722(8)
1.718 (8)
1.330(13)
ω, deg
Angle
ω, deg
O(3)Re(2)O(1) 85.5(3)
O(3)Re(2)O(5) 103.9(4)
O(4)Re(2)O(1) 79.8(4)
O(4)Re(2)C(15) 115.6(5)
O(5)Re(2)C(15) 90.2(5)
C(1)O(1)Re(2) 131.9(7)
O(3)Re(2)O(4) 116.4(4)
O(3)Re(2)C(15) 120.1(4)
O(4)Re(2)O(5) 104.1(4)
O(5)Re(2)O(1) 166.3(4)
C(15)Re(2)O(1) 76.3(4)
C(7)N(1)C(9) 126.8(11)
structure
I have been deposited with the Cambridge
Crystallographic Data Centre (no. 751342;
deposit@ccdc. cam.ac.uk or http://www.ccdc.cam.
ac.uk).
Catalytic cyclooctene epoxidation. To a stirred
solution of olefin (0.38 ml, 2.93 mmol), and H2O2
(0.60 ml, 19.59 mmol) in CH2Cl2 was added
43.97 mol), and mixture was maintained at room
I (1.5 mol %,
μ
temperature. The course of the reactions was moniꢀ
tored by quantitative GC analysis, while the samples
were taken at regular time intervals and treated with a
catalytic amount of MgSO4 and MnO2 to remove water
the IR matrix. Qualitative and quantitative analyses of
organic products were conducted with gas chromatogꢀ
raphy on a SP 2100 instrument equipped with a FID
and a capillary column (30 m
×
320
μm
×
0.25 m) HJ and to destroy the unreacted peroxide. The resulting
μ
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2010

SYNTHESIS, STRUCTURE, AND CATALYTIC APPLICATION
Table 3. Geometric parameters of hydrogen bond for structure
549
I
Distance,
Å
Angle D–H···A,
deg
Symmetry
operations for A
Contact D–H···A
D–H
H···A
D···A
N(1)–H(1)···O(1) (intra)
N(1)–H(1)···O(4) (intra)
C(14)–H(14)···O(4) (intra)
C(15)–H(15B)···O(2) (intra)
C(4)–H(4)···O(4) (inter)
C(7)–H(7)···O(3) (inter)
C(11)–H(11)···O(5) (inter)
0.88
0.88
0.95
0.98
0.95
0.95
0.95
1.95
2.40
2.50
2.33
2.53
2.57
2.58
2.648
3.164
3.277
3.134
3.205
3.398
3.474
135
145
140
138
128
146
157
x
x
x
x
x
,
,
,
,
y
y
y
y
,
,
,
,
z
z
z
z
,
,
,
,
, –1 +
, 1 –
y
, z
–
x
y, –
z
x, y, –1 + z
compound was filtered. The filtrate (0.1 ml), 8.6 mg of fragment in
mesitylene (internal standard), and CH2Cl2 were tion, the phenol ring and the phenyl ring lie in the
added in 10ꢀml flask. A 1ꢀ sample was injected into a same plane (the C(6)–C(7)–N(1)–C(9) torsion angle
I vary from 103.9(4)° to 116.4(4)°. In addiꢀ
μl
GC column. The conversion of cisꢀcyclooctene and is 179.82°). The presence of an intramolecular hydroꢀ
the formation of cyclooctene oxide were calculated gen bond between the donating oxygen atom and the
from calibration curves (
reaction.
r
= 0.99) recorded prior to the hydrogen atom riding on the imine nitrogen atom as
well as some weaker intramolecular hydrogen bonds
can be seen (Table 3). The intermolecular hydrogen
bonds link the molecules of the complex into a 2D
RESULTS AND DISCUSSION
The crystal structure of
singleꢀcrystal Xꢀray analysis, which reveals that
layer structure (Fig. 2). The presence of the
has been characterized by stacking interactions enhances the stability of the layꢀ
disꢀ ers [25]. The layers are further linked via
ꢀstacking
π
– ꢀ
π
I
I
π–π
plays a distorted trigonalꢀbipyramidal geometry, interactions forming a threeꢀdimensional supramoꢀ
whose fundamental unit is shown in Fig. 1. The Re lecular network (Fig. 3). The distance between Cg(I)
center is a fiveꢀcoordinate structure and surrounded and Cg(II) is 3.705(7) Å, in which Cg(I) is the ring
by four oxygen atoms and one carbon atom. For I, the center of C(1)–C(6) and Cg(II) is the ring center of
two oxo ligands and one methyl group occupy the C(9)–C(14).
equatorial positions, while the remaining oxo ligand
A comparison between the FTꢀIR spectra of the
ligand and reveals considerable changes due to the
and the donating phenol group occupy the axial posiꢀ
tions. It is noteworthy that the compound forms a cis
complex with MTO. To the best of our knowledge, a
lot of transꢀconfigured complexes of MTO are known,
but very few cis complexes have been reported to date
[13, 14], More recently, however, one of the Schiff
I
ꢀ
coordination reaction of the Re atom and Schiff base
ligand. IR spectroscopy reveals the symmetric and
asymmetric ReO3 vibrations at 1092, 934, and 922 cm–1
.
Compared to the vibrations of nonꢀcoordinated MTO
bases of MTO that displays both cisꢀ and trans
ꢀ
arrangement in the solid state is described [15]. This is
a strong indication that packing effects have been
thought to be responsible for the coordination modes,
as has previously been noted [13, 14, 16]. The Re–C
distance of I is 2.119(12) Å, which is slightly longer
than that in free MTO (2.063(2) Å). This also explains
that the Re–C bond is weakened and the complexes of
MTO are generally somewhat less stable than the nonꢀ
coordinated MTO alone. The Re=O bond distances
are 1.722(8), 1.714(8), and 1.718(8) Å, respectively,
which are similar to those in other MTO complexes.
The Re–Obridge distance is 2.230(8) Å, which is shorter
than the Re–O distance or the Re–N distance in some
organorhenium(VII) complexes [23, 24]. The shorter
C(11)
C(4)
C(5)
C(10)
C(9)
C(7)
C(12)
C(13)
C(6)
C(1)
C(3)
N(1)
C(14)
C(2)
O(1)
O(3)
O(2)
C(8)
O(4)
Re(2)
C(15)
Re–O bond in I indicates the movement of the origiꢀ
O(5)
nally Oꢀbound proton to the –N=C– moiety to
create a zwitterionic structure with the negatively
charged oxygen atom binding to the Lewis acidic rheꢀ
nium center [13]. The O=Re=O angles of the ReO3
Fig. 1. Coordination environment of the Re atom in I with
thermal ellipsoids at 30% probability.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 36
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550
YUE et al.
Fig. 2. The 2D layer formed by intermolecular hydrogen bands.
Fig. 3. View of the 3D supramolecular network along the
y
axis showing the presence of
π
– ꢀstacking interactions.
π
(998, 965 cm–1), the Re=O bands of
shifted due to the pronounced donor capacity of the change is about 0.038 ppm. The proton signals of the
ligand in the solid state, which indicates that the oxyꢀ NH groups appear at about = 13.212 ppm for . The
gen atom of the Schiff base coordinates to the Re chemical shift change is about 0.007 ppm. The 1H sigꢀ
atom. For and the free ligand, the C=N stretchings nals of the aromatic group both the ligand and about
are visible at 1638 and 1615 cm–1. As pointed out in our
= 6.861–7.480 ppm. The observed chemical shifts
previous work [13], the displacement can be explained match the ligand pattern very well.
I are strongly redꢀ changed coordination situation. The chemical shift
δ
I
I
I
δ
by the presence of an intramolecular hydrogen
bond between the donating oxygen atom and the
hydrogen atom riding on the imine nitrogen atom.
The catalytic activity of I, which possesses the
OCH3 moiety on the phenolic ring with respect to oleꢀ
fin epoxidation is moderate. After further 24 h, the
epoxide yield (70%) does not increase significantly
compared to the yield (65%) after 4 h. This shows a
similar high catalytic activity with the complex, which
possesses the OCH3 moiety on the phenolic ring and
the phenyl ring, respectively [15]. These results match
well with the spectroscopic data of the complex and
show that a stronger donating ligand leads to a more
stable catalyst, which is, however, less active.
The formation
[C(1)O(1)H(1)N(1)C(7)C(6)] results in the absence
of OH stretching bonds in the region about 3400 cm–1
of
the
sixꢀmembered
ring
.
1
It is observed from the H NMR spectra that the
proton signals are only very slightly shifted unfilled
(
Δ δ
to Schiff baseꢀcoordinated MTO. 1H NMR data indiꢀ
cate only a weak interaction of the Re atom to the
( ) = 0.052 ppm) from the nonꢀcoordinated MTO
Schiff base. The 1H signals of the imine group of
I
are
Thus, the MTO Schiff base complex that displays
shifted downfield slightly, in agreement with a cisꢀcoordination about the ligand coordination mode
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 36
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SYNTHESIS, STRUCTURE, AND CATALYTIC APPLICATION
551
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This project was supported by the NSFC
(20671047), National Science Foundation of China,
and the Foundation of Education Bureau of Liaoning
Province (nos. 2008S103 and 2009S041).
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