Synthesis, x-ray crystal structure, and oxidation catalytic property of a dioxomolybdenum(VI) complex derived from 5-diethylamino-2-[(2-hydroxyethylimino) methyl]phenol

Article abstract of DOI:10.1080/15533174.2012.750352

A new dioxomolybdenum(VI) complex, [MoO₂L(CH₃OH)], where L is the dianion of 5-diethylamino-2-[(2-hydroxyethylimino) methyl]phenol, was prepared and structurally characterized by physicochemical and spectroscopic methods and single-crystal X-ray determination. The Mo atom in the complex is in octahedral coordination. The crystal of the complex is stabilized by hydrogen bonds. The complex functions as an effective olefin epoxidation catalyst with hydrogen peroxide as terminal oxidant and sodium hydrogen carbonate as a cocatalyst under air atmosphere at room temperature.

Full text of DOI:10.1080/15533174.2012.750352

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Synthesis, X-Ray Crystal Structure, and Oxidation
Catalytic Property of a Dioxomolybdenum(VI)
Complex Derived From 5-Diethylamino-2-[(2-
hydroxyethylimino)methyl]phenol
Shao-Bing Ding a
a College of Chemical Engineering and Pharmacy, Jingchu University of Technology, Jingmen
Hubei, P. R. China
Accepted author version posted online: 01 Mar 2013.Published online: 04 Apr 2013.
To cite this article: Shao-Bing Ding (2013): Synthesis, X-Ray Crystal Structure, and Oxidation Catalytic Property of a
Dioxomolybdenum(VI) Complex Derived From 5-Diethylamino-2-[(2-hydroxyethylimino)methyl]phenol, Synthesis and Reactivity
in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:7, 877-881
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:877–881, 2013
Copyright ꢀ Taylor & Francis Group, LLC
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2012.750352
Synthesis, X-Ray Crystal Structure, and Oxidation Catalytic
Property of a Dioxomolybdenum(VI) Complex Derived From
5-Diethylamino-2-[(2-hydroxyethylimino)methyl]phenol
Shao-Bing Ding
College of Chemical Engineering and Pharmacy, Jingchu University of Technology,
Jingmen Hubei, P. R. China
A new dioxomolybdenum(VI) complex, [MoO2L(CH3OH)],
where L is the dianion of 5-diethylamino-2-[(2-hydroxyethylimino)
methyl]phenol, was prepared and structurally characterized by
physicochemical and spectroscopic methods and single-crystal X-
ray determination. The Mo atom in the complex is in octahedral
coordination. The crystal of the complex is stabilized by hydrogen
bonds. The complex functions as an effective olefin epoxidation
catalyst with hydrogen peroxide as terminal oxidant and sodium
hydrogen carbonate as a cocatalyst under air atmosphere at room
SCH. 1. H2L.
temperature.
EXPERIMENTAL
Keywords catalytic property, crystal structure, molybdenum com-
All chemical reagents were of analytical reagent grade, and
plex, Schiff base, synthesis
purchased from Xiya Chemical Reagent Company (Chengdu,
P. R. China). Microanalyses (C, H, N) were performed using
Perkin-Elmer 2400 elemental analyzer (Jingchu University of
Technology, P. R. China). Infrared spectra were carried out using
JASCO FT-IR model 420 spectrophotometer (Jingchu Univer-
sity of Technology, P. R. China) with KBr disk in the region
4000–200 cm–1. Electronic spectra were recorded on Shimadzu
UV 3101 spectrophotometer (Jingchu University of Technology,
P. R. China). GC analyses were carried out using a Shimadzu
GC-2014C gas chromatograph (Jingchu University of Technol-
ogy, P. R. China).
INTRODUCTION
Selective oxidation of hydrocarbons has attracted consider-
able attention in organic industry.[1–3] The synthesis, characteri-
zation, and reactivity studies of a number of dioxomolybdenum
complexes with Schiff bases have been reported.[4–7] Some of
the complexes have been shown to possess oxygen atom trans-
fer properties as they were found to oxidize thiols, hydrazine,
polyketones, tertiary phosphines, and olefins, etc.[8–11] However,
the number of reported dioxomolybdenum complexes used as
catalysts is still very limited. I report herein the synthesis, X-ray
crystal structure, and catalytic property of a new dioxomolybde-
num(VI) complex, [MoO2L(CH3OH)], where L is the dianion of
5-diethylamino-2-[(2-hydroxyethylimino)methyl]phenol (H2L;
Scheme 1). The search in Cambridge Crystallographic Database
(version 5.31 with addenda up to August 2012) revealed that no
complexes derived from H2L have reported so far.
Synthesis of H2L
A hot methanol solution (20 mL) of 4-diethylaminosa
licylaldehyde (1.93 g, 10 mmol) was added to a hot methanol
solution (20 mL) of 2-aminoethanol (0.61 g, 10 mmol). The
mixture was stirred for 30 min at reflux, and the solvent was
evaporated to dry, to give yellow gummy product of H2L. Anal.
Calcd. for C13H20N2O2: C, 66.1; H, 8.5; N, 11.8. Found: C,
65.9; H, 8.6; N, 11.9%.
Synthesis of the Complex
A hot methanol solution (15 mL) of MoO2(acac)2 (0.33 g,
1 mmol) was added to a hot methanol solution (15 mL) of
H2L (0.24 g, 1 mmol). The mixture was stirred for 30 min at
reflux, and then cooled to room temperature, to give yellow so-
Received 8 November 2012; accepted 13 November 2012.
The author greatly acknowledges Jingchu University of Technology
for financial support.
Address correspondence to Shao-Bing Ding, College of Chemical
Engineering and Pharmacy, Jingchu University of Technology, Jingmen lution. Single crystals of the complex, suitable for X-ray diffrac-
Hubei 448000, P. R. China. E-mail: shaobingding@163.com
tion, were formed by slow evaporation of the methanol solution
877

878
S.-B. DING
TABLE 2
containing the complex in air for a week. Yield: 53%. Anal.
Calcd. for C14H22MoN2O5: C, 42.6; H, 5.6; N, 7.1. Found: C,
42.5; H, 5.7; N, 7.1%.
Selected bond lengths (Å) and angles (◦) for the complex
1
Bond lengths
Mo1-O1
Mo1-O3
X-Ray Diffraction
1.9510(19)
1.690(2)
2.387(2)
Mo1-O2
Mo1-O4
Mo1-N1
1.956(2)
1.707(2)
2.229(3)
X-ray diffraction was performed using a Bruker Smart 1000
CCD diffractometer with graphite monochromated Mo Kα ra-
diation (λ = 0.71073 Å) using the ω-scan technique. Determi-
nation of the Laue class, orientation matrix, and cell dimensions
were performed according to the established procedures where
Lorentz polarization and absorption corrections were applied.
Absorption corrections were applied by fitting a pseudoellip-
soid to the ψ-scan data of selected strong reflections over a
wide range of 2θ angles. The positions of non-hydrogen atoms
were located with direct methods. Subsequent Fourier synthe-
ses were used to locate the remaining non-hydrogen atoms. All
non-hydrogen atoms were refined anisotropically. H5A attached
to O5 in the complex was located from a difference Fourier
map and refined isotropically, with O–H distance restrained to
0.85(1) Å and Uiso fix at 0.08 Å2. The remaining hydrogen
atoms were placed in calculated positions and constrained to
Mo1-O5
Bond angles
O3-Mo1-O4
O4-Mo1-O1
O4-Mo1-O2
O3-Mo1-N1
O1-Mo1-N1
O3-Mo1-O5
O1-Mo1-O5
N1-Mo1-O5
106.35(12)
101.23(9)
95.31(10)
97.54(12)
81.09(8)
171.84(11)
79.89(8)
74.65(9)
O3-Mo1-O1
O3-Mo1-O2
O1-Mo1-O2
O4-Mo1-N1
O2-Mo1-N1
O4-Mo1-O5
O2-Mo1-O5
96.78(10)
98.99(11)
152.89(9)
155.46(10)
75.10(9)
81.68(10)
81.45(9)
ride on their parent atoms. The analysis was performed with the
aid of the SHELXS-97 and SHELXL-97 suite of codes.[12,13]
Crystallographic data for the complex are summarized in Ta-
ble 1. Selected bond lengths and angles are given in Table 2.
TABLE 1
Crystal data for the complex
Catalytic Epoxidation of Olefins
To a solution of olefins (0.28 mmol), NaHCO3 (0.11 mmol),
and catalyst (9.4 × 10−4 mmol) in MeCN (0.5 mL) was added
H2O2 (1.1 mmol, 30% H2O solution) as oxidant. After the re-
action was over, for the products analysis, the solution was
subjected to multiple ether extraction, and the extract was also
concentrated down to 0.5 cm3 by distillation in a rotary evapo-
rator at room temperature and then a sample (2 μL) was taken
from the solution and analyzed by GC. The retention times of
the peaks were compared with those of commercial standards,
and chlorobenzene was used as an internal standard for GC yield
calculation.
Chemical formula
Fw
Crystal shape/colour
Crystal size (mm)
T (K)
λ (MoKα) (Å)
Crystal system
Space group
a (Å)
C14H22MoN2O5
394.3
Block/yellow
0.20 × 0.18 × 0.18
298(2)
0.71073
Monoclinic
P21/c
16.422(3)
7.898(1)
14.142(2)
114.831(2)
1664.6(4)
4
0.811
0.8546
0.8677
1.573
b (Å)
c (Å)
β (◦)
RESULTS AND DISCUSSION
V (Å3)
The Schiff base ligand H2L was readily prepared by
the condensation reaction of equimolar quantities of 4-
diethylaminosalicylaldehyde with 2-aminoethanol in methanol.
The complex was synthesized by reaction of MoO2(acac)2 with
H2L in methanol in a 1:1 mole proportion at reflux. The reac-
tion progress is shown in Scheme 2. Chemical formula of the
complex has been confirmed by elemental analyses, IR spectra,
and X-ray single-crystal structure determination.
Z
μ (MoKα) (cm–1)
T (min)
T (max)
Dc (g cm–3)
Reflections/parameters
Restraints
3602/205
1
Unique reflections
Goodness of fit on F2
Rint
R1 [I ≥ 2σ(I)]
wR2 [I ≥ 2σ(I)]
R1 (all data)
wR2 (all data)
ρmax
2876
1.044
0.0251
0.0329
0.0781
0.0453
0.0857
0.576
Structure Description of the Complex
The molecular structure of the complex is shown in Figure 1.
The coordination geometry around the Mo atom can be de-
scribed as slightly distorted octahedral, with one phenolate O,
one imino N, and one amino N atoms of the dianionic Schiff base
ligand, and with one oxo O atom defining the equatorial plane,
and with one O atom of a methanol ligand and the other oxo
O atom occupying the axial positions. The Schiff base ligand
coordinates to the Mo atom in a meridional fashion forming
ρmin
–0.381

SYNTHESIS, X-RAY CRYSTAL STRUCTURE, AND OXIDATION
879
SCH. 2. The synthesis procedure of the complex.
of the –C N– group is shifted to 1597 cm–1 for the complex,
which is much lower than that of the free Schiff base ligand.
The new weak peaks observed at 637, 535, and 435 cm–1 may
be attributed to the Mo–O and Mo–N vibrations in the complex.
five- and six-membered chelate rings with bite angles of
75.10(9)◦ and 81.09(8)◦, respectively. The displacement of the
Mo atom from the equatorial mean plane towards the axial oxo
atom O3 is 0.342(2) Å. The Schiff base ligand is coordinated in
its dianionic form, which are evident from the absence of the H
atoms of the hydroxyl groups. The Mo–O, Mo–N, and Mo O
bonds are within normal ranges and are similar to those ob-
served in similar dioxomolybdenum(VI) complexes with Schiff
bases.[14–16]
In the crystal structure of the complex, adjacent two complex
molecules are linked through intermolecular O5—H5A···O2 hy-
drogen bonds [O5—H5A = 0.85(1) Å, H5A···O2 = 1.787(11)
Å, O5···O2 = 2.625(3) Å, O5—H5A···O2 = 177(4)◦; symmetry
code for A: – x, 1 – y, – z], to form a dimer, as shown in Figure 2.
Catalytic Property
The complex shows effective catalytic property in the oxi-
dation of several olefins, including cyclohexene, vinylbenzene,
1-butylene, and 1-pentene, to their corresponding epoxides. The
detailed information of catalytic property with respect to epox-
idation of olefins with the complex as a catalyst is given in
Table 3. In general, high epoxide yields and selectivity were
observed for all aliphatic and aromatic substrates. The results
of catalytic studies using the complex reveal that the efficiency
of catalysts toward all the substrates are similar with maximum
conversion, TON, and selectivity. The mechanism (Scheme 3)
for the epoxidation of various olefins to epoxides using the
IR Spectra
The weak and broad band centered at 3447 cm–1 in the IR complex as a catalyst has been proposed by comparison with
spectrum of the complex can be assigned to the νOH vibrations the literature report.[18] When H2O2 was used as a sole oxi-
of the methanol ligand. The Mo O stretching modes occur as dant the catalytic efficiency is not high, but when NaHCO3
a pair of sharp strong bands at 928 and 905 cm–1, assigned was added as a cocatalyst the efficiency of the system increases
to the antisymmetric and symmetric stretching modes of the many fold. The key aspect of such a reaction is that H2O2 and
dioxomolybdenum(VI) moieties.[17] The intense band indicative hydrogen carbonate react in an equilibrium process to produce
FIG. 1. Molecular structure of the complex with 30% probability thermal ellipsoids.

880
S.-B. DING
TABLE 3
Detailed information of the catalytic oxidation of olefins
catalyzed by the complexa
Conversion
Selectivity
Substrate
Product
(%)b (TON)c
(%)d
91 (267)
100
94 (283)
100
97 (295)
97 (302)
100
100
aThe molar ratios for catalyst: substrate:NaHCO3:H2O2 are
1:298:117:1170. The reactions were performed in (70:30) mixture of
CH3OH/CH2Cl2 (1.2 mL) under air atmosphere at room temperature.
bThe GC conversion (%) are measured relative to the starting olefin
after 75 min.
cTON = (mmol of product)/mmol of catalyst.
dSelectivity to epoxide = [epoxide%/(epoxide% + aldehyde%)] ×
100.
The basic principle of the catalytic reaction is the conversion of
oxoperoxo-complex to dioxo-complex transferring oxo species
to the olfins and the conversion of dioxo complex to the ox-
−
operoxo complex reacting with HCO4 to regain the catalytic
activity.
FIG. 2. Molecular packing of the complex, viewed along the c-axis. Hydrogen
bonds are drawn as thin dashed lines.
peroxymonocarbonate, HCO4−, which is a more reactive nu-
cleophile than H2O2 and speeds up the epoxidation reaction.[18]
SCH. 3. Probable mechanism of catalytic oxidation of olefins to epoxides.

SYNTHESIS, X-RAY CRYSTAL STRUCTURE, AND OXIDATION
881
CONCLUSION
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zation of some dioxomolybdenum(VI) complexes with O, N, S donor Schiff
bases derived from S-methyldithiocarbazate, S-benzyldithiocarbazate, 2-
aminoethanethiol, and substituted salicylaldehydes. Synth. React. Inorg.
Met.-Org. Nano-Met. Chem. 2001, 31, 859–871.
8. Jin, N.-Y.; Li, W.-H. Synthesis and crystal structures of dioxomolybde-
num(VI) complexes with catalytic property. Synth. React. Inorg. Met.-Org.
Nano-Met. Chem. 2012, 42, 1167–1171.
A new dioxomolydenum(VI) complex derived from the
Schiff base ligand 5-diethylamino-2-[(2-hydroxyethylimino)
methyl]phenol, has been prepared and structurally character-
ized. The Schiff base ligand coordinates to the Mo atom through
phenolate O, imino N and amino N atoms. The Mo atom in the
complex is in octahedral coordination. The complex shows ef-
fective catalytic property in the oxidation of several olefins to
their corresponding epoxides.
9. Xu, W.-X.; Li, W.-H. Synthesis, crystal structure and catalytic prop-
erty of
a dioxomolybdenum(VI) complex derived from N’-[1-(2-
hydroxynaphthyl)ethylidene]-3-methylbenzohydrazide. Synth. React. In-
org. Met.-Org. Nano-Met. Chem. 2012, 42, 160–164.
10. Liimatainen, J.; Lehtonen, A.; Sillanpaa, R. cis-Dioxomolybdenum(VI)
complexes with tridentate and tetradentate Schiff base ligands. Preparation,
structures and inhibition of aerial oxidation of aldehydes. Polyhedron 2000,
19, 1133–1138.
11. Ambroziak, K.; Pelech, R.; Milchert, E.; Dziembowska, T.; Rozwadowski,
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SUPPLEMENTARY MATERIALS
CCDC 909613 contains the supplementary crystallographic
data for the complexes. These data can be obtained free of
charge via http://www.ccdc.ac.uk/conts/retrieving.html, or from
the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44)1223–336-033; or email:
deposit@ccdc.cam.ac.uk.
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Refinement; Go¨ttingen University, Germany, 1997.
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Madison, WI, 1995.
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molybdenum complex catalyzed sulfide oxidation with hydrogen peroxide.
Inorg. Chim. Acta 2011, 376, 57–63.
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