Synthesis, crystal structures, and catalytic property of dioxomolybdenum(VI) complexes with hydrazones1

Article abstract of DOI:10.1134/S107032841202011X

Two new dioxomolybdenum(VI) complexes, [MoO₂(L ¹)]_n · 0.5nCH₃OH (I) and [MoO ₂(L²)(CH₃OH)] (II), where L¹ and L² are the dianionic form of N′-[1-(4-diethyla

Full text of DOI:10.1134/S107032841202011X

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2012, Vol. 38, No. 2, pp. 92–98. © Pleiades Publishing, Ltd., 2012.
Synthesis, Crystal Structures, and Catalytic Property
of Dioxomolybdenum(VI) Complexes with Hydrazones1
W. X. Xu and W. H. Li*
College of Chemical Engineering and Pharmacy, Jingchu University of Technology, Jingmen 448000, P.R. China
*eꢀmail: liwh066@163.com
Received February 24, 2011
Abstract—Two new dioxomolybdenum(VI) complexes, [MoO2(L1)]n
MoO2(L2)(CH3OH)] (II), where L1 and L2 are the dianionic form of
ꢀ[1ꢀ(4ꢀdiethylaminoꢀ2ꢀhydroxyꢀ
phenyl)methylidene]isonicotinohydrazide and ꢀ(2ꢀhydroxyꢀ4ꢀmethoxybenzylidene)ꢀ3ꢀmethylbenzohyꢀ
drazide, respectively, were prepared and structurally characterized by physicochemical and spectroscopic
⋅
0.5n
CH3OH
(I)
and
[
N'
N'
methods and singleꢀcrystal Xꢀray determination. For complex I, a polymeric structure is obtained, which is
linked by coordination of the pyridine N atoms to the Mo atoms of other [MoO2(L1)] units. Complex II is a
mononuclear molybdenum compound. In both complexes, the Mo atoms are in octahedral coordination.
The catalytic properties of the complexes indicate that they are efficient catalysts for sulfoxidation.
DOI: 10.1134/S107032841202011X
1
INTRODUCTION
num(VI) complexes, [MoO2(L1)]n
and [MoO2(L2)(CH3OH)] (II
ligands ꢀ[1ꢀ(4ꢀdiethylaminoꢀ2ꢀhydroxypheꢀ
nyl)methylidene]isonicotinohydrazide (H2L1) and
ꢀ(2ꢀhydroxyꢀ4ꢀmethoxybenzylidene)ꢀ3ꢀmethylꢀ
benzohydrazide (H2L2), have been reported. It
should be noted that complex is the first polymeric
dioxomolybdenum(VI) compound. The catalytic
properties of the complexes indicate that they are
efficient catalysts for sulfoxidation.
⋅
0.5
nCH3OH (I)
)
with hydrazone
The mechanism of molybdenum oxotransferase
N
'
has extensively been investigated for a long time.
The synthesis, characterization, and reactivity studꢀ
ies of a number of dioxomolybdenum complexes
with Schiff bases have been reported [1–4]. Some of
the complexes have been shown to possess the oxyꢀ
gen atom transfer properties as they were found to
oxidize thiols, hydrazine, polyketones, and tertiary
phosphines [5, 6]. Sulfoxidation activity has been
reported for molybdenum salts, composite metal
oxides, molybdate doped porous carbons, and
molybdenumꢀcontaining molecular sieves [7–10].
The catalytic ability of dioxomolybdenum(VI)
complexes with hydrazone ligands toward the oxiꢀ
dation of sulfides have obtained satisfactory results
[11, 12]. Even though, the number of documented
dioxomolybdenum(VI) complexes catalyzing the
peroxidic oxidation of sulfides is still very limited.
The search in the Cambridge Crystallographic
Database (version 5.31 with addenda up to August,
2010) [13] has revealed that only 36 monoꢀ and
dinuclear molybdenum(VI) complexes with hydraꢀ
zone ligands have been reported. It should be noted
that there were no polymeric molybdenum(VI)
complexes with hydrazone ligands reported so far.
In the present paper, two new dioxomolybdeꢀ
N
'
I
N
H
N
N
O
Et2N
OH
(H2L1)
H
N
N
O
MeO
OH
(H2L2)
1
The article is published in the original.
92

SYNTHESIS, CRYSTAL STRUCTURES, AND CATALYTIC PROPERTY
93
EXPERIMENTAL
complexes in air for a few days. The yield was 43%
for and 54% for II
I
.
All chemicals and solvents were of analytical
reagent grade and purchased from the Beijing
Chemical Reagent Company. Microanalyses (C, H,
N) were performed using a PerkinElmer 2400 eleꢀ
mental analyzer. Infrared spectra were carried out
using a JASCO FTꢀIR model 420 spectrophotomeꢀ
ter with KBr disk in the region 4000–200 cm–1.
Electronic spectra were recorded on a Shimadzu
For C35H40Mo2N8O9 (I)
anal. calcd., %: C, 46.3;
H, 4.4;
H, 4.5;
N, 12.3.
N, 12.1.
Found, %:
C, 46.0;
For C17H18MoN2O6 (II)
anal. calcd., %:
Found, %:
C, 46.2;
C, 46.4;
H, 4.1;
H, 4.0;
N, 6.3.
N, 6.2.
1
UV 3101 spectrophotometer. H NMR and 13C
NMR spectra were recorded on Bruker Avance 300
and 500 MHz spectrometers.
Xꢀray structure determination. Xꢀray measureꢀ
ments were performed using a Bruker Smart 1000
CCD diffractometer with graphite monochromated
Synthesis of H2L1.
4ꢀDiethylaminoꢀ2ꢀhydroxyꢀ
benzaldehyde (1.93 g, 0.01 mol) dissolved in methanol
(30 mL) was added to a stirred methanol solution
(20 mL) of isonicotinohydrazide (1.37 g, 0.01 mol).
The mixture was refluxed for 2 h on a water bath, and
the solvent was evaporated to give a colorless solid
product. The product was recrystallized from methaꢀ
nol and dried in air. The yield was 83%.
Mo
K
radiation (
λ
= 0.71073 Å) using the
ω
scan
α
technique. Determinations of the Laue class, orienꢀ
tation matrix, and cell dimensions were performed
according to the established procedures, where
Lorentz polarization and absorption corrections
were applied. Absorption corrections were applied by
For C17H20N4O2
fitting a pseudoꢀellipsoid to the
selected strong reflections over a wide range of
angles. The positions of nonꢀhydrogen atoms
ψ
scan data of
anal. calcd., %: C, 65.4;
Found, %: C, 65.2;
H, 6.4;
H, 6.5;
N, 17.9.
N, 18.0.
2
θ
were located with direct methods. Subsequent Fouꢀ
rier syntheses were used to locate the remaining nonꢀ
hydrogen atoms. All nonꢀhydrogen atoms were
refined anisotropically. Hydrogen atoms were placed
in calculated positions and constrained to ride on
their parent atoms. The analysis was performed with
the aid of the SHELXSꢀ97 and SHELXLꢀ97 suite of
codes [14, 15]. The crystallographic data for the
complexes are summarized in Table 1. Selected
bond lengths and angles are given in Table 2. Crysꢀ
tallographic data for the complexes have been
deposited with the Cambridge Crystallographic
Data Centre (nos. 813896 for I and 813897 for II;
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.
ac.uk).
1H NMR (CDCl3;
, ppm): 1.16 (t., 6H), 3.40 (q.,
4H), 6.31 (s., 1H), 6.36 (d., 1H), 7.46 (d., 1H), 7.82
(d., 2H), 8.75 (s., 1H), 8.88 (d., 2H), 10.17 (b., 1H).
δ
Synthesis of H2L2
. The colorless solid product of
H2L2 was prepared by the same method
as that described for H2L1, with 2ꢀhydroxyꢀ4ꢀ
methoxybenzaIdehyde (1.52 g, 0.01 mol) reacts
with 3ꢀmethylbenzohydrazide (1.50 g, 0.01 mol).
The yield was 87%.
For C16H16N2O3
anal. calcd., %: C, 67.6;
Found, %: C, 67.8;
H, 5.7;
H, 5.7;
N, 9.8.
N, 9.7.
1H NMR (CDCl3;
, ppm): 2.32 (s., 3H), 3.83 (s.,
δ
1H), 6.49 (s., 1H), 6.63 (d., 1H), 7.35 (q., 1H), 7.48
(d, 1H), 7.70 (d., 1H), 7.74 (s., 1H), 7.83 (d., 1H),
8.75 (s., 1H), 10.23 (b., 1H).
RESULTS AND DISCUSSION
Two hydrazone ligands were readily prepared by
the condensation reaction of the aldehydes with
benzohydrazones in methanol with high yields and
purity. The dioxomolybdenum(VI) complexes were
synthesized by the reaction of the hydrazone ligands
and MoO2(Acac)2 in methanol in a 1 : 1 mole proꢀ
portion at reflux. The reaction progress is accompaꢀ
nied by a color change of the solution from colorless
Synthesis of I and II. Complexes
I and II were
prepared by the following general method. 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 the hydrazone (1 mmol). The mixture
was stirred for 30 min at reflux and then cooled to
room temperature to give a red solution. Single
crystals suitable for Xꢀray diffraction were formed
by slow evaporation of the methanol solution of the of red.
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2012

94
XU, LI
N
N
H
N
N
N
N
O
OH
Et2N
OH
Et2N
OH
(H2L1)
MoO (Acac)
2
2
N
N
N
O
Et2N
O
Mo
O
N
O
O
O
Mo
O
N
N
O
Et2N
n
(I)
H
N
N
N
N
O
OH
MeO
OH
MeO
MeO
OH
(H2L2)
MoO (Acac)
2
2
N
N
O
O
Mo
OMe
H
O
O
(II)
We have attempted to prepare and grow quality difꢀ Mo atoms, forming zigzag polymeric chains (Fig. 2). In
fraction crystals from various solvents; however, good
quality crystals were finally obtained from methanol.
The chemical formulas of the complexes have
been confirmed by elemental analyses, IR spectra,
and Xꢀray singleꢀcrystal structure determination.
the complex, a distorted octahedral geometry is
observed for the Mo atom with the phenolic O, imino
N, and enolic O atoms of the dianionic hydrazone
ligand (L1) and with one oxo O atom defining the
equatorial plane and with one pyridine N atom of
another hydrazone ligand and another oxo O atom
occupying the two axial positions. The displacement
of the Mo atom from the equatorial mean plane
toward the apical oxo atom O(3) is 0.356(2) Å. The
The molecular structure of
asymmetric unit of the compound consists of a
MoO2(L1)] moiety and half a methanol molecule of
crystallization. The [MoO2(L1)] moieties are linked
I is shown in Fig. 1. The
[
through the coordination of the pyrdine N atoms to the hydrazone ligand coordinates to the Mo atom in a
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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SYNTHESIS, CRYSTAL STRUCTURES, AND CATALYTIC PROPERTY
95
Table 1. Crystallographic data and refinement parameters for complex
I
and II
Value
Parameter
I
II
Fw
908.63
Block/red
0.18 × 0.17 × 0.15
298(2)
442.27
Block/red
0.23 × 0.20 × 0.20
298(2)
Crystal shape/colout
Crystal size, mm
T
, K
Crystal system
Space group
Monoclinic
Monoclinic
C
2/
c
P21/n
a
b
c
β
V
Z
μ
, Å
, Å
, Å
21.052(3)
18.415(3)
13.071(3)
114.827(3)
4598.9(15)
4
8.035(2)
14.831(3)
15.386(3)
102.865(3)
1787.5(6)
4
, deg
, Å3
(Mo
K
), cm–1
0.598
0.770
α
Tmin
Tmax
0.9000
0.9156
1.312
0.8428
0.8612
1.643
ρ
, g cm–3
θ
Range, deg
1.94–27.00
2.65–27.00
Index ranges
h
,
k
,
l
–26
≤
h
≤
26, –21
≤
k
≤
23, –16
≤
l
≤
15
–10
≤
h
≤
10, –18
≤
k
≤
17, –19
≤
l ≤ 18
Reflections/parameters
Unique reflections
Rint
5002/257
3646
0.0403
1.069
3849/241
2727
0.0406
1.032
Goodness of fit on F2
R
R
Δρmax
factor,
factor (all data)
Δρmin
Å–3
I
≥
2
σ
(
I
)
R
R
1 = 0.0557, wR2 = 0.1804
1 = 0.0755, wR2 = 0.1980
1.074/–0.661
R
R
1 = 0.0374, wR2 = 0.0741
1 = 0.0627, wR2 = 0.0860
0.596/–0.565
/
, e
Table 2. Selected bond lengths (Å) and angles (deg) for comꢀ
plexes and II
meridional fashion forming fiveꢀ and sixꢀmembered
chelate rings with bite angles of 71.3(1) and 82.0(1)
I
°
°
,
respectively. The dihedral angle between the benzene
ring and the pyridine ring of the hydrazone ligand is
10.2(3)°. The hydrazone ligand is coordinated in its Mo(1)–O(1)
dianionic form, which is evident from the N(2)–C(8)
and O(2)–C(8) bond lengths with values of 1.302(5)
and 1.304(5) Å, respectively, indicating the presence of
the enolate form of the ligand amide group. The
Mo⎯O, Mo–N, and Mo=O bonds are within normal
ranges and are comparable to those observed in similar
dioxomolybdenum(VI) complexes [16, 17].
Bond
d
, Å
Bond
d, Å
I
1.919(3) Mo(1)–O(2)
2.003(3)
1.707(3)
2.549(4)
Mo(1)–O(3)
Mo(1)–N(1)
1.695(4) Mo(1)–O(4)
2.219(4) Mo(1)–N(3A)
II
Mo(1)–O(1)
Mo(1)–O(4)
Mo(1)–O(6)
1.924(2) Mo(1)–O(3)
1.696(3) Mo(1)–O(5)
1.691(2) Mo(1)–N(1)
2.008(2)
2.362(3)
2.232(3)
Angle
ω, deg
Angle
ω, deg
I
O(3)Mo(1)O(4) 106.4(2) O(3)Mo(1)O(1)
O(4)Mo(1)O(1) 103.1(2) O(3)Mo(1)O(2)
99.4(2)
98.6(2)
95.4(2) O(1)Mo(1)O(2) 149.2(2)
96.2(2) O(4)Mo(1)N(1) 155.4(2)
The molecular structure of II is shown in Fig. 3.
The coordination geometry around the Mo atom can
be described as a slightly distorted octahedral geomeꢀ
try with the phenolic O, imino N, and enolic O atoms
of the dianionic hydrazone ligand L2 and with one
oxo O atom defining the equatorial plane and with
one O atom of the methanol ligand and the other oxo
O atom occupying the axial positions. The hydrazone
ligand coordinates to the Mo atom in a meridional
fashion forming fiveꢀand sixꢀmembered chelate rings
O(4)Mo(1)O(2)
O(3)Mo(1)N(1)
O(1)Mo(1)N(1)
O(3)Mo(1)N(3
O(1)Mo(1)N(3
N(1)Mo(1)N(3
82.0(2) O(2)Mo(1)N(1)
71.3(2)
79.9(2)
81.2(2)
A) 173.6(2) O(4)Mo(1)N(3A)
A
)
78.1(2) O(2)Mo(1)N(3
A)
A
)
77.7(2)
II
O(6)Mo(1)O(4) 106.1(1) O(6)Mo(1)O(1) 101.8(1)
O(4)Mo(1)O(1)
O(4)Mo(1)O(3)
O(6)Mo(1)N(1) 156.6(1) O(4)Mo(1)N(1)
98.8(1) O(6)Mo(1)O(3)
97.7(1) O(1)Mo(1)O(3) 149.7(1)
96.2(1)
71.6(1)
82.2(1) O(4)Mo(1)O(5) 171.2(1)
82.1(1) O(3)Mo(1)O(5) 77.9(1)
75.2(1)
97.8(1)
O(1)Mo(1)N(1)
O(6)Mo(1)O(5)
O(1)Mo(1)O(5)
N(1)Mo(1)O(5)
81.4(1) O(3)Mo(1)N(1)
with bite angles of 71.6(1) and 81.4(1)°, respectively.
°
The dihedral angle between the two benzene rings of
the hydrazone ligand is 5.2(3)°. The displacement of
the Mo atom from the equatorial mean plane toward
* Symmetry code for A:
x, 1 – y, 1/2 + z.
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96
XU, LI
C(15)
C(14)
N(4)
C(5)
C(17)
C(6)
C(1)
C(16)
C(4)
C(3)
O(5)
Mo(1A)
C(7)
N(1)
C(18)
C(2)
O(1)
N(2)
N(3A)
Mo(1)
C(8)
C(10)
O(3)
C(11)
N(3)
O(2)
C(9)
O(4)
C(13)
C(12)
Fig. 1. Molecular structure of
the symmetry position , 1 –
I
with 30% probability thermal ellipsoids. Unlabled atoms and those labeled with the suffix
A are at
x
y
, 1/2 +
z.
x
z
0
y
Fig. 2. Molecular packing of
I
viewed along the x axis.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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SYNTHESIS, CRYSTAL STRUCTURES, AND CATALYTIC PROPERTY
97
C(6)
C(5)
C(16)
C(7)
O(4)
C(11)
N(2)
C(8)
C(10)
C(1)
O(2)
C(4)
C(12)
N(1)
C(2)
C(3)
C(9)
C(15)
Mo(1)
O(1)
O(3)
C(13)
C(14)
O(5)
O(6)
C(17)
Fig. 3. Molecular structure of II with 30% probability thermal ellipsoids.
x
z
0
y
Fig. 4. Molecular packing of II viewed along the y axis.
the apical oxo atom O(4) is 0.340(2) Å. The hydrazone at 926 and 845 cm–1 assigned to the antisymmetric and
ligand is coordinated in its dianionic form, which is symmetric stretching modes of the dioxomolybdeꢀ
evident from the N(2)–C(8) and O(3)–C(8) bond num(VI) moieties. The bands due to the
ν(C=O) and
lengths with values of 1.307(4) and 1.316(4) Å, respecꢀ
ν
(NH) were absent in the complexes, and new C–O
tively, indicating the presence of the enolate form of stretches appear at 1263 cm–1. This suggests occurꢀ
the ligand amide group. The Mo–O, Mo–N, and rence of ketoꢀimine tautomerization of the hydrazone
Mo=O bonds are within normal ranges and are comꢀ ligands during the coordination. The strong bands
parable to those observed in
molybdenum(VI) complexes [18–20]. In the crystal plexes are shifted to 1603 cm–1 for
structure of the complex, adjacent molecules are The
(C=N) appear at 1615 and 1617 cm–1 in comꢀ
linked through intermolecular O–H⋅⋅⋅ hydrogen plexes and II, respectively. The new weak peaks
I
and other similar dioxoꢀ indicative of the C=N–N=C groups in the two comꢀ
I
and 1601 cm–1 II
.
ν
N
I
bonds to form a dimer, as shown in Fig. 4.
The weak bands in the range 3360–3450 cm–1 in
the IR spectra of both complexes can be assigned to
observed in the range 400–800 cm–1 may be attributed
to the Mo–O and Mo–N bonds in the complexes. The
comparison of the IR spectra of the free hydrazone
ligands and the dioxomolybdenum(VI) complexes
confirms the enolate coordination mode of the
ligands.
the (OH) vibrations of the methanol molecules. The
ν
hydrazone ligands show stretching bands attributed to
C=O, ON, C–OH, and NH at about 1668, 1645,
1181, and 3237 cm–1, respectively. The Mo=O
The electronic spectra for the complexes recorded
stretching modes occur as a pair of sharp strong bands in absolute methanol displayed absorption maxima in
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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98
XU, LI
2. Tangestaninejad, S., Moghadam, M., Mirkhani, V.,
the ranges 390–423, 303–320, and 255–278 nm. The
bands at 303–320 and 255–278 nm can be attributed
to the internal ligand transitions. The absorption maxꢀ
ima at 390–423 nm could be assigned to the ligandꢀtoꢀ
et al., Catal. Commun., 2009, vol. 10, no. 6, p. 853.
3. ElꢀTabl, A.S., Issa, R.M., and Morsi, M.A., Transition
Met. Chem., 2004, vol. 29, no. 5, p. 543.
4. Grivani, G., Tangestaninejad, S., and Halili, A., Inorg.
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metal Mo(dπ)
←
O( ) chargeꢀtransfer (LMCT) tranꢀ
π
sition. This is in the range usually observed for the
MoO2 complexes [19].
Polyhedron, 2009, vol. 28, no. 4, p. 733.
6. Rao, S.N., Kathale, N., Rao, N.N., et al., Inorg. Chim.
Acta, 2007, vol. 360, no. 14, p. 4010.
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mun., 2006, vol. 7, no. 4, p. 236.
8. Choi, S., Yang, J.D., Ji, M., et al., J. Org. Chem., 2001,
vol. 66, no. 24, p. 8192.
9. Drago, R.S. and Burns, D.S., J. Catal., 1997, vol. 166,
The catalytic oxidation test of the complexes on the
oxidation of sulfides under homogeneous conditions
in solution using methyl phenyl sulfide (thioanisol) as
a substrate was carried out according to the literature
method [12]. Hydrogen peroxide was used as an oxiꢀ
dant in a slight excess of 1.25 equivalents based on the
sulfide substrate. Reactions are run with 1 mol % of the
catalyst based on the substrate at a temperature of
no. 2, p. 377.
10. Raghavan, P.S., Ramaswamy, V., Upadhya, T.T., et al.,
10°C. The reaction was started by the addition of
J. Mol. Catal., A, 1997, vol. 122, no. 1, p. 75.
hydrogen peroxide. A control reaction under the same
conditions without any complex present leads to less
than 1% sulfide conversion within 4 h. In the presence
of both complexes, a conversion of about 60% of sulꢀ
fide to the corresponding sulfoxide within 30ꢀmin
reaction time was observed. After about 2 h, in all
cases, the conversion of total the amount of sulfide was
complete. Under the given conditions, no overoxidaꢀ
tion to sulfone could be detected.
11. Debel, R., Buchholz, A., and Plass, W., Z. Anorg. Allg.
Chem., 2008, vol. 634, nos. 12–13, p. 2291.
12. Mancka, M. and Plass, W., Inorg. Chem. Commun.
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,
13. Allen, F.H., Acta Crystallogr., Sect. B: Struct. Sci., 2002,
vol. 58, no. 3, p. 380.
14. Sheldrick, G.M., SHELXꢀ97. Program for Crystal
Structure Solution and Refinement, Göttingen (Gerꢀ
many): Univ. of Göttingen, 1997.
15. Sheldrick, G.M., SHELXTL, Version 5, Siemens,
Madison (USA): Industrial Automation, Inc., 1995.
16. Zhai, Y.ꢀL., Xu, X.ꢀX., and Wang, X., Polyhedron
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18. Dinda, R., Sengupta, S., Ghosh, S., et al., Dalton
Trans., 2002, no. 23, p. 4434.
,
,
ACKNOWLEDGMENTS
The authors greatly acknowledge the Jingchu Uniꢀ
versity of Technology for financial support.
19. Gupta, S., Barik, A.K., Pal, S., et al., Polyhedron, 2007,
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