Synthesis, Characterization, and Crystal Structures of Dioxomolybdenum(VI) Complexes Derived from Similar Tridentate Hydrazone Compounds with Catalytic Property

Article abstract of DOI:10.1134/S1070328418090063

Abstract: Two hydrazone compounds 2-chloro-N'-(2-hydroxy-4-methoxybenzylidene)benzohydrazide (H₂L¹) and N'-(2-hydroxy-4-methoxybenzylidene)-3-methylbenzohydrazide (H₂L²) were prepared and characterized by IR, UV-Vis and ¹H NMR spectra. Based on the hydrazone compounds, two new structurally similar dioxomolybdenum(VI) complexes, [MoO₂L¹(CH₃OH)] (I) and [MoO₂L²(CH₃OH)] (II), were prepared and characterized by IR and UV-Vis spectra, and single crystal X-ray diffraction (CIF files nos. 1566491 (I) and 1566492 (II)). Complex I crystallizes as the triclinic space group (Formula presented.) with unit cell dimensions a = 8.0750(5), b = 10.5223(7), c = 10.8110(7) ?, α = 96.975(2)°, β = 97.909(2)°, γ = 104.497(2)°, V = 869.2(1) ?³, Z = 2, R₁ = 0.0323, wR₂ = 0.0620, GOOF = 1.089. Complex II crystallizes as the monoclinic space group P2₁/n with unit cell dimensions a = 11.680(1), b = 10.496(2), c = 14.879(2) ?, β = 98.862(2)°, V?= 1802.2(4) ?³, Z = 4, R₁ = 0.0270, wR₂ = 0.0675, GOOF = 1.111. X-ray analysis indicates that the complexes are mononuclear dioxomolybdenum(VI) species with the Mo atoms in octahedral coordination. The complexes were studied for their catalytic oxidation property on some olefins with tert-butyl hydrogen peroxide as oxidant.

Full text of DOI:10.1134/S1070328418090063

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2018, Vol. 44, No. 9, pp. 572–578. © Pleiades Publishing, Ltd., 2018.
Synthesis, Characterization, and Crystal Structures
of Dioxomolybdenum(VI) Complexes Derived from Similar Tridentate
Hydrazone Compounds with Catalytic Property1
H. Y. Liua, b, *, H. H. Yanga, b, Y. X. Diaoa, b, Y. F. Yea, b, and X. L. Zoua, b
aSchool of Chemistry and Chemical Engineering, Guangdong Pharmaceutical University, Zhongshan, 528453 P.R. China
bGuangdong Cosmetics Engineering & Technology Research Center, Zhongshan, 528453 P.R. China
*e-mail: liuhuanyu03@163.com
Received September 24, 2017
Abstract—Two hydrazone compounds 2-chloro-N'-(2-hydroxy-4-methoxybenzylidene)benzohydrazide (H2L1)
and N'-(2-hydroxy-4-methoxybenzylidene)-3-methylbenzohydrazide (H2L2) were prepared and characterized by
IR, UV-Vis and 1H NMR spectra. Based on the hydrazone compounds, two new structurally similar dioxomolyb-
denum(VI) complexes, [MoO2L1(CH3OH)] (I) and [MoO2L2(CH3OH)] (II), were prepared and characterized
by IR and UV-Vis spectra, and single crystal X-ray diffraction (CIF files nos. 1566491 (I) and 1566492 (II)). Com-
plex I crystallizes as the triclinic space group P with unit cell dimensions a = 8.0750(5), b = 10.5223(7), c =
1
10.8110(7) Å, α = 96.975(2)°, β = 97.909(2)°, γ = 104.497(2)°, V = 869.2(1) Å3, Z = 2, R1 = 0.0323, wR2 = 0.0620,
GOOF = 1.089. Complex II crystallizes as the monoclinic space group P21/n with unit cell dimensions a =
11.680(1), b = 10.496(2), c = 14.879(2) Å, β = 98.862(2)°, V = 1802.2(4) Å3, Z = 4, R1 = 0.0270, wR2 = 0.0675,
GOOF = 1.111. X-ray analysis indicates that the complexes are mononuclear dioxomolybdenum(VI) species with
the Mo atoms in octahedral coordination. The complexes were studied for their catalytic oxidation property on
some olefins with tert-butyl hydrogen peroxide as oxidant.
Keywords: hydrazone, molybdenum complex, mononuclear complex, crystal structure, catalytic property
DOI: 10.1134/S1070328418090063
INTRODUCTION
reported some metal complexes with Schiff bases, and
their biological aplications [14–16], as well as catalytic
properties [17]. In this paper, as a continuation of
the work on the exploration of new catalytic materials
based on molybdenum complexes, two new molybde-
num(VI) complexes derived from hydrazone com-
pounds 2-chloro-N'-(2-hydroxy-4-methoxybenzy-
lidene)benzohydrazide (H2L1) and N'-(2-hydroxy-4-
Study on the oxidation of olefins has received par-
ticular interest in recent years. High-valent molybde-
num complexes have attracted continuing attention
due to their important practical applications as cata-
lysts in the ammoxidation of propene, the sulfoxida-
tion and epoxidation of olefins etc. [1–7]. The ability
of molybdenum to form stable complexes with oxy-
gen- and nitrogen-containing ligands led to the devel-
opment of molybdenum Schiff base complexes
which are efficient catalysts both in homogeneous and
heterogeneous reactions [8–13]. Recently, we have
methoxybenzylidene)-3-methylbenzohydrazide (H2L2)
were prepared. They are [MoO2L1(CH3OH)] (I) and
[MoO2L2(CH3OH)] (II).
H
N
H
N
N
N
O
Cl
O
MeO
OH
MeO
OH
(H2L1 )
(H2L2 )
1
The article is published in the original.
572

SYNTHESIS, CHARACTERIZATION, AND CRYSTAL STRUCTURES
573
EXPERIMENTAL
upon slowly evaporation within a few days. The crys-
tals were isolated by filtration, washed with methanol
and dried in vacuum containing anhydrous CaCl2.
Materials and methods. MoO2(Acac)2 and organic
materials were purchased from Sigma-Aldrich and
used as received. All other reagents were of analytical
reagent grade. Elemental analyses of C, H and N were
carried out in a Perkin-Elmer automated model 2400
Series II CHNS/O analyzer. FT-IR spectra were
obtained on a Perkin-Elmer 377 FT-IR spectrometer
with samples prepared as KBr pellets. UV-Vis spectra
were obtained on a Lambda 900 spectrometer. X-ray
diffraction was carried out on a Bruker APEX II CCD
diffractometer. 1H NMR spectrum of the complex was
recorded on a Bruker FT-NMR 300 MHz spectrome-
ter using (CD3)2SO as solvent. GC analyses were per-
formed on a Shimadzu GC-2010 gas chromatograph.
For C16H15N2O6ClMo (I)
Anal. calcd., %
Found, %
C, 41.5
C, 41.7
H, 3.3
H, 3.4
N, 6.1
N, 6.2
Yield 63%. IR (KBr; νmax, cm–1): 3447 w ν(OH),
1613 m ν(C=N), 1441 m ν(C=C), 1373 m ν(Ar–O),
1162 s ν(C–O), 952 s, 851 s ν(Mo=O). UV-Vis data
(MeOH; λmax, nm): 270, 335, 450.
For C17H18N2O6Mo (II)
Anal. calcd., %
Found, %
C, 46.2
C, 46.3
H, 4.1
H, 4.1
N, 6.3
N, 6.5
Synthesis of the hydrazones. The hydrazones were
synthesized as follows. To the methanolic solution
(30 mL) of 2-methoxybenzohydrazide (0.02 mol) was
added a methanolic solution (20 mL) of 3-bromosa-
licylaldehyde or 3-methylsalicylaldehyde (0.02 mol)
with stirring. The mixtures were stirred for 30 min at
room temperature, and left to slowly evaporate to give
colorless crystalline product, which were recrystal-
lized from methanol and dried in vacuum containing
anhydrous CaCl2.
Yield 43%. IR (KBr; νmax, cm–1): 3443 w ν(OH),
1613 m ν(C=N), 1441 m ν(C=C), 1372 m ν(Ar–O),
1164 s ν(C–O), 949 s, 852 s ν(Mo=O). UV-Vis data
(MeOH; λmax, nm): 270, 330, 445.
X-ray crystallography. X-ray diffraction was carried
out at a Bruker APEX II CCD area diffractometer
equipped with MoKα radiation (λ = 0.71073 Å). The
collected data were reduced with SAINT [18], and
multi-scan absorption correction was performed using
SADABS [19]. The structures of the complexes were
solved by direct method, and refined against F2 by full-
matrix least-squares method using SHELXTL [20].
All of the non-hydrogen atoms were refined aniso-
For C15H13ClN2O3 (H2L1)
Anal. calcd., %
Found, %
C, 59.1
C, 59.3
H, 4.3
H, 4.4
N, 11.6
N, 11.5
Yield 91%. IR (KBr; νmax, cm–1): 3435 w ν(OH), tropically. The methanol hydrogen atoms were located
from electronic density maps and refined isotropically.
The remaining hydrogen atoms were placed in calcu-
lated positions and constrained to ride on their parent
atoms. The crystallographic data and refinement
parameters for the compounds are listed in Table 1.
Selected bond lengths and angles are listed in Table 2.
3327 w ν(NH), 1653 s ν(C=O), 1601 w ν(C=N),
1517 m ν(Ar–O), 1287 m ν(C–O). UV-Vis data
(MeOH; λmax, nm): 285, 330. 1H NMR (300 MHz, d6-
DMSO; δ, ppm): 12.12 (s., 1H, OH), 11.70 (s., 1H,
NH), 8.61 (s., 1H, CH=N), 7.72–7.40 (m., 5H, ArH),
6.65 (d., 1H, ArH), 6.45 (s., 1H, ArH), 3.75 (s., 3H,
OCH3).
The supplementary crystallographic data for I and
II have been deposited with the Cambridge Crystallo-
graphic Data Centre (CCDC nos. 1566491 and
1566492, respectively; deposit@ccdc.cam.ac.uk or
http://www.ccdc.ac.uk/conts/retrieving.html).
For C16H16N2O3 (H2L2)
Anal. calcd., %
Found, %
C, 67.6
C, 67.4
H, 5.7
H, 5.6
N, 9.8
N, 9.9
Yield 87%. IR (KBr; νmax, cm–1): 3441 w ν(OH),
3323 w ν(NH), 1653 s ν(C=O), 1602 w ν(C=N),
1515 m ν(Ar–O), 1285 m ν(C–O). UV-Vis data
Catalytic oxidation experiment. Catalytic experi-
ment was carried out in a 50 mL glass round-bottom
flask fitted with a reflux condenser and placed in an oil
bath at prearranged temperature under continuous
stirring. The catalytic oxidation experiment was car-
ried out as follows: molybdenum(VI) complex
(0.032 mmol) was dissolved in 10 mL 1,2-dichlo-
roethane. Then 10 mmol alkene was added to the reac-
tion mixture and 30 mmol tert-butyl hydroperoxide
(TBHP) was added. The reaction mixture was
refluxed for 1 h. The reaction products were moni-
1
(MeOH; λmax, nm): 290, 335. H NMR (300 MHz,
d6-DMSO; δ, ppm): 12.23 (s., 1H, OH), 11.58 (s., 1H,
NH), 8.63 (s., 1H, CH=N), 7.87–7.36 (m., 5H, ArH),
6.65 (d., 1H, ArH), 6.45 (s., 1H, ArH), 3.75 (s., 3H,
OCH3), 2.31 (s., 3H, CH3).
Synthesis of the complexes. The hydrazone com-
pounds (0.1 mmol each) and MoO2(Acac)2
(0.1 mmol) were mixed in methanol (10 mL). The tored at periodic time intervals using gas chromatogra-
mixture was refluxed for 1 h and then cooled to room phy. The oxidation products were identified by com-
temperature. Single crystals of the complexes, suitable parison with authentic samples (retention times
for X-ray diffraction, were grown from the solution in GC).
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574
LIU et al.
Table 1. Crystallographic and refinement data for complexes I and II
Value
Parameter
I
II
Formula weight
Crystal shape/color
T, K
462.69
Block/yellow
298(2)
442.27
Block/yellow
298(2)
Crystal dimensions, mm
Crystal system
Space group
0.26 × 0.23 × 0.20
Triclinic
0.31 × 0.27 × 0.23
Monoclinic
P21/n
P
1
a, Å
b, Å
c, Å
8.0750(5)
10.5223(7)
10.8110(7)
96.975(2)
97.909(2)
104.497(2)
869.2(1)
11.680(1)
10.496(2)
14.879(2)
90
98.862(2)
90
α, deg
β, deg
γ, deg
V, Å3
1802.2(4)
Z
2
4
ρ
calcd, g cm–3
1.768
1.630
μ(MoKα), mm–1
0.945
0.764
F(000)
464
896
Measured reflections
Unique reflections
Observed reflections (I ≥ 2σ(I))
Min. and max. transmission
Parameters
8275
3211
2755
15338
3326
3029
0.7977 and 0.8439
0.7913 and 0.8335
240
1
240
1
Restraints
Goodness of fit on F 2
R1, wR2 (I ≥ 2σ(I)*
R1, wR2 (all data)*
1.089
1.111
0.0323, 0.0620
0.0439, 0.0657
0.0270, 0.0675
0.0308, 0.0699
2
2
2 1/2
* R = F – F /F , wR = [Σw(
–
2)/Σw( ) ]
.
Fo Fc
Fo
1
o
c
o
2
RESULTS AND DISCUSSION
to the vibration of N–H bonds. The position of the
bands demonstrates that the N–H hydrazone protons
are engaged in hydrogen bonds. The intense bands at
1653 cm–1 of the hydrazone compounds are generated
by ν(C=O) vibrations, whereas the bands at about
1600 cm–1 by the ν(C=N) ones. The non-observation
of the ν(C=O) bands, that present in the spectra of the
hydrazone compounds, indicates the enolization of
the amide functionality upon coordination to the Mo-
center. Instead strong bands at 1613 cm–1 for the com-
plexes are observed, which can be attributed to the
asymmetric stretching vibration of the conjugated
CH=N–N=C–O groups, characteristic for the coor-
dination of the enolate form of the compounds. The
medium ν(Mo=O) bands at about 950 and 850 cm–1
The hydrazone compounds H2L1 and H2L2 were
readily prepared by the condensation reaction of a 1 : 1
molar ratio of 2-hydroxy-4-methoxybenzohydrazide
with 2-chlorobenzohydrazide and 3-methylbenzohy-
drazide, respectively, in methanol. Complexes I and II
were prepared by the reaction of the hydrazone com-
pounds with MoO2(Acac)2 in methanol, followed by
recrystallization. Elemental analyses of the complexes
are in accordance with the molecular structures pro-
posed by the X-ray analysis.
In the spectra of the hydrazone compounds and the
complexes, the weak and broad bands centered at
about 3440 cm–1 are assigned to the vibration of O–H
bonds. The weak and sharp bands located at about
3330 cm–1 of the hydrazone compounds are assigned could be clearly identified for both complexes [21].
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 44 No. 9 2018

SYNTHESIS, CHARACTERIZATION, AND CRYSTAL STRUCTURES
Table 2. Selected bond distances (Å) and angles (deg) for complexes I and II
575
Bond
d, Å
Bond
d, Å
I
Mo(1)−O(1)
Mo(1)−O(4)
Mo(1)−O(6)
1.933(2)
2.348(2)
1.691(2)
Mo(1)−O(2)
Mo(1)−O(5)
Mo(1)−N(1)
2.010(2)
1.694(2)
2.234(2)
II
Mo(1)−O(2)
Mo(1)−O(5)
Mo(1)−N(1)
Mo(1)−O(1)
Mo(1)−O(4)
Mo(1)−O(6)
1.906(2)
2.323(2)
1.714(2)
ω, deg
1.975(2)
1.688(2)
2.229(2)
ω, deg
Angle
Angle
I
O(6)Mo(1)O(5)
O(5)Mo(1)O(1)
O(5)Mo(1)O(2)
O(6)Mo(1)N(1)
O(1)Mo(1)N(1)
O(6)Mo(1)O(4)
O(1)Mo(1)O(4)
N(1)Mo(1)O(4)
105.84(11)
102.33(9)
98.57(9)
96.67(10)
80.95(8)
171.64(9)
82.08(9)
75.19(8)
O(6)Mo(1)O(1)
O(6)Mo(1)O(2)
O(1)Mo(1)O(2)
O(5)Mo(1)N(1)
O(2)Mo(1)N(1)
O(5)Mo(1)O(4)
O(2)Mo(1)O(4)
98.71(10)
96.94(10)
149.27(9)
156.34(10)
71.07(8)
82.02(9)
78.77(8)
II
O(5)Mo(1)O(1)
O(5)Mo(1)O(6)
O(6)Mo(1)O(1)
O(6)Mo(1)O(2)
O(5)Mo(1)N(1)
O(1)Mo(1)N(1)
O(5)Mo(1)O(4)
O(1)Mo(1)O(4)
N(1)Mo(1)O(4)
105.21(10)
103.37(8)
96.44(8)
94.92(8)
81.08(7)
170.95(8)
78.68(8)
76.04(7)
99.64(10)
98.53(9)
148.44(7)
158.15(8)
71.81(7)
O(5)Mo(1)O(2)
O(1)Mo(1)O(2)
O(6)Mo(1)N(1)
O(2)Mo(1)N(1)
O(6)Mo(1)O(4)
O(2)Mo(1)O(4)
83.80(8)
79.32(8)
In the electronic spectra of the complexes, the low- chelate rings with bite angles of 71.07(8)° (I) and
est energy transition bands are observed at 450 nm for
I and 445 nm for II, which are attributed to LMCT
transition as charge transfer from p-orbital
on the lone-pair of ligands’ oxygen atoms to the empty
d-orbital of the vanadium atoms. The other strong
bands in the range of 320–340 nm in the spectra of
both complexes are similar to the absorption bands in
the spectra of the corresponding hydrazone com-
pounds, so they are attributed to the intra-ligand π →
π* absorption peak of the ligands. The other mainly
LMCT and to some extent π → π* bands appear at
270 nm for both I and II.
71.81(7)° (II) (N(1)V(1)O(2)), and 80.95(8)° (I) and
81.08(7)° (II) (N(1)V(1)O(1)), respectively, typical for
this type of ligand systems [22]. Each chelating hydra-
zone ligand lies in a plane with one hydroxylato ligand
which lies trans to the hydrazone imino N atom. One
methanol O atom trans to one of the oxo groups com-
pletes the distorted octahedral coordination sphere at
a rather elongated distance of about 2.3 Å due to the
trans influence of the oxo group. As expected, the
hydrazone compounds coordinate in their doubly
deprotonated enolate form which is consistent with
the observed O(2)–C(8) and N(2)–C(8) bond lengths
of 1.308(3) and 1.307(4) Å in I, and 1.323(3) and
1.290(3) Å in II, respectively. This agrees with
reported molybdenum or vanadium complexes con-
taining the enolate form of this ligand type [23, 24]. In
Molecular structures of complexes I and II are
shown in Fig. 1. The coordination geometry around
the Mo atoms can be described as distorted octahedral
with the tridentate hydrazone ligand coordinated in a
meridional fashion, forming five- and six-membered the crystal packing structure of complex I, hydrazone
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 44 No. 9 2018

576
LIU et al.
(a)
C(14)
C(13)
C(6)
C(3)
N(2)
C(7)
N(1)
C(1)
C(2)
C(5)
C(4)
C(12)
C(11)
C(9)
O(6)
C(8)
C(15)
C(10)
O(3)
O(2)
O(4)
O(1)
Mo(1)
Cl(1)
O(5)
C(16)
(b)
C(15)
C(12)
C(11)
C(5)
C(6)
C(10)
C(9)
C(7)
N(2)
C(4)
C(1)
O(5)
N(1)
C(16)
O(3)
C(8)
O(2)
C(13)
C(3)
C(2)
O(1)
C(14)
Mo(1)
O(4)
C(17)
O(6)
Fig. 1. Perspective views of complexes I (a) and II (b) with the atom labeling scheme. Thermal ellipsoids are drawn at the 30%
probability level.
molecules are linked by methanol molecules through hydrogen bonds of O–H···O (Table 3), leading to the
formation of 1D chains along the b axis (Fig. 2b).
intermolecular hydrogen bonds of O–H···N (Table 3),
leading to the formation of dimers (Fig. 2a). In the
crystal packing structure of complex II, hydrazone
1-Butene, 1-pentene, 4-chloro-1-butene, phenyl-
ene 4-methylphenylene, 3-methylphenylene, 2-meth-
molecules are linked together through intermolecular ylphenylene, 4-chlorophenylene, 3-chlorophenylene,
Table 3. Geometric parameters of hydrogen bonds for complexes I and II*
Distance, Å
D−H∙∙∙A
Angle D−H∙∙∙A, deg
D−H
H∙∙∙A
D∙∙∙A
I
O(4)−H(4)∙∙∙N(2)i
0.85(1)
1.93(1)
2.769(3)
2.748(3)
170(4)
178(3)
II
1.92(1)
O(4)−H(4)∙∙∙O(6)ii
0.85(1)
i
ii
* Symmetry codes: 2 – x, –y, 1 – z; 1/2 – x, 1/2 + y, 1/2 – z.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
Vol. 44
No. 9
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SYNTHESIS, CHARACTERIZATION, AND CRYSTAL STRUCTURES
Table 4. Details of the catalytic oxidation of olefins catalyzed by complexes*
577
Conversion, %**
Substrate
Product
I
II
90.6
85.4
O
93.8
95.2
87.1
90.5
O
Cl
O
Cl
O
97.2
98.7
95.1
99.2
O
O
O
96.3
97.1
98.5
99.0
O
100
100
Cl
Cl
O
O
100
100
100
100
Cl
Cl
Cl
Cl
* The molar ratio of catalyst : substrate : TBHP is 1 : 300 : 1000. The reaction was performed in mixture of CH OH–CH Cl (v : v = 3 : 1).
3
2
2
** The GC conversion (%) was measured relative to the starting substrate after 1 h.
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and 2-chlorophenylene were used as the substrates.
The catalytic oxidation results are given in Table 4.
The selectivities for both aliphatic and aromatic sub-
strates are 100%. High epoxide yields (85–95%) are
obtained for aliphatic substrates. While for aromatic
substrates, the epoxide yields (96–100%) are higher
than aliphatic substrates. In general, the methyl-sub-
stituted substrates gave lower epoxide yields when
compared to the chloro-substituted ones. And, as for
the catalysts, the electronic-withdrawing effect of the
Cl group is better than the electronic-donating effect
of the Me group for the catalytic property.
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The national high technology research and devel-
opment program (863 program, 2012AA020304).
Guangdong province science and technology plan
program (no. 2012145). Guangdong province science
and technology plan program (no. 2015110).
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
Vol. 44
No. 9
2018