Syntheses, crystal structures, and catalysis by polymeric dioxomolybdenum(VI) complexes with similar (iso)nicotinohydrazones

Article abstract of DOI:10.1080/00958972.2013.816416

Polymeric dioxomolybdenum(VI) complexes, [MoO₂L]_n(L= L¹= N'-(2-hydroxybenzylidene) nicotinohydrazide for 1, L=L ²= N'-(2-hydroxy-5-methoxybenzylidene)isonicotinohydrazide for 2), were prepared and characterized by physico-chemical, spectroscopic methods, and single-crystal X-ray determination. Complex 1 crystallizes in the orthorhombic space group P2₁2₁2₁with a=7.6568(4), b =11.6315(7), c = 15.2211(9)A, V= 1355.59(13) A³, Z = 4, R₁= 0.0181, wR₂= 0.0464, and S = 1.097. Complex 2 crystallizes in the monoclinic space group P2₁/n with a=11.2516(6), b=11.8134(7), c= 12.4371(6) A, β = 116.2210(10)°, V=1483.02(14) A³, Z= 4, R₁= 0.0399, wR₂= 0.0874, and S=1.096. X-ray analysis indicates that Mo in each complex is octahedral with two oxo groups and N₂O₂donor set of the nicotinohydrazone or isonicotinohydrazone. The complexes are efficient catalysts for oxidation of olefins.

Full text of DOI:10.1080/00958972.2013.816416

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Syntheses, crystal structures,
and catalysis by polymeric
dioxomolybdenum(VI) complexes with
similar (iso)nicotinohydrazones
a
a
a
Wei-Xiu Xu , Yong-Mei Yuan & Wen-Hui Li
a
College of Chemical Engineering and Pharmacy , Jingchu
University of Technology , Jingmen , P.R. China
Accepted author version posted online: 18 Jun 2013.Published
online: 16 Jul 2013.
To cite this article: Wei-Xiu Xu , Yong-Mei Yuan & Wen-Hui Li (2013) Syntheses, crystal structures,
and catalysis by polymeric dioxomolybdenum(VI) complexes with similar (iso)nicotinohydrazones,
Journal of Coordination Chemistry, 66:15, 2726-2735, DOI: 10.1080/00958972.2013.816416
To link to this article: http://dx.doi.org/10.1080/00958972.2013.816416
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Journal of Coordination Chemistry, 2013
Vol. 66, No. 15, 2726–2735, http://dx.doi.org/10.1080/00958972.2013.816416
Syntheses, crystal structures, and catalysis by polymeric
dioxomolybdenum(VI) complexes with similar
(
iso)nicotinohydrazones
WEI-XIU XU*, YONG-MEI YUAN and WEN-HUI LI
College of Chemical Engineering and Pharmacy, Jingchu University of Technology,
Jingmen, P.R. China
(Received 2 February 2013; in final form 10 May 2013)
1
Polymeric dioxomolybdenum(VI) complexes, [MoO
L]
2 n
(L= L = N′-(2-hydroxybenzylidene)
2
nicotinohydrazide for 1, L= L = N′-(2-hydroxy-5-methoxybenzylidene)isonicotinohydrazide for 2),
were prepared and characterized by physico-chemical, spectroscopic methods, and single-crystal
X-ray determination. Complex 1 crystallizes in the orthorhombic space group P2
1
2
1
2
1
with
= 0.0181,
= 0.0464, and S = 1.097. Complex 2 crystallizes in the monoclinic space group P2 /n with
3
a = 7.6568(4), b = 11.6315(7), c = 15.2211(9) Å, V= 1355.59(13) Å , Z = 4,
wR
a = 11.2516(6), b = 11.8134(7), c = 12.4371(6) Å, β = 116.2210(10)°, V = 1483.02(14) Å , Z = 4,
= 0.0399, wR = 0.0874, and S = 1.096. X-ray analysis indicates that Mo in each complex is octa-
hedral with two oxo groups and N donor set of the nicotinohydrazone or isonicotinohydrazone.
R
1
2
1
3
R
1
2
2 2
O
The complexes are efficient catalysts for oxidation of olefins.
Keywords: Hydrazone; Schiff base; Molybdenum complex; Crystal structure; Catalytic property
1. Introduction
The mechanism of molybdenum oxotransferase has been investigated. Molybdenum
complexes are used in organic chemistry, in particular, for oxidations of various
compounds [1–5]. Dioxomolybdenum complexes have been investigated as oxidation
catalysts, particularly for sulfoxidation and epoxidation of olefins [6–9]. The synthesis,
characterization, and reactivity studies of a number of dioxomolybdenum complexes with
Schiff bases have been reported [10–13]. Some of the complexes possess oxygen transfer
properties, oxidizing thiols, hydrazine, polyketones, and tertiary phosphines [14, 15]. The
catalytic ability of dioxomolybdenum(VI) complexes with benzohydrazones toward
the oxidation of sulfides has received satisfactory results [16, 17]. However, the number
of documented dioxomolybdenum(VI) complexes catalyzing the peroxidic oxidation of
sulfides is still very limited. There are no reports on the catalytic properties of
dioxomolybdenum complexes with nicotinohydrazone or isonicotinohydrazone ligands.
The rare reports on such complexes focus on preparation and structural characterization
1
[
18–21]. In the present paper, two dioxomolybdenum(VI) complexes, [MoO L ] (1) and
2
n
*
Corresponding author. Email: xuweixiu2012@163.com
Ó 2013 Taylor & Francis

Dioxomolybdenum(VI) nicotinohydrazones
2727
1
2
Scheme 1. Ligands L (left) and L (right).
2
1
2
[
MoO L ] (2) (scheme 1; L = N′-(2-hydroxybenzylidene)nicotinohydrazide for 1, L = N′-
2 n
(2-hydroxy-5-methoxybenzylidene)isonicotinohydrazide for 2), were prepared and studied
for structures and catalytic properties.
2
2
. Experimental
.1. Materials and methods
All chemicals and solvents were of analytical reagent grade, purchased from Beijing
1
2
Chemical Reagent Company. L and L were prepared according to the literature method
22]. Microanalyses (C, H, N) were performed using a Perkin-Elmer 2400 elemental
[
analyzer. Infrared spectra were carried out using the JASCO FT-IR model 420 spectropho-
À1
tometer with KBr disks from 4000 to 200 cm . GC analyses were performed on a
Shimadzu GC-2014 gas chromatograph.
2
2
.2. Syntheses of the complexes
1
.2.1. [MoO L ] (1). A hot ethanol solution (15 mL) of MoO (acac) (0.33 g, 1 mM)
2
n
2
2
1
was added to a hot ethanol solution (15 mL) of L (0.24 g, 1 mM). The mixture was
refluxed for 30 min and then cooled to room temperature to give an orange solution. Single
crystals suitable for X-ray diffraction were formed by slow evaporation of the solution
containing the complex in air for a few days. Yield: 55%. Anal. Calcd for C H MoN O :
1
3
9
3 4
C, 42.5; H, 2.5; N, 11.4. Found: C, 42.3; H, 2.6; N, 11.6%.
2
2
.2.2. [MoO L ] (2). A hot ethanol solution (15 mL) of MoO (acac) (0.33 g, 1 mM)
2
n
2
2
2
was added to a hot ethanol solution (15 mL) of L (0.27 g, 1 mM). The mixture was
refluxed for 30 min and then cooled to room temperature to give an orange solution. Single
crystals suitable for X-ray diffraction were formed by slow evaporation of the solution
containing the complex in air for a few days. Yield: 62%. Anal. Calcd for C H MoN O :
1
4
11
3 5
C, 42.3; H, 2.8; N, 10.6. Found: C, 42.4; H, 2.8; N, 10.5%.
2
.3. X-ray structure determination
X-ray measurements were performed using a Bruker Smart 1000 CCD diffractometer with
graphite-monochromated MoKα radiation (λ = 0.71073 Å) using the ω-scan technique.
Determinations of the Laue class, orientation matrix, and cell dimensions were performed
according to the established procedures where Lorentz polarization and absorption

2
728
W.-X. Xu et al.
Table 1. Crystal data for 1 and 2.
1
2
Chemical formula
Fw
Crystal shape/color
Crystal size (mm)
T (K)
C
13
H
9
MoN
3
O
4
C
14 3 5
H11MoN O
367.2
Block/orange
397.2
Block/orange
0.21 Â 0.18 Â 0.18
0.23 Â 0.20 Â 0.20
298(2)
298(2)
λ (MoKα) (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
0.71073
Orthorhombic
0.71073
Monoclinic
P2 /n
1
11.252(1)
11.813(1)
12.437(1)
116.221(1)
1483.0(1)
4
P2
1
2 2
1 1
7.657(1)
11.632(1)
15.221(1)
90
1355.6(1)
4
β (°)
V (Å )
3
Z
À1
μ (MoKα) (cm
T (min)
)
0.987
0.914
0.8196
0.8424
1.799
0.8173
0.8383
1.779
T (max)
À3
D
c
(g cm
)
Reflections/parameters
Unique reflections
Goodness of fit on F
2513/191
2443
1.097
2087/209
2717
1.096
2
R
R
wR
R
wR
int
0.0191
0.0181
0.0464
0.0191
0.0468
0.0485
0.0399
0.0874
0.0625
0.1006
1
[I P 2σ(I)]
[I P 2σ(I)]
(all data)
2
(all data)
2
1
corrections were applied. Absorption corrections were applied by fitting a pseudoellipsoid
to the ψ-scan data of selected strong reflections over a wide range of 2h angles. The
positions of nonhydrogen atoms were located with direct methods. Subsequently, Fourier
syntheses were used to locate the remaining nonhydrogen atoms. All nonhydrogen atoms
were refined anisotropically. Hydrogens were placed in calculated positions and
constrained to ride on their parent. The analysis was performed with SHELXS-97 and
SHELXL-97 [23, 24]. The crystallographic data for the complex are summarized in table 1.
Selected bond lengths and angles are given in table 2.
3
3
. Results and discussion
.1. Synthesis
The hydrazones were readily prepared by condensation of salicylaldehyde with
nicotinohydrazide, and 5-methoxysalicylaldehyde with isonicotinohydrazide, respectively,
in ethanol. The dioxomolybdenum(VI) complexes were synthesized by refluxing
hydrazones and MoO (acac) in ethanol in a 1 : 1 M proportion. The reaction progress
2
2
(scheme 2) is accompanied by a change of the solution from colorless to orange. We have
attempted to prepare and grow diffraction quality crystals from various solvents; however,
good quality crystals were finally obtained from ethanol. The chemical formulae of the
complexes have been confirmed by elemental analyses, IR spectra, and X-ray single crystal
structure determination.

Dioxomolybdenum(VI) nicotinohydrazones
Table 2. Selected bond lengths (Å) and angles (°) for 1 and 2.
2729
1
Bond lengths
Mo1–O1
Mo1–O3
Mo1–N1
C8–O2
1.927(2)
1.691(2)
2.234(2)
1.319(3)
1.392(3)
Mo1–O2
Mo1–O4
Mo1–N3A
C8–N2
2.012(2)
1.700(2)
2.476(2)
1.295(3)
N1–N2
Bond angles
O3–Mo1–O4
O4–Mo1–O1
O4–Mo1–O2
O3–Mo1–N1
O1–Mo1–N1
O3–Mo1–N3A
O1–Mo1–N3A
N1–Mo1–N3A
106.1(1)
O3–Mo1–O1
O3–Mo1–O2
O1–Mo1–O2
O4–Mo1–N1
O2–Mo1–N1
O4–Mo1–N3A
O2–Mo1–N3A
99.5(1)
96.4(1)
149.3(1)
157.6(1)
71.7(1)
82.9(1)
77.6(1)
103.0(1)
97.5(1)
94.8(1)
80.9(1)
170.0(1)
82.5(1)
75.7(1)
2
Bond lengths
Mo1–O1
Mo1–O4
Mo1–N1
C9–O2
1.922(3)
Mo1–O2
Mo1–O5
Mo1–N3B
C9–N2
2.021(3)
1.687(3)
2.455(4)
1.297(5)
1.689(3)
2.235(4)
1.313(5)
1.394(5)
N1–N2
Bond angles
O5–Mo1–O4
O4–Mo1–O1
O4–Mo1–O2
O5–Mo1–N1
O1–Mo1–N1
O5–Mo1–N3B
O1–Mo1–N3B
N1–Mo1–N3B
105.7(2)
O5–Mo1–O1
O5–Mo1–O2
O1–Mo1–O2
O4–Mo1–N1
O2–Mo1–N1
O4–Mo1–N3B
O2–Mo1–N3B
100.9(2)
96.7(2)
148.5(1)
159.1(2)
72.1(1)
82.2(2)
77.2(1)
103.9(2)
96.0(2)
93.0(2)
81.1(1)
170.7(2)
81.6(1)
78.4(1)
Symmetry codes: A: 1/2 + x, 3/2 – y, 1 – z; B: 3/2 – x, 1/2 + y, 1/2 – z.
Scheme 2. The preparation of the complexes.

2
730
W.-X. Xu et al.
Figure 1. Molecular structure of 1 with 30% probability thermal ellipsoids. Atoms labeled with the suffix A and
unlabeled are at the symmetry position 1/2 + x, 3/2 – y, 1 – z.
Figure 2. Molecular structure of 2 with 30% probability thermal ellipsoids. Atoms labeled with the suffix B and
unlabeled are at the symmetry position 3/2 – x, 1/2 + y, 1/2 – z.
3.2. Structure description of the complexes
The asymmetric units of the structures of 1 and 2 are shown in figures 1 and 2,
respectively. The coordination geometry around Mo can be described as slightly distorted
octahedral, with phenolic O, imino N, and enolic O of the hydrazone, one oxo defining
the equatorial plane, one N of a (iso)nicotinyl, and the other oxo occupying axial
positions. The hydrazones coordinate to Mo meridional forming five- and six-membered
chelate rings with bite angles of 71.71(6) and 80.90(7)° for 1, and 72.07(12) and 81.09
(13)° for 2. The dihedral angles between the benzene ring and the pyridine ring of the
hydrazone are 32.9(3)° for 1 and 17.4(3)° for 2. Displacements of Mo in both 1 and 2
from the equatorial mean planes toward the apical oxo are 0.33(1) Å. The hydrazones
coordinate in their dianionic form, evident from N2–C8 and O2–C8 bond lengths in 1, and
N2–C9 and O2–C9 bond lengths in 2 (table 2). The abnormal bond values indicate the

Dioxomolybdenum(VI) nicotinohydrazones
2731
Figure 3. Molecular packing of 1 viewed along the c axis.
Figure 4. Molecular packing of 2 viewed along the c axis.

2
732
W.-X. Xu et al.
a
Table 3. Catalytic oxidation of olefins catalyzed by 1 and 2.
b
c
Substrate
Product
Conversion (%) (TON)
Selectivity (%)
1
2
91 (263)
90 (255)
100
100
1
2
87 (271)
85 (277)
100
100
1
2
93 (268)
93 (265)
100
100
1
2
100 (289)
100 (285)
100
100
1
2
100 (281)
100 (276)
100
100
1
2
100 (292)
100 (288)
100
100
1
2
100 (280)
100 (285)
100
100
1
2
100 (272)
100 (281)
100
100
a
The molar ratio of catalyst : substrate : TBHP is 1 : 300 : 1000. The reactions were performed in mixture of
OH/CH Cl (V : V = 6 : 4; 1.5 mL).
CH
3
2
2
b
The GC conversion (%) was measured relative to the starting substrate after 1 h.
TON= (mM of product)/(mM of catalyst).
c
presence of the enolate form of the amide groups. The Mo–O, Mo–N, and Mo=O bonds
are within normal ranges and similar to those observed in similar dioxomolybdenum(VI)
complexes [18–21, 25–28]. The distances between Mo and nitrogen of the (iso)nicotinyl
moieties, 2.476(2) Å in 1 and 2.455(4) Å in 2, represent the largest bond lengths within the
distorted octahedral coordination.
In crystal structures of the complexes, [MoO L(CH OH)] units are linked via hydrazone
2
3
ligands to form infinite one-dimensional zigzag chains running parallel to the a axis for 1
figure 3) and b axis for 2 (figure 4).
(

Dioxomolybdenum(VI) nicotinohydrazones
2733
Scheme 3. Proposed catalytic oxidation mechanism.
3.3. IR spectra
The hydrazones show stretches attributed to C=O, C=N, C–OH, and NH at 1654, 1615,
À1
1
180, and 3200 cm , respectively [29]. For the complexes, absence of the bands
characteristic of N–H and C=O indicates enolization of the hydrazone and coordination
through the deprotonated enolic-oxygen. The Mo=O stretches occur as single and strong
À1
bands at 912 cm for 1 and 2, assigned to the asymmetric stretch of MoO [29, 30].
2
À1
Strong bands indicative of C=N groups of the complexes are located at 1612 cm for 1
and 1605 cm for 2 [31]. Weak peaks observed at 460–600 cm may be attributed to
Mo–O and Mo–N vibrations [30].
À1
À1
3
.4. Catalytic oxidation
Catalysis was carried out according to the literature by using tert-butyl hydrogen peroxide
TBHP) as oxidant [9]. The results are listed in table 3. Generally, excellent epoxide yields
(
and selectivities were observed for all aliphatic and aromatic substrates. Oxidation of
aromatic substrates gave the corresponding epoxides in 100% yields, while in oxidation of
aliphatic substrates, the conversion is less than 100%. Based on this, isolated double bonds
are less reactive than conjugated ones, in agreement with those reported previously [9].
There are no distinct differences for catalytic properties between the two complexes. The
proposed mechanism of the catalytic reactions is shown in scheme 3. First, TBHP was
activated by coordination to Mo with formation of seven-coordinate molybdenum. Then a
molecule of an olefin as a nucleophile attacks the electrophilic oxygen of the coordinated
TBHP, forming the corresponding epoxides. TBHP was reduced to tert-butyl alcohol. The
catalytic properties of the complexes reported here are superior to those of manganese
complexes derived from hydrazone or tetraphenylporphyrin ligands [32, 33], and also
superior to that of the tungsten complexes supported by multi-wall carbon nanotube [34].

2
734
. Conclusion
W.-X. Xu et al.
4
A pair of polymeric dioxomolydenum(VI) complexes with similar (iso)nicotinohydrazone
ligands, N′-(2-hydroxybenzylidene)nicotinohydrazide and N′-(2-hydroxy-5methoxybenzyli-
dene)isonicotinohydrazide, have been prepared and structurally characterized by a single
crystal X-ray structure determination and infrared spectroscopy. The hydrazones coordinate
to Mo through phenolic O, imino N, ethanolic O, and pyridine N. Both complexes have
catalytic properties on oxidation of various olefins to their corresponding epoxides.
Supplementary material
CCDC 922464 (1) and 922465 (2) contain the supplementary crystallographic data for the
complex. These data can be obtained free of charge via http://www.ccdc.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Center, 12 Union Road,
Cambridge CB2 1EZ, UK; Fax: (+44)1223-336-033; or E-mail: deposit@ccdc.cam.ac.uk.
Acknowledgment
The authors greatly acknowledge Jingchu University of Technology for financial support.
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