Synthesis, structure, and catalytic oxidation of a molybdenum(VI) complex [MoO2(CH3OH)L]

Article abstract of DOI:10.1134/S1070328415070052

A new molybdenum(VI) complex, [MoO₂(CH₃OH)(L)] (L = N′-(4-diethylamino-2-hydroxybenzylidene)-4-hydroxybenzohydrazide), was prepared and characterized by spectroscopy methods and single crystal X-ray diffraction (CIF file CCDC no. 1038153). The crystal of the complex, C₁₉H₂₃MoN₃O₆, crystallizes in the triclinic space group P1 with unit cell dimensions a = 6.9824(9), b = 10.206(1), c = 15.302(2) ?, α = 94.399(2)°, β = 101.877(2)°, γ = 104.062(2)°, V = 1025.9(2) ?³, Z = 2, R₁ = 0.0317, wR₂ = 0.0796, S = 1.060. The Mo atom in the complex is in an octahedral coordination with phenolate O, imino N, enolate O atoms of the ligand L, and one oxo O in the equatorial plane, and with one methanol O and the other oxo O in the axial sites. Crystals of the complex are stabilized by hydrogen bonds. The complex was studied for its catalytic oxidation property on some olefins, with tert-butyl hydrogen peroxide as oxidant.

Full text of DOI:10.1134/S1070328415070052

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2015, Vol. 41, No. 7, pp. 451–455. © Pleiades Publishing, Ltd., 2015.
Synthesis, Structure, and Catalytic Oxidation
of a Molybdenum(VI) Complex [MoO2(CH3OH)L]1
,
H. Y. Liua *, L. Q. Zangb, and J. L. Lva
aSchool of Chemistry and Chemical Engineering, Guangdong Pharmaceutical University, Zhongshan, 528453 P.R. China
bSchool of Pharmacy, Guangdong Pharmaceutical University, Guangzhou, 510006 P.R. China
*eꢀmail: liuhuanyu03@163.com
Received December 9, 2014
Abstract—A new molybdenum(VI) complex, [MoO2(CH3OH)(L)] (L =
benzylidene)ꢀ4ꢀhydroxybenzohydrazide), was prepared and characterized by spectroscopy methods and sinꢀ
gle crystal Xꢀray diffraction (CIF file CCDC no. 1038153). The crystal of the complex, C19H23MoN3O6,
N'ꢀ(4ꢀdiethylaminoꢀ2ꢀhydroxyꢀ
crystallizes in the triclinic space group
with unit cell dimensions
a
= 6.9824(9), = 10.206(1),
b
c
=
=
P1
15.302(2) Å,
0.0796,
α
= 94.399(2)°,
β
= 101.877(2)°,
γ
= 104.062(2)°,
V
= 1025.9(2) Å3,
Z
= 2, R1 = 0.0317, wR2
S
= 1.060. The Mo atom in the complex is in an octahedral coordination with phenolate O, imino N,
enolate O atoms of the ligand L, and one oxo O in the equatorial plane, and with one methanol O and the
other oxo O in the axial sites. Crystals of the complex are stabilized by hydrogen bonds. The complex was
studied for its catalytic oxidation property on some olefins, with tertꢀbutyl hydrogen peroxide as oxidant.
DOI: 10.1134/S1070328415070052
1
INTRODUCTION
trum was recorded on a Shimadzu UV−Vis scanning
spectrophotometer (Model 2101 PC). Elemental
analyses (C, H and N) were performed using a Carlo
Erba Model EA 1108 analyzer. GC analyses were perꢀ
formed on a Shimadzu GCꢀ2010 gas chromatograph.
The development of processes for oxidation of oleꢀ
fins is a goal that has long been pursued. Highꢀvalent
molybdenum complexes have attracted continuing
attention due to their important practical applications
as catalysts in the ammoxidation of propene, the sulꢀ
foxidation and epoxidation of olefins, etc. [1–7]. The
ability of molybdenum to form stable complexes with
oxygenꢀ and nitrogenꢀcontaining ligands led to the
development of molybdenum Schiff base complexes
which are efficient catalysts both in homogeneous and
heterogeneous reactions [8–13]. Recently, we have
reported some metal complexes with Schiff bases, and
their biological aplications [14–16]. As a continuation
of the work on the exploration of new catalytic materials
based on Schiff base complexes, in this paper, a new
Syntheses of I. To a solution of 4ꢀdiethylaminosalꢀ
icyldehyde (1 mmol) in 25 mL methanol was added a
solution of 4ꢀhydroxybenzohydrazide (1 mmol) in
15 mL methanol, and the reaction mixture was heated
at reflux for 1 h. Then a solution of MoO2(Acac)2
(1 mmol) in 15 mL methanol was added dropwise
under stirring. The solution color changed immediꢀ
ately to yellow. After the reflux was continued for
30 min, three quarter of the solvent was evaporated.
The solid product was filtered and washed with methꢀ
anol (67% yield). Single crystals, suitable for Xꢀray
diffraction, were obtained by slow evaporation of the
methanolic solution of the product.
molybdenum(VI) complex, [MoO2(CH3OH)(L)] (
I),
where 'ꢀ(4ꢀdiethylaminoꢀ2ꢀhydroxybenꢀ
L
=
N
zylidene)ꢀ4ꢀhydroxybenzohydrazide), is described.
For C19H23N3O6Mo
EXPERIMENTAL
anal. calcd., %: C, 47.02;
Found, %: C, 46.86;
H, 4.78;
H, 4.89;
N, 8.66.
N, 8.82.
Materials and instrumentations. MoO2(Acac)2 was
obtained by published method [17]. The remaining
reagents were supplied by Merck and Fluka, and were
employed without further purification. IR spectra
were recorded on a Shimadzu Varian 4300 spectroꢀ
photometer. H NMR spectrum of the complex was
recorded on a Bruker FTꢀNMR 300 MHz spectromeꢀ
IR frequencies (KBr;
, cm–1): 3276, 2971, 2923,
ν
2857, 1612, 1579, 1507, 1402, 1350, 1245, 1136, 1016,
935, 887, 835, 787, 711, 650. Electronic absorption
1
spectrum in acetonitrile (
280 (10232), 346 (13870), 472 (12880). H NMR
(300 MHz; DMSOꢀd6; , ppm): 10.06 (s., 1H), 8.54
(s., 1H), 7.78 (d., 2H), 7.40 (d., 1H), 6.83 (d., 2H),
λ
, nm (
ε
, mol–1 cm–1)):
L
1
ter using (CD3)2SO as solvent. The electronic specꢀ
δ
1
The article is published in the original.
451

452
LIU et al.
Table 1. Crystallographic data and structure refinement for
I
Parameter
Value
Fw
485.34
273(2)
T
, K
Crystal system
Space group
Triclinic
P1
6.9824(9)
10.206(1)
15.302(2)
94.399(2)
101.877(2)
104.062(2)
1025.9(2)
2
a
, Å
, Å
b
c
, Å
, deg
, deg
, deg
α
β
γ
V
Z
ρ
μ
λ
, Å3
, g cm–3
, mm–1
1.571
0.680
(Mo
K
), Å
0.71073
496
α
F(000)
Collected reflections
Unique reflections
Observed reflections (
Parameters
9837
3868
I
≥
2σ,(I
))
3648
265
GOOF (F2
)
1.060
R1
,
,
wR2
(
I
≥
2
σ
,(
I
))
0.0317, 0.0796
0.0341, 0.0811
0.779 and –0.669
R1
wR2, all data
Largest peak and deepest hole,
e
Å–3
6.40 (d.d.,
(s., 1H), 3.5–3.1 (m., 6H), 1.13 (t., 6H).
J
= 8.9, 2.3 Hz, 1H), 6.13 (d., 1H), 4.09
Catalytic oxidation experiment. Catalytic experiꢀ
ment was carried out in a 50 mL glass roundꢀbottom
flask fitted with a reflux condenser and placed
in an oil bath at prearranged temperature under conꢀ
Xꢀray structure determination. The intensity data
were collected on a Bruker SMART 1000 CCD area
diffractometer using graphiteꢀmonochromatized
tinuous
stirring.
The
catalytic
oxidation
experiment was carried out as follows: molybdeꢀ
num(VI) complex (0.032 mmol) was dissolved in
10 mL 1,2ꢀdichloroethane. Then 10 mmol alkene was
added to the reaction mixture and 30 mmol TBHP was
added. The reaction mixture was refluxed for 1 h. The
reaction products were monitored at periodic time
intervals using gas chromatography. The oxidation
products were identified by comparison with authentic
samples (retention times in GC).
Mo
K
radiation ( = 0.71063 Å). The structure was
λ
α
solved by direct methods (SHELXSꢀ97) [18] and
refined by fullꢀmatrix leastꢀsquares techniques against
F2 (SHELXLꢀ97) [18]. The positions of nonꢀhydroꢀ
gen atoms were located with direct methods. Subseꢀ
quent Fourier syntheses were used to locate the
remaining nonꢀhydrogen atoms. The nonꢀhydrogen
atoms were refined anisotropically. The hydrogen
atoms were placed in calculated positions and conꢀ
strained to ride on their parent atoms. The data collecꢀ
tion and refinement processes are summarized in
Table 1.
RESULTS AND DISCUSSION
The complex was synthesized by the reaction of
The supplementary crystallographic data for comꢀ equimolar quantities of 4ꢀdiethylaminosalicylaldeꢀ
plex has been deposited with the Cambridge Crysꢀ hyde, 4ꢀhydroxybenzohydrazide and MoO2(Acac)2 in
tallographic Data Centre (no. 606971; methanol. It was found that the ligand and metal ratio
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam. from 1 : 1 to 1 : 3 resulted the same product. Crystals
ac.uk). of the complex are stable in open atmosphere.
I
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SYNTHESIS, STRUCTURE, AND CATALYTIC OXIDATION
453
C(5)
C(17)
C(11)
C(4)
C(6)
C(1)
C(16)
O(3)
C(15)
C(18) N(3)
C(10)
C(9)
C(7)
N(2)
C(12)
O(6)
N(1)
C(2)
C(13)
C(3)
O(1)
C(14)
O(2)
Mo(1)
C(8)
O(4)
C(19)
O(5)
Fig. 1. The molecular structure of complex I. Thermal ellipsoids are drawn by 30% probability level.
The oxidoperoxido metal moieties are characterꢀ with a distorted octahedral arrangement around the
center Mo atom. In the octahedral coordination of the
complex, ONO donor set of the ligand L and one
oxido group are in the equatorial plane, and the other
oxido group and methanol molecule oxygen atom
occupying the axial positions. In the coordination
sphere about the molybdenum atom the oxido ligands
are trans respectively to the imino nitrogen atom and
the methanol oxygen atom. The selected bond lengths
and angles are listed in Table 2, which are consistent
with those observed in similar structures [22, 23]. The
Schiff base ligand coordinates to the Mo atom in a
meridional fashion forming fiveꢀ and sixꢀmembered
ized by
ν
(Mo=O) and (O–O) vibrations at 935 and
ν
887 cm–1, respectively [19, 20]. Also the IR spectrum
of the complex confirms the presence of imine bond
(C=N) mode at 1612 cm–1 [21]. In the electronic
spectrum of the complex, the lowest energy transition
band is observed at 472 nm, which is attributed to
LMCT transition as charge transfer from
the loneꢀpair of ligands’ oxygen atoms to the empty
ꢀorbital of the Mo atom. The bands centered at 280
and 346 nm are attributed to the intraꢀligand π → π
absorption of the ligand. In the 1H NMR spectrum of
the complex, the signals appearing at = 10.06 and
4.09 ppm are due to the phenolic and methanol
OH groups, respectively. The signal appearing at
pꢀorbital on
d
*
δ
chelate rings with bite angles of 72.0(1)
°
and 81.5(1) .
°
The displacement of the Mo atom from the equatorial
leastꢀsquares plane towards the axial oxido group is
0.33 Å. In the crystal structure of the complex, the
complex molecules are linked through intermolecular
δ
=
8.54 ppm is assigned to the azomethine (CH=N) proꢀ
ton of the ligand in the complex.
The molecular view of the complex is shown in
O–H⋅⋅⋅O hydrogen bonds (Table 3), to form 2D layer
Fig. 1. The structure of the complex is mononuclear, structure along the xy plane direction (Fig. 2).
Table 2. Selected bond lengths (Å) and angles (deg) for complex
Bond , Å
Mo(1)–O(1)
I
d
Bond
d, Å
1.918(2)
2.342(2)
2.218(2)
Mo(1)–O(2)
Mo(1)–O(5)
Mo(1)–O(6)
1.972(2)
1.719(2)
1.690(2)
Mo(1)–O(4)
Mo(1)–N(2)
Angle
ω
, deg
Angle
ω
, deg
O(1)Mo(1)O(2)
O(2)Mo(1)N(2)
O(5)Mo(1)N(2)
O(5)Mo(1)O(1)
O(6)Mo(1)O(1)
O(6)Mo(1)O(5)
O(6)Mo(1)O(4)
N(2)Mo(1)O(4)
149.4(1)
72.03(7)
158.5(1)
102.4(1)
98.4(1)
O(1)Mo(1)N(2)
O(1)Mo(1)O(4)
O(5)Mo(1)O(4)
O(5)Mo(1)O(2)
O(6)Mo(1)O(2)
O(6)Mo(1)N(2)
O(2)Mo(1)O(4)
81.5(1)
78.1(1)
83.3(1)
97.1(1)
98.7(1)
94.6(1)
81.1(1)
105.6(1)
171.0(1)
76.7(1)
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454
LIU et al.
Table 3. Details of the catalytic oxidation of olefins catalyzed by complex
I*
Substrate
Product
Conversion, %**
88.5
O
86.2
93.3
O
O
Cl
Cl
O
98.1
100
O
O
O
100
100
100
O
Cl
Cl
O
O
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.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 41
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2015

SYNTHESIS, STRUCTURE, AND CATALYTIC OXIDATION
Table 4. Geometric parameters of hydrogen bonds for complex
455
I*
Distance, Å
H···A
D–H···A
D–H···A
D–H
D···A
O(4)–H(4)···O(3)i
O(3)–H(3)···O(5)ii
0.93
0.82
1.82
2.741(3)
2.679(3)
171
175
1.86
i
ii
* Symmetry operation used to generate the related atoms: x, –1 + y, z; 1 + x, 1 + y, z.
(863 program, 2012AA020304). Guangdong Province
science and technology plan (no. 2010B031500034).
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4ꢀmethylphenylene, 3ꢀmethylphenylene, 2ꢀmethylpheꢀ
nylene, 4ꢀchlorophenylene, 3ꢀchlorophenylene, and
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selectivities for both aliphatic and aromatic substrates
are 100%. High epoxide yields (86–93%) are obtained
for aliphatic substrates. While for aromatic substrates,
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ACKNOWLEDGMENTS
c
Calogovic,
The major new special Ministry of Science and
Technology (no. 2011zx09102ꢀ001ꢀ31). The national
high technology research and development program
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 41
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2015