Binuclear vanadium(V) complexes of bis(aryl)adipohydrazone: Synthesis, spectroscopic studies, crystal structure and catalytic activity

Article abstract of DOI:10.1007/s11243-011-9517-8

Three new binuclear vanadium(V) complexes of bis(aryl)adipohydrazones (H₄L¹ = bis((2-hydroxynaphthalen-1-yl)methylene) adipohydrazide, H₄L² = bis(5-bromo-2-hydroxybenzylidene) adipohydrazide, and H₄L<

Full text of DOI:10.1007/s11243-011-9517-8

Transition Met Chem (2011) 36:669–677
DOI 10.1007/s11243-011-9517-8
Binuclear vanadium(V) complexes of bis(aryl)adipohydrazone:
synthesis, spectroscopic studies, crystal structure and catalytic
activity
Nasim Asghari Lalami
•
Hassan Hosseini Monfared
•
Hashem Noei Peter Mayer
•
Received: 19 May 2011 / Accepted: 7 July 2011 / Published online: 29 July 2011
Ó Springer Science+Business Media B.V. 2011
Abstract Three new binuclear vanadium(V) complexes
1
of bis(aryl)adipohydrazones (H L = bis((2-hydroxynaphth-
and chemical activities. Hydrazones exhibit physiological
and biological activities in the treatment of several diseases
such as tuberculosis [1], for the treatment of Fe overload
disease [2–4], and as inhibitors for many enzymes [5].
These properties of the hydrazones are attributed to the
formation of stable chelate complexes with transition
metals that catalyze physiological processes. Their metal
complexes have also found applications in various chemi-
cal processes like non-linear optics, sensors, and medicine
[6]. They are of interest in the field of electrochromism
where a change in the oxidation state of the metal is pos-
sible [7, 8]. Aroylhydrazone complexes, on the other hand,
seem to be a good candidate for catalytic oxidation studies
because of their stability towards oxidation. Acyl and aroyl
4
2
alen-1-yl)methylene)adipohydrazide, H L = bis(5-bromo-
4
3
-hydroxybenzylidene)adipohydrazide, and H L = bis(2-
2
4
hydroxy-3-methoxybenzylidene)adipohydrazide) were syn-
thesized by direct reaction of [VO(acac) ] with the hydrazone
2
ligands. The ligands and complexes were characterized by
FT–IR, UV–Vis, and NMR spectroscopic methods. The
1
3
crystal structures of the complexes of L and L were deter-
mined by X-ray analyses. The solid-state structure of
1
the complex of L features a 1D hydrogen-bonded chain
from N_H–O hydrogen bonding. The catalytic activities
of these complexes have been tested in the oxidation of
various hydrocarbons using H O as the terminal oxidant.
2
2
0
0
Generally, good to excellent conversions have been obtained.
hydrazones –CO–NH–N=CRR (R and R =H, alkyl, aryl)
contain trigonal N- and O-donor atoms that can coordinate
to metal ions [9, 10]. Hydrazone ligands can act as
bidentate, tridentate, or tetradentate ligands depending on
the nature of heterocyclic ring substituents attached to the
hydrazone unit. These ligands due to their facile keto–enol
tautomerization and the availability of several potential
donor sites can coordinate with metals. In the field of
hydrazone chemistry, the study of bis(aryl)hydrazone
complexes is of interest for several reasons: (1) the study
of the bis(aryl)hydrazone complexes is justified by the
presence of two hydrazone coordinating units in ditopic
ligands, which may yield supramolecular architectures or
coordination polymers [11], (2) the coordination of a metal
ion by one unit may induce changes in the coordinative
properties of the other unit, and (3) binuclear complexes
of these ligands are suitable for weak spin–spin exchange
interactions studies [12].
Introduction
Hydrazones, especially acyl and aroyl hydrazones, are a
multipurpose class of ligands having a range of biological
Electronic supplementary material The online version of this
article (doi:10.1007/s11243-011-9517-8) contains supplementary
material, which is available to authorized users.
N. Asghari Lalami ꢀ H. Hosseini Monfared (&) ꢀ H. Noei
Department of Chemistry, Zanjan University, 45195-313 Zanjan,
Islamic Republic of Iran
e-mail: monfared@znu.ac.ir; monfared_2@yahoo.com
URL: http://www.znu.ac.ir/members/hosseini_hassan
P. Mayer
Fakult a¨ t f u¨ r Chemie und Pharmazie, Ludwig-Maximilians-
Universit a¨ t, M u¨ nchen, Butenandtstr. 5-13, Haus D,
2?
The coordination chemistry of vanadium containing VO
3?
or VO moieties has received considerable attention probably
duetotheirassociationinmanyvanadium-dependentenzymes,
8
1377 M u¨ nchen, Germany
123

6
70
Transition Met Chem (2011) 36:669–677
such as nitrogenases [13], haloperoxidases [14], phosp-
homutases [15], and nitrate reductases [16]. Functional
model compounds have been developed by studies in
structures, chemical, and medical properties of these
vanadium enzymes [13, 17]. Hydrazides and hydrazones
have interesting ligation properties due to the presence of
several coordination sites, and these ligands have a ten-
dency to stabilize the vanadium in its highest oxidation
state [18, 19]. Vanadium compounds have been widely
used as catalysts in peroxidic as well as dioxygenic
oxidation of hydrocarbons [20, 21], but so far yields
and turnover number obtained are not very remarkable
Results and discussion
The bis(aryl)adipohydrazone ligands (H L , H L , and
1
2
4
4
3
H L ) were synthesized in high yield and excellent purity
4
by condensation reaction of adipohydrazide with 2 equiv-
alents of the corresponding arylaldehydes (2-hydrox-
ynaphthaldehyde, bromosalicylaldehyde, and 3-methoxy
1
-3
salicylaldehyde). Ligands H4L
react with [VO(acac)2]
to give binuclear metal complexes of formulae [{VO(CH OH)-
3
1
(OCH )} L ] (1), [{VO(CH OH)(OCH )} L ] (2) and [{VO-
2
3
2
3
3 2
3
(CH OH)(OCH )} L ]ꢀ2CH OH (3) (Scheme 1).
3
3
2
3
[
22].
Because of the importance of vanadium complexes, and
Spectroscopic characterization
as a part of our search in the study of coordinating capa-
bilities of aroyl hydrazones and their coordination com-
pounds, we are extending our research on the efficacious
compounds of binuclear vanadium. Here, we report the
synthesis, characterization, and catalytic activity (as mod-
A list of IR spectral data is presented in Table 1. A com-
parison of the spectra of the complexes with the ligands
provides evidence for the coordination mode of the ligands
in the complexes. The non-observation of the m(C=O)
-
1
bands, present in the ligands at 1,658–1,668 cm , indi-
cates the enolization of the amide functionality upon
eling the haloperoxidase activity) of binuclear oxovana-
1
dium(V) complexes of bis(aryl)hydrazone ligands H L ,
V
coordination to the V -center. Instead, strong bands at ca.
4
2
H L , and H L derived from 2-hydroxynaphtaldehyde/
3
-1
1,602–1,617 cm are observed, which can be attributed
4
4
adipichydrazide, 3-bromosalicylaldehyde/adipichydrazide,
and 3-methoxysalicylaldehyde/adipichydrazide, respectively
to the asymmetric stretching vibration of the conjugated
CH=N–N=C group [23], characteristic of the coordination
of the enolate form of the ligands.
(
Scheme 1). The crystal structures of two of these vanadium
complexes were also determined.
On complexation, the absence of N–H band and red-
shifts in azomethine (–C=N–) band of the ligands show
1
-3
coordination of H4L
as tetraianionic ligands in enol
form through the deprotonated hydroxyl group (Ophenolate),
azomethine nitrogen (Nazomethine), and enol oxygen groups
(
OO–C(naphthyl)=N) in the complexes 1, 2, 3 (Table 1). A
H
V
CH
3
-1
strong C=N stretch (around 1,610 cm ) indicates the C=N
O
H
3
CO
O
group of the coordinated Schiff base ligands [24]. The
-
strong m(VO) band around 990 cm
identified for all the complexes.
O
1
O
N
could be clearly
N
N
N
O
1
2
H L , H L , and H L were soluble in polar and com-
3
O
4
4
4
V
O
mon organic solvents like methanol and formed green,
white-cream, and cream solutions, respectively. These
solutions have been used to record the electronic spectra.
OCH
3
O
3
H C
H
1
[
{VO(CH
3
OH)(OCH
3
)}
2
L ], 1
Table 1 IR spectral data of the ligands and the vanadium complexes
H
CH
3
O
-1
Selected IR bands (cm )
X
3
H CO
V
O
a
O
Compound m(C=N) ? d(NH) m(C=O) m(NH) m(OH) m(V=O)
O
Y
N
N
1
4
H L
4
H L
4
H L
1,624, 1,599
1,617, 1,544
1,631, 1,579
m(C=N–N=C)
1,602
1,658
1,677
1,668
3,196 3,463
3,275 3,431
3,215 3,454
N
N
Y
O
2
3
O
V
O
OCH
3
X
O
H
3
C
H
1
2
3
a
994
983
999
2
[
[
{VO(CH
{VO(CH
3
3
OH)(OCH
OH)(OCH
3
3
)}
)}
2
L ], 2
:X=H,
OH, 3 :X=OCH
Y=Br
, Y=H
1,617
3
2
L ].2CH
3
3
1,610
Scheme 1 The synthesized hexadentate adipichydrazone-vanadium(V)
complexes
The bands assigned to m(C=N) (azomethine) may not be pure, as
they may be associated with the aromatic (C=C) stretching bands
1
23

Transition Met Chem (2011) 36:669–677
671
1
Table 2 H NMR of ligands
H L –H L
4 4
1
3
Compound
Solvent
–CO–CH
2
–CH=N–
NH
–OH
1
H
4
L
L
(CD
(CD
(CD
(CD
(CD
(CD
(CD
3
)
3
)
3
)
3
)
3
)
3
)
3
)
2
2
2
2
2
2
2
SO
2.30, 2.65
2.30, 2.63
1.73, 2.05
2.22, 2.60
2.45
8.90, 9.15
8.87, 9.10
9.60
11.23, 11.66
12.63
1
H
4
SO ? D
SO
2
O
–
–
–
Complex 1
–
2
H
4
H
4
H
4
H
4
L
L
L
L
SO
8.10, 8.20
8.31
10.26, 11.10
11.17, 11.58
2
3
3
SO ? D
SO
2
O
O
–
–
2.22, 2.58
2.20, 2.55
8.20, 8.30
8.30, 8.25
9.48, 10.86
–
11.15, 11.50
–
SO ? D
2
The hydrazone ligands showed three bands in the range
00–800 nm (Fig. S1). Based on their extinction coeffi-
cients and energies, these are assigned to p ? p*
227–237 nm bands), p ? p* and n ? p* (282–320 nm
form through phenolate oxygen (Ophenolate) and enol oxy-
gen atoms (OO–C(naphthyl)=N) to V(V).
2
1
X-ray structures of [{VO(CH OH)(OCH )} L ] (1)
(
3
3
2
3
bands), and n ? p* (331–370 nm) transitions. The dark
brown complexes 1–3 were not soluble in polar or non-
polar solvents; therefore, their UV–Vis spectra could not be
recorded in solution.
and [{VO(CH OH)(OCH )} L ]ꢀ2CH OH(3 )
3
3
2
3
The molecular structures and labeling of the atoms for
complexes 1 and 3 are displayed in Figs. 1 and 2, and
selected bond lengths and angles are given in Table 3. There
are two non-coordinated methanol molecules present in 3.
Since structural analyses show that compounds 1 and 3 are
both binuclear vanadium compounds and contain the similar
building unit [{VO(CH OH)(OCH )} L], compound 1 is
1
H NMR data of the ligands and the complex 1 are given
in Sect. 2 and Table 2. On the basis of intensity, chemical
shift values, and deutration experiments, we assigned the
signals. In all the three ligands, two groups of methylene
next to carbonyl, azomethine, and NH are not equivalent
and gave different signals (Table 2). Aromatic protons of
the ligands appear well within the expected range
3
3
2
selected to represent their structures. Compounds 1 and 3 are
binuclear centrosymmetric compounds. The two dianionic,
tridentate domains of the ligand adopt a trans configuration,
and each coordinates a V(V) ion forming a dimetal complex.
In 1, vanadium adopts a distorted octahedral coordination
geometry with two oxygen atoms and one nitrogen atom (O1,
O2, and N2) from L ligand with an oxygen atom (O5) of
methoxylate occupying anequatorialpositionand twooxygen
atoms occupying two axial positions, where one oxygen (O3)
is terminal and the other (O4) is from methanol. The axial
(
6.55–7.70 ppm). The azomethine group –CH=N that is
1
-3
formed in the condensation reaction in H4L
showed
singlet signals in the range 8.10–9.15 ppm. The NH and
2
3
OH groups of the ligands H L and H L have signals
4
4
6
about 9.48–11.10 and 11.15–11.58 ppm (in DMSO-d ),
respectively. These signals disappear in the presence of
D O. The chemical shifts for NH (11.23, 11.66) and OH
2
1
12.63) groups of H L are higher than the corresponding
(
4
2
groups in H L and H L . While complexes 2 and 3 were
3
˚
V=O bond distance of the terminal oxygen 1.586(3) A in 1 is
4
4
˚
0.17 A shorter than those of the equatorial oxygen atoms
not soluble in DMSO, D O, and CDCl , complex 1 was
2
3
˚
(1.756(3)–1.957(3) A), while the other axial V–O bond
˚
(2.304(3) A) is significantly longer than the equatorial V–O
slightly soluble in DMSO. The absence of NH and OH
1
signals in the H NMR spectrum of 1 confirmed the
1 4-
coordination of the tetra-deprotonated ligand (L ) in enol
bonds due to the trans effect of V=O bond. The V=O distance
Fig. 1 Thermal ellipsoid
plot (50% probability)
of the repeat unit in
[
1
L ]
{VO(CH
3
OH)(OCH
)}
3 2
(1); bond lengths and angles are
provided in Table 3; symmetry
transformations A = 2-x, -y,
-z. Only one of two symmetry-
independent halves of
molecules is shown in the
figure. Non-labeled non-
hydrogen atoms are generated
by symmetry operation A
123

6
72
Transition Met Chem (2011) 36:669–677
Fig. 2 Thermal ellipsoid plot
50% probability) of the repeat
unit in [{VO(CH OH)-
OH (3),
(
3
3
(
OCH
3
)}
2
L ]ꢀ2CH
3
bond lengths and angles are
given in Table 3; symmetry
transformations A = -x, 1-y,
-
z. Non-labeled non-hydrogen
atoms are generated by
symmetry operation A
˚
Table 3 Selected bond distances (A) and angels (deg) for complexes
and 3
1
Complex 1
Complex 3
V1–O1
1.957(3)
1.862(3)
V1–O1
1.9,786(19)
1.8523(18)
1.596(2)
1.776(2)
2.116(2)
2.295(2)
151.60(9)
98.48(10)
93.83(9)
78.06(8)
74.20(9)
99.89(10)
103.73(9)
81.70(8)
83.96(9)
91.09(10)
100.79(11)
174.23(9)
164.36(9)
84.14(8)
83.54(8)
V1–O2
V1–O2
V1–O3
1.586(2)
V1–O4
V1–O4
2.304(3)
V1–O5
V1–O5
1.756(3)
V1–N2
V1–N2
2.102(3)
V1–O6
O1–V1–O2
O1–V1–O3
O1–V1–O4
O1–V1–O5
O1–V1– N2
O2–V1–O3
O2–V1–O4
O2–V1–N2
O2–V1–O5
O3–V1–O4
O3–V1–N2
O3–V1–O5
O4–V1–N2
O4–V1–O5
O5–V1–N2
151.76(12)
98.41(13)
80.19(10)
95.62(12)
74.54(12)
99.44(14)
81.06(11)
82.08(12)
101.92(12)
177.44(14)
95.61(14)
101.78(13)
81.95(11)
80.55(11)
161.18(13)
O1–V1–O2
O1–V1–O4
O1–V1–O5
O1–V1–O6
O1–V1–N2
O2–V1–O4
O2–V1–O5
O2–V1–O6
O2–V1–N2
O4–V1–N2
O4–V1–O5
O4–V1–O6
O5–V1–N2
O5–V1–O6
O6–V1–N2
Fig. 3 Infinite supramolecular chains along [100] in 1 established by
hydrogen bonds of the typeN_H–O
vanadium atom is displaced toward the terminal oxygen atom
˚
O3 by 0.30 A in complex 1. C1, C2, and the atoms of the
naphthyl units are almost coplanar with the mean deviation
˚
from the plane 0.144–0.163 A. The coordinating atom plane
(
O1/N2/O2/O5) makes a dihedral angle of 16.65° with the
naphthyl plane.
The binuclear entities of 1 form a supramolecular 1D
chain as a result of two hydrogen bonds of the type N_H–O
(
Fig. 3, Table 4). In 3, each dinuclear complex is linked to
four adjacent complexes through hydrogen bonds involving
either methanol atoms (Fig. 3).
˚
˚
in complex 1 (1.586 A) and 3 (1.5,957 A) are close to another
reported complex [25]. The larger V–O4 bond distance indi-
cates a markedly weaker coordination of the axial methanol
molecule. The L anion bridges two vanadium ions. The
deprotonated bis(aryl)adipohydrazone ligand forms an equa-
torial plane (O1, N2, O2, O5 for molecule 1) through the
naphtholate oxygen atom O2, imine nitrogen atom N2, and
enolate oxygen atom O1 together with the oxygen atom O5
from the methoxylate ligand. Relative to this plane, the
Catalytic reactivity
The catalytic oxidation of cyclooctene as a representative
substrate with hydrogen peroxide was studied in the pres-
ence of complexes 1, 2, and 3. The results of control
experiments revealed that the presence of catalyst and
1
23

Transition Met Chem (2011) 36:669–677
673
Table 4 Hydrogen bonding interaction in 1 and 3
D–H_A ( A˚ )
˚
D–H (A)
H_A ( A˚ )
D_A ( A˚ )
D–H_A (deg)
Complex
1
1
O4–H4_N1
0.90(2)
0.84(3)
0.96
1.87(2)
1.90(3)
1.79
2.761(4)
2.726(4)
2.723(3)
2.782(3)
168(3)
166(3)
163.4
177.1
2
O10–H10_N3
3
3
O6–H6_O7
O7–H7_N1
0.91
1.87
D Donor, A acceptor
SD are given in parentheses
1
2
Symmetry transformation: 1-x, -y, -z; 1-x, -y, 1-z; x, 1/2-y, -1/2 ? z
3
Table 5 Catalytic epoxidation of cyclooctene with H
O
2 2
in CH
3
CN
2 2
Table 6 Catalytic epoxidation of cyclooctene with 3/H O
a
Entry
Catalyst
Yield (%)
Time (h)
Entry
H
2
O
2
Solvent Temp.
(°C)
Yield
a
(%)
Time
(h)
(
mmol)
b
1
2
3
1
2
3
22 (53)
1 (5)
1 (5)
1 (3)
b
1
2
3
4
5
6
7
1
2
3
3
3
3
3
CH CN 80
3
3 (43)
44 (75)
58 (97)
0 (30)
0 (0)
1 (5)
1 (5)
1 (3)
1 (5)
1 (5)
1 (5)
1 (5)
33 (62)
b
CH CN 80
3
58 (97)
CH
CH
3
CN 80
OH 80
Reaction conditions: catalyst, 1.3 lmol; cyclooctene, 1 mmol; inter-
nal standard (chlorobenzene), 0.1 g; CH CN, 3 mL; H O2, 3 mmol;
3 2
3
and reaction temperature, 80 °C
CHCl
3
80
80
a
Yields are based on the starting cyclooctene
CH
CH
2
Cl
2
0 (0)
b
The number in the bracket refer to the yield after the second time
3
CN 60
40 (88)
Reaction conditions: catalyst (3), 1.3 lmol; cyclooctene, 1 mmol;
internal standard (chlorobenzene), 0.1 g; and solvent, 3 mL
oxidant (H O ) is essential for the oxidation. Results of the
2
2
a
Yields are based on the starting cyclooctene
studies are summarized in Table 5. Cyclooctene was con-
verted to the corresponding epoxide with 100% selectivity
by all three complexes. The catalyst 3 showed the highest
activity (yield 97% after 3 h), followed by 2 (yield 62%
after 5 h), and the catalyst 1 showed the least reactivity.
Other parameters for suitable reaction conditions to
achieve the maximum oxidation of cyclooctene such as
the oxidant concentration (moles of oxidant per moles of
cyclooctene), solvent, and temperature of the reaction were
investigated. The effect of oxidant concentration on the
oxidation of cyclooctene by 3 is illustrated in Table 6,
entries 1–3. Different oxidant/cyclooctene molar ratios
were used as solvents. Of the various solvents examined,
acetonitrile was found to be the most suitable solvent for the
reaction. The highest conversion of 97% was obtained in
acetonitrile after 3 h. It was observed that the catalytic
activity of the catalyst 3 decreased with respect to acetoni-
trile (relative dielectric constant e/e =36, donor number
0
DN = 14.1 [27]) [ methanol (e/e = 32.6, DN = 20) [
0
chloroform (e/e = 4.8) & dichloromethane. Overall, the
0
reactivity of catalyst 3 in other solvents was very much lower
than acetonitrile (Table 6, entries 3–6). From Table 6, one
could see that solvents with moderate donation ability and
high polarities seemed to favor this reaction. Solvents with
high coordinating property such as methanol (DN = 20)
inhibited this reaction.
(
1:1, 2:1, and 3:1) were considered while the ratio of
cyclooctene (1.0 mmol) to catalyst (1.3 lmol) in 3 mL
of acetonitrile at 80 ± 1 °C was constant. The conversion
of cyclooctene increased with increasing the amount of
hydrogen peroxide in the reaction mixture. When H O /
The cyclooctene yield decreased when the reaction was
carried out at lower temperature, 60 °C. With 3 as catalyst,
a yield of 88% was obtained after 5 h at 60 °C (Table 6,
entry 7), which was lower than the yield 97% at 80 °C.
The catalytic activities of 1–3 were examined in the
oxidation of some hydrocarbons in optimized conditions
(Table 6) that were proved to be the best for cyclooctene
oxidation, and the results are summarized in Tables 7 and
8. Cyclooctene was converted to the corresponding epoxide
with 100% selectivity with catalyst 1–3. But in oxidation of
cyclohexene by 3 in addition to cyclohexene oxide (yield
2
2
substrate mole ratio was 3, the maximum conversion of
7% was obtained, showing that about 2 equivalents of the
9
oxidant are decomposed in the non-productive way. This
is, however, much less than the decomposition of hydrogen
peroxide by bare transition metals [26]. Aqueous hydrogen
peroxide was selected by considering its high selectivity,
atom economy, and environmentally benign properties.
Table 6 also illustrates the influence of the solvent
nature in the catalytic oxidation of cyclooctene by 3.
Methanol, dichloromethane, acetonitrile, and chloroform
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74
Transition Met Chem (2011) 36:669–677
Table 7 Oxidation of various
hydrocarbons with
a
a
b
Entry
1
Substrate
Product(s)
Yield (%)
97
Selectivity (%)
100
Conv. (%)
time/h)
TON
373
(
[
3
{VO(CH OH)-
3
(OCH
using H
3
)}
2
L ]ꢀ2CH
3
OH (3)
97 (3)
O
2 2
and acetonitrile
o
2
21
53
22
55
96 (3)
369
O
OH
O
22
60
41
18
23
Reaction conditions: catalyst,
.3 lmol; substrate, 1 mmol;
chlorobenzene, 0.1 g;
acetonitrile, 3 mL; H
1
3
4
5
CH2OH
CHO
100
100
100
60 (5)
41 (4)
18 (5)
231
158
69
2 2,
O
3
8
a
mmol; and temperature,
0 ± 1 °C
Yields and conversions are
O
based on the starting substrate
and determined by GC
b
CHO
TON turnover
number = number of moles of
product formed per mole of V in
the catalyst
1
00% selectivity and in reasonable yield. Electron-rich
Table 8 Comparison of catalytic activities of catalysts 1–3 in the
oxidation of various hydrocarbons with hydrogen peroxide
alkenes (cyclohexene and cyclooctene) displayed a greater
activity than aromatic compounds (benzylalcohol, toluene,
and ethylbenzene).
-1 a
)
TOF (h
Substrate
Catalyst 1
Catalyst 2
Catalyst 3
Catalytic activities of three catalysts 1–3 in the oxida-
tion of various hydrocarbons are compared in Table 8.
Catalyst 3 is more efficient than 1 and 2. In addition to
solubility differences between the catalysts, there are some
electronic and steric differences in the corresponding
ligands of the complexes. One could conclude that the
Cyclooctene
Cyclohexene
Benzylalcohol
Ethyl benzene
Toluene
74
63
31
12
0
54
91
33
0
124
123
46
40
0
14
presence of electron donor OCH group on the phenolate
3
For reaction conditions, see Table 6; in the oxidations with catalysts
and 2, NaHCO (0.25 mmol) was used as a co-catalyst to obtain
maximum conversion
3
unit of L improves the catalytic activity of 3 relative to 1
and 2. The presence of electron withdrawing groups (aryl
1
3
1
2
a
in 1 and Br in 2) on the phenolate unit of L and L makes
catalysts 1 and 2 less reactive than 3. These findings are in
contrast to our previous studies with mononuclear V(V)=O
complexes that proved there was no significant difference
in activities between similar structure catalysts [29, 30].
Conclusive interpretation of this subject needs further
studies in the future.
TOF turnover frequency = the catalytic turnover per unit time
2
1%), also two other products were formed, namely 2-
cyclohexene-1-ol (yield 53%) and 2-cyclohexene-1-one
yield 22%). Cyclohexene is more prone to both epoxida-
(
tion and allylic oxidation [28]. Allylic oxidation has been
reported in the metalloporphyrin systems [31] in the oxi-
dation of alkenes such as cyclohexene and reflects the
radical nature of the active oxidizing species.
The exact mechanism of the reaction is not fully clear.
However, on the basis of the oxidation products of the
various hydrocarbons (Table 8), it is predicted that the
oxidation reactions proceed by intermediacy of a perox-
ovanadium-hydrazone Schiff base species formed in the
reaction mixture in the presence of hydrogen peroxide
[29].
Catalysts 1–3 were also tested in oxidation of benzyl-
alcohol and aromatic compounds (ethylbenzene and tolu-
ene). Complex 3 showed the potential to oxidize the side
chain of the unreactive aromatic toluene and ethyl benzene
to benzaldehyde and acetophenone, respectively, with
1
23

Transition Met Chem (2011) 36:669–677
675
-
1
Conclusion
(KBr, cm ): 3,463 (w, O–H), 3,196 (m, N–H), 3,049 (m),
,947 (m), 1,658 (vs, C=O), 1,624 (s, C=N), 1,599 (w),
2
Three new binuclear vanadium(V) complexes of bis(aryl)
adipohydrazones were synthesized and characterized by
spectroscopic methods. The crystal structures of two of the
complexes were determined by X-ray analyses. The presence
of two hydrazone coordinating units in ditopic ligands yields
1,575 (w), 1,555 (w), 1,469 (s), 1,418 (w0, 1,395 (w), 1,321
1
(w), 1,284 (w), 1,243 (m), 1,144 (m), 819 (w), 748 (m). H
6
NMR (250.13 MHz, DMSO-d , ppm): 1.00 (m, 2H, CH ),
2
1.68 (m, 2H, CH ), 2.30 (m, 2H, CO–CH ), 2.65 (m, 2H,
2
2
CO–CH ), 7.15–8.35 (m, 12H, aryl), 8.90 (s, 1H, CH=N),
2
1
D supramolecular architecture in the complex 1. The cata-
lytic activities of these complexes have been explored in the
oxidation of various hydrocarbons using H O as the terminal
9.15 (s, 1H, CH=N), 11.23 (s, 1H, amid N–H), 11.66 (s,
1H, N–H), 12.63 (s, 2H, O–H). UV–Vis spectrum in
3
-1
-1
CH OH [k
(e, dm mol cm )]: 237 (151,600), 257
(97,400), 312 (48,200), 323 (61,700), 371 nm (47,000).
2
2
3
max
oxidant. Generally, good to excellent conversions have been
obtained.
1
6
N’ E,N’ E)–N’ ,N’ -bis(5-bromo-2-
1
6
(
2
hydroxybenzylidene)adipohydrazide (H L )
4
Experimental
Yield: 92%. Anal. Calc. for C H Br N O (MW 540.21):
2 4 4
2
0
20
2
-hydroxynaphthaldehyde, 3-bromosalicylaldehyde, 3-meth-
C, 44.5; H, 3.7; N, 10.4. Found: C, 44.4; H, 3.8; N, 10.4. IR
-
oxysalicylaldehyde, adipichydrazide, bis(acetylacetonato)oxo-
1
(
KBr, cm ): 3,431 (m, br, O–H), 3,275 (m, N–H), 3,069
w), 2,958 (w), 1,677 (vs, C=O), 1,617 (s, C=N), 1,544 (m),
vanadium(IV), [VO(acac) ], and other materials with high
2
(
purity were purchased from Merck and Fluka and used as
received. IR spectra were recorded as KBr disks with a Matson
1
,478 (vs), 1,350 (m), 1,276 (vs), 1,193 (s), 1,141 (w), 979
1
w), 700(m), 628 (w). H NMR (250.13 MHz, DMSO-d ,
6
(
1000 FT–IR spectrophotometer in the range of 4,000–450
ppm): 1.59 (m, 4H, CH ), 2.22 (m, 2H, CO–CH ), 2.60
2
-1
2
cm . UV–Vis spectra in solution were recorded on a Shima-
(m, 2H, CO–CH ), 6.55–7.70 (m, 6H, aryl), 8.10 (s, 1H,
2
1
13
6
dzu 160 spectrometer. H and C NMR spectra in DMSO-d
solution were recorded on a Bruker 250.13 MHz spectrometer,
and chemical shifts are indicated in ppm relative to tetrameth-
ylsilane. The reaction products of oxidation were determined
and analyzed by HP Agilent 6890 gas chromatograph equipped
with a HP-5 capillary column (phenyl methyl siloxane
CH=N), 8.20 (s, 1H, CH=N), 10.26 (s, 1H, amid NH),
1
1
1.10 (s, 1H, amid NH), 11.17 (s, 1H, aryl–OH), 11.58 (s,
1
H, aryl–OH). C NMR (62.90 MHz, DMSO-d , ppm)
3
6
(ismer I ? isomer II): ? 25.04 (–CH –), 34.19 ? 34.22
2
(
CH CO–), 110.79 ? 110.81, 118.80 ? 119.02, 121.63 ?
2
1
23.08, 130.93 ? 133.76, 138.88, 144.40 (–CH=N–),
55.88 ? 156.71, 168.94 (–CO–). UV–Vis spectrum in
30 m 9 320 lm 9 0.25 lm). The elemental analyses (car-
1
bon, hydrogen, and nitrogen) were obtained with a Carlo ERBA
Model EA 1108 analyzer. Vanadium percentages of complexes
were measured by a Varian spectrometer AAS-110.
3
-1
-1
CH OH [k
(e, dm mol cm )]: 227 (44,000), 282
3
max
(49,300), 334 nm (22,500).
1
N’ E,N’ E)–N’ ,N’ -bis(2-hydroxy-3-
6
1
6
(
1-3
Synthesis of H4L
3
methoxybenzylidene)adipohydrazide (H L )
4
1
-3
All the three hydrazone ligands (H4L ) were synthesized
by the same general method. To a methanol solution
Yield: 91%. Anal. Calc. for C H N O (MW 442.47): C,
22 26 4 6
5
9.7; H, 5.9; N, 12.7. Found: C, 59.7; H, 5.9; N, 12.7. IR
(
15 mL) of adipichydrazide (0.5 mmol), the appropriate
-
KBr, cm ): 3,454 (s, O–H), 3,215 (m, N–H), 3,083 (w),
1
(
aldehyde (2-hydroxy naphthaldehyde, 5-bromo-2-hydro-
xybenzaldehyde or 2-hydroxy-3-methoxybenzaldehyde)
2,943 (m), 2,863 (w), 1,668 (vs, C=O), 1,631 (m), 1,579
(
(
w), 1,471 (m), 1,412 (m), 1,254 (vs, phenolic O–H), 1,153
1
w), 1,081 (m), 973 (w), 777 (w), 731 (m), 563 (w). H
(
1.0 mmol) was added and the mixture refluxed for 5 h.
The resulting precipitate was filtered off, washed with
methanol, and dried in air. NMR data show that each ligand
is probably in two forms or is composed of two isomers
6
NMR (250.13 MHz, DMSO-d , ppm): 1.60 (m, 4H, CH ),
2
2
6
8
.22 (m, 2H, –CO–CH ), 2.58 (m, 2H, CO–CH ), 3.70 (s,
2 2
H, OCH ), 6.80–7.2 (m, 6 H, aryl), 8.20 (s, 1H, CH=N),
3
(
isomer I ? isomer II).
.30 (s, 1H, CH=N), 9.48 (s, 1 H, N–H), 10.86 (s, 1H, N–
1
3
H), 11.15 (s, 1H, O–H), 11.50 (s, 1H, O–H). C NMR
6
(62.90 MHz, DMSO-d , ppm) (ismer I ? isomer II):
1
6
1
N’ E,N’ E)-N’ ,N’ -bis((2-hydroxynaphthalen-1-
6
(
1
yl)methylene)adipohydrazide (H L )
25.03 ? 25.10 (–CH –), 32.15 ? 34.16 (CH CO–), 56.21
2
4
2
(CH ), 113.27 ? 114.11, 118.67 ? 119.15, 119.48 ? 119.52,
3
Yield: 95%. Anal. Calc. for C H N O (MW 482.53): C,
28 26 4 4
146.32 (–CH=N–), 147.01, 147.36, 148.26 ? 148. 36,
174.38 ? 168.99 (–CO–).
6
9.7; H, 5.4; N, 11.6. Found: C, 69.8; H, 5.5; N, 11.6. IR
123

6
76
Transition Met Chem (2011) 36:669–677
3
-1
UV–Vis spectrum in CH OH [k
(e, dm mol
2,937 (m), 2,841 (w), 1,610 (vs, C=N–N=C), 1,564 (vs),
1,470 (m), 1,438 (s), 1,353 (m), 1,259 (vs), 1,226 (m),
1,108 (m), 1,088 (m), 999 (s), 963 (s), 876 (m), 786 (s) 741
3
max
-
1
cm )]: 205 (30,800), 230 (29,800), 290 (37,100), 331 nm
11,400).
(
(vs), 620 (m), 472 (w).
1-3
Synthesis of [{VO(CH OH)(OCH )} L ] (1–3)
3
3
2
X-ray structure determination
These complexes were synthesized by the same general
1
method as follows: the appropriate ligand (H L , H L , or
2
Single crystals of 1 and 3 were carefully selected under
a polarizing microscope. Dark brown crystals of 1
(0.12 mm 9 0.06 mm 9 0.05 mm) and 3 (0.20 mm 9
0.17 mm 9 0.10 mm) were investigated in diffraction
experiments at 173 (2) K on an Oxford XCalibur diffrac-
tometer with monochromated Mo–Ka radiation (k =
4
4
3
H L ) (0.27 mmol) was dissolved in methanol (10 mL),
4
[
VO(acac) ] (0.54 mmol) was added, and the solution was
2
gently refluxed for 4 h. After cooling, the resulting solid
was filtered off, washed with methanol, and dried in air.
For the preparation of suitable single crystals for X-ray
1
3
˚
analysis, the appropriate ligand (H L or H L ) (0.027
4
0.71073 A). Crystallographic data and data collection
4
mmol) and VO(acac) (0.054 mmol) were placed in the
2
parameters are given in Table 9. The structures were
main arm of a branched tube (‘branched tube’ method). A
mixture of methanol and acetonitrile (15:85 v/v, 15 mL)
was carefully added to fill the arms, the tube was sealed,
and reagents containing arm immersed in an oil bath at
Table 9 Crystal data and structure refinement for [{VO(CH
3
3
OH)-
1
L ] (1) and [{VO(CH
(OCH
3
)}
2
3
OH)(OCH
3
)}
2
L ]ꢀ2CH
3
OH (3)
Complex
1
3
6
0 °C while the other arm was kept at ambient tempera-
Net formula
C
32
H
36
N
4 10
O V
2
28 44 4 14 2
C H N O V
ture. After week, dark brown crystals that were suitable for
X-ray analysis were deposited in the cooler arm, which
were filtered off, washed with methanol, and dried in air.
-1
r
M /g mol
738.532
Triclinic
P1 bar
762.551
Monoclinic
P2 /c
Crystal system
Space group
1
1
{VO(CH OH)(OCH )} L ] (1)
˚
a/A
9.5393(7)
10.6862(6)
13.6334(7)
9.2255(4)
13.4991(7)
90
[
3
3
2
˚
b/A
˚
c/A
Yield: 72%. Anal. Calc. for C H N O V (MW 738.53):
32 36 4 10 2
17.3371(11)
79.098(5)
85.175(5)
68.961(6)
1,619.48(18)
2
C, 52.0; H, 4.9; N, 7.6; V, 13.8. Found: C, 51.9; H, 4.9; N,
a/°
b/°
c/°
-
1
7
2
1
.6; V, 14.0. IR (KBr, cm ): 3,466 (m, O–H), 3,073 (w),
,957 (m), 2,810 (w), 1,602 (vs, C=N–N=C), 1,557(s),
,451 (m), 1,391 (m), 1,332 (s), 1,303 (s), 1,200 (s), 1,148
101.249(5)
90
3
˚
V/A
1,665.23(14)
2
(
(
m), 1,048 (s), 994 (s, V=O), 832 (m), 756 (m), 631 (s), 596
6
Z
1
-3
m), 520 (w). H NMR (250.13 MHz, DMSO-d , ppm):
.41 (m, 2H, CH ), 1.73 (m, 4H, CH and CH –CO), 2.05
Calc. density/g cm
-
l/mm
1.51453(17)
0.641
1.52083(13)
0.634
1
1
2
2
2
(
m, 2H, CO–CH ), 3.15 (s, 12 H, methoxy), 7.08–8.42 (m,
2
Absorption correction
Transmission factor range
Refls. measured
Rint
‘Multi-scan’
‘Multi-scan’
1
2H, aryl), 9.60 (s, 2 H, CH=N).
0.99240–1.00000 0.97681–1.00000
11537
0.0759
0.2708
4.14–25.24
2,257
0, 0
7,063
2
{VO(CH OH)(OCH )} L ] (2)
[
3
3
2
0.0415
0.0787
4.29–26.32
2,227
Mean r(I)/I
Yield: 74%. Anal. Calc. for C H Br N O V (MW
10
2
4
30
2
4
2
h range
7
3
3
96.21): C, 36.2; H, 3.8; N, 7.0; V, 12.8. Found: C, 36.2; H,
-
Observed refls.
x, y (weighting scheme)
Hydrogen refinement
Refls in refinement
Parameters
1
.8; N, 7.1; V, 12.5. IR (KBr, cm ): 3,443 (s, vbr, O–H),
,091 (w), 2,944 (m), 2,868 (w), 2,811 (w), 1,617 (vs,
0.0549, 0
Constr.
3,388
Mixed
5,834
443
C=N–N=C), 1,547 (vs), 1,461 (s), 1,415 (m), 1,377 (m),
1
1
,352 (m), 1,279 (s), 1,197 (m), 1,140 (w), 1,056 (m),
,007 (m), 983 (m), 921 (w), 826 (s), 786 (w), 711 (m), 668
221
Restraints
2
0
(
m), 629 (m), 574 (m), 475 (m).
R(Fobs
)
0.0487
0.0560
0.652
0.001
0.398
-0.364
0.0457
0.1134
0.938
2
(F )
R
w
3
[
{VO(CH OH)(OCH )} L ]ꢀ2CH OH (3)
3
3
2
3
S
Shift/errormax
0.001
Yield: 73%. Anal. Calc. for C H N O V (MW 762.55):
2
8
44
4
12
2
-3
˚
Max electron density/e A
0.894
C, 44.1; H, 5.8; N, 7.4; V, 13.4. Found: C, 44.2; H, 5.9; N,
-3
˚
Min electron density/e A
-0.564
-
.3; V, 13.5. IR (KBr, cm ): 3,457 (s,vbr), 3,071 (w),
1
7
1
23

Transition Met Chem (2011) 36:669–677
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Acknowledgments The authors are grateful to the Zanjan Univer-
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Maximilians-Universit a¨ t M u¨ nchen, and the School of Chemistry for
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3
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