Syntheses, structures, and catalytic activity of copper(II)-aroylhydrazone complexes

Article abstract of DOI:10.1002/zaac.201200395

Two Cu^II complexes of tridentate Schiff base ligands, [Cu(L ¹)(CH₃OH)₂]NO₃·CH ₃OH (1) and [Cu₂(L²)₂(CH ₃OH)₂](NO₃)₂ (2), were prepared and characterized by elemental analyses and spectroscopic methods [H ₂L¹ = (E)-N-(4-hydroxy benzoic acid (2-hydroxy-3- methoxybenzylidene)benzohydrazide, and H₂L² = (E)-N-4-hydroxy benzoic acid (5-bromo-2-hydroxybenzylidene)benzohydrazide]. The crystal structures of 1 and 2 were established by X-ray crystallography. The complex cation in 1 is based on a square pyramid with the uninegative Schiff base coordinating in a tridentate mode via O, N, O′-donor atoms with the remaining sites being occupied by two methanol oxygen atoms with one of these in the axial position. By contrast, the Schiff base coordinates in a tridentate ligand fashion in dinuclear compound 2 as the phenoxide oxygen atom bridges two central copper atoms. The NO₄ coordination donor set is completed by a methanol oxygen atom, which occupies an axial position in the distorted square pyramidal arrangement. Complexes 1 and 2 are very active catalysts in clean epoxidation reactions using aqueous hydrogen peroxide and acetonitrile. The effects of reaction parameters such as solvent and oxidant in the epoxidation of cis-cyclooctene were investigated and showed that cyclooctene and cyclohexene were oxidized efficiently to their corresponding epoxide with 100 and 31 % selectivity, respectively, in the presence of catalyst 2. This catalytic system showed also excellent selectivity in the oxidation of benzyl alcohol. Copyright

Full text of DOI:10.1002/zaac.201200395

ARTICLE
DOI: 10.1002/zaac.201200395
Syntheses, Structures, and Catalytic Activity of Copper(II)-Aroylhydrazone
Complexes
[
a]
[a]
[a]
Hassan Hosseini-Monfared,* Elaheh Pousaneh, Somayeh Sadighian,
Seik Weng Ng,[ and Edward R. T. Tiekink
b,c]
[b]
Keywords: X-ray crystal structures; Copper; Catalysis; Oxidation; Hydrogen peroxide
II
Abstract. Two Cu complexes of tridentate Schiff base ligands,
Schiff base coordinates in a tridentate ligand fashion in dinuclear com-
pound 2 as the phenoxide oxygen atom bridges two central copper
atoms. The NO coordination donor set is completed by a methanol
4
oxygen atom, which occupies an axial position in the distorted square
pyramidal arrangement. Complexes 1 and 2 are very active catalysts
in clean epoxidation reactions using aqueous hydrogen peroxide and
acetonitrile. The effects of reaction parameters such as solvent and
oxidant in the epoxidation of cis-cyclooctene were investigated and
showed that cyclooctene and cyclohexene were oxidized efficiently to
their corresponding epoxide with 100 and 31% selectivity, respec-
1
2
[
Cu(L )(CH
3
OH)
2
]NO
3
·CH
3
OH (1) and [Cu
2
(L )
2
(CH
3
OH)
2
](NO
3
)
2
(
2), were prepared and characterized by elemental analyses and spec-
1
2
troscopic methods [H L = (E)-N-(4-hydroxy benzoic acid (2-hydroxy-
2
3
-methoxybenzylidene)benzohydrazide, and H L = (E)-N-4-hydroxy
2
benzoic acid (5-bromo-2-hydroxybenzylidene)benzohydrazide]. The
crystal structures of 1 and 2 were established by X-ray crystallography.
The complex cation in 1 is based on a square pyramid with the unineg-
ative Schiff base coordinating in a tridentate mode via O,N,OЈ-donor
atoms with the remaining sites being occupied by two methanol oxy- tively, in the presence of catalyst 2. This catalytic system showed also
gen atoms with one of these in the axial position. By contrast, the
excellent selectivity in the oxidation of benzyl alcohol.
Introduction
Salicylaldehyde benzoylhydrazone (H sb) has mild bacterio-
2
static activity[ and inhibits DNA synthesis and cell growth.[2]
The copper(II) complex was shown to be significantly more
potent than the metal-free chelate, leading to the suggestion
that the metal was the biologically active species. Salicylalde-
1]
hyde acetylhydrazone (H sa) displays radioprotective proper-
2
ties,[ and a range of acylhydrazones have been shown to be
cytotoxic, the copper complexes again showing enhanced ac-
tivity. Because of the biological interest in this type of chelate
system, several structural studies have been carried out on cop-
3]
the phenolic and amide protons are ionized and the ligands
[7,8]
coordinate in the enol form.
In neutral and mild acidic solu-
tion the ligands are monoanionic and coordinate in the keto
form. Strongly acidic conditions are necessary to form com-
pounds formulated with a neutral ligand. Catalytic oxidation
of hydrocarbons is of great interest to the chemical industry
for the conversion petroleum-based feedstocks into useful
[
4,5]
per
with H sb and analogues. Structurally there is a prefer-
2
II
ence for planar, phenolato bridged Cu dimers with these li-
gands, which often exhibit antiferromagnetism.[
5,6]
chemicals such as diols, epoxides, alcohols, and carbonyl com-
This class of diprotic ligands typically acts as tridentate,
planar chelate ligands coordinating through the phenolic and
amide oxygen atoms and the imine nitrogen atom. The actual
ionization state is dependent upon the reaction conditions and
pounds.[
9,10]
From both economic and environmental perspec-
tives, H O and O (or air) are the most attractive oxidants
2
2
2
because of their high contents of active oxygen species and
co-production of only water. Epoxidation reactions with H O ,
II
metal employed (Scheme 1). With Cu in basic media, both
2 2
one of the “greenest” terminal oxidants, are of great interest
*
Prof. Dr. H. Hosseini-Monfared
Fax: +98-241-2283203
due to the importance of epoxides in the manufacture of both
[11,12]
bulk and fine chemicals.
Epoxidation reactions that use
E-Mail: monfared@znu.ac.ir
H O in conjunction with cheap, manageable and relatively
[
[
[
a] Department of Chemistry
University of Zanjan 45195–313
Zanjan, Iran
b] Department of Chemistry
University of Malaya
Kuala Lumpur 50603, Malaysia
c] Chemistry Department
2 2
non-toxic metal-based catalysts are potentially viable for large-
scale production. However, good epoxidation catalysts must
activate H
O without radical formation. Metal-catalyzed
2 2
epoxidation of alkenes with H O has been reviewed re-
2
2
cently.[ However, there are a few reports on the copper cata-
13]
Faculty of Science, King Abdulaziz University 80203
Jeddah, Saudi Arabia
[
13,14]
lyzed epoxidation of alkenes with H O or other oxidants.
2
2
Z. Anorg. Allg. Chem. 2013, 639, (2), 435–442
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
435

H. Hosseini-Monfared et al.
ARTICLE
–1
2
–1
lar conductance of 129 ohm ·cm ·mol was observed, which
is slightly lower than that expected for 2:1 electrolytes (160–
–1
2
–1
2
20 ohm ·cm ·mol ). This difference can be related to the
high molecular weight of dinuclear 2, which decreases mo-
bility in solution.
A list of salient IR spectroscopic data is presented in
Table 1. A comparison of the spectra of the complexes with
the ligands provides evidence for the coordination mode of the
ligands in the complexes. For example, the presence of a N–
–1
H band, and shifts in the azomethine (–C=N–, 4 cm ) and
–
1
1 –
carbonyl bands (6 cm ) of (HL ) compared to free ligand
1
1 –
H L indicate coordination of (HL ) through the phenolate
2
oxygen, azomethine nitrogen, and amide oxygen atoms in
complex 1. Appearance of the carbonyl stretching vibration
band, ν(C=O), with slight shift supports the presence of the
Scheme 1. Keto-enol tautomerization in the ligands.
1
–
2 –
coordinated (HL ) and (HL ) in keto form in 1 and 2, respec-
tively. This finding also suggests that the –N–C=O bond is
delocalized to a certain extent in the free and the coordinated
ligands. Presence of the delocalization was supported by obser-
vation that vibrational stretching of the ligand C–O is among
the lowest ν(C=O) of the reported aroylhydrazone ligands
Herein, we report the synthesis, structures, and catalytic ac-
tivities of two new copper(II) containing Schiff bases derived
from (E)-N-(4-hydroxy benzoic acid (2-hydroxy-3-methoxy-
1
benzylidene)benzohydrazide (H L ) and (E)-N-4-hydroxy ben-
2
zoic acid (5-bromo-2-hydroxybenzylidene)benzohydrazide
–1 [15]
[
ν(C=O) 1649–1673 cm ].
That 1 and 2 are ionic com-
2
(
H L ) (Scheme 1). This paper describes their characterization
2
plexes is demonstrated by the presence of the nitrate counter-
ion as indicated by the intense absorption at 1383 and
and a description of their catalytic role in the efficient and
highly selective epoxidation of alkenes with 30% aqueous
H O .
–1
1
372 cm , respectively.
2
2
Table 1. Selected IR spectroscopic data of the ligands and complexes
–
1
/
cm .
Results and Discussion
Compound
ν(O–H)
ν(N–H)
ν(C=O)
ν(C=N)
1
H
H
1
2
L
L
3451 (m)
3433 (m)
3408 (w)
3419 (m)
3215 (w)
3219 (m)
3283 (m)
3171 (m)
1646 (w)
1624 (s)
1652 (w)
1631 (m)
1610 (s)
1606 (s)
1606 (s)
1612 (s)
Syntheses of Complexes and Spectroscopy
2
2
The Schiff base ligands were synthesized following a litera-
ture procedure in one step and in high yield and purity.
keto-enol tautomerism of the aroylhydrazones H L and H L
is illustrated in Scheme 1. IR spectroscopy confirmed that in
the solid state each of these ligands exists as the keto tautomer.
Copper complexes with hydrazone Schiff base ligands were
prepared by treating a methanol solution of the respective
ligand with an equimolar amount of Cu(NO ) ·3H O
[
15]
2
The
1
2
2
2
As a result of complexation, the UV/Vis spectra in methanol
show absorbance bands at λmax (ε, dm ·mol ·cm ) = 239
45,500), 322 (37,000), 391 (20,000), and 685 nm (46) for
3
–1
–1
(
3
–1
–1
complex 1, and at λmax (ε, dm ·mol ·cm ) = 230 (78,000),
10 (84,000), 403 (45,000), and 670 nm (79) for complex 2
Figure 1). The complexes show UV/Vis spectra similar to
their corresponding ligands. Based on their extinction coeffi-
cients they can be assigned to intraligand πǞπ* (230, 239 nm)
and nǞπ* (310, 322 nm) transitions. The higher energy bands
at 391 nm (complex 1) and 403 nm (complex 2) with high ex-
tinction coefficient values are due to the coordinated phenolate
3
(
3
2
2
(Scheme 2).
II
oxygen atom to Cu charge transfer (LMCT) transitions.
Furthermore, the complexes 1 and 2 show ligand field d–d
transitions at 685 (46) and 670 nm (79), respectively (the insets
in Figure 1a and b). The later finding suggests very similar
II
coordination environments for the central Cu atoms.
Crystallography
Scheme 2. Syntheses of complexes 1 and 2.
Unambiguous structure determination for 1 and 2 was
The molar conductance (Λ ) for [Cu(HL )(CH OH) ]NO · achieved by X-ray crystallography. The crystallographic asym-
CH OH (1) in methanol solution was 79 ohm ·cm ·mol , a metric unit of 1 comprises a complex cation, a nitrate anion,
value consistent with a 1:1 electrolyte type (80–115 ohm · and a solvent methanol molecule (Figure 2). As indicated by
1
M
3
2
3
–
1
2
–1
3
–1
2
–1 [16]
2
2 2 3 2 3 2
cm ·mol ).
For [Cu (HL ) (CH OH) ](NO ) (2), the mo- spectroscopy, the Schiff base is uninegative and coordinates in
4
36 www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 435–442

Copper(II)-Aroylhydrazone Complexes
Figure 2. Molecular structures of the complex cation, nitrate anion and
solvent methanol molecule in 1. Key geometric parameters: Cu–O2
1
1
.8982(16), Cu–O3 1.9905(16), Cu–O5 2.2552(18), Cu–O6
.9610(17), Cu–N1 1.9201(19), O3–C9 1.257(3), C9–N2 1.353(4) Å;
O2–Cu–O3 172.39(7), O6–Cu–N1 165.91(8)°.
Figure 3. The molecular structure of the dinuclear cation in 2; the
nitrate anions are omitted for clarity. Unlabelled atoms are related ac-
ross a center of inversion (i: 1–x, 1–y, 1–z). Key geometric parameters:
i
Cu–O1 1.9406(15), Cu–O2 1.9493(15), Cu–O4 2.2396(16), Cu–O1
L1 (c
Figure 1. UV/Vis spectra recorded in methanol of (a) 1 and H
2
1.9853(15), Cu–N1 1.9406(18), O2–C8 1.263(3), C8–N2 1.348(3) Å;
O1–Cu–O2 169.48(7), O1 –Cu–N1 163.71(7)°.
i
2ϫ10–5 m), and (b) 2 and H
2
–5
=
2
L
(c = 1.165ϫ10 m). The insets
II
–3
show d–d transitions in the Cu (c = 1ϫ10 m).
bridges asymmetrically two central copper atoms [Cu–O1
i
a tridentate mode via the O,N,OЈ-donor atoms. The remaining 1.985(2) Å / Cu –O1 1.941(2) Å] with the concomitant ex-
sites in the pentacoordinate arrangement are occupied by two clusion of one of the coordinating methanol molecules seen
methanol oxygen atoms. The coordination sphere is best de- in 1; the remaining methanol oxygen atom occupies the axial
scribed as distorted square pyramidal in accordance with the position in 2 (Figure 3). The NO coordination donor set de-
4
value of the trigonality index [τ = (β – α)/60° = 0.11], where fines a distorted square-pyramidal coordination arrangement
α and β are the largest angles in the coordination sphere.[ In (τ = 0.10). The five- and six-membered chelate rings are planar
this description, the methanol-O5 atom occupies an axial posi- (r.m.s. deviations = 0.027 and 0.057 Å, respectively) but a
tion. The long distance of the Cu1–O5 bond with 2.2552(18) Å slightly greater twist in the overall Schiff base molecule [dihe-
shows weak bonding of the methanol to the central copper dral angle between the benzene rings = 12.96(10)°] is observed
atom due to the Jahn-Teller effect.[ The bond lengths in 1 in 2 compared with the situation in 1.
17]
18]
1
2
and 2 (see captions to Figure 2 and Figure 3 for selected geo-
The hydrazone ligands HL and HL are monoanionic and
metric parameters) are within the expected range for copper(II) coordinate in the keto form, which can be verified from C–O
[
19]
complexes with Schiff base ligands.
The entire Schiff base and C–NH bond lengths of the amide unit: O3–C9 1.257(3) Å,
1
ligand HL is close to being planar with a small twist exhibited C9–N2 1.353(4) Å in 1 and O2–C8 1.263(3) Å, C8–N2
by the hydroxybenzene group from the remaining atoms; the 1.348(3) Å in 2 (see Figure 2 and Figure 3). Amide unit bond
dihedral angle between the two benzene rings is 3.54(12)°. lengths for aroyl hydrazones are in the ranges of 1.218–
This overall planarity is consistent with the observation that 1.292 Å (C–O), 1.313–1.365 Å (C–N), and 1.284–1.314 Å
each of the five- and six-membered chelate rings is planar hav- (C–O), 1.291–1.331 Å (C–N) in the keto and enol form,
respectively.[
20]
ing r.m.s. deviations of 0.040 and 0.011 Å, respectively.
A different mode of coordination of the Schiff base ligand
As anticipated from the chemical composition, significant
is observed in 2. The key difference is the dimerization of the hydrogen bonding interactions are present in the crystal struc-
molecule about a center of inversion as the phenoxide-O1 atom tures of 1 and 2. In 1, the solvent methanol molecule straddles
Z. Anorg. Allg. Chem. 2013, 435–442
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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437

H. Hosseini-Monfared et al.
ARTICLE
three hydrogen bonding sites in the oxygen-rich bay of the
complex cation (Figure 4a), and the resulting two molecule ag-
gregates are connected into a linear supramolecular chain
along the b axis by hydrogen bonds formed between nitrate
oxygen atoms and the hydroxyl hydrogen and hydrazide hy-
drogen atoms. The remaining nitrate oxygen atom forms a hy-
drogen bond with the axially coordinated methanol of an inver-
sion related molecule so that a double layer parallel to (101)
ensures (Figure 4b). The most prominent interactions between
layers are of the type π···π, where the π systems are the five-
and six-membered chelate rings; such interactions are increas-
ingly being recognized as supramolecular synthons.[ While
the π···π interactions bring copper atoms into close proximity,
the Cu···Cu separation of 3.9235(6) Å is not considered to rep-
resent significant bonding interactions between these atoms.
21]
Figure 5. Crystal packing in 2: (a) supramolecular chain sustained by
O–H···O and N–H···O hydrogen bonds shown as dashed lines; (b) view
of the unit cell contents in projection down the a axis highlighting the
stacking of layers and the C–H···O connections between them (dashed
lines).
Catalytic Activities
The catalytic activities of the complexes were first tested
in the oxidation of cis-cyclooctene. In this regard, we were
particularly interested to evaluate the advantages of H O as a
2
2
green and inexpensive terminal oxidant. The catalyzed oxi-
dation of cis-cyclooctene was carried out with H O to give
2
2
cis-cyclooctene oxide as the sole product. Control experiments
revealed that the presence of oxidant and catalyst were essen-
tial for the oxidation. While H O is a widely used oxidant
2
2
with high active oxygen content[ it is rather slow in the ab-
sence of activators. Oxidation of cis-cycloocetene was
achieved only up to 11% conversion under optimal conditions
by Cu(NO ) ·3H O (0.0011 mmol)/H O (3 mmol) at 80 °C
24]
3
2
2
2 2
after 5 h.
The catalytic activities of complexes 1 and 2 show a similar
trend in the oxidation of cis-cycooctene with slight higher ac-
tivity for 2, as shown in Figure 6. This finding reflects their
Figure 4. Crystal packing in 1: (a) supramolecular chain sustained by
O–H···O and N–H···O hydrogen bonds shown as dashed lines; (b)
double layers sustained by O–H···O hydrogen bonds are formed in the
structural similarity and the presence of similar coordination
II
(
101) plane. Connections between the layers are mediated by π(Cu- environments for Cu in each complex.
OCN
2
)···π(CuO
2
C
3
N) interactions (dashed lines).
To determine the optimal experimental conditions, the ef-
fects of H O /cis-cyclooctene molar ratio, reaction tempera-
2
2
ture, and influence of solvent were studied. We have monitored
the progress of cis-cyclooctene epoxidation for different molar
ratios of oxidant and substrate (Figure 7). Molar H O /cis-cy-
clooctene ratios of 1, 2 and 3 were considered, while keeping
a fixed amount of cis-cyclooctene (1.0 mmol) and catalyst
The crystal packing in 2 bears some similarities to that
found in 1. Supramolecular chains along [1 –1 1] are formed
by hydrogen bonds formed between nitrate oxygen atoms with
2
2
[22]
the hydroxyl hydrogen and hydrazide hydrogen atoms.
Ow-
ing to symmetry, these are formed on both sides of the dinu-
clear molecule and result in the formation of centrosymmetric
(1.0 mg) in 3 mL of acetonitrile at 80 °C. At a ratio of oxi-
dant:alkene of 1:1, conversion occurred up to 42% after 5 h.
2
4-membered {···ONO···HNC OH} synthons (Figure 5a). In-
5 2
Increasing the H O /cis-cyclooctene ratio to 2:1 increased the
2
2
version related chains are connected by bifurcated methanol-
conversion from 42 to 54% after 5 h. Further increase in the
OH···O-nitrate hydrogen bonds into layer parallel to (011) ratio to 3:1 gave additional increase of the conversion, 64%
(
Figure 5b). The most prominent interactions between the lay- after 5 h. Hence, a H O /cis-cyclooctene ratio of 3:1 was se-
2 2
[23]
ers are of the type methyl-C–H···O-nitrate.
lected for further studies. Oxidant requirements of the order
4
38
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© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 435–442

Copper(II)-Aroylhydrazone Complexes
Figure 6. Effects of the catalyst on the oxidation of cyclooctene. Reac-
Figure 8. Effect of the reaction temperature on the oxidation of cyclo-
octene by 2. Reaction conditions: catalyst 2 1.0 mg (0.0011 mmol),
CH CN 3.0 mL, cyclooctene 1.0 mmol, chlorobenzene 0.1 g, H O
tion conditions: catalyst 1.0 mg, CH
3
CN 3.0 mL, cyclooctene
1
6
.0 mmol, chlorobenzene 0.1 g, H
0Ϯ1 °C. [H ]/[cyclooctene] ratio 1:1.
2 2
O 1.0 mmol and temperature
3
2
2
2
O
2
3.0 mmol.
Figure 9. Effect of solvent on the oxidation of cyclooctene by 2. Cata-
lyst 1.0 mg (0.0011 mmol), cyclooctene 1.0 mmol, solvent 3.0 mL,
Figure 7. Effect of H
by 2. Reaction conditions: catalyst [Cu
.0 mg (0.0011 mmol), CH CN 3.0 mL, cyclooctene 1.0 mmol, chloro-
benzene 0.1 g, temperature 60Ϯ1 °C.
2 2
O concentration on the oxidation of cyclooctene
2 2
chlorobenzene 0.1 g, aqueous 30% H O 3.0 mmol, temperature
80Ϯ1 °C.
2
2
2 3 2 3 2
(HL ) (CH OH) ](NO ) (2)
1
3
conversion with change of solvent from methanol (ε/ε = 32.7)
0
to acetonitrile suggests the possible involvement of acetonitrile
of 10:1 epoxidation reactions have been documented in the in the oxidation of cyclooctene by H O . This idea was not
2
2
literature.[
25,26]
supported by the absence of acetamide in the GC analyses and
The oxidation of cyclooctene was studied at 20, 40, 60, and in the H NMR spectra of cis-cyclooctene oxidation products.
1
80 °C. Increasing the reaction temperature resulted in signifi- Bases such as NaOH and KOH are known to catalyze the
cantly higher yields of cis-cyclooctene oxide (Figure 8). A epoxidation of alkenes by using H O in the presence of ni-
2
2
27]
triles.[ The catalyst decomposes H O to some extent but
yield of 73% was achieved at 80 °C after 5 h.
The catalytic efficiency was studied in a variety of solvents the decomposition rate is much lower than H O activation for
2 2
2
2
(Figure 9). Catalytic activity of 2 was lowest in chloroform oxidation of hydrocarbons.
with conversion of 25% after 5 h. Oxidation of cis-cyclooctene
With the optimal reaction conditions for this catalyst to
increased when ethanol (conversion 54%) and methanol (con- hand, we proceeded to investigate the scope for other hydro-
version 61%) were used as solvents. The best performance of carbons. The molar ratio of catalyst:H O :hydrocarbon for
2
2
the catalyst was observed in acetonitrile (conversion 73% after these experiments was 1:3000:1000. The results for the cata-
h), possibly due to its dielectric constant (ε/ε = 37.5), which lytic oxidation of different substrates are summarized in
5
0
is the highest of all the solvents used. It is the optimal polarity Table 2. Cis-cyclooctene, cyclohexene and benzyl alcohol
of acetonitrile, which enables dissolution of both alkene and were oxidized. Cyclohexene gave the corresponding epoxide
H O . That is likely to be factor facilitating the epoxidation as the main product with 48% selectivity, other products were
2
2
reaction. Furthermore, the improvement in the cis-cyclooctene 2-cyclohex-1-ol (selectivity 35%) 2-cyclohex-1-one (selectiv-
Z. Anorg. Allg. Chem. 2013, 435–442
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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H. Hosseini-Monfared et al.
ARTICLE
Table 2. Oxidation of various substrates catalyzed by 2a).
Substrate
Product(s)
Epoxide
Selectivityb) /%
Conversionc) /%
TONd)
TOFe) /h–1
Cyclooctene
Cyclohexene
100
48
35
73
65
365
325
73
65
f)
Epoxide
g)
Enol
h)
Enone
17
Benzyl alcohol
Aldehyde
100
43
215
43
2 2 3 2 3 2 3 2 2
a) Reaction conditions: Catalyst [Cu (CH OH) ](NO ) (2) 1.0 mg (1.0 μmol), CH CN 3.0 mL, substrate 1.0 mmol, H O 3.0 mmol,
(HL2)
chlorobenzene 0.1 g, time 5 h, temperature 80Ϯ1 °C. b) Selectivity = ([desired product]/[conversion])ϫ100. c) Conversions are based on the
starting substrate and determined by GC analysis. d) TON: turnover number = number of moles of product formed per mole of copper in the
catalyst. e) TOF: turnover frequency = number of moles of product formed per mole of copper in the catalyst per unit time = (Conv.ϫ1.0 mmol)/
(0.001 mmolϫ5 h). f) Cyclohexene oxide. g) 2-Cyclohexene-1-ol. h) 2-Cyclohexene-1-one.
3
ity 17%). Cyclohexene is more prone to both epoxidation and (51.7 mg). M.p.: 273 °C. C18H25CuN O10 (506.95): calcd. C 42.65, H
allylic oxidation[28] and oxygenation of cyclohexene is a good
probe to provide evidence for or against a non-radical mecha-
nism and to evaluate the catalyst selectivity. We observed for
cyclooctene and cyclohexene oxidation a decrease in product
4.97, N 8.29, Cu 12.53%; found C 42.61, H 4.99, N 8.26, Cu 12.63%.
IR (KBr): ν˜ = 3408 (w, O–H), 3283 (m, N–H), 1606 (s C=O),
–
–1
1
(
6
568 (s, C=N), 1383 (vs, NO
3
) cm . UV/Vis (methanol): λmax
ε, dm mol cm ) = 239 (45,500), 322 (37,000), 391 (20,000) and
85 nm (46).
3
–1
–1
yields when O was absent (conversions 55% for cyclohexene
2
and 65% for cyclooctene) by repeating the reaction in a nitro-
gen atmosphere. This finding confirms the presence of free
(HL2) (HL2)
2 3 2 3 2 2 2
(CH OH) ](NO ) (2): Complex [Cu -
Synthesis of [Cu
3 2
CH OH) ](NO ) (2) was synthesized and olive-green single crystals
2
(
3
2
diffusing radicals as intermediate. Free diffusing radicals are grown by a procedure similar to the synthesis of complex 1 but using
2
greatly enhanced because of radical chains in the presence of
2 2 2 6 14
H L . Yield: 90% (51.2 mg). M.p.: 282 °C. C30H28Br Cu N O
O .
(983.48): calcd. C 36.64, H 2.87, N 8.55, Cu 12.92%; found C 36.65,
2
H 2.89, N 8.44, Cu 13.03%. IR (KBr): ν˜ = 3419 (m, O–H), 3171 (m,
–
–1
N–H), 1631 (m, C=O), 1612 (s, C=N), 1372 (vs, NO
3
) cm . UV/Vis
(methanol): λ max (ε, dm mol cm ) = 230 (78,000), 310 (84,000),
03 (45,000) and 670 nm (79).
3
–1
–1
Conclusions
4
II
This work revealed that coordination complexes of Cu with
polydentate hydrazone Schiff base ligands obtained by reaction X-ray Crystallography: Intensity data for 1 and 2 were measured at
of 2-hydroxybenzhydrazide and 2-hydroxy-3-methoxybenzal- 100 K with an Agilent Technologies SuperNova Dual CCD with an
II
dehyde derivatives afford a new class of Cu catalysts for the Atlas detector fitted with Cu-K
α
radiation so that θmax = 76.6° (1) and
7
6.3° (2). Data processing and absorption correction were ac-
oxidation of alkenes and benzylalcohol. It was demonstrated
that these dissymmetric hydrazone copper(II) complexes are
highly selective catalysts for the oxidation of cyclooctene, cy-
clohexene, and benzyl alcohol by H O under mild conditions.
[
29]
complished with CrysAlis PRO.
rect methods with SHELXS-97
The structures were solved by di-
and refinement (anisotropic dis-
[
30]
placement parameters, C-bound hydrogen atoms in the riding model
2
2
2
2
approximation and a weighting Scheme of the form w = 1/[σ (F
o
) +
)/3) was on F by means of SHELXL-
7. For 1, the O- and N-bound hydrogen atoms were located from a
2
2
2
2
(
9
o c
aP) + bP] for P = (F + 2F
[
30]
Experimental Section
difference map and refined with distance restraints of 0.84 and 0.88 Å,
respectively. For 2, the O- and N-bound hydrogen atoms were again
located from a difference map and refined with 0.84Ϯ0.01 and
0.88Ϯ0.01 Å, respectively. Crystallographic data and final refinement
details are given in Table 3. Figure 2 and Figure 3 were drawn with
All solvents and materials were purchased in high purity from Merck
and Fluka. IR spectra were taken with a Matson FT-IR spectropho-
–1
tomer in the range of 400–4000 cm as KBr disks. UV/Vis spectra of
solutions were recorded with a Shimadzu 160 spectrophotometer. A
HP Aglient 6890 gas chromatograph, which was equipped by HP-5
capillary column (phenyl methyl siloxane 30 mmϫ320 μmϫ0.25 μm),
a flame-ionization detector and gas chromatograph-mass spectrometer
[
31]
ORTEP-3 for Windows
at the 70% probability level and the re-
maining crystallographic figures were drawn with DIAMOND using
[
32]
arbitrary spheres.
(
Hewlett-Packard 5973 Series MS-HP gas chromatograph with a mass-
General Oxidation Procedure: The liquid phase catalytic oxidations
were carried out in air (atmospheric pressure) in a 25 mL round-bot-
tomed flask equipped with a magnetic stirrer and immersed in a ther-
mostatted oil bath at 80 or 60 °C. In a typical experiment, a mixture of
selective detector) was used for identification of the oxidation reaction
products. The Schiff base ligands H L and H L were prepared ac-
2 2
cording to a reported procedure.
1
2
[
15]
1
Synthesis of [Cu(HL )(CH
3
OH)
2
]NO
3
·CH
3
OH (1): Single crystals
2 2
30% H O (3 mmol), solvent (3 mL), chlorobenzene (0.1 g) as internal
1
of [Cu(HL )(CH
gradient method. Molecule H
O (0.03 g, 0.12 mmol) were placed in the main arm of a branched
tube. Methanol (10 mL) was carefully added to fill the arms, the tube
3
OH)
2
]NO
3
·CH OH (1) were obtained by the thermal standard, and cyclooctene (1 mmol) was added to a flask containing
3
1
2
L (0.02 g, 0.07 mmol) and Cu(NO
3
)
2
·
the catalyst, i.e. 1 or 2. The course of the reaction was monitored using
a gas chromatograph equipped with a capillary column and a flame
ionization detector. The oxidation products were identified by compar-
3H
2
was sealed and the arm containing reagents was immersed in an oil ing their retention times with those of authentic samples or alterna-
1
bath at 60 °C, while the other arm was kept at ambient temperature.
After 10 d, blue crystals of 1 were deposited in the cooler arm, which substrate were determined by a calibration curve. Control reactions
were filtered off, washed with methanol and dried in air. Yield: 95% were carried out in the absence of catalyst and H under the same
tively by H NMR and GC-mass analyses. Yields based on the added
2 2
O
4
40
www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 435–442

Copper(II)-Aroylhydrazone Complexes
[
6] E. W. Ainscough, A. M. Brodie, A. Dobbs, J. D. Ranford, J. M.
Table 3. Crystal data and refinement details for 1 and 2.
Waters, Inorg. Chim. Acta 1998, 267, 27–38.
1
2
[7] H. Hosseini-Monfared, Z. Kalantari, M. A. Kamyabi, C. Janiak,
Z. Anorg. Allg. Chem. 2007, 633, 1945–1948.
8] H. Hosseini-Monfared, J. Sanchiz, Z. Kalantari, C. Janiak, Inorg.
Chim. Acta 2009, 362, 3791–3795.
9] R. A. Sheldon, J. K. Kochi, Metal Catalyzed Oxidations of Or-
ganic Compounds, Academic Press, New York 1981.
Formula
Formula weight
Crystal color
C
18
H
25CuN
3
O
10
C
30 2 2 6 14
H28Br Cu N O
[
[
506.95
blue
983.48
olive-green
0.15ϫ0.25ϫ0.35
triclinic
P1
7.4497(3)
10.4994(5)
11.5358(5)
99.599(4)
95.081(4)
104.917(4)
851.46(6)
1
Crystal dimensions /mm 0.10ϫ0.20ϫ0.30
Crystal system
Space group
a /Å
b /Å
c /Å
triclinic
P1
¯
¯
[10] T. Punniyamurthy, S. Velusamy, J. Iqbal, Chem. Rev. 2005, 105,
329–2364.
11] M. G. Clerici, G. Bellussi, U. Romano, J. Catal. 1991, 129, 159–
67.
2
9.7384(8)
11.1472(9)
11.2985(10)
60.855(9)
88.886(7)
79.792(7)
1051.08(15)
2
1.602
526
2.029
7835
[
[
1
12] a) R. I. Kureshy, N. H. Khan, S. H. R. Abdi, S. Singh, I. Ahmed,
R. S. Shukla, R. V. Jasra, J. Catal. 2003, 219, 1–7; b) L. L. Lou,
K. Yu, F. Ding, X. Peng, M. Dong, C. Zhang, S. Liu, J. Catal.
2007, 249, 102–110.
13] a) I. Garcia-Bosch, X. Ribas, M. Costasa, Adv. Synth. Catal. 2009,
351, 348–352; b) G. De Faveri, G. Ilyashenko, M. Watkinson,
Chem. Soc. Rev. 2011, 40, 1722–1760.
α /°
β /°
γ /° 3
V /Å
[
Z
D
/g·cm–3
x
1.918
490
4.997
6161
F(000)
μ(Cu-K
) /mm–1
[14] a) L. Yang, J. He, Q. Zhang, Y. Wang, J. Catal. 2010, 276, 76–
4; b) C. W. Ho, W. C. Cheng, M. C. Cheng, S. M. Peng, K. F.
α
8
Reflections collected
R
int
0.027
4303
3921
0.020
3478
3393
Cheng, C. M. Che, J. Chem. Soc. Dalton Trans. 1996, 405–414;
c) W. Zhu, Q. Zhang, Y. Wang, J. Phys. Chem. C 2008, 112,
7731–7734.
Unique reflections
Obs. reflections [I Ͼ
2σ(I)]
[15] O. Pouralimardan, A. C. Chamayou, C. Janiak, H. Hosseini-Mon-
fared, Inorg. Chim. Acta 2007, 360, 1599–1608.
[16] W. J. Geary, Coord. Chem. Rev. 1971, 7, 81–122.
[17] A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn, G. C. Ver-
schoor, J. Chem. Soc. Dalton Trans. 1984, 1349–1356.
R [obs. reflns]
a, b, in weighting
scheme
0.044
0.080, 1.084
0.029
0.054, 0.753
wR (all data)
0.128
0.083
[
18] S. Roy, P. Mitra, A. K. Patra, Inorg. Chim. Acta 2011, 370, 247–
53.
2
[
19] a) A. D. Garnovskii, A. L. Nivorozhkin, V. I. Minkin, Coord.
Chem. Rev. 1993, 126, 1–69; b) S. Mandal, G. Das, R. Singh, K.
Bhuradwaj, Coord. Chem. Rev. 1997, 160, 191–235; c) H. Hosse-
ini-Monfared, M. Vahedpour, M. Mahdavi Yeganeh, M. Ghorban-
loo, P. Mayer, C. Janiak, Dalton Trans. 2011, 40, 1286–1294.
20] a) H. Hosseini-Monfared, H. Falakian, R. Bikas, P. Mayer, Inorg.
Chim. Acta 2013, 394, 526–534; b) J. M. Zhang, L. Wang, J. Liu,
Y. C. Li, H. J. Li, Acta Crystallogr. Sect. E 2011, 67, m537.
21] Supramolecular interactions in the crystal structure of 1. Between
the solvent methanol molecule and the complex cation to form
two molecule aggregates: O6–H6···O10 = 2.13 Å, O6···O10 =
conditions. These runs confirmed that no products, or at most, only
trace yields, were detected.
Some degradation of the ligand was obvious from changes in solution
color from light green to pale yellow after 5 h.
[
[
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies
of the data can be obtained free of charge on quoting the depository
numbers CCDC-894934 (1) and CCDC-894935 (2) (Fax: +44-1223-
2.586(3) Å with angle at H6 = 114°; O10–H10···O1 = 2.27 Å,
336-033; E-Mail: deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.
O10···O1 = 2.940(3) Å with angle at H10 = 137°; O10–H10···O2
= 2.01 Å, O10···O2 2.709(3) Å with angle at H10 = 140°. Be-
tween the nitrate and complex cation to form a supramolecular
uk)
i
i
chain: O4–H4···O9 = 1.98 Å, O4···O9 = 2.793(3) Å with angle
at H4 = 161°; N2–H2···O7 = 2.06 Å, N2···O7 = 2.930(3) Å with
angle at H2 = 167°. Between nitrate and axial methanol to form
Acknowledgements
ii
ii
The authors are grateful to the University of Zanjan for financial assist-
ance. The Ministry of Higher Education (Malaysia) is thanked for
funding studies through the High-Impact Research Scheme (UM.C/
HIR.-MOHE/SC/3).
a double layer: O5–H5···O7 = 1.96 Å, O5···O7 = 2.777(3) Å
with angle at H5 = 164°. Between chelate rings: π(CuOCN2)
iii
·
··π(CuO
2
C
3
N) = 3.6430(11) Å with angle of inclination =
2.63(8)°. Symmetry operations: i = x, –1+y, z; ii: –x, 1–y, 2–z;
iii: 1–x, 1–y, 2–z.
[
22] a) Z. D. Tomi c´ , D. N. Sredojevi c´ , S. D. Zari c´ , Cryst. Growth Des.
2
006, 6, 29–31; b) D. N. Sredojevi c´ , Z. D. Tomi c´ , S. D. Zari c´ ,
References
Cryst. Growth Des. 2010, 10, 3901–3908; c) E. R. T. Tiekink,
Crystal Engineering. in Supramolecular Chemistry: from Mole-
cules to Nanomaterials (Eds.: J. W. Steed, P. A. Gale), John
Wiley & Sons Ltd, Chichester, UK, 2012, pp. 2791.
[
[
[
[
1] H. A. Offe, W. Siefken, G. Domagk, Z. Naturforsch. 1952, 7b,
462–468.
2] L. Pickart, W. H. Goodwin, W. Burgua, T. B. Murphy, D. K. John-
son, Biochem. Pharmacol. 1983, 32, 3868–3871.
3] O. V. Arapov, O. F. Alferva, E. I. Levocheskaya, I. Krasil’nikov,
Radiobiologiya 1987, 27, 843–846.
4] a) A. A. Aruffo, T. B. Murphy, D. K. Johnson, N. J. Rose, V. Cho-
maker, Acta Crystallogr., Sect. C 1984, 40, 1164; b) E. W. Ain-
scough, A. M. Brodie, A. Dobbs, J. D. Ranford, J. M. Waters, In-
org. Chim. Acta 1995, 236, 83–88.
[
23] Supramolecular interactions in the crystal structure of 2. Between
nitrate and dinuclear complex cations to form a chain: O3–
i
i
H3···O7 = 1.88(3) Å, O3···O7 = 2.711(2) Å with angle at H3 =
ii
175(3)°; N2–H2···O5 = 1.91(2) Å, N2···O5 = 2.762(3) Å with
angle at H2 = 161(2)°. Between chains to form a layer: C15–
iii
iii
H15···O7 = 2.58 Å, C15···O7 = 3.439(3) Å with angle at H15
= 146°. Symmetry operations: i = 1–x, –y, 2–z; ii: 1+x, y, z;
iii: –x, –y, 1–z.
[5] S. C. Chan, L. L. Koh, P.-H. Leung, J. D. Ranford, K. Y. Sim,
Inorg. Chim. Acta 1995, 236, 101–108.
[24] R. A. Sheldon, Top. Curr. Chem. 1993, 164, 21–43.
Z. Anorg. Allg. Chem. 2013, 435–442
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
441

H. Hosseini-Monfared et al.
ARTICLE
[
25] B. S. Lane, M. Vogt, V. J. DeRose, K. Burgess, J. Am. Chem. Soc.
002, 124, 11946–11954.
26] S. Ueno, K. Yamaguchi, K. Yoshida, K. Ebitani, K. Kaneda,
Chem. Commun. 1998, 295–296.
[30] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
[31] L. J. Farrugia, J. Appl. Crystallogr. 1997, 30, 565–566.
2
[
[
32] K. Brandenburg, Diamond (Version 3.2d), Crystal and Molecular
Structure Visualization, Crystal Impact, K. Brandenburg & H.
Putz Gbr, Bonn (Germany), 2009.
[
[
27] G. B. Payne, Tetrahedron 1962, 18, 763–765.
28] A. J. Appleton, S. Evans, J. R. Lindsay Smith, J. Chem. Soc. Per-
kin Trans. 2 1996, 281–285.
Received: September 4, 2012
Published Online: December 20, 2012
[
29] Agilent Technologies. CrysAlis PRO. Agilent Technologies,
Yarnton, Oxfordshire, England, 2010.
4
42
www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 435–442