Copper(II) Schiff base complexes derived from 2,2′-dimethyl- propandiamine: Synthesis, characterization and catalytic performance in the oxidation of styrene and cyclooctene

Article abstract of DOI:10.1016/j.poly.2011.09.048

Two new mononuclear copper(II) complexes ([CuL¹] ·CHCl₃ (1) and [CuL²] (2)) have been prepared by the reaction of two ONNO type Schiff base ligands, ([bis(2-hydroxy- propiophenone)2,2′-dimethylpropan-diamine] (H₂

Full text of DOI:10.1016/j.poly.2011.09.048

Polyhedron 31 (2012) 443–450
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
0
Copper(II) Schiff base complexes derived from 2,2 -dimethyl-propandiamine:
Synthesis, characterization and catalytic performance in the oxidation
of styrene and cyclooctene
Felora Heshmatpour , Saeed Rayati a, , Mona Afghan Hajiabbas , Payam Abdolalian ,
Bernhard Neumüller
a
a,
⇑
⇑
a
a
b
Department of Chemistry, K.N. Toosi University of Technology, P.O. Box 16315 – 1618, Tehran 15418, Iran
Fachbereich Chemie der Universität, Hans-Meerwein-Straße, D-35032 Marburg, Germany
b
a r t i c l e i n f o
a b s t r a c t
1
2
Article history:
Two new mononuclear copper(II) complexes ([CuL ]ꢀCHCl (1) and [CuL ] (2)) have been prepared by the
3
Received 17 August 2011
Accepted 30 September 2011
Available online 15 November 2011
0
reaction of two ONNO type Schiff base ligands, ([bis(2-hydroxy-propiophenone)2,2 -dimethylpropan-dia-
1
0
2
mine] (H
2
L ) and [bis(5-bromosalicylaldehyde)2,2 -dimethyl-propandiamine] (H
in 1:1 molar ratios. The complexes have been characterized by elemental analyses, IR and UV–Vis spec-
troscopy. The structures have been confirmed by X-ray single crystal analysis at 100 K. The Cu(II) atom in
2
L )) with Cu(OAc)
2
ꢀH
2
O
Keywords:
Catalyst
Crystal structure
Copper
Oxidation
Schiff base
1 2ꢁ
1
2 2
is coordinated equatorially by a N O donor set of the tetradentate, dinegative Schiff-base (L ) in a
2
distorted square planar arrangement. While in [CuL ] (2), the Cu(II) ion possesses an additional weak
intermolecular contact with one bromine atom of the ligand, thus the coordination sphere of 2 can be
described as strongly distorted square pyramidal. The catalytic performance of the prepared copper com-
plexes for the oxidation of styrene and cyclooctene with tert-butyl hydroperoxide has been evaluated.
Ó 2011 Elsevier Ltd. All rights reserved.
1
. Introduction
Transition metal catalyzed transfer of oxygen atoms to organic
Copper(II) Schiff base complexes are amongst the most versatile
catalysts known for oxygenation reactions. The role played by the
copper ions in the active sites of a large number of metalloproteins
has stimulated efforts to design and characterize copper complexes
as models for a better understanding of biological systems [41].
2-Hydroxy Schiff base ligands have recently received particular
attention owing to their different crystallographic, structural and
magnetic characteristics [60–64]. More and more studies are still
being carried out on the synthesis of modified and supported re-
agents for catalysis and material chemistry [65].
substrates is of interest in the study of bioinorganic mechanisms.
In particular, the catalysis of alkene oxidation by soluble transition
metal complexes is of interest in both biomimetic and synthetic
chemistry [1,2]. Schiff base ligands and their metal complexes
can be easily synthesized. They are efficient catalysts under homo-
geneous and heterogeneous conditions. The catalytic activity of
these complexes depends on the nature of the substituents as well
as the metal center [3–6]. Therefore, these compounds have been
extensively used as catalysts in various reactions, such as oxidation
As part of our interestin hydrocarbon oxidation catalyzedby cop-
per(II) complexes, we are reporting here the synthesis, characteriza-
tion and X-ray single crystal determination of mononuclear Cu(II)
[
7–9], ring opening reactions of epoxides [10,11], aldol condensa-
0
tion [12–14] and epoxidation [3,15–24]. The major advances in this
field have been achieved with chiral Mn(III) Schiff base complexes
complexes of two Schiff base ligands derived from 2,2 -dimethylpro-
pandiamine, with a view to use them as active catalysts for oxida-
tion/epoxidation of styrene and cyclooctene using tert-butyl
hydroperoxide (TBHP) as an oxidant.
[25–32]. The activity of Cr(III) [33], Mn(II) [34,35], oxovanadyl(IV)
[36,37], Co(II) [38,39], Ni(II) [40], Cu(II) [41–51], Zn(II) [22], Ru(III)
[29,30,52] and Ru(II) [53,54] Schiff base complexes in oxidation
reactions have also been explored. Oxidants, such as iodosylben-
zene [28], molecular oxygen [55], H [56], Bu NIO [57],
dimethyldioxirane [58] and m-chloroperbenzoic acid [59], with
2. Experimental
2
O
2
4
4
2.1. General considerations
these complexes were also considered.
Solvents (ethanol, chloroform, methanol, dichloromethane,
1
,2-dichloroethane and acetonitrile) were dried and distilled by stan-
⇑
Corresponding authors. Tel.: +98 21 2285 3308/3309; fax: +98 21 2285 3650 (F.
Heshmatpour).
dard methods before use [66]. 2,2-Dimethylpropylenediamine
0
(Merck, 98%), 2 -hydroxypropiophenone (Across, 97%), 5-bromosali-
E-mail addresses: heshmatpour@kntu.ac.ir, f.heshmatpour@yahoo.com (F.
Heshmatpour).
cylaldehyde (Across, 97%) were used as received. Infrared spectra
0
277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.09.048

4
44
F. Heshmatpour et al. / Polyhedron 31 (2012) 443–450
were recorded as KBr pellets using a Unicam Mattson 1000 FT-IR. Ele-
mental analysis (C, H, and N) were performed using a Heraeus Ele-
mental Analyzer CHN-O-Rapid (Elemental-Analyse systeme, GmbH,
Germany). A digital melting point measuring device (Electrothermal
H
2
L2, respectively, in ethanol (30 mL). The bright yellow solutions
were stirred and heated to reflux for 1 h. The desired yellow precip-
itates were obtained, and these were filtered off, washed with
diethyl ether (2 ꢂ 5 mL) and finally dried in air.
9
2
100) was used. A double beam spectrophotometer (Shimadzu, UV-
40) was used for the UV–Vis absorption determination. The oxida-
2
.3.2. Synthesis of complex 1
tion products were analyzed with a gas chromatograph (Shimadzu,
GC-14B) equipped with a SAB-5 capillary column (phenyl methyl
1
L1 (0.366 g, 1 mmol) in ethanol
[
3 2
CuL ]ꢀCHCl (1): A solution of H
(
20 mL) was added to a suspension of Cu(OAc)
2 2
ꢀH O (0.199 g,
siloxane 30 m ꢂ 320 mm ꢂ 0.25 mm) and
a
flame ionization
1
mmol). The reaction mixture was refluxed for 1 h. The colored
detector.
solution that formed was concentrated to yield a colored powder.
The dark green precipitate that was obtained was filtered off and
washed with diethyl ether (2 ꢂ 5 mL). The crude product was dis-
solved in 1:1 chloroform and hexane (5 mL) and kept at room tem-
perature to give crystals of the complex after a few days. Yield:
2.2. Crystal structure analyses of 1 and 2 (Table 1)
1
2
The selected crystals of [CuL ]CHCl
3
(1) and [CuL ] (2) were cov-
ered with perfluorinated oil and mounted on the top of a glass capil-
lary under a flow of cold gaseous nitrogen. The orientation matrix and
the unit cell dimensions were determined from 8000 (1) and 4000 (2)
0
.407 g, 95%. M.p.: 253 °C. Anal. Calc. for
24 3 2 2
C H29Cl CuN O
(
547.38): C, 52.66; H, 5.34; N, 5.12; Cu, 11.61. Found: C, 52.29; H,
ꢁ
1
5
.73; N, 5.66; Cu, 11.28%. IR (KBr) [
m
, cm ]:
m
(C@N) 1581 s,
nm
reflections (Stoe IPDS 2T, graphite-monochromated MoK
a radiation
m(C@C) 1534 s,
m
(C–O) 1220 m. UV–Vis (CHCl ) [kmax,
3
ꢁ1
ꢁ1
(k = 71.037 pm); see Table 1). The intensities were corrected for Lor-
(e
, v cm )]: 262 (23040), 373 (9010), 388 (6890), 600 (310).
entz and polarizations effects. In addition, absorption corrections
were applied for 2 (numerical). The structures were solved by direct
methods for both compounds using SIR-92 and were refined against
2.3.3. Synthesis of complex 2
2
L2 (0.468 g, 1 mmol) in ethanol
ꢀH O (0.199 g,
mmol). The reaction mixture was refluxed for 1 h. The colored
[
CuL ] (2): A solution of H
2
2
F by full-matrix least-squares using the program SHELXL-97.
(
20 mL) was added to a suspension of Cu(OAc)
2
2
The hydrogen atoms were calculated in ideal positions and were
refined with a common displacement parameter. Programs used
were SHELXL-97 [67], SIR-92 [68], SHELXTL-Plus [69] and PLATON [70].
1
solution that formed was concentrated to yield a colored powder.
The dark green precipitate that was obtained was filtered off and
washed with diethyl ether (2 ꢂ 5 mL). The crude product was dis-
solved in 1:1 dichloromethane and diethyl ether (5 mL) and kept at
room temperature to give crystals of the complex after a few days.
2
2
.3. Syntheses
1
2
2 2
.3.1. Synthesis of the Schiff base ligands (H L and H L )
Yield: 0.471 g, 89%. M.p.: 241 °C. Anal. Calc. for C19
H18Br
2 2 2
CuN O
The Schiff bases were prepared by standard methods [71,72].
(
529.71): C, 43.08; H, 3.42; N, 5.30; Cu, 12.00. Found: C, 43.71; H,
0
Briefly, a solution of 2,2 -dimethylpropandiamine (0.102 g, 1 mmol)
ꢁ1
3
.52; N, 5.01; Cu, 11.53%. IR (KBr) [
m
, cm ]:
m
(C@N) 1617 s,
nm
was mixed with 2-hydroxypropiophenone (0.300 g, 2 mmol) and
m(C@C) 1519 s,
m
(C–O) 1170 m. UV–Vis (CHCl ) [kmax,
3
1
5
-bromosalicylaldehyde (0.402 g, 2 mmol) for the ligands H
2
L and
ꢁ1
ꢁ1
(e
, v cm )]: 266 (23480), 374 (7230), 393 (7840), 613 (290).
Table 1
Crystal data and structure refinement for 1 and 2.
2.3.4. General oxidation procedure
Catalytic experiments were carried out in a 50 mL glass reaction
1
2
flask fitted with a water condenser. In a typical procedure,
.032 mmol of the copper(II) complexes were dissolved in 10 ml
Empirical formula
Formula mass
Crystal size (mm)
Crystal system
Space group
a (pm)
C
24
H
29Cl
3
CuN
2
O
2
C
19 2 2 2
H18Br CuN O
0
547.38
529.71
0.25 ꢂ 0.16 ꢂ 0.11 0.12 ꢂ 0.10 ꢂ 0.05
of the appropriate solvent. Then 10 mmol alkene was added to
the reaction mixture and 30 mmol TBHP was added. The reaction
mixture was refluxed for 6 h. The reaction products were moni-
tored after periodic time intervals using gas chromatography. The
oxidation products were identified by comparison with authentic
samples (retention times in GC).
monoclinic
P2 /n
triclinic
P1ꢀ
1
1155.2(1)
881.1(1)
2467.1(1)
90
102.09(1)
90
2455.4(4)
4
1.481
none
915.0(1)
965.1(1)
1153.4(1)
75.12(1)
78.65(1)
73.50(1)
935.4(2)
2
1.881
numerical
54.55
100
56.76
b (pm)
c (pm)
a
(°)
b (°)
(°)
c
3
6
3. Results and discussion
V (pm ꢂ 10 )
Z
D
calc (g cm 3
ꢁ
)
3.1. Characterization of the Schiff base ligands and copper(II)
Absorption correction
ꢁ
1
complexes
l
(cm ) (MoK
T (K)
max (°)
a)
0.75
100
56.74
2h
The complexation behavior of the two Schiff base ligands to-
Index ranges
ward Cu(II) acetate has been investigated (Scheme 1). The new
mononuclear complexes 1 and 2 are remarkably stable to air, water
and heat. The complexes are neutral, with the metal charge being
entirely neutralized by the doubly deprotonated Schiff base li-
gands. The complexes were characterized by UV–Vis and IR spec-
troscopy and elemental analysis. The results are in agreement
with the formulae drawn in Scheme 1.
h
k
l
ꢁ15 ? 15
ꢁ11 ? 11
ꢁ30 ? 32
15894
6048
0.0393
4801
294
ꢁ12 ? 12
ꢁ12 ? 12
ꢁ15 ? 15
8519
4522
0.0483
4066
Reflections collected
Unique reflections
R
int
o o
Reflections with F > 4r(F )
Parameters
238
The infrared spectra of complexes 1 and 2 and a comparison of
them with the spectra of the ligands provides evidence for the
coordination mode of the ligands in the complexes. The Schiff base
ligands exhibit broad medium intensity bands in the 2969–
3430 cm region, which are assigned to intramolecular hydrogen
bonding vibrations (O–Hꢀ ꢀ ꢀN). Disappearance of these bands in the
R
wR
1
0.0301
0.0732
0.473
0.0384
0.0997
1.724
a
b
2
(all data)
Maximum residual electron
ꢁ
3
ꢁ6
density (e pm ) ꢂ 10
ꢁ1
a
2
2
.
2
2, 0) + 2.F
2]/3.
w = 1/[
w = 1/[
r
r
(F
(F
o
) + (0.044 P) ]; P = [max(F
o
c
b
2
2
.
2
o
) + (0.0747 P) ].

F. Heshmatpour et al. / Polyhedron 31 (2012) 443–450
445
Scheme 1. General structure of the Cu(II) complexes.
Table 2
UV–Vis data for the ligands and the complexes.
ꢁ
1
ꢁ1
Compound
L1
k
max/nm (
250(18780)
30(7740)
262(23040)
73(9010)
88(6890)
00(310)
e
/v cm
)
Assignment
⁄
⁄
H
2
p ? p
3
n ?
p
CuL1 (1)
p ?
n ? p
p
⁄
⁄
3
3
6
MLCT
d ? d
L2
260(2050)
p
p
n ?
?
?
p
⁄
H
2
⁄
3
4
35(9380)
30(280)
p
⁄
p
CuL2 (2)
266(23480)
p ? p
n ? p
MLCT
d ? d
⁄
⁄
3
3
6
74(7230)
93(7840)
13(290)
1
Fig. 1. Molecular structure of [CuL ] in 1 (thermal ellipsoids are at the 40%
probability level).
spectra of the complexes indicates coordination of the phenolic
oxygen after deprotonation. A sharp band due to the (C@N) (azo-
methine) group of the free ligands is observed at 1614 (in H
m
1
2
L )
complexes 1 and 2, respectively, indicating coordination through
the phenolic oxygen [74,75].
ꢁ1
2
and 1627 cm (in H
2
L ). Another broad band around 1570 and
ꢁ1
1
1
H
575 cm is related to the aromatic C@C vibration for H
2
L
and
L , respectively. For the synthesized complexes the C@N band
was shifted to lower frequency and appeared at 1581 (in 1) and
The electronic absorption spectral data for the Schiff base li-
gands and the Cu(II) complexes are given in Table 2. In the visible
region, the broad absorption band at about 600–613 nm, which is
assigned to a d–d transition, is consistent with the distorted
square-planar geometry of the Cu(II) complexes [76]. At the higher
energy region, charge transfer bands were located for both com-
plexes. The broad, slightly intense bands between 350–380 nm
and a shoulder around 390 nm could be assigned to O(pheno-
2
2
ꢁ1
1
617 cm (in 2), indicating the coordination of the azomethine
nitrogen to the metal ion. The bonds are broad, probably due to
their overlapping with the aromatic ring-carbon stretching [73].
The phenolic (C–O) stretching frequency was observed in the re-
ꢁ
1
1
2
gions around 1230 and 1185 cm for H
2 2
L and H L , which shifted
ꢁ1
II
to the lower frequency regions around 1220 and 1170 cm in
late) M Cu (LMCT or MLCT) [77–80]. More intense bands appeared

4
46
F. Heshmatpour et al. / Polyhedron 31 (2012) 443–450
Fig. 2. Coordination sphere of Cu1 in 1.
Fig. 4. Molecular structure of [CuL2] (2) (thermal ellipsoids are at the 40%
probability level).
Fig. 3. Molecular packing in the crystal structure of 1.
Fig. 5. Coordination sphere of Cu1 in 2.
Table 3
1
Selected bond lengths (pm) and bond angles (°) for [CuL ]ꢀHCCl
3
(1).
Cu(1)–O(1)
Cu(1)–N(1)
O(1)–C(2)
N(1)–C(7)
N(1)–C(10)
C(1)–C(2)
1.890(1)
1.961(1)
1.312(2)
1.296(2)
1.473(2)
1.427(2)
1.469(2)
1.519(2)
1.884(1)
1.962(1)
1.308(2)
1.300(2)
1.476(2)
1.431(2)
1.471(2)
1.516(2)
N(1)–Cu(1)–N(2)
O(1)–Cu(1)–N(1)
C(2)–O(1)–Cu(1)
C(7)–N(1)–Cu(1)
C(2)–C(1)–C(7)
92.85(6)
91.90(6)
125.2(1)
128.2(1)
122.7(2)
120.9(2)
122.5(1)
92.16(6)
88.22(5)
127.3(1)
128.6(1)
123.0(2)
120.9(2)
122.0(1)
164.21(6)
160.89(6)
N(1)–C(7)–C(1)
C(1)–C(7)
C(7)–C(8)
C(7)–N(1)–C(10)
O(2)–Cu(1)–N(2)
O(2)–Cu(1)–O(1)
C(17)–O(2)–Cu(1)
C(15)–N(2)–Cu(1)
C(17)–C(16)–C(15)
N(2)–C(15)–C(16)
C(15)–N(2)–C(12)
O(1)–Cu(1)–N(2)
O(2)–Cu(1)–N(1)
Cu(1)–O(2)
Cu(1)–N(2)
O(2)–C(17)
N(2)–C(15)
N(2)–C(12)
C(16)–C(17)
C(15)–C(16)
C(15)–C(22)
Fig. 6. Molecular packing in the crystal structure of 2.
in the range 250–340 nm. Based on their extinction coefficients,
⁄
⁄
these are assigned to
p ? p and n ? p ligand transitions.
are coordinated as phenolate groups, which neutralizes the 2+
II
charge of Cu . The coordination sphere of Cu1 in 1 may be described
3
3
.2. Crystal structures of the Cu(II) complexes 1 and 2
.2.1. Complex 1
as strongly distorted square planar (Fig. 2). The molecules are sta-
pled in columns along [010], as shown in Fig. 3. Selected bond
lengths and bond angles for the complex are summarized in Table 3.
1
.
Brown needles of [CuL ] HCCl
studies, were obtained from a CHCl
pound crystallizes in the monoclinic space group P2
molecules in the unit cell. An ORTEP view of 1 is shown in Fig. 1.
3
(1), suitable for X-ray diffraction
/C solution (1:1). The com-
/n with four
3
6 6
H
1
3.2.2. Complex 2
2
Reddish brown needles of [CuL ] (2), suitable for suitable for X-
ray diffraction studies, were obtained from a CH
1
2ꢁ
(
L ) acts as a tetradentate ligand. The most interesting phenome-
2 2 2
Cl /Et O solution
non observed is the fact that both of the phenol groups of the ligand
(1:1). The compound crystallizes in the triclinic space group

F. Heshmatpour et al. / Polyhedron 31 (2012) 443–450
447
Table 4
Selected bond lengths (pm) and bond angles (°) for [CuL ] (2).
The bond distances and angles are in agreement with the values
for tetracoordinate divalent copper complexes. The Cu–O(1)
(189.0(1) pm in 1 and 191.9(2) pm in 2), Cu–O(2) (188.4(1) pm in
2
Cu(1)–O(1)
Cu(1)–N(1)
O(1)–C(2)
N(1)–C(7)
N(1)–C(8)
C(1)–C(7)
1.919(2)
1.952(2)
1.297(3)
1.282(3)
1.471(3)
1.442(3)
1.429(3)
1.901(2)
1.957(2)
1.302(3)
1.283(3)
1.471(3)
1.443(3)
1.420(4)
N(1)–Cu(1)–N(2)
O(1)–Cu(1)–N(1)
C(2)–O(1)–Cu(1)
C(7)–N(1)–Cu(1)
C(2)–C(1)–C(7)
90.23(9)
93.36(8)
126.2(2)
126.1(2)
123.0(2)
124.9(2)
119.3(2)
93.53(8)
92.59(8)
127.8(2)
125.8(2)
123.3(2)
125.2(2)
118.5(2)
151.69(9)
159.98(9)
1
and 190.1(2) pm in 2), Cu–N(1) (196.1(1) pm in
1 and
1
95.2(2) pm in 2) and Cu–N(2) (196.2(1) pm in 1 and 195.7(2) pm
in 2) distances are comparable with the corresponding Cu–O
1
(
190 pm) and Cu–N (imine) (194 pm) distances in [Cu(L H
2
)]
N(1)–C(7)–C(1)
C(1)–C(2)
C(7)–N(1)–C(8)
(ClO
4
)
1.25Cl0.75ꢀ1.25H
2
O [81], Cu–O (188 pm) and Cu–N (193 pm)
)]ClO [82], Cu–O (190 pm) and Cu–N (195 pm)
4
Cu(1)–O(2)
Cu(1)–N(2)
O(2)–C(13)
N(2)–C(11)
N(2)–C(10)
C(11)–C(12)
C(12)–C(13)
O(2)–Cu(1)–N(2)
O(2)–Cu(1)–O(1)
C(13)–O(2)–Cu(1)
C(11)–N(2)–Cu(1)
C(13)–C(12)–C(11)
N(2)–C(11)–C(12)
C(11)–N(2)–C(10)
O(1)–Cu(1)–N(2)
O(2)–Cu(1)–N(1)
distances in [Cu(L
distances in [CuL ] [83]. The bond lengths and angles within the
coordinated ligand are closed to the expected values.
2
3
3.3. Catalytic activity studies
The oxidation of cyclooctene and styrene using tert-butyl
hydroperoxide (TBHP) did not proceed in the absence of catalyst
under mild or reflux conditions. Therefore the oxidation of styrene
and cyclooctene was carried out with the complexes as catalysts,
and in a series of controlled experiments we evaluated the influ-
ence of several solvents and various oxygen donors.
Table 5
Oxidation of styrene catalyzed by CuL and CuL2 using different oxygen donors in
1
CHCl3.a
Conversion (%)b
TOF (h )c
ꢁ1
Entry
Oxidant
3.3.1. Oxidation of styrene
CuL1
CuL2
The selective oxidation of styrene to benzaldehyde was carried
1
2
out with CuL and CuL as catalysts using different oxidants, and
the results are presented in Table 5. With H , urea hydrogen per-
oxide (UHP) and NaIO no significant product formation was ob-
1
2
3
4
NaIO
4
2 2
O
H
2
O
2
5
4
100
4
4
100
12.5
12.5
134.3
Urea hydrogen peroxide
tert-Butyl hydroperoxide
4
served, but using tert-butyl hydroperoxide 100% conversion was
obtained. Production of benzaldehyde in the oxidation of styrene
may be due to the further oxidation of the epoxide formed with
the tert-butyl hydroperoxide [84].
a
The molar ratios for Cat.:Styrene:Ox are 0.032:10:30. The reactions were per-
formed in chloroform under air at reflux.
b
The GC yields (%) are measured relative to the starting styrene after 6 h.
Turnover frequency (TOF) = [mol of epoxide/(mol of catalyst)] per hour.
c
The styrene conversion was found to be strongly dependent on
the solvent nature. Accordingly, different solvents were tested in
the oxidation of styrene in the presence of a catalytic amount of
1
2
ꢀ
CuL and CuL (Figs. 7 and 8) and maximum conversion was ob-
tained in the chloroform.
P1 with two molecules in the unit cell. An ORTEP drawing of 2 is
shown in Fig. 4. The quadridentate ligand, H
2
2
L , is doubly deproto-
II
nated (at the phenolate oxygen atoms) and bind Cu through two
oxygen phenolate atoms and two iminic nitrogen atoms. In addi-
tion, a weak contact Cu1–Br1a of 346.6(1) pm can be observed.
This influences the coordination sphere of Cu1 (Fig. 5). A strongly
distorted square pyramidal arrangement of the ligands around
Cu1 is the result. The molecules in 2 are packed in layers parallel
to (100) (Fig. 6). Selected bond lengths and bond angles for 2 are
collected in Table 4.
3.3.2. Oxidation of cyclooctene
Oxidation of cyclooctene with TBHP gave cyclooctene oxide as
the sole product. The results for the oxidation of cyclooctene
1
2
catalyzed by CuL and CuL in various solvents are presented in
Figs. 9 and 10. Four different solvents (chloroform, dichlorometh-
ane, acetonitrile and 1,2-dichloromethane) were used, and the
maximum conversion was obtained in acetonitrile. A comparison
Fig. 7. Effect of solvent on the oxidation of styrene with TBHP in the presence of [CuL1].

4
48
F. Heshmatpour et al. / Polyhedron 31 (2012) 443–450
Fig. 8. Effect of solvent on the oxidation of styrene with TBHP in the presence of [CuL2].
Fig. 9. Effect of solvent on the oxidation of cyclooctene with TBHP in the presence of [CuL1].
Fig. 10. Effect of solvent on the oxidation of cyclooctene with TBHP in the presence of [CuL2].

F. Heshmatpour et al. / Polyhedron 31 (2012) 443–450
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binuclear Cu
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containing two ONNO type Schiff bases, [bis(2-hydroxy-propio-
0
1
phenone)2,2 -dimethylpropan-diamine] (H
2
L ) and [bis(5-bromo-
0
2
salicylaldehyde)2,2 -dimethyl-propandiamine] (H
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1
2
crystallizes in the monoclinic space group P2
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ꢀ
in 1 is described as strongly distorted square planar. In 2, a weak
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sphere of Cu1, and a strongly distorted square pyramidal arrange-
ment of the ligands around Cu1 is the result. The oxidation of sty-
rene and cyclooctene was carried out with the complexes as
catalysts. We evaluated the influence of several solvents and vari-
ous oxygen donors. In the oxidation of styrene and cyclooctene in
the presence of a catalytic amount of CuL and CuL , the maximum
conversion was obtained respectively with chloroform and aceto-
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Acknowledgement
(
[
The financial support of this work by K.N. Toosi University of
Technology research council is acknowledged.
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Appendix A. Supplementary data
(
CCDC 833742 and 833743 contain the supplementary crystallo-
graphic data for complexes 1 and 2. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
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