M. Maiti et al.
Bull. Chem. Soc. Jpn. Vol. 87, No. 6 (2014)
725
¹
1
1
3
(
148, ꢀ 4ꢀ 1081, ν(CoN) 459 cm . ESI-MS. m/z [Co(L )-
HL )] = 844.
ðClO
Þ
2
+
Physical Measurements.
The FT-IR spectra of the
compounds were recorded on a Perkin-Elmer RX I FT-IR
¹
1
spectrometer with KBr pellets in the range 4000400 cm . The
electronic spectra were recorded at 300 K on a Perkin-Elmer
Lambda 40 (UVvis) spectrometer using HPLC grade aceto-
nitrile as solvent in the range 800200 nm. Elemental ana-
lyses were carried out on a Perkin-Elmer 2400 II Elemental
Analyzer. Electrochemical studies were performed on a
VersaStat-PotentioStat II cyclic voltammeter using HPLC
grade acetonitrile as solvent where tetrabutylammonium per-
chlorate was used as supporting electrolyte at different scan
rates. Platinum and saturated calomel (SCE) were the working
and the reference electrodes in the process, respectively. Mass
spectra of both the complexes were analyzed in a Qtof Micro
YA263 mass spectrometer. HPLC experiments were performed
with a Varian ProStar chromatograph equipped with DAD 335
detector using a Varian Microsorb-MV 1005 C18 column
Figure 1. Perspective view of the di- and mono-condensed
Schiff base ligands.
emphasis on the catalytic efficiency and structurefunction
correlation in alkene epoxidation with respect to the octahedral
Co(III) complex, where the salen ligand adopts a different
configuration.
(
250 © 4.6 © 1/4”), with a Zeltec thermostatted heater. Sam-
Experimental
ples were eluted with a 70:30 acetonitrile/methanol mixture at
¹1
Syntheses. All chemicals and solvents employed for the
syntheses were of analytical grade and used as received with-
out further purification. 5-Bromo-o-vanillin (i.e., 5-bromo-2-
hydroxy-3-methoxybenzaldehyde) and 1,3-propylenediamine
a flow rate of 0.4 mL min at 40 °C. Under these experimental
conditions, retention times tR were as it follows: styrene (tR =
7.88 min), styrene epoxide (t = 7.17 min), cis-stilbene (t =
R
R
8.51 min), cyclohexene (t = 9.47 min), cyclohexene oxide
R
(
i.e., 1,3-diaminopropane) were purchased from Aldrich
(t = 7.13 min), trans-4-octene (t = 11.39 min). Calibration
R
R
Chemical Co. Copper(II) acetate monohydrate was purchased
from Loba. Cobalt(II) perchlorate hexahydrate was prepared by
the treatment of cobalt carbonate (E. Merck, India) with 80%
perchloric acid (E. Merck, India) followed by slow evapora-
tion. It was then filtered through a fine glass-frit and preserved
curves of authentic alkene and product samples were used
to quantify the alkene conversion and product selectivity. At
least two independent experiments were performed for each set
of reaction conditions. Blank experiments with the oxidant
using the same experimental conditions except catalyst were
performed. Alkene conversion in absence of the complex was
05%.
in CaCl desiccator. Caution! Perchorate salts are potentially
2
explosive and should be handled with much care and in small
amount, though no problem was accounted.
Crystal Data Collection and Refinement. Intensity data
of 1 were collected at 293 K using Mo Kα radiation ( =
0.71069 ¡) with an Oxford Diffraction Gemini diffractometer,
while the data collection of 2 was carried out on a rotating
anode diffractometer equipped with Kappa-CCD plate and
1
1
Synthesis of [Cu(L )]¢H O (1).
The ligand H L was
2
2
40
prepared following a method reported in literature. Cu(CH3-
COO) ¢H O (0.199 g, 1 mmol) was dissolved in 20 mL of
2
2
MeOH followed by the addition of 10 mL of yellow methanolic
1
41
solution of H2L (1 mmol, 0.502 g). The mixture was stirred for
Cu Kα radiation ( = 1.54178 ¡). CrysAlis RED and Denzo/
4
2
3
0 min at 40 °C. The dark green solution was kept in a refrig-
Scalepack programs were used for data reduction of 1 and 2,
respectively. The structures were solved by direct methods
erator at 16 °C. After one day brown needle-shaped single
crystals suitable for X-ray diffraction were obtained. Yield:
4
3
44
using the program SIR97 and SHELXS-97 and refined by
4
5
0
.493 g (85%). Elemental analysis. Found: C, 39.38; H, 3.40;
full-matrix least-squares methods with programs CRYSTALS
and SHELXL-97 for 1 and 2, respectively. The ¦ Fourier
4
4
N, 4.79%. Calcd for C H Br Cu N O (579.73): C, 39.36;
19
20
2
1
2
5
H, 3.48; N, 4.83%. FT-IR bands. ν
1610, ꢀðCOPhenolicÞ 1226,
map of 2 revealed the presence of a lattice CH CN molecule.
(
C=N)
3
¹
1
1
ν(CuN) 438 cm . ESI-MS. m/z [Cu(L )] = 562.
Being this molecule rather disordered, it was refined with
restrained thermal parameters. All the H atoms were generated
geometrically and included in the final cycles of refinement
with the riding model approximation. Selected crystallog-
raphic data, experimental conditions, and relevant features of
the structural refinements for the structures of 1 and 2 are
summarized in Table S1 and Table 1, respectively.
Crystallographic data have been deposited with Cambridge
Crystallographic Data Centre: Deposition number CCDC-
Centre, 12, Union Road, Cambridge, CB2 1EZ, U.K.; Fax:
+44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk).
1
2
Synthesis of [Co(L )(HL )]ClO4¢CH3CN (2). Co(ClO4)2¢
H O (1 mmol, 0.366 g) was dissolved in 10 mL of CH CN.
0 mL of methanolic solution of the Schiff base H L (2 mmol,
.004 g) was added to this solution. The mixture was stirred for
0 min at a temperature of 40 °C. Then the resulting dark brown
6
1
1
3
2
3
1
2
solution was kept at room temperature. Orange square-shaped
single crystals suitable for X-ray diffraction were obtained
within two days. Here, the ligand HL (Figure 1) has not been
2
prepared separately; rather it is formed in situ by the hydrolytic
1
cleavage of H L . Yield: 0.709 g (72%). Elemental analysis.
2
Found: C, 38.90; H, 3.62; N, 7.09%. Calcd for C H Br -
3
2
36
3
Cl Co N O (984.77): C, 39.03; H, 3.68; N, 7.11%. FT-IR
1
1
5
10
bands. ν(C=N) 1591, ꢀðCOPhenolicÞ 1234, ν(OH) 3432, ν(NH) 3232