M.R. Maurya et al. / Inorganica Chimica Acta 440 (2016) 172–180
173
OH
precipitation of brown solid. The precipitate was filtered, washed
with methanol and dried over silica gel.
OH
OH
O
O
O
N
N
N
Data for [WVIO2(hap-nah)] (3): Yield: 0.528 g (56%). Anal. Calc.
for C14H11N3O4W (469): C, 35.85, H, 2.36; N, 8.96, Found: C,
35.57; H, 2.28; N, 8.66%.
N
N
H
N
H
N
H
N
H2hap-bhz (II)
H2hap-nah (I)
H2hap-inh (III)
Data for [WVIO2(hap-bhz)] (4): Yield: 0.665 g (71%). Anal. Calc. for
Scheme 1. Structures of ligands selected for this study.
C15H12N2O4W (468): C, 38.49; H, 2.58; N, 5.98. Found: C, 38.21; H,
2.50; N, 5.77%.
Complexes [WVIO(O2)(hap-inh)(MeOH)] and [WVIO2(hap-nah)]
(mentioned in Section 2.1) are numbered 5 and 6, respectively,
for simplicity. X-ray diffraction quality crystals for 5 were grown
by slow evaporation of its methanolic solution.
chloride and hydrazine hydrate (Loba Chemie, India) were used as
obtained. Benzoylhydrazide [22], tungstic acid (WO3ꢁH2O) [13–16],
ligands, H2hap-nah (I) H2hap-bhz (II) and H2hap-inh (III) [23,24],
and complexes, [WVIO(O2)(hap-inh)(MeOH)] and [WVIO2(hap-
inh)] [25] were prepared as reported in the literature. All other
chemicals and solvents employed were of analytical reagent grade
and used without further purification.
2.4. X-ray crystal structure determination
Three-dimensional X-ray data were collected on a Bruker Kappa
Apex CCD diffractometer at room temperature for 2 and 5 by the
2.2. Instrumentation and characterization procedure
/–x
scan method. Reflections were measured from a hemisphere
. A
of data collected from frames, each of them covering 0.3° in
x
CHN elemental analysis of ligands and complexes were deter-
mined on an Elementar analyzer Vario-EL-III. IR Spectra were
recorded as transparent KBr pellet, prepared by grinding the sam-
ple with KBr, on a Nicolet NEXUS Aligent 1100 FT-IR spectrometer.
UV–Vis spectra of ligands and complexes were recorded in DMSO
on a Shimadzu 1601 UV–Vis spectrometer. 1H and 13C NMR spectra
were obtained in DMSO-d6 using TMS as an internal standard on
Bruker Avance III 500 MHz spectrometer. Thermogravimetric anal-
ysis was carried out using TG Stanton Redcroft STA 780. Catalytic
reaction products were analyzed on a Shimadzu 2010 plus gas-
total of 49180 reflections for 2 and 19980 for 5 were measured
and all of them were corrected for Lorentz and polarization effects
and for absorption by multi-scan methods based on symmetry-
equivalent and repeated reflections. Out of these reflections,
9134 in 2 and 2163 in 5 independent reflections exceeded the sig-
nificance level (|F|/r|F|) > 4.0. After data collection, in each case an
multi-scan absorption correction (SADABS) [26] was applied, and the
structures were solved by direct methods and refined by full
matrix least-squares on F2 data using SHELX suite of programs
[27]. Hydrogen atoms were included in calculated positions and
refined in the riding mode in the two crystals, except for O(2M)
in compound 2, which was located in a difference Fourier map
and left to refine freely and after DFIX restraint was applied to
fix the HAO distance (see Table 3). Refinements were done with
allowance for thermal anisotropy of all non-hydrogen atoms. For
2, the absolute configuration has been established by refinement
of the enantiomorph polarity parameter [x = 0.466(7)] [28]. A
final difference Fourier map showed no residual density in 5:
0.998 and ꢀ0.544 e Åꢀ3 and high residual electron density in 2:
2.723 and ꢀ1.090 e Åꢀ3, next to W atoms. A weighting scheme
chromatograph fitted with
a
Rtx-1 capillary column
(30 m ꢂ 0.25 mm ꢂ 0.25
l
m) and a FID detector, and their quan-
tifications were made on the basis of the relative peak area of
the respective product. The identity of the products was confirmed
using a Perkin–Elmer Clarus 500 GC–MS and 1H NMR instruments.
2.3. Preparations
2.3.1. [WVIO(O2)(hap-nah)(MeOH)] (1) and [WVIO(O2)(hap-bhz)
(MeOH)] (2)
w = 1/[r 5 and w = 1/[r
2(F2o) + (0.0184P)2 + 4.2092P] for 2(F2o) +
These complexes were prepared following the method reported
for [WVIO(O2)(hap-inh)(MeOH)] [25]. WO3ꢁH2O (1.249 g, 5 mmol)
was dissolved in aqueous 30% H2O2 (20 mL) and stirred at room
temperature for 5 h. The obtained clear light yellow solution was
filtered and to this a methanolic solution (30 mL) of appropriate
ligand (5 mmol) was added with stirring. After few hours yellow
solid slowly separated which was filtered, washed with cold
methanol (2 ꢂ 2 mL) and dried in desiccator over silica gel.
Data for [WVIO(O2)(hap-nah)(MeOH)] (1): Yield: 1.48 g (57%).
Anal. Calc. for C15H15N3O6W (517): C, 34.84, H, 2.92; N, 8.13.
Found: C, 34.46; H, 2.76; N, 8.04%.
(0.0138P)2 + 5.4274P] for 2, where P = (|Fo|2 + 2|Fc|2)/3, were used
in the latter stages of refinement. Further details of the crystal
structure determination are given in Table 1.
2.5. Catalytic activity study: oxidative bromination of thymol
All complexes were used as potential catalysts for the oxidative
bromination of thymol under the appropriate condition. All reac-
tions were carried out in a 50 mL round bottom flask at room
temperature.
Thymol (1.50 g, 10 mmol), 30% aqueous H2O2 (2.27 g, 20 mmol),
KBr (2.38 g, 20 mmol), and catalyst (0.002 g, 3.87 ꢂ 10ꢀ3 mmol)
were mixed in a flask containing 20 mL water and stirred at room
temperature. The 70% HClO4 (2.86 g, 20 mmol) was added in four
equal portions at 30 min intervals). After 3 h, the reaction products
were extracted using diethyl ether, dried over anhydrous Na2SO4,
filtered and analyzed quantitatively by gas chromatograph. The
confirmation of products was carried out by GC–MS.
Data for [WVIO(O2)(hap-bhz)(MeOH)] (2): Yield: 1.68 g (65%).
Anal. Calc. for C16H16N2O6W (516): C, 37.23; H, 3.12; N, 5.43.
Found: C, 37.42; H, 3.04; N, 5.27%. Orange crystal for 3 were
obtained in methanol by slow evaporation.
2.3.2. [WVIO2(hap-nah)] (3) and [WVIO2(hap-bhz)] (4)
These complexes were prepared from the corresponding oxi-
doperoxido complexes by the method reported in literature [25].
A representative example is given here. Oxidoperoxido complex
[WVIO(O2)(hap-nah)(MeOH)] (1) (1.03 g, 2 mmol) was dissolved
in 3:5 ratio of DMF–methanol (10 mL) and to this was added a
methanolic solution (5 mL) of PPh3 (0.65 g, 2.5 mmol). The result-
ing mixture was heated in oil bath for 30 h at ca. 65 °C and then
cooled to room temperature. After removing the solvent volume
to ca. 5 mL, 5 mL methanol was introduced which resulted in the
3. Results and discussion
3.1. Synthesis and characterization of complexes
Synthesis and partial characterization of complexes [WVIO(O2)
(hap-inh)(EtOH)] (5a) and [WVIO2(hap-inh)] (6) have been