Catalytic oxidation of internal and terminal alkenes by oxidoperoxidomolybdenum(VI) and dioxidomolybdenum(VI) complexes

Article abstract of DOI:10.1016/j.ica.2015.01.040

Reaction of oxidoperoxidomolybdenum(VI) species, generated in situ by the reaction of MoO₃ in the presence of H₂O₂, with three Schiff bases H₂hap-inh (I), H₂hap-nah (II) and H₂hap-bhz (III), (derived from the condensation of 2-hydroxyacetophenone with isonicotinoylhydrazide, nicotinoylhydrazide and benzoylhydrazide) results in the formation of oxidoperoxidomolybdenum(VI) complexes, [MoO(O₂)(hap-inh)(MeOH)] (1), [MoO(O₂)(hap-nah)(MeOH)] (2) and [MoO(O₂)(hap-bhz)(MeOH)] (3), respectively. Their dioxidomolybdenum(VI) analogues [MoO₂(hap-inh)]_n (4) [MoO₂(hap-nah)(MeOH)] (5) and [MoO₂(hap-bhz)(MeOH)] (6) have also been prepared by reacting equimolar ratio of [MoO₂(acac)₂] and corresponding ligands. These complexes have been characterized in the solid state as well as in solution namely by spectroscopic techniques (IR, electronic, ¹H and ¹³C NMR), elemental and thermogravimetric analysis. Structures of complexes 3, 4, and 6a ([MoO₂(hap-bhz)(DMSO)]) have been confirmed by single crystal X-ray study which reveals that ligands behave as a dibasic tridentate coordinating through ONO functionalities. Sodium bicarbonate assisted oxidation of styrene and cyclohexene using 30% H₂O₂ as oxidant has been carried out using these catalysts. Under the optimized reaction conditions styrene gave mainly styrene oxide and minor amount of phenylacetaldehyde. Oxidation of cyclohexene gave cyclohexene epoxide selectively. The corresponding dioxidomolybdenum(VI) complexes have relatively lower catalytic activities.

Full text of DOI:10.1016/j.ica.2015.01.040

Accepted Manuscript
Catalytic oxidation of internal and terminal alkenes by oxidoperoxidomolyb-
denum(VI) and dioxidomolybdenum(VI) complexes
Mannar R. Maurya, Lata Rana, Fernando Avecilla
PII:
S0020-1693(15)00076-6
http://dx.doi.org/10.1016/j.ica.2015.01.040
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Reference:
Inorganica Chimica Acta
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Please cite this article as: M.R. Maurya, L. Rana, F. Avecilla, Catalytic oxidation of internal and terminal alkenes
by oxidoperoxidomolybdenum(VI) and dioxidomolybdenum(VI) complexes, Inorganica Chimica Acta (2015), doi:
http://dx.doi.org/10.1016/j.ica.2015.01.040
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Catalytic oxidation of internal and terminal alkenes by
oxidoperoxidomolybdenum(VI) and dioxidomolybdenum(VI) complexes
Mannar R. Maurya a,*, Lata Rana a, Fernando Avecilla b
a Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India
bDepartamento de Química Fundamental, Universidade da Coruña, Campus de A Zapateira,
15071 A Coruña, Spain
Keywords: Tridentate ONO Donor Schiff base Ligands; Molybdenum(VI) complexes; NMR
spectroscopy; Oxidation of styrene; Oxidation of cyclohexene.
__________
* Corresponding author. Tel.: +91 1332 285327; fax: +91 1332 273560.
E-mail address: rkmanfcy@iitr.ac.in (M.R. Maurya).
1

Abstract
Reaction of oxidoperoxidomolybdenum(VI) species, generated in situ by the reaction
of MoO3 in the presence of H2O2, with three Schiff bases H2hap-inh (I), H2hap-nah (II) and
H2hap-bhz (III), (derived from the condensation of 2-hydroxyacetophenone with
benzoylhydrazide, nicotinoylhydrazide and isonicotinoylhydrazide ) results in the formation
of
oxidoperxidomolybdenum(VI)
complexes,
[MoO(O2)(hap-inh)(MeOH)]
(1),
[MoO(O2)(hap-nah)(MeOH)] (2) and [MoO(O2)(hap-bhz)(MeOH)] (3), respectively. Their
dioxidomolybdenum(VI) analogues [MoO2(hap-inh)]n (4) [MoO2(hap-nah)(MeOH)] (5) and
[MoO2(hap-bhz)(MeOH)] (6) have also been prepared by reacting equimolar ratio of
[MoO2(acac)2] and corresponding ligands. These complexes have been characterized in the
solid state as well as in solution namely by spectroscopic techniques (IR, electronic,1H and
13C NMR), elemental and thermogravimetric analysis. Structures of complexes 3, 4, and 6a
([MoO2(hap-bhz)(DMSO)]) have been confirmed by single crystal X-ray study which
reveals that ligands behave as a dibasic tridentate coordinating through ONO functionalities.
Sodium bicarbonate assisted oxidation of styrene and cyclohexene using 30 % H2O2 as
oxidant has been carried out using these catalysts. Under the optimized reaction conditions
styrene gave mainly styrene oxide and minor amount of phenylacetaldehyde. Oxidation of
cyclohexene
gave
cyclohexene
epoxide
selectively.
The
corresponding
dioxidomolybdenum(VI) complexes have relatively lower catalytic activities.
1. Introduction
During catalytic oxidation of organic substrates by molybdenum complexes in the
presence of a cleaner industrial oxidant H2O2, the oxidoperoxido species have mostly been
considered as intermediate responsible for the oxygen transfer, irrespective of the Mimoun or
Sharpless pathways of the reaction mechanism [1,2]. Catalytic oxidation by
peroxidomolybdenum(VI) {[MoO(O2)]2+} complexes, therefore, must show better results
than their corresponding dioxomolybdenum(VI) {[MoO2]2+} analogues because dioxido
complexes may not form peroxido species instantly during catalytic cycle in the presence of
oxidant H2O2 while peroxido complexes already present in the activated intermediate form
may proceed instantly. Such generalization cannot be predicted for the catalytic reaction
where tert-butylhydroperoxide is used as an oxidant because catalytic reactions follow
different mechanism. In fact, a peroxido complex [MoO(O2)(sal-phz)(MeOH)] (H2sal-phz =
salicylidene 2-picoloyl hydrazone) was found inert towards catalytic activity for the
epoxidation of olefins using tert-butylhydroperoxide while the dioxidomolybdenum(VI)
2

analogue was found active [3]. On the other hand complex [MoO(O2)(sal-bhz)(MeOH)]
(H2sal-bhz = salicylidene 2-benzoylhydrazone ) showed efficient catalytic activity for the
epoxidation of olefins [4] in the presence of NaHCO3 using H2O2 as terminal oxidant. Our
experience is that [MoO2]2+ as well as [MoO(O2)]2+ complexes are, in general, moderate
catalysts particularly for the oxidation reactions [5-8] in spite of the fact that molybdenum
complexes are well known for their catalytic applications in the oxidation [9–19] and
oxidative bromination of organic substrates [5,20–23], and the oxidation of sulfides [24–26].
However, their catalytic efficiency for oxidation reaction could be enhanced by adding
NaHCO3 as an additive (not as co-catalyst), in the presence of H2O2 as terminal oxidant.
Additive NaHCO3 efficiently enhances the formation of oxidoperoxidomolybdenum(VI)
intermediate during catalytic cycle [4,8,27,28].
Earlier, we reported dioxidomolybdenum(VI) complexes and tested them as catalysts
in the oxidation and oxidative bromination of organic substrates using H2O2 as terminal
oxidant [8,22,23]. The great applicability of molybdenum complexes prompted us to prepare
oxidoperoxidomolybdenum(VI) complexes of ligands I, II and III (Scheme 1). We have also
prepared the corresponding dioxidomolybdenum(VI) complexes of these ligandsto compare
their catalytic potentials.
<<Scheme 1>>
2.Experimental
2.1 Materials
MoO3, nicotinoylhydrazide, isonicotinoylhydrazide (S.D. fine, India), aqueous 30%
H2O2 (Qualizens, India), ammonium molybdate, benzoyl chloride, hydrazine hydrate (Loba
Chemie, India), acetylacetone (Hacac), styrene (Acros organics, USA) and cyclohexene
(Aldrich Chemicals, USA) were used as obtained. Benzoyl hydrazide was prepared from
methyl benzoate by standard procedure. [MoO2(acac)2] was prepared following the method
reported in literature [29]. All other chemicals and solvents used were of AR grade.
2.2 Instrumental and Characterization procedure
Elemental analyses of ligands and complexes were carried out by an Elementar model
Vario-EL-III. IR Spectra were recorded as KBr pellet on a Nicolet NEXUS Aligent 1100 FT-
IR spectrometer after grinding sample with KBr. Electronic spectra were recorded in DMSO
1
on a Shimadzu 1601 UV-Vis spectrometer. H and 13C NMR spectra were obtained on a
3

Bruker Avance III 500 MHz spectrometer. NMR spectra were usually recorded in DMSO-d6
using TMS as an internal standard. Thermogravimatric analysis was carried out under oxygen
atmosphere using TG Stanton Redcroft STA 780. A Shimadzu 2010 plus gas-chromatograph
fitted with a Rtx-1 capillary column (30 m × 0.25 mm × 0.25 µm) and a FID detector was
used to analyze the catalytic reaction products and their quantifications were made on the
basis of the relative peak area of the respective product. The identity of product(s) was
confirmed by comparing with standard sample as well as using a GC-MS Perkin-Elmer,
model Clarus 500 and comparing the fragments of each product with the library available.
2.3Preparations
2.3.1. H2hap-inh (I), H2hap-nah (II) and H2hap-bhz (III)
Ligands H2hap-inh (I), H2hap-nah (II) and H2hap-bhz (III) were prepared using
procedure described by Prabhakaran et al. [30].
Data of H2hap-inh (I): Yield 91.8%. Anal. Calc. for C14H13N3O2 (255): C, 65.87; H, 5.13; N,
16.46. Found C, 65.43; H, 4.94; N, 16.92%.
Data of H2hap-nah (II): Yield 70%. Anal. Calc. for C14H13N3O2 (255): C, 65.87; H, 5.13; N,
16.46. Found C, 65.04; H, 4.92; N, 16.67%.
Data of H2hap-bhz (III): Yield 75.5%. Anal. Calc. for C15H14N2O2 (254): C, 70.85; H, 5.55;
N, 11.02. Found C, 71.56; H, 5.45; N, 11.38%.
2.3.2. [MoO(O2)(hap-inh)(MeOH)] (1)[31]
MoO3 (0.28 g, 2 mmol) was suspended in aqueous 30% H2O2 (5 mL) and stirred for 5
h to give clear light yellow solution. It was filtered and added to a methanolic solution (10
mL) of H2hap-inh (0.51 g, 2 mmol) with stirring. After 2 h of stirring the excess solvent was
evaporated by passing air to it where orange solid slowly precipitated. This was filtered,
washed with cold methanol (2 × 2 mL) and dried in air. Yield 0.645 g (75%). Anal. Calc. for
C15H15N3O6Mo (429): C, 41.97; H, 3.52; N, 9.79. Found C, 41.8; H, 3.4; N, 9.7%.
2.3.3.[MoO(O2)(hap-nah)(MeOH)] (2) and [MoO(O2)(hap-bhz)(MeOH)] (3)
These complexes were prepared from respective ligand using procedure outlined for
1.
Data for [MoO(O2)(hap-nah)(MeOH)] (2): Yield 0.50 g (64%). Anal. Calc. for
C15H15N3O6Mo (429): C, 41.97; H, 3.52;N, 9.79. Found C, 42.0; H, 3.4; N, 9.6.
4

Data for [MoO(O2)(hap-bhz)(MeOH)] (3): Yield 0.695 (81%). X-ray diffraction quality
crystals for 3 were obtained by slow evaporation of its methanolic solution in air. Anal. Calc.
for C16H16MoN2O6 (428): C, 44.87; H, 3.77; N, 6.54. Found C, 44.7; H, 3.6; N, 6.6%.
2.3.4.Preparations of [MoO2(hap-inh)]n (4), [MoO2(hap-nah)(MeOH)] (5) and [MoO2(hap-
bhz)(MeOH)](6).
Complexes [MoO2(hap-inh)]n (4), [MoO2(hap-nah)(MeOH)] (5) and [MoO2(hap-
bhz)(MeOH)] (6) were prepared by a general method [30]; the preparation of [MoO2(hap-
inh)] (4) is described here. A solution of [MoVIO2(acac)2] (0.66 g, 2 mmol) dissolved in 10
mL of methanol was added to a stirred solution ofH2hap-inh (0.51 g, 2 mmol) in methanol
(20 mL) and the obtained reaction mixture was refluxed on a water bath for 6 h. After
reducing the solvent volume to ca. 10 mL it was kept at room temperature whereupon a
yellow solid slowly separated. This was filtered, washed with methanol and dried in a
vacuum desiccator over silica gel. X-ray diffraction quality crystals for 4 and [MoO2(hap-
bhz)(DMSO)] (6a) were obtained by slow evaporation of its DMSO solution in air.
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 3, 4 and 6a by the φ-ω scan method. Reflections were
measured from a hemisphere of data collected from frames, each of them covering 0.3º in ω.
Of the 28233 for 3, 37489 for 4 and 23631 for 6a reflections were measured, all were
corrected for Lorentz and polarization effects and for absorption by multi-scan methods based
on symmetry-equivalent and repeated reflections, 7733, 3845 and 3153 respectively,
independent reflections exceeded the significance level (F/σF) > 4.0. Complex
scattering factors were taken from the program package SHELXTL [32]. The structures were
solved by direct methods and refined by full matrix least-squares on F2. In 3, hydrogen atoms
were located in difference Fourier map and left to refine freely, except for C(16), C(24), and
C(32), which were included in calculation position and refined in the riding mode. In 4,
hydrogen atoms were located in difference Fourier map and left to refine freely, except for
C(8), which were included in calculation positions and refined in the riding mode.
Refinements were done with allowance for thermal anisotropy of all non-hydrogen atoms. In
6a, hydrogen atoms were located in difference Fourier map and left to refine freely, except
for C(1S), C(2S), C(3), C(4), C(5) and C(9), which were included in calculation positions and
refined in the riding mode. A final difference Fourier map showed no residual density
5

outside: 0.697 and -0.530 e.Å–3 for 3, 0.444 and -0.439 e.Å–3 for 4, 0.666 and -0.761e.Å–3 for
2
2
6a. A weighting scheme w = 1/[σ2(Fo ) + (0.035100 P)2 + 0.779800 P] for 3, w = 1/[σ2(Fo ) +
2
(0.052800 P)2 + 0.345400 P] for 4 and w = 1/[σ2(Fo ) + (0.062400 P)2 + 1.423400 P] for 6a,
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.
<<Table 1>>
2.5.Catalytic activity studies
2.5.1. Oxidation of styrene
In a typical reaction, styrene (0.52 g, 5 mmol); aqueous 30% H2O2 (2.27 g, 20 mmol),
NaHCO3 (0.168 g, 2 mmol) and catalyst (0.0005 g) were taken in acetonitrile (5 mL) in a two
o
necked round bottom flask and temperature of the reaction was set at 60 C. The reaction
mixture was stirred slowly and was monitored by withdrawing few drops of the reaction
mixture at every 30 min interval and analysing quantitatively by gas chromatograph equipped
with a FID detector. Different parameters such as amount of oxidant, catalyst, NaHCO3,
volume of solvent and temperature were studied to see their effect on the conversion of
styrene and selectivity of reaction products.
2.5.2. Oxidation of cyclohexene
Cyclohexene (0.410 g, 5 mmol), aqueous 30% H2O2 (2.27 g, 20 mmol), NaHCO3
(0.084 g, 1 mmol) and catalyst (0.0005 g) were taken in acetonitrile (5mL). The temperature
o
of the reaction was set at 60 C and the reaction mixture was stirred slowly for ca. 2 h. At
every 30 min, small aliquots of the reaction mixture were withdrawn and analysed
quantitatively by gas chromatograph. Different parameters such as amount of oxidant,
catalyst, NaHCO3, volume of solvent and temperature of the reaction mixture were studied to
see their effect on the conversion of cyclohexene and selectivity of reaction products.
3. Result and discussion
3.1. Synthesis and characterization of complexes
Synthesis and characterization of complex [MoO(O2)(hap-inh)(H2O)] has been
reported earlier by the reaction of in situ generated (non isolable) aqueous
oxidoperoxidomolybdenum species with H2hap-inh (I) in ethanol at room temperature.
Similar synthesis of oxidoperoxidomolybdenum(VI) complexes of ligands H2hap-inh (I),
6

H2hap-nah (II) and H2hap-bhz (III) in methanol followed by their crystallization from
methanol gave [MoO(O2)(hap-inh)(MeOH)] (1), [MoO(O2)(hap-nah)(MeOH)] (2) and
[MoO(O2)(hap-bhz)(MeOH)] (3), respectively. Syntheses of dioxidomolybdenum(VI)
complexes [MoO2(hap-inh)]n (4), [MoO2(hap-nah)(MeOH)] (5) and [MoO2(hap-
bhz)(MeOH)] (6) by the reaction of [MoO2(acac)2] with the respective ligand have been
reported in the literature and are straight forward [30]. However, their single crystal X-ray
structures are not reported.
Scheme 2 provides structures of the complexes which are based on the spectroscopic
(IR, UV/Vis, 1H and 13C NMR) data, elemental analyses, TGA and X-ray diffraction study of
3. As dioxido complexes are reported in the literature [30], characterization details of these
1
are not considered here (See SI section for Fig. S1 for H NMR of 5). However, the single
crystal X-ray study of complexes 4 and 6a ([MoO2(hap-bhz)(DMSO)]) are reported here.
<<Scheme 2>>
3.2. Thermogravimatric analysis
Thermogravimetric analysis of [MoO(O)2]2+ complexes 1, 2 and 3 has been studied
under an oxygen atmosphere. Representative profiles are presented in Figs. S2 and S3 (See SI
section). Initial phase of all three complexes have different trends of decomposition. Complex
o
1 loses 7.8% weight at 165 C equivalent to one methanol (cal 7.46%). The anhydrous
complex on further increasing the temperature decomposes exothermically in two steps and
form MoO3 at ca. 550 oC (Found: 33.2; Calc.: 33.6%). Complex 2 loses weight equivalent to
o
one methanol at ca. 120 C. Later part of decomposition is similar to 1 and completes at ca.
o
o
540 C with the formation of MoO3. A weight loss of ca. 2% occurs at 125 C in complex 3.
Above this temperature complex starts decomposing which completes in two overlapping
o
steps with the formation of MoO3 at ca. 520 C (Found: 33.4; Calc.: 33.6%). The obtained
o
o
residue at ca. 550 C is of cream colour. Above temperature 550 C, the final product MoO3
in all three cases undergoes continuous weight loss and reaches to nearly 0% at ca. 1000 oC.
3.3. Structure descriptions of [MoO(O2)(hap-bhz)(MeOH)] (3), [MoO2(hap-inh)]n (4) and
[MoO2(hap-bhz)(DMSO)] (6a)
ORTEP diagram for the compounds [MoO(O2)(hap-bhz)(MeOH)] (3), [MoO2(hap-
inh)]n (4) and [MoO2(hap-bhz)(DMSO)] (6a) are shown in Figs. 1, 2 and 3, respectively. Fig.
7

4 shows the π-π stacking interaction present in the asymmetric unit of compound 3, which
contains two Mo complexes. Selected bond distances and angles are given in Table 2.
The structure of complex 3 is mononuclear and adopts a distorted seven-coordinated
pentagonal bipyramidal geometry with the (hap-bhz)2– ligand, which acts as tridentate,
coordinating through the one Ophenol, one Nazo and Obenzoyl atoms, and Mo centre completes
the coordination sphere bonding to one Ooxide terminal, one Omethoxy and to two Osuperoxide
atoms, O(3) and O(4). The axial sites are occupied by the oxido group O(2) and the oxygen
atom of methoxy group, O(6). The equatorial plane is slightly distorted respect to the
planarity, [mean deviation from planarity: 0.0386(9) for O(1), N(2), O(3), O(4) and O(5) and
0.0700(8) for O(7), N(4), O(9), O(10), O(11)]. The Mo-Ooxido, Mo-Operoxido and O-O bond
lengths (see Table 2) are within the ranges for the bond distances typically observed in these
types of compounds [33]. The angles between the oxido ligand and the oxygen atoms of the
peroxido group from 104.05(6) and 104.73(7)º also falling within the typically observed
range (97-108º). The distance of peroxido bond O(3)-O(4) is 1.4548(17) Å, which is in the
usual range (ca. 1.4-1.5 Å) [33]. Other bond lengths and angles are similar to those in other
published complexes.
In the complex 6a, Ophenol, Nazo and Obenzoyl atoms of the ligand, which acts as
tridentate, and two oxido groups coordinate to molybdenum centre. The equatorial plane is
formed for these three atoms of the ligand and one of the terminal oxygen atoms. One DMSO
molecule completes the coordination sphere of a distorted octahedral geometry. The
O=Mo=O angle is 105.97(13)º and Mo=O distances are 1.698(3) and 1.702(2) Å. The Mo–
O–S angle and Mo–O distance for Mo–DMSO are 125.44(13)° and 2.262(2) Å, respectively,
similar to other examples in literature [34].
The structure of 4 is more complicated. The supramolecular structure consist in
zigzag chains of complexes which are connected through the Npy atoms, which binds to next
complex of Mo (see Fig. 3), occupying the sixth position of coordination. Such Npy
coordination of inh moiety of ligand is rare [35]. The ligand acts as tridentate bonding by
Ophenol, Nazo and Obenzoyl atoms. The equatorial plane is formed for these three atoms of the
ligand and one of the terminal oxygen atoms. The other terminal oxygen and the Npy atoms
occupy the axial sites of a distorted octahedral geometry. The distance Mo-Npy [2.4444(19)
Å] is bigger than the other Mo-Nazo bond [2.267(3) Å]. The O=Mo=O angle is 105.86(9)º and
Mo=O distances are 1.6976(17) and 1.6990(17) Å.
8

The asymmetric unit of complex 3 contains two complex [MoO(O2)(hap-
bhz)(MeOH)]. The phenol groups of the two complexes interact by π-π interactions (see Fig.
4). The distance between centroids is: dc1-c2 = 3.939 Å {c1 [C(1)-C(2)-C(3)-C(4)-C(5)-C(6)],
c2 [C(17)-C(18)-C(19)-C(20)-C(21)-C(22)]}. Intermolecular hydrogen bonds are not present
in the crystal packing of the three compounds.
<<Figures 1 to 4>><<Table 2>>
3.4 FT-IR Studies
The IR spectra of the ligands exhibit a sharp band at 1604 – 1608cm–1due to ν(C=N)
(azomethine) and this band shifts to a lower wavenumber by 5-13 cm–1 in the complexes
(Table 3), thereby indicating the coordination of the azomethine nitrogen atom. Bands due to
ν(C=O) and ν(NH) stretches appear in the regions 1662-1667 and 3210-3280 cm–1,
respectively. Absence of these bands in the spectra of complexes indicates the enolisation of
the carbonyl moiety followed by replacement of H by the metal ion. A new band appearing in
the1230-1238 cm–1 region was assigned to the ν(C=O) (enolato) mode.
All peroxido complexes exhibit a sharp band at 961-970 cm–1 which is assigned due
to ν(Mo=O) stretch. In addition, they exhibit three IR active vibrational modes associated
with the peroxido moiety ([Mo(O2)]2+) at 853-859, 618-635 and 552-556 cm–1 which are
assigned due to the O–O intra stretching, asymmetric Mo(O2) stretching and symmetric
Mo(O2) stretching, respectively [36]. These bands confirmed the η2-coordination of the
peroxido group to the molybdenum.
<<Table 3>>
3.5. Electronic spectral studies
Fig. 5 reproduces UV-visible spectra of [MoO(O2)]2+ complexes and Table 4 includes
UV-visible spectral data of ligands as well as complexes. Ligands exhibit three spectral bands
at 284-287, 294-301 and 327-331 nm in the UV region. First two bands with close values
correspond possibly due to splitting of π→π* while second band belongs to n→π* transition.
All these bands also appear in the spectra of complexes with slight variations. In addition,
they also exhibit a low intensity band at 405 nm due to the transfer of charge from phenolate
oxygen atom to an empty d-orbital of the molybdenum atom (LMCT) [37].
<<Figure 5>><<Table 4>>
9

3.6. 1H NMR and 13C NMR Studies
The coordinating modes of H2hap-inh (I), H2hap-nah (II) and H2hap-bhz (III) were
1
also confirmed by comparing their H NMR spectral data with the respective complexes.
1
Table 5 presents relevant spectral data and Fig.6 reproduces H NMR spectra of H2hap-inh
1
(I) and [MoO(O2)(hap-inh)(MeOH)] (1). The H NMR spectra of ligands exhibit two signals
at δ =13.19-13.36 (s, 1H) and 11.33-11.58 (s, 1H) ppm due to phenolic OH and NH,
respectively. Absence of these signals in complexes is in conformity with the coordination of
the phenolato and enolato oxygen to the molybdenum. The appearance of a signal due to
azomethine proton with a good coordination-induced shifts [∆δ = [δ (complex) – δ (free
ligand)] (see Table 5) in complexes demonstrates the coordination of the azomethine group to
the molybdenum. All complexes register a singlet at 3.16-3.57 ppm due to methyl protons of
coordinated methanol. Signals due to aromatic and CH3 protons appear in the expected
regions in the spectra of ligands as well as of complexes, with slight shifts in their positions.
1
The H NMR spectrum of [MoO2(hap-nah)(MeOH)] (5) presented in Fig. S1 confirms the
coordination of methanol (δ = 3.17) and existence of complex in the monomeric form.
The 13C NMR spectra of ligands and their complexes also delivered actionable
information confirming the structures of the complexes. Spectra of H2hap-bhz (III) and its
peroxido complex [MoO(O2)(hap-bhz)(MeOH)] (3) are shown in Fig.7 while Table 6
provides spectral data of all ligands and complexes. All the complexes unveil a distinct peak
at ca. δ = 48 ppm due to carbon of the coordinated methanol. A considerable coordination-
induced shifts (∆δ) [∆δ = [δ (complex) – δ (free ligand)] of the signals for carbon atoms C1,
C3, C8 and C9 i.e. in the vicinity of the coordinating atoms [38] suggests the involvement of
the azomethine nitrogen, phenolic oxygen and enolic oxygen atoms in coordination. Signals
for other aromatic carbon atoms in ligands and complexes appear in the usual expected
region.
<<Tables 5 and 6>><<Figures 6 and 7>>
3.7. Catalytic activity studies
3.7.1. Oxidation of styrene
The oxidation of styrene catalysed by vanadium complexes has extensively been
studied and at least five oxidation products have been obtained using H2O2 as a terminal
oxidant [39]. Dioxidomolybdenum(VI)/ oxidoperoxidomolybdenum(VI) complexes catalysed
oxidation of styrene considered here using aqueous 30% H2O2 as oxidant did not proceed to
10

give any oxidation product(s). Addition of NaHCO3 in the reaction mixture, however,
activated the catalytic oxidation process; several such NaHCO3 assisted oxidation of styrene
has been reported in the literature [4,24,28,29,40]. Oxidation of styrene catalysed by
molybdenum complexes reported here gave two products namely, styrene oxide and phenyl
acetaldehyde (Scheme 3) in the presence of 30% H2O2 and NaHCO3.
<<Scheme 3>>
Considering [MoO(O2)(hap-bhz)(MeOH)] (3) as a representative for this catalytic
reaction, reaction conditions were optimized using 5 mmol (0.52 g) of styrene, varying the
amount of catalyst (0.0005, 0.010 and 0.015 g), 30 % aqueous H2O2 (10, 15 and 20 mmol),
o
NaHCO3 (1, 2 and 3 mmol), temperature of the reaction mixture (40, 50 and 60 C) and
volume of acetonitrile (5, 7 and 10 mL). About 2 h was required to acquire equilibrium with
maximum conversion. Fig. S4 (a to e) provides profiles for the conversion of styrene at
various reaction conditions as a function of time and Table 7 provides conditions applied to
optimize the reaction conditions for the maximum conversion of styrene considering
[MoO(O2)(hap-bhz)(MeOH)] (3) as catalyst.
From various reaction conditions presented in Fig. S4 and data in Table 7, it is clear
that for catalyst [MoO(O2)(hap-bhz)(MeOH)] (3), the best suited reaction conditions for the
maximum oxidation (97 %) of 5 mmol (0.52 g) of styrene (entry no. 1 of Table 7) are: H2O2
(2.27 g, 20 mmol), catalyst (0.0005 g), NaHCO3 (0.168 g, 2 mmol), CH3CN (5 mL) and 60
oC reaction temperature.
Other two catalysts, [MoO(O2)(hap-inh)(MeOH)] (1) and [MoO(O2)(hap-
nah)(MeOH)] (2) were also tested under the above optimized reaction conditions for the
maximum conversion of styrene. The results are presented in Table 8. It is clear from the data
that all three complexes show comparable catalytic activity (94 to 99 %) along with high
turnover frequency; reason unknown [MoO(O2)(hap-nah)(MeOH)] (2) being less active. The
[MoO2]2+ complexes are equally good catalyst precursors with slightly less but similar trend
of conversion. In general, the selectivity of styrene oxide under the optimised reaction
conditions is extremely high (85 – 97%) for all catalysts while it is only 3 – 15% for phenyl
acetaldehyde. No conversion was obtained in the absence of NaHCO3, thus demonstrating the
importance of NaHCO3. A blank reaction (i.e. in the presence of H2O2 and NaHCO3 but in
the absence of catalyst under above reaction conditions resulted in only 32% conversion at 60
oC and only 11% at room temperature.
<<Tables 7 and 8>>
11

3.7.2. Oxidation of Cyclohexene
The NaHCO3 activated oxidation of cyclohexene by H2O2 using [MoO(O2)(hap-
bhz)(MeOH)] (3) as a representative catalyst was also carried out and the formation of
cyclohexene epoxide was obtained selectively. Again reaction conditions were optimized
using 5 mmol (0.410 g) of cyclohexene, varying the amount of catalyst (0.0005, 0.010 and
0.015 g), 30 % aqueous H2O2 (10, 15 and 20 mmol), NaHCO3 (1, 2 and 3 mmol), temperature
o
of the reaction mixture (40, 50 and 60 C) and volume of acetonitrile (5, 7 and 10 mL).
Conversion as a function of time under various conditions is presented in Fig. S5 (a to d) and
Table 9 summarizes conditions applied to optimize the reaction conditions for the maximum
conversion of cyclohexene in 2 h.
It is concluded from the data presented in Table 9 and various profiles in Fig S5 that
the optimised reaction conditions for the maximum oxidation of 5 mmol (0.410 g) of
cyclohexene for the catalyst [MoO(O2)(hap-bhz)(MeOH)] (3) are (entry no. 4 of Table 9):
H2O2 (2.27 g, 20 mmol), catalyst (0.0005 g, 1.16×10–3 mmol), NaHCO3 (0.084 g, 1 mmol),
o
CH3CN (5 mL) and reaction temperature 60 C. Under these conditions the conversion of
cyclohexene is 98%. The peroxido complex 1 is equally good but complex 2 shows only 86
% conversion (Table 10).
The corresponding [MoO2]2+ complexes are equally good catalyst precursors with
similar trend of conversion (Table 10). A maximum of 36 % conversion was obtained in the
absence of catalyst under similar conditions stated above but a blank reaction i.e. in the
absence of NaHCO3 as well as catalyst gave only 14% conversion. All these demonstrated
that catalysts and NaHCO3 both play important role in the oxidation of cyclohexene.
<<Tables 9 and 10>>
3.8. Reactivity of [MoO2(hap-bhz)(MeOH)] (3) with H2O2and possible mechanism for
catalytic oxidation of substrates.
Effort to isolate [MoVIO(O2)]2+ complexes by reacting corresponding [MoVIO2]2+
complexes with H2O2 in methanol always resulted in a mixture of both species possibly due
to incomplete conversion of dioxido species. We have monitored this reactivity by electronic
absorption spectroscopy. In a typical reaction, 25 mL of 1.25×10–6 M solution of [MoO2(hap-
bhz)(MeOH)] in DMSO was treated with one drop portion of 30% aqueous H2O2 (0.108 g,
0.95 mmol) dissolved in 5 mL of DMSO and the observed spectral changes are presented in
Fig. 8 (a). As shown in in figure, the movements of 396 band to 400 nm with only slight
12

decrease in intensity without any isosbestic point suggests the existence of dioxido and
oxidoperoxido species in equilibrium. Addition of a mixture of NaHCO3 and H2O2 (for detail
see caption of Fig 8) to a fresh solution of above complex reduced the time period in
achieving the same spectral changes with similar equilibrium and this suggests the faster
conversion of dioxido complex into oxidoperoxido species. It has been observed that
–
NaHCO3 reacts with H2O2 instantly and produces HCO4 (peroxymonocarbonate)
[4,28,29,40]. This species reacts with dioxidomolybdenum(VI) complex to give
oxidoperoxidomolybdenum(VI) intermediate more rapidly as compared to H2O2 alone via
another plausible intermediate formation [4,40], as shown in Scheme 4. The
oxidoperoxidomolybdenum(VI) complex transfers oxygen to the substrate to effect oxidation.
Globally, mechanism for catalytic reactions will be same for all complexes as intermediate
species form or present in catalytic reaction mixture will be monomeric
oxidoperoxidomolybdenum(VI) complex.
<<Figure 8>><<Scheme 4>>
4. Conclusion
The oxidoperoxidomolybdenum(VI) complexes, [MoO(O2)(hap-inh)(MeOH)] (1),
[MoO(O2)(hap-nah)(MeOH)] (2) and [MoO(O2)(hap-bhz)(MeOH)] (3) have been prepared
from potential dibasic tridentate ligands H2hap-inh (I), H2hap-nah (II) and H2hap-bhz (III),
respectively. These complexes have fully been characterized by employing various
spectroscopic techniques and one of them by single crystal X-ray study. The
dioxidomolybdenum(VI) analogues [MoO2(hap-inh)]n (4) [MoO2(hap-nah)(MeOH)] (5) and
[MoO2(hap-bhz)(MeOH)] (6) have also been prepared. In complex 4, nitrogen of the
pyridine ring coordinates to the molybdenum which is rarely observed in literature while this
coordination site is occupied by methanol in other complexes.
In the presence of sodium bicarbonate, these complexes are efficient homogenous
catalysts for the oxidation of styrene and cyclohexene using 30 % H2O2 as an oxidant. Under
optimized reaction conditions styrene gave mainly styrene oxide and minor amount of
phenylacetaldehyde. Oxidation of cyclohexene gave cyclohexene epoxide selectively. Very
poor conversion of substrates in the absence of NaHCO3 was obtained which demonstrates
the importance of NaHCO3 for such catalysts. The corresponding dioxidomolybdenum(VI)
complexes have relatively lower catalytic activities. The dioxidomolybdenum(VI) complexes
upon treatment with NaHCO3 and H2O2 in methanol instantly generate oxidoperoxido species
13

in solution which is considered to be the intermediate species responsible for the transfer of
oxygen to the substrates during catalytic oxidation.
Appendix A. Supplementary data
CCDC 1025792 for 3, 1025793 for 4 and 1025794 for 6a contain the supplementary
crystallographic data for the structures reported in this paper. 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: deposit@ccdc.cam.ac.uk. Supplementary data associated with this article
can be found, in the online version, at doi: $$$$$.
Acknowledgements
One of the authors (LT) is thankful to Council of Scientific and Industrial Research, New
Delhi for Junior Research Fellowship.
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16

Schemes
Scheme 1. Structure of ligands selected for this study.
Scheme 2. Proposed structures of oxidoperoxido- and dioxido-molybdenum(VI) complexes.
In the structure of 4, pyridyl nitrogen of the other ligand also interacts with Mo.
17

O
O
Catalyst
H2O2, NaHCO3
Scheme 3. NaHCO3 activated oxidation products of styrene using H2O2 as oxidant.
Scheme 4. Proposed catalytic mechanism for the oxidation of alkenes [adopted from ref. 4].
18

Figures
Fig. 1. ORTEP plot of complex [MoO(O2)(hap-bhz)(MeOH)] (3). All the non-hydrogen
atoms are presented by their 30% probability ellipsoids. Hydrogen atoms are omitted for
clarity.
Fig. 2. ORTEP plot of complex [MoO2(hap-bhz)(DMSO)] (6a). All the non-hydrogen atoms
are presented by their 30% probability ellipsoids. Hydrogen atoms are omitted for clarity.
19

Fig. 3. ORTEP plot of complex [MoO2(hap-inh)]n (4). All the non-hydrogen atoms are
presented by their 30% probability ellipsoids. Hydrogen atoms are omitted for clarity.
Fig. 4. Intermolecular π-π interactions in [MoO(O2)(hap-bhz)(MeOH)] (3). Dashed lines link
the centres of the π clouds involved in each interaction.
20

[MoO(O2)(hap-inh)(MeOH)] (1)
[MoO(O2)(hap-nah)(MeOH)] (2)
[MoO(O2)(hap-bhz)(MeOH)] (3)
0.6
0.5
0.4
0.3
0.2
0.1
0.0
250
300
350
400
450
500
550
Wavelength (nm)
Fig. 5. UV-vis spectra of peroxido complexes recorded in DMSO.
Fig. 6. 1H NMR spectra of H2hap-inh (I) and [MoO(O2)(hap-inh)(MeOH)] (1).
21

Fig. 7. 13C NMR spectra of H2hap-bhz (III) and [MoO(O2)(hap-bhz)(MeOH)] (3). For details
of carbon numbering see Table 6.
2.5
2.5
2.0
1.5
1.0
0.5
0.0
314
314
262
262
2.0
1.5
1.0
0.5
0.0
(a)
(b)
396
396
250
300
350
400
450
500
250
300
350
400
450
500
Wavelength/nm
Wavelength/nm
Fig. 8. Plots representing the spectral changes during the titration of [MoO2(hap-
bhz)(MeOH)] with H2O2. (a) Spectra were obtained after successive addition of one drop
portion of H2O2 [0.108 g (0.95 mmol) of 30% H2O2 dissolved in 5 mL of DMSO] to 25 mL
of 1.25×10–6 M solution of [MoO2(hap-bhz)(MeOH)] in DMSO. (b) Spectra were obtained
after successive addition of one drop portion of a mixture of NaHCO3 and H2O2 [0.001 g
(0.11 mmol) NaHCO3 and 0.054 g (0.47 mmol) 30% H2O2 dissolved in 5 mL of DMSO] to
25 mL of 1.25×10–6 M solution of [MoO2(hap-bhz)(MeOH)] in DMSO.
22

Tables
Table 1.Crystal data and structure refinement for complexes [MoO(O2)(hap-bhz)(MeOH)]
(3), [MoO2(hap-inh)] (4) and [MoO2(hap-bhz)(DMSO)] (6a).
3
4
6a
Formula
C16H15MoN2O6
427.24
C14H11MoN3O4
381.20
293(2)
C17H18MoN2O5S
458.33
293(2)
Formula weight
T, K
293(2)
Wavelength, Å
0.71073
Triclinic
P1
0.71073
Orthorhombic
Pbca
0.71073
Monoclinic
P21/c
Crystal system
Space group
a/Å
9.5715(19)
14.076(3)
14.979(3)
114.994(9)
97.283(10)
102.260(9)
1733.2(6)
4
10.3424(14)
12.1287(16)
22.674(3)
90
17.117(3)
8.3432(14)
13.535(2)
90
b/Å
c/Å
α/º
β/º
90
99.503(6)
90
γ/º
V/Å3
90
2844.2(7)
8
1906.4(5)
4
Z
F000
860
1520
928
Dcalc/g cm-3
µ/mm-1
1.637
1.780
1.597
0.791
0.944
0.827
1.55 to 28.30
0.0240
1.80 to 30.55
0.0385
1.21 to 28.19
0.0538
θ/ (º)
Rint
Crystal size/ mm3
Goodness-of-fit on F2
R1[I>2σ(I)] a
wR2 (all data) b
Largest differences peak and
hole (eÅ-3)
0.16 × 0.12 × 0.10
1.146
0.22 × 0.19 × 0.17 0.26 × 0.19 × 0.11
1.111
1.102
0.0215
0.0294
0.0995
0.0373
0.1207
0.0676
0.697 and -0.530
0.444 and -0.439 0.666 and -0.761
4
aR1 = ΣFo - Fc/ΣFo. bwR2 = {Σ[w(Fo2 -Fc2)2]/Σ[w(Fo )]}1/2
23

Table 2
Bond lengths [Å] and angles [°] for [MoO(O2)(hap-bhz)(MeOH)] (3), [MoO2(hap-inh)]n (4)
and [MoO2(hap-bhz)(DMSO)] (6a).
Bond lengths
3
4
6a
Mo(1)-O(1)
Mo(1)-O(2)
Mo(1)-O(3)
Mo(1)-O(4)
Mo(1)-O(5)
Mo(1)-O(6)
Mo(1)-N(2)
Mo(1)-N(3)#1
N(1)-N(2)
2.0064(13)
1.6801(14)
1.9280(14)
1.9378(13)
1.9908(12)
2.3142(13)
2.2010(15)
2.0076(16)
1.6990(17)
1.9321(17)
1.6976(17)
2.005(2)
1.944(2)
1.698(3)
1.702(2)
Mo(1)-O(1S) 2.262(2)
2.270(2)
2.4444(19)
1.406(3)
1.289(3)
1.303(3)
2.267(3)
1.400(3)
1.410(2)
1.300(2)
1.310(2)
N(1)-C(9)
N(2)-C(7)
N(1)-C(7)
1.302(4)
N(2)-C(8)
1.304(4)
Mo(2)-O(7)
Mo(2)-O(8)
Mo(2)-O(9)
Mo(2)-O(10)
Mo(2)-O(11)
Mo(2)-O(12)
Mo(2)-N(4)
N(3)-N(4)
2.0131(12)
1.6794(13)
1.9435(12)
1.9289(13)
1.9933(12)
2.2999(13)
2.1886(15)
1.4092(19)
1.295(2)
N(3)-C(25)
N(4)-C(23)
O(3)-O(4)
1.308(2)
1.4548(17)
Angles
3
4
6a
O(2)-Mo(1)-O(3)
O(2)-Mo(1)-O(4)
O(3)-Mo(1)-O(4)
O(2)-Mo(1)-O(5)
O(3)-Mo(1)-O(5)
O(4)-Mo(1)-O(5)
O(3)-Mo(1)-O(1S)
O(4)-Mo(1)-O(1S)
O(2)-Mo(1)-O(1S)
O(1)-Mo(1)-O(1S)
O(2)-Mo(1)-O(1)
O(3)-Mo(1)-O(1)
O(4)-Mo(1)-O(1)
O(5)-Mo(1)-O(1)
O(2)-Mo(1)-N(2)
O(3)-Mo(1)-N(2)
O(4)-Mo(1)-N(2)
O(5)-Mo(1)-N(2)
O(1S)-Mo(1)-N(2)
O(1)-Mo(1)-N(2)
O(4)-Mo(1)-N(3)#1
O(2)-Mo(1)-N(3)#1
O(3)-Mo(1)-N(3)#1
O(1)-Mo(1)-N(3)#1
N(2)-Mo(1)-N(3)#1
O(2)-Mo(1)-O(6)
O(3)-Mo(1)-O(6)
O(4)-Mo(1)-O(6)
104.73(7)
104.05(6)
44.21(5)
98.68(6)
121.61(5)
78.59(5)
105.18(7)
105.86(9)
99.00(8)
97.85(12)
102.87(11)
105.97(13)
167.80(10)
86.16(12)
80.31(9)
78.26(10)
148.54(9)
98.26(13)
98.40(11)
100.55(6)
77.22(5)
120.29(5)
148.19(5)
91.75(6)
148.56(6)
155.66(5)
80.84(5)
95.22(8)
146.70(7)
100.37(8)
161.18(8)
80.67(6)
90.55(8)
80.70(9)
90.72(10)
162.09(12)
77.08(9)
72.26(9)
73.50(5)
72.34(7)
170.77(8)
83.37(7)
77.96(7)
78.60(7)
80.38(7)
169.44(6)
85.40(5)
85.24(5)
24

O(5)-Mo(1)-O(6)
O(1)-Mo(1)-O(6)
N(2)-Mo(1)-O(6)
O(8)-Mo(2)-O(10)
O(8)-Mo(2)-O(9)
O(10)-Mo(2)-O(9)
O(8)-Mo(2)-O(11)
O(10)-Mo(2)-O(11)
O(9)-Mo(2)-O(11)
O(8)-Mo(2)-O(7)
O(10)-Mo(2)-O(7)
O(9)-Mo(2)-O(7)
O(11)-Mo(2)-O(7)
O(8)-Mo(2)-N(4)
O(10)-Mo(2)-N(4)
O(9)-Mo(2)-N(4)
O(11)-Mo(2)-N(4)
O(7)-Mo(2)-N(4)
O(8)-Mo(2)-O(12)
O(10)-Mo(2)-O(12)
O(9)-Mo(2)-O(12)
O(11)-Mo(2)-O(12)
O(7)-Mo(2)-O(12)
N(4)-Mo(2)-O(12)
78.00(5)
78.48(5)
77.86(5)
103.77(6)
103.20(6)
44.23(5)
100.27(6)
121.51(5)
78.72(5)
101.04(6)
77.39(5)
120.39(5)
146.65(5)
90.97(6)
149.22(5)
156.99(5)
81.00(5)
73.30(5)
169.99(5)
85.92(5)
85.45(5)
76.23(5)
78.37(5)
79.26(5)
Symmetry transformations used to generate equivalent atoms:
#1 -x+1,y-1/2,-z+3/2
Table 3
IR Spectral data (in cm–1) of the compounds.
Compounds
ν(C=N) ν(Mo=O) ν(O-O)
ν(MoO2)asym. ν(MoO2)sym.
H2hap-inh (I)
1606
1608
1604
1599
1595
1599
H2hap-nah(II)
H2hap-bhz(III)
[MoO(O2)(hap-inh)(MeOH)] (1)
[MoO(O2)(hap-nah)(MeOH)] (2)
[MoO(O2)(hap-bhz)(MeOH)] (3)
970
961
967
853
857
859
635
626
618
556
553
552
25

Table 4
Electronic spectral data of ligands and [MoO(O2)]2+ complexes
λmax/nm (ꢀ/M-1cm-1
Compounds
H2hap-inh (I)
287 (9835), 300 (8427), 331 (7950)
H2hap-nah (II)
285 (8315), 301 (6857), 329 (6330)
H2hap-bhz (III)
284 (14505), 294 (13992), 327 (11630)
[MoO(O2)(hap-inh)(MeOH)] (1)
[MoO(O2)(hap-nah)(MeOH)] (2)
[MoO(O2)(hap-bhz)(MeOH)] (3)
260 (9547), 281 (9415), 325 (9307), 405 (3000)
257 (11005),282 (10170),321 (9767), 405 (3082)
258 (12735), 284 (10647), 325 (10607), 405 (3317)
Table 5
1H NMR chemical shifts (δ in ppm) of the ligands and their complexes recorded in DMSO-d6
Compou OH
-NH
Aromatic protons
CH3
-OCH3
-OH
nds
(Phenolic)
(alcoholic)
I
13.19 (br,1H)
11.58 (s,1H)
8.69-8.80 (m, 2H), 7.84-7.85 (d, 2H), 7.48- 3.37 (s, 3H)
7.72 (m, 1H), 7.31-7.34 (t, 1H), 6.84-6.94 (m,
2H)
-
-
II
III
1
13.23 (br,1H)
11.51 (s,1H)
9.08 (d, 1H), 8.77-8.78 (t, 1H), 8.27-8.28 (d, 3.32 (s, 3H)
IH), 7.64-7.66 (d, 1H), 7.56-7.59 (q, 1H),
7.30-7.33 (t, 1H), 6.89-6.92 (t, 2H)
-
-
-
-
13.36 (br,1H)
11.33 (s,1H)
7.94-7.96 (d, 2H), 7.62-7.66 (q, 2H), 7.54- 3.33 (s, 3H)
7.57 (t, 2H), 7.30-7.33 (t, 1H), 6.90-6.93 (t,
2H)
-
-
-
-
-
-
8.30 (s, 2H), 8.04-8.05 (d, 2H), 7.97-7.99 (q, 3.05 (s, 3H)
1H), 7.61-7.64 (m, 1H), 7.14-7.16 (d, 1H),
7.08-7.11 (m, 1H)
3.16 (s, 3H) 4.11 (br, 1H)
3.16 (s, 3H) 4.08 (br, 1H)
3.18 (s, 3H) 4.08 (br, 1H)
2
8.80 (d, 2H), 8.04-8.06 (t, 2H), 7.92-7.99 (m, 3.06 (s, 3H)
2H), 7.52-7.64 (m, 1H), 7.14-7.17 (dd, 1H),
7.09-7.11 (q, 1H)
3
8.24-8.25 (t, 2H), 7.90-7.92 (dd, 1H), 7.54- 3.30 (s, 3H)
7.59 (m, 2H), 7.48-7.51(t, 2H), 7.17-7.19 (d,
1H), 7.05-7.08 (m, 1H)
26

Table 6
13C NMR spectral data of ligands and complexes
Compounds a
C1
C3
C8
C9
C10
-
Aromatic carbons
161.86
157.62
13.15
158.31
149.05 (C13, C14), 138.97 (C11), 130.43 (C5),
127.59 (C7), 120.89 (C12, C15), 118.10 (C6),
117.48 (C2), 116.23 (C4)
I
166.09
(4.23)
161.30
(3.68)
17.83
(4.68)
165.38 48.14 150.10 (C13, C14), 137.09 (C11), 134.73 (C5),
1
(7.07)
130.74 (C7), 122.26 (C12, C15), 120.70 (C6),
118.91 (C2,C4)
∆δ
163.48
159.07
14.69
159.25
-
152.92 (C12), 149.52 (C13), 136.48 (C15),
131.94 (C11), 129.36 (C5), 129.14 (C7),
124.01 (C14), 119.80 (C6), 119.09 (C2),
117.85 (C4)
II
166.11
(2.63)
160.79
(1.72)
17.36
(2.67)
165.49 48.10 152.79 (C12), 149.47 (C13), 138.03 (C15),
2
(6.24)
134.64 (C5), 134.38 (C7), 131.80 (C11),
127.39 (C14), 123.24 (C6), 122.35 (C2),
119.21 (C4)
∆δ
164.89
158.60
14.54
159.26
-
133.45 (C11), 132.45 (C14), 131.75 (C7)
128.99 (C5), 128.89 (C13), 128.61 (C12),
119.88 (C6), 118.99 (C2), 117.80 (C4)
III
3
167.08
(2.19)
161.17
(2.57)
17.74
(3.20)
164.27 48.14 134.23 (C14), 131.50 (C5), 130.44 (C7),
(5.01)
129.42 (C12, C16), 128.33 (C11), 128.04 (C13,
C15), 122.44 (C6), 120.48 (C2), 118.81 (C4)
∆δ
(∆δ) [∆δ = [δ (complex) – δ (free ligand)]
27

Table 7
Conversion of 5 mmol (0.52 g) of styrene using [MoO(O2)(hap-bhz)(MeOH)] (3) as a
catalyst in 2 h of reaction time under various reaction conditions.
Entry
No.
Catalyst
H2O2
NaHCO3
[g (mmol)]
0.168 (2)
CH3CN
[mL]
5
Temp.
(oC)
60
Conv. %
[g (mmol)]
[g (mmol)]
2.27 (20)
–
6
1
97
77
59
77
74
21
59
76
33
92
63
0.0005 (1.16×10 )
–
6
2
2.27 (20)
2.27 (20)
2.27 (20)
2.27 (20)
1.14 (10)
1.69 (15)
2.27 (20)
2.27 (20)
2.27 (20)
2.27 (20)
0.168 (2)
0.168 (2)
0.084 (1)
0.252 (3)
0.168 (2)
0.168 (2)
0.168 (2)
0.168 (2)
0.168 (2)
0.168 (2)
5
5
60
60
60
60
60
60
60
60
50
40
0.0010 (2.33×10 )
–
6
3
0.0015 (3.50×10 )
–
6
4
5
0.0005 (1.16×10 )
–
6
5
5
0.0005 (1.16×10 )
–
6
6
5
0.0005 (1.16×10 )
–
6
7
5
0.0005 (1.16×10 )
–
6
8
7
0.0005 (1.16×10 )
–
6
9
10
5
0.0005 (1.16×10 )
–
6
10
11
0.0005 (1.16×10 )
–
6
5
0.0005 (1.16×10 )
Table 8
Conversion, turn over frequency and selectivity parameters for various catalysts for the
catalytic oxidation of styrene.
Catalyst
TOF
[h-1]a
2133
1896
2090
1940
1740
1884
-
Conv.
[%]
Selectivity [%]b
so
Phac
2.8
[MoO(O2)(hap-inh)(MeOH)] (1)
[MoO(O2)(hap-nah)(MeOH)] (2)
[MoO(O2)(hap-bhz)(MeOH)] (3)
[MoO2(hap-inh)]n (4)
99.0
88.0
97.0
97.0
87.0
95.0
32.0
97.2
85.6
95.2
95.2
85.0
93.3
96.0
14.4
4.8
4.8
[MoO2(hap-nah)(MeOH)] (5)
[MoO2(hap-bhz)(MeOH)] (6)
Blank reaction
15.0
6.7
4.0
aTOF values calculated at 2 h of reaction time.
bso = styrene oxide, phac = phenyl acetaldehyde.
28

Table 9
Conversion of cyclohexene (0.410 g, 5 mmol) using [MoO(O2)(hap-bhz)(MeOH)] (3) as a
catalyst in 2 h reaction time under various reaction conditions.
Entry
No.
Catalyst
H2O2
NaHCO3
[g (mmol)]
0.168 (2)
CH3CN
[mL]
5
Temp.
(oC)
60
Conv. %
[g (mmol)]
[g (mmol)]
2.27 (20)
–
3
1
98
94
82
98
93
46
92
84
72
92
89
0.0005 (1.16×10 )
–
3
2
2.27 (20)
2.27 (20)
2.27 (20)
2.27 (20)
1.14 (10)
1.69 (15)
2.27 (20)
2.27 (20)
2.27 (20)
2.27 (20)
0.168 (2)
0.168 (2)
0.084 (1)
0.252 (3)
0.168 (2)
0.168 (2)
0.084 (1)
0.084 (1)
0.084 (1)
0.084 (1)
5
5
60
60
60
60
60
60
60
60
50
40
0.0010 (2.33×10 )
–
3
3
0.0015 (3.50×10 )
–
3
4
5
0.0005 (1.16×10 )
–
3
5
5
0.0005 (1.16×10 )
–
3
6
5
0.0005 (1.16×10 )
–
3
7
5
0.0005 (1.16×10 )
–
3
8
7
0.0005 (1.16×10 )
–
3
9
10
5
0.0005 (1.16×10 )
–
3
10
11
0.0005 (1.16×10 )
–
3
5
0.0005 (1.16×10 )
Table 10
Conversion, turn over frequency and selectivity parameters for various catalysts for the
catalytic oxidation of cyclohexene.
Catalyst
% Conv.
TOF
[h-1]a
2112
1853
2112
1940
1700
1845
-
% Selectivity
(cyclohexene epoxide)
[MoO(O2)(hap-inh)(MeOH)] (1) 98
[MoO(O2)(hap-nah)(MeOH)] (2) 86
[MoO(O2)(hap-bhz)(MeOH)] (3) 98
100
100
100
100
100
100
100
[MoO2(hap-inh)]n (4)
96
85
93
41
[MoO2(hap-nah)(MeOH)] (5)
[MoO2(hap-bhz)(MeOH)] (6)
Blank reaction
29