Oxy-functionalization of olefins with neat and heterogenized binuclear V(IV)O and Fe(II)complexes: Effect of steric hindrance on product selectivity and output in homogeneous and heterogeneous phase

Article abstract of DOI:10.1016/j.mcat.2019.110424

Neat {[VO(sal₂bz)]₂; [Fe(sal₂bz)(H₂O)₂]₂·2H₂O} and zeolite-Y immobilized {[VO(sal₂bz)]₂-Y; [Fe(sal₂bz)(H₂O)₂]₂-Y} binuclear complexes have been prepared and characterized by spectroscopic techniques (IR, UV–vis), elemental analyses (CHN, ICP-OES), thermal study (TGA), scanning electron micrograph (SEM), adsorption study (BET)and X-ray diffraction (XRD)patterns. Neat (homogeneous)and immobilized (heterogeneous)complexes were employed as catalysts in the oxidation of olefins, namely, cyclohexene, limonene and α-pinene in the presence of 30% hydrogen peroxide. 100% conversion of cyclohexene and α-pinene was obtained while limonene was oxidized up to 90%. Homogeneous catalysts showed highly selective result as neat [VO(sal₂bz)]₂ complex has provided 87% cyclohexane-1,2-diol and neat [Fe(sal₂bz)(H₂O)₂]₂·2H₂O complex has provided 79% verbenone in oxidation of cyclohexene and α-pinene, respectively. We have observed that due to steric hindrance, formation of olefinic oxidation products increases on moving from α-pinene to limonene and limonene to cyclohexene. Additionally. recovered heterogeneous catalysts showed intact results up to two consecutive runs. Probable catalytic mechanism has been proposed for oxidation of cyclohexene.

Full text of DOI:10.1016/j.mcat.2019.110424

MolecularCatalysis474(2019)110424
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Oxy-functionalization of olefins with neat and heterogenized binuclear V
(IV)O and Fe(II) complexes: Effect of steric hindrance on product selectivity
and output in homogeneous and heterogeneous phase
Digvijaysinh K. Parmara,⁎, Pinal M. Butanib, Niraj J. Thumarb, Pinal M. Jasanib, Ravi V. Padaliyab,
Paba R. Sandhiyab, Haresh D. Nakumc, Md. Nasim Khand, Dipak Makwanae
a Diu College, DHES, Diu (U.T.), 362520, India
b Department of Chemistry, School of Science, RK University, Rajkot 360020, Gujarat, India
c Oil and natural gas corporation limited, Hazira, Surat, Gujarat, India
d School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK
e Inorganic Materials and Catalysis Division, CSIR-Central Salt and Marine Chemicals Research Institute, Bhavnagar 364002, Gujarat, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
Binuclear complex
Zeolite-Y
Olefin oxidation
Steric hindrance
Neat {[VO(sal2bz)]2; [Fe(sal2bz)(H2O)2]2·2H2O} and zeolite-Y immobilized {[VO(sal2bz)]2-Y; [Fe(sal2bz)
(H2O)2]2-Y} binuclear complexes have been prepared and characterized by spectroscopic techniques (IR,
UV–vis), elemental analyses (CHN, ICP-OES), thermal study (TGA), scanning electron micrograph (SEM), ad-
sorption study (BET) and X-ray diffraction (XRD) patterns. Neat (homogeneous) and immobilized (hetero-
geneous) complexes were employed as catalysts in the oxidation of olefins, namely, cyclohexene, limonene and
α-pinene in the presence of 30% hydrogen peroxide. 100% conversion of cyclohexene and α-pinene was ob-
tained while limonene was oxidized up to 90%. Homogeneous catalysts showed highly selective result as neat
[VO(sal2bz)]2 complex has provided 87% cyclohexane-1,2-diol and neat [Fe(sal2bz)(H2O)2]2·2H2O complex has
provided 79% verbenone in oxidation of cyclohexene and α-pinene, respectively. We have observed that due to
steric hindrance, formation of olefinic oxidation products increases on moving from α-pinene to limonene and
limonene to cyclohexene. Additionally. recovered heterogeneous catalysts showed intact results up to two
consecutive runs. Probable catalytic mechanism has been proposed for oxidation of cyclohexene.
1. Introduction
zeolite-Y due to its structural diversity, redox behaviour [19–23] and
possess potentials such as, thermal stability, reactivity, recyclability,
Framework of zeolites is formed by an array of the corner-sharing
AlO4 or SiO4 tetrahedra [1–3]. Periodic arrangement of these building
blocks forms micropores of very regular dimensions. Micropores of the
zeolites are accessible as they allow the diffusion of molecules through
them. It makes zeolites at the top of the list of solids exhibiting huge
surface areas, typically above 300 m2 g−1 with an inner pore volume
above 0.1 cm3 g−1 [4].
In recent time, the meadow of inclusion materials has pulled up as
eco‐sustainable catalytic systems transforming various organic sub-
strates into valuable intermediates for environmentally benign in-
dustrial process [5–10]. Amongst the various type of modified micro-
porous materials [11–18], zeolite-Y immobilized metal complexes
occupy a special place in catalysis. Starting from the preparation of ship
in bottle complexes, various complexes have been immobilized in
and reusability [24] over homogeneous counterparts. Moreover, flex-
ibility of Schiff base ligands has given direction to produce various
zeolite-Y immobilized metal complexes as heterogeneous catalysts for
organic transformation [25–27].
Oxy-functionalized derivatives of cyclic olefins are used in the
preparation of several industrially important products [28–32]. Oxi-
dation of olefinic positions provides epoxides and diols when high-va-
lent metal oxo complexes are involved, whereas allylic oxidation results
in allylic alcohols and ketones when one-electron processes or radical
intermediates are involved [33]. Generally, the oxidation of olefins
leads to a mixture of both the olefinic and allylic products. Therefore, it
is a challenging task to achieve selectivity among olefinic and allylic
products.
Herein we report the oxidation of olefins by using neat and zeolite-Y
⁎ Corresponding author.
E-mail address: parmardk@outlook.com (D.K. Parmar).
https://doi.org/10.1016/j.mcat.2019.110424
Received 14 December 2018; Received in revised form 16 April 2019; Accepted 23 May 2019
2468-8231/©2019ElsevierB.V.Allrightsreserved.

D.K. Parmar, et al.
MolecularCatalysis474(2019)110424
Table 1
Chemical composition of Schiff base ligand and neat complexes.
Entry
Material
Elements found (calculated) (%)
C
H
N
M
C/N
1
2
3
sal2bzH2
[VO(sal2bz)]2
[Fe(sal2bz)(H2O)2]2 ·2H2O
79.61 (79.57)
67.16 (68.28)
62.37 (62.42)
5.17 (5.14)
3.84 (3.97)
4.54 (4.83)
7.13 (7.14)
6.00 (6.12)
5.60 (5.60)
–
11.16 (11.14)
11.19 (11.15)
11.13 (11.14)
10.82 (11.14)
11.27 (11.16)
immobilized binuclear V(IV)O and Fe(II) complexes as catalysts to
check their output in homogeneous and heterogeneous catalytic system,
respectively.
analyzer. Percentage of Na(I), Al(III), Si(IV), V(IV)O and Fe(II) ions
were checked by ICP-OES using Perkin Elmer optima 2000 DV model.
BET analysis was done using ASAP 2010, micromeritics surface area
analyser. SEM images were taken on LEO 1430 VP. Powder XRD pat-
terns were recorded on Bruker AXS D8 Advance X-ray powder dif-
fractometer with a CuKα radiation as the incident beam. TGA was
carried out using Perkin Elmer equipment and with the heating rate of
10 K/min. FT-IR spectra (4000–400 cm−1) were recorded on a Thermo
Nicolet FT-IR spectrometer in KBr. Magnetic property was measured by
the magnetic susceptibility balance (Johnson Metthey and Sherwood
model). UV–vis spectra were recorded on a Shimadzu UV-1800 spec-
trophotometer, using a quartz cell of 1 cm3 optical path. Reaction
products were identified using GC–MS having a DB-5 capillary column
(30 m ×0.30 mm ×0.25 μm) 95% silicoxane surface and FID detector.
Area % method was used to quantify the products.
2. Experimental section
2.1. Materials
Benzidine, 2-hydroxybenzaldehyde, DMF, 1,4-dioxane, acetonitrile,
VOSO4⋅5H2O, FeSO4⋅7H2O, 30% H2O2, cyclohexene, limonene, α-
pinene and zeolite-Y (Si/Al = 2.60) of AR grade were purchased from
Hi-media (India) and used without further purification.
2.2. Preparation of ligand ‘sal2bzH2’
Schiff base ligand (Z)-2-[4′-Methyleneamino-biphenyl-4-ylimino)-
methyl]-phenol (sal2bzH2) was prepared by heating a mixture of ben-
zidine (1.84 g, 10 mmol) with salicylaldehyde (2.13 mL, 20 mmol) in
DMF medium under reflux condition with constant stirring for 4 h (see
supplementary material, Scheme S1) [34]. The golden yellow solid
product obtained was filtered off at room temperature and dried.
sal2bzH2: Yellow crystals; m.p. > 250 °C; 1H NMR (DMSO d6,
400 MHz), δ: 13.08 (s, 1H, Ar-OH); 9.05 (s, 1H, Ar-OH); 7.95–6.99 (m,
16H, Ar-H); 6.65 (d, 1H, HC = N); 5.25 (d, 1H, HC = N) ppm (see
supplementary material, Fig. S1).
2.6. Catalytic oxidation reactions
The catalytic oxidation of cyclohexene, limonene and α-pinene were
carried out by taking 10 mmol of substrate and 15 mg of catalyst in the
acetonitrile medium. Meanwhile, 20 mmol of 30% H2O2 was added
dropwise with constant stirring. The resulted reaction mixtures were
heated at 80 °C for 24 h. Inspection of reaction progress and identifi-
cation of products were carried out by GC-MS.
3. Results and discussion
2.3. Preparation of neat complexes
3.1. Characterization
Aqueous solution of VOSO4⋅5H2O (1.26 g, 5 mmol) and FeSO4⋅7H2O
(1.39 g, 5 mmol) was mixed separately with the solution of ligand
sal2bzH2 (1.96 g, 5 mmol) in 1,4-dioxane with constant stirring (see
supplementary material, Scheme S2). pH of the solution was adjusted
around 5–6 by addition of CH3COONa. The resulting solution was re-
fluxed at 110 °C for 4–5 h. The mixture was cooled, filtered, washed and
dried to obtain neat [VO(sal2bz)]2 and [Fe(sal2bz)(H2O)2]2·2H2O com-
plexes.
3.1.1. Chemical analysis data
As per the CHN analysis data, neat complexes (Table 1, entries 2 &
3) resulting from ligand sal2bzH2 (Table 1, entry 1) are formed by co-
ordination with metal in 1:1 (metal:ligand) molar ratios. CHN data of
zeolite-Y immobilized binuclear complexes (Table 2, entries 4 & 5)
shows C/N ratio almost comparable with respect to neat complexes
(Table 1, entries 2 & 3). It confirms the presence of binuclear complexes
in framework of zeolite-Y [36].
Content of Al(III) and Si(IV) in the metal exchanged zeolite-Y
(Table 2, entries 2 & 3) and immobilized complexes (Table 2, entries 4
& 5) are almost in the equivalent ratio with respect to pure zeolite-Y
(Table 2, entry 1). It supports de-alumination in the framework of
zeolite-Y during the metal ion exchange and complex formation. Low
concentration of V(IV)O and Fe(II) ions in immobilized complexes than
their respective metal exchanged zeolite-Y is owing to leaching of metal
ions during the immobilization [37].
2.4. Preparation of zeolite-Y immobilized binuclear V(IV)O and Fe(II)
complexes
Preparation of [VO(sal2bz)]2-Y and [Fe(sal2bz)(H2O)2]2-Y was done
by Flexible Ligand method (see supplementary material, Scheme S3)
[35]. Initially, V(IV)O and Fe(II) ions were incorporated separately in
zeolite-Y through ion exchange method to prepare V(IV)O-Y and Fe(II)-
Y. 1.0 g activated V(IV)O-Y and Fe(II)-Y was added separately to a so-
lution of ligand sal2bzH2 in 1,4-dioxane (50 mL). The resulting mixture
was heated at reflux condition with continuous stirring for 12 h, which
gives immobilized binuclear V(IV)O and Fe(II) complexes. Soxhlet ex-
traction was performed with 1,4-dioxane and acetonitrile solvent to
remove complex or ligand adsorbed on the outer surface of zeolite. The
resulting catalysts were named as [VO(sal2bz)]2-Y and [Fe(sal2bz)
(H2O)2]2-Y.
Table 2
Chemical composition of zeolite-Y and zeolite-Y modified materials.
Entry Material
Elements found (%)
C
–
–
–
N
–
–
M
–
0.59
0.63
C/N
Si
Al
Si/Al
1
2
3
4
5
Na-Y
V(IV)O-Y
Fe(II)-Y
–
–
–
17.04 6.54 2.60
16.52 6.36 2.59
16.57 6.37 2.60
–
2.5. Characterization of catalysts
[VO(sal2bz)]2-Y
1.01 0.09 0.34 11.22 16.23 6.24 2.60
[Fe(sal2bz)(H2O)2]2-Y 1.90 0.17 0.41 11.17 16.10 6.19 2.60
CHN analysis was carried out on Perkin Elmer, USA 2400-II CHN
2

D.K. Parmar, et al.
MolecularCatalysis474(2019)110424
Table 3
show bands at 1612 cm−1 and 1596 cm−1, respectively, are corre-
sponding to ν(C=N) group [45]. It confirms the coordination of metal
ions with azomethine nitrogen. Moreover, this band also found in both
immobilized complexes.
BET analysis data of zeolite-Y and zeolite-Y modified materials.
Entry Material
BET surface area
Pore volume
(%)a (%)b
(m2 g−1
)
(cm3 g−1
)
Moreover, ν(Ce
band for both neat complexes shifted towards
O)
1
2
3
4
5
Na-Y
V(IV)O-Y
Fe(II)-Y
[VO(sal2bz)]2-Y
[Fe(sal2bz)
(H2O)2]2-Y
627
541
532
156
223
0.309
0.234
0.276
0.104
0.120
–
24.2
10.6
66.3 55.5
61.2 56.5
–
–
–
lower frequency with respect to ν(C–O) band of free ligand sal2bzH2,
which indicates the coordination of metal ions with oxygen atom [46].
A broadband around ∼3200-3400 cm−1, and two weaker bands around
827 cm−1 and 601 cm−1 in zeolite-Y immobilized complexes are at-
tributed to −OH stretching, rocking and wagging vibrations, respec-
tively [47]. Absence of ν(Oe
in neat V(IV)O complex is due to the
H)
a
b
Reduction in pore volume compared to Na-Y.
Reduction in pore volume compared to M(II)-Y.
absence of water molecule in the coordination sphere. Moreover,
O)
ν(V] vibration in neat V(IV)O complex is found at 977 cm−1 which
indicates the absence of intermolecular V]O⋯V]O bonding. How-
3.1.2. BET analysis
ever, ν(V]
vibration is missing in zeolite-Y immobilized V(IV)O
BET data reveal that zeolite-Y possess 627 m2 g−1 surface area and
0.309 cm3 g−1 pore volume (Table 3, entry 1) [38]. The immobilization
of metal ions and complex reduces the available pore volume which
leads to decrease in adsorption ability of zeolitic pores. Mainly, it de-
pends on the geometry of immobilized complex in framework of zeolite-
Y. BET surface area and pore volume of immobilized complexes
(Table 3, entries 4 & 5) gets reduced to ∼55% upon immobilization
with respect to their respective metal exchanged zeolite-Y (Table 3,
entries 2 & 3). The falling in the value clearly suggest the presence of
complex within the zeolite-Y cavities [39].
O)
complex due to the overlapping with zeolitic vibration.
3.1.6. UV–vis study and magnetic property
Electronic spectra of ligand sal2bzH2 and neat binuclear complexes
of V(IV)O and Fe(II) were taken in DMSO, while of zeolite-Y and im-
mobilized binuclear complexes were taken in diluted HF solution. The
free ligand sal2bzH2 (Table 5, entry 1) exhibit three bands at 240, 294,
and 364 nm due to ILCT, π → π* (aromatic moiety) and n → π* (C]N
chromophore) transitions, respectively [48].
As per the data, spectra of neat V(IV)O complex (Table 5, entry 2)
showed strong bands at 286 and 370 nm are corresponding to π → π*
transition and charge transfer transition, respectively. It also shows
weak bands at 418, 532 and 620 nm due to d-d transition. It suggests
the square-pyramidal geometry V(IV)O complex [49]. The bands at
291, 361 and 769 nm in case of neat [Fe(sal2bz)(H2O)2]2 ·2H2O complex
(Table 5, entry 3) are attributable to π → π*, charge transfer and d-d
transition, respectively. It recommends the octahedral environment
around the Fe(II) [50].
Dehydrated zeolite-Y (Table 5, entry 4) displays an intense band at
306 nm due to charge transfer transition for oxygen to aluminium
atoms of two different Al-O units present in zeolite-Y [51]. Zeolite-Y
immobilized binuclear V(IV)O and Fe(II) complexes (Table 5, entries 5
& 6) also shows d-d transition, which suggest the presence of complex
within zeolite-Y.
3.1.3. Powder XRD study
Except a slight change in the peak intensity, there are no major
differences in XRD patterns of M(II)-Y and immobilized complexes
while comparing them with XRD patterns of zeolite-Y (see supple-
mentary material, Fig. S2) [40]. The intensities of the 3 1 1 and 2 2 0 in
zeolite-Y, that is, I2 2 0 > I3 1 1, was varied to I3 1 1 > I2 2 0 in the case of
XRD patterns of M(II)-Y and immobilized complexes. This variation is
influenced by the immobiliztion of metal complex which leads to dis-
turb the randomly distributed sodium ions of zeolite-Y framework.
These remarks suggest that crystallinity of zeolite-Y remained intact
even after immobilization process [41].
3.1.4. SEM analysis
Soxhlet extraction was carried out to remove the ligand or metal
complex adsorbed on the external surface of zeolite-Y [42]. To confirm
the removal of exraneous particles, SEM images of [VO(sal2bz)]2-Y were
taken before and after Soxhlet extraction process (see supplementary
material, Fig. S3).
The magnetic moment of the neat V(IV)O complex is found to be
1.59 B.M at room temperature which is quite less than that of V(IV)O
monomer complexes. The lower magnetic moment of this dimer com-
plex is due to magnetically dilute nature of the complexes in which the
one metal ion is not involved in magnetic exchange (due to no bridging
ligand between two metal centres) with the neighbouring metal ions
[52]. The V(IV)O complexes of the magnetically dilute complexes
should record magnetic moments very close to the spin-only value
when the orbital contribution is completely quenched. However, if the
orbital contribution is not completely quenched the magnetically dilute
V(IV)O complexes may exhibit magnetic moments even less than the
spin-only (1.73 BM) value [53,54].
3.1.5. FT-IR study
The FT-IR spectra of ligand sal2bzH2 as well as neat and immobilized
binuclear complexes have been studied to characterize their structures
(see supplementary material, Fig. S4). As per the data given in Table 4,
a band at ∼1045 cm−1 seen in immobilized complexes (Table 4, entries
4 & 5) is corresponding to the asymmetric stretching vibrations of SiO4/
AlO4 units [43]. Most of the bands of zeolite framework found around
1193, 827 and 451 cm−1 [44].
3.1.7. TGA study
Ligand sal2bzH2 shows a band at 1616 cm−1 is corresponding to
ν(C]N). Neat V(IV)O and Fe(II) complexes (Table 4, entries 2 & 3)
Thermal degradation of neat V(IV)O complex (Table 6, entry 1) took
place in two stages. The first decomposition stage in the range of
Table 4
FTIR spectral data of zeolite-Y and prepared materials.
Entry
Material
Internal vibrations
External vibrations
ν(V=O)
ν(C=N)
ν (C-O)
ν (O-H)
νasym T-O
–
νsym T-O
–
νbend T-O
–
D-R
–
νsym T-O
–
νasym T-O
–
1
2
3
4
5
sal2bzH2
[VO(sal2bz)]2
[Fe(sal2bz)(H2O)2]2⋅2H2O
[VO(sal2bz)]2-Y
[Fe(sal2bz)(H2O)2]2-Y
–
977
–
–
–
1616
1612
1596
1608
1610
1097
1087
1062
1140
1193
3050
–
3319
3480
3470
–
–
–
–
599
601
–
–
447
451
–
–
514
574
–
–
827
827
–
–
1045
1045
1192
1170
3

D.K. Parmar, et al.
MolecularCatalysis474(2019)110424
Table 5
UV–vis spectral data of zeolite-Y and zeolite-Y modified materials.
Entry
Material
Electronic transition (nm)
π-π* (strong)
240, 294
286
291
–
n-π* (weak)
CT (strong)
–
d-d (weak)
–
418, 532, 620
769
1
2
3
4
5
6
sal2bzH2
[VO(sal2bz)]2
[Fe(sal2bz)(H2O)2]2 ·2H2O
Na-Y
[VO(sal2bz)]2-Y
[Fe(sal2bz)(H2O)2]2-Y
364
302
306
–
306
321
370
361
306
374
365
–
218, 254, 281
206, 267
418, 527, 624
752
Table 6
TGA data of prepared materials.
Entry Material T range
Weight loss
(%)
Group loss
(°C)
1
2
[VO(sal2bz)]2
280-350
550-700
80-250
78.18
21.92
9.69
Ligand
V2O3 residue
H2O
Scheme 1. Catalytic oxidation of cyclohexene.
[Fe(sal2bz)
(H2O)2]2⋅2H2O
280-350
550-700
30-120
74.13
16.28
11.84
4.61
Ligand
Fe2O3 residue
H2O
3
4
Na-Y
[VO(sal2bz)]2-Y
80-120
H2O
450-700
12.97
Decomposition of
complex
H2O
5
[Fe(sal2bz)(H2O)2]2-Y 80-250
5.47
480-700
14.51
Decomposition of
complex
Scheme 2. Catalytic oxidation of limonene.
mainly two products, that is, cyclohexane-1,2-diol (1a) and 2-hydroxy
cyclohexanone (1b) as shown in Scheme 1 [(see supplementary mate-
rial, Fig. S5 (a & b)].
280–350 °C is corresponding to the loss of ligand sal2bzH2, with 78.18%
mass loss. The final residues were estimated as vanadium oxide. De-
composition of neat Fe(II) complex (Table 6, entry 2) fall in three
stages. The first decomposition stage involves loss of hydrated and
coordinated H2O molecules in the range of 80–250 °C. Further, loss of
ligand sal2bzH2 take place in the range of 280–350 °C with mass loss of
74.13% and leaving the residue of iron oxide.
Degradation of zeolite-Y (Table 6, entry 3) about 11.84% was found
within 30–120 °C due the loss of free intra zeolite H2O molecules [55].
The first decomposition stage of zeolite-Y immobilized binuclear com-
plexes (Table 6, entries 4 & 5) falls in the range of 80–250 °C. It is due to
removal of intrazeolite and coordinated H2O molecules. The second
decomposition stage involves ∼13% mass loss around 480 °C due to the
degradation of metal complex.
The formation of water due to the decomposition of H2O2 is
somehow responsible for the hydrolysis of cyclohexene oxide to 1a.
Other products (formation of 1b through further oxidation of 1a) found
in relatively low amounts in this reaction. The formation of the olefinic
oxidation products reflects the attack over the double bond of cyclo-
hexene [56]. The selectivity of the products follows the order:
1a > 1b. The percentage of product selectivity is different in case of
neat and immobilized complexes. Among the catalysts used, neat [VO
(sal2bz)]2 (Table 7, entry 3) showed higher selectivity by providing 87%
1a, while immobilized [VO(sal2bz)]2-Y (Table 7, entry 4) showed 70%
selectivity of 1a. On the other hand, immobilized [VO(sal2bz)]2-Y
showed 9989 TON, while [VO(sal2bz)]2 displayed only 314 TON.
3.2. Catalytic activity
3.2.2. Oxidation of limonene
As displayed in Scheme 2, prepared catalysts also catalyzed the
oxidation of limonene (2) by 30% H2O2 to give limonene glycol (2a),
dihydro-carveol (2b), (S)-perillyl alcohol (2c), and carvone (2d) [see
supplementary material, Fig. S6 (a, b, c & d)]. Amongst the catalysts
3.2.1. Oxidation of cyclohexene
In present study, 100% conversion of cyclohexene (1) was achieved
(Table 7, entries 1–4). The catalyzed oxidation of cyclohexene gave
Table 7
Catalytic activity of prepared materials over oxidation of cyclohexenea.
Entry
Catalyst
Conversion (%)
Olefinic product (%)
Other product (%)
Metal (μmol) in catalystb
TONc
1a
1b
1
2
3
4
5
6
[Fe(sal2bz)(H2O)2]2⋅2H2O
[Fe(sal2bz)(H2O)2]2-Y
[VO(sal2bz)]2
100
100
100
100
96
54
50
87
70
69
70
10
12
7
10
11
10
36
38
6
20
20
19
30.2
1.10
31.8
1.00
1.00
1.00
331
9090
314
10000
9600
9500
[VO(sal2bz)]2-Y
[VO(sal2bz)]2-Yd
[VO(sal2bz)]2-Ye
95
a
Reaction conditions: 10 mmol (1.01 mL) cyclohexene, 20 mmol (2.03 mL) 30% H2O2, 15 mg catalyst, 3 mL acetonitrile, 80 °C, 24 h.
b
c
Amount of metal (μmol) present per 15 mg of catalyst.
TON: Turnover number = mol of cyclohexene converted/mol of M(II).
First reuse of catalyst.
d
e
Second reuse of catalyst.
4

D.K. Parmar, et al.
MolecularCatalysis474(2019)110424
Table 8
Catalytic activity of prepared materials over oxidation of limonenea.
Entry
Catalyst
Conversion (%)
Olefinic product (%)
Allylic product (%)
Other product (%)
Metal (μmol) in catalystb
TONc
2a
2b
2c
2d
1
2
3
4
5
6
[Fe(sal2bz)(H2O)2]2⋅2H2O
[Fe(sal2bz)(H2O)2]2-Y
[VO(sal2bz)]2
79
80
84
90
87
87
52
43
43
39
40
40
13
17
18
20
18
18
15
15
14
17
16
16
10
14
14
12
14
12
10
11
11
12
12
14
30.2
1.10
31.8
1.00
1.00
1.00
262
7272
264
9000
8700
8700
[VO(sal2bz)]2-Y
[VO(sal2bz)]2-Yd
[VO(sal2bz)]2-Ye
a
Reaction conditions: 10 mmol (1.61 mL) limonene, 20 mmol (2.03 mL) 30% H2O2, 15 mg catalyst, 3 mL acetonitrile, 80 °C, 24 h.
Amount of metal (μmol) present per 15 mg of catalyst.
TON: Turnover number = mol of limonene converted/mol of M(II).
First reuse of catalyst.
b
c
d
e
Second reuse of catalyst.
(90%). It proves that metal complex delivers the active site for the
oxidation of olefins.
Though, both the homogeneous and heterogeneous catalysts have
their own excellence and drawback. Here, homogeneous V(IV)O and Fe
(II) catalysts have demonstrated good product selectivity while het-
erogeneous V(IV)O and Fe(II) catalysts have provided better TON in
olefins oxidation. On looking towards demerit, homogeneous catalysts
suffering with separation problem as they were decomposed after first
run while heterogeneous catalysts possess selectivity issues. The cata-
lytic system (homogeneous and heterogeneous) for the oxidation of
olefins studied previously is shown in Table 10.
Scheme 3. Catalytic oxidation of α-pinene.
used, neat [VO(sal2bz)]2 complex has provided highest 84% conversion
(Table 8, entry 3), while 90% conversion was achieved by immobilized
[VO(sal2bz)]2-Y complex (Table 8, entry 4).
Literature reports that temperature and steric hindrance are the
factors that affect the selectivity among olefinic and allylic oxidation
[71]. Allylic oxidative products predominate over olefinic products at
higher temperature (above 40 °C). Though, in our case, despite of
higher reaction temperature (80 °C), oxidation of cyclohexene provides
major selectivity for olefinic oxidation and yields cyclohexane-1,2-diol
after hydrolysis. It may be due to the flexible nature of cyclohexene
with no such steric crowding makes free space available for active site
to approach. Whereas, oxidation of α-pinene proceed via allylic route
due to steric hindrance of rigid moiety which makes difficult for closet
approach of active site towards C]C double bond.
3.2.3. Oxidation of α-pinene
Catalyzed oxidation of α-pinene (3) mainly gave allylic products
[57], that is, verbenone (3a) and verbenol (3b) (Scheme 3) [see sup-
plementary material, Fig. S7 (a & b)]. The conversion of α-pinene and
the selectivity of different reaction products are presented in Table 9.
All catalysts were able to provide 100% conversion of α-pinene to oxy-
functionalized products. Neat [Fe(sal2bz)(H2O)2]2·2H2O demonstrated
79% selectivity of 3a, which is highest among the catalysts used.
Though, selectivity percentage of the products differ in neat and re-
spective immobilized complexes.
Here, we have observed that steric hindrance decreases on moving
from α-pinene to limonene and from limonene to cyclohexene.
Subsequently, formation of olefinic oxidation products increases and of
allylic products decreases (Scheme 4).
Catalytic oxidation of cyclohexene by [VO(sal2bz)]2 complex pro-
ceeds via olefinic oxidation path as shown in Scheme 5. Initially, [VO
(sal2bz)]2 (A) interacts with H2O2 to form metal peroxo species which
further undergoes homolytic cleavage to give product (B). Oxidative
addition of product (B) to the C]C of cyclohexene gives intermediate
(C) which undergoes migratory insertion to give cyclohexene epoxide
For recycling study, immobilized complexes were successfully re-
covered after completion of reaction by simple filtration, washing with
acetonitrile and drying at ca. 150 °C. Catalysts could be reused at least
two times without loss of olefin conversion and product selectivity
under similar reaction conditions (Table 7–9; entries 5 & 6).
Na-Y, V(IV)O-Y and Fe(II)-Y are unable to carry out oxidation of
cyclohexene, limonene and α-pinene to their oxy-functionalized pro-
ducts with greater amount [55,56]. In this study, both the neat and
immobilized binuclear V(IV)O and Fe(II) complexes showed excellent
conversion of cyclohexene (100%), α-pinene (100%) and limonene
Table 9
Catalytic activity of prepared materials over oxidation of α-pinenea.
Entry
Catalyst
Conversion (%)
Allylic product (%)
Other product (%)
Metal (μmol) in catalystb
TONc
3a
3b
1
2
3
4
5
6
[VO(sal2bz)]2
[VO(sal2bz)]2-Y
[Fe(sal2bz)(H2O)2]2⋅2H2O
[Fe(sal2bz)(H2O)2]2-Y
[Fe(sal2bz)(H2O)2]2-Yd
[Fe(sal2bz)(H2O)2]2-Ye
100
100
100
100
98
54
40
79
46
43
43
15
30
11
34
34
35
32
30
10
20
23
22
31.8
1.00
30.2
1.10
1.10
1.10
314
10000
331
9090
8909
8909
98
a
Reaction conditions: 10 mmol (1.58 mL) α-pinene, 20 mmol (2.03 mL) 30% H2O2, 15 mg catalyst, 3 mL acetonitrile, 80 °C, 24 h.
Amount of metal (μmol) present per 15 mg of catalyst.
TON: Turnover number = mol of α-pinene converted/mol of M(II).
First reuse of catalyst.
b
c
d
e
Second reuse of catalyst.
5

D.K. Parmar, et al.
MolecularCatalysis474(2019)110424
Table 10
Comparison of reported homogeneous and heterogeneous catalytic systems with present study over oxidation of olefins 1, 2 and 3.
Sr. No.
1
Olefin
Homogeneous catalyst /oxidant; Heterogeneous catalyst /oxidant
Conversion (%)*
TONa
Selectivityb (%)*
Ref
1
1
1
1
1
1
1
1
2
2
2
2
2
3
3
3
3
3
[VO(sal2bz)]2 /H2O2
[VO(sal2bz)]2-Y /H2O2
[VO(hacen)] /H2O2
[VO(hacen)]-Y /H2O2
[VO(L1)(acac)] /H2O2
[VO(L1)(acac)]-Y /H2O2
[VO(tmbmz)2] /H2O2
PS-[VO(ligand)n] /H2O2
[VIVO(acac)(pydx-aepy)] /H2O2
[VVO2(pydx-aepy)]-Y /H2O2
3 /H2O2
100
100
96
100
87
75
64
86
82
99
71
99
54
79
32
93
84
90
86
98
97
82
66
79
51
87
100
100
81
73
59
67
40
45
5
314
9989
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Cydiol (87)
Cydiol (70)
Cyone (49)
Cyone (37)
Cyol (46)
Cyone (48)
Cydiol (85)
Cydiol (81)
Cyone (45)
Cyone (∼50)
Cyol (51)
Cyol (39)
Cyol (53)
Cyol (48)
Cyol (57)
Cyol (44)
Lgly (36)
Lgly (35)
Lgly (34)
Hycyone (13)
Hycyone (10)
Cyol (48)
Cyol (49)
Cyox (28)
Cyox (25)
Cyone (12)
Cyone (15)
Cyol (33)
Cyol (∼35)
Cyone (48)
Cyone (56)
Cyox (39)
Cyox (35)
Cyone (32)
Cyone (47)
Pal (6)
Pal (4)
Col (10)
Col (8)
Col (17)
Col (11)
Col (17)
Col (14)
Col (20)
This study
This study
[58]
[58]
[59]
[59]
[60]
[60]
[61]
[61]
[62]
[62]
[63]
[63]
[64]
[64]
This study
This study
[65]
[65]
[66]
[66]
[67]
[67]
[68]
2
3
4
5
6
3Y /H2O2
7
[VIVO(fsal-DL-Ala)(H2O)] /H2O2
PS-[VIVO(fsal-DL-Ala)(H2O)] /H2O2
[VIVO(pydx-1,3-pn)] /H2O2
[VIVO(pydx-1,3-pn)]-Y /H2O2
[VO(sal2bz)]2 /H2O2
[VO(sal2bz)]2-Y /H2O2
[VO(VTCH)2] /TBHP
[VO(VTCH)2]-Y /TBHP
5 /H2O2
8
9
262
9020
–
10
11
12
13
14
15
16
17
18
–
Lgly (45)
50
2273
205
2372
–
Cone (70)
Cone (78)
Cone (63)
Cone (71)
Cone (39)
Cone (41)
Vone (79)
Vone (46)
Vone (77)
Vone (73)
Vone (59)
Vone (64)
Vone (44)
Vone (41)
Vol (40)
5Y /H2O2
[Fe(L)2(H2O)2]·2H2O /H2O2
[Fe(L)2(H2O)2]-Y /H2O2
[VO(L)·H2O] /H2O2
[VO(L)·H2O]-Y /H2O2
[Fe(sal2bz)(H2O)2]2·2H2O /H2O2
[Fe(sal2bz)(H2O)2]2-Y /H2O2
5 /H2O2
–
Col (32)
[68]
349
9082
–
Vol (11)
Vol (34)
Vol (11)
Vol (12)
Vol (14)
Vol (19)
Vol (39)
Vol (42)
Vone (20)
Piox (26)
This study
This study
[66]
[66]
[67]
[67]
[69]
[69]
[70]
5Y /H2O2
–
[Fe(L)2(H2O)2]·2H2O /H2O2
[Fe(L)2(H2O)2]-Y /H2O2
VOJL2 /TBHP
VOJL2-Y /TBHP
Fe3O4 /O2
183
2012
47
598
–
Co-Fe3O4 /O2
36
100
Vol (40)
[70]
a
TON: Turn over number.
b
Selectivity: Cydiol = Cyclohexane-1,2-diol; Hycyone = 2-hydroxy cyclohexanone; Cyox = Cyclohexene oxide; Cyol = 2-Cylohexen-1-ol; Cyone = 2-
Cyclohexen-1-one; Lox = Limonene oxide; Lgly = Limonene glycol; Pal= (S)-Perillyl alcohol; Cone = Carvone; Col = Carveol; Vone = Verbenone; Vol = Verbenol;
Piox = Pinene oxide.
* Conversion and selectivity % are rounded off.
Scheme 4. Effect of steric hindrance on product selectivity.
6

D.K. Parmar, et al.
MolecularCatalysis474(2019)110424
[9] A. Corma, R.M. Martin-Aranda, J. Catal. 130 (1991) 130–137.
[10] T. Joseph, S.S. Deshpande, S.B. Halligudi, A. Vinu, S. Ernst, M. Hartmann, J. Mol.
Catal. A Chem. 206 (2003) 13–21.
[11] J. Pérez-Ramírez, C.H. Christensen, K. Egeblad, C.H. Christensen, J.C. Groen, Chem.
Soc. Rev. 37 (2008) 2530–2542.
[12] N. Pal, A. Bhaumik, Adv. Colloid Interface Sci. 189–190 (2013) 21–41.
[13] S. Lopez-Orozco, A. Inayat, A. Schwab, T. Selvam, W. Schwieger, Adv. Mater. 23
(2011) 2602–2615.
[14] A. Corma, Chem. Rev. 97 (1997) 2373–2420.
[15] A. Taguchi, F. Schüth, Microporous Mesoporous Mater. 77 (2005) 1–45.
[16] C. Perego, R. Millini, Chem. Soc. Rev. 42 (2013) 3956–3976.
[17] R.M. Martín-Aranda, J. Cejka, Top. Catal. 53 (2010) 141–153.
[18] S. Fujita, S. Inagaki, Chem. Mater. 20 (2008) 891–908.
[19] P.K. Dutta, J.A. Incavo, J. Phys. Chem. 91 (1987) 4443–4446.
[20] M. Salavati-Niasari, Chem. Lett. 34 (2005) 1444–1445.
[21] M. Salavati-Niasari, Mahnaz Dadkhah, Fatemeh Davar, Inorg. Chim. Acta Rev. 362
(2009) 3969–3974.
[22] M. Salavati-Niasari, Chem. Lett. 34 (2005) 244–245.
[23] M. Salavati-Niasari, Zohreh Salimi, Mahdi Bazarganipour, Fatemeh Davar, Inorg.
Chim. Acta Rev. 362 (2009) 3715–3724.
[24] W.J. Roth, P. Nachtigall, R.E. Morris, J. Cejka, Chem. Rev. 114 (2014) 4807–4837.
[25] M. Salavati-Niasari, M. Shakouri-Arani, F. Davar, Microporous Mesoporous Mater.
116 (2008) 77–85.
Scheme 5. Proposed mechanism for oxidation of cyclohexene by [VO(sal2bz)]2.
(D) and regenerates [VO(sal2bz)]2 (A). Furthermore, cyclohexene ep-
oxide (D) undergoes in situ hydrolysis to produce cyclohexane-1,2-diol
(E), which further oxidized to 2-hydroxy cyclohexanone (F).
[26] M.R. Maurya, A.K. Chandrakar, S. Chand, J. Mol. Catal. A Chem. 270 (2007)
225–235.
[27] B. Dutta, S. Jana, S. Bhunia, H. Honda, S. Koner, Appl. Catal. A Gen. 382 (2010)
90–98.
[28] M. Salavati-Niasari, Microporous Mesoporous Mater. 95 (2006) 248–256.
[29] P. Oliveira, M.L. Rojas-Cervantes, A.M. Ramos, I.M. Fonseca, A.M.B. Rego, J. Vital,
Catal. Today 118 (2006) 307–314.
4. Conclusions
[30] B. Cornils, W.A. Herrmann, Applied Homogeneous Catalysis With Organometallic
Compounds, second ed., Wiley-VCH, Weinheim, 2002, pp. 1–1383.
[31] M. Salavati-Niasari, P. Salemi, F. Davar, J. Mol. Catal. A Chem. 238 (2005)
215–222.
[32] M. Salavati-Niasari, J. Mol. Catal. A Chem. 229 (2005) 159–164.
[33] A.B. Sorokin, Chem. Rev. 113 (2013) 8152–8191.
[34] R.K. Al shemary, Z.A. Shafiq, Asian J. Pharm. Sci. Tech. 5 (2015) 172–178.
[35] F. Farzaneh, J. Soleimannejad, M. Ghandi, J. Mol. Catal. A Chem. 118 (1997)
223–227.
As outlined, homogeneous and heterogeneous binuclear complexes
of V(IV)O and Fe(II) were prepared and characterized. V(IV)O and Fe
(II) complexes efficiently catalyzed the oxidation of olefins. In the
oxidation of cyclohexene, 100% conversion was obtained by each cat-
alyst and selectivity of the products varied in the order: cyclohexane-
1,2-diol > 2-hydroxycyclohexanone. Conversion of limonene found in
the order: [VO(sal2bz)]2-Y (90%) > [VO(sal2bz)]2 (84%) > [Fe(sal2bz)
(H2O)2]2-Y (80%) > [Fe(sal2bz)(H2O)2]2·2H2O (79%). While selectivity
order of the two main products being: limonene glycol > (S)-perillyl
alcohol. α-pinene was also oxidized completely (100%) by each catalyst
and two reaction products with the selectivity order: verbenone >
verbenol have been obtained during the oxidation.
Steric hindrance plays the major role in the selectivity of products as
less hindered cyclohexene gave epoxide products and more hindered α-
pinene provided allylic products. Almost similar results in recycling
study proves the ability of solid support to prevent decomposition of
complex during the reaction. While absence of metal leaching proves
the heterogeneous character of immobilized catalysts. In contrast to
homogeneous counterparts, advantage of being recyclable, reusable,
and higher stability makes heterogeneous catalysts significantly more
environmentally benign.
[36] T.A. Yousef, G.M. Abu El-Reash, O.A. El-Gammal, R.A. Bedier, J. Mol. Struct. 1035
(2013) 307–317.
[37] K.J. Balkus, A.G. Gabrielov, J. Incl. Phenom. Mol. Recognit. Chem. 21 (1995)
159–184.
[38] S.P. Varkey, C. Ratnasamy, P. Ratnasamy, J. Mol. Catal. A Chem. 135 (1998)
295–306.
[39] S.P. Varkey, C.R. Jacob, Indian J. Chem. 37A (1998) 407–412.
[40] W.H. Quayle, J.H. Lunsford, Inorg. Chem. 21 (1982) 97–103.
[41] C.K. Modi, N. Solanki, R. Vithalani, D. Patel, Appl. Organometal Chem. 32 (2017)
1–13.
[42] S.P. Varkey, C. Ratnasamy, P. Ratnasamy, J. Mol. Catal. A Chem. 135 (1998)
295–306.
[43] C.K. Modi, P.M. Trivedi, Adv. Mat. Lett. 3 (2012) 149–153.
[44] K.B. Kusum, C.D. Ramesh, J. Phys. Chem. C 116 (2012) 14295–14310.
[45] H.S. Abbo, S.J.J. Titinchi, Top. Catal. 53 (2010) 254–264.
[46] C.K. Modi, P.M. Trivedi, Microporous Mesoporous Mater. 155 (2012) 227–232.
[47] C.K. Modi, B.G. Gade, J.A. Chudasama, D.K. Parmar, H.D. Nakum, A.L. Patel,
Spectrochim. Acta, Part A. 140 (2015) 174–184.
[48] J.P. Mehta, D.K. Parmar, H.D. Nakum, D.R. Godhani, N.C. Desai, J. Porous Mater.
23 (2016) 1507–1518.
[49] J.P. Mehta, D.K. Parmar, D.R. Godhani, H.D. Nakum, N.C. Desai, J. Mol. Catal. A
Acknowledgements
Chem. 421 (2016) 178–188.
[50] J.C. Bailar, H.J. Emeleus, R. Nyholm, A.F. Trotman-Dickenson, Comprehensive
Inorganic Chemistry, Pergamon Press, New York, 1973.
[51] R.K. Agarwal, I. Chakraborti, S.K. Sharma, Pol. J. Chem. 68 (1994) 1085–1092.
[52] A. Syamal, Coord. Chem. Rev. 16 (1975) 309–339.
[53] Y.A. Kasparova, V.V. Zelentsov, Zh. Strukt. Khim. 9 (1968) 532.
[54] T.D. Smith, T. Lund, J.R. Pilbrow, J.H. Price, J. Chem. Soc. A. (1971) 2936–2939.
[55] M.R. Maurya, S.J.J. Titinchi, S. Chand, Appl. Catal. A Gen. 228 (2002) 177–187.
[56] P.P. Knops-Gerrits, M. L’abbe, A. Jacobs, Epoxidation With Manganese N,N-bis(2-
Pyridinecarboxamide) Complexes Encapsulated in Zeolite Y, Elsevier Science,
Amsterdam, 1997, pp. 445–452.
We thank School of Science, RK University, Rajkot, India for pro-
viding laboratory and instrument facilities.
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mcat.2019.110424.
[57] I.Y. Skobelev, A.B. Sorokin, K.A. Kovalenko, V.P. Fedin, O.A. Kholdeeva, J. Catal.
298 (2013) 61–69.
References
[58] D.R. Godhani, H.D. Nakum, D.K. Parmar, J.P. Mehta, N.C. Desai, J. Mol. Catal. A
Chem. 415 (2016) 37–55.
[1] J. Zhu, X. Meng, F. Xiao, Front. Chem. Sci. Eng. 7 (2013) 233–248.
[2] W.J. Roth, P. Nachtigall, R.E. Morris, J. Cejka, Chem. Rev. 114 (2014) 4807–4837.
[3] K. Na, G.A. Somorjai, Catal. Lett. 145 (2015) 193–213.
[4] International Zeolite Association Database, (2011) http://www.izastructure.org/
databases.
[59] G.V. Willingh, H.S. Abbo, S.J.J. Titinchi, Catal. Today 227 (2014) 96–104.
[60] M.R. Maurya, A. Arya, P. Adao, J.C. Pessoa, App. Catal. A: Gen. 351 (2008)
239–252.
[61] M.R. Maurya, M. Bisht, F. Avecilla, J. Mol. Catal. A Chem. 344 (2011) 18–27.
[62] D.R. Godhani, H.D. Nakum, D.K. Parmar, J.P. Mehta, N.C. Desai, Microporous
Mesoporous Mater. 235 (2016) 233–245.
[5] C. Teixeira, New J. Chem. 32 (2008) 2263–2269.
[6] Y.S. Park, J. Am. Chem. Soc. 124 (2002) 7123–7135.
[7] M.R. Maurya, U. Kumar, I. Correia, P. Adão, J.C. Pessoa, Eur. J. Inorg. Chem. 4
(2008) 577–587.
[63] M.R. Maurya, M. Kumar, A. Kumar, J.C. Pessoa, Dalton Trans. 28 (2008)
4220–4232.
[64] M.R. Maurya, P. Saini, A. Kumar, J.C. Pessoa, Eur. J. Inorg. Chem. 31 (2011)
[8] A.R. Silva, H. Albuquerque, S. Borges, R. Siegel, L. Mafra, A.P. Carvalho, J. Pires,
Microporous Mesoporous Mater. 158 (2012) 26–38.
4846–4861.
[65] C.K. Modi, J.A. Chudasama, H.D. Nakum, D.K. Parmar, A.L. Patel, J. Mol. Catal. A
7

D.K. Parmar, et al.
MolecularCatalysis474(2019)110424
[69] N.C. Desai, J.A. Chudasama, B.Y. Patel, K.A. Jadeja, T.J. Karkar, J.P. Mehta,
Chem. 395 (2014) 151–161.
[66] D.R. Godhani, H.D. Nakum, D.K. Parmar, J.P. Mehta, N.C. Desai, J. Mol. Catal. A
Chem. 426 (2017) 223–237.
[67] J.P. Mehta, D.K. Parmar, H.D. Nakum, D.R. Godhani, N.C. Desai, J. Porous Mater.
25 (2018) 1649–1658.
D.R. Godhani, Microporous Mesoporous Mater. 242 (2017) 245–255.
[70] L. Menini, M.C. Pereira, L.A. Parreira, J.D. Fabris, E.V. Gusevskaya, J. Catal. 254
(2008) 355–364.
[71] H. Wójtowicz-Młochowska, Rec. adv. Arkivoc part ii (2017) 12–58.
[68] C.K. Modi, R.S. Vithalania, D.S. Patela, N.N. Somb, P.K. Jha, Microporous
Mesoporous Mater. 261 (2018) 275–285.
8