Zeolite Y encaged Ru(III) and Fe(III) complexes for oxidation of styrene, cyclohexene, limonene, and α-pinene: An eye-catching impact of H2SO4 on product selectivity

Article abstract of DOI:10.1016/j.molcata.2016.11.020

A novel Ru(III) and Fe(III) complexes of ligands 1 and/or 2 {where 1 = 2,2'-((1E,1'E)-((azanediylbis(ethane-2,1-diyl))bis(azanylylidene))bis(methanylylidene))diphenol and 2 = 2,2'-((1E,1'E)-((azanediylbis(ethane-2,1-diyl))bis(azanylylidene))bis(methanylylidene)) bis(4-nitrophenol)} have been synthesized as ‘neat’ and zeolite Y encapsulated complexes. These catalysts are characterized by various analytical tools such as FTIR, UV–vis, elemental analysis, ICP-AES, molar conductivity, ¹H- and ¹³C NMR, TGA, SEM, AAS, BET, magnetic susceptibility and powder XRD to endorse the complex formation, absence of peripheral redundant ligands and complexes, conservation of zeolite Y morphology and crystallinity, and the encapsulation of complexes without devastation in the zeolite Y framework. Out of these synthesized catalysts, 5Y is found to be a potent candidate for styrene (Conv. 76.1%, TOF: 2130 h^?1), cyclohexene (Conv. 84.4%, TOF: 2351 h^?1), limonene (Conv. 81.6%, TOF: 2273 h^?1), and α-pinene (Conv. 72.6%, TOF: 2023 h^?1) oxidation with high selectivity of respective allylic products excluding the styrene oxidation, which undergoes epoxidation only. The addition of H₂SO₄ in an identical reaction catalyzed by 5Y not only surge the conversion up to 100% in a short time span with high TOF but also increase the selectivity of respective epoxidation products. This switchover in the selectivities could be credited to the presence of H₂SO₄ that facilitates the heterolytic [sbnd]O[sbnd]O[sbnd] bond cleavage of metal hydroperoxide and stimulates the epoxidation over allylic oxidation. Furthermore, the results establish that the heterogeneous systems are effortlessly recovered and reused without ample drop in the activity and selectivity.

Full text of DOI:10.1016/j.molcata.2016.11.020

Accepted Manuscript
Title: Zeolite Y encaged Ru(III) and Fe(III) complexes for
oxidation of styrene, cyclohexene, limonene, and ␣-pinene: an
eye-catching impact of H2SO4 on product selectivity
Author: Dinesh R. Godhani Haresh D. Nakum Digvijaysinh
K. Parmar Jignasu P. Mehta Nisheeth C. Desai
PII:
S1381-1169(16)30496-4
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2016.11.020
MOLCAA 10117
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
9-9-2016
7-11-2016
14-11-2016
Please cite this article as: Dinesh R.Godhani, Haresh D.Nakum, Digvijaysinh K.Parmar,
Jignasu P.Mehta, Nisheeth C.Desai, Zeolite Y encaged Ru(III) and Fe(III) complexes
for oxidation of styrene, cyclohexene, limonene, and ␣-pinene: an eye-catching
impact of H2SO4 on product selectivity, Journal of Molecular Catalysis A: Chemical
http://dx.doi.org/10.1016/j.molcata.2016.11.020
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Zeolite Y encaged Ru(III) and Fe(III) complexes for oxidation of
styrene, cyclohexene, limonene, and α-pinene: an eye-catching
impact of H2SO4 on product selectivity
Dinesh R. Godhani*, Haresh D. Nakum, Digvijaysinh K. Parmar, Jignasu P. Mehta and
Nisheeth C. Desai
Department of Chemistry, (UGC NON-SAP & DST-FIST sponsored Department)
Mahatma Gandhi Campus, Maharaja Krishnakumarsinhji Bhavnagar University,
Bhavnagar-364 002, Gujarat, India
*Corresponding author: Dinesh R. Godhani, e-mail: drgodhani@yahoo.com
Graphical Abstract

Highlights
 A Ru(III) and Fe(III) complexes are successfully encapsulated and is buttressed
by ICP-OES, BET, FTIR, Uv-Vis and TG analysis.
 The addition of H2SO4 yields 100% conversion with epoxidation products mainy,
whereas, lower conversion of substrates with high selectivity of allylic products is
obtained in the absence of H2SO4.
 The absence of metal ion leaching from zeolite Y during catalytic study is
reinforced by AAS and ICP-AES.
ABSTRACT
A novel Ru(III) and Fe(III) complexes of ligands 1 and/or 2 {where 1=2,2'-((1E,1'E)-
((azanediylbis(ethane-2,1-diyl))bis(azanylylidene))bis(methanylylidene))diphenol and 2=
2,2'-((1E,1'E)-((azanediylbis(ethane-2,1-diyl))bis(azanylylidene))bis(methanylylidene))
bis(4-nitrophenol)} have been synthesized as ‘neat’ and zeolite Y encapsulated
complexes. These catalysts are characterized by various analytical tools such as FTIR,
UV–Vis, elemental analysis, ICP-AES, molar conductivity, 1H- and 13C-NMR, TGA,
SEM, AAS, BET, magnetic susceptibility and powder XRD to endorse the complex
formation, absence of peripheral redundant ligands and complexes, conservation of
zeolite Y morphology and crystallinity, and the encapsulation of complexes without
devastation in the zeolite Y framework. Out of these synthesized catalysts, 5Y is found
to be a potent candidate for styrene (Conv. 76.1%, TOF: 2130 h-1), cyclohexene (Conv.
84.4%, TOF: 2351 h-1), limonene (Conv. 81.6%, TOF: 2273 h-1), and α-pinene (Conv.
72.6 %, TOF: 2023 h-1) oxidation with high selectivity of respective allylic products
excluding the styrene oxidation, which undergoes epoxidation only. The addition of
H2SO4 in an identical reaction catalyzed by 5Y not only surge the conversion up to 100
% in a short time span with high TOF but also increase the selectivity of respective
epoxidation products. This switchover in the selectivities could be credited to the
presence of H2SO4 that facilitates the heterolytic ‒O‒O‒ bond cleavage of metal
hydroperoxide and stimulates the epoxidation over allylic oxidation. Furthermore, the
results establish that the heterogeneous systems are effortlessly recovered and reused
without ample drop in the activity and selectivity.

Keywords: Metal complex; Oxidation; Metal-oxo intermediate; H2SO4; Selectivity
1. Introduction
Transition metal-catalyzed allylic C−H oxidation is facilitating approach for sustainable
synthesis and has grown remarkable attention due to its ability to simplify the
transformation of olefins having an allylic C−H bond to the oxy-functionalized derivatives
[1, 2]. Applications of oxyfunctionalization range from the synthesis of the natural
product, perfume, pharmaceutical, plasticizers, coating materials and drug discovery to
the synthesis of fine and commodity chemicals [3, 4]. Although a number of transition
metal-catalyzed oxyfunctionalization reactions are available at present [5-7], the use of
precious metal complexes such as Rh, Ru, Ir and Pt are relatively less studied and are
preferred extensively due to its high selectivity towards the formation desired products
with the lower amount of by-products [8]. In such oxidation, a high-valent metal−oxo
active species engendered in situ with an oxidant can act as effective oxidizing agents
and facilitate allylic C−H oxidation of substrate with trivial provoking epoxidation [9, 10].
The homogeneous neat metal complexes are a lot more active and more
selective due to presence of easily accessible active sites in it; however, apart from the
demerits of trouble in the separation and recycling of these catalysts, the contamination
of toxic metal due to homogeneous neat complex degradation in the products is an
acute matter, especially for the synthesis of biologically active intermediates and
products. In this context heterogenization of homogeneous catalyst seek utmost
attention as it confines the leaching of toxic metal ions in the products, easily recyclable,
highly stable, can operate at severe conditions and can be reused over and over again
[11- 21].
For heterogenization, zeolites are superlative supports and incisive choice for the
metal complex encapsulations [22-32]. Once an active metal complex formed inside the
ordered supercages of zeolite Y, it impedes the diffusion of metal complexes from the
supercages, which minimize the possibility of toxic metal ion leaching into the products.

In these architectures, zeolite Y obliges as a substitute scaffold for the metal complexes
and provides a controlled steric environment, where the reaction can proceed [33].
The present article focus on synthesis, characterization and catalytic aspects of
zeolite Y encapsulated Fe(III) and costly Ru(III) complexes bearing 1 and/or 2 ligands
along with the respective neat metal complexes (homogeneous catalysts). The catalytic
potential of these novel hybrid catalysts and neat complexes was studied over the
selective oxidation of limonene, cyclohexene, styrene, and α-pinene with 30% H2O2 as
an oxygen donor. Moreover, the identical reaction catalyzed by 5Y was carried out
using 2.5 mmol H2SO4 as an additive to investigate the change in % conversion and
selectivity of products. The detailed mechanistic study using UV-Vis and the changes
observed while using H2SO4 during the reaction clearly point out that M(V)=O and
M(IV)=O species may involve during the oxidation, which are formed by heterolytic
and/or homolytic ‒O‒O‒ bond cleavage of sluggish metal-hydroperoxide, respectively.
2. Experimental section
2.1 Materials
All chemicals such as 2-hydroxybenzaldehyde, 2-hydroxy-5-nitrobenzaldehyde,
diethylenetriamine, R-(+)-limonene, styrene, α-pinene, cyclohexene, RuCl3·3H2O,
Fe(NO3)3·9H2O and zeolite Y (Si/Al: 5.62) were purchased from Aldrich, Rankem (India)
and Hi-media with the maximum purity available and used as received unless otherwise
specified.
2.2 Physical methods and analysis
Many analytical tools have been used to characterize the synthesized materials or
complexes and ligands. Before the analysis, zeolite Y based materials were dehydrated
at 100 °C for 3 h to confiscate the maximum amount of physically and chemisorbed
water molecules. The quantitative analysis of Si, Al, Na, Fe(III), and Ru(III) was carried
out by ICP-AES using a model Perkin Elmer Optima 2000 DV. Electronic spectra were
carried out on “SHIMADZU” UV-2450 spectrophotometer using a quartz cell of 1 cm3
optical path in 10–3 M methanol, and/or dilute HF solutions. FTIR (4000-400 cm-1) was
recorded with KBr on a FTIR-8400S Shimadzu. TG analysis was carried out in an air

atmosphere in the temperature range 30-700 °C using Shimadzu TGA-50 instrument.
The powder XRD was carried out using Bruker AXS D8 advance X-ray powder
diffractometer with a CuKα (λ=1. 54058) target and movable detector. Scanning
electron micrographs (SEMs) of RuY and 5Y were carried out using SEM instrument
(model-JSM-5610LV), JEOL to analyze the morphology of the samples. BET surface
area and pore volume of the zeolite Y based materials were measured by a multipoint
BET method using Micromeritics, ASAP 2010 surface area analyzer. Atomic absorption
spectra (AAS) of filtrate were recorded on a PerkinElmer 4100-1319. 1H and 13C NMR
spectrum of both ligands were carried out by Varian- Gemini (200 MHZ) instrument
using MeOD and CDCl3 as a solvent, respectively. The magnetic property of neat metal
complexes was measured by the magnetic susceptibility balance of models Johnson
Matthey & Sherwood.
2.3 Synthesis section
The synthetic pathway of ligands (1, 2), neat metal complexes (3-6), metal exchanged
zeolite Y (RuY and Fe), and zeolite Y encapsulated complexes (3Y-6Y) are
demonstrated in scheme 1.
2.3.1 Preparation of ligands 1 and 2
2-hydroxybenzaldehyde and/or 2-hydroxy-5-nitrobenzaldehyde of two molar ratios
dissolve in methanol in a two-neck round bottom flask and refluxed for 15 min.
Subsequently; one molar ratio of diethylenetriamine was added dropwise and refluxed
again for 1 h at 70 °C. The movement of the reaction was verified by using TLC with the
appropriate solvent system. Once the reaction completed, the excess of methanol was
evaporated and an oily reddish product was obtained in the case of ligand 1. In
preparation of ligand 2, a red crystalline solid product was filtered and washed with
methanol and dried in air. Moreover, the purity of the ligand 1 and 2 was analyzed using
IR and UV-Vis spectroscopic techniques. Ligand 1: reddish oily liquid, yield 89.2%, 1H
NMR (200 MHz, MeOD): δ (ppm) 8.21 (2H, s, ‒OH), δ 3.73 (4H, t, HC=N‒CH2), δ 3.28
(4H, q, ‒H2C‒NH), δ 7.89 (2H, s, ‒HC=N), δ 2.98 (1H, t, ‒NH), δ 7.39- 6.63 (8H, m,
aromatic protons); 13C NMR (200 MHz, MeOD) δ(ppm): 49.6 (‒CH2‒NH‒), 58.5
(=C=N‒CH2‒), ~117.2, ~120.8, ~121.9, ~132.8, ~133.4 (carbons of the aromatic ring

moiety), 162.2 (‒C‒OH), 168.6 (‒C=N). Ligand 2: red crystalline solid, yield 94.6%, 1H
NMR (200 MHz, MeOD) δ (ppm): 3.03 (4H, q, ‒H2C‒NH), 2.79 (1H, t, ‒NH), 3.83 (4H, t,
HC=N‒CH2), 7.97-6.69 ppm (6H, dd, aromatic protons) 8.56 (2H, s, ‒HC=N), 8.89 (2H,
s, ‒C‒OH); 13C NMR (200 MHz, MeOD) δ: 48.4 (‒CH2‒ NH‒), 52.5 (=C=N‒CH2‒),
~114.3, ~122.5, ~122.8, ~128.2 139.1 (carbons of the aromatic ring moiety),
153.5(‒C‒OH), 179.5 (‒C=N).
2.3.2 Preparation neat Fe(III) and Ru(III) complexes (3-6)
The neat metal complexes were synthesized by the addition of a methanolic metal salt
solution (1.25 mmol of RuCl3·3H2O and/or Fe(NO3)3·9H2O) to the well stirred methanolic
solution of the ligand 1 and/or 2 (1.25 mmol). The resulting reaction medium was
refluxed with continuous stirring on a water bath for 4 h. The obtained solid products
were filtered, washed with methanol, recrystallize with chloroform, and then finally dried
in vacuum at 60 °C.
2.3.3 Preparation of metal exchanged RuY and FeY
A mixture of 6 g of the zeolite Y and 1 mmol of RuCl3·3H2O (0.242 g) and/or
Fe(NO3)3·9H2O (0.403 g) solution in deionized water was stirred under reflux at 110 °C
for 16 h. The pH of the reaction medium was adjusted within 4.0−4.5 using buffer tablets
in order to avert the formation of respective metal hydroxides. The slurry was then
filtered, washed with deionized water to take out the excess of metal ions (inveterate by
AAS), chlorides, and/or nitrate ions, and finally dried overnight in an oven at 100−110
°C.
2.3.4 Preparation zeolite Y encapsulated metal complexes (3Y-6Y)
Zeolite Y encapsulated complexes were prepared by the ‘flexible ligand’ method [34]. A
stoichiometric excess amount of the ligand 1 and/or 2 was allowed to diffuse through
the supercages of the pre-metal exchanged zeolite Y (RuY and FeY) which form a
metal complex in its supercages. The mixture was then refluxed for 16 h under constant
stirring. The change in the color of solid mass after reaction gives preliminary clue about
the formation of complexes inside the supercages of zeolite Y. The slurry was then
filtrated, washed frequently with water and dried at room temperature under vacuum. To

remove the unreacted excess ligands and the complexes formed on the surface of the
zeolite Y, the resultant products were further purified by Soxhlet extractor using various
solvents such as methanol, acetonitrile, chloroform, and DMF until a colorless filtrate
was obtained in each case. Finally, the products were dried under vacuum and kept in a
muffle furnace overnight at 80−110 °C to obtain anhydrous encapsulated complexes.
2.3.5 Catalytic activity
To carry out the catalytic oxidation of limonene, styrene, α-Pinene, and cyclohexene,
the catalyst (12.5 mg) was initially stirred for 10 min with substrate (25 mmol),
subsequently, a solution containing the stoichiometric amount of 30% H2O2 (25 mmol)
and 6 ml of acetonitrile was added dropwise to it. The resulting catalytic medium was
reacted with continuous stirring on an oil bath at 353 K for 18 h. The zeolite Y based
heterogeneous catalysts could be extracted by simple filtration and reused for several
times, whereas the neat metal complexes were found to be degraded during the
catalytic study. Besides that, the crude reaction mixture (filtrate) was quantitatively
analyzed by gas chromatography.
3. Results and discussion
3.1 Powder X-ray Diffraction (XRD) Studies
To confirm the conservation of the zeolite Y framework and the encapsulation of metal
complexes inside the supercages of zeolite Y, the powder XRD of pure NaY, FeY, RuY,
3Y-6Y, and recycled 5Y (denoted as 5YR1, used once over α-pinene oxidation) were
recorded. As shown in figure 1, analogous XRD patterns of pure NaY, FeY, RuY, 3Y-
6Y, and 5YR1 indeed signpost the preservation of the zeolite Y framework during the ion
exchange, encapsulation, and even during the catalytic study. Nonetheless, a marked
variance is observed in the XRD of 3Y-6Y and 5YR1 from that of the pure zeolite Y, FeY,
and RuY in the relative intensities of peak positions of I2 2 0 and I3 3 1 reflections
appearing at 10° and 12°, respectively. In the case of pure NaY, FeY, and RuY, the
relationship I220 > I311 retained, whereas, in the case of 3Y-6Y and 5YR1, I311 > I220 is
observed. This alteration in the intensities is may be due to the rearrangement of
randomly coordinated free cations and the existence of a large metal complex within the
supercages of zeolite Y [35-37].

3.2 Scanning electron microscopy
The formation of metal complexes is basically targeted inside the supercages of zeolite
Y; however, some uncoordinated ligands and complex can always be there on the
peripheral surface of zeolite Y during the synthesis of 3Y-6Y. As shown in the figure 2
some redundant particles such as uncoordinated ligands and the complexes are visible
on the surface of zeolite Y in the SEM of 5Y taken before the soxhlet extraction. To
minimize the leaching of surface redundant particles during the utilization of these
materials as catalysts, each zeolite-Y encapsulated complex was extensively purified by
soxhlet extractor using various solvents (methanol, acetonitrile, chloroform, and DMF)
until the filtrate becomes colorless and free from any metal ions (confirmed by AAS). In
the SEM of finished products 5Y (after soxhlet extraction), no surface complexes or
ligands are seen and the particle boundaries on the peripheral surface of zeolite Y is
clearly discernible, which indicate an effective removal of redundant particles from the
peripheral surface of zeolite Y [34, 38]. Besides, no new crystalline patterns are seen in
the SEM of 5Y which may be due to fine dispersal of metal complexes inside the
supercages of zeolite Y [39].
3.3 ICP-AES, Molar conductivity, and BET surface area analysis
As shown in table 1, elemental analysis data divulges that the Ru(III) and Fe(III) metal
ions form a mononuclear neat metal complexes (3-6) with the ligand 1 and/or 2 in
equimolar (1:1) ratio by the deprotonation of two phenolic groups present in 1 and/or 2,
which is found in an agreement with the theoretical consideration. Furthermore, the
lower molar conductivity values (Table 1) suggest non-ionic nature of each neat metal
complex that clearly indicates that monodentate uninegative (Cl-1 in 5 and 6, NO-3 in 3
and 4) ligand must be present in the coordination sphere of complexes along with
chelating ligand 1 and/or 2. In addition, the negative result of qualitative analysis for Cl-1
(In 5 and 6) and NO-3 (In 3 and 4) reinforce the non-ionic nature of each neat metal
complex [40, 41].
The Si and Al content (%) in each zeolite Y based nanohybrid material is rather
different (due to variation in the water content, see TGA); however, the similar Si/Al ratio
(Table 2) in each catalyst signpost the absence of dealumination and it also supports

the fact that no destruction has occurred in the zeolite Y framework upon ion exchange,
encapsulation and even during the catalytic study. The prepared catalysts 3Y-6Y were
treated with the 0.01 M NaCl immediately after the soxhlet extraction in order to replace
the extra uncoordinated Fe(III) and/or Ru(III) by Na(I) but the higher M/C ratio in the 3Y-
6Y compared (Table 2) to 3-6 (Table 1) indicate that a little extra amount of
uncoordinated Fe(III) and/or Ru(III) ions are still remains in the supercages of zeolite Y.
The decrease in the quantity of Fe(III) and Ru(III) in the 3Y-5Y compared to FeY and
RuY could be recognized to either the coordination of metal ion in the formation of metal
complexes inside the supercages of zeolites or metal ion leaching during the
encapsulation. The presence of carbon and nitrogen in 3Y-6Y, 5YR1, and 5YR11 with
almost similar C/N ratio to that of their homogeneous counterparts 3-6 evidently
supports the presence of organic moiety inside the supercages of zeolite Y.
The encapsulation of metal complexes inside the supercages of zeolite Y can
also be confirmed by BET surface area analysis. As presented in table 2, upon ion
exchange of zeolite Y with Ru(III) and/or Fe(III), only a minor reduction in the surface
area and pore volume (13-15%) is observed, whereas a drastic fall in the surface area
and pore volume (60-50%) in 3Y-6Y undoubtedly specify the formation of bulky metal
complexes inside the supercages of zeolite Y.
Interestingly, the absence of nitrogen, inferior concentration of carbon (Table 2)
and the minor weight loss up to 700 °C in the TGA of 5YR12 (Where 5YR12 is catalyst 5Y
dehydrated at 600 °C prior to the analysis) supports the fact that chelating ligands has
already been removed as a gases (CO2, NO, NO2) from zeolite Y by complex
decomposition during the dehydration, whereas no considerable deviation in the surface
area and pore volume was observed upon dehydration (Table 2) This could be
accredited to the formation of respective metal oxide from chelate complex inside the
supercages zeolite Y at high temperature, which halts the surface area and pore volume
as it is with a diminutive change; however, the considerable change was expected due
to loss of bulky chelating ligands from the supercages of zeolites.
3.4 Infrared spectroscopy

The FTIR spectra of ligands 1 and 2 mainly exhibit characteristic bands in the region
1636-1600 and 3600-3250 cm-1 (Weak broad band due to H‒bonding) due to ʋ(C=N) and
ʋ(O‒H), respectively. As shown in figure 3, ʋ(C=N) band is shifted toward lower
wavenumbers (1616-1587 cm-1) in the neat metal complexes compared to their
respective ligands, which demonstrate the coordination of azomethine nitrogen with a
transition metal ion. A weak ʋ(O‒H) broadband present at 3600–3250 cm−1 in ligand 1
and/or 2 might have disappeared in 3-6 due to coordination of phenolic ‒OH to a metal
ion via deprotonation; however, the presence of extra strong broad bands in the region
of 3600–3250 cm−1 clearly signpost the presence of crystal water molecules in each
neat complexes, further supported by TG analysis [42]. The coordination of –NH group
to metal ion could not be resolute due to the presence of broadband of crystal water in
the region of 3600–3250 cm−1 where ‒NH group normally exhibits [43]. Furthermore, the
appearances of new weak broad band (Due to overlapping of ʋ(M-O)phenolic, ʋ(M-N) azomethine,
ʋ(M-N) –NH group and ʋ(M-Cl) and/or ʋ(M-NO3) bands) in the low frequency region of 600–400
cm−1 specify the coordination of azomethine nitrogen, phenolic –OH, ‒NH group, and
Cl-1 (in 5 and 6) and/or NO3-1 (in 3 and 4) to the transition metal ion [43-45].
As shown in the figure 3, zeolite Y, RuY, FeY, 3Y-6Y, 5YR1, 5YR11, and 5YR12
mainly exhibit bands nearly at 3600-3200, 1640, 1056, 816, 448, 600, 1200, and 672
cm−1 due to surface –OH group, lattice water molecules, ʋasymT–O (internal), ʋsymT–O
(internal), ʋbendT–O (internal), double ring external linkage, ʋasymT–O (external), and
ʋsymT–O (external, T= Si, Al), respectively [46]. In 3Y-6Y, the bands exhibited by
trapped complexes are covered up by these strong zeolitic bands; however, the
presence of weak bands due to trapped complexes in the region 1570-1300 cm−1
(where the zeolite matrix does not absorb) clearly indicates that the metal complexes
are existing inside the zeolite Y supercages. The trivial shifting of these peak positions
compared to the respective neat complexes can be accredited to the influence of zeolite
Y matrix on the geometry of the encapsulated complexes [27]. The FTIR spectra of the
5YR1 and 5YR11 (Recycled 5Y dehydrated at 250 and 350 °C, respectively) are found to
be extra strong due to the removal of disquieting intrazeolite water molecules which
veneer the weak bands exhibited by trapped complexes. In the case of 5YR12 (Recycled
5Y dehydrated at 600 C°), the absence of weak bands in the region 1570-1300 cm−1

indicates that the trapped complex might have decomposed completely during the prior
dehydration. Moreover, the analogous FTIR pattern of zeolite Y, RuY, FeY, 3Y-6Y,
5YR1, 5YR11, and 5YR12 (except, the region 1570-1300 cm−1 in 3Y-6Y, 5YR1 and 5YR11
support the fact that the zeolite Y framework remains intact upon ion exchange,
encapsulation, after being used as a catalyst and even upon dehydration at high
temperature [47].
)
3.5 UV-visible spectroscopy and Magnetic susceptibility measurements
The peak values for the electronic transitions detected in ligands 1 and 2, neat metal
complexes 3-6 and modified zeolite Y based materials are presented in table 3. The
absorption spectrum of ligand 1 displays two lower energy bands at 400 and 315 nm
and three higher energy bands at 254, 213, and 206 nm (Figure 4). The bands at higher
wavelength are ascribed to n → π* and the bands at lower wavelength are due to π →
π* transitions. In the ligand 2, five absorption bands are observed at 392, 318, 229, 212,
and 205 nm. The former two bands are attributed to n → π* and the remaining are
assigned to π → π* transition. The neat iron (III) complexes (3 and 4) display absorption
peaks above and below 250 nm due to π → π* and n → π* (overlapped by strong
LMCT in complex) originating from the ligands. In addition to these transitions, the band
at 321 nm in complex 3 and band at 323 nm in complex 4 is attributable to the ligand to
metal charge transfer transition (LMCT), a transition from pπ orbitals of phenolate
oxygen to the dπ* orbitals of the Fe(III). The existence of an weak additional band in the
region of 508-497 nm in 3 and 4 are attributed to 6A1g →T2g (G) transition (d-d) and the
observed magnetic moment value in the range of 5.81-5.69 B.M is a characteristic value
of Fe(III) ion in an octahedral geometry [48-52]. The neat Ru(III) complexes (5 and 6) of
ligands 1 and 2 exhibits bands below 287 nm (Table 3) due to π → π* and n → π*
(dominated by strong LMCT in the complex) occurring due to ligands system. The
presence of strong band nearly at 339 nm in complex 5 and at 316 nm in complex 6 can
be ascribed to the ligand to metal charge transfer (LMCT) transition. Moreover, the
existence of very weak low energy d-d band (2T2g→4T2g) at 647- 602 nm and lower
obtained magnetic moment value (Table 1) mutually suggest an octahedral geometry of
both the Ru(III) complexes [53, 54].

As displayed in figure 4, pure zeolite Y commonly features two weak absorption
peaks at 306 and 345 nm owing to the charge transfer transition (Al ← O) of two
different Al–O units present zeolite Y framework [55, 56]. The presence of similar bands
at 306 nm in FeY, RuY, and in 3Y-6Y confirmed the absence of dealumination during
the synthesis (ion exchange and encapsulation) of these materials. However, in 3Y-6Y,
a weak host zeolitic band (345 nm) is exclusively covered by the appearance of new
strong charge transfer transition exhibited by the trapped metal complexes.
Besides these zeolitic bands, the presence of weak bands at 655 nm in FeY and
at 760 nm in RuY can be recognized as a d-d transition, which is characteristic of an
octahedral configuration around to M(III) ions designed by oxygens and/or physically or
chemisorbed water molecules present in the zeolite Y framework. In the case of 3Y-6Y,
the absorption bands due to trapped complexes are less intense than those of the
respective neat complexes 3-6 due to its lower concentration inside the supercages of
zeolite Y. Nevertheless, the 3Y-6Y exhibits absorption bands nearly at the similar
wavelength as those observed in the neat complex 3-6, a slight shifting of the bands
towards lower or higher wavelengths are observed either under the influence of zeolite
Y matrix or the distortion in the geometry of metal complexes itself upon encapsulation.
3.6 TG analysis
Table 4 demonstrates the thermal activities of synthesized neat and encapsulated
complexes on the basis of TG analysis. The TG curve of 3 and 4 undergoes
decomposition in three stages (Figure 5). The first stage arises in the temperature
ranges of 30–110 °C with the mass loss of 8.0% (cal. 7.8%) in 3 and 6.1% (cal. 6.5%) in
4 due to the removal of two moles of lattice water molecules. In the second stage, which
is observed in the range of 111–220 °C, a weight loss of about 11.4% (cal. 13.4%) in
complex 3 and 11.9% (cal. 11.2%) in 4 can be attributed to the removal of the
monodentate ligand from the complexes. In the third stage, 3 and 4 decompose within
the temperature range of 221- 450 °C with the weight loss of about 45.6% (cal. 44.3%)
and 52.8% (cal.53.4%), respectively, which is ascribed to the removal of chelating
ligands via complex decomposition and leaving behind the ferric oxide (Fe2O3) as
residue. In the case of Ru(III) complexes, 5 shows weight loss of about 3.8 (cal. 3.9), 7.4
(cal. 7.7), and 35.8% (cal. 34.1%) due to the stepwise removal of one mole of lattice

water, monodentate ligand Cl ‒, and chelating ligand in first (30-150 °C) second (151-
260 °C) and third (261-500°C) decomposition stage, respectively. As shown in figure 5,
complex 6 displays weight loss of about 3.2 % (cal. 3.2%) in the first stage (30-120°C),
6.0% (6.4%) in the second stage (121-240 °C) and 46.2% (cal. 45.0%) in the third stage
(241-500 °C) due to elimination of one mole of lattice water, monodentate ligand Cl ‒,
and chelating ligand, respectively. Beyond 500 °C, complex 5 and 6 leaves residue
about 53.8 (cal. 54.3) and 44.6% (45.4%) of ruthenium oxide, respectively.
In case the of zeolite Y based materials, the thermal decomposition mainly
occurs in the temperature range of 30 to 400 °C due to the abstraction of physically and
chemisorbed water molecules (10.32-0.39) from the zeolite Y framework [57, 58]. As
shown in figure 5 (magnified), the encapsulated complexes (except 5Y12) exhibit one
more thermal decomposition stage of about 1.90- 1.46 % beyond 450 °C. This minor
weight loss can be recognized the existence of only trivial amounts of the metal
complex inside the supercages of zeolite Y (Table 4), which is in an agreement with the
low percent metal content measured by the ICP-AES. Moreover, the weight loss due to
trapped complex is prolonged (up to 450 °C) compared to respective homogeneous
counterparts 3-6. This observation indicates that the thermal stability of the complexes
is considerably enriched upon its encapsulation into zeolite Y supercages. Moreover, no
significant weight loss in 5Y12 beyond 400 °C clearly (Figure 5) indicates the trapped
complex has been decomposed during its dehydration at 600 °C prior to the TG
analysis. In view of the above, we may conclude that zeolite Y encapsulated complexes
can be treated thermally below 600 °C without degradation of the trapped complexes.
4. Catalytic activity
The catalytic oxidation of styrene, cyclohexene, limonene, and α-pinene was performed
in a two-necked 25 ml round bottomed flask. In a typical reaction, 12.5 mg catalyst and
the substrate (25 mmol) are initially stirred for 10 min. Subsequently, a solution
containing the stoichiometric amount of 30% H2O2 (25 mmol) and 6 ml of acetonitrile is
added dropwise into it and equilibrated at 353 K in an oil-bath with continuous stirring
for 18 h. The products were collected after 18 h and quantitatively analyzed by GC.

4.1 Oxidation of styrene, cyclohexene, limonene, and α-pinene
The catalytic activity and product selectivity of neat and encapsulated complexes along
with ligand 1, 2, zeolite Y, RuY, and FeY for styrene, cyclohexene, limonene, and α-
pinene are presented in table 5, 6, 7, and 8, respectively. A blank experiment carried
out without any catalyst shows only 1.1, 2.6, 1.2, and 1.0% conversions of styrene,
cyclohexene, limonene, and α-pinene, respectively. The negligible conversion of
styrene, cyclohexene, limonene, and α-pinene (below 5%) in the presence of ligand 1 or
2, and NaY clearly gesture that the zeolite and ligands (1 and/or 2) are futile alone for
the catalytic purpose. Despite the fact that the use of RuY and FeY as catalyst displays
high TOF about 316-188 h-1 which is more than 3-fold to that of the homogeneous
complexes 3-6, it shows much lower conversions (22-12%) of styrene, cyclohexene,
limonene, and α-pinene compared to the neat metal complexes 3-6.
As shown in table 5, neat metal complexes 3-6 shows the higher conversion of
the styrene as compared to their respective zeolite-Y encapsulated complexes 3Y-6Y;
however, it shows lower TOF (52-41 h-1) and cannot be recycled as well. In the case of
3Y-6Y, which has shown a much higher TOF in the range of 2130-936 h-1 and offered
high selectivity towards benzaldehyde (93.6-86.8%), a lower conversion (81.2-62.3%) of
styrene was observed compared to their homogeneous counterparts 3-6 (100-70.1%).
The high selectivity towards benzaldehyde and moderate styrene conversion shown by
3Y-6Y could be attributed to the shape selectivity and high diffusion resistance of
styrene through the small windows of zeolite Y, respectively [59]. Styrene oxidation
mostly results into benzaldehyde as a major product due to a later nucleophilic attack of
H2O2 on pre-formed styrene oxide [60-62]. Other minor products such as 1-
phenylethane-1,2-diol and phenylacetaldehyde are formed due to hydrolysis and
isomerization of styrene oxide, respectively.
As presented in table 6, the 3-6 achieved high cyclohexene conversions up to
97.5–71.4%, whereas, 3Y-6Y showed lower conversions up to 84.4-64.0% with higher
TOF (2351-970 h-1) compared to 3-6 (50-41 h-1). Even though the use of H2O2 as an
oxidant, usually gives cyclohexene oxide as a major product via epoxidation, in the
present work, both homo 3-6 and heterogeneous catalysts 3Y-6Y affords higher

selectivity towards Cyone and Cyol around 81-70%, suggesting that the reaction mainly
proceeds via the radical pathway.
As observed in the case of cyclohexene and styrene, the heterogeneous
catalysts 3Y-6Y are not as efficient (81.6-55.5%) as homogeneous catalysts 3-6 (96.6-
69.0%) for limonene oxidation (Table 7); however, it shows high TOF around 2273-1028
h-1, which is more than 30-fold to that of 3-6. Moreover, both homo- and heterogeneous
catalysts are highly selective towards the formation of allylic products (95-80%) such as
carveol and carvone with a minor yield of epoxidation products (20-5%) like limonene
oxide, limonene dioxide, and limonene glycol.
In the case of α-pinene oxidation, table 8, catalyst 3-6 are found to be more
active (81.3-54.4%) than the heterogeneous catalyst 3Y-6Y (72.6-56.8%) but the TOF
of 3Y-6Y catalysts (2023-816 h-1) are grander than the 3-6 catalysts (42.34-31.75 h-1).
Furthermore, these two types of catalysts are extremely selective towards the allylic
products verbenol, verbenone, and myrtenol with the trace amount pinene oxide and
campholenal.
Generally, oxidation of cyclohexene, limonene, and α-pinene can occur on allylic
C‒H bond or onto C=C bond or can occurs on both sites simultaneously, which can lead
a number of products that are difficult to separate out at the end of reaction. As shown
in table 6, 7, and 8, the higher selectivity of neat metal complexes 3-6 and zeolite-Y
encapsulated complexes 3Y-6Y towards allylic products (Cyol, Cyone, Col, Cone, Vol,
Vone, and Mnol) clearly indicate that our catalysts are facilitating allylic oxidation of said
the substrates over their epoxidation. The common activity trends for 3-4, RuY, FeY,
and 3Y-6Y catalysts derived on the basis of % conversion are found to be different for
each substrate and therefore it is difficult to find out the most active catalyst among
them. Consequently, the common activity trend derived on the basis of turn over
frequency (TOF), which is defined as moles of substrate converted per mole of active
metal ion per hour, is found a more suitable trend to pick up the most active catalyst
among all. The activity trend of each catalysts on the basis of TOF for styrene,
cyclohexene, limonene, and α-pinene is 4 < 3 < 6 < 5 < FeY < RuY < 4Y < 3Y< 6Y <
5Y. The above activity trend is further supported by the data of H2O2 conversion and
H2O2 efficiency whose reaction was carried out separately at identical reaction

condition. As shown in table 5, the H2O2 % conversion is found to be 14.1% at 353 K
due to its self-decomposition at reaction temperature (353 K) and it remains almost
similar even after the addition of ligand 1, and/or 2, and/or NaY, suggesting
ineffectiveness of ligands and zeolite-Y framework in the decomposition of H2O2. The
use of RuY, FeY, 3-6, and 3Y-6Y significantly upsurges the conversion of H2O2 that
demonstrate its imperative role in catalyzing the substrate; however, higher H2O2
efficiency of 3-6 and 3Y-6Y could be attributed to the formation of an active chelate
intermediate which can easily attack less hinder site of the substrate (allylic C‒H) and
leads high conversion and the selectivity.
Moreover, the presence of electron withdrawing groups (Nitro) at the para
position to the hydroxyl group in complexes of ligand 2 (4, 6, 4Y and 6Y) drops an
electron density at ligating “Oxygen” atom in complexes that give rise to an electron
deficient metal center compared to the complex of ligand 1 having no electron
withdrawing group (R=H) [63, 64]. Subsequently, 3, 5, 3Y, 5Y can be easily oxidized
compared to the 4, 6, 4Y and 6Y and therefore found highly active (higher TOF) and
selective. Amongst all, encapsulated complex 5Y is found to be a most active catalyst
and therefore it was taken as a representative catalyst to check the stability,
recyclability, and the effect of H2SO4 on oxidation of styrene, cyclohexene, limonene,
and α-pinene at identical reaction condition.
4.2 Stability and recyclability of the catalyst
The stability and reusability of 5Y were inspected on α-pinene oxidation at identical
reaction condition. The catalyst 5Y was revived by filtration, purified by soxhlet extractor
using acetonitrile, and then dried at different temperatures such as 250, 350, and 600
°C (denoted as 5YR1, 5YR11 and 5YR12, respectively, Table 8) to notice the effect of
catalyst dehydration upon its activity and selectivity. In the case of 5YR1 and 5YR11, the
α-pinene conversion slightly upsurges (Table 8) due to the removal of an intrazeolite
water molecule from the small windows of zeolite Y which reduce the diffusion resistant
for the reacting substrate during the catalytic reaction. A drastic fall in the α-pinene
conversion using 5YR12 clearly indicates that the active trapped complex has
decomposed during its dehydration at 600 °C prior to catalytic activity, further supported
by FTIR (Figure 3), TGA (Figure 5), and ICP-OES analysis (Table 2). Consequently, the

encapsulated complexes are found to be highly active, selective, and stable at current
reaction condition. Moreover, two consecutive runs of 5Y (Table 8, denoted as 5YR3 and
5YR4, dehydrated at 250 °C prior to the reaction) show no significant loss in the α-
pinene conversion and selectivity of the products. Moreover, the AAS did not show any
ruthenium metal content in the filtrate and approves no leaching of metal ions from the
catalyst during α-pinene oxidation.
4.3 Impact of H2SO4 on styrene, cyclohexene, limonene, and α-pinene oxidation
An impact of H2SO4 on styrene, cyclohexene, limonene, and α-pinene oxidation
catalyzed by 5Y was studied at identical reaction condition. As shown in figure 6, the
addition of 2.5 mmol of sulfuric acid during the styrene oxidation boost up the rate of
reaction and yield 100% styrene conversion in only 8 h with Bzald (28.0), Styo (57.5),
Phetdiol (13.1), and Phacetal (1.4%). On continuing reaction up to 18 h, the selectivity
of styrene oxide drops to 9.2%, whereas, the selectivity of Phetdiol (19.1), Phacetal
(3.2%) and Bzald (68.5) upsurge due to hydrolysis, isomerization and later nucleophilic
attack of H2O2 on Styo, respectively [60-62].
In the case of cyclohexene (Figure 7), limonene (Figure 8) and α-pinene (Figure
9) oxidation, the addition 2.5 mmol of H2SO4 catalyzed by 5Y yield 100% conversions
only in 12-10 h that may take more than 18 h to complete the reaction without sulfuric
acid. Interestingly, the addition of H2SO4 mainly produces epoxidation products,
whereas allylic products are obtained as major products in the absence of H2SO4.
Moreover, on continuing reaction up to 18 h after 100% conversion of cyclohexene
limonene and α-pinene with H2SO4, the selectivity of allylic alcohols (CyOl, Vol, and Col)
and the epoxides (Cyox, Limox, and Piox) decreases gradually due to its farther
oxidation into the respective allylic ketones (Cyone, Vone, and Cone) and diols or
aldehydes (Cydiol, Limgly, and Camal), respectively.
The catalyst 5Y was recovered by filtration, washed with acetonitrile, dried at 250
°C and then used as a catalyst in the subsequent catalytic run to notice whether the use
of 2.5 mmol H2SO4 during the first catalytic cycle has affected on activity of the catalyst
or not. As presented in table 9, the successive runs of catalyst 5Y lead to a
considerable lowering in the conversion of α-pinene. This lowering in the catalytic
activity can be attributed to a minor distraction of the zeolite-Y encapsulated complexes

under the influence of strong oxidizer caro’’s acid which is produced in situ by the
reaction of H2SO4 with H2O2 during the catalytic oxidation. Moreover, we could not
recover the catalyst 5Y when 25 mmol H2SO4 was used instead of 2.5 mmol H2SO4.
From the above observation, it can be concluded that the use of catalytic amount
of H2SO4 (2.5 mmol) may help to increase the rate of the oxidation reaction and
selectivity of epoxidation products but it decreases the stability and activity of the
catalyst in their successive catalytic runs. This lowering in the activity of the catalyst 5Y
could only be attributed to the degradation of zeolite-Y encapsulated complexes in the
highly acidic reaction medium. Moreover, the possibility of H2SO4 to react with hydroxyl
(-OH) and amine (-NH2) of ligands can be excluded as the used complex has no free
hydroxyl group and an amine group to react with acid or any substrate that is being
used throughout the catalytic oxidation.
5. Plausible reaction pathway of catalysts
The reaction mechanism for oxidation catalyzed by Fe(III) complexes with H2O2 has
been studied over the last two decades and the involvement of metal hydroperoxide
Fe(IV)‒OOH has been anticipated as an active intermediate [65, 66]. At the same time,
the involvement of metal-oxo species such as M(IV)=O and/or M(V)=O, which are
usually resulted by homo- or heterolytic –O‒O‒ bond cleavage of sluggish oxidant
Fe(IV)‒OOH, has also been anticipated as an active intermediate [67-71]. Moreover,
Fujii et al. inveterate Fe(III)-monophenoxyl radical as potent oxidizing species for Fe
salen complex at very low temperature (193 K); however, the possibility of Fe(III)-
monophenoxyl radical can be ruled out here in our case as our reaction temperature is
very close to 353 K [72, 73] .
In order to figure out the possible reaction pathway, 10−3 M solutions of 3- 6 are
first dissolved in the least possible amount of methanol and treated distinctly with a
methanolic solution of H2O2. The change in the spectra of 3- 6 by the addition of
methanolic H2O2 is studied by UV−Vis spectroscopy (Figure 10). The constant addition
of H2O2 to the solution of 3-6 parades a decrease in intensity of the peaks at 497 and
321 nm in 3, 508 and 323 nm in 4, 603 and 339 nm in 5, 647 and 316 nm in 6, whereas
an elevation in the intensity of peaks below 300 nm in 3-6 complexes are observed. The

appearance of an isobestic point at 308 nm in 3, at 296 nm in 4, at 295 nm in 5, and at
311 nm in 6, decrease in intensity of the MLCT and d−d bands upon addition of H2O2
can be attributed the direct interaction of H2O2 with M(III) and its transformation into
M(IV/V) oxo intermediates. In the case of 3Y-6Y, the detail mechanistic study cannot be
carried out due to the lower concentration of complexes inside the supercages of zeolite
Y; however the involvement of M(IV)=O or M(V)=O may be predicted due to restraint in
dimerization of complexes executed by zeolite-Y nanopores.
In our case, predominant allylic oxidation of cyclohexene (Table 6), limonene
(Table 7), and α-pinene (Table 8) clearly indicate that the reaction is radical type
reaction (without H2SO4), which is instigated by homolytic –O‒O‒bond cleavage of
metal hydroperoxide. Interestingly, the predominant epoxidation instead of allylic
oxidation with H2SO4 may infer that the reaction is not a radical type and may proceed
via electrophilic M(V)=O intermediate formed by H+ promoted heterolytic –O‒O‒ bond
cleavage of metal hydroperoxide, which further attack on nucleophilic C=C of the
substrate and results epoxide as a major product.
As shown in the scheme 2, the reaction of H2O2 with complex forms sluggish
oxidative metal-hydroperoxide species II. Consequently, the intermediate II undergoes
homolytic –O‒O‒ bond cleavage and form reactive free radical intermediate III. This
highly reactive free radical III immediately attack weak allylic C‒H bond of α‒pinene and
form intermediate V and VI, which further results into verbenol and myrtenol. The
oxidation of verbenol with the help of free radical intermediate III leads to the formation
of verbenone as a major product via formation of intermediate IV. In the presence of
H2SO4, the proton stimulates the heterolytic –O‒O‒ bond cleavage of intermediate II
and form electrophilic intermediate VII, which attack on electron rich site of α-pinene
and form pinene oxide. Moreover, this pinene oxide is converted into campholenal
under acidic reaction medium.
Conclusion
A novel zeolite Y encapsulated Fe(III) and Ru(III) complexes has been effectively
encapsulated by FL method. The encapsulation of metal complexes without any kind of
devastation in the zeolite Y framework was assured by FTIR, UV-vis, ICP-AES, powder
XRD, TGA, SEMs, as well as BET surface area analysis. In addition to that, respective

neat Fe(III) and Ru(III) homogeneous complexes 3-6 were also synthesized for the sake
of comparison with their heterogeneous counterpart 3Y-6Y. It can be concluded that the
synthesized catalysts utilized over oxidation of styrene, cyclohexene, limonene, and α-
pinene follows a common activity trend (4 < 3 < 6 < 5 < FeY < RuY < 4Y < 3Y< 6Y < 5Y)
which is derived on the basis of TOF and not on % conversions. The identical oxidation
reactions carried out for 8, 10, 12, and 12 hrs with H2SO4 using 5Y as representative
catalyst yield 100% conversion of styrene, cyclohexene, limonene and α-pinene with
styrene oxide (67.8), cyclohexene oxide (57.3), limonene oxide (55.2) and pinene oxide
(57%) as major products with high TOF values, respectively. The encapsulated
heterogeneous catalyst could be easily retrieved and used without remarkable loss in
the catalytic activity, which makes it grander to neat metal complexes. Furthermore, no
metal ion content in the filtrate clearly indicates that no leaching of the metal ion from
the catalyst throughout oxidation.
Acknowledgements
We express our gratefulness to the Head, Department of Chemistry, M. K. Bhavnagar
University, Bhavnagar, Gujarat, India, for providing the necessary laboratory facilities.
This research did not receive any specific grant from funding agencies in the public,
commercial, or not-for-profit sectors.
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Figure and scheme Captions
Figure 1. Powder X-ray Diffraction (XRD) patterns pure NaY, FeY, RuY and zeolite Y
encapsulated complexes (3Y- 6Y).
Figure 2. Scanning electron micrographs of RuY and 5Y before soxhlet and after
soxhlet extraction.
Figure 3. FTIR spectra of ligands (1 and 2), neat complexes (3-6), FeY, RuY, and
zeolite Y encapsulated complexes (3Y- 6Y).
Figure 4. Electronic spectra of ligands (1 and 2), neat complexes (3-6), FeY, RuY, and
zeolite Y encapsulated complexes (3Y- 6Y).
Figure 5. TGA patterns of neat complexes (3-6), FeY, RuY, and zeolite Y encapsulated
complexes (3Y- 6Y).
Figure 6. Influence of reaction time on styrene conversion and product selectivity with
their respective TOF values. Reaction condition: 25 mmol styrene, 25 mmol 30% H2O2,
12.5 mg catalyst 5Y, 2.5 mmol (0.13 ml) of H2SO4, 6 ml of acetonitrile, 353 K.
Figure 7. Influence of reaction time on cyclohexene conversion and product selectivity
with their TOF values. Reaction condition: 25 mmol cyclohexene, 25 mmol 30% H2O2,
12.5 mg catalyst 5Y, 2.5 mmol (0.13 ml) of H2SO4, 6 ml of acetonitrile, 353 K.
Figure 8. Influence of reaction time on limonene conversion and product selectivity with
their TOF values. Reaction condition: 25 mmol limonene, 25 mmol 30% H2O2, 12.5 mg
catalyst 5Y, 2.5 mmol (0.13 ml) of H2SO4, 6 ml of acetonitrile, 353 K.
Figure 9. Influence of reaction time on α-pinene conversion and product selectivity with
their TOF values. Reaction condition: 25 mmol α-pinene, 25 mmol 30% H2O2, 12.5 mg
catalyst 5Y, 2.5 mmol (0.13 ml) of H2SO4, 6 ml of acetonitrile, 353 K.
Figure 10. UV–visible spectral studies of neat complexes (3-6) taken during the
consecutive addition of a methanolic H2O2 (isobestic point were observed, light green
arrows).
Scheme 1. Synthetic route of the ligands (1 and 2), neat complexes (3-6), FeY, RuY,
and zeolite Y encapsulated complexes (3Y- 6Y).
Scheme 2. The merely tentative reaction mechanism for oxidation of α-pinene with
H2O2 catalyzed by transition metal complexes.

Figure 1.

Figure 2

Figure 3.

Figure 4.