Zeolite enslaved transition metal complexes as novel heterogeneous catalysts for synthesis of polycyclic heterocycles using suzuki–miyaura cross coupling reaction under greener conditions

Article abstract of DOI:10.1016/j.inoche.2020.108230

In the present work we report the construction of zeolite enslaved transition metal complexes (Pd2+, Ni2 + ) as novel heterogenous catalysts for synthesis of polycyclic heterocycles using suzuki–miyaura cross coupling reaction in ethanolic medium. The synthesized catalysts were characterized by employing UV–Vis, FT-IR, magnetic susceptibility, N₂ sorption, XRD, XPS, FE-SEM analysis. Results of the study advocate that newly developed catalysts give rise to a rapid and easy synthesis of various polycyclic heterocycles by Suzuki coupling reactions in impressive yields. In conclusion, developed catalyst may be used as versatile tool in the synthesis of various industrially and pharmaceutically important polycyclic heterocycles under greener conditions.

Full text of DOI:10.1016/j.inoche.2020.108230

Journal Pre-proofs
Short communication
Zeolite enslaved transition metal complexes as novel heterogeneous catalysts
for synthesis of polycyclic heterocycles using suzuki--miyaura cross coupling
reaction under greener conditions
Shalu Sain, Dharam Kishore, Sonika Jain, Vivek Sharma, Manish Srivastava,
Nalini Sankararamakrishnan, Shruti Mishra, Jaya Dwivedi, Saikh M
Wabaidur, Swapnil Sharma
PII:
S1387-7003(20)30820-0
DOI:
https://doi.org/10.1016/j.inoche.2020.108230
INOCHE 108230
Reference:
To appear in:
Inorganic Chemistry Communications
Received Date:
Revised Date:
Accepted Date:
21 July 2020
7 September 2020
7 September 2020
Please cite this article as: S. Sain, D. Kishore, S. Jain, V. Sharma, M. Srivastava, N. Sankararamakrishnan, S.
Mishra, J. Dwivedi, S.M. Wabaidur, S. Sharma, Zeolite enslaved transition metal complexes as novel
heterogeneous catalysts for synthesis of polycyclic heterocycles using suzuki--miyaura cross coupling reaction
under greener conditions, Inorganic Chemistry Communications (2020), doi: https://doi.org/10.1016/j.inoche.
2
020.108230
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ZEOLITE ENSLAVED TRANSITION METAL COMPLEXES AS NOVEL
HETEROGENEOUS CATALYSTS FOR SYNTHESIS OF POLYCYCLIC
HETEROCYCLES USING SUZUKI--MIYAURA CROSS COUPLING REACTION
UNDER GREENER CONDITIONS
a
a
a
a
a
Shalu Sain , Dharam Kishore , Sonika Jain , Vivek Sharma , Manish Srivastava , Nalini
b
b
*a
a,c
Sankararamakrishnan , Shruti Mishra , Jaya Dwivedi Saikh M Wabaidur and Swapnil
Sharmad
a
Department of Chemistry, Banasthali Vidyapith, Banasthali, India
Centre for Environmental Science and Engineering, Indian Institute of Technology, Kanpur,
b
India
c
Department of Chemistry, College of Science, King Saud University, Riyadh, Saudi Arabia
Department of Pharmacy, Banasthali Vidyapith, Banasthali, India
c
*Corresponding author
Prof. Jaya Dwivedi
Department of Chemistry
Banasthali Vidyapith-304 022 (Rajasthan), India
E mail: jayadwivedi@yahoo.co.in

Abstract
In the present work we report the construction of zeolite enslaved transition metal complexes
(
Pd2+, Ni2+) as novel heterogenous catalysts for synthesis of polycyclic heterocycles using
suzuki—miyaura cross coupling reaction in ethanolic medium. The synthesized catalysts were
characterized by employing UV-Vis, FT-IR, magnetic susceptibility, N sorption, XRD, XPS, FE-
2
SEM analysis. Results of the study advocate that newly developed catalysts give rise to a rapid
and easy synthesis of various polycyclic heterocycles by Suzuki coupling reactions in impressive
yields. In conclusion, developed catalyst may be used as versatile tool in the synthesis of various
industrially and pharmaceutically important polycyclic heterocycles under greener conditions.
Key words: Zeolite; Heterogeneous Catalyst; Suzuki-Miyaura Cross Coupling Reaction; Schiff
Base
1
. Introduction
The formation of new carbon-carbon bond is of central importance in organic chemistry and is a
pre-requisite for all life on earth. Over the years these coupling reactions were developed using
more efficient catalytic systems by incorporating a variety of ligands. These powerful ligands led
to the discovery of new cross-coupling reactions generating other bonds as well (such as the C –
N, C – O, C – P, C –S, C –B, etc.). Since then though, researchers pioneered to explore (i) on metal
catalyst capability promoting these transformation (ii) its expansion to a variety of coupling
partners (iii) extension of each reaction types through the ligand variation, covering a wider
substrate scope, so much so that all palladium mediated cross-coupling reactions coupling reaction
have continued to enjoy an avid attention of chemists [1,2]. Suzuki-Miyaura reaction involves
cross-coupling of organoboronic acids with aryl halides to form bi-aryls in presence of organic
solvent which get catalyzed by various pd/ligand systems [3,4]. In early stage, Suzuki reaction
used to perform in homogeneous system using palladium-based complexes as catalyst. However,
these homogeneous catalyst systems exhibit some fundamental problems in terms of the
separation, recycling of the catalysts and they often acts as a principal source of contamination of
the products. Heterogeneous catalysis (Supported metal complexes) systems have achieved

significant attention now a day due to efficient recovery of the catalysts by filtration, reusability,
robustness, increased air and moisture stability etc. which in turn makes it eco-friendly [5,6].
Homogenous catalyst can be heterogenize by various methods including fabrication of multi
component catalysts or by using various supports including silica, sepiolites, zeolites and polymers
for enslavement of metal complexes [7,8]. Particularly, the area of transition metal complexes
enslaved in the nanovoids of microporous materials such as zeolite Y is a subject that is still
stimulating the researchers for development of novel catalysts [9,10].
Schiff base complexes have been intensively reported for its catalytic properties in homogeneous
and heterogeneous catalysis [11,12]. Catalytic activity offered by transition metal complexes has
invigorated the researchers to develop novel catalysts for coupling reactions which could be safe,
cost effective and most importantly recyclable. Complexes of first series transition metals has been
widely employed as precatalysts in coupling reaction activity and is still achieving massive
attention of researchers due to key features viz. high availability, facile scale-up, low cost and ease
of synthesis etc. [13]. Nickel (II) complexes particularly phosphine-based complexes have been
widely explored as catalyst in various coupling reactions [14]. Nickel(II) Schiff base complexes
have also been used as catalyst in coupling reactions including Suzuki-Miyaura reaction [15,13].
In quest of an efficient, robust and eco-friendly catalyst for Suzuki-Miyaura coupling reaction,
herein we report preparation of Schiff base complexes of Pd and Ni as neat and zeolite-Y
immobilized complexes with an assumption that newly developed catalysts will offer rapid and
efficient synthesis of versatile polycyclic heterocycles via Suzuki coupling reactions.
2
2
. Experimental
.1 Materials
All chemicals are commercially attainable and used as received without purification.
Salicylaldehyde, phenyl hydrazine, 2-aminobenzoic acid, 3-nitrobenzaldehydeand, NiSO .6H O,
-formylthiophen-3-yl)boronic acid, aryl halide (2-amino-3-bromo pyridine, 2-Amino-3-Chloro-
-trifluoromethyl pyridine,5-Amino-4-Chloro pyrimidine, 5-Amino-4,6-di-Chloro pyrimidine, 5-
Cl ) were obtained from Sigma Aldrich Ltd.
O and microporous zeolite Y with Si/Al were procured from Hi-media.
4
2
2
5
Amino-4,6-dichloro-2-methyl pyrimidine), (Pd[PPh
Pd(NO .2H
3
]
2
2
3
)
2
2
2
.2 Physical methods and analysis

Various physicochemical techniques were used to characterize the ligands and zeolite Y enslaved
complexes. Electronic spectra were recorded on UV/ VIS/ NIR spectrophotometer ((Lambda 750
3
Perkin Elmer) with a quartz cell of 1cm using methanol and chloroform solutions. FTIR was
recorded with KBr on a FTIR (ALPHA-T Bruker) Instrument. Differential scanning calorimetry
(DSC) experiments were studied with NETEZCH DSC 204 F1 phoenix differential scanning
1
2
1
2
calorimeter. The magnetic susceptibility of the neat complexes [Pd(L ), Pd(L ), Ni(L ), Ni(L )]
was measured using a magnetic susceptibility balance of models Sherwood. The XRD was
effectuated using Bruker AXS D8 Advance X-ray powder diffractometer with a CuKα
(λ=1.54058) target and movable detector, which can scan the intensity of diffracted radiation
ͦ
ͦ
within shift at the range of 5 -70 as a function of the angle 2Ө between the incident and diffracted
beams. XPS study was performed using a PHI 5000 Versa Prob II (FEI Inc.) spectrometer with
nonmonochromatic Al Ka radiation (1486.6 eV) equipped with XPSPEAK41 software. Specific
BET surface area was examined by using surface area analyzer (Autosorb-iQ2, Quantachrome
Instruments, USA), all samples were de-gasified at 120 °C to get rid of any adsorbed gasses.
Scanning electron micrographs (SEMs) of Na-Y, Ni-Y, Pd-Y and Zeolite Y enslaved metal
complex was obtained using Tescan, Mira 3, FE-SEM.
2
.3 Preparation of zeolite Y enslaved metal complexes
The Preparation pathway of the ligands (1 and 2), metal exchanged zeolite Y (Pd-Y and Ni-Y) and
zeolite Y enslaved metal complexes ([Pd(L )]-Y], [Ni(L )]-Y], [Pd(L )]-Y] [Ni(L )]-Y]) and neat
complexes Pd(L ), Pd(L ), Ni(L ), Ni(L ) are presented in Scheme 1 and 2.
1
1
2
2
1
2
1
2
2
.3.1 Preparation of (E)-2-((2-phenylhydrazineylidene) methyl) phenol
The (E)-2-((2-phenylhydrazineylidene) methyl) phenol [ligand 1] was prepared by the reaction of
salicylaldehyde 1 (0.9 mmol) with phenyl hydrazine 2 (1.5 mmol) in ethanol under reflux (2 h)
and progress of the reaction was monitored by TLC. After completion of the reaction the hot
solution was poured into ice-cold water. Then, the product was filtered under suction and washed
with distilled water [16]. The yellow colored solid product was obtained, dried at ambient
temperature and recrystallized with ethanol (Scheme 1).

Scheme 1
2
.3.2 Preparation of [(Z)-2-((4-hydroxybenzylidene) amino) benzoic acid
Schiff base ligand [(Z)-2-((4-hydroxybenzylidene) amino) benzoic acid (L2) was synthesized by
the reaction 2-aminobenzoic acid 4 (1.37 g, 10 mmol) with 4-hydroxy benzaldehyde 5 (1.22 g, 10
mmol) in ethanol with constant heating and stirring for 4 h under reflux [17]. The solid dark yellow
product formed was filtered and dried (Scheme 2).
Scheme 2
2
+
1
2
2
.3.3 Preparation of neat Pd complexes Pd(L ) and Pd(L )
A methanolic solution of Pd (NO .2H O (1.3 mmol) was added to the methanolic solution of
3
)
2
2
ligands (1.3 mmol 1 and/or 2) with constant stirring. The pH of the reaction mixture was adjusted
°
to 5-6, by addition of sodium acetate and then refluxed for 5 h at 80 C. The solid light brown
product was obtained after the evaporation of solvent; subsequently, it was crystallized with
2
+
1
2
chloroform, methanol and acetone. Similarly, neat Ni complexes Ni(L ) and Ni(L ) was prepared
using NiSO .6H O (Fig. S-1) [18].
4
2

2
.3.4 Preparation of Pd-Y and Ni-Y
Metal-exchanged zeolite Y was prepared by the conventional ion-exchange method. As extremely
concentrate (1 M) metal salt solution cause dealumination in the zeolite Y framework, a lower
concentrate metal salt aqueous solution (0.003 M of Pd(NO
3
)
2
.2H
2
O and/or NiSO
4
.6H O in 500
2
ml deionized water) having 4-4.5 pH was stirred under refluxed condition with 5.0 g of pure zeolite
Y for 24 h. The resultant Pd-Y and Ni-Y were isolated and washed with de-ionized water to remove
any free metal ion on the exterior surface of the zeolite-Y and then dried. The resultant metal
exchanged zeolite-Y, Pd (ll)-Y (light brown) and Ni (ll)-Y (light green) was found (Fig. S-2).
1
2
1
2
.3.4.1 Preparation of zeolite Y enslaved metal complexes {[Pd(L )-Y], [Pd(L )-Y], [Ni(L )-
2
Y] and [Ni(L )-Y]}
A 1.0 g of activated metal exchanged zeolite-Y [Pd-Y and/or Ni-Y] was refluxed for 12 h with an
excess amount of ligands 1 [(E)-2-((2-phenylhydrazineylidene) methyl) phenol] and/or ligands
2
[(Z)-2-((4-hydroxybenzylidene)amino) in 1,4-dioxane. The resulting material was isolated and
purified by soxhlet extraction using chloroform, methanol, 1,4-dioxane and acetonitrile until the
filtrate become colorless. The resultant material was dried and washed with an aqueous solution
of 10 mmol NaCl to remove undesired free metal ions. Further, it was washed with deionized water
and dried overnight (Fig. S-2) [19].
2
.4 Suzuki Miyaura cross-coupling reaction
Suzuki cross-coupling reaction was carried out using different catalyst viz. Bis-(triphenyl
phosphine) palladium (ll) dichloride (Pd[PPh Cl ),prepared zeolite-Enslaved transition metal
3
]
2
2
1
2
1
2
1
2
complexes [Pd(L )-Y], [Pd(L )-Y], [Ni(L )-Y],[Ni(L )-Y] and neat complexes Pd(L ), Pd(L ),
1
2
Ni(L ) , Ni(L ) [20,21] .
2
.5 General procedure for Suzuki cross-coupling reaction:
Efficiency of prepared catalyst in Suzuki cross-coupling reaction was examined. Briefly, a
weighed quantity of aryl halide (1.152 mmol), catalysts (Bis-(triphenyl phosphine) palladium (ll)
dichloride, enslaved metal complexes and neat complexes) (5 mol %), boronic acid (1.0
equivalents), NaOH (3.0 equivalents), and solvent (5 mL) was taken in a reaction vessel. The
reaction mixture was heated at 75°C under microwave irradiation for 20–50 min. After cooling the
reaction mixture was filtered and dried; extra solvent was evaporated and compound was extracted

with methanol, washed with brine solution then dried over MgSO to afford coupling products
4
(Scheme 3). The 1H NMR spectra of products are given below.
Scheme 3
3
3
. Results and discussion
.1 Optimization of reaction conditions
In order to determine the optimum reaction conditions, the effects of catalyst concentration,
temperature, solvent system and different bases on the yield of product was investigated and the
obtained results are presented below.
Various combinations of aryl halides and boronic acid were coupled in the presence of different
catalyst viz. Bis-(triphenyl phosphine) palladium (ll) dichloride, enslaved metal complexes and
neat complexes under microwave irradiation and it was noticed that the zeolite Y enslaved metal
1
complexes {[Pd(L )-Y] displayed highest catalytic activity. The reaction conditions were
optimized using 3-bromopyridin-4-amine and 2-formyl-3-thienyl boronic acid as coupling
partners under various conditions as shown in fig. S-3. Numerous solvents viz. DMF, water and
tetrahydrofuran, ethanol, methanol were evaluated for reaction yields. Amongst all, ethanol,
resulted in highest reaction yields and chosen for further reactions (Fig. S-3a).
Similarly, NaOH was identified as ideal base amongst K
2
CO
3
, Na
2
CO
3
, NaHCO and NaOH for
3
SM coupling reaction as it provided highest yield (Fig. S-3b) and optimum reaction temperature
was taken as 75°C (approximately 98%) for SM coupling reaction. Similarly, optimization with
respect to catalytic loading was performed with an initial catalytic amount of 2-7 mol% and 5
mol% of catalytic loading was considered as optimum concentration for SM reaction (Fig. S-3c).
Finally, the results of optimization indicated the following as the best suitable conditions for the
Suzuki–Miyaura coupling reaction: 5 mol% of catalytic loading, 75°C temperature, approximately
1
0 min, NaOH as base, and ethanol as solvent under microwave irradiation.
3
.2 Characterization of ligands

3
.2.1 (E)-2-((2-phenylhydrazineylidene) methyl) phenol [ligand 1]
◦
Yield: 80%; M.p.:185 C. IR (KBr, / cm−1): 3058 [intramolecular hydrogen bonded -OH group],
1
b1684 [C=N Str.], 1449 [C-O Str. Vibrations]. H NMR (δ, ppm in CH
3
OH-d
4
): 8.07-8.05 (t, 3H),
1
3
8
.46-8.36 (t, 3H),8.80-8.70 (t, 3H), 8.95 (s, 1H), 10.44 (s, 1H), 12.11 (s, 1H) . C NMR (δ, ppm in
CH
19.92, 116.55, 112.51. Anal. calc. for C13
H 5.75, N 13.12%.
3
OH-d
4
): 157.10, 144.90, 140.96, 132.93, 132.14, 129.83, 129.80, 129.64, 120.31, 120.04,
1
H
12
2
N O: C, 73.56; H, 5.70; N, 13.20%. Found: C 73.52,
3
.3.2 [(Z)-2-((4-hydroxybenzylidene) amino) benzoic acid [ligand 2]
◦
Yield 80-85%; M.p.:199 C. IR (KBr, / cm−1): 2921 [intramolecular hydrogen bonded -OH group],
1
1
7
1
1
5
651 [C=N Str.], 1449 [C-O Str. Vibrations]. H NMR (δ, ppm in CH
3
OH-d
4
): 6.80-6.76 (m, 5H),
OH-d ): 171.10,
64.66, 158.29, 152.32, 134.47, 132.93, 132.14, 129.88, 128.51, 117.19, 116.33, 116.00, 115.27,
1
3
.83-7.81 (t, 3H), 8.15 (s, 1H), 9.32 (s, 1H), 9.79 (s, 1H) . C NMR (δ, ppm in CH
3
4
11.13.Anal. calc. for C14
.73%.
H
11NO : C, 69.70; H, 4.60; N, 5.81%. Found: C, 69.66; H, 4.65; N,
3
3
3
.3 Characterization of catalysts
.3.1 Electronic spectra and magnetic moments
1
2
1
2
The absorption spectra of the neat complexes Pd(L ), Pd(L ), Ni(L ) , Ni(L ) and enslaved metal
1
2
1
2
complexes {Na-Y, Ni-Y, Pd-Y, [Pd(L )-Y], [Pd(L )-Y], [Ni(L )-Y],[Ni(L )-Y] }are displayed in
2
+
1
2
fig. S-4(a-c) and Table 1. The neat Pd complexes Pd(L ) and Pd(L ) showed a number of bands
in the region 238, 240, 270, 326, 367, 422, 509 nm which could be attributed to π→π*, n → π*,
charge transfer (LMCT) and the d-d transitions. The host zeolite Y displayed one strong band at
3
11 nm and the other very weak band nearly at 351 nm due to the charge transfer transition (Al
O) of two different Al-O units of zeolite Y. The absence of dealumination during the
modification (Ion exchange and enslavement) of zeolite Y was sufficiently evidenced by the
presence of these bands (at 311 and 343 nm) at the exactly similar spectral region in Ni-Y, Pd-Y,
1
2
1
2
Pd(L )-Y, Pd(L )-Y, Ni(L )-Y and Ni(L )-Y) as that was observed in pure zeolite Y. The
absorption spectra of Ni-Y and Pd-Y showed two additional bands at 335, 964 nm in addition to
bands exhibited by host zeolite Y (At 311 and 343 nm), characteristic of the charge transfer (Due

2
+
to an interaction of Ni with the O atoms of zeolite Y) and the d-d transition, respectively. The
1
2
1
2
peaks corresponding to enslaved complexes Pd(L )-Y, Pd(L )-Y, Ni(L )-Y and Ni(L )-Y) was
appeared into the virtually similar spectral regions as those in the corresponding neat complexes
1
2
1
2
Pd(L ), Pd(L ), Ni(L ) and Ni(L ). The only difference observed was the peak values due to charge
transfer transitions significantly shifted to lower wavelengths upon enslavement. Shifting toward
the higher-energy values might be due to the effect of the zeolite wall on the electronic and
2
+
1
2
structural properties of the enslaved complex. The neat Ni complexes Ni(L ) and Ni(L ) showed
bands in the region 242, 254, 269, 292, 339, 344, 450, 397 and 648-549 nm corresponding to the
2
+
π→π*, n → π*, charge transfer (LMCT), and d-d transitions, respectively. The neat Ni complexes
1
2
Ni(L ) and Ni(L ) weak band in the range of 420-725 nm may be assigned to d-d transitions which
suggests an octahedral environment around the metal ions in Pd and Ni complexes. The spectra of
entrapped complexes showed absorption band in the region 435-550 nm may be attributed to d-d
transition. This specifies the existence of complexes inside the nanopores of zeolite-Y (Table 1).
3
.3.2 Fourier transform infrared (FTIR) spectroscopy
The FTIR of ligands [(E)-2-((2-phenylhydrazineylidene)methyl)phenol] and/or ligand 2[(Z)-2-
((4-hydroxybenzylidene)amino) exhibited characteristic bands in the region of 1626-1615, 1110-
-1
1
082, and 3600-3200 cm due to ʋ(C=N), ʋ(C-O)and ʋ(O-H) (weak broad band due to
2
+
intramolecular hydrogen bonding), respectively [22]. Upon complexation of ligands with Ni and
2
+
-1
Pd ions (fig. S-5), a shift towards the lower wave numbers of ʋ(C=N)(1688-1515 cm ),ʋ(C-O)(1104-
-1
1
090 cm ) bands and the disappearance of ʋ(O-H)broad band indicated coordination of metal to the
azomethine nitrogen and the phenolic oxygen via deprotonation. The coordination of metal ions
to the nitrogen and oxygen atoms was further supported by the presence of new weak bands in the
_
1
region 576-532 and 480-420 cm in complexes due to the ʋ(M-O) and ʋ(M-N) modes respectively
23].
[
1
2
1
2
Zeolite Y based materials (Na-Y, Ni-Y, Pd-Y, Pd(L )-Y,Pd(L )-Y, Ni(L )-Y and Ni(L )-Y)
displayed bands at 3440(s), 1633(s), 1102 (s), 820 (m), 456 (m), 597 (w), 1180 (w), and 672 (w)
_
1
cm attributed 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
1
2
(
external, T= Si, Al), respectively [24]. In the case of enslaved complexes Pd(L )-Y, Pd(L )-Y,
1
2
Ni(L )-Y and Ni(L )-Y the presence of weak bands (Due to a low concentration of the complexes)

_
in the region 1525-1339 cm 1, where the zeolite Y matrix did not absorb evidently which describe
the existence of metal complexes inside the nanovoids of zeolite Y. The equivalent FTIR spectra
1
2
1
2
of Na-Y, Pd-Y, Ni-Y, Pd(L )-Y, Pd(L )-Y, Ni(L )-Y and Ni(L )-Y (Except, the region 1504-1363
_
cm 1in 3Y-6Y) again support the fact that the zeolite Y framework has preserved upon
modification (fig. S-5).
3
.3.3 Powder X-ray diffraction (XRD) study of microporous zeolite Y based material
The powder X-ray diffraction (XRD) patterns of pure Na-Y, Pd(II)-Y, Ni(II)-Y, and zeolite-Y
1
2
1
2
enslaved complexes (Pd(L )-Y, Pd(L )-Y, Ni(L )-Y and Ni(L )-Y) are shown in fig. 1. A minor
alteration in peak intensity has noticed in the entrapped complexes from that of parent zeolite-Y.
In pure zeolite-Y, Pd(II)-Y and Ni(II)-Y, the order of peak intensity is:I331>>I220>I311, where as in
the immobilized complexes, the order of peak intensity becomes I331>>I311>I220. This intensity
2
+
2+
alteration was due to the reordering of coordinated free cations (Pd , Ni ) at different sites in
structure of zeolite-Y during complex formation (fig. 1) (25a). The similar XRD patterns of
modified zeolites with that of the parent zeolite-Y specifies the holding of the crystallinity of the
zeolite-Y framework during the metal exchange, and entrapment process. Furthermore, the cavities
are capable enough to hold complexes without any loss in morphology of the zeolite-Y structure
[
25b].
3
.3.4 X-ray photoelectron spectroscopy (XPS) study
1
2
The survey spectra of [Pd(L )-Y] and [Pd(L )-Y] depict the peaks of C, O, N and Pd (Fig. 2a).
1
2
Elemental composition of [Pd(L )-Y] and [Pd(L )-Y] are shown in Table 2. Apart from the
elements present in anchored complexes peaks corresponding to zeolites (Na, Al, Si) were also
observed. Molecular level peak positions of C1s, O1s, N1s, Pd 2d are listed in Table 2. The peaks
of O1s region could be deconvoluted into 2 peaks at binding energies 532.36 eV and 533.36 eV
1
for [Pd(L )-Y] which could be attributed to Pd –O and C-O bond respectively. In the case of
2
[
Pd(L )-Y], O1S region is deconvoluted into two peaks at binding energies 532.47 and 530.97 eV
1
corresponding Pd-O and carboxyl bonds respectively. XPS binding energy data of both [Pd(L )-
2
3
2
Y] and [Pd(L )-Y] suggested the presence of two different types of carbon atoms in sp and sp
1
2
forms for the complex in both the states. In both [Pd(L )-Y] and [Pd(L )-Y] C-C and C=C peaks
appeared around 284 and 286 eV respectively. Further the peak C-N bond was merged with sp2
1
peak of carbon. The peak corresponding to C-O was found at 287.82 and 288.08 in [Pd(L )-Y] and

2
[
Pd(L )-Y] respectively. In Schiff’s base, strong N1s peak at 399.7 eV correspond to azomethine
nitrogen (N=C-H) and coordinated with metal ion, and the peak appeared at 402.2 eV
corresponding to π-π* type due to additional π bond between N and Carbon (C-N*) respectively.
1
In the case of [Pd(L )-Y] after coordination with Pd atom, the azomethine group binding energy
2
shifted to a higher binding energy of 400.42 eV (3). Similarly, in [Pd(L )-Y] the peaks correspond
1
2
to Pd-N and C=N appeared at 399.3 and 400.47 eV respectively. Both in [Pd(L )-Y] and [Pd(L )-
Y] Pd exhibited three peaks which indicated the +2-oxidation state of Pd in the complex (Table
3
). Results were found in agreement with previously published reports [26-28].
The survey spectra (Fig. 2b) depict the peaks of C, O, N, Si, Al, Na and Ni. Elemental composition
1
2
of [Ni(L )-Y] and [Ni(L )-Y] are shown in Table 4. It is evident from both survey spectra and
elemental composition that elements corresponding to both zeolite (Na, Al and Si) were present
which confirmed the efficient anchoring of Ni complex onto the silicate template.
It is evident from Table 4, that owing the presence of carboxyl group instead of carbonyl group
2
1
oxygen content is higher in [Ni(L )-Y] compared to [Ni(L )-Y]. Molecular level peak positions of
O1s, N1s, Ni 2p are listed in Table 4. The peaks of O1s region could be deconvoluted into 2 peaks
1
at binding energies 532.4 eV and 533.76 eV for [Ni(L )-Y] which could be attributed to carbonyl
2
and Ni –O respectively. In the case of [Ni(L )-Y] the peaks were observed at 531.39 and 532.33
eV owing to the presence of carboxyl instead of carbonyl group. XPS binding energy data of
1
2
[
Ni(L )-Y] and [Ni(L )-Y] have suggested the presence of two different types of carbon atoms in
3
2
1
sp and sp forms for the complex in both the states. In [Ni(L )-Y] C-C and C=C peaks appear at
84.67 and 285.23 eV respectively. Further the peak at 285.23 eV also represents the C-N bond.
2
1
2
The peak corresponding to C-O was found at 288.23 in [Ni(L )-Y]. In the case [Ni(L )-Y] small
shifts in binding energies were observed owing to the presence of carboxyl group.
In Schiff’s base, strong N1s peak at 399.7 eV corresponds to azomethine nitrogen (N=C-H) and
coordinated with metal ion, and the peak appears at 402.2 eV corresponding to π-π* type due to
1
2
additional π bond between N and Carbon (C-N*) [29, 30]. In the case of [Ni(L )-Y] and [Ni(L )-
Y] after coordination with Ni atom, the azomethine group binding energy shifted to a higher
binding energy of 400.46 eV and 400.65 respectively. Increased binding energy of N1s peak could
be attributed to decreased electron density after coordination with Ni atom. Thus, formation of a
σ bond occurs involving the lone electron pair of the nitrogen atom of the Schiffs base and a partial
electron density transfer to the metal center.

1
Further, in [Ni(L )-Y], Ni exhibits two main peaks corresponding to Ni2p3/2 and Ni 2p1/2 at
8
74.97 and 857.08 eV respectively which indicated the +2-oxidation state of Ni in the complex.
1
Apart from this shake up and satellite peaks with higher intensity are observed (Ni 2p3 of [Ni(L )-
2
1
Y] and Table 5) indicating an octahedral geometry. In [Ni(L )-Y] complex, similar to [Ni(L )-Y]
major peaks at 855.86 and 873.21 eV were observed for Ni 2p which again indicates the +2-
oxidation state of Ni in the complex [31]. Apart from these, four other satellite peaks were observed
Table 5).
2
(
3
.3.5 Gas sorption analysis
The N
Na-Y. The N
Quantachrome Instruments, USA). The N
2
sorption analysis was used to study the impregnation of metal complexes into the pores of
sorption analyses of all the specimens were carried out using Autosorb-iQ2
sorption isotherms are presented in fig. 3. All the
2
(
2
specimens except Na-Y exhibited Type-II isotherms indicating non-porous nature of the materials.
The specimen Na-Y exhibited type-IV isotherm with sharp uptake at low relative pressure and
hysteresis in the P/P
pore volume of Na-Y was calculated at P/P
total pore volumes of all the metal complexes (0.097, 0.015, 0.034, 0.045, 0.028 and 0.014 for Ni-
Y, Ni[L ]-Y, Ni[L ]-Y, Pd-Y, Pd [L ]-Y and Pd [L ]-Y, respectively) are much lesser than that of
Na-Y, indicating the embedding of Pd(II) and Ni(II) complexes into the nano-voids of Na-Y (fig.
0
range of 0.42 to 0.99, which indicates the presence of mesopores. The total
-1
0
= 0.99 and found to be 0.26 cc g . Interestingly the
1
2
1
2
3
).
3
.3.6 Field Emission Scanning Electron Microscopy (FESEM) analysis
The Pd-Y and/or Ni-Y reacted with an excess amount of ligand1and/or 2 during the preparation of
1
2
1
2
Pd(L )-Y, Pd(L )-Y, Ni(L )-Y and Ni(L )-Y the possibility of uncoordinated ligands and the
formation of metal complex on the exterior surface of zeolite Y cannot be excluded with the
simultaneous metal complex formation within the nanovoids of zeolite Y. These exterior particles
can be easily seen in the FESEM image of catalyst taken after the soxhlet extraction (fig. 4). To
avoid the leaching of such redundant particle from the exterior surface of zeolite-Y during the
1
2
1
2
catalytic study, each enslaved complexes Pd(L )-Y, Pd(L )-Y, Ni(L )-Y, Ni(L )-Y were purified
by soxhlet extraction using various solvents until the filtrate becomes colorless and free from any
metal ions. The FESEM images, after the soxhlet extraction specifies the existence of well defined
zeolite-Y crystals without any shadow of exterior metal ions or the complexes. This confirmed that

the morphology and surface crystallinity of zeolite Y remnants integral upon the enslavement of
the complexes. In addition, energy-dispersive X-ray (EDX) spectrum revealed presence of Na, Si,
Al, O, C, N, Ni and Pd elements in synthesized catalyst which corroborated the entrapment of
complex into zeolite pores (fig. 5).
3
.4 Catalytic study
The efficiency of synthesized catalyst (one conventional and four newly synthesized) was
examined with five different substrates of varying structures. Notably, moderated to
excellent yields were achieved in different combination of catalysts and substrates.
Amongst all, Palladium-(Z)-2-((4-hydroxybenzylidene)amino) benzoic acid-Zeolite
2
complex [Pd(L )-Y] gave excellent performance with impressive yield and highest
recyclability. In addition, bromo aryl halide (2-amino-3-bromo pyridine) displayed better
tolerance towards reaction with good yield (Table 6).
The catalyst reusability was studied up to five times for different set of reactions and there
was inevitable loss of catalyst during recovery process. Besides this no significant loss in
2
catalytic activity was observed for [Pd(L )-Y]. However, loss of efficiency was observed
1
2
with Ni(L )-Y, Ni(L )-Y and neat complexes after fourth run of reaction (Table 7).
4
. Conclusion
In present study, we have successfully prepared zeolite Y enslaved metal complexes using green
method and evaluated their catalytic activity for Suzuki-Miyaura coupling reaction. The
synthesized compounds were achieved in short reaction times in excellent yield with a recoverable
catalyst under microwave irradiation. Outcome of the present study clearly indicated that newly
synthesized and well-characterized heterogeneous catalyst which could be employed as an
alternate to previously available catalysts in Suzuki-Miyaura cross-coupling reactions. In future,
efforts will be also be made to further optimize reaction conditions to make the catalytic system
more efficient, greener and versatile for other substrates.
Acknowledgement: The authors are deeply grateful for financial support provided by Department
of Science and Technology (DST), New Delhi under their CURIE (Consolidation of University
Research for Innovation and Excellence in Women Universities) ((SR/CURIE-II I/01/2015(G))
Scheme.

Conflict of Interest
The authors declare that they have no conflict of interest.
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Figure captions:
Figure 1. XRD pattern of pure Na-Y, Pd-Y, Ni-Y, Pd(L )-Y, Pd(L )-Y, Ni(L )-Y, Ni(L )-Y
1
2
1
2
1
2
1
Figure 2. a) Survey spectra of [Pd(L )-Y] and [Pd(L )-Y b) Survey spectra of [Ni(L )-Y] and
2
[
Ni(L )-Y]
Figure 3. N
2
sorption isotherms of Na-Y and metal complexes measured at 77K
Figure 4. FE-SEM images of Na-Y, Pd-Y, Ni-Y and complex catalyst

1
2
1
Figure 5. Energy-dispersive X-ray (EDX) spectrum of (a) Pd(L )-Y, Pd(L )-Y, (b) Ni(L )-Y,
2
Ni(L )-Y
Scheme Captions:
Scheme 1: Synthesis of Schiff base ligand (L1) (E)-2-((2-phenylhydrazineylidene) methyl)
phenol
Scheme 2: Synthesis of Schiff base ligand (L2) [(Z)-2-((4-hydroxybenzylidene) amino) benzoic
acid
Scheme 3: Suzuki-Miyaura cross-coupling reaction
TABLE 1. Electronic spectroscopy of zeolite-Y based materials and neat complexes
Electronic Transition (nm)
π - π*
n - π*
MLCT
d-d transition
(Weak)
Compound
Strong)
(Weak)
(Strong)
Na-Y
Pd-Y
-
-
-
-
311
313
416, 595

Ni-Y
-
-
314, 401
331, 373
321, 364
331, 373
341
519, 576
442, 677
413, 726
435,505, 553
408, 533, 640
509
1
[
[
[
[
[
[
[
Pd(L )]-Y
226, 276
224
2
Pd(L )]-Y
284
278
286
1
Ni(L )]-Y
223
2
Ni(L )]-Y
250
Pd(L1)
(H
O)
O)
].2H
].2H
O]
240
370
2
2
2
2
2
Pd(L2)
(H
O]]
238
270
-
351
422
2
2
2
1
Ni(L )2(H
2
O)2].2H
2
O]
254
350
450
[
Ni(L2)
2
(H
2
O) ].2H
2
2
O
242, 269
292
360, 366
549
1
2
TABLE 2. Elemental composition of [Pd(L )-Y] and [Pd(L )-Y]
Complex
C1s
N1s
5.15
4.19
O1s
45.63
27.38
Na1s
0.20
0.00
Al2p
1.19
2.18
Si2p
0.24
2.82
Pd3d
1
[
Pd(L )-Y]
46.54
62.13
1.05
1.30
2
[
Pd(L )-Y]

TABLE 3. Binding energy of the enslaved complexes of Pd
Compound
C(1s)
O(1s)
N(1s)
Pd (3d)
1
[
Pd(L )-Y]
284.73,
532.36,
533.36
400.42,
401.97
337.62,
338.65,
343.15
2
2
86.04,
87.82

2
[
Pd(L )-Y]
284.66,
532.47,
530.92,
399.33,
400.47
335.25,
340.45,
341.75
2
2
86.02,
88.08
1
2
TABLE 4. Elemental Composition of [Ni(L )-Y] and [Ni(L )-Y]
Complex
C1s
N1s
O1s
Na1s
Al2p
Si2p
Ni2p3
1
[
Ni(L )-Y]
70.17
58.46
9.97
5.53
16.52
29.50
0.00
0.63
0.37
0.27
1.64
0.13
1.33
5.49
2
[
Ni(L )-Y]

TABLE 5. Binding energy of the enslaved complexes of Ni
Compound C(1s) O(1s) N(1s)
2
+
Ni (2p)
Δ2p

1
[
[
Ni(L )-Y]
284.67,
532.40,
533.76
400.46,
402.10
857.02,862.80, 17.95
874.97, 880.18
2
2
85.61,
88.23
2
Ni(L )-Y]
284.70,
531.39,
532.33
399.59,
400.65
855.86,
860.08,
863.86,
17.35
2
2
85.83,
88.41
8
8
73.21,
76.26, 880.93
TABLE 6. The Suzuki-Miyaura cross-coupling reactions of aryl halides and phenylboronic acid.

Entry
Aryl halides
Boronic acid
Products (Triaryls) Reaction Time min % Yield
1
0
98
1
.
3
2
5
0
95
93
2
3
.
.
4
3
0
0
84
85
4
.
5
6
.
.
30
40
90
82
7
.

8
9
.
.
40
40
78
85
Reaction conditions: 2-formyl-3-thienyl boronic acid (1.0 mmol), aryl halide (1.152 mmol), base
using NaOH (3.0 mmol), catalyst (5 mol %) reaction run at 75 °C temperature in ethanol solvent.

TABLE 7. The reusability of catalyst in the coupling of 3-bromopyridin-4-amine and 2-formyl-3-
thienyl boronic acid.
Coupled product
No. of reaction cycles
% Yield
1
98
2
3
95
93
Sonika Jain, Vivek Sharma, Manish Srivastava, Nalini Sankararamakrishnan and Shruti Mishra:
Conceptualization of the work and performing the experiments, or data/evidence collection.
Shalu Sain and Dharam Kishore: Development or design of methodology; creation of models
and Formal analysis of the experiments.
Saikh M Wabaidur and Swapnil Sharma: Verification, whether as a part of the activity or
separate, of the overall replication/ reproducibility of results/experiments, other research outputs
and review & editing.
Jaya Dwivedi: Supervision, conducting a research and investigation process, and provided the
Resources, writing original Draft
Conflicts of interest
All the authors declare that they have no conflict of interest.

Highlights
2
+
2+





Zeolite enslaved Pd , Ni complexes were used novel as heterogenous catalysts
Polycyclic heterocycles was synthesized in ethanolic medium
Characterized by FTIR, magnetic susceptibility, N sorption, XRD, XPS, FE-SEM
The synthesis by Suzuki coupling reactions was provided impressive yields
Catalyst may be used for important polycyclic heterocycles under greener conditions
2