Syntheses and characterization of monobasic tridentate Cu(II) Schiff-base complexes for efficient oxidation of 3,5-di-: tert -butylcatechol and oxidative bromination of organic substrates

Article abstract of DOI:10.1039/c7nj00957g

Two monomeric copper complexes [Cu^II(sal-ppzH)Cl₂] (1) and [Cu^II(hyap-ppzH)Cl₂] (2) were synthesized by reacting CuCl₂·2H₂O with the monobasic tridentate Schiff-base ligands [Hsal-ppz] (I) and [Hyap-ppz] (II) (derived by reacting 1-(2-aminoethyl) piperazine with salicylaldehyde and 2-hydroxyacetophenone) respectively. Elemental analysis, IR, UV-Vis, ¹H NMR and ¹³C NMR data confirm the structures of the ligands and those of the complexes. Both complexes are monomeric in nature in the solid state and in solution as well. Single crystal XRD data suggest a distorted square pyramidal geometry for 1 crystallized in the P1 space group. DFT studies established a similar molecular structure for 2. The synthesized metal complexes [Cu^II(sal-ppzH)Cl₂] (1) and [Cu^II(hyap-ppzH)Cl₂] (2) successfully catalyzed the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) in methanol in the presence of H₂O₂ with high K_cat values of 1.182 × 10⁴ mmol h^-1 and 2.880 × 10⁴ mmol h^-1, respectively. [Cu^II(sal-ppzH)Cl₂] (1) and [Cu^II(hyap-ppzH)Cl₂] (2) were also anchored into the polymeric matrix of chloromethylated polystyrene and were analyzed by TGA, atomic absorption spectroscopy (AAS), EPR, scanning electron microscopy (SEM) as well as energy dispersive X-ray (EDX) analysis. The polymer grafted metal complexes were used as catalyst precursors in the oxidative bromination of salicylaldehyde in the presence of H₂O₂, KBr and HClO₄. Under optimized reaction conditions, both catalysts show nearly quantitative oxidative bromination of salicylaldehyde, with the order of % products formed being 5-bromosalicylaldehyde > 3,5-dibromosalicylaldehyde > 3-bromosalicylaldehyde. Plausible reactive species involved in the catalytic cycle are identified by UV-Vis spectroscopy, pH metric titration, ESI-MS, EPR and DFT studies.

Full text of DOI:10.1039/c7nj00957g

View Article Online
View Journal
NJC
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: S. Kumari, A. K.
Mahato, A. Maurya, V. K. Singh, N. Keshwarwani, P. Kachhap, I. O. Koshevoy and C. Haldar, New J. Chem.,
2017, DOI: 10.1039/C7NJ00957G.
Volume 40 Number
1
January 2016 Pages 1–846
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
NJC
New Journal of Chemistry
www.rsc.org/njc
A journal for new directions in chemistry
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
rsc.li/njc

Page 1 of 48
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00957G
Syntheses and characterization of monobasic tridentate Cu(II) Schiff-base complexes for efficient
oxidation of 3,5-di-tert-butylcatechol and oxidative bromination of organic substrates.
a
a
a
a
Sweta Kumari , Arun Kumar Mahato , Abhishek Maurya , Vijay Kumar Singh , Neha
a
a
b
a
Keshwarwani , Payal Kachhap , Igor Koshevoy , Chanchal Haldar *
a
Department of Applied Chemistry, Indian Institute of Technology (Indian School of Mines),
Dhanbad 826004, Jharkhand, India
bDepartment of Chemistry, University of Eastern Finland, Joensuu, 80101, Finland
*
To whom correspondence should be addressed. E-mail: chanchal0007@gmail.com
haldar.c.ac@ismdhanbad.ac.in; Fax: +91-326-2235115; Tel: +91-326-2235115
_____________________________________________________________________________
ABSTRACT
Two monomeric copper complexes [Cu (sal-ppzH)Cl
synthesized by reacting CuCl2.2H O with the monobasic tridentate Schiff-base ligands [Hsal-ppz]
I) and [Hyap-ppz] (II) (derived by reacting 1-(2-Aminoethyl) piperazine with salicylaldehyde and
_
II
II
2
] (1) and [Cu (hyap-ppzH)Cl ] (2) were
2
2
(
1
13
2
-hydroxyacetophenone) respectively. Elemental analysis, IR, UV-Vis, H NMR and C NMR
data confirms the structures of the ligands and that of the complexes. Both complexes are
monomeric in nature in solid state and in solution as well. Single crystal XRD data suggests a
–
distorted square pyramidal geometry for 1 and crystallized in P1 space group. DFT studies
II
established the similar molecular structure for 2. Synthesized metal complexes [Cu (sal-ppzH)Cl
2
]
II
(
1) and [Cu (hyap-ppzH)Cl
2
] (2) successfully catalyzed the oxidation of 3, 5-di-tert-butylcatechol
4
-1
(
3,5-DTBC) in methanol in the presence of H
2
O
2
with a high Kcat value, 1.182×10 mmolh and
4
-1
II
II
2
.880×10 mmolh respectively. [Cu (sal-ppzH)Cl
2
] (1) and [Cu (hyap-ppzH)Cl
2
] (2) also
anchored into the polymeric matrix of chloromethylated polystyrene and analyzed by TGA,
Atomic Absorption Spectroscopy (AAS), EPR, Scanning Electron Micrographs (SEM) as well as
Energy Dispersive X-ray (EDX) analysis. Polymer grafted metal complexes were used as catalyst
precursors in the oxidative bromination of salicylaldehyde in the presence of H
HClO .Under optimized reaction conditions, both catalysts show nearly quantitative oxidative
bromination of salicylaldehyde with the order of % products formed, 5-bromosalicylaldehyde>3,5-
2
O
2
,KBr and
4

New Journal of Chemistry
Page 2 of 48
View Article Online
DOI: 10.1039/C7NJ00957G
dibromosalicylaldehyde>3-bromosalicylaldehyde. Plausible reactive species involved in the
catalytic cycle are identified by UV-Vis spectroscopic, pH metric titration, ESI-MS, EPR and DFT
studies.
KEYWORDS: Mononuclear copper (II) complexes, Crystal structure, Catalysts, Oxidation of 3, 5-
di-tert-butylcatechol, EPR, Polymer anchored copper (II) complexes, DFT study.
1
. Introduction
For the development of new metal complexes with novel structure and reactivity, design of the
ligand is the most crucial step. In coordination chemistry, schiff-base complexes have been studied
extensively. Schiff-base complexes are easy to synthesize, have structural diversities and endless
possibilities towards various applications including catalysis.1-3 Whereas piperazine containing
4
5,6
schiff-base complexes are also known for their anthelmintic , antimicrobial acetyl cholinesterase
inhibition , melanocortin-4-receptor (MC4-R) , drug designer anti-PAF11,12, anti-HIV13,14 and
7
8,9
10
1
5
anti-obesity activities.
Copper containing enzyme, catechol oxidase is responsible for the two electron oxidation of
various ortho-diphenols into corresponding ortho-diquinones (shown in the Scheme 1). It was
believed that oxidation of polyphenols into corresponding quinones and their polymerization is the
major route for melanin formation. In humans, progressive accumulation of melanin or
redistribution of epidermal melanin is the main reason for the dark or light patches which may be
considered esthetically displeasing.16,17 In plants polymerization of polyphenols creates enzymatic
browning of fruits and vegetables which causes changes in nutritional and organoleptic properties
1
8
and also diminished storage life and product values. However, oxidation of polyphenols can be
beneficial and even considered essential to the quality of a product. Oxidation of polyphenols in
processing of black tea, coffee and cocoa enhances their quality, making products richer in flavor
and providing unique organoleptic properties.16,17 Polyphenols oxidation reactions are also of great
importance in medical diagnosis for the determination of the hormonally active catecholamines:
adrenaline, noradrenaline and l-dopa (l-3, 4-dihydroxyphenylalanine).19,20 In plants auto
polymerization of polyphenols produces melanin. One of the main functions of melanin is to
2
1
protect the damaged tissues against pathogens and insects. Catechol oxidase enzyme thus
provides the disease resistance power in higher plants.

Page 3 of 48
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00957G
Scheme 1:Oxidation of 3,5-Di-tert-butylcatechol
There are more than 250 structural/functional mimics known for the above enzymes.22
Inmajorityof the model complexes, the main focus was to mimic the active site coordination
environment as close as possible, that lead to the development of various mono nuclear and bi-
nuclear metal complexes. Though several binuclear copper complexes successfully emulate the
enzyme, both structurally and functionally.23-26 While few mononuclear copper complexes are also
known to exhibit catecholase activity.27–29 A few non-copper complexes like, Co (II/III)30-34, Mn
(
II/III)35-38, Ni (II)39-42, Zn (II)43,44 etc. were also reported as functional models of catechol oxidase
and show significant catecholase activity. Besides these, a few FeII/III44-49 complexes are also
known for their catecholase activity. The main aim of mimicking the active site is to design the
molecules that are as efficient as the parent enzyme. But so far none of the reported mono or
binuclear Cu(II) complexes reaches the activity that is close to the native enzyme.
Along with the oxidation of polyphenols, oxidative bromination of organic compounds is also one
of the important organic transformation in the field of synthesis and industrial applications.50
Although the classic bromination of organic substrate faces a number of environmental and
economical challenges.51,52 In recent time, using vanadium haloperoxidase model complexes as a
catalyst, in presence of KBr and aqueous hydrogen peroxide, is the most green, economical and
mild alternative for the oxidative bromination of organic substrates. Vanadium haloperoxidase is
a vanadium containing metalloenzyme,53-58 which primarily oxidizes halides into hypohalous acid
in the presence of H
organic molecules. A number of vanadium oxo-complexes along with some metal phthalocyanines
M = Cu(II), Fe(II) and Co(II)]have been reported as functional models of vanadium
2
O
2
, and if suitable organic substrate is available then it can halogenate the
[
haloperoxidase, homogeneously as well as heterogeneously.59-62
However, recyclability and separation from reaction mixture are main disadvantages of
homogeneous catalysis, which can be overcome by anchoring catalysts in to an insoluble support.
Presently Merrifield Resin (Chloromethylated polystyrene cross linked with divinylbenzene) is
extensively used for immobilization of homogeneous catalysts. Polymer matrix controls the

New Journal of Chemistry
Page 4 of 48
View Article Online
DOI: 10.1039/C7NJ00957G
activity and selectivity of the catalytic reaction, while giving the advantages of homogeneous as
well as heterogeneous catalysts. However, there are few literature reports available regarding the
catalytic activity of oxidative bromination of salicylaldehyde by polymer anchored copper
complexes.63-64
Hence, we have designed two monobasic tridentate ligands (derived by reacting 1-(2-aminoethyl)
piperazine with Salicylaldehyde and 2-Hydroxyacetophenone) in such a way that the
corresponding copper complexes can provide required steric as well as electronic environment for
the oxidation of polyphenols and oxidative bromination of organic substrates. These synthesized
mono nuclear copper(II)complexes possess following structural features which may enhance their
catalytic activity.
i. Both mono nuclear Cu(II) complexes adopt a distorted square pyramidal geometry. According
to literature non-planar geometry is necessary for the catecholase activity.65
ii. Reported copper complexes were isolated by reacting CuCl with monobasic tridentate ligands.
2
Tridentate ligands allow lower coordination number around the metal centre.
iii. There are two labile -Cl groups, which can be easily removed and allow the easy association
of substrate molecule with the metal complex.
Although similar ligand systems are known,66-68 but for the first time we are reporting here the
copper complexes of the ligands [Hsal-ppz] (I) and [Hyap-ppz] (II)with bi-functional catalytic
activity towards the oxidation of 3,5-DTBC and oxidative bromination of salicylaldehyde, along
II
with the single crystal XRD data of [Cu (sal-ppzH)Cl
2
] (1).
2
. Experimental
.1. Chemicals and materials
2
All chemicals were obtained from commercial sources and used as received. Analytical grade
reagent salicylaldehyde (Lobachemie, India), 2-hydroxyacetophenone (Lobachemie, India), 30 %
aqueous H
India), 70% Perchloric acid (Merck, India), KBr (Merck, India),5-bromosalicylaldehyde (TCI,
Japan),3,5-dibromosalicylaldehyde (TCI, Japan),2,4,6-tribromophenol (TCI, Japan) and 1-(2-
2
O
2
(TCI, Japan),3,5-di-tert-butylcatechol (TCI, Japan), CuCl
2
.2H
2
O (Lobachemie,
,
Aminoethyl)piperazine (Sigma Aldrich, USA) were used as obtained without further purification.
All other chemicals and solvents were of analytical reagent grade and used without further
purification.

Page 5 of 48
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00957G
2
.2. Instrumentation and Characterization Procedures
Infra-Red spectra of ligands were recorded in solid states as a KBr pellet /ATR mode on a Thermo-
NICOLET 8700 Research Spectrometer /Carry 660FTIR spectrometer within the range of
-1
4
00˗4000 cm .Electronic spectra were recorded in methanol/nujol with a Shimadzu UV-1800 UV-
1
13
Vis spectrophotometer. H and C NMR spectra of the ligands were recorded on a Bruker Avance
II 400 MHz NMR spectrometer with the common parameter settings in DMSO-d solvent. Cyclic
Voltammograms (CVs) were recorded using a conventional three electrode arrangement using CHI
60C electrochemical analyzer. Thermo gravimetric analyses were performed using NETZSCH-
Gerätebau GmbH, STA 449 F3Jupiter instrument, SEM and Energy Dispersive X-ray analyses
EDX)were done by using HITACHI S-3400N, Atomic Absorption Spectroscopic analyses were
6
6
(
carried out in LABINDIA AA8000. EPR spectra of the metal complexes were recorded in DMSO
on a Bruker EMX X-band spectrometer operating at 100-kHz field modulation at room
temperature. For polymer anchored metal complexes spectra were recorded on a Jeol JES-X3
+
Series ESR spectrometer at 77K. The ESI mass of the metal complexes were estimated on Waters
Q-Tof Micromass instrument. Anagilent 7890 B gas-chromatograph fitted with a HP-5 capillary
column (30 m × 0.25 mm × 0.25 i.d.) and a FID detector was used to analyze the reaction products
and % conversions were calculated on the basis of the relative peak area of the respective products
with the reactant. Identity of the products were confirmed by using commercially available
standards and GC-MS (thermo ISQ QD single quadrupole mass analyzer coupled with Trace 1300
GC system).
2
.3. X-ray crystallography
II
The crystal of [Cu (sal-ppzH)Cl
2
] (1) was immersed in cryo-oil, mounted in a Nylon loop, and
measured at a temperature of 150 K. The diffraction data was collected with Bruker Kappa APEX
6
9
II diffractometer using Mo Kα radiation (λ = 0.71073 Å). The APEX2 program package was
used for cell refinements and data reductions. The structures were solved by direct methods using
the SHELXS-201470 program with the WinGX71 graphical user interface. A semi empirical
7
2
absorption correction (SADABS) was applied to all data. Structural refinements were carried out
using SHELXL-2014.71
Some of the crystallization solvent was lost from the crystal and could not be resolved
unambiguously. The contribution of the missing solvent to the calculated structure factors was

New Journal of Chemistry
Page 6 of 48
View Article Online
DOI: 10.1039/C7NJ00957G
7
3
taken into account by using a SQUEEZE routine of PLATON. The missing solvent was not taken
into account in the unit cell content.
The NH
2
hydrogen atoms were located from the difference Fourier map and constrained to ride on
II
their parent atom, with Uiso = 1.2 Ueq (parent atom). All other hydrogen atoms in [Cu (sal-
ppzH)Cl
2
] (1) were positioned geometrically, with C–H = 0.95–0.99 Å, O–H = 0.84 Å, Uiso = 1.2
Ueq (parent atom). CCDC No. 1539445contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. The crystallographic details are summarized in table 1.
II
Table 1:Crystal data and structure refinement for [Cu (sal-ppzH)Cl
2
] (1)
Identification code
Empirical formula
Formula weight
Temperature
1
C
13
H
19Cl
2
CuN O
3
367.75
150(2) K
Wavelength
0.71073 Å
Triclinic
Crystal system
–
Space group
P1
Unit cell dimensions
a = 11.8119(4) Å
b = 13.0851(4) Å
c = 13.4912(4) Å
α = 90.401(1)°
β = 91.035(1)°
γ = 107.506(2)°
3
Volume
1988.13(11) Å
Z
4
3
Density (calculated)
Absorption coefficient
F(000)
1.229 Mg/m
-1
1
.366 mm
756
.721 x 0.688 x 0.278mm
2.039 to 34.679°
Crystal size
θ range for data
3
0

Page 7 of 48
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00957G
collection
1
8<=h<=16, -20<=k<=20,
Index ranges
-20<=l<=20
Reflections collected
44563
Independent reflections 14061 [R(int) = 0.0204]
Completeness to θ=
9
7.8 %
Numerical
.703 and 0.439
Full-matrix least-squares
2
5.242°
Absorption correction
Max. and min.
0
transmission
Refinement method
2
on F
Data / restraints /
parameters
1
4061 / 0 / 361
Goodness-of-fit on F2
1.031
Final R indices
R1 = 0.0327, wR2 =
0.0778
[
I>2sigma(I)]a
R1 = 0.0497, wR2 =
R indices (all data)
0
.0839
Largest diff. peak and
hole
-3
0
.528 and -0.500e.Å
a
2
2 2
2 2 1/2
R1 = ||F
o
| – |F
c
||/|F
o
|; wR2 = [[w(F
o
– F
c
) ]/ [w(F ) ]] .
o
2
.4. Computational methods
Density functional theory was used to explore the structural and chemical properties for the
synthesized metal complexes1 and 2. All the calculations were performed using Gaussian '0974
program package with the Gauss View 5.0 and Chemcraft75-76 molecular visualization program
II
using a HP workstation Z440. X-ray refinement data of the mononuclear [Cu (sal-ppzH)Cl
2
] (1)
was taken as an initial guess for the liquid phase geometry optimization. The molecular structure
of the compounds in the ground state is optimized by Density Functional Theory (DFT) in its
unrestricted forms, employing the LANL2DZ with an effective core potential for Cu atom and 6-

New Journal of Chemistry
Page 8 of 48
View Article Online
DOI: 10.1039/C7NJ00957G
3
11G (d,p) for the rest of the atoms in methanol using a conductor-like polarizable continuum
model (CPCM). In DFT calculation electron correlations were included using Becke3–Lee–Yang–
Parr (B3LYP) procedure.77–79 This includes Becke’s gradient exchange corrections, Lee, Yang and
8
0
Parr correlation functional. Frequency calculation at the same level of theory was performed to
ensure that the equilibrium system represents true minima on the potential energy surface. No
symmetry constrain was imposed during the geometry optimization.
2
2
1
.5. Catalytic activity
.5.1. Oxidation of 3,5-di-tert-butycatechol (catecholase like activity?)
and 2 were tested against the catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC). 3,5-
DTBC was chosen because the tert-butyl substituent on the ring makes it highly stable and a low
quinone–catechol reduction potential makes it easily oxidizable to the corresponding o-quinone.
-4
II
-2
In a typical reaction, 1.0×10 M [Cu (hyap-ppzH)Cl
2
] (2) was reacted with 2.85×10 M 3,5-DTBC
-1
and 1.0×10 M H
2
O
2
in a total 20 ml methanolic reaction mixture at room temperature and
pressure. Reaction progress was monitored spectrophotometrically for 70 minutes (figure 1). With
the course of time, a new absorption band at 400 nm arises. It is well established that 3,5-DTBQ
shows characteristic band maxima at 400 nm in methanol which proves catalytic oxidation of 3,5-
DTBC. Figure1 shows the spectral changes during the catalytic oxidation of 3,5-DTBC by taking
catalyst 2 as a representative. In the absence of catalyst, no conversion was observed. We have
observed that the oxidative conversion of 3,5-DTBC is silent in presence of aerial oxygen as well
as H
2
O
2
individually. To verify the effect of aerial O
2
, on the oxidation of 3,5-DTBC, 2.85 × 10-2
-4
-1
M 3,5-DTBC was reacted with 1.0×10 M of catalyst 2 with and without 1×10 M H
2
2
O under
nitrogen atmosphere separately (plot S2). Plot S2 clearly indicates that, H
2
2
O is necessary for the
oxidation of 3,5-DTBC and eliminates any effect of aerial O during oxidation of 3,5-DTBC.
2

Page 9 of 48
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00957G
2
1
0
0
.7
.8
.9
.0
4
00 nm
3
00
350
400
450
500
Wavelength (nm)
Figure 1: Spectral changes observed during oxidation of 3,5-DTBC (2.85×10-2 M) to
-1
-4
corresponding o-quinone in the presence of 1.0 × 10 M H
2
O by 2 (1.0 ×10 M) in a total 20 ml
2
methanolic reaction mixture at room temperature.
2
.5.1.1. Kinetics of catalytic oxidation of 3,5-di-tert-butycatechol
The kinetics of the catalytic oxidation of 3,5-DTBC to corresponding o-quinone in the presence of
catalysts was monitored by observing the change in absorbance at λmax 400 nm. All the catalysts
follow Michaelis-Menten equation of saturated kinetics. To check the catalytic efficiency we have
calculated their rate and kcat (i.e. turn over number) by an initial rate method. Plot 1 shows the
change in absorbance with time at λmax 400 nm for the conversion of 3,5-DTBC to 3,5-DTBQ with
catalyst and without catalyst in the presence of dilute H
2
O
2
in methanol for 10 min at room
temperature. Multicolored graph in plot 1 shows the effect of various increasing concentrations
-1
-2
-2
-2
-2
-2
(
1×10 M, 1×10 M, 2×10 M, 4×10 M, 6×10 M and 8×10 M) of 3,5-DTBC on the catalytic
-4
-1
oxidation reaction by 1×10 M methanolic solution of 2 in presence of 1×10 M H
2
2
O in methanol.

New Journal of Chemistry
Page 10 of 48
View Article Online
DOI: 10.1039/C7NJ00957G
-
-
-
-
-
2
2
2
2
1
2
4
6
8
1
1
×10
×10
×10
×10
×10
×10
M
M
M
M
M
M
0
0
0
0
.3
.2
.1
.0
In presence of Catalyst 2
-2
Blank
}
600
0
150
300
450
Time (sec.)
-1
-2
-2
Plot 1: Absorbance vs. time plots for the oxidation of 3,5-DTBC (1×10 M, 1×10 M, 2×10 M,
-2
-2
-2
-4
4
×10 M, 6×10 M and 8×10 M) with and without catalyst 2(1×10 M) for 10 minutes in the
-1
presence of 1.0×10 M dilute H
2
2
O in methanol at room temperature. (Reaction conditions: 1 ml
-
1
-2
-2
-2
-2
-2
-1
2 2
substrate (1×10 M, 1×10 M, 2×10 M, 4×10 M, 6×10 M, 8×10 M) was reacted with 1 ml H O (1×10 M) and
-
4
0
.5 ml catalyst (1×10 M) in presence of 1 ml MeOH.)
2
.5.2. Oxidative Bromination of Salicylaldehyde
II
II
Polymer anchored metal complexes PS-[Cu (sal-ppz)Cl] (3) and PS-[Cu (hyap-ppz)Cl] (4) were
used as a catalyst in the oxidative bromination of salicylaldehyde. Salicylaldehyde (1.22g, 10
mmol), 30% aqueous H
2
O
2
(2.27 g, 20 mmol), and an aqueous KBr (2.38 g, 20 mmol) solution
II
(
20 ml) were mixed in a 100 ml round bottom flask. To this, catalyst ([Cu (sal-ppz)Cl], (0.010 g)
and aqueous 70% HClO
4
(2.86 g, 20 mmol) (Caution: HClO is strong oxidant, must be handled
4
with care.) were mixed and kept on stirring for 2 hours at room temperature. For the improvement
of catalytic reaction, half of the perchloric acid was added initially (time=0) and rest amount was
divided in three equal portions and added after every 15 minutes. Each polymer anchored metal
complex was swelled for 6 hours in water before using in catalytic reaction. All the reaction
conditions were kept as identical as possible, namely: RPM (800), shape and size of RBF (100 ml)
and magnetic stir bar. After 2 hours of reaction, orange colored organic product was extracted with
CH
bromosalicylaldehyde,3,5-dibromosalicylaldehyde
salicylaldehyde were confirmed by matching the retention time with their commercially available
2
Cl
2
and used in GC for the analysis. The formation of three bromo derivatives (5-
and 3-bromosalicylaldehyde) of

Page 11 of 48
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00957G
standards. A single quadrupole GC-MS was also employed to confirm the identity of bromination
products of salicylaldehyde.
2
2
.6. Synthesis
.6.1. Preparation of [Hsal-ppz] (I) and [Hyap-ppz] (II)
The Schiff-base ligand [Hsal-ppz] (I) was prepared by the 1:1 condensation of salicylaldehyde
0.61 g, 5 mmol) and 1-(2-Aminoethyl)-piperazine (0.646 g, 5 mmol) in 30 ml methanol following
(
uninterruptible stirring. The color of the reaction mixture appears yellow and was further refluxed
for 2-3 hours. The progress of the reaction was monitored by TLC at regular time intervals. The
volume of the reaction mixture was reduced to ~10 ml and kept for 2-3 days at room temperature
till the yellow colored solid of [Hsal-ppz] (I) separated out. It was filtered, washed with methanol
(2×5 ml) followed by petroleum ether and dried over silica gel under vacuum.
Yield: 2.27g (97.39%); Anal. Calcd. for C13 O (MW: 233.31): C, 66.92 %; H, 8.86 %; N,
H N
19 3
-
1
1
2
2
1
4
8.01 %; Found: C, 67.15 %; H, 8.99 %; N, 17.95 %; FTIR (KBr plate method, cm )): 3369(νOH),
-1
-1
928(νN-H), 1635(νC=N), 1279(νC-O); UV-Vis(in MeOH,
λ
max(nm)/ε(litre mol cm )):
4
3
3
3
1
54(1.114×10 ),272(5.726×10 ), 316(3.609×10 ), 405(1.460×10 ); H NMR(CDCl
3
, δ in ppm):
3.27(s, 1H), 4.98(s, 1H), 8.26(s, 1H), 6.78(t, 1H), 6.88(d, 1H), 7.15(d, 1H), 7.22(t, 1H), 2.46(sb,
H), 2.55(t, 2H), 2.63(m, 2H), 2.93(t, 2H), 3.65(q, 2H).
By adopting the similar procedure as described for the synthesis of ligand [Hsal-ppz] (I), we also
prepared [Hyap-ppz] (II) by reacting 1-(2-Aminoethyl)piperazine with 2-hydroxyacetophenone in
methanol.
Data for the ligand [Hyap-ppz] (II)
Yield: 2.40 g (97.17 %),Anal. Calcd. For C14
H
21
N O (MW: 247.34): C, 67.98%; H, 8.56%; N,
3
-
1
1
2
2
5
4
6.99%. Found: C, 68.05%; H, 8.69%; N, 16.84%; FTIR (KBr plate method,cm ): 3432(νOH),
-1
-1
929(νN-H), 1615(νC=N), 1299(νC-O); UV-Vis(in MeOH,
λmax(nm)/ε(litre mol cm )):
3
3
3 1
70(7.5138×10 ),324(1.936×10 ), 388(3.508×10 ); H NMR(CDCl3, δ in ppm):16.20(s, 1H),
.87(s, 1H), 6.68(t, 1H), 6.85(d, 1H), 7.19(t, 1H), 7.43(d, 1H), 2.45(sb, 4H), 2.68(t, 2H), 2.84(sb,
H), 3.61(t, 2H), 2.26(s, 3H).
II
II
2
.6.2.Synthesis of [Cu (sal-ppzH)Cl
2
] (1) and [Cu (hyap-ppzH)Cl ] (2)
2

New Journal of Chemistry
Page 12 of 48
View Article Online
DOI: 10.1039/C7NJ00957G
A methanolic solution (20 ml) of [Hsal-ppz] (I) (2.31 g, 10 mmol) was added to a methanolic (10
ml) solution of CuCl
2
.2H
2
O (1.70g, 10 mmol) with constant stirring. After refluxing the reaction
II
mixture for 2 hours, a green colored [Cu (sal-ppzH)Cl
2
] (1) compound separated out. The product
was filtered, washed several times with methanol(3×20 ml) and finally dried over silica gel under
vacuum.
II
Data for the complex [Cu (sal-ppzH)Cl
2
] (1)
Yield: 2.82 g (76.85 %); Anal. Calcd. For C13
H N
19 3
OCl
2
Cu (MW:367.76): C, 42.46 %; H, 5.21
-1
%
; N, 11.43 %;Found: C, 42.60 %; H, 5.33 %; N, 11.32 %;FTIR (ATR mode, cm ): 3435(νOH),
-1
-1
2
2
945(νN-H), 1600(νC=N), 1201(νC-O); UV-Vis(in MeOH,
λmax(nm)/ε(litre mol cm )):
3
3
3
2
25(2.170×10 ), 238(2.126×10 ), 272(1.8953×10 ), 364(5.194×10 ), 667(88).
II
Similarly, [Cu (hyap-ppzH)Cl
2
] (2) was isolated by reacting CuCl
2
.2H O with ligand [Hyap-ppz]
2
(II) from refluxing methanol. Scheme 2 represents the probable structure for the synthesized
copper (II) complexes.
II
Data for the complex [Cu (hyap-ppzH)Cl
Yield: 2.86g (75.19%); Anal.Calcd. For C14
N, 11.01 %; Found: C, 44.19 %; H, 5.62 %; N, 10.98 %; FTIR (ATR mode, cm ): 3413 (νOH),
2
] (2)
H
21
N
3
OCl Cu (MW: 381.79): C, 44.04 %; H, 5.54 %;
2
-1
-1
-1
2
2
926(νN-H),1601(νC=N), 1233(νC-O);
UV-Vis(in MeOH,
λmax(nm)/ε(litre mol cm )):
25(2.237×103)
270 (1.446×10 ), 354(4.443×10 ), 638(67).
3
2
,
Scheme 2: Synthetic routes and structures for the synthesized ligands and copper(II) complexes.

Page 13 of 48
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00957G
II
II
2
.6.3. A general method for the preparation of PS-[Cu (sal-ppz)Cl] (3) and PS-[Cu (hyap-ppz)Cl]
(4)
Chloromethylated polystyrene (1.0 g) was allowed to swell in DMF (20 ml) for 6 hours. A solution
II
of [Cu (sal-ppzH)Cl
2
] (1) (1.838 g, 5 mmol), dissolved in DMF (40 ml) was added to the above
suspension. KI (0.830 g, 5 mmol) and triethylamine (3 ml) was added into the reaction mixture
with smooth stirring. The whole reaction mixture was refluxed for 48 hours in an oil bath fitted
with a water cooled condenser. After the completion of reaction brown colored polymer anchored
metal complex was filtered and washed thoroughly with hot DMF (5×20 ml) followed by hot
II
methanol (5×20ml). The isolated polymer anchored metal complex PS-[Cu (sal-ppz)Cl] (3) was
dried in hot air oven at ca.110 °C for 24 hours. Recovery yield: ~92%.
II
II
Similarly PS-[Cu (hyap-ppz)Cl] (4) was prepared by using [Cu (hyap-ppzH)Cl ] (2) (1.908 g, 5
2
II
mmol) in place of [Cu (sal-ppzH)Cl
2
] (1). Recovery yield: 95 %.
Scheme 3: Synthetic approach for the heterogenization of Cu(II) complexes.
3
.0. Results and Discussion
II
3
.1. Molecular structure of complex [Cu (sal-ppzH) Cl ] (1).
2
II
Single crystal XRD data analysis shows that the [Cu (sal-ppzH) Cl
2
] (1)crystallizes in space group
–
P1, with a distorted square pyramidal geometry around the copper atom. Ellipsoid plot of the 1 is
shown in the figure 2. τ-value of the complex is 0.0105 (τ =1 for perfect trigonal bipyramidal

New Journal of Chemistry
Page 14 of 48
View Article Online
DOI: 10.1039/C7NJ00957G
8
1
geometry and τ= 0 for perfect squire pyramidal geometry ) and tells about the distortion around
the metal centre.
II
Figure 2: Molecular view of the complex [Cu (sal-ppzH) Cl
2
] (1).
Basal plane position are occupied by the phenolate oxygen (O1) from salicylaldehyde ring, one
nitrogen (N1) from C=N- group, second nitrogen (N2) from piperazine ring and one chlorine (Cl1)
atom. Apical position is occupied by another chlorine (Cl2) atom. Overall negative charge in the
first coordination sphere is counterbalanced by the protonation of the piperazine amine group. Cu-
Cl(1) bond distance is 2.298 Å whereas apical position chlorine atom (Cl2) and Cu distance
significantly longer (2.694 Å).
Figure 3: Intermolecular H-bonding in the unit cell of 1.

Page 15 of 48
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00957G
Piperazine ring adopted most stable chair conformation whereas protonated piperazine ring amine
nitrogen (N3) involved into H-bond formation (figure 3) with the phenolate oxygen (O1) of
salicylaldehyde of another molecule (HN-H...O distance is 1.952 Å). Apical position chloride
atoms also show a weak H-bonding interaction with the second proton of protonated amine group
of piperazine ring (HN-H.....Cl distance 2.268 Å) makes a beautiful molecular association.
Selected bond length and bond angles are listed in table S1.
3
.2.IR spectral studies
-1
Both the ligands show one broad band in the range of 3369 to 3432 cm , due to the presence of
ν(O-H),while the same band present in the corresponding metal complexes in the range of 3413 to
-1
3
435 cm ,signify the presence of water of crystallization. All the ligands and metal complexes
-1
exhibit medium intensity bands for ν(N-H)in the range of 2926-2945 cm . Both the ligands show
two sharp bands at 1615-1635 cm-1 and 1279-1299 cm , because of the ν(C=N)and ν(C-
O)respectively. ν(C=N)and ν(C-O) bands appear in 1 and 2 at lower wave numbers with respect to their
counter ligands; indicate the coordination of azomethine (-C=N) nitrogen and phenolic (Ph-O)
oxygen to the copper atom. A broad absorption band due to ν(N-H)wagging is observed in the ligands
-1
-1
and in all the metal complexes in the range of 739-759 cm . All the polymer anchored metal
complexes exhibit the similar spectral pattern like complex 1 and 2 but with reduced intensity
because of the polymeric matrix (figure S1). Partial list of important IR spectral data of ligands
and metal complexes are shown in the table S2.
3
.3.Electronic Spectral data for the ligands and metal complexes
UV-Vis spectra of ligands and Cu(II) complexes were recorded in methanol at room temperature.
While UV-Vis spectra of polymer anchored copper(II) complexes were recorded in nujol. Partial
list of important spectral data of ligands, copper(II) complexes and polymer anchored copper(II)
complexes are listed in table S3.
In methanol, ligand [Hsal-ppz] (I) shows three bands at 254, 316 and 405 nm along with a shoulder
band at 272 nm. While ligand [Hyap-ppz] (II), exhibits two bands at270 and 388 nm and a shoulder
band at 324 nm. Absorption bands shown by both ligands in the range of 254 -316 nm are
assignable to π-π* transition. Whereas bands appearing in the range of 388-405 nm are indication
of the n-π* transition in the ligands. All these bands show a slight hypsochromic shift in the

New Journal of Chemistry
Page 16 of 48
View Article Online
DOI: 10.1039/C7NJ00957G
corresponding copper(II) complexes (figure S2) along with a new sharp band in the range of 222-
25 nm.
Complexes [Cu (sal-ppzH)Cl
at 667 nm and 638 nm, respectively (figure 4), assignable to d-d transition. Higher extinction
2
II
II
2
] (1) and [Cu (hyap-ppzH)Cl ] (2) show one broad absorption band
2
-1
-1
-1
-1
coefficient value for 1 (ε667 =88, litre mol cm ) in comparison to 2 (ε638 =67, litre mol cm )
suggests lower symmetry and maximum distortion in 1 from the ideal square pyramidal geometry
8
2
II
II
than 2. Polymer anchored metal complexes PS-[Cu (sal-ppz)Cl] (3) and PS-[Cu (hyap-ppz)Cl]
4) exhibit similar spectral behavior to that of unanchored metal complexes with reduced
(
absorbance intensity (figure S3). Presence of these absorbance bands, established the existence of
II
copper complexes into the polymeric matrix. However, PS-[Cu (sal-ppz)Cl] (3) was unable to
produce any detectable 238 nm and 667 nm absorbance band, because of very poor loading of the
metal complex into the polymer matrix.
2
1
1
0
0
.0
.5
.0
.5
.0
6
67 nm
II
[
Cu (sal-ppzH)Cl ] (1)
2
II
[Cu (hyap-ppzH)Cl ] (2)
2
6
38 nm
6
00
800
1000
Wavelength (nm)
-3
II
Figure 4: Electronic spectra of 8.837×10 M methanolic solution of [Cu (sal-ppzH)Cl ] (1)(red
2
-3
II
line) and9.429×10 M methanolic solution of [Cu (hyap-ppzH)Cl ] (2)(Black line).
2

Page 17 of 48
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00957G
3
.4. Electrochemical properties
Redox potential of the metal center has an immense role in the catalytic redox reaction. CV
measurements were performed by a computerized electrochemical trace analyzer at a scan rate of
-1
0
.1 V sec in DMF solution containing 0.1 (M) TBAP (tetrabutylammonium perchlorate) as a
supporting electrolyte, using a three-electrode configuration (glassy carbon working electrode, Pt
counter electrode, and Ag/AgCl as reference electrode). De-aerated solutions were used by purging
2
N gas for 10 min prior to measurements. The whole measurements were automated and controlled
through the programming capacity of the apparatus. The solvents used were sufficiently pure and
the concentration of the complexes was kept at 0.001 M.
0.000015
0.000010
0.000005
0.000000
-
0.000005
0.000010
-
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
Potential(V)vsAg/Agcl
-1
Figure 5: A representative cyclicvoltammogram of 2 with scan rate 0.1 V Sec and 0.1 M TBAP
in DMF.
Table 2: Electrochemical data for 1 and 2 in DMF solution.
Complex
Ea
p
(V)
Ec
p
(V)
ΔE
p
(V)
E1/2 (V)
II
[
[
Cu (sal-ppzH)Cl
2
] (1)
0.54
0.40
0.37
0.14
0.15
0.47
0.48
II
Cu (hyap-ppzH)Cl
2
] (2) 0.52
Both complexes show a quasi-reversible cyclic voltamogram corresponding to CuII/I system
shown in the figure 5) with peak separation ranging from 0.11 V to 0.15 V in DMF solution.
(
Cyclic voltagram of 1 is shown in the figure S4. Approximate formal potential (E1/2) of the
complexes was calculated by taking an average of peak potentials. Complexes 1 and 2 show E1/2
values 0.47V and 0.48V respectively (listed in table 2). Voltagram confirms the successful

New Journal of Chemistry
Page 18 of 48
View Article Online
DOI: 10.1039/C7NJ00957G
2
+
formation of Cu complexes. Close formal potential indicates similarity of their electronic
environments and expecting very close catalytic behaviors.
3
.5. Thermogravimetric analysis
II
Thermal stability of the polymer anchored copper(II) complexes, PS-[Cu (sal-ppz)Cl] (3), and PS-
II
[
Cu (hyap-ppz)Cl] (4) were examined by TGA method under nitrogen atmosphere at a
temperature rate of 10°C/ min over a temperature range of 33°C to 800 °C. Both of the polymer
anchored copper(II) complexes are considerably stable up to 330°C.Complexes 3 and 4 show a
negligibly small but progressive weight loss of ~ 3.0 % (up to 328°C)and ~ 6.0 % (up to 320°C)
respectively due to the physically adsorbed gases and water molecules. 3 exhibits maximum
weight loss (76.71 %) in the temperature range 328°C-466°C while complex 4 displays the
maximum weight loss (68.25 %) in the range of 320°C-470°C, which is attributed to the
decomposition of polymeric matrix and metal complex backbone (figure 6).
II
PS-[Cu (hyap-ppz)Cl] (4)
1
00
II
PS-[Cu (sal-ppz)Cl] (3)
7
5
2
5
0
5
1
50
300
450

600
750
Temperature ( C)
II
Figure 6: Thermogravimetric temperature vs. % weight loss plot for PS-[Cu (sal-ppz)Cl] (3), and
II
PS-[Cu (hyap-ppz)Cl] (4).
3
.6.SEM-EDX Analysis
Surface morphological changes among the pure chloromethylated polystyrene, polymer anchored
copper(II) complexes 3 and 4 were examined by scanning electron microscopic analysis
(SEM)(shown in the Figure 7). Copper(II) complexes anchored polymer bead shows no significant
morphological changes. Slightly roughening in the outer surface of the polymer bead may be due

Page 19 of 48
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00957G
to incorporation of metal complexes into the polymeric matrix as well as the frictional force
experienced during the process of heterogenization. Metal complexes anchored polymer bead
looks little shinny because of the presence of solvent molecules during the analysis.
(
C)
(
A)
(B)
II
Figure 7: SEM image of (A) Pure Chloromethylated polystyrene (B) PS-[Cu (sal-ppz)Cl] (3) and
II
(
C) PS-[Cu (hyap-ppz)Cl] (4)
Energy Dispersive X-ray (EDX) analysis of the copper(II) complexes anchored polymer bead
shown in the figure 8) indicates the presence of Cu along with C, N and O, hence confirms the
(
successful anchoring of copper complexes into the polymeric matrix of chloromethylated
polystyrene. EDX analysis of complex 3 and 4 also shows the presence of Cl signal, signifying the
very dilute dispersion of copper(II) complexes into the polymeric matrix. Metal loading calculated
from EDX analysis for complex 3 and 4 is 1.87 % and 2.75 % respectively. The actual
concentration of copper in the polymer matrix was estimated by AAS analysis which shows the
-1
-1
values 0.07836% (0.01233 mmolg ) and 0.399% (0.0628 mmolg ) for complex 3 and 4
respectively.
(
A)
(B)
II
Figure 8: Energy dispersive X-ray analysis graphs of (A) PS-[Cu (sal-ppz)Cl] (3) and (B) PS-
II
[
Cu (hyap-ppz)Cl] (4)

New Journal of Chemistry
Page 20 of 48
View Article Online
DOI: 10.1039/C7NJ00957G
1
13
3
.7. H and C NMR Spectral studies
Molecular structure of Schiff-base ligands [Hsal-ppz] (I) and [Hyap-ppz] (II) was confirmed by
1
1
H-NMR analysis. H-NMR spectra (figure S5 and S6) of the ligands were recorded in CDCl and
3
spectral data are summarized in the table 3. Ligand [Hsal-ppz] (I) shows two broad signals, one
appearing at 4.98 ppm assigned to -NH proton while another broad signal appearing at 13.27 ppm
may be due to the -OH proton which is deshielded by intramolecular H-bonding with the imine-
N. Similarly, in ligand [Hyap-ppz] (II), -NH and -OH proton signals are appearing at 5.87 ppm
and 16.20 ppm respectively. Ligand I shows one sharp singlet at 8.26 ppm because of -CH=N
proton, along with four aromatic proton (6.78-7.23 ppm) and twelve aliphatic protons (2.46-3.67
ppm) within the expected region.[Hyap-ppz] (II) shows four aromatic proton in the range of 6.66-
7
.43 ppm and twelve aliphatic proton in the range of 2.45-3.62 ppm along with one sharp singlet
signal at 2.26 ppm due to the presence of -CH protons.
3
1
Table 3: H-NMR spectral data of ligands (δ in ppm)
Compounds
- NH -OH
4.98 13.27
(s, 1H) (s, 1H) (s, 1H) (d, 1H), 7.15 (d,
-CH=N Aromatic
Aliphatic
-CH
3
[
Hsal-ppz]
8.26 6.78 (t, 1H), 6.88 2.46 (s, b, 4 H), 2.55 (t,
(
I)
2H), 2.63 (m, 2H), 2.93(t,
2.45 (s, b, 4H), 2.68(t,
-
1H), 7.22 (t, 1H) 2H), 3.65 (q, 2H)
[
(
Hyap-ppz]
5.87
16.20
-
6.68(t, 1H), 6.85
(d, 1H), 7.19 (t,
2.26
II)
(s, 1H) (s, 1H)
2H), 2.84 (s, b, 4H), 3.61 (s, 3H)
1H), 7.43 (d, 1H) (t, 2H)
1
3
Ligands’ backbone was further confirmed by C NMR spectral studies. The relevant spectral data
1
3
are collected in table 4. CDCl was used to record the C NMR spectra of the ligands. All spectra
3
are in good agreement with the proposed ligands structure. Ligand I ([Hsal-ppz]) shows two
signals, one at 166.51 ppm due to phenolic carbon (C1) (Ph-OH) and another at 164.01 ppm
because of azomethine carbon (C7). Likewise C1 and C7 signals appear in [Hyap-ppz] (II) at
1
74.40 and 169.48 ppm respectively. In ligand I, aromatic carbon atoms show four signals in the
range of 133.02-117.68 ppm (C2- C6) while all the six aliphatic carbon atoms exhibit four signals
in the range of 57.93-44.02 ppm (C9-C14). Ligand II shows five aromatic signals (134.05-115.20
ppm) and four aliphatic signals (57.39-44.08 ppm) within the expected region, along with a signal
for -CH at 37.11 ppm (table 4).
3

Page 21 of 48
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00957G
Table 4: The position of the carbon signals in the 13 C-NMR spectra of the ligands(δ in ppm).
Ligands
13C-NMR signals (ppm)
R=H
HSal-ppz] (I)
R=CH
166.51 (C1), 164.01 (C7),133.02 (C4), 131.91 (C3 & C5), 11.18 (C6), 117.68
(C2), 57.93 (C9), 54.16 (C10), 51.11 (C12 & C13), 44.02 (C11 & C14).
[
3
174.40 (C1), 169.48 (C7), 134.05 (C4), 128.99 (C5), 120.58 (C3), 117.16 (C6),
[
Hyap-ppz] (II) 115.20 (C2), 57.39 (C9 & C10), 53.28 (C12 & C13), 44.08 (C14 & C11), 37.11
C8)
(
3
.8. EPR Spectral Studies
Room temperature X-band EPR spectra of 1 and 2 in DMSO were represented in the figure 9.
They are characteristic of a typical axially symmetric paramagnetic centre. For 1, g‖= 2.249 and
g
┴
= 2.051. While for 2, g‖ = 2.262 and g
┴
= 2.052. In solution both complexes show axial
symmetric g tensor parameters g‖> g >g(2.0023) indicating that the unpaired electron lies in a
┴
2
2
dx -y ground state orbital. Absence of well resolved hyperfine lines in their spectra indicate a
situation usually observed in the case where copper-copper interaction is present.83,84
Lack of half-field transition (around 1600 G) indicates that both of the complexes exist as
monomer in the solution. In axial symmetry, G values which are related to g by G = ( g‖-22)/(g -
┴
II
II
2
) = 4. Complexes [Cu (sal-ppzH)Cl
2
] (1) and (B) [Cu (hyap-ppzH)Cl ] (2) show G values 4.88
2
and 5.04 respectively which indicates negligible copper-copper magnetic interaction.85

New Journal of Chemistry
Page 22 of 48
View Article Online
DOI: 10.1039/C7NJ00957G
II
II
Figure 9: X-band EPR spectra of (A) [Cu (sal-ppzH)Cl
DMSO at room temperature.
2
] (1); (B) [Cu (hyap-ppzH)Cl ] (2) in
2
II
X-band EPR spectra of the polymer anchored metal complexes PS-[Cu (sal-ppz)Cl] (3) and PS-
II
[
Cu (hyap-ppz)Cl] (4) at 77K are reproduced in figure 10. The calculated principle components
of g tensor for 1 are gav‖ = 2.319 and g
┴
= 2.038 while 2 shows gav‖ = 2.312 and g
┴
= 2.043. Figure
0 is characteristics of monomeric Cu centre and typical axial symmetry EPR spectra may be
due to square pyramidal geometry of the molecule shown in figure 2. The hyperfine structure, due
2
+
1
2
+
to the interaction of electron spin S=1/2 with Cu nuclear spin values S=3/2, is well resolved in
the spectra. Well resolved hyperfine structure implies the fact that copper complexes are well
dispersed into the polymer matrix where the probability of copper-copper magnetic interaction is
negligible. Additionally EPR spectrum of 1 at 77K exhibits a poorly resolved super hyperfine
2
+
splitting in the perpendicular region probably due to the interaction of Cu with nitrogen atom.
II
Figure 10: X-band EPR spectra of polymer-anchored complexes PS-[Cu (sal-ppz)Cl] (3) and PS-
II
[
Cu (hyap-ppz)Cl] (4) at 77K.

Page 23 of 48
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00957G
3
.9. Computational Studies
DFT calculations were performed to understand the structural and chemical behavior of the
synthesized complexes. In spite of our repeated efforts, we could not isolate suitable crystals for
X-ray diffraction studies of the complex 2. Hence X-ray refinement data of the mononuclear
II
[
Cu (sal-ppzH)Cl
2
] (1) complex was taken as an initial guess for the liquid phase geometry
optimization of the two complexes. Selected bond lengths and bond angles of the calculated and
experimental geometry are mentioned in the table 5. Very close agreements between the
experimental and calculated geometry were observed. Most of the calculated bond lengths are little
elongated than the X-ray crystallographic data, because X-ray crystal diffraction was applied in
the solid state while theoretical calculations were performed in the liquid phase. For the very same
reason there is slight deviation in bond angles also. Frequency calculations were performed using
similar method and basis set to check the accuracy of the optimization process. Absence of
imaginary frequency ensures minimum global energy of the optimized geometry. Geometry
optimized structure of the complexes were shown in the figure 11. All the complexes adopt a
distorted square-pyramidal geometry as suggested by the X-ray refinement data of the
II
mononuclear [Cu (sal-ppzH)Cl
2
] (1).
Table 5: Geometry optimized parameters for the 1 and 2 computed at DFT/ UB3LYP/LanL2dzƲ
6
-311G (d,p) level of theory.
Sl. No.
Bond distance (Å)
Calculated data
of1
Experimental
data of 1
1.927
Calculated data
of2
1
2
3
4
5
Cu(1)-O(1)/N4
Cu(1)-Cl(1)
Cu(1)-Cl(2)
Cu(1)-N(1)
Cu(1)-N(2)
1.949
1.92787
2.42564
2.74310
2.03184
2.17366
2.298
2.405
2.694
2.759
1.945
2.005
2.089
2.194

New Journal of Chemistry
Page 24 of 48
View Article Online
DOI: 10.1039/C7NJ00957G
Sl.
No
.
Bond angle (°)
Calculated data Calculated data
Experimental
data of 1
158.14
98.74
of 1
of 2
1
Cl(1)-Cu(1)-N(1)
Cl(2)-Cu(1)-N(1)
O(1)/N4-Cu(1)-N(2)
Cl(1)-Cu(1)-Cl(2)
Cl(1)-Cu(1)-N(2)
N(1)-Cu(1)-N(2)
159.702
97.549
169.764
102.196
91.996
82.720
91.009
91.136
97.549
97.226
91.632
160.715
97.073
166.707
101.908
91.235
84.293
90.054
90.168
97.073
99.457
93.185
2
3
174.24
102.98
92.60
4
5
6
83.71
7
O(1)/N4-Cu(1)-N(1)
O(1)/N4-Cu(1)-Cl(1)
N(1)-Cu(1)-Cl(2)
O(1)/N4-Cu(1)-Cl(2)
N(2)-Cu(1)-Cl(2)
92.71
8
89.05
9
98.74
1
1
0
1
91.92
93.08
II
II
Figure 11: Optimization structure of (A) [Cu (sal-ppzH)Cl
2
] (1) and (B) [Cu (hyap-ppzH)Cl
2
]
(2)calculated at DFT/ UB3LYP/LanL2dzU6-311G (d, p) level of theory.
We have also calculated some of the quantum chemical properties of the complexes 1 and 2, by
using mixed basis set LANL2DZU6-311G (d,p) and listed in the table 6. HOMO and LUMO are
the two most important frontier molecular orbital in a molecule (figure 12 and 13). HOMO is the
highest molecular orbital which carry electrons. So, the Ionization Potential (IP), which is an
indication of electron donating ability, is directly related to the HOMO energy. Similarly, LUMO

Page 25 of 48
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00957G
is the highest empty molecular orbital which can capable of accepting electrons. Thus LUMO
8
6
energy is related to the electron affinity (EA) of the molecules. Chemical stability of a molecule
is therefore decided by the HOMO-LUMO energy gap.
HOMO 89B (E= -0.21254 Hartree)
E=-133.370 Kcal/Mole
HOMO 90A (E= -0.21470 Hartree)
E= -134.726 Kcal/Mole
LUMO 90B (E= -0.12604 Hartree)
E= -79.091 Kcal/Mole
LUMO 91A(E= -0.06597 Hartree)
E=-41.396 Kcal/Mole
Figure 12: Frontier Molecular orbitals of [Cu (sal-ppzH) Cl ] (1)
2
HOMO 93B (E= -0.21079 Hatree)
E=-132.272 Kcal/Mole
HOMO 94A (E= -0.21225 Hatree)
E=-133.188 Kcal/Mole

New Journal of Chemistry
Page 26 of 48
View Article Online
DOI: 10.1039/C7NJ00957G
LUMO 94B (E= -0.12171 Hatree)
E=-76.374 Kcal/Mole
LUMO 95A(E= -0.06162 Hatree)
E=-38.667 Kcal/Mole
II
Figure 13: Frontier Molecular orbitals of [Cu (hyap-ppzH) Cl ] (2)
2
HOMO-LUMO energy gap is quite important in determining a number of molecular properties,
like electrical transport properties, electronegativity, chemical hardness, chemical softness,
electrophilicity index etc.87
Table6:Selected quantum chemical properties calculated by using DFT /UB3LYP methods with
mixed basis set LANL2DZU6-311G (d,p).
SL Parameters
No
1
2
1
2
3
4
5
6
7
HOMO (Kcal/mole) (IP)
-134.73
-79.09
55.64
-133.19
-76.37
56.81
LUMO (Kcal/mole) (EA)
ΔE (energy gap) (Kcal/mole)
( Kcal/mole) (Electronegativity)
 (Kcal/mole)(Chemical hardness)
( Kcal/mole) (softness)
106.91
27.82
104.78
28.41
0.017974
205.44
0.017601
193.25
( Kcal/mole) (electrophilicity index)
From table 6 it is clear that the ionization potential of 2 (-76.37 Kcal/Mole) is less in comparison
to 1 (-79.09 Kcal/Mole). Compound 2 also shows large HOMO-LUMO energy gap (56.81
Kcal/Mole) and highest chemical hardness values (28.41 Kcal/mole) which indicates its larger

Page 27 of 48
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00957G
chemical stability and high chemical hardness in comparison to 1. In summary, 2 is marginally
more stable but easily convertible to the Cu(III) than 1.
3
3
.10. Catalytic studies
.10.1. Catalytic oxidation of 3,5-DTBC
8
8
Because of its low redox potential, 3,5-DTBC is easily oxidized to 3,5-DTBQ (Scheme 4) which
is stable and shows strong absorbance band at max = 400 nm in methanol.
Scheme 4: Catalytic conversion of 3,5-DTBCto 3,5-DTBQ.
II
II
Catalytic conversion of 3,5-DTBC to 3,5-DTBQ by [Cu (sal-ppzH)Cl
2
] (1) and [Cu (hyap-
ppzH)Cl ] (2) in presence of dilute hydrogen peroxide were evaluated by UV-Vis
2
spectrophotometer in methanol by observing the increase of the 400 nm absorption band as a
function of time under pseudo first order condition (figure 1).
Formation of 3,5-DTBQ was also detected by thin layer chromatography technique using authentic
sample of 3,5-DTBQ. In absence of catalyst no conversion of 3,5-DTBQ was observed. A fixed
concentration of H
2
O
2
is essential in the catalytic cycle. To optimized the amount of H O2, four
2
-1
different amount 0.25 ml, 0.50 ml, 1.0 ml and 1.25 ml of 1.0 × 10 M H
2
O
2
were used for a fixed
-2
-4
amount of 3,5-DTBC (1.0 ml, 2.85 × 10 M) and catalyst 2 (0.5 ml, 1.0×10 M solution) in a
quartz cuvette (total volume of reaction mixture was 3.0 ml in every batch of reaction) at room
temperature and pressure (Plot S1) for 30 min. With increasing the amount of H
to 0.50 ml, product absorbance value slightly increases from 0.705 to 0.849. While a large jump
in product absorbance value (1.43) was observed with using 1.0 ml of H . Further increasing
the amount from 1.0 ml to 1.25 ml product absorbance (1.63) values increases marginally. Hence
2
2
O from 0.25 ml
O
2 2
-1
-2
1
.0 ml of 1.00×10 M H
2
O
2
in 3 ml of solution (i.e.3.33×10 M H
2
2
O ) was considered as optimum
for catalytic oxidation 3,5-DTBC. To evaluate the efficiency of the catalyst we have determined
the kinetics of the oxidation of 3,5-DTBC by initial rate method by monitoring the growth of the
4
00 nm band as a function of time.

New Journal of Chemistry
Page 28 of 48
View Article Online
DOI: 10.1039/C7NJ00957G
-4
In this process we have reacted 0.5 ml 1×10 M solution of catalysts with 1.0 ml of six different
-1
-2
-2
-2
-2
-2
substrate concentrations of 1×10 M, 1×10 M, 2×10 M, 4×10 M, 6×10 M and 8×10 M in the
-1
presence of 1 ml 1×10 MH
2
2
O and 1.0 ml of methanol for a maximum time period of 10 minutes
.
At the low substrate concentration, 1 and 2 shows the first order rate dependence while at high
substrate concentration, zero order or saturated kinetics was found for both complexes (Shown in
plot 2). Rate dependence on the substrate concentration signifies a substrate–catalyst adduct
formation in the initial steps of the reaction. The rates of the reactions versus substrate
concentration data were fitted on the basis of Michaelis-Menten approach of enzyme kinetics and
linearized by means of Lineweaver-Burk plot to calculate the various kinetic parameters (listed in
table 7) like Vmax, K , Kcat etc. for these catalysts.
m
Plot 2: Initial rate versus substrate concentration for the oxidation of 3,5-DTBC. (A) Kinetic curves
catalyzed by [Cu(sal-ppzH)Cl ] (1) monitored at 400 nm in methanol (B) Lineweaver-Burk plot
of the same reaction catalyzed by 1 (C) Kinetic curves catalyzed by [Cu(hyap-ppzH)Cl ](2) and
D) Lineweaver-Burk plot of the same reaction catalyzed by 2. Symbol and solid lines represent
2
2
(
-
1
the observed and simulated kinetic profile respectively. (Reaction conditions: 1 ml substrate (1×10 M,

Page 29 of 48
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ00957G
-
2
-2
-2
-2
-2
-1
-
1
×10 M, 2×10 M, 4×10 M, 6×10 M, 8×10 M) was reacted with 1 ml H
2 2
O (1×10 M) and 0.5 ml catalyst (1×10
4
M) in presence of 1 ml MeOH.)
Table 7: Kinetic data for the oxidation of 3,5-Di-tert-butylcatechol catalyzed by various copper
complexes.
V
max
K
cat (mmolmin-1)
K
m
K
cat/K
(min-1)
m
-
1
(
mmolmin )
(mmol)
5.3
[
[
Cu(sal-ppzH)Cl
2
] (1) 9.85 × 10-3
1.970×102
3.718×101
1.143×102
4
(
1.182×10 mmol)/h
Cu(hyap-ppzH)Cl
2
](2) 2.389 × 10-2
4.801×10 2
4.2
4
(
2.880×10 mmol )/h
From table 7, it is evident that the 1and 2 shows maximum rate (Vmax) at saturating substrate
concentration for 3,5-DTBC oxidation is9.85×10-3 mmolmin and 2.389×10 mmolmin-1
respectively. Quite larger K values for 1 and 2 indicates their less efficient binding with the
substrate hence require higher substrate concentration to reach the Vmax. Complex 1 shows an
-1
-2
m
enhanced turn over frequency of 1.182×10 mmolh while complex 2 exhibit Kcat 2.880×104
4
-1
-1
mmolh ,which are highest amongst the so far reported by monomeric copper(II) complexes and
two to three times more than the previously reported by Krebs et al., Neves et al., Monzani et al.,
and Vittal et al.89-98
.
3
.10.1.1. Reactivity in solution and possible reaction pathway.
Catechol oxidase uses molecular oxygen as an active oxidant for the catalytic conversion of o-
phenols to the corresponding o-quinones. In the current reaction condition, molecular oxygen has
little effect (dissolved oxygen under 1 atm pressure and room temperature) but presence of
hydrogen peroxide does the job efficiently. For mononuclear and binuclear complexes A.
2
2
Mukherjee et al. have suggested a number of mechanistic pathways for catechol oxidase enzyme.
Several model complexes follow the path which produces two molecules of o-quinone and water
is followed by the enzyme catechol oxidase.99,100 Many model complexes follow a different
pathway where a peroxo intermediate is responsible for the production of o-quinone along with
the hydrogen peroxide.101-110 Based on DFT calculations, M.K. Panda et al111 suggested that the
rate determining steps for the oxidation of catechol to o-quinone is the intramolecular proton