2
A. Santra et al. / Polyhedron 176 (2020) 114277
ment friendly catalysts that mimic enzymatic activities are also
very crucial in synthetic and supramolecular chemistry. The
enzymes active sites are modeled with the metal complexes using
the knowledge of redox behavior and coordination chemistry. S-
alkyl/aryl derived metal complexes are not frequently modeled
though these are bioactive compounds [1–5]. The geometry and
the structural features of enzyme active sites and the choice of
metal binding can be helpful to establish the structure–function
activities in the model experiments [21,22]. Several copper based
mononuclear and dinuclear complexes have been modeled to
study insight about the mechanism of the biological oxidation
process of 3,5-di-tert-butylcatechol (DTBC) to 3,5-di-tert-butylqui-
none (DTBQ) [23–26]. Herein, we report the synthesis, characteri-
zation and theoretical interpretation in relative stability of a
mononuclear copper(II) complex of deprotonated methyl-2-(1-
(10 mmol, 3.01 g) were allowed to react with CuCl
2
ꢁ2H
2
O
(10 mmol, 1.70 g) in methanol. The reaction mixture in each case
was stirred for 3 h at room temperature and then refluxed for
2 h in a water bath. In both the cases, solid deep green product
was separated out which is filtered and washed with dry methanol.
The solid products were dried over silica-gel. A pinch of solid prod-
ucts was taken in 1:1 methanol-DMF and placed the solution in the
open air for slow evaporation. Deep blue micro crystals suitable for
single crystal X-ray analysis were grown. Yield for 1 is 2.50 g
(77.4%). Elemental analyses (%) for C H N S ClCu (1) are C,
9 10 3 2
33.43; H, 3.12; N, 13.0; S, 19.83%. Found C, 33.39; H, 3.10; N,
13.01; S, 19.88%. Yield for 2 is 6.2 g (77.52%). Elemental analyses
(%) for C30H N S Cl CuN S (2) are C, 45.11; H, 3.53; N, 10.52; S,
28 6 4 2 6 4
16.05%. Found C, 45.01; H, 3.47; N, 10.45; S, 16.08%.
(
pyridin-2-yl)ethylidene)hydrazine-1-carbodithioate (HL
1
) and a
2.4. Characterization
dinuclear dichloro bridged copper(II) complex of deprotonated
benzyl-2-(1-(pyridin-2-yl)ethylidene)hydrazine-1-carbodithioate
FISONS EA-1108 CHN analyzer was used for elemental analysis
(C, H, N, and S) of the ligands and complexes. The FTIR spectra
(
2
HL ), and investigate their ability to catalyze catechol oxidase
ꢀ1
mimetic activity. The stability of the complexes and their tendency
toward chloro-bridged and chloro-unbridged structures were
investigated by B3LYP-D3 calculations [27–29].
(4000–500 cm ) were recorded on a Perkin Elmer Spectrum
Two FT-IR Spectrophotometer with sample prepared as KBr pellets.
Mass spectra of ligands were obtained using a Waters HRMS XEVO-
G2QTOF#YCA351. Thermogravimetric analysis was performed
using Perkin Elmer Thermal Analyzer TGA4000 instrument at a
heating rate 20 °C/min under nitrogen atmosphere. The X-band
electron paramagnetic resonance (EPR) spectrum was recorded in
a Bruker EMX X-band spectrometer operating at a field modulation
of 100 kHz, modulation amplitude of 7 G and microwave radiation
power of 10 mW at room temperature. The single crystal X-ray
diffractions of complex 1 and 2 were carried out on a Bruker
SMART APEX II X-ray diffractometer equipped with graphite-
2
. Experimental section
2.1. Materials
Reagent grade metal salts CuCl
2
ꢁ2H
2
O was purchased from
Merck India and used without further purification. Hydrazine
hydrate (99%), carbon disulfide, benzyl chloride, methyl iodide,
and 2-acetyl pyridine were purchased from Merck chemical com-
pany and used without further purification. Solvent ethanol
monochromated Mo-K
detector. The intensity data were collected in the
a
radiation (k = 0.71073 Å) and 16 CCD area
and scan
p
x
(
Changshu Yangyuan Chemical, China), methanol (Merck, India)
mode, operating at 50 kV, 30 mA at 296 K [31]. The data reduction
was performed using the SAINT and SADABS programs [32]. All cal-
culations in the structural solution and refinement were performed
using the Bruker SHELXTL program [33]. The structure was solved
by the heavy atom method and refined by full-matrix least-squares
methods. All the non-hydrogen atoms were refined anisotropi-
cally; the hydrogen atoms were geometrically positioned and fixed
with isotropic thermal parameters. The final electron density maps
showed no significant difference.
and dichloromethane (Merck, India) were dried and distilled before
use in the experiment.
2
.2. Synthesis of methyl-2-(1-(pyridine-2-yl)ethylidene)hydrazine-1-
carbodithioate (HL ) and benzyl-2-(1-(pyridine-2-yl)ethylidene)
hydrazine-1-carbodithioate (HL
1
2
)
1 2
The HL and HL were prepared by the condensation of 2-acetyl
pyridine with corresponding hydrazine carbodithioate [2,30].
Methyl hydrazine carbodithioate and benzyl hydrazine carbod-
ithioate were synthesized from 99% pure hydrazine hydrate, car-
bon disulfide, and methyl iodide. The freshly prepared methyl
hydrazine carbodithioate (10 mmol, 1.22 g) was refluxed with 2-
acetyl pyridine (10 mmol, 1.21 g) in dry methanol for half an hour
to obtain methyl-2-(1-(pyridin-2-yl)ethylidene)hydrazine-1-car-
The catecholase activities of 1 and 2 were examined by the reac-
tion of 100 equivalents of 3,5-di-tert-butylcatechol (DTBC) with
ꢀ5
1
ꢂ 10 M solutions of the complexes under aerobic conditions
at ambient temperature in methanol. The reaction was followed
spectrophotometrically by monitoring the growth of the absor-
bance as a function of time at ca. 400 nm which is characteristic
of 3,5-di-tert-butylquinone chromophore. To determine the depen-
dence of the rate of the reaction on substrate concentration and to
bodithioate (HL
1
). The crude product of HL
:1 ethanol–water. Yield: 2.01 g (89%). Elemental analyses (%) for
are C, 47.97; H, 4.92; N, 18.65; S, 28.46%. Found C,
7.69; H, 4.89; N, 18.56; S, 28.48%. Similarly, benzyl-2-(1-(pyri-
was pre-
1
was crystallized from
1
C
4
ꢀ5
evaluate various kinetic parameters, 1 ꢂ 10 M solutions of the
9 11 3 2
H N S
complexes were mixed with at least 10 equivalents of the substrate
to maintain pseudo-first order condition. To check the rate depen-
dency on catalyst concentrations similar set of experiments were
performed at a fixed concentration of substrate with various cata-
lyst concentrations. The rate of a reaction was determined by the
initial rate method, and the average initial rate over three indepen-
dent measurements was recorded.
2
din-2-yl)ethylidene)hydrazine-1-carbodithioate (HL )
pared following the condensation of benzyl hydrazine
carbodithioate (10 mmol, 1.98 g) and 2-acetyl pyridine (10 mmol,
1
.21 g) in methanol. The crude product thus obtained was crystal-
lized from 1:1 ethanol–water. Yield: 2.57 g (73.79%). Elemental
analyses (%) for C15 are C, 59.77; H, 5.02; N, 13.94; S,
1.27%. Found C, 59.62; H, 4.91; N, 13.85; S, 21.30%.
15 3 2
H N S
2
2.5. Computational details
2.3. Synthesis of copper complexes
All calculations were performed with the ORCA 4.0 program
package [34,35] by using def2-TZVP and its matching auxiliary
basis sets [36,37]. The structures were fully optimized at the unre-
stricted Kohn-Sham B3LYP [27–29] level of density functional the-
ory (DFT) calculations incorporating the atom-pairwise dispersion
Copper(II) complexes 1 and 2 were synthesized by the reaction
of the methanolic solution of HL
respectively [2]. Separately HL
1
and HL
2
with copper chloride,
1
(10 mmol, 2.25 g) and HL
2