Sulfonated salicylidene thiadiazole complexes with Co (II) and Ni (II) ions as sustainable corrosion inhibitors and catalysts for cross coupling reaction

Article abstract of DOI:10.1002/aoc.4987

Condensation of 2,5-dihydrazinyl thiadiazole with 5-sodium sulfonate salicylaldehyde afforded dibasic tetradentate pincer N,O,O,N-salicyldiene thiadiazole ligand (H₂Sanp). The novel dipolar ligand formed para-magnetic pincer complexes within Co

Full text of DOI:10.1002/aoc.4987

Received: 11 March 2019
DOI: 10.1002/aoc.4987
Revised: 13 April 2019
Accepted: 19 April 2019
F U L L P A P E R
Sulfonated salicylidene thiadiazole complexes with Co (II)
and Ni (II) ions as sustainable corrosion inhibitors and
catalysts for cross coupling reaction
1,2
1,3
1,2
Hany M. Abd El‐Lateef
| Abdelwahed R. Sayed | Mohamed Shaker S. Adam
1
Department of Chemistry, College of
Condensation of 2,5‐dihydrazinyl thiadiazole with 5‐sodium sulfonate
salicylaldehyde afforded dibasic tetradentate pincer N,O,O,N‐salicyldiene
Science, King Faisal University, P.O. Box
380, Al Hufuf 31982Al Hassa, Saudi
Arabia
thiadiazole ligand (H Sanp). The novel dipolar ligand formed para‐magnetic
2
2
Chemistry Department, Faculty of
pincer complexes within Co (II) and Ni (II) ions (Co‐Sanp and Ni‐Sanp) under
sustainable conditions. The water‐soluble ligand and its metal‐complexes were
estimated by mass, IR and UV–Visible spectroscopy, EA (elemental analyses),
TGA (Thermogravimetric analyses), magnetic susceptibility, and conductivity
measurements. The catalytic reactivity of Co‐Sanp and Ni‐Sanp were evaluated
in the Suzuki and Buchwald‐Hartwig cross coupling reaction in aqueous‐
methanol binary mixtures. Both reactions of boronic acid or aryl amines with
aryl halides gave high chemoselective yield of C―C or C―N product. The inhi-
Science, Sohag University, Sohag 82534,
Egypt
3
Department of Chemistry, Faculty of
Science, University of Beni Suef, Egypt
Correspondence
Hany M. Abd El‐Lateef and Mohamed
Shaker S. Adam, Department of
Chemistry, College of Science, King Faisal
University, P.O. Box 380 Al Hufuf 31982
Al Hassa, Saudi Arabia.
bition characteristics of H Sanp and its Ni‐ and Co‐complexes were performed
2
Email: hmahmed@kfu.edu.sa;
hany_shubra@yahoo.co.uk; madam@kfu.
edu.sa
for the C‐steel corrosion in 1.0 M HCl using electrochemical measurements
and surface analysis methods. These methods indicated that the synthesized
compounds have served as efficient mixed‐type corrosion inhibitors and their
adsorption on the steel surface obeyed isotherm model of Langmuir. Co‐Sanp
inhibitor displays the best corrosion inhibition efficiency, and the capacity is
Funding information
Deanship of Scientific Research, King
Faisal University, Grant/Award Number:
180084
−1
up to 97.11% at of 250 mg L . Surface analysis confirms formation of protec-
tive layer on the C‐steel surface.
KEYWORDS
catalysis, complexes, corrosion protection, Thiadiazole dihydrazone
1
| INTRODUCTION
holding thiadiazole, while the reactivity of 2,5‐
dihydrazinyl‐1,3,4‐thiadiazole to the active methylene
reagents afforded pyrazoles of thiadiazole derivatives.
[3,4]
Thiadiazoles are substantial class of heterocyclic com-
pounds with comprehensive framework of biological
accomplishments and applicability in parts of polymer
pharmaceutical, agricultural chemistry, industrial, bacte-
ricides, herbicides, fungicides and regulators of plant
One of the most versatile and prevalent recent syn-
thetic devises is cross coupling reactions within construct-
[5]
ing of C―C and C―N bonding of organic chains with
wide and high utility in synthesis of large number of
organic compounds, which are applicable in manufactur-
[1]
growth.
Structure and synthesis of 2,5‐dihydrazino‐
[
6,7]
1
,3,4‐thiadiazole and its derivatives was reported
ing and as pharmaceuticals.
Despite, palladium com-
[2]
previously. Reactivity of hydrazonoyl halides towards
plexes are the most effective catalysts for cross coupling
[8]
2
,5‐dihydrazinyl‐1,3,4‐thiadiazole gives
bis‐triazines
reactions with high selectivity and low by‐products,
Appl Organometal Chem. 2019;e4987.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
1 of 19
https://doi.org/10.1002/aoc.4987

2
of 19
ABD EL‐LATEEF ET AL.
nickel and cobalt pincer complexes compete for that
propose due to their low cost, high abundance in earth
crust, easily handled, and high stable. For that, recent
catalytic cross coupling reactions were achieved by many
de‐scaling. Due to the aggressiveness of the acid
[
29]
medium, C‐steel corrodes roughly.
A corrosion inhib-
[9]
itor is predominantly added to aggressive acid media for
diminishing the corrosion impact on metal surface dur-
ing the previous processes. The chosen of convenient
inhibitors fundamentally depends upon its concentra-
tion, type of acid, economic availability, temperature,
environmental side effects, the occurrence of dissolved
3
d transition metal complexes, e.g. Ni (II) and Co (II),
[10–12]
[13,14]
homogeneously
and heterogeneously.
Indeed,
nickel pincer chelates could be regarded as effective cata-
lysts for cross‐couplings of various organometallic sub-
strates with organic halides demonstrate high potential
organic and/or inorganic species and the type of metallic
[15]
[30]
with respect to palladium ones.
material.
Organic compounds containing Schiff base
High coordination behavior of cheap N^O, as hard
donor ligands, e.g. Schiff bases, towards transition metal
ions of various oxidation states, attracted inorganic
chemists to apply such complexes as effective catalysts
groups >C=N―, S, P, O, N and aromatic rings are
reported in literature as most efficient corrosion inhibi-
[31]
tors for the metals and alloys in acidic solutions.
The chelates of Schiff bases form stable complexes
neatly packed in the coordination metal ion sphere to
generate another category of compounds for corrosion
[16]
in cross coupling processes.
Cross couplings catalyzed
by Cobalt (II) chelates are interesting search point in
[
17]
[32–34]
organic syntheses,
decade.
which highly developed in last
inhibition.
[18]
Singh et al. incorporated new Co (II), Ni (II)
Herein, air‐stable and water soluble novel complex
catalysts of Ni (II) and Co (II) ions with tetradentate
N,O,O,N‐salicyldiene thiadiazole ligand is mediated in
the typical C―C and C―N cross coupling processes
under sustainable conditions, homogeneously. Their cat-
alytic potential is studied in different solvent systems.
Furthermore, to the best of our knowledge, there is no
obtainable research on the anticorrosive performance
of such type of 5‐di (sodium sulfonate salicylidene)‐2,5‐
and Cu (II) bis‐(2‐acetylthiophene) oxaloyldihydrazone
complexes in Suzuki‐Miyaura reaction of boronic acid
with aryl halides in acetonitrile with good impacted cat-
[
19]
alytic activity of the product yields (from 62% to 82%).
The active catalyst complex as Ni(0) and Ni(I) intermedi-
ate compounds in Heck and Suzuki‐Miyaura reaction
resulted from one and/or two electron processes in the
catalytic cycles, has been detected and studied
[20]
recently.
In particular, air‐stable Ni (II)‐ P^N^P
dihydrazinyl thiadiazole derivatives (i.e. H Sanp) and
2
triazine‐phosphine cationic complexes initiated the
its Ni‐ and Co‐pincer chelates in acidic solution. Hence,
the present investigation reports the involving of
[21]
C―C cross couplings.
Sun et al. reported the synergis-
tic influence of Co (II) ion on Pd (II)/Co (II) catalyzed
H Sanp, Ni‐Sanp and Co‐Sanp as corrosion inhibitors
2
Suzuki‐Miyaura cross coupling reaction in an aqueous
for C‐steel in 1.0 M HCl. The study is performed using
electrochemical measurements (PDP and EIS) and
complemented with the surface analysis (SEM/EDX).
[22]
media.
N^O‐bidentate
2‐(hydroxyimino)‐1‐
phenylpropan‐1‐one coordinated to Co (II) ion in an
octahedral geometry as an effective catalyst for
Sonogashira Hagihara cross coupling of electron‐rich
and/or electron‐poor substituted aryl halides of with
2 | EXPERIMENTAL
[23]
alkyne derivatives.
Cobalt chloride catalyzed the cross
coupling of 1,3‐dienes (additives) within homogeneous
2.1 | Materials and equipment
[24]
complexation, as reported elsewhere.
Hu et al. devel-
oped Ni (II) N,N,N‐tridentate pyrrolidine complexes as
All reagents, which used in this work, are ordered from
Merck and Acros. Particularly, they are applied without
any treatment or purification. CHN‐analyses were
progressed using a GMBH VarioEl model V2.3 CHN appa-
ratus. NMR spectroscopic scans were accomplished on a
multinuclear FT‐NMR spectrometer Bruker ARX400
within 400.1 MHz for the nucleus of hydrogen and
100.6 MHz for nucleus of carbon at ambient temperature.
catalysts for the cross coupling reaction of secondary
[25]
alkyl halides.
The high transmetalation of Co
P^N^P‐complexes as catalysts for Suzuki‐Miyaura cross
coupling reaction was discussed and reported recently
through the attack of the nucleophile to the central
[26]
metal of the catalyst.
Carbon steel (C‐steel) is a widely utilized construction
1
13
material owing to its excellent mechanical characteristics
The H and C spectral signal shifts are presented in ppm.
JHH refers to coupling constants values between H nuclei
in the spectral scans. Infrared spectroscopy (mixed with
KBr as discs) are measured with Shimadzu FTIR‐8101
Fourier Transform Infrared spectrophotometer in the
[27–29]
and cheapness.
Unfortunately, it quickly undergoes
corrosion through electrochemical and chemical reac-
tions with the components of neighboring environment.
Solutions of HCl are usually employed for industrial acid
cleaning, pickling, oil well acidifying processes, and acid
−
1
range of wave number from 4000 to 400 cm .

ABD EL‐LATEEF ET AL.
3 of 19
Ultraviolet–Visible spectroscopy was displayed within
2.3 | Preparation of metal complexes (co‐
Sanp and Ni‐Sanp)
1
.0 cm quartz cells in a holder, which temperature con-
trolled by connection to a water thermostatted bath. UV–
Vis. spectra carried out using a Jasco UV–Vis spectropho-
tometer (model V‐570) of wavelength from 200 to
In an aqueous solution (40 ml) of H Sanp (2.78 g,
2
5.0 mmol) was poured slowly to an aqueous media
9
00 nm. Conductivity magnitudes of the studied com-
(30 ml) of metal ion of CoCl
2
.6H
2
O
or Ni
pounds were estimated by a Jenway conductivity meter
model 4320 connected with an epoxy bodied conductivity
cell (two electrodes, shiny). The calibration of the cell con-
stant was carried out from 0.01 to 19.99 at room tempera-
ture. Magnetic susceptibility of Ni‐Sanp and Co‐Sanp
were evaluated using a Gouy's balance, the diamagnetic
correction was controlled by Pascal's contents and Hg[Co
(OOCCH ) .4H O (1.24 or 1.18 g, 5.0 mmol), respectively.
3
2
2
The mixed solution was heated for 3 hrs at 70 °C with
continuous stirring. Color of the reaction media was turn
into the given color of the novel complex. Water was
removed by evaporation and the residual was recrystal-
lized in water‐ethanol binary mixture (1: 1) to give pure
crystalline complex which dried in oven.
(
SCN) ] as a calibrant. EIS‐mass spectra were carried by
4
using Waters API Quatroo Micro Triple Quadrupole
electrospray ionization mass spectrophotometer in the
both modes of positive and negative. All given chemical
processes were carried out with a magnetic stirring and
held at the given temperature in a controlled thermostated
oil bath.
2
.4 | Catalytic studies
Homogeneous cross coupling of Suzuki‐Miyaura and
Buchwald‐hartwig reactions were performed in three
necked round flask with water circulated condenser con-
taining phenylboronic acid (1.0 mmol) or aryl amine
The C‐steel composition which applied for the corro-
sion processes, is composed of (wt%) S, 0.04%; C, 0.15%;
Mn, 0.70%; Si, 0.19%; Cr, 0.011%; Ni, 0.011%; the
remaining is Fe. HCl (Merck 37%) was prepared as
(
mesityl amine or 3‐chloro aniline, 1.0 mmol) in 10 ml
of the given solvent in presence of the complex catalyst
Ni‐Sanp or Co‐Sanp, 0.20 mmol) and potassium carbon-
(
ate, as a base (2.0 mmol). The reaction was initiated by
addition of aryl halide (bromobenzene or chlorobenzene,
−
3
1
.0 mol dm in the aqueous media (deionized water).
H Sanp and its metal‐pincers, Ni‐Sanp and Co‐Sanp
2
1
.1 mmol) under reflux conditions at 100 °C for 10 hrs.
All catalytic reactions were carried out contacting to air
in Schlenk system with magnetic stirring in
−
1
were prepared with different from 50 to 250 mg L in
bidistilled water.
a
thermostated oil bath at the chosen reaction temperature.
The C―C or C―N cross coupling products were
extracted by adding ethyl acetate as an organic layer. In
the organic layer, water was removed by anhydrous
2
.2 | Synthesis of 5‐di (sodium sulfonate
salicylidene)‐2,5‐dihydrazinyl thiadiazole,
H Sanp
MgSO and then filtrated out. The products percentages
4
2
were estimated and determined after reaction completion
by injection to Shimadzu Gas Chromatography mass
spectrometer (GC–MS) model QP2010 SE, which
equipped with Rxi‐5 Sil MS capillary column (30 m
length × 0.25 mm ID × 025 um film thickness) at room
temperature. The GC‐Mass oven temperature was initi-
ated to 40 °C and held for 1 min. The temperature rate
0
.73 g (5.0 mmol) of 2,5‐dihydrazinyl thiadiazole, which
dissolved in 20 ml of EtOH, added to an aqueous solu-
tion of 2.24 g 5‐sodium sulfonate salicylaldehyde
(10.0 mmol, 30 ml) dropwisely. The mixed solution
was refluxed for 2 hrs with stirred and reaction control-
ling by TLC to give yellow color solution. The binary
mixed solvents were evaporated and the ligand was
acquired in pure form by recrystallization in water‐
ethanol mixture (1: 1).
−
1
was enhanced with 10 °C min up to 200 °C. Operation
of the inlet was carried out in the mode of split less at
2
00 °C was the mass spectra temperature of transfer line.
The carrier gas was Helium with high purity up to
9.999%, which applied under rate of flowing 1 ml/min.
1
3
H NMR (DMSO‐d , 400 MHz): δ 6.97 (d, J = 7.7 Hz, 2
6
9
4
3
H), 7.75 (dd, J = 1.1 Hz, J = 7.5 Hz, 2 H), 7.94 (d,
Lab solution software, was applied to analyze the percent-
ages yields of the obtained products.
4
J = 1.2 Hz, 2 H), 10.62 (s br, 2 H, CH=N) and
1
3.77 ppm (br s, NH, 2 H).
13
C NMR (100 MHz, DMSO‐d , dept‐135): δ 117.69
6
(
1
(
CH), 119.96 (C ), 122.72 (C ), 130.28 (CH), 136.78 (C ),
2.5 | Corrosion inhibition measurements
q
q
q
40.88 (C ), 161.12 (C ) and 192.82 ppm (CH, CH=N).
q q
1
13
HNMR, CNMR and dept‐135 supported by Fig-
The electrochemical investigations were completed in a
ures S1‐S3, supplied in the supplementary materials).
traditional three‐electrode cell consisting of C‐steel

4
of 19
ABD EL‐LATEEF ET AL.
specimen as working electrode, a platinum sheet as coun-
ter electrode and a saturated calomel electrode (SCE) as
reference, using Versa STAT4 potentiostat/galvanostat
to grow single crystals of the metal complexes were failed
for X‐ray analysis (Figure 1).
The novel chelating ligand and its M‐complexes are
remarkable stable in the pH ranges from 1.6–9.7 using
(Princeton Applied Research, USA) at 30 °C. Electro-
[
34]
chemical impedance spectroscopy (EIS) were completed
utilizing AC signals of amplitude 10 mV peak‐to‐peak at
the open circuit potential (Eocp) after 60 min of immer-
sion in the frequency domain of 10 kHz–0.1 Hz. The
empirical EIS results were fitted to convenient equivalent
circuit using ZView Software.
the standard universal buffer solutions.
Furthermore,
H Sanp is soluble in water and little soluble in methanol,
2
ethanol, acetone and acetonitrile, also, Ni‐Sanp and Co‐
Sanp are soluble in water and slightly soluble in metha-
nol, ethanol and acetonitrile. All compounds are not sol-
uble in less or non‐polar solvent, e.g. dichloromethane,
carbon tetrachloride and toluene.
Potentiodynamic polarization (PDP) measurements
−
1
were carried out at a sweep rate of 0.2 mVs in the
potential range ± 250 mV vs. SCE at Eocp
The elemental analyses of H Sanp, Ni‐Sanp and Co‐
2
.
Sanp were investigated and listed in Table 1, which are
in agreement with their suggested chemical formulas
with little difference between the theoretical and the
measured values is about ±0.4%.
2.6 | Surface morphology by scanning
electron microscopic (SEM) and energy
1
13
In particular, the H, C NMR spectrum and dept‐135
of H Sanp were measured in DMSO‐d at 25 °C and listed
dispersive X‐ray spectroscopy analysis
2
6
(EDX)
in Table 2, with supported supplementary materials in
Figures S1‐S3. The function protons of H Sanp could be
2
For surface analysis investigations of C‐steel specimens in
the blank and inhibited solutions, SEM and EDX spectra
were applied using JEOL SEM, model‐5300 attached with
EDX unit with an 3.0 kV operating voltage.
estimated as a broad singlet signal at 13.77 ppm, which
corresponded to the NH― group. Additionally, the
proton of the azomethine group manifested a singlet
sharp signal at 10.62 ppm. The rest signals are belonged
to the aromatic ring. The characteristic spectral signals
13
3
3
| RESULTS AND DISCUSSION
.1 | Synthesis and characterization
of C NMR is 192 ppm for the carbon of azomethine
group. On the other hand, Ni‐Sanp and Co‐Sanp are
para‐magnetic complexes in the suggested square planar
and octahedral spherical structures with values 3.94
and 5.12 B.M., respectively, as reported magnetic values
in Table 2.
Newly, the condensation of 2,5‐dihydrazinyl thiadiazole
with 5‐sodium sulfonate salicylaldehyde carried out sus-
tainably, whereas the reaction with salicylaldehyde is
Electronic spectrum of H Sanp and its corresponding
2
[31]
already
reported
previously.
2,5‐Dihydrazinyl
pincer complexes (Ni‐Sanp and Co‐Sanp) deduces the
characteristic absorption wavelength, λmax (nm) and the
thiadiazole was prepared according to the published
[
2]
−1
−1
method previously, which reacted with 5‐sodium sulfo-
derived molar absorptivity values, ε (mol cm ) in and
nate salicylaldehyde in 1: 2 molar ratios, respectively, to
water, as depicted in Figure 2 and reported in Table 1.
afford H Sanp (Scheme 1).
The UV‐spectra for H Sanp assigned three bands at 226,
2
2
Elemental analysis, NMR, UV–Vis., IR and mass spec-
250 and 301 nm are attributable for to the intra ligand
troscopies were used to characterize the synthesized
spin‐allowed transitions π → π*, π → π* and n → π*,
2+
2+
[35]
ligand. H Sanp coordinated to Ni and Co ions, as
respectively.
An additional band in the Visible‐zone
2
nickel acetate tetrahydrate and cobalt chloride hexahy-
drate, in an aqueous media to give Ni‐Sanp and Co‐Sanp,
respectively, which synthesized in 1: 1 molar ratios of
appeared at 338 nm, which is due to ligand charge trans-
fer. All given bands of the ligand has been influenced by
its complexation to Ni or Co ions, in which the three
UV‐bands were shifted to be 229, 244 and 295 nm for Ni‐
Sanp, and 224, 248 and 302 nm for Co‐Sanp, respectively.
2+
2+
2+
H Sanp to M ion (Scheme 2). Ni‐Sanp and Co‐Sanp
2
were characterized by IR, UV–Vis. and mass spectra,
EA, TGA, conductivity measurements and magnetic sus-
ceptibility (Tables 1 and 2). Unfortunately, all attempts
Furthermore, the visible band for H Sanp was shifted also
2
at 332 and 323 nm for Ni‐Sanp and Co‐Sanp, respectively.
SCHEME 1 Synthetic route of 5‐di
(
sodium sulfonate salicylidene)‐2,5‐
dihydrazinyl thiadiazole (H Sanp)
2

ABD EL‐LATEEF ET AL.
5 of 19
2
SCHEME 2 Complexation of H Sanp
2
+
2+
with Co and Ni ions
TABLE 1 Elemental analyses, yield, appearance, melting point in Celsius and UV–Vis. spectrum of H
2
Sanp, Ni‐Sanp and Co‐Sanp at
) at [com-
−
4
−3
[
compound] = 1.0 × 10 mol dm in H
2
O at room temperature, molar conductivity measurements (Λ
m
−
3
−3
pound] = 1.0 × 10 mol dm in dimethyl sulfoxide (DMSO) and N,N‐dimethylformamide (DMF) at 25 °C
Λ
m
−
1
2
CHN analysis found %, (calc.
(Ω cm
−
mol
1
%
)
)
UV–Vis. spectra
−
1
−
MW
(g mol ) (%)
Yield
m.p.
λ
max
ε (mol cm
)
−1
1
Compound
Sanp
C
H
N
(°C) DMSO DMF Color (nm)
Assign.
H
2
573.51
71
34.02
34.41)
2.45
(2.17)
14.83
(15.05)
257
189
218 Yellow 338
301
10189
8604
12509
32811
CT
(
n → π*
π → π*
π → π*
2
2
50
26
Ni‐Sanp.1/2H
Co‐Sanp
2
O
615.15
84
30.22
30.79)
1.95
(1.78)
13.77
(13.46)
> 300 211
236 Brown 371 br
332
7614
9108
9312
26709
34921
LM‐CT
CT
n → π*
π → π*
π → π*
(
2
2
2
95
44
29
651.42
78
29.84
29.50)
2.43
(2.17)
13.10
(12.90)
> 300 223
254 Green 425 v br 1187
323 8233
LM‐CT
CT
(
3
2
2
02
48
24
9101
20093
45117
n → π*
π → π*
π → π*
vbr = very broad band
Additionally, a new broad band was observed at 371 and
25 nm for Ni‐Sanp and Co‐Sanp, respectively, which
referring to LMCT (ligand to metal charge transfer),
vibrational ν¯(azo‐methine) of H Sanp from 1655 and
2
−
1
−1
4
1621 cm to 1619 and 1579 cm for Ni‐Sanp and to
−
1
1626 and 1601 cm for Co‐Sanp, respectively. Those
shifts could be also resulted from the coordination bind-
ing of the nitrogen atom of the azo‐methine group to
Figure 2.
The significant IR analysis of H Sanp and its Ni‐ and
2
2+
2+
Co‐complexes are listed in Table 2 and supported by Fig-
ures S9‐S14 (supplied in the supplementary materials).
Ni and Co ions. The number of coordinated water
molecules in Co‐Sanp could be remarked by a very
−
1
The –OH phenolic vibrational broad band of H Sanp
broad band at 3424 cm , which is different in value
2
−
1
was detected at 3516 cm , which disappeared within
from the crystalline water molecules in Ni‐Sanp
2+
2+
[36]
−1
complexation to Ni
and Co
ions.
Such
(3338 cm ). That difference in stretching vibrational
disappearing of the –OH band could be resulted from its
coordination ability by deprotonation via oxygen to the
metal ion. Remarked shifts of the characteristic
values between the crystalline and coordinated water
[
36,37]
molecules has been recorded recently
(Scheme 2).
The significant vibrational band of the –NH has been

6
of 19
ABD EL‐LATEEF ET AL.
−
1
TABLE 2 Distinguished infrared spectra (ν¯, cm ) and magnetic
susceptibility for H2Sanp and its Ni‐ and Co‐complexes at 25 °C
intense influenced by the complexation of the azo‐
methine group to the metal ion by shifting from 3422
−
1
−1
to 3178 cm and 3166 cm in Ni‐Sanp and Co‐Sanp,
Compound
respectively, as weak broad absorption bands. The
stretching absorption bands of the S―O and S=O
Group
H
2
Sanp
Ni‐Sanp
Co‐Sanp
−
O―H(water)
O―H(phenolic)
N―H
‐‐
3338 w br
‐‐
3424 w br
‐‐
bonds of the sodium sulfonate group in H Sanp is
2
−
1
3516 br w
3422 br m
3069 m
detected at 1474 and 1283 cm , respectively, which
have not been influenced by the presence of metal
3178 w br
‐‐
3166 w br
‐‐
−
1
ion. In Ni‐Sanp, they appeared at 1472 and 1286 cm
and in Co‐Sanp at 1469 and 1286 cm .
C―Har
−
1 [34,38]
Further-
C―O(phenolic)
C=N(azomethine)
1216 w
1215 m
more, new weak to medium absorption bands have
−
1
1655 w
1619 m
1579 w
1626 m
1601 m
been reported at 665 and 668 cm for the new coordi-
1
621 m
1169 s
103 s
−1
nation bonding M―O and also at 588 and 593 cm for
C―N
C―S
1162 m
1100 s
1175 s
1104 s
the M―N bonding in Ni‐Sanp and Co‐Sanp, respectively
[
34,39]
1
(
Table 2).
The stoichiometric ratios of metal ion to
1030 s
1474 m
1283 s
‐‐
1031 s
1472 m
1286 w
665 m
588 s
1033 s
1469 m
1286 w
668 m
593 s
ligand were accomplished by applying of the spectro-
[
40]
−
photometric continuous variation method.
According
S―O
to the continuous variation plot (Figure S10), it could be
S=O
2+
2+
estimated that the Ni
or Co
ion coordinated to
M―O
H Sanp in 1: 1 molar ratios.
2
M―N
‐‐
Mass spectral measurements of H Sanp and its M‐
2
Magnetism (B.M.)
‐‐
3.94
5.12
complexes were investigated to confirm their molecular
structure as anion in the absence of Na ion in
water/methanol solution (supported by Figures S7‐S9 in
+
br = broad band, s = strong band, m = moderate band, w = weak band,
ar = aromatic ring, al = aliphatic chain
FIGURE 1 The tentative molecular
structure of H Sanp, Ni‐Sanp and Co‐Sanp
2

ABD EL‐LATEEF ET AL.
7 of 19
From the molar conductivity measurements (Λ ) of
m
H Sanp, Ni‐Sanp and Co‐Sanp in DMSO and DMF, that
2
all compounds are highly polar and consisting of four
ions in the solution at 25 °C (Table 1). The high polarity
of the studied compound is resulted from the attached
p‐sodium sulfonate group, which awards two counter
−
ions in the given solvent, particularly of ―SO and
3
+
[7]
two cations of Na ions. From all possible characteri-
zation data, Scheme presents the coordination
chemical behavior of H Sanp towards Ni and Co
2
2+
2+
2
ions, in which H Sanp acts as tetradentate dibasic
2
2+
2+
pincer chelate. H Sanp coordinated to Ni
or Co
2
ion within the two nitrogen azo‐methine groups and
the two oxygen atoms of the deprotonated hydroxyl‐
phenyl groups. Finally, there is no detected action in
the coordination behavior of the sulfur atom of the
thiadiazole ring toward the metal ion. All attempts to
crystalline the studied complexes and analyze them by
X‐ray crystallographic analyses were failed in various
conditions.
2
FIGURE 2 Electronic spectral scans of H Sanp, Ni‐Sanp and Co‐
−
4
−3
Sanp at [compound] = 1.0 × 10 mol dm in H
temperature
2
O at room
the supplementary materials). An observable sharp signal
+
in the negative mode for M‐pincer complexes [M―Na
+
1] appeared at 514 and 513 m/z for H Sanp, 570 and
2
6
06 m/z for Ni‐Sanp and Co‐Sanp, respectively. An addi-
3.2 | Catalytic studies
tional peak of the loss of the two labile coordinated water
molecules in Co‐Sanp was detected at 570 m/z. In the
3.2.1 | Catalytic efficiency
positive mode, another peak with the loss of sulfonate
−
group [M―SO3 + 1] displayed at 353 m/z for H Sanp
The catalytic efficiency of the novel prepared Ni‐ and
Co‐O,N,N,O‐complexes (Ni‐Sanp and Co‐Sanp) was
devoted to the Suzuki C―C coupling of phenylboronic
acid with 2‐halopyridine (2‐bromopyridine and 2‐
chloropyridine) and Buchwald‐Hartewig C―N coupling
of aryl amine (mesityl amine and 3‐choroaniline) with
2‐halopyridine (2‐bromopyridine and 2‐chloropyridine)
in presence of excess amount of base, K CO . The
2
and 410.0 and 410.2 m/z for both Ni‐Sanp and Co‐Sanp,
respectively, as reported elsewhere for the sodium sulfo-
[38]
nate Schiff base complexes.
The crystalline and/or coordinated solvent species in
the M‐Sanp, i.e. water, could confirm by thermogravi-
[37]
metric analyses.
TGA results confirm the diagnostic
number of water molecules in the crystal lattice in Ni‐
Sanp and Co‐Sanp. Figure S11 (in the supplementary
materials) demonstrated that Ni‐Sanp contains a half
water molecule for each Ni‐complex molecule in the lat-
tice, whereas, Co‐Sanp does not have any water mole-
cules in the crystal lattice. An observable decomposed
successive step from 100 to 130 °C from Ni‐Sanp mass
was detected with Δmrel = 1.6%, which are acceptable
with the calculated mass loss (Δmrel = 1.4%). Particu-
larly, Co‐Sanp has a remarkable mass loss of two water
molecules in the range from 170 to 230 °C in the ther-
mogram 5.8% (Figure S11), which assigned for the two
coordinated water molecules in Co‐Sanp and agreed
2
3
catalytic system carried out in ethanol, water or
ethanol‐aqueous binary mixture to meet the sustainable
conditions at 100 °C. To optimize the catalytic reaction
conditions (time in hours) all catalytic processes were
monitored by TLC and GC–MS. The reaction product
yields at the optimal conditions of both C―C and C―N
couplings are listed in Tables 3 and 4, respectively. The
choice of K CO as the base for the current catalytic
2
3
system is due to the well combination of the catalyst with
[
41]
water, i.e. the solvent, and the base.
Initially, the C―N
product yields were better than that of C―C product,
which could be resulted from the less stability of boronic
acid towards air and water compared to aryl amine as a
[35]
with the calculated mass loss (5.5%).
Considerably,
[
42]
Co‐Sanp has an octahedral geometry, which coordinated
substrate.
to H Sanp within four‐coordination bonding and com-
pleted within two labile coordinated water molecules
In addition, the catalytic C―C and C―N reactions
consumed less time with 2‐bromopyridine than that with
2‐chloropyridine for the optimized product yield percent-
ages under all different various sustainable conditions.
2
(Scheme 2). Ni‐Sanp could be considered as square pla-
nar complex.

8
of 19
ABD EL‐LATEEF ET AL.
TABLE 3 The Suzuki cross coupling reaction of phenylbronic acid with aryl halide catalyzed by either Ni‐Sanp or Co‐Sanp under various
conditions
a
b
Entry
Phenylbronic acid
Aryl halide
Catalyst
Solvent
Time, h
Yield (%)
1
2
3
4
5
6
7
8
9
Bromopyridine
Chloropyridine
Bromopyridine
Chloropyridine
Bromopyridine
Chloropyridine
Bromopyridine
Chloropyridine
Bromopyridine
Chloropyridine
Bromopyridine
Chloropyridine
Ni‐Sanp
Ni‐Sanp
Co‐Sanp
Co‐Sanp
Ni‐Sanp
Ni‐Sanp
Co‐Sanp
Co‐Sanp
Ni‐Sanp
Ni‐Sanp
Co‐Sanp
Co‐Sanp
H
H
H
H
2
2
2
2
O
O
O
O
10
12
11
14
8
9
7
9
6
64
55
60
57
79
71
75
70
83
73
80
68
EtOH:H
EtOH:H
EtOH:H
EtOH:H
EtOH
EtOH
EtOH
EtOH
2
2
2
2
O (1:1)
O (1:1)
O (1:1)
O (1:1)
1
1
1
0
1
2
7
6
8
a
2 3
Phenylbronic acid (1.0 mmol), aryl halide (1.1 mmol), base (K CO , 2.0 mmol), solvent (10 ml) and catalyst (0.20 mmol) at 100 °C.
b
The yield amount percentages of the C―C product.
TABLE 4 The Buchwald‐Hartwig amination reaction of aryl amine with aryl halide catalyzed by either Ni‐Sanp or Co‐Sanp under various
conditions
a
b
Entry
Aryl mine
Aryl halide
Catalyst
Solvent
Time, h
Yield (%)
1
2
3
4
5
6
7
8
9
Mesityl amine
Bromopyridine
Chloropyridine
Bromopyridine
Chloropyridine
Bromopyridine
Chloropyridine
Bromopyridine
Chloropyridine
Bromopyridine
Chloropyridine
Bromopyridine
Chloropyridine
Ni‐Sanp
Ni‐Sanp
Co‐Sanp
Co‐Sanp
Ni‐Sanp
Ni‐Sanp
Co‐Sanp
Co‐Sanp
Ni‐Sanp
Ni‐Sanp
Co‐Sanp
Co‐Sanp
H
H
H
H
2
2
2
2
O
O
O
O
8
8
10
11
6
7
8
10
5
5
80
74
83
72
87
85
89
82
91
86
92
84
EtOH:H
EtOH:H
EtOH:H
EtOH:H
EtOH
EtOH
EtOH
EtOH
2
2
2
2
O (1:1)
O (1:1)
O (1:1)
O (1:1)
10
11
12
5
7
13
14
15
16
17
18
19
20
21
22
23
24
Bromopyridine
Chloropyridine
Bromopyridine
Chloropyridine
Bromopyridine
Chloropyridine
Bromopyridine
Chloropyridine
Bromopyridine
Chloropyridine
Bromopyridine
Chloropyridine
Ni‐Sanp
Ni‐Sanp
Co‐Sanp
Co‐Sanp
Ni‐Sanp
Ni‐Sanp
Co‐Sanp
Co‐Sanp
Ni‐Sanp
Ni‐Sanp
Co‐Sanp
Co‐Sanp
H
H
H
H
2
2
2
2
O
O
O
O
9
10
7
7
8
8
9
8
5
83
79
88
83
90
86
91
89
90
85
88
81
EtOH:H
EtOH:H
EtOH:H
EtOH:H
EtOH
EtOH
EtOH
EtOH
2
2
2
2
O (1:1)
O (1:1)
O (1:1)
O (1:1)
6
7
8
a
Aryl mine (1.0 mmol), aryl halide (1.1 mmol), base (K
2
CO
3
, 2.0 mmol), solvent (10 ml) and catalyst (0.20 mmol) at 100 °C.
b
The yield amount percentages of the C‐N amination product.

ABD EL‐LATEEF ET AL.
9 of 19
The optimized yield of the chemoselective products of the
C―C bonding formation of phenylboronic acid with 2‐
brmopyridine catalyzed by Ni‐Sanp or Co‐Sanp were
obtained in ethanol with the less required time for the
reaction completion (Table 3, entries 9–12) affording
3.2.2 | Mechanistic proposal and catalyst
effect
Based on the reported typical mechanisms of C―C and
[
23]
C―N cross couplings,
the catalytic cycle started with
8
3% with Ni‐Sanp and 80% with Co‐Sanp. With 2‐
formation of the active catalyst complex intermediate (I)
2+
0
2+
chloropyridine, the resulted biaryl product was less than
that with 2‐brmopyridine in ethanol (entries 10 and 12,
by reduction of Ni ion to Ni in Ni‐Sanp, and Co
0
[18,26]
ion to Co in Co‐Sanp within electron transfer.
Both
7
3% for Ni‐Sanp and 68% for Co‐Sanp).
phenyl boronic acid or aryl amine and the excess K CO
2 3
However, most of C―C and C―N coupling systems
could be the reason for the reduction and formation of
[
48]
were achieved in organic solvents or in mixture of
I.
An important step in the catalytic cycle could be
[43]
aqueous‐organic solvent,
water is the most favored
proposed here due to the reaction of halopyridine, as an
solvent for such catalytic systems under sustainable con-
ditions but unsuitable solvent for the organic substrates
due to the immiscibility and less solubility of the reac-
electrophile, with I to afford an octahedral geometrical
1
0
addition of Ar ―X accompanying oxidation of Ni to
2+
0
2+
Ni or Co to Co giving the tentative intermediate (II),
i.e. within oxidative addition, (Scheme 3). The oxidative
addition of Ni‐species has been elucidated by NMR by
[44]
tion mixture.
Particularly, the amount of the reaction
products reduced from ethanol as the solvent, when
water was presented in the reaction media (1: 1 of
water: ethanol, entries 5–8), to pure water as the reac-
tion solvent (e.g. for Ni‐Sanp, 83% of the C―C product
in ethanol, 79% in water‐ethanol mixture and 64% in
water, Table 3). Moreover, in the aqueous media, the
C―C product was significantly consumed the longest
time, smoothly (Table 3, entries 1–4). It is clear, that
the solubility and miscibility of the reaction components
could inhibit the catalytic potential of Ni‐Sanp and
[
20]
[10]
Manzoor et al.
and by Rull et al. of Ni‐carbenes.
The excess amount of K CO could raise the replacement
2
3
of halide anion by the carbonate ion to give another inter-
[
26]
mediate (III). Due to the transmetalation,
the aryl
group of the phenylboronic acid or the deprotonated aryl
amine could bond to the metal ion with replacing of the
carbonate group in the III in either Suzuki‐Miyaura or
Buchwald‐Hartwig reactions, respectively, to produce an
intermediate VI. Finally, the most significant step for
reusing of the catalyst complex and formation of the
chemoselective C―C or C―N product is the reductive
elimination. In this step, the metal ion in IV reduced
again to zero valet with forming of the active intermedi-
ate I. the liberated I is reused for another catalytic cycle.
The feasibility of the complex steric demand could be
explored by the catalytic efficiency of the current com-
plexes as catalysts for the C―C and C―N cross coupling
[41,45]
Co‐Sanp.
As aforementioned, the less stability of
phenylboronic acid in the aqueous media diminished
the C―C coupling products catalyzed by Ni‐Sanp and
Co‐Sanp.
Similarly, the optimized solvent for the C―N cross
coupling system was ethanol for the C―C coupling of
mesityl amine with either 2‐bromopyridine or 2‐
chloropyridine (Table 4, entries 9–12). Whereas, both
ethanol and in the aqueous water‐ethanol binary mixture
are the optimized solvents for C―N coupling of 3‐
chloroaniline with 2‐bromopyridine or 2‐chloropyridine
[
49]
processes.
The proposed square planar geometry of
2+
Ni‐Sanp forced the reduction of Ni ion and the sub-
strate attack of halopyridine to the reduced Ni ion in
the oxidative addition step.
more electronegativity of Ni
0
[
50–56]
(entries 17–24). This is probably caused by the higher
Moreover, the little
2+
stability of aryl amines in water for the C―N coupling
ion compared to that
[46,47]
2+
reactions.
Both C―C and C―N coupling reaction
Co ion could improve the Ni‐Sanp catalytic potential
deigned respectable yields of the target products (as
recorded in Table 3, entries1–4 and in Table 4, entries
due to the faster oxidative addition step achievement in
[
23,57]
the catalytic cycle more than that Co‐Sanp.
The
1
–4 and 13–17) with Ni‐Sanp and Co‐Sanp. Also, the
octahedral geometry of Co‐Sanp could discourage its cat-
alytic potentials. Therefore, it is clear here that why Ni‐
Sanp is little more effective catalyst for such reaction
than Co‐Sanp, which could also be emphasized by the
yield of the C―C and C―N products under the optimal
conditions (Tables 3 and 4). Despite the steric hindrance
Buchwald‐Hartwig coupling reaction is more effective
with M‐Sanp than the Suzuki couplings.
The p‐sodium sulfonate group could play a major
role in the catalytic potential of the studied complexes
by two entires, the first one is the type of internal
base, e.g. K CO , K PO or NatBuO … .. within different
cations. The second entry is the salt effect with
various added salt to the catalytic processes with
different cations, which probably have a remarkable
influence.
of the hard organic coordinated pincer ligand (H Sanp)
2
3
3
4
2
2+
and the little less electronegativity of Co compared to
2+
[18]
Ni in their complexes,
Co‐Sanp has an appreciable
catalytic activity. Besides, the little more electro‐
2+
positivity of Co ion in Co‐Sanp catalyst than that of

10 of 19
ABD EL‐LATEEF ET AL.
SCHEME 3 The mechanistic proposal of the Suzuki and Buclwald‐Hartwig cross coupling reactions catalyzed by Ni‐Sanp and Co‐Sanp
2
+
Ni ‐species could proceed the reductive elimination
both active catalysts intermediate (IV) of the two
attached ―Ar and ―B groups to the central metal ions
[
21,22,50–56]
1
step in the catalytic cycle.
By comparison our results of Ni‐Sanp as square planar
geometry to other reported octahedral Ni‐O,N,N‐
could progress the reductive elimination step and
improve the catalytic potential of Ni‐Sanp and Co‐Sanp.
In the other hand, if the two functional groups in the
intermediate (IV) are in trans position to each other,
there will be no observable catalytic reactivity of the stud-
ied complexes and would give no chemoslelctive product
[11,12]
benzoylhydrazone complex,
we explored that Ni‐
Sanp is more effective and sustainable catalyst for the
Suzuki cross coupling reaction due to the steric effect.
Moreover, the cis‐structure of Ni‐Sanp and Co‐Sanp of
the replaced group is the only possibility for the high cat-
alytic potential of both Ni‐Sanp and Co‐Sanp. Cis form of
[
58]
of both C―C and C―N biaryl products.
Consequently,
the reductive elimination step could proceed with
2
FIGURE 3 PDP behavior of C‐steel in 1.0 N‐HCl in the absence and presence of (a) H Sanp and its complexes, (b) Ni‐Sanp and (c) Co‐
Sanp at 30 °C

ABD EL‐LATEEF ET AL.
11 of 19
retention of stereochemical structure of the homogeneous
catalysts intermediate.
capacity (EPDP), which were estimated from the polariza-
tion plots at 30 °C using extrapolation method.
[52–56]
[59–61]
From Table 5 and it corresponding plotting Figure 3,
comparing to the free inhibitor solution, the Ecorr value
shifts mostly towards positive direction in the solution
3
3
.3 | Corrosion inhibition performance
.3.1 | PDP studies
congaing inhibitors elucidating H Sanp, Ni‐Sanp or Co‐
2
Sanp inhibitors, retards both the cathodic and anodic
reactions. It is demonstrated that if the change in Ecorr
is more than 0.085 V verses Ecorr of blank solution,
affording the compound could be classified as a cathodic
or an anodic type inhibitor. In case that the change in
Ecorr is lower than 0.085 V, the compound could be clas-
In order to obtain information into the kinetics of metal
dissolution processes and the hydrogen evolution reac-
tion, PDP studies were carried out for C‐steel in 1.0 M
hydrochloric acid in the absence and presence of different
[
62,63]
doses of H Sanp and its Ni‐ and Co‐complex inhibitors at
sified as a mixed type inhibitor.
Currently, the
2
3
0 °C. Figure 3 shows the PDP plots for (a) H Sanp, (b)
highest displacement in Ecorr is about 37 mV, which is
2
Ni‐Sanp and (c) Co‐Sanp, respectively. It could be
inferred from the curves that the polarization plots style
is conformable in both the inhibited and uninhibited
lower than 85 mV, suggesting that H Sanp and its com-
2
plexes Ni‐Sanp and Co‐Sanp act as mixed type inhibitors.
Moreover, icorr value decreases dramatically in the pres-
ence of inhibitors, the value of icorr for 250 ppm of Ni‐
medium. However, introducing of all inhibitors (H Sanp,
2
−
2
Ni‐Sanp and Co‐Sanp) to the corrosive medium minimize
the rate of C‐steel corrosion as demonstrated in the
shifting of the values of corrosion current density to lower
regions in comparison to the uninhibited solution. Such
result refers the corrosion inhibition capability of the
investigated inhibitors. In addition, this phenomenon
Sanp or Co‐Sanp is 57.45 or 35.63 μA cm , respectively,
−
2
much lower than that for H Sanp, i.e. 150.3 μA cm .
2
These data award that the inhibitive action of the Co‐
and Ni‐complexes is better than that of H Sanp. The
2
inhibition efficiency (EPDP) and surface coverage (θ) are
[
64]
estimated according to the following equation
:
assigned that H Sanp, Ni‐Sanp and Co‐Sanp, suppressed
2
o
− ii
both cathodic hydrogen evolution and steel anodic disso-
lution. It is also observed that the C‐steel underwent
active dissolution within the potential range investigated
without propensity towards passivation in the free and
inhibited solutions.
i
corr
corr
EPDPð%Þ ¼ 100 ×
¼ 100 × θ
(1)
o
i
corr
where io and ii represent the corrosion current densi-
corr
corr
ties without and with the addition of inhibitors. From
Table 5, there is no considerable change observed in the
values of β & β by the inhibitor addition with respect
Table 5 records the related PDP illustrating the corro-
sion current density (icorr), cathodic and anodic Tafel
slope (β & β ), corrosion potential (Ecorr), and inhibition
c
a
to that blank solution, which indicate that addition of
c
a
2
TABLE 5 Corrosion parameters obtained from PDP for C‐steel in 1.0 N‐HCl in the absence and presence of the H Sanp and its Ni‐ and Co‐
complex inhibitors at 30 °C
−1
−2
−1
−1
Inhibitors code
C
inh/mg l
icorr/μAcm
E
corr/mV (SCE)
β
a
/mV dec
‐β
c
/mV dec
θ
E
PDP/%
Blank
0.0
1233
−464 ± 1%
78 ± 15%
137 ± 20%
‐
‐
H
2
Sanp
50
00
50
00
50
504.05 ± 8%
430.68 ± 5%
277.54 ± 4%
198.01 ± 7%
150.30 ± 6%
−440 ± 2%
−435 ± 2%
−427 ± 4%
−433 ± 1%
−427 ± 3%
80 ± 10%
85 ± 14%
83 ± 8%
83 ± 18%
86 ± 12%
157 ± 5%
132 ± 6%
149 ± 11%
148 ± 13%
151 ± 15%
0.591
0.650
0.774
0.839
0.878
59.12
65.07
77.49
83.94
87.81
1
1
2
2
Ni‐Sanp
Co‐Sanp
50
00
50
00
50
398.50 ± 3%
296.41 ± 9%
153.50 ± 5%
90.25 ± 5%
57.45 ± 7%
−446 ± 1%
−428 ± 2%
−454 ± 2%
−457 ± 4%
−456 ± 2%
84 ± 14%
83 ± 10%
80 ± 19%
85 ± 17%
82 ± 10%
143 ± 17%
145 ± 14%
153 ± 16%
149 ± 7%
135 ± 8%
0.676
0.759
0.875
0.926
0.953
67.68
75.96
87.55
92.68
95.34
1
1
2
2
50
00
50
00
50
354.24 ± 4%
239.32 ± 7%
118.61 ± 5%
70.40 ± 6%
35.63 ± 6%
−438 ± 4%
−450 ± 1%
−427 ± 2%
−422 ± 3%
−438 ± 5%
81 ± 8%
140 ± 13%
142 ± 8%
144 ± 7%
149 ± 14%
139 ± 20%
0.712
0.805
0.903
0.942
0.971
71.27
80.59
90.38
94.29
97.11
1
1
2
2
83 ± 12%
79 ± 11%
81 ± 10%
83 ± 20%

1
2 of 19
ABD EL‐LATEEF ET AL.
67]
[
H ‐Sanp and its complexes Ni‐Sanp and Co‐Sanp does not
may be interpreted based on of the theory of chelation.
2
effect on the hydrogen reduction mechanism and the
On chelation, the metal ion polarity would be minimized
[65]
hydrogen evolution is activation‐controlled.
Conse-
to a greater extent because of the overlap of the H Sanp
2
quently, the adsorbed compounds act by unpretentious
blocking of active sites for both cathodic and anodic reac-
orbitals and partial sharing of the positive charge of the
2+
2+
Co
and Ni
ions with donor groups. Co‐Sanp
[66]
tions.
The EPDP depends on different factors such as
displayed the highest EPDP among the other compounds.
adsorption center, interaction mode, size and struc-
Similar results were already reported for Co‐complexes
[32]
[68]
ture.
EPDP increases with the compound doses. EPDP
with Schiff base.
The sequence of EPDP for the investi-
of 250 ppm of H ‐Sanp, Ni‐Sanp and Co‐Sanp inhibitors
gated inhibitors is Co‐Sanp > Ni‐Sanp > H Sanp. This
2
2
reaches up to a maximum of 87.81%, 95.34% and
order of EPDP may also be interpreted in terms of the size
9
7.11%, respectively. This phenomenon may be explained
of the central metal ion Co (II) > Ni (II).
by that the H ‐Sanp, Ni‐Sanp and Co‐Sanp molecules
2
adsorbed on the surface of C‐steel and forming a covering
layer, which can act as a physical barrier to prevent diffu-
sion of the corrosive species to the C‐steel surface.
From Table 5, the higher EPDP of Ni‐ and Co‐
3.3.2 | EIS studies
Figure 4a illustrates the Nyquist plots for the C‐steel mea-
sured in the absence and presence of inhibitors (1‐a)
complexes compared to H Sanp could be due to their
2
big size and more active sites for adsorption. Such an
H Sanp, (2‐a) Ni‐Sanp and (3‐a) Co‐Sanp with different
2
increased activity of the Co‐ and Ni‐pincer complexes
concentrations. Obviously, the Nyquist curves for the
FIGURE 4 (a) Nyquist (b) Bode angle curves for C‐steel in 1.0 N‐HCl in the absence and presence of various dose of (1) H
Sanp and (3) Co‐Sanp at 30 °C
2
Sanp, (2) Ni‐

ABD EL‐LATEEF ET AL.
13 of 19
inhibited and uninhibited solutions are consisting of one
depressed capacitive semicircle corresponding to one‐time
constant in the Bode curve (Figure 4b). The Nyquist plot
shape is the same in the blank and inhibited solutions
indicating no change in the mechanism of corrosion pro-
cess. However, the diameter of the capacitive semicircle
remarkably increased with the addition of inhibitors indi-
cating that these compounds formed an effective layer on
C‐steel. Moreover, Nyquist curves display several induc-
tive loops in the low frequency area, which is related to
the relaxation adsorbed molecule of inhibitors on the sur-
data by Z‐view software (line): (a) Nyquist plot and (b)
bode phase modules are presented in Figure 5. Inset
(Figure 5a) suggested equivalent electric circuit (EEC)
utilized to fit the EIS data. This EEC consists of the
constant phase element (CPE), the solution resistance
(R ) and the polarization resistance (R ). In the current
s
p
EEC analysis, the difference between the real impedance
at higher and lower frequencies described as Rp
rather than more usually applied resistance of charge
transfer (R ). The standard behind using R is according
ct
p
to the fact that the C‐steel corroding in acidic solution
is mostly commitment to other kinds of resistances
[69,70]
face of electrode.
The Bode modulus, Figure 4 (1‐b, 2‐
b and 3‐b), showed a single time constant, which agreed
with the Nyquist plots. The absolute Bode modulus values
are shifted to the higher values in the low frequency area
with increment in the inhibitor doses. In another words,
the corrosion inhibition could be performed by higher
concentration of inhibitors than lower concentrations.
Comparison of empirical EIS results (points) measured
for C‐steel in blank 1.0 M HCl (1) and containing
including film resistance (R ), accumulation resistance
f
(R ), diffusion resistance (R ) and along with R ,
a
d
ct
[
71–73]
i.e. R = R + R + R + R .
Some EIS parameters
p
ct
f
a
d
like R and R , double layer capacitance (C ) and phase
s
p
dl
shift (n) were derived using EEC and tabulated in
Table 6. The inhibition efficiencies (EEIS/%) at various
studied concentrations have been calculated from the
0
polarization resistances in the absence (R ) and presence
P
−
1
i
P
[38]
2
50 mg L of Ni‐Sanp (2) inhibitor and the simulated
(
R ) of inhibitors by using Equation 2
:
−
1
FIGURE 5 Comparison of empirical impedance results (points) measured for C‐steel in blank 1.0 N‐HCl (1) and containing 250 mg L of
Ni‐Sanp inhibitor (2) and the simulated data (line): (a) Nyquist plot and (b) Bode phase modules. Inset (Figure 4‐a) suggested equivalent
electric circuit (EEC) utilized to fit the EIS data

14 of 19
ABD EL‐LATEEF ET AL.
TABLE 6 EIS parameters for C‐steel and the inhibition efficiencies (EEIS/ %) of different doses of the synthesized H
Co‐ complexes in 1.0 N‐HCl at 30 °C
2
Sanp and its Ni‐ and
C
inh/mg
Φ
CPE
−
−
Inhibitors
code
l
R
cm
s
/Ω
C
× 10
dl/F cm
EIS
E /
%
1
2
2
−2
n
−6
2
−6
R
p
/Ω cm
Y
0
/F cm
S
× 10
n
θ
Absence
0
1.05
42.7 ± 5%
81.6 ± 3%
117.5 ± 8%
197.8 ± 6%
238.4 ± 7%
368.8 ± 4%
136.2
0.776 ± 2%
95.10 ± 11%
‐‐‐‐‐
‐‐‐‐‐
H
2
Sanp
50
00
50
00
50
1.10
1.16
1.21
1.25
1.32
78.5
54.5
36.8
21.9
10.8
0.887 ± 1%
0.876 ± 4%
0.902 ± 1%
0.907 ± 3%
0.917 ± 5%
50.2 ± 9%
33.4 ± 12%
24.6 ± 14%
15.3 ± 10%
7.3 ± 12%
0.476
0.636
0.784
0.820
0.884
47.6
63.6
78.4
82.0
88.4
1
1
2
2
Ni‐Sanp
Co‐Sanp
50
00
50
00
50
1.04
1.12
1.17
1.80
2.9
123.6 ± 9%
170.1 ± 10%
332.2 ± 8%
443.4 ± 7%
726.7 ± 9%
56.8
39.3
24.3
16.3
6.1
0.907 ± 4%
0.897 ± 3%
0.927 ± 2%
0.929 ± 5%
0.938 ± 6%
39.6 ± 10%
26.3 ± 17%
18.5 ± 16%
12.4 ± 15%
4.7 ± 11%
0.654
0.748
0.871
0.903
0.941
65.4
74.8
87.1
90.3
94.1
1
1
2
2
50
00
50
00
50
1.41
1.52
2.33
1.76
2.57
153.2 ± 6%
220.1 ± 8%
455.4 ± 5%
751.8 ± 4%
1088.5 ± 5%
50.4
31.1
20.9
12.7
4.2
0.925 ± 5%
0.917 ± 7%
0.938 ± 8%
0.948 ± 5%
0.949 ± 2%
38.4 ± 8%
22.6 ± 10%
16.6 ± 11%
10.5 ± 12%
3.3 ± 20%
0.721
0.806
0.906
0.943
0.961
72.1
80.5
90.6
94.3
96.1
1
1
2
2
ꢀ
ꢁ
0
R
from ideal behavior is related to the inhomogeneity sur-
face caused from interfacial and structural origin.
P
i
EEIS=% ¼ 1 −
× 100 ¼ θ × 100
(2)
[70]
R
P
The values capacitance of double layer (C ) was
dl
Generally, for a metal/solution corroding system, CPE
is being used instead of pure capacitor because of the
presence of inhomogeneity surface. Impedance of the
calculated from the frequency at which the imaginary
component of the impedance is extreme (ωmax) using
[
75]
the Equation 4
:
[34]
CPE (ZCPE) could be exemplified by Equation 3
:
n−1
C ¼ Y ½ωmaxꢀ
(4)
dl
0
ꢀ 1
ꢁ
−
1
ZCPE ¼
½Jωnꢀ
(3)
where ωmax = 2π fmax, fmax is the frequency at which the
imaginary impedance component is maximum. The
cautious inspection of data presented in Table 6 it dis-
plays that R value increased and C values decreased
Y0
where j, n, Y and ω are imaginary number, phase shift,
0
p
dl
CPE constant and angular frequency, respectively. The
lower value of n is associated with surface inhomogeneity
and vice versa. It is observed to an increase in n values in
the inhibited solutions compared to the blank (Table 6),
indicating that surface morphology of in the presence of
inhibitors have been smoothened uncommonly because
in the inhibited solution predominantly at higher H Sanp
2
and its Ni‐ and Co‐complexes dose. These observations
indicate that the studied ligand and its complexes
adsorbed at the C‐steel/HCl interfaces and subsequently
increased electric double layer thickness and prevent
[
76]
acidic corrosion of C‐steel.
Generally, the organic
of the adsorption of studied H Sanp and its Ni‐ and Co‐
2
inhibitors have a larger volume than H O molecule and
2
complexes on the metal surface. Similar observation has
[
77]
[
74]
a much lower dielectric constant.
The lower values of
been mentioned by our working group previously,
Cdl in the inhibited media might be also related to the
which was related to a decrease in heterogeneity resulting
from the inhibitor molecules adsorption on the surface of
C‐steel. Moreover, to the surface inhomogeneity n value
could be also applied for investigated the impedance spec-
tra nature as value of n = 1, 0.5, 0 and − 1 represent
capacitance, Warburg impedance resistances and induc-
piecemeal replacement of H O molecules by the adsorp-
2
tion of the inhibitor species at steel surface. The protec-
tive film thickness is related to C based on the
dl
[
78]
Helmholtz model
:
εε0A
Cdl
[75]
δ ¼
(5)
tance and, respectively.
In current work, n values in
the presence and absence of investigated H Sanp and its
2
Ni‐ and Co‐ complexes change from 0.776 to 0.949 and
where A, ɛ, ɛ and δ are the geometrical electrode surface
0
are partially deviated from unity. This deviation type
area, the medium dielectric constant, the vacuum

ABD EL‐LATEEF ET AL.
15 of 19
permittivity and the protective film thickness, respec-
tively. As the inhibitor dose increased, more molecules
adsorbed onto the surface of C‐steel, leading to a dimin-
ished immersion surface area of the electrode, lower local
dielectric constant and an intensive electric double‐layer.
2
TABLE 7 Adsorption parameters for H Sanp and its Ni‐, Co‐
complex inhibitors estimated from Langmuir adsorption model for
C‐steel in 1.0 N HCl at 30 °C
−
ΔGo kJ
coefficient (R ) mol
Slope
Inhibitors values
K
L
ads mol
Correlation
ads
1
2
−1
These observations caused reduce in C values. Under a
dl
4
4
4
H
2
Sanp
0.992
1.010
0.959
12.6 × 10
18.8 × 10
23.8 × 10
0.995
0.998
0.999
−39.72
−
1
specific dose (250 mg L ), E of the three studied inhib-
EIS
Ni‐Sanp
Co‐Sanp
−40.71
−41.33
itors calculated by Equation 2 obey the order of Co‐Sanp
>
Ni‐Sanp > H ‐Sanp, which is in a good consistent with
2
the data of PDP. The maximum E is 96.1% in the pres-
EIS
−
1
ence of 250 mg L Co‐Sanp.
By inspection Table 7, the Kads value of Ni‐Sanp and
Co‐Sanp complexes is greater than that of ligand, H Sanp,
2
which is in agreement with the trend of the EEIS and EPDP
calculated by EIS and PDP measurements. Moreover, the
3
.3.3 | Adsorption isotherm and corrosion
inhibition mechanism
Kads value is related to the standard free energy of adsorp-
tion process (ΔG 0a ds) by Equation 8
[82]
:
Adsorption of organic inhibitor species at the C‐steel/
solution interface consists of the modification of H O
2
0
ΔG ¼ −RTlnðKads × 55:50Þ
(8)
molecules by inhibitor species based on the following
ads
[79]
process (Equation 6)
:
where R and T represent the universal gas constant and
the absolute temperature, respectively. The value of
Inhibitorsol þ zH O
→ Inhibitorads
ads
2
þ zH2Osol
(6)
where z is the number of H O molecules substituted by
2
the inhibitor species, Inhibitor(ads) and Inhibitor(sol) are
inhibitor species in the adsorbed on the steel surface
and solution, respectively. Several adsorption isotherms
including Freundlich, Bockris–Swinkels, Langmuir,
Flory–Huggins and Temkin isotherms could be applied
to fit the values of surface coverage (θ) at various concen-
trations in order to determine the adsorption behavior of
the investigated inhibitors. Langmuir adsorption model is
the preferable characterization of the adsorption behavior
of the inhibitor species on the C‐steel surface. Langmuir
[80]
model was presented in Equation 7
:
Cinh
1
¼
Cinh þ K
(7)
θ
ads
where θ is the surface coverage, which is calculated from
Equations 1 and 2; Cinh. is the inhibitor dose and K is
ads
−
1
the adsorption equilibrium constant (L mol ). Plot of
Cinh./θ versus Cinh. yield a straight line and the slope is
2
close to unity (Table 7). The value of R (correlation coef-
ficient) is more than 0.995 for all studied inhibitors
(
H Sanp, Ni‐Sanp and Co‐Sanp). Therefore, the model
2
of Langmuir is suitable for the adsorption behavior of
H Sanp, Ni‐Sanp and Co‐Sanp inhibitors on C‐steel sur-
2
face (Figure 6). Then, the values of Kads are estimated
from the straight lines intercepts, and the calculated
values are listed in Table 7. The higher Kads values indi-
cate the higher coverage rate and therefore a best protec-
FIGURE 6 Langmuir adsorption model for (a) H Sanp, (b) Ni‐
Sanp and (c) Co‐Sanp on the C‐steel surface in 1.0 N‐HCl at 30 °C
2
[
81]
tive film of the compounds on the surface of C‐steel.

16 of 19
ABD EL‐LATEEF ET AL.
−
5
5.50 is the molar concentration of H O. Generally, the
of H Sanp, Ni‐Sanp and Co‐Sanp. Therefore, Cl ions in
2
2
0
ΔG values in the range of −20 to −40 kJ/ mol are con-
sistent with the physical‐adsorption.
ΔG values than −40 kJ/ mol is dedicated to the
chemical‐adsorption.
Table 7, the values of ΔG
Co‐Sanp are −39.72, −40.71 and − 41.33 kJ/mol, respec-
tively. Therefore, H Sanp, Ni‐Sanp and Co‐Sanp inhibi-
tors are adsorbed onto the steel surface by mixed
aqueous solutions of HCl get adsorbed on the surface of
C‐steel. After the Cl ions adsorption, the C‐steel surface
becomes negatively charged. Subsequently, the proton-
ated positively charged form H Sanp, Ni‐Sanp and
Co‐Sanp inhibitors adsorbed on the C‐steel surface by
physical adsorption by electrostatic interactions with the
Cl ions, which previously adsorbed on surface of metal.
In addition to physical adsorption, donor–acceptor
interactions between the π‐electrons of aromatic benzene
ring and the unshared electron pairs of heteroatoms N
and O with the vacant d‐orbitals of Fe, this process is a
The schematic repre-
sentation of the adsorption behavior of H Sanp on C‐steel
in 1.0 M HCl solution is shown in Figure 8. Therefore, the
results approved that both chemical and physical adsorp-
tion together existed on the HCl/inhibitor/C‐steel inter-
face obtained from adsorption isotherm.
ads
[83]
−
While, higher
0
ads
[84]
According to the data in
2
0
ads
for H Sanp, Ni‐Sanp and
2
−
2
mechanism that involves chemical and physical adsorp-
[85]
In addition, the more negative ΔG0 value of
ads
tion.
Co‐Sanp and Ni‐Sanp inhibitors represents a more stable
adsorption film of Co‐Sanp and Ni‐Sanp molecules on the
surface of metal in comparison with that of H Sanp.
The process of adsorption is affected by the inhibitor
chemical structure, the charge of the steel surface and
the charge of the inhibitor species. The potential of zero
charge (EPZC) of C‐steel in 1.0 M HCl solution containing
[
85]
chemical adsorption mechanism.
2
2
2
50 ppm of H Sanp, Ni‐Sanp and Co‐Sanp inhibitors was
2
estimated by using EIS method. The minimum on Cdl
versus applied potential (E) plots (Figure 7) is considered
as the EPZC value of C‐steel. The charge of metal surface
can be determined by the position of Eocp towards the
EPZC. The net C‐steel charge at Eocp was estimated based
on Equation 9:
3
.3.4 | Surface analysis by SEM and EDX
In order to recognize any changes occurred during pro-
cess of corrosion in the absence and presence of studied
ligand and its complexes, SEM analysis is carried out.
SEM images of C‐steel substrate exposure to blank
1
.0 M HCl and in the inhibited solution containing
Er ¼ Eocp − EPZC
(9)
−
1
250 mg L of Co‐Sanp inhibitor for 48 hr are shown in
[
85]
where E is the Antropov's corrosion potential.
values of E at E values are +0.045, +0.041 and + 0.05 V
for H Sanp, Ni‐Sanp and Co‐Sanp, respectively. This
means that the C‐steel surface in the inhibited solutions
The
Figure 9 (a‐I and b‐I). The C‐steel morphology in the
absence of inhibitor (blank HCl) (Figure 9 a‐I) is very
coarse and the surface is severely damaged because of dis-
solution of metal and contains some pores and cavities
(represented by arrows). In contrast, the presence of
r
r
ocp
2
−
1
is positively charged at Eocp in presence of 250 mg L
−
1
2
50 mg L of Co‐Sanp prohibits the corrosion rate and
the surface damage has been minimized frequently
(
(
Figure 9 b‐I) as compared to the uninhibited solution
Figure 9 a‐I), indicating formation of a covering inhibitor
layer at the surface of C‐steel, which isolates the contact
between the corrosive medium and the metal surface.
EDX analysis was performed to obtained knowledge
about the composition of the C‐steel surface in the blank
and inhibited solutions. The EDX spectrums of C‐steel
after immersion in blank HCl and in the presence of
250 ppm of Co‐Sanp for 48 hr are presented in Figures 9
(
a‐II and b‐II). The EDX spectrum in blank solution
shows peaks of Mn, C, Cr, Ni, Si, Fe, Cl, and O, indicating
the formation of corrosion products (iron chloride and
iron oxides) on the surface of C‐steel. These observations
indicate that the metal surface was strongly corroded in
blank HCl. Whereas in the inhabited solution additional
peaks for Na, N, S, and Co corresponding to the elements
present in the Co‐Sanp molecules, indicating the Co‐Sanp
molecules adsorption at the C‐steel surface. Moreover,
FIGURE 7 The plot of Cdl vs. applied potential for C‐steel in
.0 N‐HCl solution containing 250 ppm of (a) H Sanp (black line),
b) Ni‐Sanp (red line) and (c) Co‐Sanp (blue line) at 303 K
1
2
(

ABD EL‐LATEEF ET AL.
17 of 19
2
FIGURE 8 Schematic exemplification of the adsorption behavior of H Sanp on C‐steel surface in 1.0 N‐HCl solutions
FIGURE 9 SEM pictures (I) and EDX spectra (II) of the C‐ steel surfaces after 48 hr exposure in 1.0 N‐HCl solutions in the absence (a) and
−
1
presence of 250 mg L Co‐Sanp (b) at 30 °C
the EDX spectra displays that there is a reduction in the
corrosion products amount (iron chloride and iron
oxides) where the peaks consistent with Cl and O formed
because of the corrosion process are minimized. These
results confirmed the inhibitory layer formed on the sur-
face of C‐steel.
by complexeation to tetradentate pincer N,O,O,N‐
salicyldiene thiadiazole ligand (H Sanp). The catalytic
2
efficiency of the two complexes was studied under sus-
tainable conditions in the Suzuki C―C and Buchwald‐
Hartwig C―N cross coupling reactions. Both complexes
afforded moderate to high catalytic potential towards
C―C and C―N couplings, whereas Ni‐Sanp showed
higher catalytic reactivity. The steric hindrance of octahe-
dral geometry of Co‐Sanp compared to the square planar
of Ni‐Sanp and types of the central metal ion have distin-
guished effects on their potentials. The best solvent
system for the C―C and C―N couplings is ethanol,
4
| CONCLUSIONS
High stable and water soluble Ni‐ and Co‐complexes (Ni‐
Sanp and Co‐Sanp) were synthesized and characterized

18 of 19
ABD EL‐LATEEF ET AL.
ethanol‐water (1: 1) and then water under sustainable
conditions, which could be due to the solubility and mis-
cibility of the substrates in the catalytic processes.
EIS and PDP measurements have showed that the syn-
[12] P. K. Suganthy, R. N. Prabhu, V. S. Sridevi, Inorg. Chim. Acta
2
016, 449, 127.
13] A. R. Hajipour, F. Rezaei, Z. Khorsandi, Green Chem. 2017, 19,
353.
[
[
1
14] R. Ghanbaripour, M. Samadizadeh, G. Honapisheh, M.
thesized H Sano and its complexes Ni‐Sanp and Co‐Sanp
2
Abdolmohammadi, Synlett 2015, 26, 2117.
are good inhibitors for the C‐steel corrosion in acidic
solution and the EEIS/% and/or EPDP/% increases with
the inhibitor dose. The maximum inhibition capacity
[15] F.‐S. Han, Chem. Soc. Rev. 2013, 42, 5270.
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and Co‐Sanp are 87.81%, 95.34% and 97.11% at
−
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Chem. 2010, 8, 5692.
2
50 mg L , respectively. The investigated H Sano and
2
[
[
18] L. M. Kumar, B. R. Bhat, J. Organomet. Chem. 2017, 827, 41.
its complexes Ni‐Sanp and Co‐Sanp act as mixed‐type
corrosion inhibitors. Adsorption of compounds is
characterized according to Langmuir model. Both
chemical and physical adsorption phenomena are present
but the chemisorption is predominant. Surface morpho-
logical analyses (SEM and EDX) emphasize the formation
of adsorption layer of these inhibitors on the surface of
C‐steel.
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[
[
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ACKNOWLEDGMENTS
[23] J.‐Y. Song, X. Zhou, H. Song, Y. Liu, H.‐Y. Zhao, Z.‐Z. Sun,
W.‐Y. Chu, ChemCatChem 2018, 10, 758.
This work was supported by the grants from the Dean-
ship of Scientific Research, King Faisal University
[
[
[
[
24] F. Kreyenschmidt, K. Koszinowski, Chem. – Eur. J. 2018, 24,
1168.
(project number 180084). The financial contribution is
25] P. M. P. Garcia, T. D. Franco, A. Epenoy, R. Scopelliti, X. Hu,
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Khalaf, Egypt. J. Pet. 2015, 24, 175.
Hany M. Abd El‐Lateef
https://orcid.org/0000-0002-6610-
https://orcid.org/0000-0001-
3
93X
Mohamed Shaker S. Adam
826-3558
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How to cite this article: Abd El‐Lateef HM,
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