Air-Stable Cobalt(II) and Nickel(II) Complexes with Schiff Base Ligand for Catalyzing Suzuki–Miyaura Cross-Coupling Reaction

Article abstract of DOI:10.1134/S1070328418010013

The Co(II) complex [Co{C₆H₄–1,2-(N=CH–C₆H₄O)₂}] (I) and Ni(II) complex [Ni{C₆H₄–1,2-(N=CH–C₆H₄O)2}] (II) with Schiff base of o-phenylenediamine and salicylaldehyde have been synthesized. The structure of the ligand and its complexes were derived on the basis of various techniques such as elemental analysis, mass, FT-IR, electronic spectra and magnetic susceptibility. From the Singal crystal X-ray diffraction (SCXRD) analysis techniques (CIF file CCDC no. 1498772 (II)), it has been confirmed that the Schiff base ligand (L), coordinates to the metal ion in a tetradentate fashion through the nitrogen and oxygen atom. In addition, the square planar geometry of Ni(II) complex also has been confirmed from SCXRD. Electronic spectra, mass spectra, and magnetic susceptibility measurements reveal square planar geometry for the Co(II) complex. Synthesized complexes were used in cross-coupling of arylhalides with phenylboronic acid. The transformation offers products in good yields using 0.02 mmol catalysts loading, thereby proving the efficiency of the complexes as catalysts for Suzuki–Miyaura reaction.

Full text of DOI:10.1134/S1070328418010013

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2018, Vol. 44, No. 1, pp. 1–8. © Pleiades Publishing, Ltd., 2018.
Air-Stable Cobalt(II) and Nickel(II) Complexes with Schiff Base
Ligand for Catalyzing Suzuki–Miyaura Cross-Coupling Reaction1
R. M. Ansari, L. M. Kumar, and B. R. Bhat*
Department of Chemistry, Catalysis and Material Chemistry Laboratory, National Institute of Technology Karnataka,
Mangalore, Karnataka, 575025 India
*
e-mail: ram@nitk.edu.in
Received February 20, 2017
Abstract⎯ The Co(II) complex [Co{C H –1,2-(N=CH–C H O) }] (I) and Ni(II) complex [Ni{C H –1,2-
6
4
6
4
2
6
4
(
N=CH–C H O) }] (II) with Schiff base of o-phenylenediamine and salicylaldehyde have been synthesized.
6 4 2
The structure of the ligand and its complexes were derived on the basis of various techniques such as elemen-
tal analysis, mass, FT-IR, electronic spectra and magnetic susceptibility. From the Singal crystal X-ray dif-
fraction (SCXRD) analysis techniques (CIF file CCDC no. 1498772 (II)), it has been confirmed that the
Schiff base ligand (L), coordinates to the metal ion in a tetradentate fashion through the nitrogen and oxygen
atom. In addition, the square planar geometry of Ni(II) complex also has been confirmed from SCXRD.
Electronic spectra, mass spectra, and magnetic susceptibility measurements reveal square planar geometry
for the Co(II) complex. Synthesized complexes were used in cross-coupling of arylhalides with phenylbo-
ronic acid. The transformation offers products in good yields using 0.02 mmol catalysts loading, thereby
proving the efficiency of the complexes as catalysts for Suzuki–Miyaura reaction.
Keywords: Suzuki–Miyaura cross coupling, transition metal complex, Schiff base, biphenyl
DOI: 10.1134/S1070328418010013
INTRODUCTION
be promising chemical tool for the formation of C–C
bonds [13, 14]. Palladium has been extensively applied
A Schiff base is described as a compound with an
imine group that contains a carbon-nitrogen double for the synthesis of natural products and biologically
bond with the nitrogen atom connected to an alkyl or
aryl group [1, 2]. Schiff bases and their complexes have
been reported to be widely employed for carrying out
ample reactions in synthetic chemistry [3]. Schiff
bases have the ability to bind with various metals to
form stable complexes [4, 5] and also pose to be inter-
mediates in several organic reactions. Schiff base com-
relevant organic molecules [15, 16]. Conventionally
used complexes with palladium-phosphine ligand are
efficient in C–C coupling reactions like Suzuki–
Miyaura cross-coupling reactions. However, they do
not adhere firmly to the principles of Green Chemis-
try by being highly expensive and less eco-friendly due
plexes have proven to be superior when used as a cata- to their leaching into the reaction and causing impuri-
lyst for various kinds of reactions [6]. In addition, var- ties in the product. Catalysis using low cost and less
ious Schiff bases have also been examined for their
biological activities by researchers [7–9]. Basically,
C–C bonds are crucial as an intermediate for both
organic synthesis and pharmaceutical industry.
Chemical reactions that generate new C–C bonds are
more fundamental and important tool for the forma-
toxic metals makes an appreciable and prolific attempt
of overcoming the limitations posed by Pd-catalyzed
reactions. In presented research work, we provide
contemporary catalysts which could efficiently com-
plement the coupling reaction with their high catalytic
tion of man-made chemicals such as fine chemicals, activity. The proposed catalysts possess sufficient
agrochemicals, pharmaceuticals, polymers etc. [10– thermal stability to react at elevated reaction tempera-
1
2]. From the past few decades, several catalytic meth-
tures. We report the synthesis of cobalt(II) and
nickel(II) complexes with a Schiff base ligand (L)
which has been successfully employed to study their
C–C coupling efficiency in cross-coupling between
phenylboronic acid and para-substituted aryl halides.
ods have been developed for the formation of C–C
bonds, and among various catalysts reported palla-
dium catalyzed cross coupling reaction have proven to
1
The article is published in the original.
1

2
ANSARI et al.
recorded in Bruker AV 400 instrument using
EXPERIMENTAL
tetramethylsilane (TMS) as an internal standard.
Molecular mass was determined using a Waters Q-ToF
micro mass spectrometer with an ESI source. Ther-
mogravimetric (TG) measurements were performed
on (EXSTAR-6000) using nitrogen as the carrier gas
Materials and methods. All chemicals used were of
analytical reagent (AR) grade without further any
purification. o-Phenylenediamine, salicylaldehyde,
nickel acetate tetrahydrate, cobalt acetate tetrahydrate
potassium carbonate and sodium carbonate were pro-
cured from Merck India and used as received. Aceto-
nitrile (ACN), 1,4-dioxane, dimethylformamide
(
flow rate: 50 mL/min) with a heating rate of
0°C/min.
1
(
DMF), tetrahydrofuran (THF), toluene, ethyl alco-
Synthesis of the Schiff base (Scheme 1). A solution
of o-phenylenediamine (0.108 g, 1.0 mmol) and salic-
ylaldehyde (0.244 g, 2.0 mmol) in 10 mL ethanol was
taken in a round bottom flask and refluxed for 3 h. The
reaction mixture was monitored by thin layer chroma-
tography. The completed reaction was filtered and
crude solid product obtained was washed with diethyl
ether several times till no impurities were observed and
this purified product was dried in a vacuum oven for
hol, diethyl ether, potassium tertiary butoxide, cesium
carbonate and triethylamine used in the study were
purchased from Sigma-Aldrich. The C, H, and N con-
tents of the ligand and metal complexes were exam-
ined using microanalysis Thermoflash EA1112 series
elemental analyzer. Electronic spectra of ligand and
complexes were measured on Analytik Jena SPE-
CORD S600 UV-Vis spectrophotometer in the 200–
8
00 nm range. FT-IR results were obtained on a
5
h at 60°C. The Schiff base obtained was turmeric
Bruker-Alpha ECO-ATR FT-IR spectrophotometer.
The magnetic susceptibilities of the complexes were
recorded at room temperature on a Sherwood UK
magnetic balance, mercury(II) tetrathiocyanatoco-
yellow in colour with 82% of yield.
For C H N O
2
0
16
2
2
anal. calcd., %
Found, %
C, 75.93
C, 75.22
H, 5.10
H, 4.90
N, 8.86
N, 8.74
baltate(II) (Hg[Co(SCN) ]) was used as a calibrant.
4
1
The H NMR (400 MHz) spectrum of the ligand was
N
NH2
NH2
OHC
2
HO
Ethanol
N
+
HO
(L)
OH
Scheme 1.
Synthesis of metal complexes (Scheme 2). Cobalt- using Ni(OCOCH ) · 4H O (the yield was 78%).
3
2
2
Schiff base complex was prepared by refluxing ethan-
Crystals for complex II crystal were obtained by a slow
evaporation method using ethanol.
olic solutions of Co(OCOCH ) · 4H O (1.0 mmol,
3
2
2
5
mL) and the Schiff base (0.316 g, 1.0 mmol, 10 mL)
under constant stirring for 2 h. The reaction was mon- For C H N O Co (I)
20
14
2
2
itored for the change in colour and precipitate forma-
tion. The obtained brown colored precipitate was fil-
tered, washed with ethanol and diethyl ether to remove
unreacted Schiff base. The product was dried in a vac-
uum oven at 60°C for 5 h (the yield was 64%). Simi-
larly, the nickel Schiff base complex was prepared by
anal. calcd., %
Found, %
C, 64.35
C, 64.30
H, 3.78
H, 3.67
N, 7.50
N, 7.50
For C H N O Ni (II)
20
14
2
2
anal. calcd., %
Found, %
C, 64.40
C, 64.20
H, 3.78
H, 3.55
N, 7.51
N, 7.40
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
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No. 1
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AIR-STABLE COBALT(II) AND NICKEL(II) COMPLEXES
H
3
C
N
O
Co
O
N
CH
Co(OCOCH ) ⋅ 4H O
3
2
2
(I)
N
EtOH
N
HO
L)
(
EtOH
OH
H
C
N
N
Ni(OCOCH ) ⋅ 4H O
3
2
2
O
Ni
O
CH
(II)
Scheme 2.
X-ray crystallography. The X-ray diffraction studies two oxygen atoms and two nitrogen atoms from the
for crystal II was performed on a Bruker APEX-II deprotonated Schiff base ligand, forming a perfectly
CCD diffractometer with MoKα radiation (λ = square planar geometry with the smallest angle of
0
.71073 Å) by using ω scan technique at 296 K. The O(2)Ni(1)O(1) 84.34(7)° and the biggest angle of
structure was solved by the direct method using O(2)Ni(1)N(1) 179.03(7)°. The N(2)Ni(1)N(1) angle
SHELXL-2007/2014 [17] software and refined by full is found to be 86.20(7)°. The bifurcated C–H...O
matrix least square methods. Anisotropic displace- hydrogen bond with bond distance 3.330 and 3.308 Å
ment parameters were calculated for all non-hydrogen was observed in the molecular crystal. Moreover, C–
atoms. The crystallographic data for complex II are H···π interaction with bond distance 3.506 Å was
listed in Table 1. Selected bond lengths and angles for observed between the neighboring molecular units.
complex II are given in Table 2.
Each unit is interconnected to the adjoining units
The atomic coordinates and other parameters of through a C–H···O hydrogen bond where phenyl ring
the complex have been deposited with the Cambridge hydrogen of one unit links with oxygen of another unit
Crystallographic Data Center (CCDC no. 1498772; to form one-dimensional structure. The complex
deposit@ccdc.cam.ac.uk).
General procedure for the Suzuki coupling reaction.
The synthesized catalyst (0.02 mmol), aryl halides
molecules are regularly arranged by weak van der
Waals forces to construct three dimensional struc-
tures.
The synthesized Schiff base ligand was character-
(
1.0 mmol), phenylboronic acid (1.5 mmol), K CO
2 3
1
1
ized by H NMR analysis in DMSO. The H NMR
spectrum of ligand portrays the well characteristic sin-
glet peaks at δ 12.90 which corresponds to the pheno-
lic proton. Similarly, the peak at δ 8.9–9.0 represents
the characteristic peak of azomethine protons. The
presence of a multiplet at δ 6.95–7.65 is due to the aro-
matic protons (Ar–H). Moreover, the peak at δ 12.90
in Schiff base ligand due to phenolic proton was not
(2.0 mmol), and 1,4-dioxane (2.0 mL) were heated to
10°C for 8 h. The reaction mixture was cooled to
1
room temperature and the organic phase was exam-
ined by gas chromatography. The yield was calculated
with the help of GC results.
RESULTS AND DISCUSSION
The crystallographic analysis of complex II reveals visible in the spectrum of nickel complex, which con-
that the unit cell contains one complex molecule firmed the bonding between phenolic oxygen with
(
Fig. 1). Here, nickel(II) atom is four-coordinated via nickel ions. The spectrum displays all the characteris-
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 44 No. 1 2018

4
ANSARI et al.
Table 1. Crystallographic data and structure refinements tic peaks without any impure peak confirming the pre-
for complex II
pared Schiff base ligand and complex.
Parameter
Value
The synthesized ligand and the complex molecules
were examined by the FT-IR analysis. The FT-IR
Empirical-formula
Colour
C H N NiO
2
20
14
2
–1
spectra of the ligand exhibited strong band at 1615 cm
Maroon
assignable to azomethine ν(C=N) group. The peak in
–1
Crystal system
Space group
Unit cell dimensions
a, Å
Orthorhombic
the region 1275 cm is indicative of phenolic ν(C–O)
stretching. The appearance of a band for ν(CH=N) in
the range of 1608–1599 cm– indicates a shift to the
lower frequencies compared to ligand (L) indicating
the complexion of the ligand with metal atom through
nitrogen atom [18]. Phenolic ν(C–O) stretching is
P2 2 2
1
1 1
1
5.4430(3)
16.6157(7)
17.2995(8)
b, Å
–
1
shifted to 1251–1245 cm
1
in complexes from
c, Å
V, Å3
–1
275 cm seen in the ligand spectra. The shift towards
lower wavenumbers indicates coordination of the phe-
nolic oxygen of ligand to the metal ion. The new bands
1564.55
Z
4
ρcalcd, g/cm3
–1
1.592
in the range 534–541 cm in complexes, can be ten-
tatively assigned to coordination of metal with an oxy-
gen atom. The coordination through azomethine N is
further supported by the appearance of the band at
420–455 cm– in metal complexes which can be
assigned to ν(M–N) [19].
Crystal size, mm
μ, mm–1
0.32 × 0.24 × 0.20
1.256
1
F(000)
776
ω
Scan mode
The prepared M–L complexes were confirmed by
using UV-Vis absorption measurements in ethanol
solvent as a media. Figure 2 shows the UV-Vis spectra
of L, complexes I and II. In the UV-Vis absorption
spectrum of free ligand, the molecule shows maxi-
mum wavelength values at 212 and 257 nm which are
attributed to ?? – ??* transition. Similarly, 325 and
θ Range, deg
Limiting indices h, k, l
1.699–25.997
–6 ≤ h ≥ 6,
–
–
20 ≤ k ≥ 20,
21 ≤ l ≥ 21
Reflection collected
29500
Independent reflections (Rint)
Reflections with I > 2σ(I)
Number of parameters
Goodness-of-fit
3093 (0.0189)
2987
3
87 nm can be assigned to imino n – ??* transitions in
ligand. Compared to the free L, the imine n – ??*
transitions of the complexes were shifted to some
extent, possibly the coordination of nitrogen atom of
the ligand imine group to the metal ion [20]. More-
over, quite higher absorption intensity band at 484 nm
226
1.012
R (I > 2σ(I))*
0.0230
0.0699
1
R (all data)**
1
–
1
(
20 661.2 cm ) for complex I was observed, which
Δρmin/Δρmax, e Å−3
0.156/–0.159
confirms the square planar geometry of the cobalt(II)
complex. Similarly, absorption at 470 nm
*
R = ∑(F – F )/∑(F ).
o c o
–1
(
21276.5 cm ) in complex II indicates the square pla-
2
2 2
2 2 1/2
*
* wR = {∑[w(F – F ) ]/∑(F ) }
.
2
o
c
o
nar geometry of nickel(II) complex [21].
Table 2. Selected interatomic distances (d) and bond angles (ω) in complex II
Bond
d, Å
Bond
Ni(1)–N(1)
Ni(1)–N(2)
Angle
d, Å
Ni(1)–O(1)
Ni(1)–O(2)
1.840
1.836
1.858
1.859
Angle
ω, deg
ω, deg
O(2)Ni(1)O(1)
O(2)Ni(1)N(2)
O(1)Ni(1)N(1)
84.34(7)
94.74(7)
94.72(7)
N(2)Ni(1)N(1)
O(1)Ni(1)N(2)
O(2)Ni(1)N(1)
86.20(7)
178.43(7)
179.03(7)
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
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AIR-STABLE COBALT(II) AND NICKEL(II) COMPLEXES
5
H(7)
H(8)
C(10)
C(11)
C(9)
C(12)
H(6)
H(9)
C(8)
C(7)
C(13)
N(2)
H(5)
H(10)
N(1)
C(14)
C(15)
H(4)
C(5)
H(11)
C(20)
C(6)
Ni(1)
C(1)
H(3)
C(16)
C(17)
H(14)
H(12)
C(4)
O(2)
O(1)
C(19)
C(2)
H(1)
C(3)
C(18)
H(2)
H(13)
Fig. 1. Molecular structure of II showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability
level.
The purpose of the thermal study is to confirm the 200°C confirms that no coordinated water molecules
course of the degradation and the presence of the are present in both the complexes [22, 23]. Losses of
weight are in agreement with the calculated values.
hydrated water molecules in the complexes. The ther-
mal decomposition curves for both the complexes at a
temperature range from 50 to 700°C are given in
Fig. 3. TG analysis of the complexes indicates that
removal of ligand proceeds in a single step with
The magnetic moment for complex I was found to
be 1.23 μ , which indicates that one unpaired electron
B
is present in the complex. Hence cobalt complex is
paramagnetic in nature and geometry of the complex
8
4.98% mass loss and remaining 15.02% residual is square planar. The effective magnetic moment
mass, which can be attributed to the formation of (0.0 μ ) of complex II clearly confirms the absence of
B
metal oxides. Complexes showed complete decompo- unpaired electrons and indicates the complex to be
sition at ≥450°C. The absence of peak from 100 to square planar [21].
212
100
80
256
L
2
52
I
60
I
3
69
II
4
0
0
0
3
87 470
II
484
2
1
00 200 300 400 500 600 700
Temperature, °C
200
300
400
500
600
700
Wavelength, nm
Fig. 2. UV-Vis spectra of ligand and complexes I, II.
Fig. 3. TG curve of complexes I and II.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 44 No. 1 2018

6
ANSARI et al.
Table 3. Effect of solvent on Suzuki coupling 4-bromben-
The reaction between 4-bromobenzonitrile and
phenylboronic acid were chosen for the optimization
studies. Significant parameters affecting the reaction
such as solvent, alkalinity, catalyst loading and the
reaction time were screened for optimization.
zonitrile with phenylboronic acid*
Conversion, %**
Entry
Solvent
Base Time, h
I
II
1
2
3
4
5
DMF
52
67
65
80
82
60
80
76
81
88
(i) effect of solvent. The activities of the synthesized
complex (I and II) for the coupling of 4-bromobenzo-
nitrile with phenylboronic acid was studied using dif-
Toluene
THF
K CO3
8
2
ferent solvents such as DMF, toluene, THF, CH CN,
3
CH CN
3
and 1,4-dioxane (Table 3). Reaction temperatures
were set at the reflux temperature of the chosen sol-
vent respectively. K CO was used as the base and 0.02
1,4-Dioxane
2
3
*
Reaction conditions: aryl halide (1.0 mmol), phenylboronic
acid (1.5 mmol), K CO (2.0 mmol), catalyst (0.02 mmol),
solvent (2 mL), 8 h.
* Yield determined by GC.
mmol catalyst I/II were used for the reaction. Dioxane
as a solvent media showed increased catalytic activity
with the yield output 82% for I and 88% for II, fol-
lowed by acetonitrile which also showed a consider-
able yield output. Other solvents supported the cou-
pling reaction to a substantially lesser extent. Dioxane
was chosen as an ideal solvent for carrying out the
reactions owing to its involvement in enhancing the
coupling yield.
2
3
*
Table 4. Effect of various base on Suzuki coupling of 4-bro-
mobenzonitrile with phenylboronic acid in 1,4-dioxane*
Conversion, %**
Entry Base
Solvent Time, h
I
II
88
78
72
76
63
(
ii) effect of base. Alkalinity of the reaction media
for a Suzuki coupling reaction is significant as the base
plays an important role in the catalytic cycle by ini-
tially reducing the precatalyst to its active form and
further replacing the halide ion in the oxidative addi-
tion step. We investigated the effect of various bases for
our reaction by carrying out the chosen reaction using
different bases like K CO , Na CO , Et N, Cs CO ,
1
2
3
4
5
K CO3
82
75
70
71
60
2
Na CO3
2
1
,4-Diox-
ane
Cs CO3
8
2
t
KO Bu
Et N
3
2
3
2
3
3
2
3
t
and KO Bu. Highest yield obtained was with K CO
*
Reaction conditions: aryl halide (1.0 mmol), phenylboronic
acid (1.5 mmol), catalyst (0.02 mmol), solvent (2 mL), 8 h.
* Yield determined by GC.
2
3
(Table 4, entry 1) whereas the other bases were less
effective in enhancing the catalytic conversion. K CO
*
2
3
was chosen as the optimal base for all further reac-
Table 5. Effect of catalyst concentration on Suzuki cou- tions.
pling of 4-bromobenzonitrile with phenylboronic acid*
(
iii) effect of catalyst concentration. To study the
Conversion,
Amount
effect of catalyst concentration on the reaction, cata-
lyst ratio was varied from 0.01 to 0.03 mmol (Table 5).
The increase in the catalytic yield was observed up to
Time,
h
%
**
Entry of catalyst Solvent
Base
(
mmol)
I
II
0
.02 mmol of the respective catalyst. The further
1
2
3
0.01
0.02
0.03
60
82
80
62
88
88
increase at 0.03 mmol showed a slightly reduced yield
for I, and a constant yield for II (Table 5, entries 2
and 3). Optimum catalyst loading was therefore final-
ized as 0.02 mmol of catalyst I/II.
(iv) effect of reaction time. The dependence
of product yield on reaction time for the coupling of
1
,4-Diox-
ane
K CO3
8
2
*
Reaction conditions: aryl halide (1.0 mmol), phenylboronic
acid (1.5 mmol), K CO (2.0 mmol), solvent (2 mL), 8 h.
2
3
*
* Yield determined by GC.
4-bromobenzonitrile with phenylboronic acid was
checked by analyzing the reaction mixture at regular
intervals of the time under same reaction condition.
The apparent increase in the product yields using both
catalysts I and II were noticeable until 8 h of the reac-
tion after which there was negligible change in the
yield (Fig. 4).
ESI MS data of ligand and complexes I and II are
given below:
Compound
Observed mass
Expected mass
L
I
II
317.10
373.00
373.10
316.12
373.04
372.04
All further cross-coupling reactions between phen-
ylboronic acid and different aryl halides were carried
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
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AIR-STABLE COBALT(II) AND NICKEL(II) COMPLEXES
7
100
N
M
O
O
N
(
II)
9
0
0
0
0
II
I
(a)
1
8
7
6
2 2
R B(OH) + K CO
3
N
1
2
R -R
N M OH
(
0)
2
R -X
(f)
OH
(
b)
R2
II)
R2
II)
(
e)
(c)
2
4
6
8
10
12
(
L
M
L
(
M
Time, h
R1
X
Fig. 4. Effect of reaction time on the yield of 4-cyanobi-
2
K CO
3
(
OH)2BCO3
phenyl.
(
L
d) (II) R2
KX
1
R B(OH)2
M
out with the optimized reaction conditions i.e, using
dioxane as a solvent and K CO as a base with a cata-
CO3
2
3
M = Co, Ni
lyst load of 0.02 mmol of catalyst I/II for a period of
h (Table 6).
8
Fig. 5. Proposed mechanism for cross coupling using pre-
The proposed mechanism for cross coupling is
pared complexes.
depicted in Fig. 5 for the synthesized metal−Schiff
base complex catalyzed reaction. The catalytic metal
M(II) Schiff base complex (a) which is the catalyst
precursor gets reduced to its catalytically active M(0)
form (b) initially in the presence of phenylboronic acid
halide ion and replace it with the anion of the base.
The forming intermediate (d) will further undergo
transmetalation with the phenylboronic acid to pro-
duce the organometal species (e). Reductive elimina-
tion of the coupled product (f) from (e) brings back the
original catalyst (b) which completes the catalytic
cycle.
and base (K CO ). The oxidative addition of metal
2
3
complex to the aryl halide forms the organometal spe-
cies (c). The base will then react with (c) to extract the
Table 6. Effect of catalyst on Suzuki coupling of aryl halide
Thus, we have synthesized nickel and cobalt Schiff
base complexes in a simple method to act as catalysts
for Suzuki–Miyaura coupling reaction. Characteriza-
tion disclosed the formation of the complexes. The
synthesized catalysts were successful in carrying out
Suzuki–Miyaura coupling reaction with only
with phenylboronic acid*
Yield**
Entry
R
X
I
II
1
2
3
4
5
6
7
8
9
OCH3
H
Br
60
35
82
80
70
51
44
50
68
85
64
45
88
82
71
55
44
58
72
90
0
.02 mmol catalyst being sufficient for the coupling
reaction. Type of substituent on the aryl halide highly
influenced the catalytic yield. The presence of elec-
tron with drawing groups enhanced the catalytic out-
put, while the electron donating groups ended with
low yield. The simple ligand and the low cost of nickel
and cobalt salts make these complexes complementary
to existing Pd catalysts and serve as potential non-
noble metal catalysts for organic transformations.
CN
COCH3
NHCOCH3
OH
CH3
F
OH
CN
I
ACKNOWLEDGMENTS
10
Authors would like to acknowledge DST (Depart-
ment of Science and Technology, Government of
India, New Delhi, India) for SCXRD analysis (pro-
*
Reaction conditions: aryl halide (1.0 mmol), phenylboronic
acid (1.5 mmol), catalyst (0.02 mmol), solvent (2 mL), 8 h.
*
* Yield determined by GC.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 44 No. 1 2018

8
ANSARI et al.
cured under FIST program). Ms. R.M. Ansari and 11. Dai, Z., Chen, F., Sun, Q., et al., Chin. J. Catal., 2016,
vol. 37, no. 1, p. 54.
Mrs. L.M. Kumar are thankful to NITK Surathkal for
1
1
2. Cooper, A.I., J. Mater. Chem., 2000, vol. 10, p. 207.
3. Chen, X., Engle, K.M., Wang, D.H., et al., Angew.
Chem. Int. Ed., 2009, vol. 48, p. 5094.
providing research fellowship.
REFERENCES
. Cozzi, P.G., Chem. Soc. Rev., 2004, vol. 33, p. 410.
1
4. Miyaura, N., Yanagi, T., and Suzuki, A., Synth. Com-
mun., 1981, vol. 11, p. 513.
1
2
. Gupta, K.C. and Sutar, A.K., Coord. Chem. Rev., 2008, 15. Arndtsen, B.A., Chem. Eur. J., 2009, vol. 15, p. 302.
vol. 252, p. 1420.
16. Ronson, T.O., Taylor, R.J.K., and Fairlamb, I.J., Tet-
3
4
5
6
7
8
9
. Che, C.M. and Huang, J.S., Coord. Chem. Rev., 2003,
rahedron, 2015, vol. 71, p. 989.
vol. 242, p. 97.
17. Sheldrick, G.M., SHELXS-97,Program for the Refine-
ment of Crystal Structures, Göttingen: Univ. of Göttin-
gen, 1997.
. Jin, X.D., Han, G.C., Liang, H.M., et al., Russ. J.
Coord. Chem., 2016, vol. 42, no. 8, p. 539.
. Shi, D.H., You, Z.L., Xu, C., et al., Inorg. Chem. Com- 18. Garga, B.S., Singh, P.K., and Sharma, J.L., Synth.
mun., 2007, vol. 10, no. 4, p. 404.
React. Inorg. Met.-Org. Chem., 2000, vol. 30, p. 803.
. Pouralimardan, O., Chamayou, A.C., Janiak, C., et al., 19. Chandra, S. and Kumar, U., Spectrochim. Acta, A,
Inorg. Chim. Acta, 2007, vol. 360, no. 5, p. 1599.
2005, vol. 62, p. 940.
. Parashar, R.K., Sharma, R.C., Kumar, A., et al., Inorg. 20. Temel, H. and S, ekerci, M., Synth. React. Inorg. Met.-
Chim. Acta, 1988, vol. 151, p. 201.
Org. Chem., 2001, vol. 31, p. 849.
. Ali, M.A., Mirza, A.H., Butcher, R.J., et al., J. Inorg. 21. Rashad, M.M., Hassan, A.M., Nassar, A.M., et al.,
Biochem., 2002, vol. 92, no. 3, p. 141.
Appl. Phys., A, 2014, vol. 117, p. 877.
. Neelakantan, M.A., Rusalraj, F., Dharmaraja, J., et al., 22. Tümer, M., Köksal, H., and Serin, S., Synth. React.
Spectrochim. Acta, A, 2008, vol. 71, no. 4, p. 1599.
Inorg. Met.-Org. Chem., 1997, vol. 27, p. 775.
1
0. Kozhevnikov, I.V., Catal. Rev., 1995, vol. 37, no. 2, 23. Cristóvão, B., J. Serb. Chem. Soc., 2011, vol. 76,
p. 311.
p. 1639.
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Vol. 44
No. 1
2018