Nickel(II) complexes containing ONS donor ligands: Synthesis, characterization, crystal structure and catalytic application towards C-C cross-coupling reactions

Article abstract of DOI:10.1007/s12039-015-0811-4

Nickel(II) complexes containing thiosemicarbazone ligands [Ni(L)₂] (1-3) (L = 9,10-phenanthrenequinonethiosemicarbazone (HL₁), 9,10-phenanthrenequinone-N-methylthio semicarbazone (HL₂) and 9, 10-phenanthrenequinone-N-phenylthiosemicarbazone (HL₃)) have been synthesized and characterized by elemental analysis and spectroscopic (IR, UV-Vis, ¹H, ¹³C-NMR and ESI mass) methods. The molecular structures of complexes 1 and 2 were identified by means of single-crystal X-ray diffraction analysis. The analysis revealed that the complexes possess a distorted octahedral geometry with the ligand coordinating in a uni-negative tridentate ONS fashion. The catalytic activity of complexes towards some C-C coupling reactions (viz., Kumada-Corriu, Suzuki-Miyaura and Sonogashira) has been examined. The complexes behave as efficient catalysts in the Kumada-Corriu and Sonogashira coupling reactions rather than Suzuki-Miyaura coupling. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s12039-015-0811-4

c
J. Chem. Sci. Vol. 127, No. 4, April 2015, pp. 597–608. ꢀ Indian Academy of Sciences.
DOI 10.1007/s12039-015-0811-4
Nickel(II) complexes containing ONS donor ligands: Synthesis,
characterization, crystal structure and catalytic application towards C-C
cross-coupling reactions
PANNEERSELVAM ANITHAa, RAJENDRAN MANIKANDANa, PARANTHAMAN VIJAYANa,
GOVINDAN PRAKASHa, PERIASAMY VISWANATHAMURTHIa,∗ and RAY JAY BUTCHERb
aDepartment of Chemistry, Periyar University, Salem 636011, Tamil Nadu, India
bDepartment of Chemistry, Howard University, 525 College Street NW, Washington, DC 20059, USA
e-mail: viswanathamurthi72@gmail.com
MS received 23 July 2014; revised 28 November 2014; accepted 28 November 2014
Abstract. Nickel(II) complexes containing thiosemicarbazone ligands [Ni(L)2] (1-3) (L = 9,10-phenanthre-
nequinonethiosemicarbazone (HL1), 9,10-phenanthrenequinone-N-methylthio semicarbazone (HL2) and 9,
10-phenanthrenequinone-N-phenylthiosemicarbazone (HL3)) have been synthesized and characterized by elemental
1
analysis and spectroscopic (IR, UV-Vis, H, 13C-NMR and ESI mass) methods. The molecular structures of
complexes 1 and 2 were identified by means of single-crystal X-ray diffraction analysis. The analysis revealed
that the complexes possess a distorted octahedral geometry with the ligand coordinating in a uni-negative tri-
dentate ONS fashion. The catalytic activity of complexes towards some C–C coupling reactions (viz., Kumada-
Corriu, Suzuki-Miyaura and Sonogashira) has been examined. The complexes behave as efficient catalysts in
the Kumada-Corriu and Sonogashira coupling reactions rather than Suzuki-Miyaura coupling.
Keywords. Nickel(II) complexes; X-ray structure; Kumada-Corriu reaction; Suzuki reaction; Sonogashira
reaction.
development of organic reactions,15 rather than the
catalytically active noble metals such as ruthenium,
rhodium and palladium.16
1. Introduction
Schiff bases are an important class of ligands in coor-
dination chemistry and they find extensive applications
in different fields. Schiff bases readily coordinate with
a wide range of transition metal ions, yielding stable
and intensely coloured metal complexes, which exhibit
interesting physical, chemical, biological and catalytic
properties.1–7 The Schiff bases derived from thiosemi-
carbazone are well known polydentate ligands which
can bind to the transition metal ions either in its neutral
or anionic form and the resulting transition metal com-
plexes have been receiving considerable interest largely
because of their bioinorganic relevance. Metal com-
plexes with an ONS donor set are of much interest
because of their potential applications in fundamental
and applied sciences, especially in coordination chem-
istry, due to their diverse roles in metallo-enzymes,
varied catalytic and pharmacological properties.8–10
There have been many reports on activity of Schiff
base complexes in homogeneous and heterogeneous
catalysis.11–14 The first-row late transition metals such
as iron, cobalt, nickel and copper are now the most
important transition metals used as catalysts in the
The carbon-carbon bond forming reaction is one of
the simple and versatile method in organic synthesis.
During the last three decades, advances in transition
metal catalysis made it possible to couple an organic
electrophile with an organometallic nucleophile with
high efficiencies and broad substrate scopes. The
Kumada-Corriu coupling of an aryl halide with Grig-
nard reagents is the first cross-coupling reaction for
forming a carbon-carbon bond which is a power-
ful method for constructing diverse variety of biaryl
compounds.17 This is an important industrial approach
applied for the synthesis of photonic materials, poly-
mers, pharmaceuticals, agrochemicals and a variety of
homogeneous ligands. Moreover, Kumada-Corriu reac-
tions are performed at or near room temperature and
thus reducing energy costs. Similarly, the transition
metal catalyzed Suzuki-Miyaura coupling reaction in
which phenylboronic acid and aryl halides are used
to produce unsymmetrical biaryl units which have a
wide range of applications such as drugs, herbicides,
natural products as well as in engineering.18–22 On
the other hand, the Sonogashira coupling of terminal
alkyne with aryl and alkenyl halides is one of the most
∗For correspondence
597

598
Panneerselvam Anitha et al.
powerful and straightforward methods for the forma- 2.2 Synthesis of nickel(II) complexes
tion of C(sp)-C(sp2) bonds in organic synthesis. This
method has been widely employed in the synthesis
of natural products, biologically active molecules and
materials science.23–25
2.2a [Ni(L1)2].DMF (1): An ethanolic solution (10
mL) containing HL1 (0.1 mmol) was added to
[NiCl2(PPh3)2] (0.1 mmol) in ethanol (10 mL) and
the resulting red-coloured solution was refluxed for
4 h. On cooling the contents to room temperature
through overnight, the coloured complex separated out.
It was filtered off and recrystallized from ethanol.
Red-coloured crystals, suitable for single crystal X-ray
diffraction analysis, were obtained by slow evaporation
of DMF solution of compound. Yield: 88% M.p: 218◦C.
Anal. Calc. for C33H27N7O3NiS2: C, 57.24; H, 3.93;
N, 14.16; S, 9.26. Found: C, 57.47; H, 3.74; N, 14.33;
S, 9.50% IR (KBr, cm−1): 1605 (quinone C=O), 1578
(C=N), 1557 (C=N), 752 (C-S). UV-Vis (λmax/nm):
Based on the above facts and in continuation of our
effort to develop efficient transition metal catalysts,
herein we have chosen nickel as the metal centre to
interact with thiosemicarbazones. One reason behind
the choice of this particular metal centre is its ability
to take up different coordination environments (such
as octahedral, square-planar and tetrahedral), which
makes its coordination chemistry very interesting and
also may facilitate different steps of catalytic cycle.
The other and more attractive reason is that the demon-
strated ability of complexes to catalyze C–C cross-
coupling reactions.26–30 Thus, the primary objective of
the present work has been to prepare nickel complexes
of thiosemicarbazones and find out the binding mode of
thiosemicarbazones in the complexes. The other objec-
tive has been to explore catalytic properties of the com-
plexes against Kumada-Corriu, Suzuki-Miyaura and
Sonogashira coupling reactions.
1
524, 440, 331, 273. H NMR (DMSO-d6, ppm): 9.37
(s, 2H, NH2),7.30–8.02 (m, 16H, Ar-H). 13C NMR
(DMSO-d6, ppm): 180.2 (quinone C=O), 171.1 (C-S),
164.8 (C=N), 124.8–137.2 (Ar-C). ESI-MS (m/z) =
619.2 [M+].
2.2b [Ni(L2)2] (2): It was prepared using the same
procedure as described for 1 with HL2 (0.1 mmol)
and [NiCl2(PPh3)2] (0.1 mmol). Red coloured crystals,
suitable for single crystal X-ray diffraction analysis,
were obtained by slow evaporation of DMF solution
of compound. Yield: 85% M.p.: 212◦C. Anal. Calc.
for C32H24N6O2NiS2: C, 59.37; H, 3.74; N, 12.98; S,
9.91. Found: C, 59.17; H, 3.59; N, 12.75; S, 9.78% IR
(KBr, cm−1): 1614 (quinone C=O), 1596 (C=N), 1566
(C=N), 754 (C-S). UV-Vis (λmax/nm): 522, 437, 324,
265. 1H NMR (DMSO-d6 ppm): 8.38 (s, 1H, NH-CH3),
6.92–8.08 (m, 16H, Ar-H), 2.96 (s, 3H, CH3). 13C NMR
(DMSO-d6, ppm): 179.6 (quinone C=O), 169.8 (C-S),
160.2 (C=N), 124.2–138.1 (Ar-C), 30.4 (CH3) ESI-MS
(m/z) = 647.0 [M+].
2. Experimental
2.1 Materials and methods
All the reagents used were chemically pure and AR
grade. The solvents were purified and dried according
to standard procedures. The ligands HL1−3 and starting
complex [NiCl2(PPh3)2] were prepared according to lit-
erature procedures.31,32 Microanalysis of carbon, hydro-
gen, nitrogen and sulfur was carried out using Vario EL
III Elemental analyzer at SAIF - Cochin India. The IR
spectra of the ligand and their complexes were recorded
as KBr pellets on a Nicolet Avatar model spectropho-
tometer in 4000–400 cm−1 range. Electronic spectra of
the complexes have been obtained in dichloromethane 2.2c [Ni(L3)2] (3): It was prepared using the same
using a Shimadzu UV - 1650 PC spectrophotometer procedure as described for 1 with HL3 (0.1 mmol)
1
in 800–200 nm range. H and 13C NMR spectra were and [NiCl2(PPh3)2] (0.1 mmol). Redcoloured solid
measured in Jeol GSX - 400 instrument using DMSO- obtained. Our efforts to obtain single crystal of the
1
d6 as the solvent. H NMR and 13C NMR spectra complex were unsuccessful. Yield: 80%, M.p: 215◦C.
were obtained at room temperature using TMS as the Anal. Calc. for C42H28N6O2NiS2: C, 65.38; H, 3.66; N,
internal standard. The ESI-MS spectra were performed 10.89; S, 8.31. Found: C, 65.16; H, 3.86; N, 10.71; S,
by LC-MS Q-ToF Micro Analyzer (Shimadzu) in the 8.54%. IR (KBr, cm−1): 1602 (quinone C=O), 1572
SAIF, Panjab University, Chandigarh. Melting points (C=N), 1548 (C=N), 753 (C-S). UV-Vis (λmax/nm):
1
were checked on a Technico micro heating table and 499, 417, 314, 281. H NMR (DMSO-d6, ppm): 11.22
were uncorrected. The catalytic yields were determined (s, 1H, NH-C6H5), 6.74–8.71 (m, 26H, Ar-H). 13C NMR
using ACME 6000 series GC-FID with DP-5 column (DMSO-d6 ppm): 182.1 (quinone C=O), 171.4 (C-S),
of 30 m length, 0.53 mm diameter and 5.00 μm film 161.1 (C=N), 123.5-135.8 (Ar-C). ESI-MS (m/z) =
thickness.
771.2 [M+].

Nickel(II) thiosemicarbazone complexes
599
2.3 X-ray crystallography
water and extracted with ether for three times. The
organic phase thus collected was dried with Na2SO4,
filtered and analyzed by GC. GC yield was determined
based on the amount of aryl halide employed using
n-dodecane as an internal standard.
Crystal data were collected on an Oxford/Agilent
Gemini diffractometer. Structures were solved using the
direct methods program SHELXL.33 All non-solvent
heavy atoms were located using subsequent differ-
ence Fourier syntheses. The structures were refined
against F2 with the program SHELXL,34 in which all
data collected were used including negative intensities.
All nonsolvent heavy atoms were refined anisotropi-
cally. All non-solvent hydrogen atoms were idealized
using the standard SHELXL idealization methods.
3. Results and Discussion
Reactions of HL1−3 and [NiCl2(PPh3)2] in 1:1 molar
ratio (scheme 1) were carried out in ethanolic solution
with the expectation that to yield a four coordinated
complexes (product 1). Unexpectedly, the phenan-
threnequinone N(4)-substituted thisemicarbazone lig-
ands (HL1−3) involved in this work deceived all our
expectations and formed stable six coordinated metal
chelates with 1:2 metal-ligand stoichiometry (prod-
uct 2). Reactions were also conducted changing sol-
vents as well as the molar ratios of ligands in order
to obtain the desired complexes, but in all the cases
only [Ni(L)2] was obtained. The complex [Ni(L1)2] was
also obtained by the reaction of NiCl2·6H2O with HL1
(molar ratio of NiCl2·6H2O:HL1 = 1:2) in ethanol.35
The isolated complexes were stable in air, in addi-
tion to being soluble in common organic solvents such
as dichloromethane, chloroform, benzene, acetonitrile,
ethanol, methanol, dimethylformamide and dimethyl-
sulfoxide. All the complexes were structurally char-
acterized by elemental analysis, IR, electronic, NMR
and ESI-Mass spectra. In addition, single crystal of
complexes 1 and 2, used to determine its molecular
structures by X-ray crystallographic analysis, which is
shown in figure 1 and 2.
2.4 Aryl–aryl coupling reaction
2.4a Kumada-Corriu reaction: Aryl halide (10
mmol) was added to catalyst (0.2 mol%) in 5 mL
diethyl ether. Phenylmagnesium chloride (10 mmol)
was then added dropwise and the reaction mixture
was stirred for 4 h at room temperature. Then the
reaction was ended by addition of water. The mixture
was extracted with ethyl acetate and the obtained
organic layer was dried over MgSO4. The crude mix-
ture was analyzed by gas chromatography and then
purified by column chromatography on silica gel to
afford the desired product. The conversion percentage
was determined against the remaining aryl halide. In
addition, the isolated product was characterized by
1H NMR.
2.4b Suzuki-Miyaura reaction: To a mixture of aryl
halide (1 mmol), phenylboronic acid (1.5 mmol) and
K2CO3 (1 mmol) in dimethylacetamide (4 mL) was
added the catalyst (1 mol%) as a dimethylacetamide
solution (1 mL). The resultant mixture was then heated
at 90◦C for 7 h. Then, the mixture was cooled, water
was added and the product was extracted with ethyl
acetate. The organic layer was washed with brine,
dried over Na2SO4, filtered, passed through celite, and
analyzed by GC. GC yields were obtained based on
corresponding aryl halide. The isolated yield was char-
acterized by 1H NMR.
3.1 X-ray crystallography
The complexes 1 and 2 crystallize in a triclinic and
monoclinic system with space group P-1, C2/c respec-
tively. Crystal details, crystallographic data and refine-
ment were summarized in table 1. Selected bond
lengths and bond angles have been reported in table 2.
In both the complexes, the nickel(II) atom was coordi-
nated with two ligand molecules. The complex 1 was
associated with one molecule of dimethylformamide
solvent in the crystal lattice. The two ligand molecules
in this complexes are deprotonated at the imino nitrogen
2.4c Sonogashira coupling reaction: The aryl halide N(2), resulting in two tridentate mono-anionic species
(1 mmol) and phenyl acetylene (1.5 mmol) were added coordinating to the central metal via the thiolato sul-
to methanol solution (5 mL) of catalyst (0.5 mol%), fur, imine nitrogen and the oxygen of the quinone car-
copper(I) iodide (0.5 mol%) and pyridine (1 mmol) in bonyl, resulting in a distorted octahedral moiety. Elon-
a glass flask with vigorous stirring. The mixture was gation of the C(15)-S(1) bond from 1.6705–1.6782 Å in
stirred at 70◦C for 4 h under aerobic conditions. The the ligands to 1.6947–1.704 Å in the nickel complexes
mixture was cooled to room temperature, diluted with was indication of the deprotonation of ligands upon

600
Panneerselvam Anitha et al.
H
N
C
N
O
Ni
H
Cl
N
R
S
[NiCl2(PPh3)2]
+
Product 1
O
S
N
C
H
Ethanol
N
H
N
R
Reflux 4 h
R
N
N
H
C
S
N
R = H (HL1); CH3 (HL2) or C6H5 (HL3)
O
Ni
O
S
N
C
H
N
N
R
Product 2
Scheme 1. Synthesis of Ni(II) 9,10-phenanthrenequinone N-substituted thiosemicarbazone complexes.
complexation and charge delocalization in the thiosemi- 3.2 Infrared spectra
carbazone side chain. The Ni-N, Ni-S and Ni-O bond
distances were comparable with those found in other The ligands behave as monoanionic tridentate, moiety
nickel thiosemicarbazones.36
forming two five-membered chelate rings around the
Figure 1. ORTEP view of complex 1

Nickel(II) thiosemicarbazone complexes
601
Figure 2. ORTEP view of complex 2
Table 1. Crystal data and structure refinement of the complexes 1 and 2.
1
2
Empirical formula
Formula weight
C33H27N7NiO3S2
692.44
0.45x0.33x0.29
100(2)
C32H24N6NiO2S2
647.40
0.39x0.35x0.24
120(2)
Crystal dimensions (mm3)
Temperature (K)
Wavelength (Å)
Crystal system
0.71073
Triclinic
0.71073
Monoclinic
C2/c
Space group
P-1
Unit cell dimensions (Å, ◦)
a = 10.3167(16)
b = 11.0978(17)
c = 13.564(2)
α = 105.216(2)
β = 90.618(2)
γ = 96.006(2)
1489.1(4)
a = 20.5380(3)
b = 11.5610(2)
c = 13.5606(2)
α =90
β = 93.2193(14)
γ = 90
Volume (Å3)
Z
3214.75(9)
4
2
Calculated density (Mg/m3)
Absorption coefficient (mm−1
F(000)
1.544
0.841
716
1.338
0.771
1336
3.512 to 41.269
Multi-scan
)
Theta range for data collection (◦)
Absorption correction
1.914 to 31.324
Multi-scan
Refinement method
Full-matrix least-squares on F2
8480/0/418
Full-matrix least-squares on F2
10544/0/200
Data/restraints/parameters
Goodness-of-fit on F2
1.063
1.088
R indices [I>2 σ(I)]
R1 = 0.0524, wR2 = 0.1250
R1 = 0.0794, wR2 = 0.1435
1.104 and −0.723
R1 = 0.0285, wR2 = 0.0810
R1 = 0.0340, wR2 = 0.0844
0.624 and −0.642
R indices (all data)
Largest difference in peak and hole (e.Å−3
)

602
Panneerselvam Anitha et al.
Table 2. Selected bond lengths (Å) and angles (◦) of the
complexes 1 and 2
and the shoulder at 499–533 nm was attributed to a
forbidden d → d transition.42,43
1
2
3.4 NMR spectra
Ni-N(1A)
Ni-N(1B)
Ni-O(1A)
Ni-O(1B)
Ni-S(1A)
Ni-S(1B)
2.012(3)
2.022(3)
2.073(3)
2.071(2)
2.3663(11)
2.3595(10)
1.704(4)
1.707(3)
1.370(5)
1.356(4)
175.91(10)
78.90(11)
104.01(11)
104.42(11)
78.85(11)
84.78(9)
94.35(8)
82.79(8)
91.04(8)
159.55(8)
83.33(9)
94.17(9)
160.45(8)
91.87(8)
98.41(3)
2.0243(5)
2.0243(5)
2.0832(5)
2.0832(5)
2.37228(19)
2.37228(19)
1.6947(6)
1.6947(6)
1.3859(8)
1.3859(8)
179.00(3)
78.438(19)
100.84(2)
100.84(2)
78.438(19)
89.28(3)
97.583(16)
83.100(15)
91.333(16)
161.306(13)
83.102(15)
97.583(16)
161.307(13)
91.332(16)
94.004(11)
The 1H NMR spectra of the ligands and the correspond-
ing nickel(II) complexes were compared to confirm the
presence of coordinated ligand in the complexes. The
presence of singlet at 14.41–14.81 ppm was assigned
to hydrazinic N-H proton which indicates that the lig-
ands exist in thionic forms. The peak disappears in the
spectra of complexes, which was consistent with depro-
tonation of these ligands upon metal complexation. The
terminal NH2 protons in the ligand HL1 were mag-
netically non-equivalent and have two singlets at 9.07,
9.36 ppm. These protons became equivalent upon for-
mation of complexes and were observed as singlet at
9.40 ppm. The ligands HL2, HL3 and their correspond-
ing complexes showed singlet in the region 8.35–11.22
ppm which was assigned to terminal NH-CH3 and NH-
C6H5 protons. In the spectra of all the complexes, the
multiplet observed around 6.74–8.81 ppm was assigned
to aromatic protons of the ligands. Further, the methyl
protons appeared at 2.96 ppm. The 1H NMR spectra of
complexes 1-3 was shown in figures S1–S3.
C(15A)-S(1A)
C(15B)-S(1B)
C(15A)-N(2A)
C(15B)-N(2B)
N(1A)-Ni-N(1B)
N(1A)-Ni-O(1A)
N(1B)-Ni-O(1A)
N(1A)-Ni-O(1B)
N(1B)-Ni-O(1B)
O(1B)-Ni-O(1A)
N(1A)-Ni-S(1B)
N(1B)-Ni-S(1B)
O(1A)-Ni-S(1B)
O(1B)-Ni-S(1B)
N(1A)-Ni-S(1A)
N(1B)-Ni-S(1A)
O(1A)-Ni-S(1A)
O(1B)-Ni-S(1A)
S(1B)-Ni-S(1A)
The 13C NMR spectra of the complexes have showed
a peak at 179.6–182.1 ppm region which was assigned
to quinone carbonyl (C=O) carbon. The azomethine
(C=N) carbon exhibits peak in the region of 160.2–
164.8 ppm. In addition, the presence of peak in the
region 169.8–171.4 ppm was assigned to C-S carbon.
The appearance of sharp singlet at 30.4 ppm was
assigned to methyl carbon. The aromatic carbons
appeared in the region of 123.5–138.1 ppm. The 13C
NMR spectra of complexes 1–3 was shown in figures
S4–S6.
central metal through a donor atom set comprising of
the quinone carbonyl oxygen, imine nitrogen and the
thiolate sulfur as revealed from the corresponding shifts
in IR frequencies of the respective vibrations.37 The
bands assigned to azomethine (C=N) and quinone car-
bonyl (C=O) vibrations appeared at 1596–1598 and
1630–1634 cm−1 respectively in the spectra of free lig-
ands were shifted to lower wave numbers in the spectra
of complexes while the bands at 3111–3148 and 807–
843 cm−1 ascribed to the υ(N-H), υ(C=S) stretching
vibrations respectively in the spectra of ligands disap-
peared on metal complexation, confirming the thioeno-
lization nature of the ligands and subsequent coordina-
tion through the deprotonated sulfur.38–40 This fact was
further confirmed by the appearance of two new bands
in the range 1572–1596 cm−1 and 752–754 cm−1 that
corresponds to υ(C=N–N=C) and υ(C-S) stretching
vibrations respectively.41
3.5 Mass Spectra
ESI-Mass spectral analysis of the complexes was stud-
ied in order to confirm the molecular masses of the
complexes. The m/z values of the molecular ion peaks
for the complexes 1–3 were obtained at 619.2 [M-
DMF]+, 647.0 and 771.2 [M+] respectively. The calcu-
lated molecular masses corresponds to these complexes
are 619.34, 647.40 and 771.53. The obtained molec-
ular masses were in good agreement with that of the
calculated molecular masses. The ESI mass spectra of
complexes 1–3 was shown in figures S7–S9.
3.3 Electronic spectra
The electronic spectra of the nickel(II) complexes dis-
played four bands in the region around 260−533 nm.
The bands at 260–281 nm can be ascribed to an intrali-
3.6 Kumada-Corriu coupling reaction
gand transition (π-π* and n-π*). The band appeared in In order to find optimal reaction conditions, the influ-
the region 308–440 nm has been assigned to an LMCT, ence of time, solvent and the catalyst concentration on

Nickel(II) thiosemicarbazone complexes
603
the yield were investigated. Our initial studies were from 0.005 to 0.03 mmol in diethyl ether under similar
carried out with 4-bromoanisole as standard substrate reaction conditions. The yield increased with increase
using complex 1 as catalyst. The first set reactions were in catalyst loading and reaches to the highest value of
run with constant concentration of catalyst (0.03 mmol) 83% with 0.02 mmol of catalyst (figure S11).
at various time intervals in different solvents. The best
Under the optimized conditions, we next tried to
conversion was observed in diethyl ether and the least extend the Kumada-Corriu coupling reactions to var-
conversion was observed in benzene at 4 h (figure S10). ious aryl halides and the results are summarized in
Next, we focused the effect of catalyst concentration table 3. The coupling reactions were performed well
on the catalyst activity. The catalyst amount was varied for all the substrates examined and gave moderate to
Table 3. Kumada-Corriu reaction of aryl halide with phenylmagnesium chloride by nickel(II)
complexes.
Catalyst (0.2 mol%)
+
R
MgCl
R
X
Ether, 4 h
Conversion (%)a
2 3
Entry
Aryl halide
Product
1
H3C
Cl
H3C
1
2
3
82
84 (76)b
88
80(73)b
81
77 (70)b
80 (71)b
85
H3CO
Br
H3CO
HOOC
OHC
NC
Br
HOOC
OHC
NC
87 (76)b
Cl
4
5
86 (77)b
91
84
88
83
86
Cl
O2N
Br
O2N
6
7
8
93
82
80
89
79 (70)b
78
88
77
75
Br
N
N
N
N
Cl
I
N
N
OCH3
OCH3
9
64
61
60
59
57
55
F
CHO
CHO
10
aThe conversion is determined by GC.
bIsolated yield is given in parenthesis.

604
Panneerselvam Anitha et al.
excellent yields. As shown in table 3, aryl halide con- catalyst:substrate ratio of 1:100 was the best suitable
taining electron withdrawing substituents were found
to proceed slightly higher yield than those with
electron-donating substituents. For example, higher
yield (entries 3–6) was obtained for aryl halide bearing
electron withdrawing group relative to those of elec-
tron donating ones (entries 1, 2). In addition, hetero
aromatic halides also undergo coupling reactions and
provided the coupled products in higher yield (entries
7, 8). The coupling reaction of aryl halide bearing ortho
substituents gave moderate conversions as a result of
steric hindrance. For instance, the coupling reaction of
2-iodoanisole (entry 9) and 2-flurobenzaldehyde (entry
10) with phenylmagnesium chloride gave the conver-
sion of 55–64%. Remarkably, the conversion of aryl
halides to biaryls proceeded efficiently in the present
catalytic system. Moreover, the present catalytic system
works at mild reaction conditions with low reaction
time and the efficiency in terms of the yield of products
was higher than the existing catalytic systems.26–30
for the catalytic C-C coupling reaction. We further eval-
uated the effect of solvents and bases on the reaction.
The highest yield of coupled product was obtained
in dimethylacetamide (DMAc) in presence of K2CO3
base (entries 8, 16). So, based on the results above,
we selected K2CO3 as the base and DMAc as solvent
with C:S ratio of 1:100 as the best conditions for the
Suzuki-Miyaura reaction.
Under the optimized reaction conditions, coupling of
various aryl halides with phenylboronic acid were car-
ried out in presence of synthesized nickel complexes
and the conversion of coupled products were given in
table 5. As shown in table 5 (entries 1–6), many func-
tional groups have been tolerated in the present cat-
alytic system. The coupling reaction of aryl halides
bearing an electron donating group, such as CH3 and
OCH3, with phenylboronic acid produced biaryls in
moderate yields (52–64%) (entries 1, 2). Similarly elec-
tron deficient aryl bromides, such as 4-bromobenzoinc
acid, 4-chlorobenzaldehyde, 4-chlorobenzonitrile and
4-nitro-1-bromobenzene reacted with phenylboronic
acid to produce biaryls in moderate yield, ranging
from 47 to 61% (entries 3–6) under the same reac-
tion conditions. Using this methodology, the coupling
between phenylboronic acid and aryl halides that con-
tain electron-donating as well as electron-withdrawing
3.7 Suzuki-Miyaura coupling reaction
A brief optimization of experimental conditions for
the reaction of 4-bromoanisole with phenylboronic acid
using complex 1 as catalyst was given in table 4. First, the
reaction was conducted with different catalyst:substrate
(C:S) ratios. We started the C:S ratios from 1:25 to groups, proceeded moderately to afford the correspond-
ing products. When heterocyclic aryl halides were used
for cross-coupling with phenylboronic acid, a decrease
in the yield of product (between 24% and 32%)
was observed. For example, the lowest yield was
1:100, the reaction proceeds with reasonable conver-
sions (entries 1–4). When increasing the C:S ratio
from 1:150 to 1:250, the reaction still proceeds by
decrease in yield (entries 5–7). Thus, it concluded that
Table 4. Optimization of reaction conditions for the Suzuki-Miyaura coupling reaction.
Entry
Amount of substrate (mmol)
Solvent
Base
Conversion (%)b
1
2
3
4
5
6
7
8
0.25
0.5
0.75
1
1.5
2
2.5
1
1
1
1
1
1
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMAc
DMSO
Toluene
Methanol
THF
DMAc
DMAc
DMAc
DMAc
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
–
61
58
56
55
39
22
10
60
48
29
22
07
–
9
10
11
12
13
14
15
16
1
1
1
NaOH
KOH
K2CO3
48
42
64
aReaction conditions: Phenylboronic acid (1.5 mmol), 4-bromoanisole (1 mmol), base (1 mmol) and
solvent (5 mL), stirring for 7 h at 90◦C.
bGC yield.

Nickel(II) thiosemicarbazone complexes
605
Table 5. Suzuki-Miyaura coupling reaction of aryl halides with phenylboronic acid by nickel(II) complexes.
Catalyst (1 mol%)
K2CO3 (1 mmol)
+
B(OH)2
R
R
X
DMAc
7 h, 90 °C
Yield (%)a
2
Entry
Aryl halide
Product
1
3
H3C
Cl
H3C
1
2
3
4
5
6
58 (50)b
64 (55)b
56 (48)b
50
55
60 (50)b
54
52
57
51
47
53
53
H3CO
Br
H3CO
HOOC
HOOC
OHC
NC
Br
Cl
OHC
NC
49 (38)b
55
Cl
58
O2N
Br
O2N
61
57
Br
N
N
N
7
8
28
32
31
27
30
24
N
Cl
N
N
F
CHO
CHO
9
29
24
24
23
21
20
I
OCH3
OCH3
10
aGC yield.
bIsolated yield is given in parenthesis.
found in the reaction of 2-bromopyridine and 2- solvent and substrate concentration, we carried out
chloropyrimidine with phenylboronic acid (entries 7,
8). Similarly, the coupling reaction of aryl halide bear-
ing ortho substituents gave lower conversions as a result
of steric hindrance (entries 9, 10).
the reaction of 4-bromoanisole with phenylacetylene
using complex 1 as a test catalyst. First, several bases
were screened for the Sonogashira coupling reaction
(figure S12). The reaction works very well when
organic bases, such as Et3N, pyridine and piperidine
were used, with the best result obtained in the case of
pyridine as the base. However, the addition of inorganic
bases such as K2CO3, Cs2CO3, KOH, NaOH and K3PO4
resulted in poor to moderate yields. These results indi-
cate that organic bases were more favourable than
3.8 Sonogashira coupling reaction
The activity of the obtained nickel complexes was also
examined in the Sonogashira coupling. In order to opti-
mize the reaction condition with respect to time, base,

606
Panneerselvam Anitha et al.
inorganic ones because they effectively trap hydrogen moderate yield obtained. Moreover, there was no con-
halide formed in the reaction. siderable change of yield observed when increasing the
Next, the solvent effect on the reaction rate of cou- catalyst concentration beyond 0.5 mol%.
pling has been studied. In the present study methanol
With the optimized reaction conditions in hand,
was found to be more efficient for the conversion of the scope of the reaction with respect to other aryl
coupling products. On the other hand, acetonitrile and halides was investigated (table 6). The electron-rich
1,4-dioxane gave low yields while moderate yield was or electron-poor aryl bromides reacted with pheny-
obtained when ethanol used as a solvent (figure S13). lacetylene to generate the corresponding cross-coupling
Finally, the reaction was carried out at different concen- products in high yields (entries 1–3). We next investi-
tration of catalyst (figure S14). An excellent yield was gated the coupling of various aryl chlorides with ter-
obtained for 0.5 mol% of catalyst and it can be observed minal alkynes. As shown in table 6, moderate catalytic
that even at very low catalyst loading of 0.25 mol%, the activity was observed in the coupling of aryl chlorides
Table 6. Sonogashira coupling reactions of phenylacetylene and aryl halides.
Catalyst (0.5 mol%)
CuI (0.5 mol%)
+
R
X
R
Pyridine (1 mol%)
MeOH, 70 °C, 4 h
Conversion (%)a
2
Entry
1
Aryl halide
Product
1
3
H3CO
Br
Br
H3CO
HOOC
O2N
85
80
79
HOOC
2
3
4
5
6
86
83
62
57
59
82
79
59
56
55
77
74
56
51
53
O2N
OHC
NC
Br
Cl
OHC
NC
Cl
H3C
Cl
H3C
F
CHO
CHO
7
28
26
23
I
OCH3
OCH3
8
31
64
29
58
26
55
Br
Cl
N
N
N
19
N
N
N
10
62
57
52
aThe conversion is determined by GC.

Nickel(II) thiosemicarbazone complexes
607
possessing electrondonating and electronwithdrawing India [Grant No. 01(2437)/10/EMR-II] for financial
groups (entries 4–6). For ortho substituted aryl halides, support. One of the authors (PA) thanks CSIR for
relatively lower yields were obtained (entries 7, 8). the award of Senior Research Fellowship. The authors
Heteroaromatic compounds such as 2-bromopyridine wish to record grateful thanks to Dr. Matthias Zeller,
and 2-chloropyrimidine also reacted with phenylacety- Department of Chemistry, Youngstown State Univer-
lene to give moderate yield of cross-coupling products sity, Youngstown, USA for crystal data collections.
(entries 9, 10).
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