Synthesis, crystal structures, and application of two new pincer type palladium(II)-Schiff base complexes in C-C cross-coupling reactions

Article abstract of DOI:10.1016/j.ica.2017.11.018

Two new pincer type Pd(II)-Schiff base complexes of the general formula [PdL₁(PPh₃)] 1 and [PdL₂(PPh₃)] 2, (where L₁ = 2-(2,3-Dihydroxybenzylideneamino)phenolate and L₂ = 2-(2,3-dihydroxybenzylidene)hydrazinecarbothioamidate) were synthesised by the reaction of the palladium acetate with the corresponding ligand in methanol as yellow crystalline solids in high yields. Both complexes were fully characterized by FT-IR, ¹H NMR, ¹³C NMR, ³¹P NMR, elemental analysis and single crystal X-ray diffraction studies. The crystal structures confirmed the tridentate nature of the pincer type Schiff base ligands and the distorted square planar geometry around the metal centre in both cases. The triphenylphosphine acted as an auxiliary ligand and occupied the fourth coordination site at palladium. The complexes were found to be efficient homogenous catalysts for a series of Suzuki-Miyaura, Heck-Mizoroki and Sonogashira reactions at a low catalyst loading (0.08 mol%), and without the use of any additives. All organic products were fully characterized by ¹H and ¹³C NMR studies.

Full text of DOI:10.1016/j.ica.2017.11.018

Accepted Manuscript
Research paper
Synthesis, crystal structures, and application of two new pincer type palladi-
um(II)-Schiff base complexes in C-C cross-coupling reactions
Bhumika Agrahari, Samaresh Layek, Anuradha, Rakesh Ganguly, Devendra D.
Pathak
PII:
S0020-1693(17)31156-8
https://doi.org/10.1016/j.ica.2017.11.018
ICA 17988
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
26 July 2017
4 November 2017
10 November 2017
Please cite this article as: B. Agrahari, S. Layek, Anuradha, R. Ganguly, D.D. Pathak, Synthesis, crystal structures,
and application of two new pincer type palladium(II)-Schiff base complexes in C-C cross-coupling reactions,
Inorganica Chimica Acta (2017), doi: https://doi.org/10.1016/j.ica.2017.11.018
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Synthesis, crystal structures, and application of two new pincer type
palladium(II)-Schiff base complexes in C-C cross-coupling reactions
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Bhumika Agraharia, Samaresh Layeka, Anuradhaa, Rakesh Gangulyb, Devendra D. Pathaka*
aDepartment of Applied Chemistry, Indian Institute of Technology (ISM), Dhanbad-826004, India
bDivision of Chemistry & Biological Chemistry, Nanyang Technological University, Singapore 639798
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Email: ddpathak@yahoo.com
*Phone number: +91 9431126250
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Abstract
Two new pincer type Pd(II)-Schiff base complexes of the general formula [PdL1(PPh3)] 1 and
[PdL2(PPh3)] 2, (where L1= 2-(2,3-Dihydroxybenzylideneamino)phenolate and L2= 2-(2,3-
dihydroxybenzylidene)hydrazinecarbothioamidate) were synthesised by the reaction of the
palladium acetate with the corresponding ligand in methanol as yellow crystalline solids in
high yields. Both complexes were fully characterized by FT-IR, H NMR, 13C NMR, 31P
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NMR, elemental analysis and single crystal X-ray diffraction studies. The crystal structures
confirmed the tridentate nature of the pincer type Schiff base ligands and the distorted square
planar geometry around the metal centre in both cases. The triphenylphosphine acted as an
auxiliary ligand and occupied the fourth coordination site at palladium. The complexes were
found to be efficient homogenous catalysts for a series of Suzuki-Miyaura, Heck-Mizoroki
and Sonogashira reactions at a low catalyst loading (0.08 mol %), and without the use of any
additives. All organic products were fully characterized by 1H and 13C NMR studies.
Keywords: Pd(II) complex, crystal structure, homogenous catalyst, C-C cross-coupling
reaction
1. Introduction
Transition metals and their complexes have allured much interest and played a
significant role in catalysing various organic transformations [1]. Among these
transformations, the C-C coupling reactions [2] have been studied extensively owing to their
diverse applications as intermediates in the synthesis of various types of pharmaceuticals,
agrochemicals and natural products etc [3]. Pd-complexes have been used as versatile
catalysts in Suzuki-Miyaura, Heck-Mizoroki and Sonogashira reactions [4-5]. The coupling
of aryl halides with aryl boronic acids, alkenes and alkynes represent Suzuki-Miyaura, Heck-
Mizoroki and Sonogashira reactions, respectively [6]. Palladium complexes, containing a
variety of ligands, such as imidazole [7], pyridine [8], N-heterocyclic carbenes [9],
dibenzylideneacetone [10], palladacycles [11], thiols [12], porphyrins [13], phthalocyanines
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[14], phosphines [15] and pincer [16] have been successfully employed to carry out these
reactions. As compared to these ligands, Schiff base ligands are easy to synthesize, relatively
cheap and thermally and chemically stable [17]. Therefore, emphasis is given to use Schiff
base complexes in C-C bond formation reactions [18].
An ideal catalyst should be stable, selective, and active at a low concentration.
Moreover, it needs to be acquiescent to rational design of new catalyst, giving the possibility
for upgrading the catalytic properties of the metal centre. These features of a catalyst can be
easily tuned by judicious choice of ligands. One of the thriving strategies is to use tridentate
ligands, such as pincer ligands, to accomplish a well-defined metal-ligand bonding [19].
Transition metal pincer type complexes with high stability and catalytic activity have been a
most prolific area of homogeneous catalysis and coordination chemistry. There is significant
equilibrium between stability and reactivity of the pincer complexes, which can be controlled
by exact ligand design and following structure of metal complexes [20]. In sustainable
organic synthesis, pincer-type palladium complexes have been shown to possess multifarious
catalytic applications [21-22].
They are extensively employed as a catalyst for coupling reactions [23]. The majority
of these Pd complexes incorporate CCC, CNC, PNP, SNS, NNN, NCN and SCS pincer types
[24-25]. Beside these, ONO and ONS pincer type Pd complexes have considerably allured
much interest in recent years. These complexes have shown propitious biological activities
[26]. However, studies on the corresponding ONO and ONS pincer type ligands and their
palladium complexes in catalysis are limited [27]. Consequently, as a continuation of our
ongoing research on transition metal-catalyzed organic synthesis [28-30], we report herein
the synthesis and crystal structure of two new pincer type palladium(II) Schiff-base
complexes (1 and 2) having ONO and ONS donor atom and their catalytic activity in Suzuki-
Miyaura, Heck-Mizoroki and Sonogashira cross-coupling reactions with low catalyst loading
(0.08 mol %), without use of any additives.
2. Experimental
2.1. Materials and instrumentations:
All reagents and solvents for the synthesis and analysis were purchased from Merck
and Sigma Aldrich and used as received without further purifications.
FT-IR spectra were recorded on a Perkin Elmer Spectrometer in the range of 400-4000 cm-1
using KBr pellets. Elemental analyses were carried out using a Heraeus CHN-Rapid
elemental analyzer. The 1H and 13C NMR spectra of the isolated products were recorded on a
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Bruker AvIII HD-400 MHz spectrometer in CDCl3 using TMS as the internal Standard.
Melting points were recorded on a Yazawa micro melting point apparatus.
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2.2. Synthesis of Pd complex [PdL1(PPh3)] 1
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The HL1 was synthesised by modification of the reported method [31]. A solution of
the ligand HL1 (0.114g, 0.50 mmol) in 2 mL methanol was added drop-wise to the
methanolic solution of Pd(OAc)2 (0.124g, 0.50 mmol, 4 mL) with constant stirring at room
temperature. After stirring the solution for 10 minutes, PPh3 (0.132g, 0.50 mmol) dissolved in
2 mL methanol was added via a syringe to the reaction. After 6 h of stirring at room
temperature, the resultant yellow precipitate was filtered, washed with cold ethanol and dried
in vacuum over anhydrous CaCl2. The precipitate was re-crystallized from DMF. Suitable
single crystals for X-ray crystallography were grown over a period of two weeks from a
concentrated solution of the complex in DMF. Yields: 87%, 0.155 g, Anal. Calc. for
C31H24NO3PPd: C, 62.48; H, 4.06; N, 2.35. Found: C, 62.19; H, 4.01; N, 2.43. FT-IR (KBr),
cm-1: 3435 ν (ΟΗ), 1581 ν (C=N), 3054 ν (CHar), 1217 ν (C-O), 1477 ν (C=Cring), 529 ν (Pd-
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O), 443 ν (Pd-N). H NMR (CDCl3, 25 0C, 400 MHz): δ 8.62 (s, 1H, H-CN), δ 7.84-7.79 (m,
6H, Ar H), 7.75-7.73 (m, 1H, Ar H), 7.57-7.54 (m, 3H, Ar H), 7.50-7.47 (m, 6H, Ar H) 7.12-
6.96 (m, 3H, Ar H), 6.83-6.80 (m, 1H, Ar H), 6.76-6.67 (m, 1H, Ar H), 6.62-6.58 (m, 1H, Ar
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H),
δ
5.37 (s,1H,
OH).
3C NMR (CDCl3,
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0C, 400 MHz):
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δ 168.31, 151.13, 148.09, 146.95, 137.61, 134.57, 134.46, 131.35, 131.33, 129.29, 128.90, 12
8.74, 128.24, 124.44, 119.82, 119.54, 115.78, 115.45, 114.93, 114.52. 31P NMR (CDCl3, 25
0C, 160 MHz): 24.22.
2.3. Synthesis of Pd complex [PdL2(PPh3)] 2
The ligand HL2 was prepared by the reported method [32]. The complex was synthesised by
using similar procedure as described for [PdL1(PPh3)] except using HL2 in place of ligand
HL1. Yields: 84%, 0.152 g, Anal. Calc. for C26H22N3O2PPdS: C, 54.03; H, 3.84; N, 7.27.
Found: C, 53.94; H, 3.51; N, 7.64. FT-IR (KBr), cm-1: 3135-3059 ν (NH2), 3344 ν (OH),
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1525 ν (C=N), 585 ν (Pd−Ο), 500 ν (Pd−Ν). H NMR (CDCl3, 25 C, 400 MHz): δ 8.26
(s,1H, H-CN), δ 7.71-7.68 (m, 6H, Ar H), δ 7.50-7.49 (m, 3H, Ar H), δ 7.48-7.47 (m, 6H, Ar
H), δ 6.87-6.83 (m, 2H, Ar H), 6.83-6.56 (m, 1H, Ar H), δ 5.63 (s,1H, OH), δ 4.73 (s, 2H,
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NH2). 1 C NMR (CDCl3, 25 C, 400 MHz): 150.73, 147.34, 134.49, 134.37, 131.52, 131.49,
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128.91, 128.83, 128.72, 128.39, 124.02, 116.21, 115.14, 113.96. P NMR (CDCl3, 25 C,
160 MHz): 29.31.
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2.4. General procedure for synthesis of Suzuki-Miyaura cross-coupling reaction
A mixture of aryl halide (1 mmol), arylboronic acid (1 mmol), were placed in a 25-
mL round-bottomed flask followed by addition of K2CO3 (1 mmol) and palladium(II)
complex (0.08 mol %) in iPrOH (5 mL). The resulting mixture was stirred at 80ºC for 5-6 h.
The progress of the reaction was monitored by TLC. After completion of the reaction, the
reaction mixture was cooled down to room temperature and the product was washed with
water and extracted with ethyl acetate (3x10 mL). The combined organic layers were dried
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over Na2SO4 and the solvent removed under reduced pressure to give crude product which
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was purified by column chromatography by using petroleum ether/ethyl acetate (4:1) as an
eluent. The products were confirmed by 1H and 13C NMR.
2.5. General procedure for synthesis of Heck-Mizoroki reaction
A mixture of aryl halide (1 mmol), alkene (1 mmol) were placed in a 25-mL round-
bottomed flask followed by addition of K2CO3 (1 mmol) and palladium(II) complex (0.08
mol %) in DMF (5mL). The resulting mixture was stirred at 80°C for 5-7 h. The progress of
the reaction was monitored by TLC. After completion of the reaction, the reaction mixture
was cooled to room temperature and the product was washed with water and extracted with
ethyl acetate (3x10 mL). The combined organic layers were dried over Na2SO4 and the
solvent removed under reduced pressure to give crude product which was purified by column
chromatography by using petroleum ether/ethyl acetate (4:1) as an eluent. The products were
confirmed by 1H and 13C NMR.
2.6. General procedure for synthesis of Sonogashira reaction
A mixture of aryl halide (1 mmol), alkyne (1 mmol) were placed in a 25-mL round-
bottomed flask, followed by addition of K2CO3 (1 mmol) and palladium(II) complex (0.08
mol %) in DMF (5mL). The resulting mixture was stirred at 80°C for 5-7 h. The progress of
the reaction was monitored by TLC. After completion of the reaction, the reaction mixture
was cooled to room temperature and the product was washed with water and extracted with
ethyl acetate (3x10 mL). The combined organic layers were dried over Na2SO4 and the
solvent removed under reduced pressure to give crude product which was purified by column
chromatography by using petroleum ether/ethyl acetate (4:1) as an eluent. The products were
confirmed by 1H and 13C NMR.
2.7. Crystallographic studies
The X-ray diffraction data were collected on a Bruker Kappa diffractometer at 103(2)
K and 153(2) K equipped with a CCD detector, employing Mo K α radiation (λ = 0.71073
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Å), with the SMART suite of programs [33]. All data were processed and corrected for
Lorentz and polarization effects with SAINT and for absorption effects with SADABS [34].
Structural solution and refinement were carried out with the SHELXTL suite of programs
[35]. The structures were refined (weighted least squares refinement on F2) to convergence.
All the non-hydrogen atoms in all the compounds were refined anisotropically by full-matrix
least-squares refinement. A summary of the crystallographic and refinement data of complex
1 and complex 2 are given in Table 1.
(Table 1)
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3. Results and discussion
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Two Schiff base ligands HL1 and HL2 were synthesized by modification of the
reported methods [31, 32]. The ligands HL1 and HL2 were obtained as red and off-white solid
respectively, on refluxing ethanolic solution of corresponding aldehyde and amines for 5 h.
The reaction of ligand HL1 and HL2 with Pd(OAc)2 and PPh3 in 1:1:1 ratio in methanol at
room temperature afforded the complexes [PdL1(PPh3)] 1 and [PdL2(PPh3)] 2 respectively, as
a yellow solid (scheme 1) in high yields (84-87% yields). Red block crystals suitable for X-
ray crystallography were obtained by slow evaporation of the solution at room temperature in
DMF. The complexes were air stable, insoluble in water and benzene, and soluble in other
common organic solvents such as CH2Cl2, CHCl3, CH3CN, DMF and DMSO. The complexes
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were fully characterized by FT-IR, H NMR, 13C NMR and 31P NMR, elemental analysis
(CHN) and their structures were determined by single crystal X-ray diffraction studies.
(Scheme 1)
3.1. FT-IR spectra of the complexes
The FT-IR spectra of ligand HL1 (Fig. S1) showed bands at 3388 cm-1 and 1629 cm-1
due to presence of ν OH and azomethine ν C=N group, respectively. However, the FT-IR
spectrum of the complex 1 showed ν C=N at 1581 cm-1. A comparison of the spectra
indicated that the ν C=N has been lowered by 48 cm-1, supporting the coordination of
azomethine nitrogen atom to palladium [28]. The FT-IR spectrum of the complex 1 also
displayed two peaks at 529 cm-1 and 443 cm-1 assignable to ν Pd-O and ν Pd-N, respectively
[36].
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The FT-IR spectrum of HL2 (Fig. S2) showed four peaks at 3406, 3017, 1235 and
1536 cm-1. These peaks were assigned to ν OH, ν NH, ν C=S and ν C=N respectively [26].
However, the FT-IR spectrum of the complex 2 showed ν C=N at 1525 cm-1. A comparison
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of the spectra indicated that the ν C=N has been lowered by 11 cm-1, supporting the
coordination of azomethine nitrogen atom to palladium. The absence of N-H and C=S
stretching vibrations in complex 2 confirms the coordination of sulphur in thiol form via
deprotonation of the -SH group to the palladium [26].
3.2. 1H, 13C and 31P NMR spectra
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The H NMR spectra of HL1, HL2, complexes 1 and 2 were recorded in CDCl3 at room
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temperature (Fig. S3, S6). The H NMR spectrum of HL1 showed three singlets at δ 14.19,
δ 9.69 and δ 8.88 due to presence of three phenolic OH protons. The azomethine (HC=N-)
proton appeared at δ 8.85 as a singlet and the phenyl protons of the free ligand were observed
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in the range of δ 6.7-7.4 as a complex multiplet [31]. However, the H NMR spectrum of
complex 1 showed only one singlet at δ 5.59 and the absence of other two phenolic OH
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signals confirms the coordination of two phenolic oxygen of HL1 to the metal ion. The H
NMR of complex 1, exhibited the azomethine proton (HC=N-) signal at δ 9.11 as a singlet. In
complex 1, the aromatic protons of the ligand HL1 and PPh3 observed in range δ 6.6-8.06 as a
multiplet. Also, the H NMR of complex 1 at 50 C and 80oC in DMSO-d6 was studied to
assess the stability and coordination behaviour of the complex under the catalytic conditions
(Fig.S9-S10). The complex was found to be stable in solution as no decomposition was
observed, indicating high thermal stability of the pincer type complex.
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The H NMR spectra of ligand HL2 showed singlet at δ 11.38 attributed to NH proton of
thiosemicarbazide. The presence of singlet at δ 9.13 and δ 8.85 indicates two OH protons of
2,3-dihydroxybenzaldehyde moiety [37]. However, only one singlet is observed in complex 2
at δ 5.63 which confirms the coordination of one phenolic oxygen via deprotonation of -OH
group to Pd(II). The azomethine proton (HC=N-) in ligand appeared as a singlet at δ 8.36
which is shifted to δ 8.26 in complex 2. The NH2 proton in free ligand showed a signal at
δ 7.88, however, upon complexation this is shifted to high field at δ 4.73.
The 31P NMR spectra of complexes 1 and 2 were recorded in CDCl3 at room
temperature (Fig. S5, S8).The 31P NMR spectra of complex 1 and 2 showed a singlet
resonance at δ 24.22 and δ 29.31, respectively which are in agreement with the existence of
one phosphorus nuclei [38].
The 13C NMR spectra of complexes 1 and 2 were recorded in CDCl3 at room
temperature (Fig. S4, S7).The 13C NMR spectra of complex 1 and 2 displayed signals at δ
168.31 and δ 150.73, corresponding to the azomethine carbon respectively. The signals
appeared in the region of δ 114.52-151.13 and 113.96-147.34 were accounted to various
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aromatic carbons of the ligand HL1 and HL2 as well as tripenylphosphine ligands of
complexes 1 and 2, respectively.
3.3. Single crystal X-ray Studies
Diffraction quality crystals of the complexes (1 and 2) were grown over a period of
two weeks by standing a concentrated solution of the complex in DMF at room temperature.
The structures of the complexes, 1 and 2 have been elucidated by single-crystal X-ray
diffraction studies and the ORTEP diagram of the complexes are shown in Fig. 1. ORTEP
structure and crystallographic and refinement data reveals that complexes 1 and 2 crystallizes
in triclinic and monoclinic system, respectively and are four-coordinated species with
distorted square planar geometry. Distortion is mainly caused by the presence of the doubly
deprotonated tridentate Schiff base ligand, which forms one five-membered and one six-
membered ring with palladium atom. The pincer type ligand (ONO and ONS) coordinate to
Pd ion in tridentate manner and the fourth site is occupied by an auxiliary ligand
triphenylphosphine. Selected bond distances and bond angle are given in Table 2. In
complex 1, the O1-Pd-N1, O2-Pd-N1 and N1-Pd-P bond angles are 83.61(4), 94.14(4) and
175.86(3), respectively. The Pd1-N1, Pd1-O1 and Pd1-O2 bond lengths are 2.0112(11),
1.9834(10) and 1.9846(10), respectively. The bond angle and bond length are in close
agreement with the previously reported Pd(II) complexes [39-40]. In complex 2, O(1)-Pd(1)-
N(1), N(1)-Pd(1)-S(1) and N(1)-Pd(1)-P(1) bond angles are 92.45(7), 84.35(5) and 176.79(5),
respectively. The Pd(1)-O(1), Pd(1)-N(1) and Pd(1)-S(1) bond lengths are 2.0202(16),
2.0352(17) and 2.2361(6), respectively which are similar to the previously reported Pd(II)
complexes [26].
(Fig. 1)
(Table 2)
3.4. Catalytic studies
Both complexes were screened for their catalytic activity in C-C cross-coupling
reactions, i.e. Suzuki-Miyaura, Heck-Mizoroki and Sonogashira couplings reactions (Scheme
2). The results obtained are given in Table 3-8.
Initially the catalytic studies were performed upon the Suzuki-Miyaura coupling reaction
choosing bromobenzene and 4-methylphenylboronic acid as a model substrate. Various
parameters such as catalyst loading, base system, solvent, temperature and time were studied
and optimized. The results are summarised in Table 3. When the reaction was carried out at
room temperature, in presence of 0.05 mol % of catalyst 1, trace amount of product was
obtained after 24 h (Table 3, entry1) in C6H5CH3. However, when the reaction was carried
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out at 80 C, 68 % yield of the desired coupling product was obtained in 9 h, (Table 3, entry
2). The same reaction in iPrOH, gave 75 % yield of the product in 5 h (Table 3, entry 3).
Further, the catalyst loading was increased to 0.08 mol %, resulted in 90 % yield of coupling
product, in 5h (Table 3, entries 4). However, no significant improvement in yield was
observed by further increasing the amount of catalyst to 0.5 mol % (Table 3, entry 5). Thus,
0.08 mol % of catalyst loading was optimum. Further the effect of the reaction time on the
reactions was investigated with the model reaction using 0.08 mol % catalyst at 80oC. The
most effective reaction time was found to be 5h (fig. S11). The reaction was also performed
with complex 2 as catalyst (Table 3, entry 6). The complex 1 with ONO donor atom results in
slightly higher yield as compared to complex 2 bearing ONS donor atom which may be due
to the presence of aromatic ring on N-imino group in complex 1[41]. In order to found the
best solvent, the reaction was carried out in different solvents such as C6H5CH3, iPrOH,
iPrOH:H2O (1:1), H2O and DMF (Table 3). Among all solvents, iPrOH was found to be the
best solvent (Table 3, entry 5). The reaction was performed with various bases such as
o
K2CO3, Et3N, Na2CO3 in iPrOH at different temperatures i.e. 50, 80, 70 C (Table 3, entries
10-13). The yield of desired coupling product was found to be maximum in presence of
K2CO3 at 80 oC (Table 3, entry 4). The same reaction in presence of Pd(OAc)2 results in 40 %
yield of the desired product in 5 h (Table 3, entry 14).
(Table 3)
Subsequently, all reactions were carried out under optimized conditions with a structurally
diverse range of aryl iodide and aryl/hetero-aryl bromide with different arylboronic acid to
produce the corresponding biaryls (Table 4). It can be concluded that the nature of substituent
such as electron donating and electron withdrawing group on aryl halide and arylboronic
acids results in good yield (Table 4, entries 2-10). However, substituent in p- position results
in excellent yield than substituents at m- position due to steric hindrance (Table 4, entries 2
and 9). The reaction with hetero-aryl halide i.e 2-bromopyridine with 4-methylphenylboronic
acid resulted in 75 % yield of the desired coupling product (Table 4, entry 11). The isolated
products were fully characterized by 1H and 13C NMR as given in ESI (Figure S13-S23). In
order to establish the efficacy of the new catalysts, a comparison was made with some
previously reported catalysts for Suzuki-Miyaura coupling reaction in terms of temperature,
time, catalyst loading [42] etc (Table S1). The results indicate that our catalytic system
exhibits better catalytic activity as compared to other reported. A plausible mechanism for
Suzuki coupling reaction, based on previous reports [23,40] is suggested in Scheme 3. TGA
plot of complex 1 was shown in Fig. S12. The TGA of the complex 1 was carried out in the
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temperature range of 40-700 C to assess the stability and mode of decomposition of the
synthesized complex. The results from the TGA analysis showed 52 % weight loss in the
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temperature range of 230-350 C. However, no weight loss in the temperature range of 400-
700 °C was observed. The TGA results for the used catalyst are identical to those for a fresh
catalyst signifying high thermal stability of the complex.
(Table 4)
(Scheme 3)
To enhance the scope of our studies, both catalysts were tested in Heck-Mizoroki
coupling reaction. Initially, 4-bromoacetophenone and styrene were chosen as model
substrates. In order to optimize reaction conditions various parameters such as solvent, time,
base, temperature and catalyst were studied (Table 5). When reaction was performed in
presence of 0.05 mol % of catalyst 1 at room temperature in DMF, trace amount of coupling
product was obtained in 20 h (Table 5, entry 1). However, when temperature was raised to 80
oC, yield of product was increased to 72 % in 9 h (Table 5, entry 2). Further, the catalyst
loading was increased to 0.08 mol % resulted in 90 % yield of desired coupling product in 6 h
(Table 5, entry 3). However, increase in catalyst loading to 0.5 mol % resulted in no
significant improvement in yield of the product (Table 5, entry 5). Thus, 0.08 mol % of
catalyst loading is optimum. The reaction was carried in various solvents such as H2O, DMF,
CH3C6H5, and iPrOH (Table 5). The best solvent was found to be DMF (Table 5, entry 3).
The reaction was also carried out in different bases and at different temperatures (Table 5,
entry 8-11). The best result was obtained with 0.08 mol % of catalyst, 1 equiv. K2CO3 at 80
oC (Table 5, entry 3). The same reaction in presence of Pd(OAc)2 results in 35 % yield of the
desired product in 6 h (Table 5, entry 13).
(Table 5)
Under optimized conditions, all reactions with diverse range of aryl iodides and aryl/
hetero-aryl bromides with different types of alkenes were carried out to produce the desired
coupling products. It can be concluded that substituent bearing electron donating and electron
withdrawing group on aryl halides such as -CH3, -OCH3,-COCH3 and –CHO, reacted
smoothly under optimized conditions to give the desired product in almost quantitative yields
(Table 6). Next the reaction with hetero-aryl halide i.e 2-bromopyridine with styrene resulted
in 40 % yield (Table 6, entry 11). The isolated products were fully characterized by 1H and
13C NMR, as given in ESI (Fig.S24-S34). A comparison was made with some previously
reported catalysts for Heck-Mizoroki coupling reaction in terms of temperature, time, catalyst
loading [43] etc (Table S2).
9

301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
(Table 6)
Further, we explore the compatibility of both catalysts for copper-free Sonogashira
cross-coupling reaction. Initially, 4-bromoacetophenone and phenylacetylene were chosen as
model reactants (Table 7). The reaction condition was optimized with respect to solvent,
catalyst loading, temperature, base and time. The results are summarised in Table 7. When
the reaction was carried out at room temperature in presence of 0.05 mol % of catalyst 1 in
DMF, trace amount of product was formed in 15 h (Table 7, entry1). However, when reaction
temperature was raised to 80 oC, the yield of the product was increased to 76 % in 7 h (Table
7, entry 2). Further, catalyst loading was increased to 0.08 mol % and 0.5 mol %, resulted in
o
90% and 87 % yield of the product, respectively in 5 h at 80 C (Table 7, entries 3-4). Thus
0.08 mol % of catalyst loading was optimum. The catalytic activity of complex 2 was also
investigated (Table 7, entry 5). In order to find out best solvent, the reaction was carried out
in different solvents such as H2O, DMF, C6H5CH3, C6H5CN, iPrOH (Table 7). Among all,
DMF was found to be a best solvent (Table 7, entry 3). The reaction was also carried out with
o
o
different bases such as K2CO3, Et3N, Na2CO3 and at different temperature 50 C, 80 C and
100 oC (Table 7, entries 1-13). The best results obtained with 1 equiv. K2CO3 at 80 oC (Table
7, entry 3). The same reaction in presence of Pd(OAc)2 results in 37 % yield of the desired
product in 6 h (Table 3, entry 14).
(Table 7)
Consequently, all the reactions with diverse range of aryl iodides and aryl/hetero-aryl
bromides with different alkynes were carried out under optimized conditions. Various
electron-donating and electron-withdrawing groups such as -CH3, -OCH3, -COCH3 and -
CHO on both aryl halides and alkynes are well tolerated affording the desired products in
good to excellent yields (Table 8). However, the reaction with hetero-aryl halide i.e 2-
bromopyridine with phenylacetylene resulted in 50 % yield (Table 8, entry 9). The isolated
products were fully characterized by H and 13C NMR, as given in ESI (Fig. S35-S45). A
1
comparison was made with some previously reported catalysts for Sonogashira cross-
coupling reaction in terms of temperature, time, catalyst loading [44] etc (Table S3).
(Table 8)
4. Conclusion
In conclusion, two new pincer type Pd(II)-Schiff base complexes have been
synthesized and fully characterised by various spectroscopic techniques and single crystal X-
ray diffraction studies. The complexes were found to be efficient catalysts for Suzuki-
10

334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
Miyaura, Heck-Mizoroki and Sonogashira coupling reactions. The reaction proceed smoothly
at 80 οC at a low catalyst loading (0.08 mol %).
Acknowledgment
We are thankful to the CRF, IIT(ISM), Dhanbad and SAIF Panjab University,
Chandigarh for providing help in the analysis of the samples and we also grateful to NTU,
Singapore for the single crystal X-ray analysis. Bhumika Agrahari, Samaresh Layek and
Anuradha acknowledge the receipt of IIT (ISM), Dhanbad fellowship.
Supplementary data
CCDC 1526842 and 1539658 contain the supplementary crystallographic data for
this
paper.
This
data
can
be
obtained
free
of
charge
via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or mail.
References
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350
351
352
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354
355
356
357
358
359
360
361
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364
365
366
[1]
[2]
[3]
M. Beller, C. Bolm, Trans. Metals for Org. Synthesis. 2 (2004) 1134.
N. Miyaura, A. Suzuki, Chem. Rev. 95 (1995) 2457.
C. C. C. J. Seechurn, M. O. Kitching, T. J. Colacot, V. Snieckus, Angew. Chem. Int.
Ed. 51 (2012) 5062-5085.
[4]
(a) M. Bakherad, A. Keivanloo, B. Bahramian, S. Jajarmi, J. Organomet.Chem. 724
(2013) 206-212;
(b) M. Mondal, U. Bora, Tetrahedron Lett. 55 (2014) 3038-3040.
S. M. Sarkar, Md. L. Rahman, M. M. Yusoff, New J. Chem. 39 (2015) 3564-3570.
C. J. Li, Chem. Rev. 105 (2005) 3095-3166.
[5]
[6]
[7]
[8]
[9]
C. J. Xi, Y. W. Wu, X. Y. Yan, J. Organomet.Chem.693 (2008) 3842-3846.
T. Kawano, T. Shinomaru, I. Ueda, Org. Lett. 4 (2002) 2545-2547.
(a) S. Kim, H. J. Cho, S. D. Shin, M. S. Lee Tetrahedron Lett. 58 (2017) 2421-2425;
(b) T. Begum, M. Mondal, M. P. Borpuzari, R. Kar, G. Kalita, P. K. Gogoi, U. Bora ,
Dalton Trans. 46 (2017) 539-546;
(c) M. Akkoc, F. Imik, S. Yasar, V. Dorcet, T. Roisnel, C. Bruneau, I. zdemir,
ChemistrySelect 2 (2017) 5729-5734.
[10] C. Amatore, A. Jutand, Coord. Chem. Rev. 178 (1998) 511-528.
[11] C. Baleizao, A. Corma, H. Garcia, A. Leyva, J. Org. Chem. 69 (2004) 439-446.
11

367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
[12] X. J. Feng, M. Yan, T. Zhang, Y. Liu, M. Bao, Green Chem. 12 (2010) 1758-1766.
[13] J. Zhang, G. F. Zhao, Z. Popovic, Y. Lu, Y. Liu, Mater. Res. Bull. 45 (2010) 1648-
1653.
[14] H. Ali, N. Cauchon, J. E. V. Lier, Photochem. Photobiol.Sci. 8 (2009) 868-874.
[15] T. Cheisson, A. Auffrant, Dalton Trans. 45 (2016) 2069-2078.
[16] N. C. Mehendale, J. R. A. Sietsma, K. P. De Jong, C. A. V. Walree, R. J. M. K.
Gebbink, G. V. Koten, Adv. Synth.Catal. 349 (2007) 2619-2630.
[17] (a) R. Dileep, R. B. Badekai, Appl. Organomet. Chem. 24 (2010) 663-666;
(b) S. Layek, Anuradha, B. Agrahari, D. D. Pathak, J. Organomet. Chem. 846
(2017) 105-112.
[18] (a) M. Keles, H. Keles, D. M. Emir, Appl. Organomet. Chem. 29 (2015) 543-548;
(b) T. Baran J. Colloid Interface Sci. 496 (2017) 446-455;
(c) A. P. S. Andrade, L. M. Arantes, J. Y. Kadooca, R. L. Carvalho, A.de Fatima,
A. A. Sabino, ChemistrySelect 5 (2016) 886-890.
[19] M. Asay, D. M. Morales, Dalton Trans. 44, (2015) 17432-17447.
[20] M. E. van der Boom, D. Milstein, Chem. Rev. 103 (2003) 1759-1792.
[21] C. J Moulton, B. L. Shaw, J. Chem. Soc. Dalton Trans. (1976) 1020-1024.
[22] V. Koten, G. Timmer, K. Noltes, J. G. Spek, A. L. J. Chem. Soc.,Chem. Commun.
(1978) 250-252.
[23] (a) H. Zhang, A. Lei Dalton Trans. 40 (2011) 8745-8754;
(b) T. Baran, A. Mentes J. Mol. Struct. 1134 (2017) 591-598.
[24] N. Selander, K. J. Szabo, Chem. Rev. 111 (2011) 2048-2076.
[25] I. Moreno, R. S. Martin, B. Ines, F. Churruca, E. Dominguez, Inorg. Chim. Acta 363
(2010) 1903-1911.
[26] S. Halder, S. M. Peng, G. H. Lee, T. Chatterjee, A. Mukherjee, S. Dutta, U. Sanyald,
S. Bhattacharya, New J. Chem. 32 (2008) 105-114.
[27] V. Arumugama, W. Kaminsky, D. Nallasamy, RSC Adv. 5 (2015) 77948-77957.
[28] S. Layek, B. Agrahari, Anuradha, R. Ganguly, D. D. Pathak, J. Mol. Struct. 1141
(2017) 428-435.
[29] B. Agrahari, S. Layek, S. Kumari, Anuradha, R. Ganguly, D. D. Pathak, J. Mol.
Struct. 1134 (2017) 85-90.
[30] S. Layek, S. Kumari, Anuradha, B. Agrahari, R. Ganguly, D. D. Pathak, Inorg. Chim.
Acta 453 (2016) 735-741.
12

400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
[31] T. F. F. Magalhaes, C. M. da Silva, A. de Fatima, D. L. da Silva, L.V. Modolo, C. V.
B. Martins, R. B. Alves, A. L.T.G. Ruiz, G. B. Longato, J. E. de Carvalho, M. A. d.
R. Stoianoff, Letters in Applied Microbiology 57 (2013) 137-143.
[32] A. T. Swesi, Y. Farina, I. Baba, Sains Malaysiana 36 (2007) 21-26.
[33] SMART version 5.628; Bruker AXS Inc., Madison, WI, USA, 2001.
[34] Sheldrick, G. M. SADABS; University of Gottingen, Gottingen, Germany, 1996.
[35] SHELXTL version 5.1; Bruker AXS Inc., Madison, WI, USA, 1997.
[36] M. Shabbir, Z. Akhter, I. Ahmad, S. Ahmed, M. Shafiq, B. Mirza, V. McKee, K. S.
Munawar, A. R. Ashraf, J. Mol. Struct. 1118 (2016) 250-258.
[37] H. B. Shawish, W. Y. Wong, Y. L. Wong, S. W. Loh, C. Y. Looi, P. Hassandarvish,
A. Y. L. Phan, W. F. Wong, H. Wang, I. C. Paterson, C. K. Ea, M. R. Mustafa, M. J.
Maah, Plos One 9 (2014) 100933.
[38] P. Chellan, N. S. Gounden, D. T. Hendricks, J. Gut, P. J. Rosenthal, C. Lategan, P. J.
Smith, K. Chibale, G. S. Smith, Eur. J. Inorg. Chem. (2010), 3520-3528.
[39] S. Das, S. Pal, J. Organomet.Chem. 691 (2006) 2575-2583.
[40] V. Arumugam, W. Kaminsky, N. S. P. Bhuvaneshc, D. Nallasamy, RSC Adv. 5
(2015) 59428-59436.
[41] (a) S. M. Nobre, A. L. Monteiro J. Mol. Catal. A: Chem. 313 (2009) 65-73;
(b) A. Scrivanti, V. Beghetto, U. Matteoli, S. Antonaroli, A. Marini, B. Crociani,
Tetrahedron 61 (2005) 9752.
[42] (a) T. Mahamo, M. M. Mogorosi, J. R. Moss, S. F. Mapolie, J. C. Slootweg, K.
Lammertsma, G. S. Smith, J. Organomet. Chem. 703 (2012) 34-42;
(b) M. Gholinejad, H. R. Shahsavari, Inorg. Chim. Acta 421 (2014) 433-438;
(c) K. A. Green, P. T. Maragh, K. A. Rashid, A. J. Lough, T. P. Dasgupta, Inorg.
Chim. Acta 449 (2016) 38-43.
[43] (a) F. M. Elantabli, M. P. Radebe, W. M. Motswainyana, B. O. Owaga, S. M. El-
Medani, E. Ekengard, M. Haukka, E. Nordlander, M. O. Onani J. Organomet.
Chem. 843 (2017) 40-47.
(b) M.B. Andrus, C. Song, J. Zhang, Org. Lett. 4 (2002) 2079-2082.
[44] (a) S. J. Sabounchei, M. Ahmadi, Z. Nasri, E. Shams, M. Panahimehr Tetrahedron
Lett. 54 (2013) 4656-4660.
(b) M. Bagherzadeh, N. Mousavi , M. Zare, S. Jamali, A. Ellern , L. K. Woo, Inorg.
Chim. Acta 451 (2016) 227-232.
13

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438
List of Scheme’s caption
Scheme 1 Synthesis of pincer type Pd(II) complexes
Scheme 2 The catalytic activity of Pd(II) complexes in Suzuki-Miyaura (2a), Mizoroki-Heck
(2b) and Sonogashira (2c) coupling reactions
Scheme 3 Plausible mechanism for Suzuki coupling reaction
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
List of figure caption
Fig. 1 ORTEP diagram of [PdL1(PPh3)] 1 and [PdL2(PPh3)] 2 complexes with the atom
labelling scheme (Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms
have been omitted for clarity)
List of Table’s caption
Table 1 Crystal data and refinement parameters of complexes 1 and 2
Table 2 Selected bond distances (Å) and bond angles (o) for [PdL1(PPh3)] 1 and [PdL2(PPh3)]
2 complexes.
Table 3 Optimization of reaction conditions for Suzuki-Miyaura coupling reaction
Table 4 Suzuki-Miyaura reactions with different substituents catalyzed by Pd(II) complexes
under optimized reaction conditions.
Table 5 Optimization of reaction conditions for Heck-Mizoroki coupling reaction.
Table 6 Heck-Mizoroki reactions with different substituents catalyzed by Pd(II) complexes
under optimized reaction conditions.
Table 7 Optimization of reaction conditions for Sonogashira reaction
Table 8 Sonogashira reactions with different substituents catalyzed by Pd(II) complexes
under optimized reaction conditions
14

467
SCHEMES
468
469
470
471
Scheme 1 Synthesis of pincer type Pd(II) complexes
472
473
Suzuki-Miyaura coupling reaction (2a)
474
475
Heck-Mizoroki coupling reaction (2b)
476
477
Sonogashira coupling reaction (2c)
Scheme 2 The catalytic activity of Pd(II) complexes in Suzuki-Miyaura (2a), Heck- Mizoroki
(2b) and Sonogashira (2c) coupling reactions
478
479
480
15

481
482
Scheme 3 Plausible mechanism for Suzuki coupling reaction
483
FIGURES
[PdL2(PPh3)] 2
[PdL1(PPh3)] 1
484
485
486
487
488
489
Fig. 1 ORTEP diagram of [PdL1(PPh3)] 1 and [PdL2(PPh3)] 2 complexes with the atom
labelling scheme (Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms
have been omitted for clarity)
TABLES
Table 1 Crystal data and refinement parameters of complexes 1 and 2
CCDC deposition number
Chemical formula
1526842
1539658
C31H24NO3PPd
595.88 g/mol
C26H22N3O2PPdS
578.90
Formula weight
16

Temperature
103(2) K
153(2) K
Wavelength
0.71073 Å
0.080 x 0.200 x 0.240 mm
Red block
0.71073 Å
3
Crystal size
0.200 x 0.180 x 0.140 mm
Red block
Crystal habit
Crystal system
Triclinic
Monoclinic
P21/c
Space group
P -1
Unit cell dimensions
a
8.9230(2) Å
9.9557(2) Å
14.6655(3) Å
76.8530(10)°
89.0600(10)°
77.4190(10)°
1237.44(5) Å3
2
13.0329(7) Å
10.1025(5) Å
20.2335(10) Å
90°
b
c
α
β
100.7979(15)°
90°
γ
3
Volume
2616.9(2) Å
Z
4
1.599 g/cm3
0.850 mm-1
604
3
Density (calculated)
1.469 Mg/m
0.877 mm-1
Absorption coefficient
F(000)
1172
2
Goodness-of-fit on F
1.061
1.030
Final R indices [I>2sigma(I)] R1 = 0.0225, wR2 = 0.0529
R indices (all data) R1 = 0.0261, wR2 = 0.0546
R1 = 0.0289, wR2 = 0.0628
R1 = 0.0415, wR2 = 0.0684
490
491
492
Table 2 Selected bond distances (Å) and bond angles (o) for [PdL1(PPh3)] 1 and [PdL2(PPh3)]
2 complexes.
Bond distances
Pd1-O1
[PdL1(PPh3)]
1.9834(10)
Bond distance
Pd(1)-O(1)
[PdL2(PPh3)]
2.0202(16)
Pd1-O2
Pd1-N1
Pd1-P1
1.9846(10)
2.0116(11)
2.2743(4)
Pd(1)-N(1)
Pd(1)-S(1)
Pd(1)-P(1)
2.0352(17)
2.2361(6)
2.2722(6)
493
Bond angles
[PdL1(PPh3)]
Bond angles
[PdL2(PPh3)]
O1-Pd1-O2
O2-Pd1-N1
O2-Pd1-P1
177.73(4)
94.14(4)
86.55(3)
O(1)-Pd(1)-N(1)
O(1)-Pd(1)-S(1)
N(1)-Pd(1)-S(1)
92.45(7)
176.80(5)
84.35(5)
17

O1-Pd1-N1
O1-Pd1-P1
N1-Pd1-P1
83.61(4)
95.72(3)
175.86(3)
O(1)-Pd(1)-P(1)
N(1)-Pd(1)-P(1)
S(1)-Pd(1)-P(1)
90.54(5)
176.79(5)
92.66(2)
494
495
Table 3 Optimization of reaction conditions for Suzuki-Miyaura coupling reaction
496
Entry
Catalyst
Catalyst
loading
(mol %)
Solvent
Base
Temp. Time
Yield**
(oC)
(h)
1
2
complex 1
complex 1
complex 1
complex 1
complex 1
complex 2
complex 1
complex 1
complex 1
complex 1
complex 1
complex 1
complex 1
Pd(OAc)2
0.05
0.05
0.05
0.08
0.5
C6H5CH3
C6H5CH3
iPrOH
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
RT
80
80
80
80
80
80
80
80
80
80
50
70
80
24
9
trace
68
75
90
85
85
70
-
3
5
4
iPrOH
5
5
iPrOH
5
6
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
iPrOH
5
7
iPrOH:H2O(1:1) K2CO3
5
8
H2O
K2CO3
K2CO3
Et3N
24
5
9
DMF
88
75
82
65
88
40
10
11
12
13
14
iPrOH
iPrOH
iPrOH
iPrOH
iPrOH
5
Na2CO3
K2CO3
K2CO3
K2CO3
5
5
5
5
497
498
499
500
501
*Reaction conditions: Aryl halide (0.5 mmol, 1.0 equiv), Phenylboronic acid (0.6 mmol, 1.2
equiv),
Base (0.5 mmol, 1 equiv).
**Yield after column chromatography.
502
503
504
505
506
18

507
508
Table 4 Suzuki-Miyaura reactions with different substituent catalyzed by Pd(II) complexes
under optimized reaction conditions.
509
Entry
X
Y
R1
H
R2
H
Time (h)
Yield*
92
1
2
3
4
5
6
Br
Br
Br
Br
Br
Br
CH
CH
CH
CH
CH
CH
6
6
5
5
5
6
H
4-CH3
4-CH2CH3
4-OCH3
4-CH3
H
90
H
92
H
93
OCH3
COCH3
92
92
7
8
9
Br
Br
Br
CH
CH
CH
OCH3
OCH3
H
4-F
6
6
89
91
85
4-OCH3
3-CH3
6.5
10
11
Br
Br
CH
N
H
H
4-Cl
H
5
5
87
75
510
511
512
513
514
*Yield after column chromatography
Table 5 Optimization of reaction conditions for Heck-Mizoroki coupling reaction
Entry
Catalyst
Catalyst
loading
(mol %)
0.05
Solvent
Base
Temp. Time Yield**
(oC)
(h)
1
2
3
4
5
complex 1
complex 1
complex 1
complex 1
complex 2
DMF
DMF
DMF
DMF
DMF
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
RT
80
80
80
80
20
9
trace
72
0.05
0.08
0.5
6
90
6
85
0.08
6
86
19

6
7
complex 1
complex 1
complex 1
complex 1
complex 1
complex 1
complex 1
Pd(OAc)2
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
H2O
C6H5CH3
iPrOH
DMF
K2CO3
K2CO3
K2CO3
Et3N
80
80
80
80
80
50
100
80
7
7
7
7
7
7
7
6
-
60
65
68
70
65
85
35
8
9
10
11
12
13
DMF
Na2CO3
K2CO3
K2CO3
K2CO3
DMF
DMF
DMF
515
516
517
518
519
520
521
522
523
524
525
526
527
*Reaction conditions: Aryl halide (0.5 mmol, 1.0 equiv), Alkene (0.6 mmol, 1.2 equiv),
Base (0.5 mmol, 1.0 equiv).
**Yield after column chromatography
Table 6 Heck-Mizoroki reactions with different substituents catalyzed by Pd(II) complexes
under optimized reaction conditions
Entry
X
Br
Br
Br
Br
I
Y
R1
H
R2
Time (h)
Yield*
91
1
2
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
N
C6H5
5
5
6
5
5
5
6
7
6
6
7
H
4-CH3C6H4
C6H5
88
3
COCH3
CHO
OCH3
H
90
4
4-CH3C6H4
C6H5
90
5
91
6
I
4-CH3C6H4
COOCH3
COOCH3
COOCH3
4-CH3C6H4
C6H5
87
7
Br
Br
Br
Br
Br
OCH3
CHO
COCH3
OCH3
H
92
8
89
9
90
10
11
92
40
528
529
*Yield after column chromatography
Table 7 Optimization of reaction conditions for Sonogashira reaction
530
20

Entry
Catalyst
Catalyst
loading
(mol %)
0.05
Solvent
Base
Temp. Time Yield**
(oC )
(h)
1
2
complex 1
complex 1
complex 1
complex 1
complex 2
complex 1
complex 1
complex 1
complex 1
complex 1
complex 1
complex 1
complex 1
Pd(OAc)2
DMF
DMF
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Et3N
RT
80
80
80
80
80
80
80
80
80
80
100
50
80
15
7
5
5
5
6
6
6
6
5
5
5
5
6
trace
76
90
87
85
60
80
-
0.05
0.08
0.5
3
DMF
4
DMF
5
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
DMF
6
CH3CN
iPrOH
H2O
7
8
9
C6H5CH3
DMF
68
50
70
89
60
37
10
11
12
13
14
DMF
Na2CO3
K2CO3
K2CO3
K2CO3
DMF
DMF
DMF
531
532
533
534
535
536
*Reaction conditions: Aryl halide (0.5 mmol, 1.0 equiv), Alkyne (0.6 mmol, 1.2 equiv),
Base (0.5 mmol, 1 equiv).
**Yield after column chromatography
Table 8 Sonogashira reactions with different substituents catalyzed by Pd(II) complexes
under optimized reaction conditions
537
Entry
X
Br
Br
Br
I
Y
R1
H
R2
H
Time (h)
Yield*
90
1
2
3
4
5
6
7
8
CH
CH
CH
CH
CH
CH
CH
CH
5
5
H
4-CH3
4-OCH3
4-OCH3
OCH2CH3
H
89
H
6
90
CH3
H
5.5
5
90
Br
Br
Br
I
88
COCH3
NO2
NO2
6
90
H
5
90
F
6.5
89
21

9
Br
Br
Br
N
H
H
H
5
5
50
90
89
10
11
CH
CH
CHO
CHO
OCH3
5.5
538
539
*Yield after column chromatography
22

540
Graphical Abstract Synopsis
541
542
543
544
545
Synthesis and characterization of two new pincer type palladium(II) complexes of the general
formula
[PdL1(PPh3)]
1,
and
[PdL2(PPh3)]
and L2=
2,
(where
L1=
2-(2,3-
Dihydroxybenzylideneamino)phenolate
2-(2,3-Dihydroxybenzylidene)
hydrazinecarbothioamidate) and application of the complexes in C-C cross-coupling
reactions.
546
547
23

548
Highlights
549
550
551
552
553
•
•
Synthesis and crystal structures of two new pincer type Pd(II)-Schiff base complexes
1
31
Characterized by FT-IR, H, 13C, P NMR, elemental analysis and single crystal X-
ray studies
•
•
Efficient catalyst for Suzuki-Miyaura, Heck-Mizoroki and Sonogashira reactions
Low catalyst loading
554
24