A simple and efficient tetradentate Schiff base derived palladium complex for Suzuki-Miyaura reaction in water

Article abstract of DOI:10.1016/j.tetlet.2014.01.041

A simple and efficient catalytic system based on Pd complex of tetradentate Schiff base ligands is found to be highly active (up to 99% isolated yield) for Suzuki-Miyaura reaction of aryl bromides with arylboronic acids in water at room temperature. Further the scope of this protocol has been extended to the Suzuki-Miyaura cross-coupling reaction of aryl chlorides with arylbronic acids in isopropanol.

Full text of DOI:10.1016/j.tetlet.2014.01.041

Accepted Manuscript
A simple and efficient tetradentate Schiff base derived palladium complex for
Suzuki-Miyaura reaction in water
Anindita Dewan, Utpal Bora, Geetika Borah
PII:
S0040-4039(14)00065-3
DOI:
http://dx.doi.org/10.1016/j.tetlet.2014.01.041
TETL 44073
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
6 December 2013
7 January 2014
10 January 2014
Please cite this article as: Dewan, A., Bora, U., Borah, G., A simple and efficient tetradentate Schiff base derived
palladium complex for Suzuki-Miyaura reaction in water, Tetrahedron Letters (2014), doi: http://dx.doi.org/
10.1016/j.tetlet.2014.01.041
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A simple and efficient tetradentate Schiff base
derived palladium complex for Suzuki-Miyaura
reaction in water
Anindita Dewana∗, Utpal Boraa,b and Geetika Boraha
R
X
B(OH)2
C2-Complex
+
R1
R2
R1
Water, K2CO3
R2
N
O
N
O
Pd
R1= H, CH3, OCH3, NO2, CHO, COCH3
R2= H, C(CH3)3, OCH3, Cl
X = Br (in water)
C1: R=H; C3: R=OCH3
C2: R=Cl; C4: R=NO2
X = Cl (in isopropanol)

1
Tetrahedron Letters
journal homepage: www.els evier.com
A simple and efficient tetradentate Schiff base derived palladium complex for Suzuki-
Miyaura reaction in water
Anindita Dewana∗ Utpal Boraa,b and Geetika Boraha
aDepartment of Chemistry, Dibrugarh University, Dibrugarh 786004, Assam, India
bDepartment of Chemical Sciences, Tezpur University, Tezpur 784028, Assam, India
∗ Corresponding author e-mail: ani_dewan@yahoo.co.in (A. Dewan). Tel.: +91-373-2370210; fax: +91-373-2370323
Article history:
A simple and efficient catalytic system based on Pd complex of tetradentate Schiff
base ligands is found to be highly active (up to 99% isolated yield) for Suzuki–Miyaura reaction
of aryl bromides with arylboronic acids in water at room temperature. Further the scope of this
protocol has been extended to the Suzuki-Miyaura cross coupling reaction of aryl chlorides with
arylbronic acids in isopropanol.
Received
Received in revised form
Accepted
Available online
Keywords:
2009 Elsevier Ltd. All rights reserved.
Suzuki Miyaura
Aryl halides
Tetradentate Schiff base
Water
Isopropanol
The Suzuki-Miyaura cross-coupling reaction of aryl halides with
arylboronic acids has been considered as one of the most
powerful, versatile and popular tool for selective preparation of
biaryl compounds which are important structural moieties in
numerous polymers, agrochemicals, natural products and
pharmaceutical intermediates.1 Usually catalytic system for these
transformations composed of Pd(0) or Pd(II) derivatives
associated with appropriate ligands and the efficiency of
catalytic system has been achieved by changing the ligand
environment around palladium center.2 Among the assortment
Suzuki-Miyaura reaction strategy using a unique palladium
tetradentate Schiff base complex as catalyst in water. These
tetradentate ligands, due to the existence of multiple bonding
sites is expected to increase the steric congestion around the
metal centre which is considered to be vital for facilitating the
reductive elimination step in the Suzuki-Miyaura cross-coupling
reaction pathway.
Initially, we have synthesized and characterized four
new palladium complexes C1, C2, C3 and C4 with tetradentate
Schiff base ligands N,N/-bis(salicylidene)-phenylmethanediamine
(L1), N,N/-bis(salicylidene)-2-chloro-phnylmethanediamine(L2),
N,N/-bis(salicylidene)-2-methoxy-phnylmethanediamine (L3) and
N,N/-bis(salicylidene)-2-nitro-phnylmethanediamine (L4) derived
ligands
used,
phosphine based ligands such as
tertiaryphosphines, hemilabile-type phosphines, sterically
congested biphenyl-type phosphines show excellent activity as
ligand in this transformation.3 Recently different nitrogen
containing ligands such as N-heterocyclic carbenes4 amines,5
oxime-based palladacycles6 etc have attracted considerable
attention as competent ligand for Suzuki-Miyaura reaction.
Among the various N-based ligands, Schiff bases are well
known as chelating multidentate ligands in coordination
chemistry as well as in catalysis because of their simple and
convenient synthetic route with commercially available and
economical starting material and high stability under a wide
range of redox conditions.7 Additionally, electronic and steric
properties of Schiff bases could be easily manipulated by
appropriately selecting the precursor. Tetradentate Schiff bases
are unique class of Schiff base ligand which form coordination
complex with the metal ion in a tetradentate manner.8 These
types of Schiff base complexes with various active metals
exhibit excellent performance as catalyst in different organic
transformations and recently we were able to use Cu salen
complex of tetradentate Schiff base ligands for Chan Lam cross
coupling reaction in water.9 From environmental and economic
points of view, the use of water as an environmentally benign
and economically favorable alternative to organic solvents in
chemical transformation has gained notable interest, because
water is an inexpensive, readily available, non-toxic and non-
flammable solvent.10 Therefore with an aim to develop novel
catalytic systems for Suzuki–Miyaura cross coupling reactions in
water with improved yield under simple reaction protocol we
herein wish to report a facile and efficient room temperature
from
salicylaldehyde
and
corresponding
substituted
benzaldehyde as reported in the literature.8 The new palladium
complexes C1, C2, C3 and C4 (Figure 1) were prepared by
refluxing methanolic solution of the corresponding tetradentate
ligands L1, L2, L3 and L4 with equimolar amount of palladium
acetate. It is noteworthy to mention that we have followed the
green chemistry protocol to synthesize the ligands under solvent-
free conditions.8 The newly synthesized complexes C1, C2, C3,
1
and C4 were characterized by elemental analysis, IR, H- and
13C-NMR and mass spectral data.11
R
R
N
O
N
O
N
N
Pd
OH HO
L1: R=H, L2: R=Cl,
L3: R=OCH3, L4: R=NO2
C1: R=H, C2: R=Cl,
C3: R=OCH3, C4: R=NO2
Figure 1: Screened Ligands and Complex.

2
Tetrahedron
The spectral analysis of the prepared complexes corroborates
has been well documented that in Suzuki–Miyaura reaction, the
in situ generated catalytic species and pre-formed catalyst often
show different catalytic activities.13Therefore to compare the
activities of the in situ catalyst with pre-formed catalyst we have
synthesized Pd-complexes using L1-L4 as ligand.11 It is observed
that the use of the pre-formed Pd complexes C1–C4 as a catalyst
resulted in improved yields of the desired cross coupling product
compared to that of the in situ catalyst (Table 1, entries 6-9). The
best result was obtained with the palladium complex C2 derived
with the reported one. The value of elemental analyses and the
appearances of molecular ion peaks in ESI-mass spectra of
complexes C1, C2, C3 and C4 support their proposed structure.
In the FTIR spectra of complexes, the value for v (C=N)
stretching vibration of the free ligand at about 1620 cm-1 gets
considerably shifted to lower frequency at about 1600 cm-1 after
complexation, implying the coordination of imine nitrogen with
palladium owing to the donation of electrons from nitrogen atom
to the empty d-orbitals of the metal. The v (O-H) signal
pertaining to free ligands ( 3425 cm-1 in FTIR and 13.5 ppm in 1H
NMR) was found to be absent in all the four complexes,
supporting the deprotonation of phenolic moiety and its
subsequent coordination to palladium.
from
bis(salicylidene)-2-chloro-phenylmethanediamine(L2),
(Table 1, entry 7). To optimize the amount of catalyst, we have
carried out the reaction using different amount of the Pd complex
and we found that 0.2 mol% of the C2 is sufficient to obtain 95%
yield of the product (Table 1, entry 10). However the yield of the
product was decreased to 50% when we carried the reaction with
0.1 mol% of the catalyst (Table 1, entry 11). Considering the
advantage of water as green solvent, we examine the
effectiveness of the C2 complex in water and interestingly
excellent yield of the product was obtained in water at room
temperature (Table 1, entry 12).
Table:1 Optimization of catalyst for Suzuki-Miyaura reaction
for arylbromides
X
B(OH)2
Catalyst
+
NO2
Solvent, K2CO3
O2N
It is a well-known fact that the choice of solvent and
Entry
Pd source (mol%)
X
Solvent
Time
(h)
15
15
15
15
15
3
Yielda
(%)
40
base is very important in the Suzuki-Miyaura reaction. To study
the effect of various solvents and bases in our system, we
examined the reaction between 4-bromonitrobenzene with
phenylboronic using palladium complex C2 as a catalyst and the
results are summarized in Table 2. It is seen from the Table 2 that
the reaction proceeded in both protic and aprotic solvents
although significant variations in yields were noticed. The
reaction seemed to be more facile in polar alcoholic solvent
rather than in other solvent like THF, DMF etc. (Table 2). On the
other hand the effect of the base was studied by carrying out the
reaction in water with various bases, which showed that the
reaction proceeded smoothly in presence of K2CO3, Na2CO3 and
Na3PO4 12H2O with equal ease. However the yield significantly
diminished in case of strong bases and organic bases.
Surprisingly, there was an abrupt change in the rate of the
1
Pd(OAc)2 (0.5)
Pd(OAc)2/L1(0.5)
Pd(OAc)2 /L2 (0.5)
Pd(OAc)2/L3 (0.5)
Pd(OAc)2/L4 (0.5)
C1 (0.5)
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
H2O
2
70
3
75
4
65
5
70
6
90
7
C2 (0.5)
2
95
8
C3 (0.5)
3
80
9
C4 (0.5)
3
85
10
11
12
C2 (0.2)
2
95
C2 (0.1)
15
2
50
C2 (0.2)
94
Reaction conditions: aryl halide (0.5 mol), phenylboronic acid (0.55
mmol), Base (1.5 mmol), Solvent (2 mL), 25 °C , in air. aIsolated yield.
o
reaction and yield when the reaction was carried out at 50 C in
water (Table 2, entry 15). We chose the optimized reaction
conditions, aryl halides (0.5 mmol) phenylboronic acid (0.55
mmol) K2CO3 (1.5 mmol) Pd complex C2 (0.2 mol %) using
water as solvent at 50 oC for further studies. The results are listed
in Table 3. In general, aryl bromides with electron-withdrawing
and electron donating substituent underwent the coupling
reactions with phenylboronic acid in nearly quantitative yields.
No significant differences were observed in the yield when
phenyl boronic acid was replaced by p-chlorobenzene boronic
acid (Table 3, entry 4, 8, 13, 18) and p-methoxybenzene boronic
acid (Table 3, entry 2, 6, 11, 16). In general ortho substituted aryl
bromides required more reaction time as compared to the para
substituted counterparts owing to steric hindrance afforded by
ortho substituents (Table 3, entry 9, 14).
Initially, to examine the efficiency of the tetradentate Schiff base
ligands
L1–L4
in
Suzuki–Miyaura
reaction,
4-
bromonitrobenzene (0.5 mmol) and phenylboronic acid (0.55
mmol) was chosen as model substrates and the reactions were
carried out using isopropanol (2 mL) as a solvent, K2CO3 (1.5
mmol) as a base, and at room temperature in the presence of
palladium(II) complexes as catalysts, generated in situ from
Pd(OAc)2 (0.5 mol%) and ligands L1–L4 (0.5 mol%) in 1:1
molar ratio.12 The results are summarized in Table 1. It has been
observed from Table 1 that, even in the absence of any ligand,
the coupling reaction of 4-bromonitrobenzene and phenylboronic
acid proceeded. However the yield of the desired cross coupling
product was very low and the reaction proceeded along with the
formation of significant amount of biphenyl as a by-product
(Table 1, entry 1). However, in presence of the Schiff-based
ligand L1 under the present reaction conditions, the reaction
proceeded with improved yield of the desired product (Table 1,
entry 2) along with the significant reduction of the side product
formation. Similar trend was observed with other Schiff base
ligands L2-L4 (Table 1, entries 3-5). Among the four ligands
used, L2 demonstrates the highest activity (Table 1, entry 3)
whereas ligand L3 shows the lowest activity (Table 1, entry 4). It

3
Table:2
Solvent and base effect for Suzuki-Miyaura
aryl chlorides with sterically bulky electron donating
substituent at ortho-position are reluctant to react with phenyl
boronic acid and very poor yield was obtained (Table 5, entry 9).
In general, due to strong C-Cl bond, aryl chlorides are difficult
substrates for coupling reaction. It is to be mentioned that our
catalyst can produce relatively less yields of coupling products
with aryl chlorides compared to aryl bromides as substrates. For
aryl chlorides these results are quite significant due to the use of
environmentally-benign reaction media and reasonably low
catalyst loading (1mol %).
reaction
Br
B(OH)2
Complex C2
+
NO2
Solvent, Base
O2N
Entry
Solvent
i-PrOH
H2O
Base
Time (h)
Yield (%)a
1
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Na2CO3
2
2
3
3
3
3
3
3
3
2
95
94
90
45
30
35
50
80
70
98
2
3
Ethanol
MeCN
EtOAc
Acetone
CHCl3
THF
Table 3: Suzuki-Miyaura cross-coupling reactions of various
4
aryl bromides with arylboronic acids in water
5
Br
+
B(OH)2
C2-Complex
K2CO3, Water, 50oC
R2
6
R1
R2
R1
7
8
Entry
1
R1
R2
Time (min)
Yield (%)
9
DMF
4-NO2
4-NO2
4-NO2
4-NO2
4-OMe
4-OMe
4-OMe
4-OMe
2-OMe
4-CH3
4-CH3
4-CH3
4-CH3
2-CH3
4-OCH
4-OCH
4-OCCH3
4-OCCH3
H
25
25
25
25
15
20
20
60
60
5
98
95
95
95
95
95
96
92
80
90
95
98
95
85
98
98
95
90
10
H2O
2
OMe
t-Butyl
Cl
3
11
12
13
14
15 b
H2O
H2O
H2O
H2O
H2O
Na3PO4.12H2O
NaOH
2
2
98
20
20
25
99
4
5
H
6
OMe
t-Butyl
Cl
KOH
2
7
Et3N
2
8
K2CO3
0.5
9
H
10
11
12
13
14
15
16
17
18
H
Reaction conditions: 4-bromonitrobenzene (0.5 mmol), phenylboronic
acid (0.55 mmol), Pd-complex C2 (0.2 mol %), Base (1.5 mmol),
Solvent (2 mL), 25 °C, in air.
OMe
t-Butyl
Cl
5
5
aIsolated yield.
bReaction is done at 50 °C
5
H
60
25
25
25
60
To extend the effectiveness of the current catalyst
system to aryl chlorides we have carried out the cross coupling
reaction using 4-methoxychlorobenzene as substrate under the
same experimental conditions. The reaction between 4-
methoxychlorobenzene with phenylboronic acid gave only 20%
yield of the desired cross-coupling product at room temperature
in water (Table 4, entry 1). Increase of catalyst loading up to 1.0
mol% showed only slight increase in the yield of the product
(Table 4, entry 2). However, we were able to isolate 75% yield of
the cross coupling product by using i-PrOH as solvent (Table 4,
entry 3). Similar to the aryl bromide, in this case also the Pd-
Schiff base complex C2 showed better results compared to C1,
C3 and C4 (Table 4, entries 5-7). However a longer reaction time
and reduced yields of the products were obtained for aryl
chlorides compared to those of aryl bromides.
H
OMe
H
Cl
Reaction conditions: Arylbromide (0.5 mmol), arylboronic acid (0.55
mmol), Pd-complex C2 (0.2 mol %), Base (1.5 mmol), water (2 mL), in air.
Table 4 Optimization of catalyst for Suzuki-Miyaura reaction
for aryl chlorides
Cl
B(OH)2
Catalyst
Solvent, K2CO3, 50oC
+
OMe
MeO
Entry
Catalyst (mol%)
Solvent
Time
Yield
(h)
6h
(%)
20
To evaluate the scope and limitations of the current
H2O
1
2
3
4
C2 (0.5)
C2 (1.0)
C2 (1.0)
C2(1.0)
procedure, reactions of a wide array of electronically diverse aryl
chlorides with arylboronic acids were examined using the
palladium complex C2 (Table 5). The aryl chlorides with electron
donating substituents such as 4-methoxychlorobenzene, 4-
methylchlorobenzene underwent coupling reactions with
arylboronic acids effectively to afford the desired biaryls in good
yields (70-80%) in isoproponol (Table 5, entries 1–8). Similarly
chlorobenzene also gave superior product formation with
different arylboronic acids (Table 5, entries 10-12). However the
reaction of aryl chlorides containing electron withdrawing
H2O
6h
2h
6h
35
75
40
iPrOH
iPrOH:H2O
5
6
7
C1 (1.0)
C3 (1.0)
C4 (1.0)
iPrOH
iPrOH
iPrOH
6
6
6
65
40
50
Reaction conditions: 4-methoxychlorobenzene (0.5 mmol), arylboronic
acid (0.55 mmol), Pd-complex, Base (1.5 mmol), water (2 mL), in air.
substituents
such
as
p-chloronitrobenzene
and
p-
chloroacetophenone with phenylboronic acid did not proceed
well and gave only 40-55% (Table 5, entry 13 & 14). However,

4
Tetrahedron
Tetrahedron Lett. 2002, 43, 8921; (c) Biricik, N.; Durap, F. ;
Kayan, C.; Gumgum, B.; Gurbuz, N.; Ozdemir, I.; Ang, W. H.;
Fei, Z.; Scopelliti, R. J. Organomet. Chem. 2008, 693, 2693; (d)
Molander, G. A.; Canturk, B. Angew. Chem. Int. Ed. 2009, 48,
9240; (e) Milde, B.; Schaarschmidt, D.; Rüffer, T.; Lang, H.
Dalton Trans. 2012, 41, 5377; (f) Das, P.; Bora, U.; Tairai, A.;
Sarmah, C. Tetrahedron Lett. 2010, 51, 1479, (g) Borah, G.;
Table 5: Suzuki-Miyaura cross-coupling reactions of various
aryl chlorides with arylboronic acids in isopropanol
Cl
B(OH)2
K2CO3, i-PrOH, 50oC
C2-Complex
R2
+
R1
R2
R1
Boruah, D.; Sarmah, G.; Bharadwaj, S.; Bora, U.
Organometal. Chem. 2013, 27, 688
Appl.
Entry
R1
R2
Time (h)
Yield (%)
75
1
2
4-OMe
4-OMe
4-OMe
4-OMe
4-Me
4-Me
4-Me
4-Me
2-Me
H
H
2
2
2
2
2
2
2
2
6
2
3
3
6
6
4. Fortman, G. C.; Nolan, S. P. Chem. Soc. Rev. 2011, 40, 5151.
OMe
t-Butyl
Cl
72
5. (a) Das, P.; Sarmah, C.; Tairai, A.; Bora, U. Appl. Organometal.
Chem. 2011, 25, 283; (b) Chahen, L.; Therrien, B.; Suss-Fink, G.
Eur. J. Inorg. Chem., 2007, 32, 5045.
3
75
4
70
5
H
80
6. (a) Botella, L.; Najera, C. Angew. Chem. Int. Ed. 2002, 41, 179;
(b) Botella, L.; Najera, C. J. Organomet. Chem. 2002, 663, 46; (c)
Beletskaya, I. P.; Cheprakov, A. V. J. Organomet. Chem, 2004,
689, 4055; (d) Alonso, D. A.; Najera, C. Chem. Soc. Rev, 2010,
39, 2891.
6
OMe
t-Butyl
Cl
78
7
80
8
80
9
H
40
10
11
12
13
14
H
85
7. (a) Shahnaz, N.; Banik, B.; Das, P., Tetrahedron Lett. 2013, 54,
2886; (b) Banik, B.; Tairai, A.; Shahnaz, N.; Das, P., Tetrahedron
Lett. 2012, 53, 5627; (c) Kostas, I. D.; Steele, B. R.; Terzis, A.;
Amosova, S. V.; Martynov, A. V.; Makhaeva, N. A., Eur. J.
Inorg. Chem. 2006, 2642.
H
OMe
t-Butyl
H
80
H
82
4-COMe
4-NO2
40
H
55
Reaction conditions: arylchloride (0.5 mmol), arylboronic acid (0.55 mmol),
8. (a) Pasini, A.; Ferrari, R.P.; Lanfranconi, S.; Pozzi, A.; Laurenti,
E.; Moroni, M. Inorganica Chimica Acta 1997, 266, 1-3; (b)
Naeimi, H.; Rabiei, K.; Salimi, F. Bull. Korean Chem. Soc. 2008,
29, 2445-2448.
Pd-complex C2 (1 mol %), K2CO3 (1.5 mmol), i-PrOH (2 mL), in air.
In conclusion, we have developed a simple and efficient
catalytic system based on Pd complex of tetradentate Schiff base
ligands for Suzuki–Miyaura reaction of aryl bromides with
arylboronic acids in water. Electronically diversified aryl
bromides underwent the coupling reaction with electronically
diversified arylboronic acids in excellent yields. The same
catalytic system is also effective for Suzuki Miyaura reaction of
less reactive aryl chlorides with arylbronic acids in isopropanol.
9. Gogoi, A.; Sarmah, G.; Dewan, A.; Bora, U.; Tetrahedron Lett.
2014, 55, 31 and references cited there in.
10. a) Lindstrom, U. M., Chem. Rev., 2002, 102, 2751;(b) Herrerias,
C. I.; Yao, C. X.; Li Z.; Li, C. J., Chem. Rev., 2007, 107,2546;
(c). Minakata S.; Komatsu, M., Chem. Rev., 2009, 109, 711.
11. Synthesis of complex C1: A methanolic solution of ligand L1
(330 mg, 1 mmol) was mixed with Pd(OAc)2 (224 mg, 1 mmol).
After refluxing the reaction mixture for 3 h with stirring, the
brown colour precipitate was filtered. The residue was washed
with hexane and recrystalized from chloroform. Yield: 85%. Anal.
Calcd (in %) for C21H16N2O2Pd; C: 58.01; H: 3.71; N: 6.44%.
Found, C: 58.18; H: 3.93; N: 6.13%. MS-ESI(CHCl3): m/z:
435[M+]; Selected IR frequency (cm-1, KBr): 1606 cm-1(vC=N). 1H
NMR (400 MHz, CDCl3) δ/ppm: 6.72(s, 1H, CH), 8.71(s, 2H,
CH=N), 7.01-7.09(m, 13H, Ph+Ph+Ph).
Acknowledgments
The authors acknowledge the Department of Science and
Technology, New Delhi for financial support for this work under
DST Woman Scientist Scheme (No SR/WOS-A/CS-78/2011(G).
References and notes
12. General procedure for Suzuki Miyaura reaction: A 25 mL
synthesizer tube had taken with a mixture of aryl halide (0.5
mmol), aryl boronic acid (0.55 mmol), base (1.5 mmol), Pd-
complex C1 (0.2 mol%) and the mixture was stirred in 2 mL of
water at 50 °C for the required time. After completion, the reaction
mixture was extracted with ether (3 × 20 mL). The combined
extract was washed with brine (2 × 20 mL) and dried over
Na2SO4. After evaporation of the solvent under reduced pressure,
the residue was chromatographed (silica gel, ethyl acetate–hexane:
1: 9) to obtain the desired products. The products were confirmed
by comparing the 1H and 13C NMR and mass spectral data with
authentic samples.
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