Anionic amido/carbocyclic carbene ligated palladium (II) complex for room temperature Suzuki reaction

Article abstract of DOI:10.1016/j.jorganchem.2013.01.013

The synthesis of anionic amido/carbocyclic carbene ligated Pd (II) complex has been reported. The palladium complex is an active catalyst for the cross-coupling reaction between aryl bromides and phenylboronic acids under phosphine-free conditions at room temperature.

Full text of DOI:10.1016/j.jorganchem.2013.01.013

Journal of Organometallic Chemistry 729 (2013) 9e13
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Anionic amido/carbocyclic carbene ligated palladium (II) complex
for room temperature Suzuki reaction
*
M. Lakshmi Kantam , T. Parsharamulu, Pravin R. Likhar, P. Srinivas
I & PC Division, Indian Institute of Chemical Technology, Hyderabad 500607, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of anionic amido/carbocyclic carbene ligated Pd (II) complex has been reported. The
palladium complex is an active catalyst for the cross-coupling reaction between aryl bromides and
phenylboronic acids under phosphine-free conditions at room temperature.
Ó 2013 Elsevier B.V. All rights reserved.
Received 6 October 2012
Received in revised form
7 January 2013
Accepted 16 January 2013
Keywords:
Suzuki reaction
Carbocyclic carbene
Phosphine-free
Palladium
Room temperature
1. Introduction
aryl chlorides with both high activity and high efficiency is a cur-
rent important topic of research. Phosphine-based ligands
Palladium catalyzed cross-coupling reactions represent an
extremely versatile tool in organic synthesis [1e3]. The formation
of new bonds between two carbon atoms are often key steps in
a wide range of organic processes ranging from supramolecular
chemistry [4,5] to natural product synthesis [6e9] and therefore
various research groups around the world are involved in broad-
ening the new methodologies that are able to improve the reac-
tion conditions. The great significance of palladium-catalyzed CeC
coupling reactions has been recognized by the 2010 Nobel lau-
reates Heck, Negishi, and Suzuki. Among these, the Suzuki reac-
tion involving the coupling of an aryl halide with an organoboron
reagent is one of the most important reactions in academic and
industry as well. This is because of several advantages associated
with Suzuki reactions such as air/moisture stable and availability
of boron reagents, functional group tolerance, low toxicity and
high thermal stability. However, for the success of coupling re-
actions, the selection of highly active and stable palladium catalyst
is primary requirement/highly desirable. In this context the
design of new ligands and their Pd-complexes that can catalyze
the SuzukieMiyaura reaction of less reactive aryl bromides and
are well documented as highly efficient and active ligands to
catalyze SuzukieMiyaura reaction. However they are often toxic,
air sensitive or quite expensive. Therefore, the development of
phosphine-free Pd catalysis has become another equally impor-
tant topic of research [10e12]. In recent years, N-heterocyclic
carbenes (NHCs) [13,14] have become a paradigmatically new
generation of strong sigma donor phosphine-free ligands in pal-
ladium catalyzed CeC coupling reactions. Among the class of N-
heterocyclic carbene ligands, nucleophilic carbocyclic carbenes
are less known and recently used in catalytic reactions. We herein
report the synthesis of new anionic amido/carbocyclic carbene
ligated Pd (II) complex and its catalytic activity in SuzukieMiyaura
reaction at room temperature.
2. Results and discussion
N-Heterocyclic carbene (NHC) ligands have important advan-
tages over the tertiary phosphine ligands because of their ability to
tune the electronic properties of metals, straightforward and con-
venient synthesis, less toxic and stable to air/moisture. Among the
diaminocarbenes and other heterocyclic carbenes [15], nucleophilic
carbocyclic carbene ligands are less explored in the catalysis [16e
19]. Recently Yao et al. reported the applications of nucleophilic
carbocyclic carbene ligands in palladium catalyzed Heck reaction of
aryl halides [20]. In our previous study, it has been observed that
* Corresponding author. Tel.: þ91 40 27193510; fax: þ91 40 27160921.
E-mail addresses: mlakshmi@iict.res.in, lkmannepalli@gmail.com (M. Lakshmi
Kantam).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.01.013

10
M. Lakshmi Kantam et al. / Journal of Organometallic Chemistry 729 (2013) 9e13
Table 1
Carbocyclic
carbene bond
Suzuki reaction between bromoanisole and phenylboronic acid.a
O
Strongly sigma donating
Steric bulk
HO
OH
O
B
N
N
3 (0.1 mol%)
Pd
O
O
HO
Base, Solvent,
Room Temperature
Br
Highly reactive
Chelation
Entry
Base
Solvent
Time (h)
Yield (%)b
Scheme 1. Design of multi-functional Pd (II) complex.
1
2
3
4
5
6
7
8
K2CO3
Cs2Co3
LiOH.H2O
Ba(OH)28H2O
DIPEA
Na2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
DMF
DMSO
DME
MeOH
MeOH
MeOH
MeOH
10
10
10
10
15
15
15
15
15
10
8
35
73
35
25
e
the anionic amide (deprotonated amide) ligands strongly donate
electrons to the metal center, thus stabilizing the various oxidation
states of the metals [21e25]. We envisaged the possibility by
designing the anionic amide group appended to nucleophilic car-
bocyclic carbene ligand, as a multi-functional and multi-donor
ligand for the palladium catalyzed room temperature Suzuki re-
action. As depicted in Scheme 1, we assumed that the presence of
anionic carboxylates and alkylamine could enhance the activity of
Pd toward oxidative addition and carbocyclic anionic carbene li-
gands derived from aromatic nitrones stabilized with cationic
group such as an iminium group could serve as a neutral donor to
palladium center [20] to afford additional stability to the resultant
palladium complex. Thus, we report here our efforts toward the
realization of this concept using simple and high yielding reaction
of 3-formyl benzoic acid and amino alcohol, and subsequent reac-
tion with hydroxyl amine acetate in dichloromethane (DCM)
(Scheme 2).
30
e
e
9
e
10
11
12
13
82c
92d
90e
55f
10
15
Cs2CO3
a
Reaction conditions: bromoanisole (1 mmol), phenylboronic acid (1.5 mmol),
Base (1 mmol), catalyst 3 (0.1 mol%) and Solvent (2 mL) at room temperature.
b
Yield of isolated product.
With 0.5 mol% of catalyst 3.
c
d
With 1 mol% of catalyst 3.
e
With 0.1 mol% of catalyst 3 at 60 ꢀC.
f
With 0.01 mol% of catalyst 3.
characterized by various spectroscopic tools (NMR, MS, HRMS, FT-
IR). The 1H NMR and 13C NMR study of 2 and 3 clearly dis-
tinguished the coordination of carbene and anionic amide to the
palladium center in presence of base. Further, high resolution mass
confirmed the loss of two mass units from benzene ring and amide
group of 2 during the complexation between palladium acetate and
2 to 3 (see Supporting information).
A preliminary testing of complex 3 revealed that this palla-
dium complex is highly efficient catalyst for the Suzuki coupling
reaction. In a subsequent optimization using various bases, sol-
vents and reaction parameters (Table 1, entries 1e9), it was
observed that the coupling of bromoanisole with phenylboronic
acid could be achieved with 73% yield of 4-methoxy-biphenyl
(entry 2) in presence of 0.1 mol% of 3, cesium carbonate as a base
The ligand 1 was prepared by coupling of 3-formyl benzoic acid
and 2-amino-3-phenylpropan-1-ol in dry dichloromethane in
presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hy-
drochloride (EDCI. HCl), 1-hydroxybenzotriazole hydrate (HOBT)
and ethyldiisopropylamine (DIPEA) (Scheme 2). The ligand 2 was
prepared in quantitative yield by simple addition of N-tertiary butyl
hydroxyl amine acetate and triethylamine to the solution of ligand
1 in dry dichloromethane at room temperature. The complexation
of palladium acetate with the ligand 2 was observed in the presence
of LiOH$H2O in THF at room temperature to afford air and moisture
stable yellow color complex 3 in 70% yield.
The solubility of complex 3 was tested in various solvents
however the reasonable solubility was observed only in highly
polar solvents such as CH3OH, DMSO, and DMF. Complex 3 was fully
OH
O
EDCI, HOBT, DIPEA
O
H2N
O
HN
HO
dry DCM/ rt/N2
O
OH
1
Et3N
NHOH.CH3COOH
dry DCM / rt / 12h
O
O
Pd (OAc)2
LiOH.H2O/ rt/12 h
N
Pd
N
N
HN
HO
O
O
HO
3
2
Scheme 2. Synthesis of amido/carbocyclic carbine ligated Pd (II) complex.

M. Lakshmi Kantam et al. / Journal of Organometallic Chemistry 729 (2013) 9e13
11
Table 2
Suzuki reaction of aryl halides and arylboronic acids.a
X
3 (0.1 mol%)
(HO)2B
Cs2CO3, MeOH, rt
R1
R
R1
R
X = I, Br
Entry
1
Aryl halide
Arylboronic acid
Product
Time (h)
Yield (%)b
OH
B
HO
10
60
Br
H
OH
B
2
3
10
10
73
62
O
O
Br
HO
HO
HO
OH
B
Br
Br
OH
B
4
5
10
10
61
O
O
OH
B
O
89c
HO
Br
O
OH
B
6
7
10
10
60
55
Br
Br
O
O
O
O
HO
HO
OH
B
O
O
OH
B
8
10
57
Br
HO
OH
B
9
10
10
10
75
74
80
I
HO
HO
HO
HO
OH
B
10
11
O
I
O
OH
B
I
I
OH
B
12
10
65
O
(continued on next page)
O

12
M. Lakshmi Kantam et al. / Journal of Organometallic Chemistry 729 (2013) 9e13
Table 2 (continued )
Entry
Aryl halide
Arylboronic acid
Product
Time (h)
10
Yield (%)b
OH
B
O
13
90c
HO
I
O
OH
B
14
15
10
10
95
90
O
O
I
I
O
HO
HO
OH
B
O
O
O
OH
B
16
10
10
35c
30c
Cl
Cl
HO
HO
OH
B
17
a
Reaction conditions: aryl halide (1 mmol), arylboronic acid (1.5 mmol), Cs2CO3 (1 mmol), catalyst 3 0.1 mol% and methanol (2 mL) at room temperature.
Yield of isolated product.
With 1 mol% of catalyst 3.
b
c
and methanol as a solvent at room temperature. The catalytic
4. Experimental section
activity of complex 3 was tested at different catalyst loadings
(entries 10e12) and at high temperature (entry 13). The high
catalytic efficiency of the catalyst 3 may be attributed to the
anionic nature of carbene stabilized by anionic amide group. The
catalytic activity of complex 3 was then extended to various aryl
halides and different phenylboronic acids using the entry 2 as the
standard reaction conditions and the results are shown in Table 2.
In the room temperature Suzuki reaction, aryl bromides and aryl
iodides with both electron-rich and electron-deficient substrates
were allowed to coupled with various boronic acids using catalyst
loading as low as 0.1 mol % (entries 1e15). The resulting coupling
products were obtained in moderate to good yields. Interestingly,
excellent yields of coupling products are obtained with the re-
actions of deactivated aryl iodides with different arylboronic acids
(entries 8,10,13 and 15). However, the catalyst has limited activity
in the reaction of chlorobenzene with phenyl and 4-methyl-
phenylboronic acids even at 1 mol% of catalyst loading (entries16
and 17).
4.1. Synthesis of ligand (1)
A two necked round bottom flask was charged with 3-formyl
benzoic acid (1 g, 6.66 mmol) in dry DCM (3 mL), was then added
1-(3-dimethylaminopropyl)-3-ethylcarbodiimide
(1.91 g, 9.99 mmol) and 1-hydroxybenzotriazole hydrate (1.35 g,
9.99 mmol) under nitrogen atmosphere at 0 ꢀC. The reaction mix-
ture was allowed to stir for 10 min and was added amino alcohol
hydrochloride
(1.2
g 8.00 mmol), ethyldiisopropylamine (DIPEA) (2.8 mL,
16.65 mmol) at the same temperature. After stirring for 2 h at room
temperature, the crude product was obtained and then was washed
with water, brine and extracted with ethyl acetate. The organic
layer was dried over sodium sulfate, concentrated under vacuum,
purified by column chromatography.
1H NMR (300 MHz, CDCl3, TMS)
d
2.99 (d, J ¼ 6.798 Hz, 2H), 3.31
(br,1H), 3.65e3.70 (dd, J ¼ 3.022 Hz,1H),3.75e3.80 (dd, J ¼ 5.288 Hz,
1H), 4.35e4.43 (m, 1H, CH), 6.98 (d, J ¼ 8.309 Hz, 1H, CONH), 7.18e
7.31 (m, 5H), 7.47e7.52 (t, J ¼ 7.554 Hz,1H), 7.89e7.96 (m, 2H), 8.129
(s,1H), 9.924 (s,1H); 13C NMR (300 MHz, CDCl3)
d 36.67, 53.18, 62.92,
3. Conclusion
126.21, 127.79, 128.18, 128.94, 129.20, 131.89, 132.76, 134.91, 135.78,
137.59, 166.51, 191.62; IR (KBr):
n
bar ¼ 3334 cmꢁ1 (br, OH), 3063,
We have synthesized anionic amido/carbocyclic carbene liga-
ted Pd (II) complex in high yields from the easily available sub-
strates. The multi-functional and highly stable palladium catalyst
was tested for the CeC coupling reaction of deactivated aryl ha-
lides with various boronic acids. Low loading palladium catalyst in
Suzuki reaction at room temperature affords coupling products
in good yields which were accomplished previously either by
using complicated phosphine or heterocyclic carbene ligands
[26,27], and with relatively high loading of Pd (i.e., >1 mol%)
[28,29]. Unlike previously reported catalytic systems for CeC
cross-coupling reactions, additional co-catalysts such as [NBu4]
Br or [PPh4]Cl are not required to achieve high catalytic activity
[30e34].
3028 cmꢁ1 (aromatic CeH),1698,1641 cmꢁ1 (C]O),1541 cmꢁ1 (C]
C), 1208 cmꢁ1 (CeN); ESI-MS: (M þ H)þ ¼ 284. HRMS (ESI) calcd for
C17H17NO3Na (M þ Na)þ: 306.1106; found: 306.1105.
4.2. Synthesis of ligand (2)
A two necked round bottomed flask was charged with 1 (0.8 g,
2.82 mmol) in dry DCM (3 mL), N-tertiary butyl hydroxyl amine
acetate (3.39 mmol) and Et3N (5.65 mmol) at room temperature.
The reaction mixture was allowed to stir for 12 h at the same
temperature. A green color crude product was obtained and it was
then washed with water, brine and extracted with ethyl acetate.

M. Lakshmi Kantam et al. / Journal of Organometallic Chemistry 729 (2013) 9e13
13
The organic layer was dried over anhydrous sodium sulfate, con-
4,40-Dimethylbiphenyl (Table 2, entry 8); 1H NMR (500 MHz,
centrated under vacuum, purified by column chromatography.
CDCl3 þ CD3OD, TMS)
d
¼ 2.38 (s, 6H), 7.22 (d, J ¼ 8.0 Hz, 4H), 7.46
1H NMR (500 MHz, CDCl3, TMS)
d
1.55 (s, 9H), 2.84e2.89 (dd,1H),
(d, J ¼ 7.0 Hz, 4H); 13C NMR (300 MHz, CDCl3)
d
¼ 21.06, 126.77,
2.95e2.99 (dd, 1H), 3.57e3.60 (dd, 1H), 3.69e3.71 (dd, 1H), 4.25 (m,
1H), 7.13 (d,1H, CONH), 7.20e7.31 (m, 5H), 7.40e7.41 (d, J ¼ 7.919 Hz,
1H), 7.542 (s, 1H), 7.66e7.67 (d, J ¼ 6.929 Hz, 1H), 7.88e7.89 (d,
129.40, 136.67, 138.24.
4,40-Dimethoxybiphenyl (Table 2, entry 7): 1H NMR (500 MHz,
CDCl3 þ CD3OD, TMS) ¼ 3.83 (s, 6H), 6.93 (d, J ¼ 8.84 Hz, 4H), 7.44
d
J ¼ 6.929 Hz, 1H), 8.91 (s, 1H); 13C NMR (300 MHz, CDCl3)
d
28.15,
(d, J ¼ 8.84 Hz, 4H); 13C NMR (300 MHz, CDCl3)
d
¼ 55.36, 114.18,
37.13, 53.63, 63.32, 71.17, 126.39, 128.46, 128.56, 129.30, 129.47,
127.73, 133.49, 158.69.
130.23, 130.61, 131.89, 134.57, 138.03, 167.15; IR (KBr):
n
4-Acetylbiphenyl (Table 2, entry 13): 1H NMR (300 MHz,
bar ¼ 3329 cmꢁ1 (br, OH), 3065 cmꢁ1 (aromatic CeH), 1714,
1643 cmꢁ1 (C]O),1538 cmꢁ1 (C]C),1243 cmꢁ1 (C-0),1192 cmꢁ1 (Ce
N); ESI-MS: (M þ Na)þ ¼ 377; HRMS (ESI) calcd for C21H26N2O3Na
(M þ Na)þ: 377.1841; found: 377.1838.
CDCl3 þ CD3OD, TMS) ¼ 2.61 (s, 3H), 7.34e7.47 (m, 3H), 7.57e7.67
d
(m, 4H), 8.00 (d, J ¼ 8.30 Hz, 2H); 13C NMR (300 MHz, CDCl3)
d
¼ 26.57, 127.16, 127.21, 128.17, 128.85, 128.89, 135.83, 139.83,
145.72, 197.63.
4.3. Synthesis of palladium complex (3)
Acknowledgments
To a round bottom flask containing a stirred suspension of pal-
ladium acetate (224.49 mg, 1 mmol) in THF (20 mL) was added 2
(424.8 mg, 1.2 mmol) in one portion followed by LiOH$H2O
(151.2 mg, 3.6 mmol). Upon stirring the solution for 12 h at room
temperature, pale yellow precipitation was obtained. The reaction
mixture was filtered, crude solid was washed with excess THF, water
and finally with methanol to obtain the pure complex in 70% yield.
T.P.R thanks UGC, New Delhi for the award of senior research
fellowship.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.01.013.
1H NMR (300 MHz, CDCl3þCD3OD, TMS)
d 1.650 (s, 9H), 2.95e3.11
(m, 2H), 3.35 (m, 2H), 3.69e3.73 (m, 1H), 7.17e7.47 (m, 8H), 8.019 (s,
References
1H); 13C NMR (300 MHz, CDCl3)
d 27.99, 36.81, 57.10, 65.98, 70.84,
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n
bar ¼ 3416 cmꢁ1 (br, OH),1577 cmꢁ1 (C]O),
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boronic acid (1.5 mmol), cesium carbonate (1 mmol) and the cat-
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stirred at room temperature and the progress of reaction was
monitored by TLC. After completion of the reaction, methanol was
removed under reduced pressure and the reaction mixture was
diluted with EtOAc (20 mL), washed with 1 N aq. HCl and water. The
combined organic phase was dried over anhydrous Na2SO4. After
removal of the solvent, the residue was subjected to column
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4.5. Analytical data for the products of the Suzuki reaction
Biphenyl (Table 2, entry 1): 1H NMR (300 MHz, CDCl3, TMS)
d
¼ 7.29e7.31 (m, 2H), 7.39 (t, J ¼ 7.74 Hz, 4H), 7.54 (d, J ¼ 8.49 Hz,
4H); 13C NMR (300 MHz, CDCl3)
¼ 96.19, 127.18, 128.73, 141.30.
4-Methoxybiphenyl (Table 2, entry 2): 1H NMR (300 MHz,
d
CDCl3 þ CD3OD, TMS)
d
¼ 3.83 (s, 3H), 6.92 (d, J ¼ 9.0 Hz, 2H), 7.24
(m, 1H), 7.35 (t J ¼ 8.0 Hz, 2H), 7.48e7.50 (m, 4H); 13C NMR
(300 MHz, CDCl3)
133.78, 140.86, 159.09.
d
¼ 55.24, 114.14, 126.59, 126.71, 128.10, 128.70,
4-Methylbiphenyl (Table 2, entry 3): 1H NMR (300 MHz,
CDCl3 þ CD3OD, TMS) ¼ 2.39 (s, 3H), 7.23e7.26 (m, 2H), 7.29e7.34
d
(m, 1H), 7.39e7.44 (t, J ¼ 8.3 Hz, 2H), 7.50 (d, J ¼ 8.31 Hz, 2H), 7.58
(d, J ¼ 6.79 Hz, 2H); 13C NMR (300 MHz, CDCl3)
d
¼ 21.07, 126.93,
128.67, 129.44, 136.96, 138.30, 141.1.
4-Methoxy-40-methyl-biphenyl (Table 2, entry 6): 1H NMR
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Chem. Int. Ed. 45 (2006) 3859e3862.
(500 MHz, CDCl3 þ CD3OD, TMS)
d
¼ 2.37 (s, 3H), 3.82 (s, 3H), 6.90
(d J ¼ 8.0 Hz, 2H), 7.16 (d, J ¼ 8.0 Hz, 2H), 7.38 (d J ¼ 8.0 Hz, 2H), 7.44
(d, J ¼ 8.0 Hz, 2H); 13C NMR (300 MHz, CDCl3)
d
¼ 21.20, 55.09,
114.15, 126.63, 127.94, 129.42, 133.82, 135.97, 138.18, 158.95.