Palladium complexes containing multidentate phenoxy-pyridyl-amidate ligands: Highly efficient catalyst for Heck coupling of deactivated aryl halides

Article abstract of DOI:10.1016/j.jorganchem.2012.08.037

N,N′,N″,O-Tetrafunctional Pd(II) complexes prepared from the easily available amino acids are shown to be highly efficient catalysts for the Heck reaction of deactivated aryl bromides and iodides with high turnover numbers up to ca.10⁴ and moderate activity for the activation of aryl chlorides under phosphine-free conditions.

Full text of DOI:10.1016/j.jorganchem.2012.08.037

Journal of Organometallic Chemistry 723 (2013) 129e136
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Palladium complexes containing multidentate phenoxyepyridyleamidate
ligands: Highly efficient catalyst for Heck coupling of deactivated aryl halides
,
b
,
a
a
a
c
M. Lakshmi Kantam a , Manne Annapurna , Pravin R. Likhar , P. Srinivas , Nedaossadat Mirzadeh ,
*
,
c
Suresh K. Bhargava b
a I & PC Division, Indian Institute of Chemical Technology, Hyderabad 500607, India
b RMIT-IICT Center, Indian Institute of Chemical Technology, Hyderabad 500607, India
c Advanced Materials & Industrial Chemistry, School of Applied Sciences, RMIT University, GPO Box 2476V, Melbourne, Victoria 3001, Australia
a r t i c l e i n f o
a b s t r a c t
N,N0,N00,O-Tetrafunctional Pd(II) complexes prepared from the easily available amino acids are shown to
be highly efficient catalysts for the Heck reaction of deactivated aryl bromides and iodides with high
turnover numbers up to ca.104 and moderate activity for the activation of aryl chlorides under
phosphine-free conditions.
Article history:
Received 8 June 2012
Received in revised form
9 August 2012
Accepted 31 August 2012
Ó 2012 Elsevier B.V. All rights reserved.
Keywords:
Heck reaction
N-ligand
Phosphine-free
Palladium
High turnover
1. Introduction
different donor-functionalities such as N-, O-, and S-centred ligands
namely N-heterocyclic [10e12], carbocyclic [13,14], anionic carbo-
The palladium catalyzed arylation of olefins (Heck reaction) is
one of the most versatile tools for CeC bond formation [1e3]. The
application of this reaction is mainly exploited in the synthesis of
natural products, materials science and bioorganic chemistry [4e
6]. The great importance of CeC bond-forming reactions has
encouraged the chemical community to search for highly active and
stable palladium catalysts, which should also be versatile and
efficient. The efficiency of the catalytic system mainly depends on
the types of ligand used in the coupling reactions. The catalytic
system consisting of palladium and phosphine ligands has been
widely studied for CeC bond forming process [7e9]. However,
these ligands are expensive and demand tedious synthetic proce-
dures for their preparation. Furthermore, they are often toxic and
also air- and moisture-sensitive; generally undergoing phosphine
degradation by PeC bond cleavage. Therefore, the development of
phosphine-free palladium-catalysts has become an important
research focus. Consequently, many catalytic systems consisting of
cyclic carbenes [15], oxazolines [16], Schiff bases [17], pyridines
[18,19], amines [20], bisimidazoles [21,22], pyrazoles [23e27], ureas
[28], thioureas [29e31], tetrazoles [32], and amino acids [33] have
been developed. These phosphine-free ligands are potentially
advantageous as they are relatively less expensive, less toxic and
stable to air and moisture.
In the same context, recently we have reported phosphine-free
tetradentate dicarboxyamidate/dipyridyl palladium and uridate/
pyridyl palladium complexes as highly stable and efficient catalysts
for the Heck reaction of deactivated aryl halides with high turnover
numbers [34,35]. In this paper, we report the simple synthesis of
palladium(II) complexes of multi-donor and multi-functional
amido/pyridyl/phenolic/amine ligands and their catalytic activity
in the CeC bond-forming reactions under phosphine-free
conditions.
2. Results and discussions
In our previous report, we investigated that in N-based ligands,
the presence of pyridine ring as a neighbouring group enhances the
chelating effect of a carboxylate group in Pd catalysis [36]. There-
fore, it was our current interest to design and synthesize the ligands
* Corresponding author. I & PC Division, Indian Institute of Chemical Technology,
Hyderabad 500607, India. Tel.: þ91 40 27193510; fax: þ91 40 27160921.
E-mail
addresses:
mlakshmi@iict.res.in,
lkmannepalli@gmail.com
(M.L. Kantam).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.08.037

130
M.L. Kantam et al. / Journal of Organometallic Chemistry 723 (2013) 129e136
using amino acid, pyridine and aldehyde to examine the effect of
multi-functional donor groups in Pd catalysis. The synthesis of the
ligand commenced with the formation of amide bond from the Boc-
protected amino acid (1) and 2-picolylamine using N,N0-dicyclo-
hexylcarbodiimide (DCC) as coupling reagent in CH2Cl2 at 0 ꢀC.
Upon deprotection of compound 2 with trifluoroacetic acid,
compound 3 was obtained in high yields. The condensation of 3
with salicylaldehydes followed by imine reduction at low temper-
ature afforded N,N0,N00,O-tetrafunctional ligands (4a, 4b) in 75e80%
yields (Scheme 1).
bis-50-chelated palladium complex [Pd(C17H18NO)2] [1.974(11) Å,
1.989(10) A] [39].
ꢀ
To examine the catalytic activity of the complexes, 5a and 5b in
the Heck reaction, 4-methoxy bromobenzene and styrene were
chosen as substrates to obtain the CeC coupled product, using
variety of reaction conditions including different catalyst loading.
The progress of the reaction was monitored by GC analysis; the
results are shown in Table 3. Among the bases employed, LiOH$H2O
was found to be best in the present protocol. Similarly, N,N-dime-
thylformamide (DMF) was found to be most suitable solvent among
the solvents studied in combination with LiOH$H2O. Eventually, 4-
methoxy-trans-stilbene was obtained in 90% yield (TON 90,000)
with 0.001 mol% of 5a in DMF at 145 ꢀC for 15 h (Table 3, entry 5).
Newly prepared complexes were compared with ligand-less Pd-
catalyst, Pd(OAc)2, under optimized reaction conditions [40e42];
results showed that maximum yield of formation of 4-methoxy-
stilbene does not exceed 12% (Table 3, entry 7).
The catalytic activities of 5a and 5b were also compared
following identical optimized reaction conditions; the former
exhibited higher efficiency (low catalyst loading and less reaction
time). We assume that steric factor (presence of two bulky tert-
butyl groups at 3 and 5 position of the aromatic ring) might be
responsible for the less efficiency of complex 5b in the coupling
reaction (Table 3, entry 6).
To explore the scope of the reactions catalyzed by 5a, we next
examined the application of 5a to the cross-coupling of deactivated
aryl bromides with olefins under the optimized conditions
(0.001 mol% 5a, 1.2 mmol of LiOH$H2O, DMF 2.0 mL, 145 ꢀC); the
results are presented in Table 4 (entries 1e6). The reactions of aryl
bromides bearing a methyl or methoxy group with either styrene or
4-methyl styrene (entries 1e4) gave high yields of the coupled
product. In addition to aryl bromides, aryl iodides were also tested
under the same reaction conditions at lower temperature ca.120 ꢀC
(entries 7e12).
The novel N,N0,N00,O-tetrafunctional Pd(II) complexes were
readily prepared in quantitative yields by addition of N,N0,N00,O-
tetradentate ligands (4a, 4b) to a solution of Pd(OAc)2 in tetrahy-
drofuran at room temperature (Scheme 2).
The solubility study suggests that complexes 5a and 5b are fairly
soluble in highly polar solvents such as MeOH, DMF, DMA and
DMSO. Thermogravimetry analysis (TGA) confirmed that
complexes 5a and 5b have high thermal stability up to 250 ꢀC (see
Supporting information). The complexes have been fully charac-
terized by NMR, FT-IR and HRMS techniques. The formation of
amidate bonding to palladium in 5a and 5b was initially studied by
1H and 13C NMR spectroscopy; the chemical shifts were similar to
those observed in our previous work. The structure of 5a has also
been confirmed by X-ray diffraction study (shown in Fig. 1);
selected bond lengths and angles are summarized in Table 1.
The structure of 5a consists of one palladium(II) atom coordi-
nated in a distorted square planar geometry [bond angles deviate
from 90ꢀ or 180ꢀ by more than 5ꢀ (av.)] by three amine, amide, and
pyridine type of nitrogen atoms and one phenoxy-type oxygen
atom (Table 2). In 5a, the deviation of the palladium atom from the
least-squares plane between the five atoms Pd(1), O(1), N(1), N(2)
ꢀ
and N(3) is 0.048(1) A. The Pd(1)eN(1), Pd(1)eN(2) and PdeN(3)
ꢀ
bond lengths [2.030(2) Å, 1.930(2) A and 2.018(2), respectively]
are within the expected range for PdeNamine, PdeNamide and Pde
Npyridine bond distances [37,38]. The PdeO bond length of
We also examined the catalytic activity of palladium complex 5a
in CeC coupling of aryl chlorides and observed that the catalyst was
ꢀ
2.0040(18) A in 5a is slightly longer than corresponding bond in
Scheme 1. Synthesis of tetrafunctional N,N0,N00,O-tetradentate ligands.

M.L. Kantam et al. / Journal of Organometallic Chemistry 723 (2013) 129e136
131
Scheme 2. Synthesis of tetrafunctional N,N0,N00,O-tetradentate Pd(II) complexes.
ꢀ
stable and active enough to handle electron-deficient aryl chlorides
at 160 ꢀC (Table 5, entries 1e2). Although the optimized reaction
conditions used in Table 3 were less effective for the Heck reaction
of aryl chlorides (Table 5, entries 3e8), moderate yields of the cross
coupled products could obtain by increasing the catalyst loading up
to 1 mol%, LiOH$H2O (2.0 mmol), TBAB (0.5 mmol).
The important advantages associated with these catalysts,
compared to the previously reported phosphine-free catalysts, are
their stability towards air, moisture and heat, and also their long life
time.
monochromated Mo-K
a
radiation (
l
¼ 0.71073 A) from a 1
mS
microsource. Geometric and intensity data were collected using
SMART software [43]. The data were processed using SAINT [44],
and corrections for absorption were applied using SADABS [45]. The
structure was solved by direct methods and refined with full-
matrix least-squares methods on F2 using the SHELX-TL package
[46]. Crystallographic data are summarized in Table 2. The CCDC
reference number 87542 refers to the crystal structure reported in
this paper.
4.2. Typical procedure for the preparation of ligands (4a and 4b)
3. Conclusion
A 50 mL round bottom flask was charged with a stir bar, sali-
cylaldehyde (0.6 mmol), EtOH (20 mL) and anhydrous Na2SO4
(2.0 g). Chiral amine 3 (1 mmol) was added, followed by K2CO3
(1.5 mmol). The mixture was stirred at room temperature until
completion of the reaction (monitored by TLC). The mixture was
then filtered, and volatiles were removed in vacuo. The residue thus
obtained was dissolved in MeOH (15 mL) and NaBH4 (1.5 mmol)
was added at 0 ꢀC. The resulting mixture was allowed to stir for 3 h
at room temperature. After evaporation of MeOH, the residue was
subjected to column chromatography purification in order to get
the desired N,N0,N00,O-tetrafunctional ligands 4a, 4b in 75e80%
yield.
The tetrafunctional N,N0,N00,O-tetradentate ligands prepared
from easily available amino acid in high yields, have been used to
synthesis novel palladium(II) compounds (5a, 5b); whose catalytic
activities were tested in the CeC coupling reactions under
phosphine-free condition. The highly stable palladium catalyst 5a is
able to catalyze the CeC coupling of deactivated aryl bromides and
iodides with styrenes to afford extremely high yield of coupled
products (up to 104 TON).
4. Experimental section
4.1. X-ray crystallography
4.2.1. N,N0,N00,O-Tetrafunctional ligand (4a)
X-ray diffraction data were collected from single crystal on a D8
Bruker diffractometer with APEX2 area detector using graphite
4.2.1.1. 2-(tert-Butoxycarbonylamino)-3-methylbutanoic acid (1).
1H NMR (300 MHz, CDCl3, TMS):
d
0.93e1.02 (m, 6H), 1.45 (s, 9H),
2.12e2.24 (m, 1H), 4.19e4.26 (m, 1H), 5.04 (d, J ¼ 9.0 Hz, 1H), 9.75
(br s, 1H); 13C NMR (75 MHz, CDCl3)
17.23, 18.82, 28.10, 30.89,
d
58.26, 79.85, 155.81, 176.23; ESI-MS: (M
þ
H)þ
¼
218,
(M þ Na)þ ¼ 240.
4.2.2. tert-Butyl 3-methyl-1-oxo-1-(pyridin-2-ylmethylamino)
butan-2-ylcarbamate (2)
Mp: 93e95 ꢀC; 1H NMR (300 MHz, CDCl3, TMS):
d 0.90e0.98 (m,
6H), 1.42 (d, J ¼ 5.5 Hz, 9H), 2.02e2.21 (m, 1H), 4.01 (br s, 1H), 4.54
(t, J ¼ 5.09 Hz, 2H), 5.23 (br s, 1H), 7.12e7.18 (m, 1H), 7.24e7.38 (m,
2H), 7.58e7.66 (m, 1H), 8.49 (br s, 1H); 13C NMR (75 MHz, CDCl3)
d
17.70, 19.13, 28.08, 30.90, 44.24, 59.75, 79.28, 121.66, 122.02,
Table 1
Selected bond lengths (A) and angles ( ) in 5a.
ꢀ
ꢀ
Pd(1)eN(1)
Pd(1)eN(2)
N(1)ePd(1)eN(3)
N(2)ePd(1)eO(1)
N(3)ePd(1)eO(1)
2.030(2)
1.930(2)
167.33(8)
175.81(9)
94.88(8)
Pd(1)eN(3)
Pd(1)eO(1)
N(1)ePd(1)eN(2)
N(2)ePd(1)eN(3)
O(1)ePd(1)eN(1)
2.018(2)
2.0040(18)
84.91(9)
82.76(9)
97.24(8)
Fig. 1. Molecular structure of N,N0,N00,O-tetradentate Pd(II) complexes 5a. Thermal
displacement ellipsoids are drawn at 50% probability level. C-bound hydrogen atoms
(not depicted) were refined in idealized positions. The N-bound H-atom H1 was
located from residual electron density and was refined without restraints.

132
M.L. Kantam et al. / Journal of Organometallic Chemistry 723 (2013) 129e136
(CO); IR (Neat, cmꢁ1): 3290 (NeH), 2963 (CeH), 1652, 1593 (C]O),
1253 (CeN), 1153 (CeO); ESI-MS (m/z): (M 314,
H)þ
Table 2
Crystal data and details of data collection and structure refinement for complex 5a.
þ
¼
(M
þ
Na)þ
¼
336; HRMS: calcd for C18H24N3O2
Formula
C18H21N3O2Pd
417.78
Orthorhombic
P212121
6.1084(6), 11.7860(12), 23.162(2)
90, 90, 90
1667.5(3)
(M þ H)þ ¼ 314.1868, Found: 314.1877; Anal. Calc. for C18H23N3O2:
Molecular weight
Crystal system
Space group
C, 68.98; H, 7.40; N, 13.41. Found: C, 68.85; H, 7.22; N, 13.37%.
ꢀ
ꢀ
ꢀ
a (A), b (A), c (A)
4.2.5. N,N0,N00,O-Tetrafunctional ligand (4b)
a
(ꢀ),
b g
(ꢀ), (ꢀ)
Mp: 153e155 ꢀC; 1H NMR (300 MHz, CDCl3, TMS):
d
¼ 0.95 (d,
3
ꢀ
V (A )
Z
4
J ¼ 6.8 Hz, 3H, CH(CH3)2), 1.02 (d, J ¼ 6.8 Hz, 3H, CH(CH3)2), 1.23 (s,
9H, t-BueH), 1.40 (s, 9H, t-BueH), 1.86e1.97 (m, 1H, CH(CH3)2), 2.43
(br s, 1H, NH), 2.82 (br d, J ¼ 6.0 Hz, 1H, CHCH(CH3)2), 3.59 (d,
J ¼ 13.6 Hz, 1H, CH2NH), 4.06 (d, J ¼ 12.8 Hz, 1H, CH2NH), 4.53e4.71
(m, 2H, CH2), 6.72 (d, J ¼ 2.3 Hz, 1H, PheH), 6.95 (t, J ¼ 4.2 Hz, 1H,
CONH), 7.14 (d, J ¼ 2.3 Hz, 1H, PheH), 7.17e7.22 (m, 1H), 7.29 (d,
J ¼ 7.6 Hz,1H), 7.64e7.70 (m,1H) [PyeH], 8.49 (d, J ¼ 4.5 Hz,1H, Pye
Dcalc (mg mꢁ3
)
1.664
1.128
200(2)
m
(mmꢁ1
T (K)
Crystal size (mm)
range (ꢀ)
Reflections collected
Unique (Rint
Data/restrains/parameters
)
0.26 ꢂ 0.04 ꢂ 0.04
q
1.94e33.99
26,195
7289(0.0569)
7289/0/223
R1 ¼ 0.0373, wR2 ¼ 0.0617
R1 ¼ 0.0514, wR2 ¼ 0.0656
0.414 and ꢁ0.580
)
H), 10.41 (br s, 1H, OH); 13C NMR (75 MHz, CDCl3):
d
¼ 18.86, 19.77
Final R indices [I > 2
R indices (all data)
Largest diff. peak and hole (e A
s
(I)]
(CH(CH3)2), 29.59, 31.58 (C(CH3)3), 31.61 (CH(CH3)2), 34.07, 34.85
C(CH3)3), 44.15, 51.63 (CH2), 67.00 (CHCH(CH3)2), 121.86, 122.10,
122.46, 123.02, 123.65 (PheC, PheCH, PyeCH), 135.88, 136.76 (Phe
C), 140.59 (PyeCH), 149.00 (PheC), 154.27 (PyeCH), 155.81 (PyeC),
173.11(CO); IR (KBr, cmꢁ1): 3270 (NeH), 2958 (CeH), 1645, 1565
(C]O), 1235 (CeN), 1103 (CeO); ESI-MS (m/z): (M þ H)þ ¼ 426;
HRMS: calcd for C26H40N3O2 (M þ H)þ ¼ 426.3120, Found:
426.3140; Anal. Calc. for C26H39N3O2: C, 73.37; H, 9.24; N, 9.87.
Found: C, 73.25; H, 9.17; N, 9.83%.
ꢀꢁ3
)
136.55, 148.66, 155.74, 156.62, 171.89; ESI-MS: (M þ H)þ ¼ 308,
(M þ Na)þ ¼ 330.
4.2.3. 2-Amino-3-methyl-N-(pyridin-2-ylmethyl)butanamide (3)
1H NMR (300 MHz, CDCl3, TMS):
d
0.84 (d, J ¼ 6.8 Hz, 3H), 1.00
(d, J ¼ 6.8 Hz, 3H), 2.25e2.35 (m, 1H), 3.26 (d, J ¼ 3.8 Hz, 1H), 4.55
(d, J ¼ 5.3 Hz, 2H), 7.15e7.19 (m, 1H), 7.29 (s, 1H), 7.61e7.67 (m, 1H),
8.10 (br s, 1H), 8.53 (d, J ¼ 3.8 Hz, 1H); 13C NMR (75 MHz, CDCl3)
4.3. Typical procedure for the preparation of palladium complexes
(5a, 5b)
d
16.24, 19.65, 31.06, 49.15, 60.36, 122.19, 122.32, 136.86, 148.98,
157.05, 174.61; ESI-MS: (M þ H)þ ¼ 208.
A single necked 25 mL round bottom flask was charged with the
ligand (4a/4b) (1.0 mmol), LiOH$H2O (3.0 mmol) and THF (10 mL).
To this stirred solution, Pd(OAc)2 (0.9 mmol) was added in one
portion at room temperature. After stirring the mixture for 24 h at
room temperature, a yellow coloured solution was obtained. The
solvent was removed under reduced pressure and the residue was
washed with water to remove excess base (note: complex is
insoluble in water). The resulting solid was dried under high
vacuum. The complexes were crystallized from methanol to obtain
the pure complex (5a/5b) in 85e88% yield.
4.2.4. N,N0,N00,O-Tetrafunctional ligand (4a)
1H NMR (300 MHz, CDCl3, TMS):
d
¼ 0.86e0.94 (m, 6H,
CH(CH3)2), 1.80e1.91 (m, 1H, CH(CH3)2), 2.01 (br s, 1H, NH), 2.89 (d,
J ¼ 6.8 Hz, 1H, CHCH(CH3)2), 3.56 (d, J ¼ 13.6 Hz, 1H, CH2NH), 3.94
(d, J ¼ 13.6 Hz, 1H, CH2NH), 4.51 (br s, 2H, CH2), 6.35 (br s, 1H, OH),
6.65 (t, J ¼ 7.2 Hz, 1H), 6.73e6.81 (m, 2H), 7.07 (t, J ¼ 7.6 Hz, 1H)
[PheH], 7.14e7.18 (m, 1H), 7.28e7.30 (m, 1H), 7.63 (t, J ¼ 7.6 Hz, 1H)
[PyeH], 7.86 (br s, 1H, CONH), 8.40 (s, 1H, PyeH); 13C NMR (75 MHz,
CDCl3):
d
¼ 18.65, 19.52 (CH(CH3)2), 31.35 (CH(CH3)2), 44.06, 50.64
(CH2), 67.02 (CHCH(CH3)2), 116.13, 119.07 (PheCH, PyeCH), 122.31,
122.47 (PheCH and PheC),122.55 (PyeCH), 128.73 (PheCH), 136.92
(PyeCH), 148.67 (PyeCH), 156.16 (PyeC), 157.60 (PheC), 173.01
4.3.1. Palladium complex (5a)
Mp: decomposed to black metal above 243 ꢀC; 1H NMR
(300 MHz, DMSO-d6, TMS):
d
1.07 (d, J ¼ 6.9 Hz, 3H, CH(CH3)2), 1.16
Table 3
Heck reaction between 4-bromo anisole and styrene.a
Entry
Base
Solvent
Yield (%)b
TON
1
2
3
4
5
6
7
Na2CO3
K2CO3
K3PO4
DMF
DMF
DMF
DMF
DMF
DMF
DMF
15
25
17
22
90
60c
12d
15,000
25,000
17,000
22,000
90,000
60,000
12,000
NaOAc
LiOH$H2O
LiOH$H2O
LiOH$H2O
a
Reaction conditions: 4-bromo anisole (1.0 mmol), styrene (2.0 mmol), catalyst (0.001 mol%), base (1.2 mmol), solvent (2.0 mL).
Isolated yields.
Catalyst 5b.
Pd(OAc)2 used as a catalyst.
b
c
d

M.L. Kantam et al. / Journal of Organometallic Chemistry 723 (2013) 129e136
133
Table 4
Heck reaction of aryl halides and olefins.a
Entry
Ary1 halide
Olefin
Product
Yield (%)b
TON
Br
Br
1
90
90,000
91,000
MeO
MeO
MeO
2
91
MeO
Br
Br
3
4
5
6
7
91
92
94
92
90c
91,000
92,000
94,000
92,000
90,000
Br
Br
I
I
MeO
MeO
MeO
MeO
8
91c
91,000
I
9
94c
93c
94,000
93,000
I
10
11
I
I
92c
95c
92,000
95,000
12
a
Reaction conditions: aryl halide (1 mmol), olefin (2 mmol), catalyst (0.001 mol%), LiOH$H2O (1.2 mmol), DMF (2 mL) at 145 ꢀC, for 15 h.
Isolated yields.
At 120 ꢀC.
b
c
(d, J ¼ 6.9 Hz, 3H, CH(CH3)2), 2.39e2.50 (m, 1H, CH(CH3)2), 3.57e
1H), [PyeH], 8.49 (d, J ¼ 4.6 Hz, 1H, PyeH); 13C NMR (75 MHz,
3.66 (m, 2H, 1H of CHCH(CH3)2 and 1H of CH2NH), 3.84 (br s, 1H,
NH), 4.58e4.67 (m, 2H, CH2), 4.96 (d, J ¼ 19.6 Hz, 1H, CH2NH), 6.47
(t, J ¼ 6.9 Hz,1H), 6.86 (d, J ¼ 8.1 Hz,1H), 6.96 (d, J ¼ 6.9 Hz, 1H), 7.12
(t, J ¼ 7.5 Hz, 1H) [PheH], 7.37 (t, J ¼ 8.1 Hz, 2H), 7.88 (t, J ¼ 7.5 Hz,
DMSO-d6) d 17.78, 17.96 (CH(CH3)2), 30.46 (CH(CH3)2), 53.21, 55.21
(CH2), 74.90 (CHCH(CH3)2), 112.46, 118.77 (PheCH, PyeCH), 122.56,
122.90 (PheCH, PheC), 122.94 (PyeCH), 129.37, 130.56 (PheCH),
138.94, 146.12 (PyeCH), 165.34 (PyeC), 167.39 (PheC), 175.80

134
M.L. Kantam et al. / Journal of Organometallic Chemistry 723 (2013) 129e136
Table 5
Heck reaction of aryl chlorides and olefins.a
Entry
Ary1 halide
Olefin
Product
Yield (%)b
Cl
Cl
1
75
O2N
O2N
O2N
2
82
O2N
Cl
Cl
3
4
5
33
36
28
Cl
Cl
MeO
MeO
MeO
MeO
6
7
31
Cl
Cl
38
40
8
a
Reaction conditions: aryl chloride (1 mmol), olefin (2 mmol), catalyst (1 mol%), LiOH$H2O (2.0 mmol), DMF (2 mL) TBAB 0.5 mmol at 160 ꢀC for 24 h.
Isolated yields.
b
(CO); IR (KBr, cmꢁ1): 3143 (NeH), 2925 (CeH), 1714, 1604 (C]O),
C(CH3)3), 74.65 (CHCH(CH3)2), 122.48, 122.81, 122.86, 123.12, 125.39
(PheC, PheCH, and PyeCH), 133.03, 135.86, 138.91 (PheC, of Pye
CH), 146.26 (PyeCH), 162.13 (PheC), 167.64 (PyeC), 175.79 (CO); IR
(KBr, cmꢁ1): 3267 (NeH), 2955 (CeH), 1611 (C]O), 1273 (CeN),
1095 (CeO); ESI-MS (m/z): (M þ H)þ ¼ 530; HRMS: calcd for
C26H38N3O2Pd (M þ H)þ ¼ 530.1998, Found: 530.1976; Anal. Calc.
for C26H37N3O2Pd: C, 58.92; H, 7.04; N, 7.93. Found: C, 58.87; H,
7.01; N, 7.88%.
1306 (CeN), 1100 (CeO); ESI-MS: (M þ H)þ ¼ 418; HRMS: calcd for
C18H21N3O2NaPd (M þ Na)þ ¼ 440.0566, Found: 440.0562; Anal.
Calc. for C18H21N3O2Pd: C, 51.75; H, 5.07; N, 10.06. Found: C, 51.59;
H, 5.02; N, 10.04%.
4.3.2. Palladium complex (5b)
Mp: decomposed to black metal above 190 ꢀC; 1H NMR
(300 MHz, DMSO-d6, TMS):
d
¼ 1.087e1.13 (m, 6H, CH(CH3)2), 1.24
(s, 9H, t-BueH), 1.45 (s, 9H, t-BueH), 2.17e2.33 (m, 1H, CH(CH3)2),
3.47e3.64 (m, 2H, 1H of CH2NH and 1H of CHCH(CH3)2), 4.37 (t,
J ¼ 11.7 Hz, 1H, NH), 4.52 (d, J ¼ 20.2 Hz, 1H, CH2NH), 4.94 (d,
J ¼ 20.2 Hz, 2H, CH2), 6.77 (s, 1H), 7.09 (s, 1H) [PheH], 7.38e7.54 (m,
2H), 7.88e7.99 (m, 1H) [PyeH], 8.56 (br d, J ¼ 4.2 Hz, 1H, PyeH); 13C
4.4. Typical procedure for Heck reaction of aryl bromides
The 100 mL round bottom flask was charged with aryl bromides
(1.0 mmol), alkenes (2.0 mmol), LiOH$H2O (1.2 mmol) and the
catalyst (0.001 mol%) in N,N-dimethylformamide (2.0 mL). The
reaction mixture was heated at 145 ꢀC for 15 h and the progress of
reaction was monitored by TLC. At the end of the reaction, the
NMR (75 MHz, DMSO-d6):
d
¼ 17.69, 18.62 (CH(CH3)2), 29.47, 30.30,
31.64, 33.30, 34.95 (C(CH3)3, CH(CH3)2,and CH2), 53.41, 55.58

M.L. Kantam et al. / Journal of Organometallic Chemistry 723 (2013) 129e136
135
reaction mixture was cooled to room temperature and was diluted
4.7.5. trans-Stilbene (Table 4, entry 5)
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
chromatography on silica gel using ethyl acetate and hexane to
afford the Heck product in high purity.
1H NMR (300 MHz, CDCl3, TMS)
d
7.05 (s, 2H), 7.20 (t, J ¼ 7.74 Hz,
2H), 7.31 (t, J ¼ 7.5 Hz, 4H), 7.46 (d, J ¼ 7.4 Hz, 4H); 13C NMR
(75 MHz, CDCl3)
d 126.46, 127.56, 128.64, 137.25; EI-MS (m/z)
(M)þ ¼ 180.
4.7.6. 4-Nitro-trans-stilbene (Table 5, entry 1)
1H NMR (300 MHz, CDCl3, TMS)
4.5. Typical procedure for Heck reaction of aryl iodides
d
7.10 (d, J ¼ 16.6 Hz,1H), 7.23 (d,
J ¼ 16.6 Hz,1H), 7.30 (d, J ¼ 7.5 Hz,1H), 7.36 (t, J ¼ 7.5 Hz, 2H) 7.51 (d,
The 100 mL round bottom flask was charged with aryl bromides
(1.0 mmol), alkenes (2.0 mmol), LiOH$H2O (1.2 mmol) and the
catalyst (0.001 mol%) in N,N-dimethylformamide (2.0 mL). The
reaction mixture was heated at 120 ꢀC for 15 h and the progress of
reaction was monitored by TLC. At the end of the reaction, the
reaction mixture was cooled to room temperature and was diluted
with EtOAc (20 mL), washed with 1 N aq. HCl and water. The
combined organic phase was dried over anhydrous Na2SO4. After
removal of the solvent, the residue was subjected to column
chromatography on silica gel using ethyl acetate and hexane to
afford the Heck product in high purity.
J ¼ 6.7 Hz, 2H), 7.61 (d, J ¼ 9.1 Hz, 2H), 8.21 (d, J ¼ 9.1 Hz, 2H); 13C
NMR (75 MHz, CDCl3)
d 124.04, 126.16, 126.76, 126.95, 128.82,
133.20, 136.06, 143.74, 146.62; EI-MS (m/z) (M)þ ¼ 225.
4.7.7. 4-Nitro-40-methyl-trans-stilbene (Table 5, entry 2)
1H NMR (500 MHz, CDCl3, TMS)
d 2.38 (s, 3H), 7.04 (d,
J ¼ 16.8 Hz, 1H), 7.15 (m, 3H), 7.39 (d, J ¼ 7.91 Hz, 2H), 7.58 (d,
J ¼ 8.9 Hz, 2H), 8.18 (d, J ¼ 8.9 Hz, 2H); 13C NMR (300 MHz, CDCl3)
d
21.33, 124.08, 125.20, 126.64, 126.92, 129.57, 133.22, 133.35,
138.98, 144.04, 146.51; EI-MS (m/z) (M)þ ¼ 239.
Acknowledgements
4.6. Typical procedure for Heck reaction of aryl chlorides
M. Annapurna thanks UGC, New Delhi for the award of senior
research fellowship.
The 100 mL round bottom flask was charged with aryl bromides
(1.0 mmol), alkenes (2.0 mmol), LiOH$H2O (2.0 mmol), TBAB
(0.5 mmol), and the catalyst (1 mol%) in N,N-dimethylformamide
(2.0 mL). The reaction mixture was heated at 155 ꢀC for 24 h and the
progress of reaction was monitored by TLC. At the end of the
reaction, the reaction mixture was cooled to room temperature and
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 chromatography on silica gel using ethyl acetate and
hexane to afford the Heck product in high purity.
Appendix A. Supplementary material
CCDC 87542 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Appendix B. Supporting information
Supporting information related to this article can be found at
http://dx.doi.org/10.1016/j.jorganchem.2012.08.037.
4.7. Analytical data for the products of the Heck reaction
4.7.1. 4-Methoxy-trans-stilbene (Table 4, entry 1)
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