Uridate/pyridyl Pd(II) complexes: Phosphine-free high turnover catalysts for the Heck reaction of deactivated aryl bromides

Article abstract of DOI:10.1016/j.jorganchem.2010.09.075

The synthesis and structure of palladium(II) complexes bearing uridato/pyridyl ligands as an anionic N-donor coordination sites are reported. The complexes have been shown to be highly active catalysts for the Heck reaction of aryl bromides (TON 4.0×10

Full text of DOI:10.1016/j.jorganchem.2010.09.075

Journal of Organometallic Chemistry 696 (2011) 795e801
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Uridate/pyridyl Pd(II) complexes: Phosphine-free high turnover catalysts for the
Heck reaction of deactivated aryl bromides
,
b
Pottabathula Srinivas a, Keesara Srinivas a, Pravin R. Likhar a , Balsubramanian Sridhar ,
*
Kakita Veera Mohan c, Suresh Bhargava d, Mannepalli Lakshmi Kantam a
,
*
a I & PC Division, Indian Institute of Chemical Technology, Hyderabad 500607, India
b X-ray Crystallography Center, Indian Institute of Chemical Technology, Hyderabad 500607, India
c NMR Center, Indian Institute of Chemical Technology, Hyderabad 500607, India
d School of Applied Sciences, RMIT University, Melbourne, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and structure of palladium(II) complexes bearing uridato/pyridyl ligands as an anionic
N-donor coordination sites are reported. The complexes have been shown to be highly active catalysts for
the Heck reaction of aryl bromides (TON 4.0ꢀ104e9.1ꢀ104) and moderate activity for the activation of
aryl chlorides under phosphine-free conditions.
Received 20 July 2010
Received in revised form
29 September 2010
Accepted 30 September 2010
Available online 12 October 2010
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Heck reaction
N-Ligand
Phosphine-free
Palladium
High turnover
1. Introduction
As the choice of ligand plays a major role in the efficiency of the
catalyst, phosphine ligands are the first choice to catalyze the Heck
The Heck reaction [1], since its popularity started to flourish in
the mid 19800s, has become not only one of the most exciting
organic transformations for CeC bond formation but also a bench-
mark to estimate the efficiency of a catalytic system [2]. This
powerful reaction has received considerable attention due to its
functional group tolerance and its application to a broad range of
endeavors, ranging from synthetic organic chemistry to materials
science [3]. Therefore, several goals have to be achieved for its
industrial application, such as the use of inexpensive starting
materials, achievement of high turnover numbers (TON’s) with less
reactive aryl bromides and aryl chlorides, and the use of stable and
inexpensive ligands. In this context, the design of new ligands and
their palladium complexes that can catalyze the Heck reaction of
less reactive aryl bromides and aryl chlorides with both high
activity and high efficiency is a current important topic of research.
reaction more actively and efficiently [4]. However, they are often
toxic, air-sensitive or quite expensive. Moreover, there is no need to
use electron-rich phosphines to generate nucleophilic Pd(0) species
for promoting the oxidative-addition step in the catalytic cycle [5].
Therefore, the development of phosphine-free Pd-catalysts has
become another equally important topic of research [6].
Although palladacycles [7], N-heterocyclic [8] and carbocyclic
[9] carbene Pd-catalysts are well performing phosphine-free cata-
lysts, their tedious multi-step synthesis, inert atmosphere or dry
conditional catalytic performance and the use of various additives,
limit their use in industrial applications. In addition, alternative
catalytic systems such as N-, O- and S-centered ancillary ligand
complexes of Pd have appeared with moderate catalytic activity
and efficiency [10]. Recently, we have shown that anionic carbox-
yamide is a good supporting N-donor functional group which
increases the thermal stability and activity of the palladium
complexes for CeC bond-formation reactions [11]. We now report
the synthesis and structure of new palladium(II) complexes bearing
uridato/pyridyl ligands as an anionic N-donor coordinating site,
together with its performance in the Heck reaction.
* Corresponding authors. Tel.: þ91 40 27193510; fax: þ91 40 27160921.
E-mail addresses: plikhar@iict.res.in(P.R. Likhar), mlakshmi@iict.res.in (M.L. Kantam).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.09.075

796
P. Srinivas et al. / Journal of Organometallic Chemistry 696 (2011) 795e801
2. Results and discussion
R
O
O
R
N
R
N
H
Many N-based ligands are stable and have been reported to be
efficient ligands for the palladium catalyzed Heck and Suzuki
reactions [10b,f,12]. Among the N-based ligands, urea derivatives
are very stable and less explored ligands in CeC bond formation
reactions. Recently, Liu et al. reported N-phenyl urea as an efficient
ligand for Heck and Suzuki reactions [10d]. Since it was shown that
a pyridine ring was a good neighboring group to enhance the effect
of a carboxylate group in Pd catalysis [10e,11b], it was of interest to
design and synthesize the ligands using urea and pyridine as
pendant donor-functionalities. Thus, in a simple and high yielding
reaction, uridato/pyridyl ligands were prepared by the reaction of
widely available aryl isocyanates with 2-picolylamine in dichloro-
methane (DCM) (Scheme 1).
N
N
N
H
O
N
H
M
N
O
M
N
N
M
Bidentate
R
R
N
N
O
M
N
O
R
R
O
N
N
N
N
N
M
M
M
N
N
M
N
M N
Chelating
Bridging
Fig. 1. Some of the possible bonding modes of uridato/pyridyl ligands.
The steric and electronic properties of these ligands can be
varied by a variety of substitutions, allowing for a variety of possible
coordination modes that uridato/pyridyl ligands can adopt when
bonding to a metal (Fig. 1).
0.001 mol% 2c, and the progress of the reaction was monitored by
gas chromatography (see Table 2). We were pleased to find that the
olefination of less reactive 4-bromoanisole proceeded smoothly in
N,N-dimethylformamide when LiOH$H2O was used as the base.
Thus, we obtained the product 4-methoxy-trans-stilbene in 76%
yield by carrying out the reaction at 145 ꢁC for 10h, with a turnover
number of 105 (entry 8). This is of particular interest to industry as
catalyst with TON’s of 105 or higher minimizes industrial problems
such as the high cost of the metal catalyst and contamination of the
product by metal-leaching [13].
The activity of the catalysts 2a and 2b were also tested in the
Heck reaction, and the cross coupled product was obtained in good
yields (Table 2, entries 12 and 13). Thus, the electronic properties of
the phenyl ring of the uridato/pyridyl ligands do not appear to have
a significant effect on the reactivity of their palladium complexes.
As it is always advisable to compare the activity of new complexes
with ligandless Pd-catalysts [13,14], the Heck coupling reaction
using Pd(OAc)2 and our optimized reaction condition was under-
taken. In this case, the 4-methoxy-stilbene product was only
obtained in a yield of 8%, considerably less than the 76% using 2c as
catalyst (Table 2, entries 14 and 8).
As depicted in Scheme 2, the new uridate/pyridyl Pd(II)
complexes (2ae2c) were readily prepared, in almost quantitative
yields, upon treatment of the ligands with Pd(OAc)2 in the presence
of LiOH$H2O in MeOH at room temperature. Complexes 2ae2c are
insoluble in solvents such as dichloromethane, chloroform and
diethyl ether, but soluble in highly polar solvents such as DMF, DMA,
DMSO and methanol. The complexes have been fully characterized
by NMR, MS and FT-IR techniques. The solution structure of the
ligands and their complexes were studied by 1H and 13C NMR
spectroscopy and showed, respectively, the presence of uridyl
(RNHCONHR1) hydrogen atoms and the presence of uridate bonding
to Pd similar to amidate-Pd bonding that observed in our previous
work [11]. Moreover, the molecular structure of complex 2c was
determined by X-ray diffraction analysis on a crystal obtained by
slow evaporation of a methanol solution at room temperature. The
molecular structure, shown in Fig. 2, and crystal data (Table 1)
confirms complex 2c is mononuclear, with distorted square planar
geometry around the metal center and the uridate ligands disposed
cis relative to each other. Bidentate N,N-coordination of the ligand to
palladium atom takes place through the N-atoms of two different
functionalities, namely uridate (deprotonated urea) (N2 and N5) and
pyridine (N1 and N4).
In case of N-phenyl urea, Liu et al. [10d] proposed that N,O-
coordination takes place through an anionic O-donor atom of
deprotonated N-phenyl urea in the rate-determining oxidative-
addition step. By analogy, the proposed intermediate in the present
case may be a species containing a bidentate N,N-ligand in which
the palladium atom is coordinated by anionic N-donor atom of
deprotonated urea functionality and the pyridyl group.
To evaluate the usefulness of these N-donor, phosphine-free Pd
(II) complexes in CeC bond forming reactions, we investigated their
application to the Heck reaction of aryl bromides and chlorides. The
results are tabulated in Tables 2e4. To optimize the reaction, we
initially examined the reaction of 4-bromoanisole with styrene in
the presence of the ‘uridate’ complex 2c. A variety of reaction
conditions were used in order to get a high turnover number with
Having optimized the reaction conditions (0.001 mol% 2c,
1.2 equiv LiOH$H2O, DMF, 145 ꢁC), we next examined the coupling
of less reactive aryl bromides on a 30 mmol scale and the results are
listed in Table 3. Reactions involving deactivated aryl bromides
bearing a methyl or methoxy group with either styrene or 4-methyl
R1
O
MeOH,LiOH.H2O
Pd(OAc)2
NH
N
R2
NH
1(a-c)
R3
R1
O
R2
R3
N
N
a R1 = R3 = H, R2 = CH3
b R1 = R3 = H, R2 = OCH3
c R1 = R3 = CF3, R2 = H
N
N
N
H
R1
R1
R3
O
DCM
H
N
NH
N
R2
NCO
+
R2
NH
0°C to RT
N
R1
R2
R3
a R1 = R3 = H, R2 = CH3
NH2
1(a-c)
O
b R1 = R3 = H, R2 = OCH3
c R1 = R3 = CF3, R2 = H
R3
2(a-c)
Scheme 1. Synthesis of uridato/pyridyl ligands.
Scheme 2. Synthesis of uridato/pyridyl-based palladium(II) complexes.

P. Srinivas et al. / Journal of Organometallic Chemistry 696 (2011) 795e801
797
Table 2
Heck reaction between 4-bromoanisole and styrene.a
Br
+
Ph
2c (0.001mol%)
Ph
base, solvent
145 °C, 10h
MeO
MeO
Entry
Base
Solvent
Yield (%)b
TON
TOFc
1
2
3
4
5
6
7
8
Na2CO3
Li2CO3
K2CO3
NaOAc
K3PO4
DIPEA
MDCHA
LiOH$H2O
LiOH$H2O
LiOH$H2O
LiOH$H2O
LiOH$H2O
LiOH$H2O
LiOH$H2O
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMSO
DMA
NMP
DMF
DMF
DMF
59
42
28
37
24
10
0
59000
42000
28000
37000
24000
10000
e
5900
4200
2800
3700
2400
1000
e
76
9
76000
9000
7600
900
9
10
11
12
13
14
74
46
73d
74e
8f
74000
46000
73000
74000
8000
7400
4600
7300
7400
800
Fig. 2. X-ray structure of Pd(II) complex 2c (hydrogen atoms are included to highlight
uridate anion bonding to palladium atom). Displacement ellipsoids are drawn at the
30% probability level and H atoms are shown as small spheres of arbitrary radius.
Selected bond lengths [Å] and bond angles [ꢁ]: Pd1eN2 ¼ 2.006(2); Pd1eN5 ¼ 2.009
a
Reaction conditions: 4-bromoanisole (1 mmol), styrene (2 mmol), catalyst
(0.001 mol%), base (1.2 mmol), solvent (2 mL).
b
Isolated yields.
(2); Pd1eN1
¼
2.040(2); Pd1eN4
¼
2.060(2); :N2eC7eN3
¼
114.2(3);
c
TOF-turnover frequency (mol product per mol catalyst hꢂ1).
:N5eC22eN6 ¼ 113.0(2).
d
Complex 2a was used.
Complex 2b was used.
Pd(OAc)2 used as catalyst. DIPEA ¼ N,N-diisopropylethylamine, MDCHA ¼ N-
e
f
styrene (entries 5e11) gave high yields of the coupled product.
Sterically hindered 2-bromoanisole could also be coupled in
moderate yields using as low as 0.001 mol% catalyst loading
(entries 9 and 10). We also applied these optimized reaction
conditions to coupling of deactivated aryl bromides and n-butyl
acrylate. However, the best results could be obtained with
increasing the catalyst concentration by 0.01 mol% in presence of
Li2CO3 as a base (entries 12e14). Although the above optimized
reaction conditions were ineffective for the Heck reaction of aryl
chlorides (Table 4, entry 1), moderate yields of the coupled prod-
ucts could be obtained by increasing the catalyst loading to 1 mol%
and using N,N-dimethylacetamide (DMA) as solvent at 160 ꢁC
(Table 4).
Methyl-dicyclohexylamine.
The uridate/pyridyl Pd(II) complexes find their superiority over
most of the phosphine-free catalysts with at least one of the
following advantages: facile synthesis, thermal stability and
structural versatility, easy handling, catalytic performance in air
without any additives [9a,15], achievement of high TON’s and TOF’s
with deactivated aryl bromides and with hindered aryl bromides
[9b,12c,16], and activation of less reactive aryl chlorides [5a,17].
3. Conclusion
New palladium(II) complexes containing uridato/pyridyl ligands
have been prepared and their ability to catalyze the Heck reaction
under phosphine-free reaction conditions has been studied. High
turnover numbers can be achieved in the coupling of aryl bromides
and olefins, including sterically hindered deactivated 2-bromoani-
sole. The complexes also show moderate catalytic activity for the
coupling of aryl chlorides. The concept of anionic urea as an
ancillary ligand with a number of possible modes of coordination
opens a new opportunity for the development of phoshpine-free
metal catalysts.
Table 1
Crystallographic data for 2c.
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
C30H20 F12N6O2Pd
830.92
293(2) K
0.71073 Å
Triclinic
P1
Unit cell dimensions
a ¼ 9.3740(4) Å
b ¼ 12.1320(5) Å
c ¼ 15.2710(6) Å
1616.32(12) Å3
2
a
b
g
¼ 90.723(1)ꢁ.
¼ 100.252(1)ꢁ.
¼ 108.489(1)ꢁ.
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
4. Experimental section
1.707 Mg/m3
0.683 mmꢂ1
824
4.1. Typical procedure for the preparation of ligands (1ae1c)
Crystal size
0.17 ꢀ 0.11 ꢀ 0.08 mm3
1.36e25.00ꢁ.
ꢂ11<¼h<¼11, ꢂ14
<¼k<¼14, ꢂ18<¼l<¼18
15559
To an RB-flask containing 2-(aminomethyl)pyridine (1g,
9.24 mmol) in 20 mL dichloromethane (DCM) was added drop wise
to a solution of aryl isocyanate (1.5 equiv) in DCM (10 mL) at 0 ꢁC
and the resulting mixture was allowed to stir at room temperature
for 10 h. The solvent was removed under reduced pressure and the
residue was purified by repeated crystallization from ethyl acetate
to give the desired product in 80e90% yield.
q
range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to
Refinement method
5669 [R(int) ¼ 0.0183]
q
¼ 25.00ꢁ 99.7%
Full-matrix least-squares on F2
Data/restraints/parameters 5669/218/532
Goodness-of-fit on F2
1.047
Final R indices [I > 2
R indices (all data)
s
(I)]
R1 ¼ 0.0332, wR2 ¼ 0.0891
4.1.1. 1-(Pyridin-2-ylmethyl)-3-p-tolylurea (1a)
R1 ¼ 0.0359, wR2 ¼ 0.0912
1H NMR (400 MHz, CDCl3 þ DMSO-d6, TMS)
d 2.24 (s, 3H), 4.43
Largest diff. peak and hole 0.573 and ꢂ0.407 e Åꢂ3
(d, J ¼ 5.2 Hz, 2H), 6.59 (t, J ¼ 5.2 Hz,1H), 6.96 (d, J ¼ 7.8 Hz, 2H), 7.17

798
P. Srinivas et al. / Journal of Organometallic Chemistry 696 (2011) 795e801
Table 3
Heck reaction of aryl bromides and olefins.a
Entry
Arylh alide
Olefin
Product
Yield (%)b
Time (h)
10
TON
TOF
Br
1
91
91000
9100
Br
Br
2
3
82c
10
10
82000
83000
8200
8300
83d
CH3
Br
4
5
90
82
10
10
90000
82000
9000
8200
CH3
Br
H3C
H3C
H3C
Br
CH3
6
7
83
76
10
10
83000
76000
8300
7600
CH3
H3C
Br
H3CO
H3CO
Br
CH3
8
80
40
52
10
10
10
80000
40000
52000
8000
4000
5200
CH3
H3CO
Br
H3CO
9
OCH3
OCH3
OCH3
CH3
Br
10
CH3
CH3
OCH3
CH3
Br
11
73
10
73000
7300
OCH3
OCH3

P. Srinivas et al. / Journal of Organometallic Chemistry 696 (2011) 795e801
799
Table 3 (continued )
Entry
Arylh alide
Olefin
Product
Yield (%)b
Time (h)
12
TON
TOF
O
Br
O
O
12
92e
9200
766
O
O
Br
O
O
O
O
13
86e
12
12
8600
6300
716
525
H3C
H3C
Br
O
O
14
63e
O
H3CO
H3CO
a
Reaction conditions: aryl bromide (30 mmol), olefin (60 mmol), 2c (0.001 mol%), LiOH$H2O (36 mmol), DMF (50 mL) at 145 ꢁC.
Isolated yields.
Complex 2a was used.
Complex 2b was used.
With 2c (0.01 mol%), Li2CO3 (2 eq).
b
c
d
e
(t, J ¼ 6.0 Hz, 1H), 7.24 (d, J ¼ 8.6 Hz, 2H), 7.31 (d, J ¼ 7.8 Hz,1H), 7.66
remove water and excess ligand. The resulting solid was dried under
high vacuum to obtain the pure complexes (2ae2c) in 94e96% yield.
(t, J ¼ 7.8 Hz, 1H), 8.38 (s, 1H), 8.49 (d, J ¼ 4.3 Hz, 1H); 13C NMR
(100 MHz, CDCl3 þ DMSO-d6)
d 19.5, 44.0, 117.2, 120.3, 120.9, 128.0,
129.5, 135.5, 136.5, 147.7, 154.9, 157.6; IR (KBr, cmꢂ1): 3340, 3301
4.2.1. Complex 2a
(CONH), 1633 (C]O); ESI-MS (m/z): (M 242,
þ
H)þ
¼
Mp: decomposed to black metal at 202 ꢁC; 1H NMR (400 MHz,
(M
þ
Na)þ
¼
264; HRMS (m/z): calcd for C14H15N3ONa
CDCl3 þ CD3OD, TMS) 2.22 (s, 6H), 4.67 (d, J ¼ 16.8 Hz, 2H), 5.45 (d,
d
(M þ Na)þ ¼ 264.1112, found: 264.1122.
J ¼ 16.8 Hz, 2H), 6.98 (d, J ¼ 8.1 Hz, 4H), 7.20 (d, J ¼ 8.1 Hz, 4H),
7.30e7.40 (m, 2H), 7.66 (d, J ¼ 7.3, Hz, 2H), 7.93 (t, J ¼ 7.3 Hz, 2H),
8.16 (d, J ¼ 4.4 Hz, 2H), 8.98 (s, 1H); 13C NMR (100 MHz,
4.1.2. 1-(4-Methoxyphenyl)-3-(pyridin-2-ylmethyl)urea (1b)
1H NMR (400 MHz, CDCl3 þ DMSO-d6, TMS)
d
3.73 (s, 3H), 4.51
CDCl3 þ CD3OD)
d 20.4, 56.3, 118.3, 118.4, 121.6, 123.5, 129.0, 130.6,
(d, J ¼ 5.1 Hz, 2H), 6.56 (t, J ¼ 5.1 Hz, 1H), 6.76 (d, J ¼ 8.8 Hz, 2H),
7.14e7.17 (m, 1H), 7.28e7.31 (m, 3H), 7.63 (t, J ¼ 6.6 Hz, 1H), 8.23 (s,
1H), 8.49 (d, J ¼ 5.1 Hz, 1H); 13C NMR (100 MHz, CDCl3 þ DMSO-d6)
137.7, 137.8, 139.3, 147.9, 163.2, 166.8; IR (KBr, cmꢂ1): 3255 (CONH),
1647 (C]O); ESI-MS (m/z): (M þ H)þ ¼ 587; HRMS (m/z): calcd for
C28H29N6O2Pd (M þ H)þ ¼ 587.1386, found: 587.1369.
d
44.5, 54.6, 113.2, 119.7, 120.7, 121.3, 132.4, 135.9, 148.0, 154.0, 155.6,
158.0; IR (KBr, cmꢂ1): 3329, 3286 (CONH), 1630 (C]O); ESI-MS (m/
z): (M þ H)þ ¼ 258; HRMS (m/z): calcd for C14H15N3O2Na
(M þ Na)þ ¼ 280.1061, found: 280.1071.
4.2.2. Complex 2b
Mp: decomposed to black metal at 194 ꢁC; 1H NMR (400 MHz,
CDCl3 þ CD3OD, TMS) 3.87 (s, 6H), 4.61 (d, J ¼ 16.1 Hz, 2H), 5.35 (d,
d
J ¼ 16.8 Hz, 2H), 6.68 (d, J ¼ 8.8 Hz, 4H), 7.13 (d, J ¼ 8.8 Hz, 4H),
7.30e7.35 (m, 2H), 7.59 (d, J ¼ 8.1, Hz, 2H), 7.88 (t, J ¼ 8.1 Hz, 2H),
8.12 (d, J ¼ 5.1 Hz, 2H), 8.78 (s, 0.5H); 13C NMR (100 MHz,
4.1.3. 1-(3,5-Bis(trifluoromethyl)phenyl)-3-(pyridin-2-ylmethyl)
urea (1c)
1H NMR (400 MHz, CDCl3 þ DMSO-d6, TMS)
d
4.49 (d, J ¼ 4.4 Hz,
CDCl3 þ CD3OD)
d 55.2, 56.3, 113.8, 120.2, 121.5, 123.5, 133.6, 139.3,
2H), 6.66 (t, J ¼ 4.4 Hz,1H), 7.14 (t, J ¼ 5.9 Hz,1H), 7.26e7.34 (m, 2H),
7.61 (t, J ¼ 7.3 Hz, 1H), 7.89 (s, 2H), 8.46 (d, J ¼ 5.1 Hz, 1H), 9.04 (s,
147.9,154.4,163.2,166.7; IR (KBr, cmꢂ1): 3257 (CONH),1643 (C]O);
ESI-MS (m/z): (M þ H)þ ¼ 619; HRMS (m/z): calcd for C28H29N6O4Pd
(M þ H)þ ¼ 619.1285, found: 619.1287.
1H); 13C NMR (100 MHz, CDCl3 þ DMSO-d6)
d 44.6, 113.9, 117.2,
121.4, 121.9, 124.4, 130.8, 131.1, 131.4, 131.8, 136.5, 141.5, 148.4, 155.1,
157.4; IR (KBr, cmꢂ1): 3364, 3279 (CONH), 1685 (C]O); ESI-MS (m/
4.2.3. Complex 2c
z): (M
þ
H)þ
¼
364; HRMS (m/z): calcd for C15H12F6N3O
Mp: decomposed to black metal at 204 ꢁC; 1H NMR (400 MHz,
(M þ H)þ ¼ 364.0884, found: 364.0888.
CDCl3 þ DMSO-d6, TMS)
d 4.74 (s, 2H), 5.42 (s, 2H), 7.19 (s, 2H), 7.43 (t,
J ¼ 5.9 Hz, 2H), 7.69 (d, J ¼ 7.3 Hz, 2H), 7.77 (s, 4H), 7.97 (t, J ¼ 7.3 Hz,
2H), 8.22 (d, J ¼ 5.9 Hz, 2H), 9.32 (s, 2H); 13C NMR (100 MHz,
4.2. Typical procedure for the preparation of palladium complexes
(2ae2c)
CDCl3 þ DMSO-d6)
d 54.9,112.0,115.7,120.4,122.9,123.4,129.7,129.8,
130.1, 130.5, 138.6, 141.4, 147.4, 160.7, 164.8; IR (KBr, cmꢂ1): 3285
(CONH), 1657 (C]O); ESI-MS (m/z): (M þ H)þ ¼ 831; HRMS (m/z):
calcd for C30H21F12N6O2Pd (M þ H)þ ¼ 831.0569, found: 831.0558.
A single-necked 25 mL RB-flask was charged with the ligand
(1ae1c) (2.2 mmol), LiOH$H2O (3 equiv) and MeOH (10 mL). To this
stirred solution, Pd(OAc)2 (1 mmol) was added in one portion at
room temperature. After stirring the solution for 24 h at room
temperature, a yellow colored precipitate was obtained. The solvent
was removed under reduced pressure and the resulting solid was
washed with water to remove excess base (note: complex is insol-
uble in water). The solid was then washed with ethyl acetate to
4.3. Typical procedure for the Heck reaction of aryl bromides
A 100 mL RB-flask was charged with aryl bromide (30 mmol),
alkene (60 mmol), LiOH$H2O (36 mmol) and catalyst (2c)
(0.001 mol%). N,N-Dimethylformamide (50 mL) was added and the

800
P. Srinivas et al. / Journal of Organometallic Chemistry 696 (2011) 795e801
Table 4
temperature, diluted with EtOAc (20 mL) and washed successively
Heck reaction of aryl chlorides and olefinsa.
with 1 N aq. HCl and water. The combined organic phases were dried
over anhydrous Na2SO4. After removal of the solvent, the residue
was subjected to column chromatography on silica gel (ethyl acetate
and hexane 5:95) to afford the Heck product in high purity.
Entry
Arylhalide
Olefin
Product
Yield
(%)b
Cl
0c
4.5. Analytical data for the products of the Heck reaction
1
4.5.1. trans-Stilbene (Table 3, entry 1)
1H NMR (300 MHz, CDCl3, TMS)
d 7.05 (s, 2H), 7.17e7.22 (m, 2H),
Cl
Cl
7.30 (t, J ¼ 7.5 Hz, 4H), 7.46 (d, J ¼ 7.5 Hz, 4H); 13C NMR (75 MHz,
d
126.5, 127.6, 128.6, 137.3; IR (KBr, cmꢂ1) 3021, 2925, 1593,
2
3
42
CDCl3)
1445, 958, 687; EI-MS (m/z) (M)þ ¼ 180.
4.5.2. 4-Methyl-trans-stilbene (Table 3, entry 4)
CH3
1H NMR (300 MHz, CDCl3, TMS)
d 2.35 (s, 3H), 7.01 (s, 2H), 7.11
(d, J ¼ 8.3 Hz, 2H), 7.16e7.22 (m,1H), 7.29 (t, J ¼ 7.5 Hz, 2H), 7.35 (d,
28
15
J ¼ 8.3 Hz, 2H), 7.44 (d, J ¼ 7.5 Hz, 2H); 13C NMR (75 MHz, CDCl3)
CH3
d
21.2, 126.3, 126.4, 127.3, 127.7, 128.6, 129.3, 134.5, 137.4, 137.5; IR
(KBr, cmꢂ1) 3021, 2917, 2855, 1589, 1506, 967, 804, 527; EI-MS (m/z)
Cl
(M)þ ¼ 194.
4.5.3. 4,40-Dimethyl-trans-stilbene (Table 3, entry 6)
4
5
6
H3C
1H NMR (300 MHz, CDCl3, TMS)
d 2.34 (s, 6H), 6.97 (s, 2H), 7.09
H3C
H3C
(d, J ¼ 7.9 Hz, 4H), 7.33 (d, J ¼ 7.9 Hz, 4H); 13C NMR (75 MHz, CDCl3)
d
21.3, 126.3, 127.6, 129.4, 134.8, 137.3; IR (KBr, cmꢂ1) 3017, 2920,
CH3
Cl
2854, 1511, 1111, 969, 818; EI-MS (m/z) (M)þ ¼ 208.
26
4.5.4. 4-Methoxy-trans-stilbene (Table 3, entry 7)
CH3
H3C
1H NMR (300 MHz, CDCl3, TMS)
d
3.80 (s, 3H), 6.83 (d, J ¼ 8.3 Hz,
2H), 6.90 (d, J ¼ 15.9 Hz, 1H), 7.01 (d, J ¼ 16.6 Hz, 1H), 7.15e7.31 (m,
4H), 7.38e7.44 (m, 3H); 13C NMR (75 MHz, CDCl3)
55.3, 114.1,
d
Cl
126.3, 126.7, 127.2, 127.7, 128.2, 128.7, 130.2, 137.7, 159.3; IR (KBr,
cmꢂ1) 3015, 2920, 2847, 1602, 1511, 1250, 1030, 826, 538; EI-MS (m/
z) (M)þ ¼ 210.
8
H3CO
H3CO
H3CO
4.5.5. 4-Methoxy-40-methyl-trans-stilbene (Table 3, entry 8)
1H NMR (300 MHz, CDCl3, TMS)
d 2.34 (s, 3H), 3.80 (s, 3H), 6.82
CH3
Cl
(d, J ¼ 8.7 Hz, 2H), 6.87 (d, J ¼ 16.2 Hz, 1H), 6.95 (d, J ¼ 16.4 Hz, 1H),
7.09 (d, J ¼ 7.9 Hz, 2H), 7.33 (d, J ¼ 8.1 Hz, 2H), 7.38 (d, J ¼ 8.7 Hz,
7
21
2H); 13C NMR (75 MHz, CDCl3)
d 21.2, 55.3, 114.1, 126.1, 126.5, 127.2,
CH3
H3CO
127.5, 129.3, 130.3, 134.8, 137.0, 159.1; IR (KBr, cmꢂ1) 3015, 2920,
2847, 1602, 1511, 1250, 1030, 826, 538; EI-MS (m/z) (M)þ ¼ 224.
a
Reaction conditions: aryl chloride (1 mmol), olefin (2 mmol), 2c (1 mol%),
LiOH$H2O (1.2 mmol), DMA (2 mL) at 160 ꢁC for 20 h.
4.5.6. 2-Methoxy-trans-stilbene (Table 3, entry 9)
b
1H NMR (300 MHz, CDCl3, TMS)
d
3.88 (s, 3H), 6.84 (d, J ¼ 8.3 Hz,
Isolated yields.
c
Using the reaction conditions described in Table 2.
1H), 6.91 (t, J ¼ 7.5 Hz,1H), 7.04 (d, J ¼ 16.6 Hz,1H), 7.18 (t, J ¼ 7.5 Hz,
2H), 7.30 (t, J ¼ 7.5 Hz, 2H), 7.42 (d, J ¼ 16.6 Hz, 1H), 7.49 (d,
J ¼ 7.5 Hz, 2H), 7.55 (d, J ¼ 7.5 Hz, 1H); 13C NMR (75 MHz, CDCl3)
reaction mixture was heated to 145 ꢁC for 10 h and the progress of
the reaction was monitored by GC. Upon the completion of the
reaction, the mixture was cooled to room temperature, diluted with
EtOAc (200 mL) and the solution washed successively with 1 N aq.
HCl and water. The combined organic phases were dried over
anhydrous Na2SO4. After removal of the solvent, the residue was
subjected to column chromatography on silica gel (ethyl acetate
and hexane 5:95) to afford the Heck product in high purity.
d
55.5, 110.9, 120.7, 123.5, 126.4, 126.5, 127.3, 128.5, 128.6, 129.1,
137.9, 156.9; IR (KBr, cmꢂ1) 3023, 2936, 1593, 1483, 1244, 1027, 750,
691; EI-MS (m/z) (M)þ ¼ 210.
4.5.7. 2-Methoxy-40-methyl-trans-stilbene (Table 3, entry 10)
1H NMR (300 MHz, CDCl3, TMS)
d 2.35 (s, 3H), 3.88 (s, 3H), 6.83
(d, J ¼ 8.3 Hz, 1H), 6.90 (t, J ¼ 7.5 Hz, 1H), 7.00 (d, J ¼ 16.6 Hz, 1H),
7.09 (d, J ¼ 8.3 Hz, 2H), 7.16 (t, J ¼ 8.3 Hz, 1H), 7.33e7.39 (m, 3H),
7.53 (d, J ¼ 7.5 Hz, 1H); 13C NMR (75 MHz, CDCl3)
d 29.8, 55.5, 110.9,
4.4. Typical procedure for the Heck reaction of aryl chlorides
120.8, 122.5, 126.3, 126.5, 128.5, 129.0, 129.3, 137.2, 156.9; IR (KBr,
cmꢂ1) 2922, 2851, 1602, 1511, 1249, 1029, 826, 537; EI-MS (m/z)
(M)þ ¼ 224.
The reaction vessel was charged with aryl chloride (1 mmol),
alkene (2 mmol), LiOH$H2O (1.2 mmol) catalyst (2c) (1 mol%) and
N,N-dimethylacetamide (3 mL). The reaction mixture was heated to
160 ꢁC for 20 h and the progress of reaction was monitored by GC. At
the end of the reaction, the reaction mixture was cooled to room
4.5.8. 3-Methoxy-40-methyl-trans-stilbene (Table 3, entry 11)
1H NMR (300 MHz, CDCl3, TMS)
d
2.35 (s, 3H), 3.82 (s, 3H), 6.72
(d, J ¼ 7.9, 1H), 7.25e6.97 (m,7H), 7.35 (d, J ¼ 7.9, 2H); 13C NMR (75

P. Srinivas et al. / Journal of Organometallic Chemistry 696 (2011) 795e801
801
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134.3, 137.5, 138.9, 159.7; IR (KBr, cmꢂ1) 3013, 2924, 2840, 1586,
1478, 1256, 1045, 807, 684; EI-MS (m/z) (M)þ ¼ 224.
4.5.9. n-Butyl cinnamate (Table 3, entry 12)
1H NMR (300 MHz, CDCl3, TMS)
d
0.97 (t, J ¼ 7.30 Hz, 3H), 1.44 (m,
2H),1.69 (m, 2H), 4.18 (t, J ¼ 6.61 Hz, 2H), 6.39 (d, J ¼ 16.05 Hz,1H), 7.34
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d 13.6, 19.1, 30.6, 64.3, 118.1, 127.9, 128.7, 130.0, 134.3, 144.4,
166.9; IR (KBr, cmꢂ1) 2959,1713,1638,1310,1172,1066, 981, 767; EI-MS
(m/z) (M)þ ¼ 204.
4.5.10. n-Butyl-4-methyl cinnamate (Table 3, entry 13)
(c) X. Gai, R. Grigg, M.I. Ramzan, V. Sridharan, S. Collard, J.E. Muir, Chem.
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690 (2005) 3193;
1H NMR (300 MHz, CDCl3, TMS)
d 0.97 (t, 3H), 1.43 (m, 2H), 1.66
(m, 2H), 2.37 (s, 3H), 4.17 (t, J ¼ 6.90 Hz, 2H), 6.34 (d, J ¼ 16.05 Hz,1H),
7.19 (d, J ¼ 7.93 Hz, 2H), 7.39 (d, J ¼ 8.12 Hz, 2H),7.60 (d, J ¼ 15.86 Hz,
1H); 13C NMR (50 MHz CDCl3)
d 13.7,19.2, 21.3, 30.8, 64.2,117.1,127.9,
129.5, 131.7, 140.4, 144.5,167.1; IR (KBr, cmꢂ1)2925, 2855, 1715, 1637,
1311, 1168, 1060, 938, 813; EI-MS (m/z) (M)þ ¼ 218.
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4.5.11. n-Butyl-4-methoxy cinnamate (Table 3, entry 14)
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1H NMR (300 MHz, CDCl3, TMS)
d 0.97 (t, 3H), 1.43 (m, 2H), 1.66
(m, 2H), 3.82 (s, 3H),4.16 (t, J ¼ 6.61 Hz, 2H), 6.25 (d, J ¼ 15.86 Hz,
(b) S.K. Yen, L.L. Koh, F.E. Hahn, H.V. Huynh, T.S.A. Hor, Organometallics 25
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1H), 6.85 (d, J ¼ 8.68 Hz, 2H), 7.43 (d, J ¼ 8.68 Hz, 2H), 7.57
(c) J. Ye, W. Chen, D. Wang, Dalton Trans. (2008) 4015;
(d) N. Marion, S.P. Nolan, Acc. Chem. Res. 41 (2008) 1440;
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(d, J ¼ 15.86 Hz,1H); 13C NMR (75 MHz CDCl3)
d 13.6,19.1, 30.7, 55.2,
64.2, 114.1, 115.6, 127.0, 129.5, 144.1, 161.2, 167.4; IR (KBr, cm-1) 2959,
1708, 1603, 1253, 1169, 1029, 829; EI-MS (m/z) (M)þ ¼ 234.
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Acknowledgements
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P.S. thanks UGC and K.S. thank CSIR, India for their fellowships.
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Appendix. Supplementary material
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Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.jorganchem.2010.09.075.
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