Palladium and copper complexes with oxygen-nitrogen mixed donors as efficient catalysts for the Heck reaction

Article abstract of DOI:10.1016/j.ica.2011.10.040

A simple bidentate ligand, 2-(2′-hydroxyphenyl)-5,6-dihydro-1,3- oxazine, was readily prepared with a two-step synthesis. Two novel complexes of Pd(II) and Cu(II) with this (N,O) oxazine ligand have been prepared and the molecular structures of these complexes have been confirmed by X-ray structure analysis, NMR, IR and UV-Vis spectroscopy. These complexes efficiently catalyze the Heck reaction of aryl halides with olefins at 120 °C in 8 h. The reaction conditions for the Heck coupling of iodobenzene with styrene was optimized by varying the amount of the catalyst, reaction temperature, solvent and exogenous base.

Full text of DOI:10.1016/j.ica.2011.10.040

Inorganica Chimica Acta 383 (2012) 46–51
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Inorganica Chimica Acta
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Palladium and copper complexes with oxygen–nitrogen mixed donors
as efficient catalysts for the Heck reaction
a
b
b
Mojtaba Bagherzadeh a, , Mojtaba Amini , Arkady Ellern , L. Keith Woo
⇑
a Chemistry Department, Sharif University of Technology, Tehran, P.O. Box 11155-3615, Iran
b Chemistry Department, Iowa State University, Ames, IA 50011-3111, USA
a r t i c l e i n f o
a b s t r a c t
A simple bidentate ligand, 2-(20-hydroxyphenyl)-5,6-dihydro-1,3-oxazine, was readily prepared with a
two-step synthesis. Two novel complexes of Pd(II) and Cu(II) with this (N,O) oxazine ligand have been pre-
pared and the molecular structures of these complexes have been confirmed by X-ray structure analysis,
NMR, IR and UV–Vis spectroscopy. These complexes efficiently catalyze the Heck reaction of aryl halides
with olefins at 120 °C in 8 h. The reaction conditions for the Heck coupling of iodobenzene with styrene
was optimized by varying the amount of the catalyst, reaction temperature, solvent and exogenous base.
Ó 2011 Elsevier B.V. All rights reserved.
Article history:
Received 7 October 2010
Received in revised form 25 September
2011
Accepted 10 October 2011
Available online 18 October 2011
Keywords:
Oxazine ligand
Palladium
Copper
Heck reaction
1. Introduction
Notably, palladium complexes with oxygen–nitrogen donors as li-
gands have been rarely used as catalysts for the Heck reaction [8].
The Mizoroki–Heck reaction has become one of the most useful
carbon–carbon bond-forming reactions in organic synthesis and
therefore the Heck reaction has been intensively developed from
synthetic and mechanistic points of view, as articulated by the
impressive number of reviews and book chapters [1]. The reaction
has been applied to many areas, including bioactive compounds,
natural products, drug intermediates, fine chemicals syntheses,
UV absorbers, antioxidants and industrial applications [2].
In most transition-metal catalyzed reactions, the control of cat-
alytic processes is achieved through the choice, refinement and
adjustment of stable ancillary ligands remaining in the coordina-
tion shell throughout all steps of the catalytic cycle. Thus, ligand
design is vital to the advancement of catalytic science. The ligands
on the metal play a key role in tuning the catalyst reactivity by bal-
ancing steric and electronic factors. Identification of the best class
of ligands for a given reaction is based on the elucidation of the fac-
tors that affect each step of the catalytic cycle [3].
Ligands having the five-membered bidentate (N,O) oxazoline
moiety or the six-membered bidentate (N,O) oxazine moiety have
been widely used throughout organometallic and inorganic chem-
istry, and are particularly important in homogeneous catalysis [9].
The presence of N and O donor sites in oxazolines and oxazines
may modify significantly the ligand roles for the variation of steric
and electronic properties. Therefore, such systems are worth
exploring for new catalytic uses [10].
During the last two decades, the palladium catalyzed Heck
reaction has become a versatile and often standard method for the
formation of C–C bonds in the organic synthesis of olefinic com-
pounds. In contrast, there is few reported survey on the use of cop-
per(II) complexes as homogenous catalysts in the Heck reaction [11].
Herein we describe the synthesis of 2-(20-hydroxyphenyl)-5,6-
dihydro-1,3-oxazine (HL) and the use of this ligand in the prepara-
tion and structural characterization of two novel complexes [PdL2]
and [CuL2]. The catalytic activity in the Heck reaction of these new
complexes is compared. This study is the first report of the cata-
lytic activity for a copper(II) complex in the Heck reaction.
The application of metal-catalyzed carbon–carbon bond forma-
tion methods to the synthesis of polyfunctional compounds is
related to the capability of the catalyst to control the chemo-,
regio-, and stereoselectivity of the reaction at a reasonable rate un-
der mild conditions.
2. Experimental
The series of ligand combinations of palladium(II) that showed
good catalytic activity in the Heck reaction are cyclometalated
phosphines [4], imines [5], carbenes [6] and dimethylglycine [7].
2.1. Chemical materials and solvents were purchased from the Fluka
and Merck Chemical companies
⇑
The elemental analysis (carbon, hydrogen, and nitrogen) of
compounds were obtained from Carlo ERBA Model EA 1108
Corresponding author. Tel.: +98 21 66165354; fax: +98 21 66012983.
E-mail address: bagherzadehm@sharif.edu (M. Bagherzadeh).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.10.040

M. Bagherzadeh et al. / Inorganica Chimica Acta 383 (2012) 46–51
47
H
O
OCH2CH3
OH
OH
O
N
OH
OH
H2N
OH
+
reflux
H
N
OH
O
O
N
1)
SOCl2
NaHCO3
OH
2)
Scheme 1. Synthesis of ligand (HL).
O
O
N
Pd(OAc)2
CH2Cl2
N
O
Pd
2a
2b
Fig. 2. ORTEP diagram of complex 2b with thermal ellipsoids are drawn at a 50%
probability limit.
O
N
O
2.2. Synthesis of ligand (HL)
OH
O
Ethyl salicylate (10 mmol) and 3-amino-1-propanol (10 mmol)
were refluxed together for 4 h and the resulting EtOH was removed
under reduced pressure. The residue thus obtained was dissolved
in CH2C12 (20 mL) at 0 °C (10 mL) and thionyl chloride (1 mL)
was slowly added to this solution. The reaction was allowed to
warm gradually to room temperature, and was left stirring for
6 h. The resulting solid was then filtered, made basic with satu-
rated aqueous NaHCO3, and extracted with diethyl ether
(330 mL). The ether extracts were combined, dried with MgSO4,
and concentrated under reduced pressure to give a white solid
which was then recrystallized from methanol and then dried at va-
cuo. (1.2 g, 74% based on ethyl salicylate); m.p. 79 °C. Anal. Calc. for
N
O
O
N
Cu(OAc)2.H2O
CH3OH
Cu
O
Scheme 2. Synthesis of [PdL2] and [CuL2] complexes.
C
10H11NO2: C, 67.78; H, 6.26; N, 7.90. Found: C, 67.71; H, 6.28; N,
7.86%. Selected IR frequency (KBr disk, cmꢀ1): 1641(s,
C=N). Elec-
(Mꢀ1 cmꢀ1)):
m
tronic absorption spectrum in CH2Cl2 kmax (nm) (
e
304 (19473), 246 (29362). 1H NMR (500 MHz, CDCl3, d): 2.07
(2H, t), 3.64 (2H, t), 4.42 (2H, t), 6.82 (1H, t), 6.96 (1H, d), 7.33
(1H, t), 7.70 (1H, d), 14.21 (1H, s). 13C NMR (500 MHz, CDCl3, d):
22.1, 41.3, 65.8, 115.0, 117.6, 118.0, 127.1, 132.8, 159.8, 161.4.
2.3. Preparation of complex [PdL2] (2a)
To a mixture of Pd(II) acetate (224 mg, 1 mmol) in 15 mL of
CH2Cl2 was added a solution of ligand (354 mg, 2 mmol) in
10 mL of CH2Cl2, and the mixture was stirred at room temperature
for 1 h. The resulting precipitate was filtered, washed with a small
amount of CH2Cl2, and dried under vacuum. The crude product was
recrystallizd from CH2Cl2 to give yellow crystals (381 mg, yield;
83%). Anal. Calc. for C20H20N2O4Pd: C, 52.31; H, 4.36; N, 6.10.
Found: C, 52.13; H, 4.31; N, 6.03%. Selected IR frequency (KBr disk,
Fig. 1. ORTEP diagram of complex 2a with thermal ellipsoids are drawn at a 50%
probability limit.
cmꢀ1) = 1614(s,
mC=N). Electronic absorption spectrum in CH2Cl2
analyzer. FT-IR spectrum was obtained by using a Unicam Matson
1000 FT-IR spectrophotometer using KBr disks at room tempera-
ture. UV–Vis spectrum was recorded by CARY 100 Bio VARIAN
UV–Vis spectrophotometer in methanol. Molar conductance of
complexes were determined in methanol (ca. 10ꢀ3 M) at room
temperature using a Toa CM 405 conductivity meter. The 1H and
13C NMR spectra of the free ligand and complex in CDCl3 were ob-
tained using a Bruker FT-NMR 500 MHZ spectrometer. Melting
point was taken on a Gallenkamp melting point apparatus. The
reaction products of Heck reaction were determined and analyzed
by HP Agilent 6890 gas chromatograph equipped with a HP-5 cap-
kmax (nm) (
e
(Mꢀ1 cmꢀ1)): 245 (11266). 1H NMR (500 MHz, CDCl3,
d): 2.11 (2H, t), 3.86 (2H, t), 4.43 (2H, t), 6.57 (1H, t), 6.82 (1H, d),
7.16 (1H, t), 7.62 (1H, d). 13C NMR (500 MHz, CDCl3, d): 22.1, 43.4,
66.4, 115.1, 119.3, 121.2, 129.4, 133.2, 158.3, 167.4.
2.4. Preparation of [CuL2] (2b)
A methanolic solution (15 mL) of Cu(CH3COO)2.H2O (199.6 mg,
1 mmol) was mixed with a methanolic solution (15 mL) of the li-
gand (354 mg, 2 mmol). The mixture was stirred for 2–3 h and
the resulting product was recovered by filtration, washed with
methanol and dried in vacuum. Suitable crystals for X-ray analysis
illary column (phenyl methyl siloxane 30 m ꢁ 320
l
m ꢁ 0.25
lm)
and flame-ionization detector.

48
M. Bagherzadeh et al. / Inorganica Chimica Acta 383 (2012) 46–51
Table 1
Crystal data and structure refinement for complexes.
[PdL2] (2a)
[CuL2] (2b)
Formula
Formula weight
T (K)
C
20H20N2O4Pd
C20H20CuN2O4
415.92
173(2)
458.78
173(2)
k (Å)
0.71073
monoclinic
P2(1)/c
0.71073
monoclinic
P2(1)/c
Crystal system
Space group
Unit cell dimensions
a (Å)
11.122(10)
10.102(3)
b (Å)
9.130(8)
8.824(3)
c (Å)
8.787(8)
10.089(3)
a
(°)
b (°)
(°)
90
90
95.804(16)
90
103.737(4)
90
c
V (Å3)
887.6(14)
873.6(4)
Z
q
l
2
2
(mg mꢀ3
(mmꢀ1
)
1.716
1.075
1.581
1.280
)
F(000)
464
430
Crystal size (mm3)
h (°)
0.40 ꢁ 0.36 ꢁ 0.12
2.89–28.39
ꢀ14<=h<=14
ꢀ12<=k<=12
ꢀ11<=l<=11
7508
0.30 ꢁ 0.30 ꢁ 0.15
2.08–28.27
ꢀ13<=h<=13
ꢀ11<=k<=11
ꢀ13<=l<=13
6456
Index ranges
Reflections collected
Independent reflections (Rint
Completeness to h = 25.00 (°)
Absorption correction
)
2080 = 0.0701]
99.7%
Semi-empirical from equivalents
1 and 0.56
Full-matrix least-squares on F2
1.061
2062 = 0.0544]
99.9%
Semi-empirical from equivalents
1 and 0.78
Full-matrix least-squares on F2
1.033
Maximum and minimum transmission
Refinement method
Goodness-of-fit (GOF) on F2
Final R indices [I>2
r
(I)]
R1 = 0.0466,
wR2 = 0.1016
R1 = 0.0743,
wR2 = 0.1120
1.337 and ꢀ1.165
R1 = 0.0413,
wR2 = 0.0898
R1 = 0.0898,
wR2 = 0.1059
0.620 and ꢀ0.649
R indices (all data)
Largest difference in peak and hole (e Åꢀ3
)
2
2
R1
=
R
||F0| ꢀ ||Fc||/
R
|F0| and wR2 = {
R
[wðF2c ꢀ F2c Þ ]/
R
ðF20Þ ]}1/2
.
Table 2
Table 3
Significant bond lengths [Å] and angles [°] for complexes.
Effect of base and solvent on the heck coupling of idobenzene with Styrene.a
[PdL2]
catalyst
Pd(1)-O(1)
Pd(1)-N(1)
C(1)-O(1)
C(2)-C(3)
C(7)-N(1)
C(10)-N(1)
1.981(3)
2.020(4)
1.326(6)
1.379(8)
1.301(6)
1.484(6)
O(1)#1-Pd(1)-N(1)#1
O(1)-Pd(1)-N(1)#1
O(1)-Pd(1)-N(1)
C(7)-N(1)-Pd(1)
C(10)-N(1)-Pd(1)
C(1)-O(1)-Pd(1)
90.75(15)
89.25(15)
90.75(15)
123.0(3)
116.7(3)
120.5(3)
I
+
base, solvent
120 0C, 8h
Entry
Base
Solvent
Yield (%)b
[PdL2]
[CuL2]
[CuL2]
1
2
3
4
5
6
7
8
9
NEt3
NaCH3COO
K2CO3
NEt3
NaCH3COO
K2CO3
NEt3
NaCH3COO
K2CO3
DMAc
DMAc
DMAc
DMF
DMF
DMF
DMSO
DMSO
DMSO
100
54
73
92
61
59
89
43
59
98
47
66
91
43
50
85
36
40
Cu(1)-O(1)
Cu(1)-N(1)
C(1)-O(1)
C(2)-C(3)
C(7)-N(1)
C(10)-N(1)
1.883(2)
2.000(2)
1.322(3)
1.410(4)
1.481(4)
1.300(4)
O(1)#1-Cu(1)-O(1)
O(1)#1-Cu(1)-N(1)
O(1)-Cu(1)-N(1)
C(10)-N(1)-Cu(1)
C(7)-N(1)-Cu(1)
C(1)-O(1)-Cu(1)
180.00(12)
90.65(9)
89.35(9)
124.6(2)
116.31(18)
124.20(19)
were obtained by slow evaporation of a methanolic solution of
complex at room temperature (358 mg, yield; 86%). Anal. Calc.
for C20H20CuN2O4: C, 57.70; H, 4.81; N, 6.73. Found: C, 57.62; H,
4.79; N, 6.76%. Selected IR frequency (KBr disk, cmꢀ1): 1611(s,
a
Reaction conditions: 1.0 mmol of PhI, 1.1 mmol of styrene, 0.004 mmol of cat-
alyst 2a or 0.02 mmol catalyst 2b, 1.1 mmol of base, 1 mL of solvent.
b
Determined by GC, based on iodobenzene; average of two runs.
m
C=N). Electronic absorption spectrum in CH2Cl2 kmax (nm) (e
(Mꢀ1 cmꢀ1)): 244 (6298).
After the reaction mixture was cooled to room temperature, hydro-
chloric acid (1 M, 6 mL) was added and the product was extracted
with diethyl ether (315 mL). The aqueous solution was separated
from the organic layer. The diethyl ether solution was washed with
water (315 mL), dried over MgSO4, and evaporated to dryness un-
der reduced pressure to afford the desired product, which was then
washed with hexane (35 mL). The purity of the compounds was
checked by GC and NMR and yields are based on the aryl halide.
3. General procedures for the Heck reaction
A flask was charged with 2a or 2b (0.004 mmol and 0.02 mmol,
respectively for each single experiment) along with an appropriate
amount of aryl halide (1.0 mmol), olefin (1.1 mmol), NEt3
(1.1 mmol), and DMAc (1 mL) and a magnetic stir bar. The mixture
was heated to 120 °C with stirring for a specified period of time.

M. Bagherzadeh et al. / Inorganica Chimica Acta 383 (2012) 46–51
49
Table 4
100
The effect of the amount of catalyst on the Heck coupling of iodobenzene with
styrene.a
80
60
40
20
0
Entry
Catalyst (mmol)
Yield (%)b
1
2
3
4
5
6
7
8
9
10
2a (0.001)
2a (0.002)
2a (0.002)
2a (0.004)
2a (0.005)
2b (0.005)
2b (0.010)
2b (0.015)
2b (0.020)
2b (0.025)
49
61
88
100
100
52
73
85
98
97
2a
2b
60
80
100
120
a
Reaction conditions: 1.0 mmol of PhI, 1.1 mmol of styrene, 1.1 mmol of NEt3,
1 mL of DMAc.
Reaction Temperature
b
Determined by GC, based on iodobenzene; 120 °C, 8 h. average of two runs.
Fig. 3. The effect of the reaction temperature on the Heck coupling of iodobenzene
with styrene. (a) Reaction conditions: 1.0 mmol of PhI, 1.1 mmol of styrene,
0.004 mmol of catalyst 2a or 0.02 mmol catalyst 2b, 1.1 mmol of NEt3, 1 mL of
DMAc. The yields determined by GC, based on iodobenzene; average of two runs.
4. X-ray structure analysis for complexes
A yellow plate and a pale block were selected respectively for
[PdL2] and [CuL2] complexes under ambient conditions. The crystal
was mounted and centered in the X-ray beam by using a video
camera.
of 10ꢀ3 M solutions of these complexes lie in the range 10–
15
behavior. Moreover, the molecular structures of these complexes
were confirmed by single-crystal X-ray crystallography.
X
ꢀ1cm2 molꢀ1 in CH2Cl2 indicating their non-electrolytic
The crystal evaluation and data collection were performed at
173 K on
a
Bruker CCD-1000 diffractometer with Mo
K
a
The complexes are insensitive to oxygen or moisture; no change
in their catalytic efficiencies was observed even if the Heck cou-
pling reactions were carried out under aerobic conditions.
1H and 13C NMR spectra were obtained for the ligand and for the
diamagnetic complex 2a as well. The 1H NMR spectrum of the com-
plex showed the disappearance of the phenoxy-OH proton. The ab-
sence of this signal suggests that this proton has been lost upon
coordination of the oxygen with the metal atom [9]. However,
other protons exhibited only slight changes in chemical shifts com-
pared with those of the corresponding unbound ligand. The 13C
NMR spectra also lacked significant changes in chemical shifts be-
tween the complexed and the free ligand.
(k = 0.71073 Å) radiation and the detector to crystal distance of
5.03 cm. The initial cell constants were obtained from three series
of
x
scans at different starting angles. Each series consisted of 30
with
frames collected at intervals of 0.3° in a 10° range about
x
the exposure time of 10 s per frame. The obtained reflections were
successfully indexed by an automated indexing routine built in the
SMART program. The final cell constants were calculated from a set
of strong reflections from the actual data collection.
The data were collected using the full sphere routine by collect-
ing four sets of frames with 0.3° scans in
10 s per frame. This dataset was corrected for Lorentz and polariza-
tion effects. The absorption correction was based on a fit of a
spherical harmonic function to the empirical transmission surface
as sampled by multiple equivalent measurements [12] using SAD-
ABS software [13].
x with an exposure time
The mC=N vibrations for two complexes were found in the range
1611–1614 cmꢀ1, and are shifted by at least 27–30 cmꢀ1 to a lower
frequency compared to that of the free ligand indicating that the
imine nitrogen of the oxazine ring is strongly coordinated to the
metal center [9]. Also, the broad OH vibrational band in the
3300 cmꢀ1 region of the free ligand is absent from the spectra of
the complexes, indicating the deprotonation of this group on coor-
dination with the metal atoms.
5. Results and discussion
5.1. Oxazine ligand
The ligand, 2-(20-hydroxyphenyl)-5,6-dihydro-1,3-oxazine, (HL)
was easily prepared in good yields in two steps by the condensa-
tion of 3-amino-1-propanol with ethyl salicylate followed by
dehydrative cyclization of the resulting o-hydroxyamide.
The 2-(20-hydroxyphenyl)-5,6-dihydro-1,3-oxazine functions as
a bidentate ligand via the phenolate oxygen and the oxazine nitro-
gen (Scheme 1).
5.3. Molecular structures of complexes 2a and 2b
The molecular structures of 2a and 2b are depicted in Figs. 1
and 2, and both complexes are isostructural. The coordination
geometry around the palladium and copper centers is square pla-
nar with two bidentate (N, O) oxazine ligands.
Crystallographic data are summarized in Table 1, and selected
bond lengths and angles are given in Table 2. The preferred stereo-
chemical arrangement has the phenolate oxygens trans to each
other, which is consistent with oxazoline complexes of palladium
and copper that have been structurally characterized [14,15].
The bond lengths and angles of the primary coordination sphere
are comparable to other reported palladium and copper complexes
with bidentate (N,O) ligands [14,15].
The Heck reaction is an old and versatile method for palladium-
catalyzed arylation and vinylation of alkenes [14]. In order to eval-
uate catalytic activities of 2a and 2b for Heck reaction, we chose to
examine the coupling of iodobenzene with styrene for the survey
of the reaction parameters such as temperature, solvent, base
and catalyst loading with Pd complex 2a. Specifically, four bases
5.2. Palladium(II) and copper (II) complexes
The new palladium(II) complex [PdL2] (2a), was obtained as yel-
low crystals in quantitative yield by the reaction of palladium(II)
acetate with HL in dichloromethane at room temperature. The cop-
per(II) complex [CuL2] (2b), was obtained as brown crystals in 82%
yield by treatment of copper(II) acetate mono-hydrate with HL in
methanol at room temperature (Scheme 2).
Complexes 2a and 2b were fully characterized by spectroscopy
(1H, 13C NMR, IR, and UV–Vis) and by elemental analysis. Analyses
for C, H, and N in each complex are consistent with the formula-
tions of bis(1igand)metal species. The molar conductance values

50
M. Bagherzadeh et al. / Inorganica Chimica Acta 383 (2012) 46–51
Table 5
Catalytic Heck reactions of aryl halides with olefins.a
catalyst, NEt3
R
R
+
X
0
DMAc,
120 C
R'
R=
, COOBu , COOEt , COOMe , CN
R'= H , CH3 , CH3O , CH3CO
Conversion (%)b (Isolated yield (%))c
X= I , Br , Cl
Entry
ArX
Olefine
TONd
2a
2a
2b
2b
1
100(94)
98(89)
250
49
I
2
89
71
223
213
230
250
250
250
250
170
128
138
158
208
220
225
220
-
36
37
40
48
50
50
49
22
18
19
3
I
H3C
3
85
73
I
CH3O
CH3CO
4
92(86)
100 (94)
100
100
100(97)
68
80(71)
96 (85)
100
100
97(91)
43
I
5
COOBu
COOEt
COOMe
CN
I
6
I
7
I
8
I
9
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
10
11
12
13
14
15
16
17
18
51
35
H3C
55
37
CH3O
63
45
CH3CO
83
57
29
31
30
33
-
COOBu
COOEt
COOMe
CN
88
61
90
60
88
65
0
0
12
0
30
-
COOBu
a
b
c
Reaction conditions: 1.0 mmol of PhX, 1.1 mmol of olefin, 1.1 mmol of NEt3, 1 mL of DMAc.
Determined by GC, based on aryl halides; 120 °C, 8 h. average of two runs.
Average isolated yield from two trials.
d
TON = (mmol of product)/mmol of catalyst.
and three solvents were surveyed under conditions where they
were compatible. As summarized in Table 3, the reaction condi-
tions involving dimethylacetamide (DMAc) and triethylamine (en-
try 1) appear to be superior to the others.
(Fig. 3). The effect of increasing the temperature of reaction was
to increase the yield of E-stilbene in the Heck reaction.
Under the determined reaction conditions, a wide range of ole-
fins bearing electron-donating and electron-withdrawing groups
coupled with aryl halides, affording the olefinic products in excel-
lent yields (Table 5). The complexes exhibited higher activity with
electron-withdrawing substituent’s relative to electron-donating
substituents on the olefins in Heck reaction. Using aryl chloride in-
stead of aryl iodide yielded only a small amount of stilbene deriv-
atives under the conditions employed for iodides and bromides
(Table 5, Entry 16–18). As illustrated in Table 5, the catalytic activ-
ity of [CuL2] appears to be as efficient as that of [PdL2].
A control experiment indicated that the coupling reaction did
not occur in the absence of catalyst. The yield of E-stilbene mono-
tonically increases with the addition of catalyst 2a of 0.001–
0.005 mmol and catalyst 2b of 0.005–0.02 mmol. (Table 4).
Temperature is a very important parameter in Mizoroki–Heck
reactions, determining the type and operation mode of catalytic
systems. As with other parameters, there are controversial views
on the role of temperature. In an attempt to gain insight into the
effect of reaction temperature on the Heck reaction, the coupling
of iodobenzene with styrene was used as a model reaction
The textbook mechanism of the Heck reaction is still widely ac-
cepted even though detailed mechanistic investigations have led to

M. Bagherzadeh et al. / Inorganica Chimica Acta 383 (2012) 46–51
51
rile: 1H NMR (500 MHz, CDCl3): d 6.27 (1H, d), 7.51 (1H, d), 7.58
ꢀ8.1 (5H, m). Anal. Calc. for C9H7N: C, 83.72; H, 5.43; N, 10.85.
Found: C, 83.74; H, 5.37; N, 10.81%. 4-Acetylstilbene: 1H NMR
(CDCl3, 500 MHz): d 7.93 (d, 2H), 7.54 (d, 2, H), 7.52 (d, 2H), 7.37
(t, 2H), 7.30 (t, 1H), 7.19 (d, 1H), 7.09 (d, 1H), 2.57 (s, 3H). Anal. Calc.
for C16H14O: C, 86.45; H, 6.35. Found: C, 86.32; H, 6.40%. CCDC
775794 and 775795; 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.a-
c.uk/data_request/cif.
N
O
O
N
M
+
R NH X
3
-
Ar
X
M=Pd, Cu
R3N
A
N
N
X
O
H
X
O
M
D
B
M
O
Ar
O
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2011.10.040.
N
Ar
N
CH
C
N
References
CH2
R
R
X
O
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M
Ar
O
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R
N
Scheme 3. Proposed mechanism for Heck reaction by 2a and 2b.
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r-
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6. Conclusions
We have synthesized the bidentate ligand ‘‘2-(20-hydroxy-
phenyl)-5,6-dihydro-1,3-oxazine’’ with a simple method and pre-
pared complexes of Pd and Cu with this chelate. All these new
compounds were characterized using X-ray structure analysis,
NMR, IR and elemental analysis. The catalytic behavior of the Pd(II)
complex 2a and Cu(II) complex 2b were investigated in the Heck
reaction. In general, 2a appears to be more efficient for the Heck
reaction of aryl iodide and bromide compared with 2b, but their
activity is much lower for the coupling of aryl chloride. The proce-
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M.B. thanks the Research Council of Sharif University of Tech-
nology for financially support of this work and L.K.W. thanks the
National Science Foundation for funding of this work.
Appendix A. Supplementary material
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(E)-Stilbene; 1H NMR (500 MHz, CDCl3): d 7.41 (s, 2H), 7.63–7.68
(m, 2H), 7.73–7.78 (m, 4H), 7.88–7.90 (m, 4H). Anal. Calc. for
C14H12: C, 93.33; H, 6.67. Found: C, 93.21; H, 6.61%. (E)-Cinnamonit-