Iminophosphine palladium(II) complexes: Synthesis, characterization, and application in Heck cross-coupling reaction of aryl bromides

Article abstract of DOI:10.1002/aoc.3158

Palladium(II) complexes containing phosphorus and nitrogen donor atoms (iminophosphine), dichlorido{N-[2-(diphenylphosphino)benzylidene]-2- trifluoromethylaniline}palladium(II) 1, dichlorido{N-[2-(diphenylphosphino) benzylidene]-3-trifluoromethylaniline}palladium(II) 2, dichlorido{N-[2- (diphenylphosphino)benzylidene]-2-methylaniline}palladium(II) 3, dichlorido{N-[2-(diphenylphosphino)benzylidene]-3-methylaniline}palladium(II) 4 have been successfully synthesized and fully characterized by FT-IR and NMR (¹H, ³¹P, ¹⁹F, and ¹³C) spectroscopy techniques. These complexes were first step tested in the reaction of bromobenzene and styrene to determine the optimal coupling reaction conditions and then successfully applied as catalysts for Heck cross-coupling reactions of activated and deactivated aryl bromides with styrene derivatives and several acrylates. Copyright

Full text of DOI:10.1002/aoc.3158

Full Paper
Received: 5 March 2014
Revised: 16 March 2014
Accepted: 6 April 2014
Published online in Wiley Online Library: 29 May 2014
(wileyonlinelibrary.com) DOI 10.1002/aoc.3158
Iminophosphine palladium(II) complexes:
synthesis, characterization, and application in
Heck cross-coupling reaction of aryl bromides
Mustafa Kemal Yılmaza* and Bilgehan Güzelb
Palladium(II) complexes containing phosphorus and nitrogen donor atoms (iminophosphine), dichlorido{N-[2-
(diphenylphosphino)benzylidene]-2-trifluoromethylaniline}palladium(II) 1, dichlorido{N-[2-(diphenylphosphino)benzylidene]-3-
trifluoromethylaniline}palladium(II) 2, dichlorido{N-[2-(diphenylphosphino)benzylidene]-2-methylaniline}palladium(II) 3,
dichlorido{N-[2-(diphenylphosphino)benzylidene]-3-methylaniline}palladium(II) 4 have been successfully synthesized and fully
characterized by FT-IR and NMR (1H, 31P, 19F, and 13C) spectroscopy techniques. These complexes were first step tested in the
reaction of bromobenzene and styrene to determine the optimal coupling reaction conditions and then successfully applied as
catalysts for Heck cross-coupling reactions of activated and deactivated aryl bromides with styrene derivatives and several acrylates.
Copyright © 2014 John Wiley & Sons, Ltd.
Keywords: iminophosphine; palladium; Heck cross-coupling reaction; aryl bromides
MHz; 13C: 100.6 MHz; 19F: 376.5 MHz) spectrometer. 1H NMR
Introduction
and 13C NMR spectra were obtained at room temperature using
tetramethylsilane as a reference. 31P NMR spectra of the ligands
The coupling of aryl or vinyl halides with terminal alkenes by the
Heck cross-coupling reaction is a powerful tool for the prepara-
tion of substituted olefins, dienes, and precursors to conjugated
polymers.[1–3] This reaction, which relates to the formation of
new C―C bonds, is generally catalyzed with Pd complexes
formed by tertiary phosphine ligands or PN-type ligands which
are thought to stabilize the active palladium intermediates.[4–7]
Heterodentate phosphine ligands bearing hard nitrogen and soft
phosphorus donor atoms have emerged as an important class of
ligands, and this feature provides that unique property to their
metal complexes. This hemilability of complexes with a mixed
donor ligands improves the catalytic activity for C―C coupling
reactions, because it changes the symmetry around the palla-
dium orbitals.[8,9] In this paper, we wish to report the synthesis
and characterization of new palladium(II) complexes coordinated
with hemilabile bidentate iminophosphine ligands (Scheme 1)
and we used our catalysts in Heck C―C bond-forming reactions.
and complexes were obtained at room temperature using o-
phosphoric acid as an internal standard. 19F NMR spectra were
obtained using trichlorofluoromethane as a reference. All chemi-
cal shifts (δ) are given in parts per million (ppm), and coupling
constants (J) in Hertz (Hz). Infrared spectra were obtained using
a PerkinElmer Spectrum 1 FT-IR spectrophotometer in the range
4000–650 cmÀ1
. Melting points were determined on a
PerkinElmer Pyris 6 differential scanning calorimetry (DSC) instru-
ment. GC analyses were performed on a PerkinElmer Clarus 500
gas chromatograph equipped with a flame ionization detector
(FID) and
a 30 m capillary column containing dimethyl
polysiloxane stationary phase.
Synthesis of Ligands
Synthesis of Ph2PC6H4CH=N(2-CF3C6H4) a
A mixture of 2-(diphenylphosphino)benzaldehyde (1.0 g, 3.4
mmol) and 2-(trifluoromethyl)aniline (0.6 ml, 4.6 mmol) was
dissolved in methanol (30 ml) with two drops of formic acid
and stirred at reflux temperature for 2 h. The mixture was allowed
to warm to room temperature, washed with saturated sodium
bicarbonate aqueous solution, and dried over anhydrous sodium
Experimental
General Comments
All ligands and complexes were synthesized using standard
Schlenk techniques under an argon atmosphere. Unless other-
wise noted, all reagents were used without further purification.
Toluene and methanol were distilled and degassed prior to
use.[10] All other solvents used were of analytical grade and dried
over activated molecular sieves (4A). Flash column chromatogra-
phy was performed on silica gel (230–400 mesh). Pd(cod)Cl2
(cod = 1,5-cyclooctadiene)[11] and 2-(diphenylphosphino)benzal-
dehyde[12] were prepared according to previously reported pro-
cedures. NMR spectra were recorded in deuterated chloroform
and DMSO on a Bruker NMR-400 MHz (1H: 400.2 MHz; 31P: 162.0
*
Correspondence to: Mustafa Kemal Yılmaz, Department of Chemistry, Faculty
of Arts and Sciences, Osmaniye Korkut Ata University, 80000 Osmaniye, Turkey.
E-mail: mkyilmaz@osmaniye.edu.tr
a Department of Chemistry, Faculty of Arts and Sciences, Osmaniye Korkut Ata
University, 80000 Osmaniye, Turkey
b Department of Chemistry, Faculty of Arts and Sciences, Çukurova University,
01330 Adana, Turkey
Appl. Organometal. Chem. 2014, 28, 529–536
Copyright © 2014 John Wiley & Sons, Ltd.

M. K. Yılmaz and B. Güzel
(methyl)aniline (0.51 ml, 3.90
mmol) in dry CH2Cl2 (50 ml), pro-
ducing a light-yellow solid (0.79
g, 55%). m.p. 107°C. IR: 1673
cmÀ1 (ν C=N, imine). 1H NMR
(400.2 MHz, CDCl3): δ (ppm)
9.03 (d, 1H, J=5.1 Hz, HC=N),
8.19 (m, 1H1, CH), 7.47 (m, 1H21,
CH), 7.36–7.15 (m, 15H2–18,22,24
,
Scheme 1. Synthesis of iminophosphine ligands a-d and palladium complexes 1-4.
CH), 6.96 (m, 1H20, CH), 2.29 (s,
3H, CH3). 31P {1H} NMR (162.0
sulfate. Evaporation of the solvent gave a crude product, which
was chromatographed on silica gel (4% ethyl acetate in hexane)
to give the pure iminophosphine a as a white solid (0.96 g,
MHz, CDCl3): δ (ppm) À13.09 (s). 13C NMR (100.6 MHz, CDCl3): δ
(ppm) 158.68 (d, JPC =21.6 Hz, HC=N), 151.76 (C19), 141.18 (d,
J
PC= 26.4 Hz, C8), 139.21 (d, JPC= 16.6 Hz, C6), 138.82 (C2,23),
65%); m.p. 117°C. IR: 1626 cmÀ1 (ν C=N, imine). H NMR (400.2
136.44 (d, JPC= 9.5 Hz, C7), 136.12 (d, JPC= 9.6 Hz, C5), 134.19
(C21), 133.99 (C1), 129.15 (C20,22), 128.89 (d, JPC= 9.2 Hz, C4,10),
128.77 (d, JPC= 7.2 Hz, C9), 128.05 (d, JPC= 3.9 Hz, C3), 118.07
(C24), 21.39 (CH3).
1
MHz, CDCl3): δ (ppm) 9.06 (d, 1H, J=5.6 Hz, HC=N), 8.32 (m, 1H1,
CH), 7.63 (m, 1H23, CH), 7.42–7.34 (m, 13H2–18, CH), 7.23(m, 1H21,
CH), 6.95 (m, 1H22, CH), 6.39 (m, 1H20, CH). 31P {1H} NMR (162.0
MHz, CDCl3): δ (ppm) À14.15 (s). 13C NMR (100.6 MHz, CDCl3): δ
(ppm) 160.26 (d, JPC= 25.2 Hz, HC=N), 150.66 (C19), 135.80 (d,
JPC= 9.1 Hz, C8), 134.22 (d, JPC= 20.1 Hz, C6), 132.95 (d, JPC=24.9
Hz, C7), 131.46 (C2,3,10), 128.81 (d, JPC= 7.3 Hz, C5), 127.97 (C1,21),
127.95 (d, JPC= 3.6 Hz, C4), 126.14 (C20,22,23), 126.11 (d, JPC= 5.4
Hz, C9), 124.97 (CF3), 119.54 (C24). 19F NMR (376.5 MHz, CDCl3): δ
(ppm) À60.25 (s).
Synthesis of Complexes
General procedure for the synthesis of the palladium(II) complexes (1–4)
For each reaction, a solution of Pd(cod)Cl2 in CH2Cl2 (5 ml) was
added in stoichiometric proportion to
a solution of an
iminophosphine ligand (1.30 mmol) (a–d) in CH2Cl2 (20 ml) and
then stirred at room temperature for 4 h. After completion of
the reaction, the reaction mixture was concentrated in vacuo
and diethyl ether was added to precipitate the product. The
resulting light-yellow solid was filtered and then dried.
Synthesis of Ph2PC6H4CH N(3-CF3C6H4) b
This compound was prepared as described for a using 2-
(diphenylphosphino)benzaldehyde (1.0 g, 3.4 mmol) and 3-
(trifluoromethyl)aniline (0.6 ml, 4.6 mmol), producing a white
1
solid (0.88 g, 60%); m.p. 75°C. IR: 1625 cmÀ1 (ν C=N, imine). H
PdCl2(a), 1. Yield 674 mg (85%). m.p. 276°C (decomposed). IR:
1619 cmÀ1 (ν C=N, imine). 1H NMR (400.2 MHz, DMSO-d6): δ
(ppm) 8.30 (s, 1H, HC=N), 7.83 (m, 1H1, CH), 7.78 (m, 1H23, CH),
7.72 (m, 1H21, CH), 7.67–7.49 (m, 13H2-18, CH), 7.41 (m, 1H22,
CH), 7.22 (m, 1H20, CH). 31P {1H} NMR (162.0 MHz, DMSO-d6): δ
(ppm) 26.68 (s). 13C NMR (100.6 MHz, CDCl3): δ (ppm) 170.08 (d,
NMR (400.2 MHz, CDCl3): δ (ppm) 9.03 (d, 1H, J=5.1 Hz, HC=N),
8.20 (m, 1H1, CH), 7.50 (m, 1H21, CH), 7.43–7.34 (m, 13H2–18, CH),
7.05 (m, 2H22,24, CH), 6.97 (m, 1H20, CH). 31P {1H} NMR (162.0
MHz, CDCl3): δ (ppm) À12.37 (s). 13C NMR (100.6 MHz, CDCl3): δ
(ppm) 160.35 (d, JPC= 20.6 Hz, HC=N), 152.16 (C19), 139.21 (d,
JPC= 20.7 Hz, C8), 138.51 (d, JPC= 15.9 Hz, C6), 134.18 (d, JPC= 20.2
Hz, C7), 133.49 (C2,3,23), 129.48 (C21), 129.12 (C1), 128.78 (d, JPC= 7.4
Hz, C5), 128.48 (d, JPC= 3.6 Hz, C4,10), 124.08 (C20,22), 122.60 (CF3),
122.33 (d, JPC= 3.6 Hz, C9), 117.86 (C24). 19F NMR (376.5 MHz,
CDCl3): δ (ppm) À62.57 (s).
J
PC= 11.4 Hz, HC=N), 149.59 (C19), 139.13 (C21), 135.58 (d, JPC= 6.6
Hz, C8), 133.49 (d, JPC= 11.2 Hz, C6), 132.14 (d, JPC= 25.5 Hz, C7),
128.90 (d, JPC= 11.9 Hz, C5), 127.26 (C2,10,22,23), 125.77 (d, JPC= 4.8
Hz, C4), 124.44 (C1), 121.68 (d, JPC= 6.6 Hz, C3,9), 121.53 (CF3),
121.23 (C24). 19F NMR (376.5 MHz, DMSO-d6): δ (ppm) À58.87 (s).
Synthesis of Ph2PC6H4CH N(2-CH3C6H4) c
PdCl2(b), 2. Yield 635mg (80%). m.p.: 275 °C (decomposed). IR:
1617 cmÀ1 (ν C=N, imine). 1H NMR (400.2 MHz, DMSO-d6): δ
(ppm) 8.76 (s, 1H, HC=N), 8.22 (m, 1H1, CH), 7.90 (m, 1H21, CH),
7.74–7.61 (m, 11H4–18, CH), 7.54(m, 4H2,3,22,24, CH), 7.07 (m, 1H20,
CH). 31P {1H} NMR (162.0 MHz, DMSO-d6): δ (ppm) 30.95 (s). 13C
NMR (100.6 MHz, CDCl3): δ (ppm) 169.49 (d, JPC= 8.5 Hz, HC=N),
151.91 (C19), 138.23 (C21), 136.35 (d, JPC= 13.8 Hz, C6,7), 133.82 (d,
The iminophosphine c has been previously reported and was
prepared according to the reported method[13] using 2-
(diphenylphosphino)benzaldehyde (0.55 g, 1.90 mmol) and 2-
(methyl)aniline (0.21 ml, 1.91 mmol) in dry CH2Cl2 (25 ml), pro-
ducing a light-yellow solid (0.58 g, 80%); m.p. 103°C. IR: 1625
1
cmÀ1 (ν C=N, imine). H NMR (400.2 MHz, CDCl3): δ (ppm) 8.97
J
PC= 11.0 Hz, C8), 133.36 (C2,3), 132.60 (C23), 129.55 (C1), 129.29
(d, 1H, J=5.2 Hz, HC=N), 8.24 (m, 1H1, CH), 7.45 (m, 1H23, CH),
(d, JPC=12.1 Hz, C5), 127.86 (C20), 125.27 (CF3), 124.68 (C22),
124.23 (d, JPC= 3.6 Hz, C4,10), 120.59 (C24), 119.93 (d, JPC= 4.5 Hz,
C9). 19F NMR (376.5 MHz, DMSO-d6): δ (ppm) À60.96 (s).
7.35–7.28 (m, 12H2,4–18, CH), 7.13 (m, 1H21, CH), 7.05 (m, 2H3,22
,
CH), 6.91 (m, 1H20, CH), 2.19 (s, 3H, CH3). 31P {1H} NMR (162.0
MHz, CDCl3): δ (ppm) À13.66 (s). 13C NMR (100.6 MHz, CDCl3): δ
(ppm) 158.31 (d, JPC= 22.7 Hz, HC=N), 151.09 (C19), 139.51 (d,
JPC= 16.9 Hz, C8), 138.47 (d, JPC= 19.9 Hz, C7), 136.36 (d, JPC= 9.7
Hz, C6), 134.19 (d, JPC= 19.9 Hz, C5), 133.40 (C2,10), 130.83 (C1,21),
130.09 (C20,22,23), 129.01 (d, JPC= 3.5 Hz, C4), 128.74 (d, JPC=7.2 Hz,
C3), 128.35 (d, JPC= 4.2 Hz, C9), 117.97 (C24), 17.77 (CH3).
PdCl2(c), 3. Yield 586 mg (81%). m.p. 225°C (decomposed). IR:
1618 cmÀ1 (ν C=N, imine). 1H NMR (400.2 MHz, DMSO-d6): δ
(ppm) 8.65 (s, 1H, HC=N), 8.19 (m, 1H1, CH), 7.95 (m, 1H23, CH),
7.80 (m, 1H3, CH), 7.72–7.48, (m, 10H8–18, CH), 7.17 (m, 3H2,4,22
,
CH), 7.03 (m, 1H21, CH), 6.91 (m, 1H20, CH), 2.14 (s, 3H, CH3). 31P
{1H} NMR (162.0 MHz, DMSO-d6): δ (ppm) 28.71 (s). 13C NMR
(100.6 MHz, CDCl3): δ (ppm) 168.64 (d, JPC= 8.9 Hz, HC=N), 151.54
(C19), 138.04 (d, JPC= 8.5 Hz, C8), 136.18 (d, JPC= 15.6 Hz, C6), 133.97
(C2,3), 133.44 (d, JPC= 11.0 Hz, C7), 132.24 (C10), 130.09 (d, JPC= 16.9
Synthesis of Ph2PC6H4CH N(3-CH3C6H4) d
This compound was prepared as described for c using 2-
(diphenylphosphino)benzaldehyde (1.10 g, 3.8 mmol) and 3-
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Copyright © 2014 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 529–536

Heck cross-coupling reactions with iminophosphine Pd(II) complexes
Hz, C1), 129.09 (d, JPC= 11.7 Hz, C21), 126.83 (C20,22,23), 125.62 (C5),
Results and Discussion
123.45 (C4,9), 119.29 (C24), 18.32 (CH3).
Infrared Spectroscopic Analysis
PdCl2(d), 4. Yield 629 mg (87%). m.p. 268°C (decomposed). IR:
1611 cmÀ1 (ν C=N, imine). 1H NMR (400.2 MHz, DMSO-d6): δ
(ppm) 8.64 (s, 1H, HC=N), 8.18 (m, 1H1, CH), 7.95 (m, 1H21, CH),
FT-IR analysis shows that important changes in the azomethine
(C=N) band can be observed from FT-IR spectra of the
iminophosphine ligands and their palladium(II) complexes. It
was determined that C=N stretching frequencies are found in
the iminophosphine ligands at 1626, 1625, 1625, and 1673
cmÀ1 for ligands a–d, respectively. These absorptions were
shifted to lower values in the iminophosphine palladium(II) com-
plexes, indicating the coordination of azomethine nitrogen to the
palladium center. This result indicate the coordination of nitro-
gen atom to the metal center, because this coordination reduces
the electron density on the azomethine bond, causing a down-
field shift of the C=N band, which is in agreement with what
was expected.[14,15]
7.80 (m, 1H3, CH), 7.72–7.48 (m, 10H8–18, CH), 7.23 (m, 2H2,22
,
P
CH), 7.12 (m, 2H4,20, CH), 7.02 (m, 1H24, CH), 2.30 (s, 3H, CH3). 31
{1H} NMR (162.0 MHz, DMSO-d6): δ (ppm) 31.23 (s). 13C NMR
(100.6 MHz, CDCl3): δ (ppm) 167.42 (d, JPC= 9.4 Hz, HC=N),
153.57 (C19), 134.73 (C21,23), 133.75 (d, JPC= 11.2 Hz, C8), 133.25
(d, JPC= 6.7 Hz, C6), 133.08 (C2,3), 132.49 (C1,20), 130.53 (C22),
129.15 (d, JPC= 11.9 Hz, C7), 128.14 (d, JPC= 15.9 Hz, C5,9), 125.11
(C2), 124.52 (C4), 123.30 (C10), 120.58 (C24), 20.78 (CH3).
General procedure for Heck cross-coupling reaction
In a typical experiment, an oven-dried, sealed tube equipped
with a magnetic stir bar was charged with aryl bromide (1.0
mmol), an olefin (1.2 mmol) and a base (1.2 mmol). The catalyst
solution (0.01 mmol catalyst in 3.0 ml solvent) was then added.
The reaction mixture was placed in a silicon oil bath at the de-
sired temperature and stirred. After the required reaction time,
the mixture was allowed to cool to room temperature, diluted
with CH2Cl2, and washed with HCl aqueous solution and brine.
The organic phase was separated and dried over Na2SO4 and
the solvent evaporated. The residue was chromatographed on
silica gel using an ethyl acetate/hexane (1:5) mixture as eluent.
Conversion percentages were determined from the solution by
GC analysis and yields were based on aryl halide.
1H NMR Spectroscopic Analysis
In the 1H NMR spectra of the iminophosphine ligands, the chem-
ical shift of the proton associated with the imine appears as a
characteristic doublet as a consequence of the coupling of phos-
phorus with corresponding azomethine protons. The peaks cor-
responding to the azomethine proton shifted downfield in the
metal complexes. They were observed as a singlet after the
ligand bound to the palladium ion via phosphorus atom.[16–19]
The 1H NMR spectra of the iminophosphine ligands a–d showed
a characteristic doublet in the region of δ 9.06–8.97 ppm with a
Table 1. Effect of base, solvent and temperature on the Heck coupling of bromobenzene with styrenea
Entry
Base
Solvent
Temp.
(°C)
Conversion %b
1
2
3
4
1
NEt3
Toluene
140
80
<5
<5
<5
18
5
<5
<5
<5
23
7
10
<5
—
14
5
6
2
NaOAc
K2CO3
NaOAc
K2CO3
NaOAc
K2CO3
NEt3
Toluene
<5
—
3
Toluene
80
4
Toluene
120
120
140
140
140
140
140
80
24
<5
33
51
<5
55
5
5
Toluene
6
Toluene
18
40
<5
40
<5
12
15
27
17
33
10
56
98
13
39
<5
40
5
20
56
<5
38
<5
28
42
34
45
47
15
68
7
Toluene
8
DMF
9
NaOAc
K2CO3
K2CO3
NaOAc
K2CO3
NaOAc
K2CO3
NEt3
DMF
10
11
12
13
14
15
16
17
18
DMF
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
17
18
76
<5
—
—
—
—
24
32
31
43
52
10
67
>99
100
100
120
120
140
140
140
NaOAc
K2CO3
>99
aConditions: Solvent (3 mL), base (1.2 mmol), bromobenzene (1.0 mmol), styrene (1.2 mmol), catalyst (0.01 mmol).
bPercentage conversions were determined by GC based on bromobenzene after 6 h.
Appl. Organometal. Chem. 2014, 28, 529–536
Copyright © 2014 John Wiley & Sons, Ltd.
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M. K. Yılmaz and B. Güzel
coupling constant of JPH=5.6–5.1 Hz due to the imine proton,
confirming coupling to the phosphorus atom. The peaks for the
imine protons in the complexes appear as singlets in the region of
δ 8.76–8.30 ppm. This shows that the phosphine donor of the
iminophosphine ligands coordinated to the palladium metal. The
peaks corresponding to the methyl protons appeared at δ 2.19
and 2.29 ppm for the ortho-substituted, c, and meta-substituted, d
ligand, respectively. Similarly, the singlet peaks of the ortho-methyl
protons in 3 and meta-methyl protons in 4 in the palladium (II)
complexes appeared at about δ 2.14 and 2.30 ppm, respectively.[20]
Table 2. Pd-catalyzed Heck coupling reactions between substituted aryl bromides and styrenesa
Entry
R1
R2
1b
2c
3b
4b
Time (h)
Conv. (%)d
Time (h)
Conv. (%)d
Time (h)
Conv. (%)d
Time (h)
Conv. (%)d
1
3-Cl
2-CH3
2-CH3
2-CH3
2-CH3
2-CH3
2-CH3
2-CH3
2-Cl
4
4
2
5
4
3
4
3
3
3
3
3
3
4
2
2
4
4
4
4
4
4
4
4
4
2
4
2
4
2
2
2
2
2
2
2
2
2
100
100
100
8
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
43
70
81
7
2
99
93
4
4
2
4
4
4
4
4
4
4
4
4
2
4
2
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
99
99
2
3-COH
4-COH
2-COCH3
3- COCH3
4- COCH3
4-CH3
4
3
2
100
13
99
4
4
0
5
100
95
47
48
19
66
20
53
67
57
70
7
4
90
100
100
99
6
2
99
7
100
99
4
70
8
3-Cl
1.5
3
100
0
100
0
9
2-COCH3
3-COCH3
4-COCH3
4-CH3
2-Cl
27
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
2-Cl
100
100
100
99
1.5
1.5
1.5
1.5
1.5
1.5
3
92
98
2-Cl
100
99
100
97
2-Cl
3-Cl
4-Cl
97
100
46
2-COCH3
4-COCH3
4-CH3
4-Cl
11
<5
99
4-Cl
100
100
32
86
35
36
9
100
100
96
4-Cl
91
3-Cl
2-Br
3
37
2-COCH3
3-COCH3
4-COCH3
4-CH3
2-Br
8
1.5
3
6
8
2-Br
39
35
52
26
58
27
71
50
83
96
97
12
79
96
72
68
93
98
87
91
56
40
52
2-Br
39
3
37
52
2-Br
35
3
28
28
3-Cl
4-Br
31
3
77
49
2-COCH3
4-COCH3
4-CH3
4-Br
6
3
15
38
4-Br
44
3
34
56
4-Br
28
3
34
41
3-Cl
2-OCH3
2-OCH3
2-OCH3
2-OCH3
2-OCH3
2-OCH3
2-OCH3
4-OCH3
4-OCH3
4-OCH3
4-OCH3
4-OCH3
4-OCH3
100
94
3
99
100
95
3-COH
4-COH
2-COCH3
3-COCH3
4-COCH3
4-CH3
3
97
100
6
3
100
<5
88
100
16
3
100
100
100
100
71
3
100
100
100
100
100
100
100
100
100
3
100
57
3
3-Cl
3
95
3-COH
4-COH
3-COCH3
4-COCH3
4-CH3
1.5
1.5
3
100
100
80
100
100
100
100
3
100
35
3
aConditions: aryl bromide (1.0 mmol), 1,4-dioxane (3 ml), K2CO3 (1.2 mmol), olefin (1.2 mmol), catalyst (0.01 mmol).
b140°C.
c100°C.
dPercentage conversions were determined by GC based on aryl bromide.
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Appl. Organometal. Chem. 2014, 28, 529–536

Heck cross-coupling reactions with iminophosphine Pd(II) complexes
31P NMR Spectroscopic Analysis
respectively. These values are in line with previously observed
results for similar compounds.[27]
The 31P NMR spectrum of iminophosphine ligands a–d showed
one phosphorus singlet in the region δ À14.15 to À12.37 ppm,
which is typical of unoxidized tertiary phosphines. The palladium
complexes also showed a downfield singlet peak in the region δ
26.68–31.23 ppm. These chemical shifts clearly demonstrated
that all iminophosphine ligands are coordinated to the palladium
metal via the phosphorus donor atom.[21,22]
Heck Coupling Reactions
The Heck coupling reaction between bromobenzene and styrene
was chosen to optimize suitable reaction conditions using differ-
ent bases (NEt3, NaOAc, K2CO3), temperatures (80, 100, 120, 140°
C), solvents (DMF, toluene, 1,4-dioxane) and 1.0 mol% of catalyst.
The results are listed in Table 1. As can be seen, poor yields were
obtained with NEt3 (Table 1, entry 8), NaOAc (Table 1, entry 9),
and K2CO3 (Table 1, entry 10) using DMF as the solvent at 140°
C. Likewise, when using toluene as solvent we could not obtain
a significant beneficial effect on catalyst performance with
K2CO3 (Table 1, entries 3, 5, and 7), Et3N (Table 1, entry 1), and
NaOAc (Table 1, entries 2, 4, and 6). On the other hand, when
1,4-dioxane was used as the solvent, relatively high conversions
were obtained depending on the temperature effect (Table 1, en-
tries 13–17); however, by increasing the temperature to 140°C
(Table 1, entry 18) almost complete conversions were obtained
for 1, 3, and 4 catalysts using K2CO3, and no palladium black for-
mation was observed during these reactions. Generally, for the
Heck coupling reactions higher reaction temperatures (normally
110–180°C) are required unless they cause catalyst decomposi-
tion, and it is also necessary to coordinate the carbon atom of
the C–Br group to Pd(0) intermediate during the catalytic
cycle.[28–30] As shown in entries 15 and 18, no activity was ob-
served for catalyst 2 at temperatures above 100°C. This can be
explained by the formation of palladium black species, which
was observed at reaction temperatures 120 and 140°C.[1] There-
fore, all other subsequent coupling reactions activated by catalyst
2 were carried out at 100°C, different from catalysts 1, 3, and 4 (at
140°C), using K2CO3 as a base in 1,4-dioxane.
13C NMR Spectroscopic Analysis
In 13C NMR spectrum of palladium complexes we observed a shift
from the ligands to the metal for the imine carbon. The signal of
the imine carbon for a–d in the 13C NMR spectrum of the free li-
gands each appeared as doublet resonance at δ 160.26, 160.35,
158.31, and 158.68 ppm with coupling constant JPC= 25.2–20.6 Hz
due to phosphorus carbon coupling, respectively. These signals
have totally shifted in the 13C NMR spectrum of the complexes,
indicating the coordination of the azomethine nitrogen to the
palladium metal.[23,24] As mentioned, the doublet signals for
the imine carbon 1–4 to δ 170.08, 169.49, 168.64, and 167.42
ppm with coupling constant JPC= 11.4–8.5 Hz was observed.
Besides that, the singlet signals of the trifluoromethyl carbon
for the a, b, 1, and 2 compounds were observed at δ 124.08,
124.97, 121.23, and 124.68 ppm, respectively.[25] Additionally, for
the methyl carbon singlet signals of the c, d, 3, and 4 compounds
were observed at δ 17.77, 21.39, 18.32, and 20.78 ppm,
respectively.[26]
19F NMR Spectroscopic Analysis
In the 19F NMR spectra, fluorine singlet peaks arising from the
trifluoromethyl group for compounds a, b, 1, and 2 were
observed at δ À60.25, À62.57, À58.87, and À60.96 ppm,
Table 3. Heck coupling of 2-bromo-6-methoxynaphthalene with substituted styrenesa
Entry
R
1
2
3
4
Time (h)
Conv. (%)d
Time (h)
Conv. (%)d
Time (h)
Conv. (%)d
Time (h)
Conv. (%)d
1
2
3
4
5
6
3-CH3
2-Cl
3
3
3
2
2
2
100
100
100
100
100
100
5
5
5
5
5
5
20
33
35
48
39
58
1.5
1.5
3
98
75
4
4
4
4
4
4
87
100
100
100
100
100
3-Cl
100
63
2-OCH3
3-OCH3
4-OCH3
3
3
63
3
11
aConditions: 2-Bromo-6-methoxynaphthalene (1.0 mmol), 1,4-dioxane (3 ml), K2CO3 (1.2 mmol), olefin (1.2 mmol), catalyst (0.01 mmol).
b140°C.
c100°C.
dPercentage conversions were determined by GC based on 2-bromo-6-methoxynaphthalene.
Appl. Organometal. Chem. 2014, 28, 529–536
Copyright © 2014 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

M. K. Yılmaz and B. Güzel
After the optimal reaction parameters were determined, the
catalytic activity for complexes with substituted aryl bromides
and styrene derivatives was investigated under those conditions
for the Heck coupling reaction. The data in Table 2 show the re-
sults obtained from the coupling of aryl bromides and styrene
derivatives.
palladium had precipitated out within the 5 h time frame, leaving
sufficient catalyst in solution to catalyze the reaction.
Ortho-substituted aryl bromides such as 2-bromoacetophenone
produced lower conversions (Table 2, entries 4, 9, 18, and 29). These
results indicate that, as expected, steric hindrance of the aryl
bromides is an important factor in the rate of reaction.[31]
Despite this, reasonable conversions were observed for the
reaction of 2-bromoacetophenone with 4-chlorostyrene and
4-bromostyrene in the presence of catalyst 4 (Table 2, entries
14 and 23). Generally, in Heck coupling reactions, deactivated
aryl bromides bearing electron-donating substituents on the
aryl bromide make the oxidative addition step of the catalytic
cycle more difficult than those with electron-withdrawing sub-
stituents (activated). In spite of this general trend, catalysts 1,
3, and 4 gave excellent conversions (>95%) for electronically
deactivated aryl bromides such as 1-bromo-3-chlorobenzene
(Table 2, entries 1, 8, 13, 26, and 33) and 4-bromotoluene (Ta-
ble 2, entries 7, 12, 16, and 32). Catalyst 2 was less active to-
ward these deactivated aryl bromides, giving moderate
conversions (Table 2, entries 1, 7, 8, 12, 13, 16, 17, 21, 22,
25, 26, 32, and 33).
As shown in Table 2, activated aryl bromides such as 3-
bromobenzaldehyde, 4-bromobenzaldehyde, 3-bromoacetophenone,
and 4-bromoacetophenone gave complete conversions when using
catalyst 1 (Table 2, entries 2, 3, 5, 10, 11, 15, 28, 30, 31, and 35–37).
Similarly, very high conversions (>80%) were obtained for the same
aryl bromides in the presence of complex 3 or 4 (Table 2, entries 2,
3, 5, 6, 10, 11, 15, 16, 26-28, 30, 31, and 34–37). In comparison, catalyst
2 showed generally poor conversion (35–71%), palladium black being
observed during the reactions (Table 2, entries 2, 5, 6, 10, 11, 19, 20,
and 24). Despite the formation of palladium black during the cou-
pling reaction of 4-bromobenzaldehyde with 4-methoxystyrene
and 2-methoxystyrene, almost complete conversions, 98%, and
97% after 5 h were achieved (Table 2, entries 28 and 35). The
formation of palladium black was due to the palladium precipitat-
ing out, leading to death of the catalyst. Presumably not all of the
Table 4. Heck coupling reactions between substituted aryl bromides and acrylatesa
Entry
R1
R2
1b
2c
3b
4b
Time (h)
Conv. (%)d
Time (h)
Conv. (%)d
Time (h)
Conv. (%)d
Time (h)
Conv. (%)d
1
3-Cl
Methyl
Methyl
Methyl
Methyl
Methyl
Methyl
Methyl
Ethyl
5
5
4
5
5
4
5
5
5
5
5
3
3
5
5
3
3
5
5
5
5
92
61
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
0
20
11
12
20
54
55
<5
41
80
16
16
61
52
9
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
62
59
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
100
88
2
3-COH
4-COH
2-COCH3
3-COCH3
4-COCH3
4-CH3
3
96
100
<5
98
100
20
4
8
5
99
93
6
91
100
85
100
95
7
54
8
3-Cl
91
85
100
100
100
29
9
3-COH
4-COH
2-COCH3
3-COCH3
4-COCH3
4-CH3
Ethyl
63
74
10
11
12
13
14
15
16
17
18
19
20
21
Ethyl
97
100
5
Ethyl
7
Ethyl
100
100
85
98
100
100
100
100
96
Ethyl
100
100
67
Ethyl
3-Cl
Butyl
82
3-COH
4-COH
2-COCH3
3-COCH3
4-COCH3
4-CH3
Butyl
100
100
<5
85
46
87
20
29
59
66
100
100
31
Butyl
100
25
Butyl
Butyl
100
100
100
100
100
97
Butyl
100
94
Butyl
aConditions: aryl bromide (1.0 mmol), 1,4-dioxane (3 ml), K2CO3 (1.2 mmol), acrylate (1.2 mmol), catalyst (0.01 mmol).
b140°C.
c100°C.
dPercentage conversions were determined by GC based on aryl bromide.
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Heck cross-coupling reactions with iminophosphine Pd(II) complexes
Table 5. Heck coupling of 2-bromo-6-methoxynaphthalene with substituted acrylatesa
Entry
R
1b
2c
3b
4b
Time (h)
Conv. (%)d
Time (h)
Conv. (%)d
Time (h)
Conv. (%)d
Time (h)
Conv. (%)d
1
2
3
Methyl
Ethyl
5
3
5
86
100
95
5
5
5
64
66
57
5
5
5
68
95
4
4
4
92
100
98
Butyl
100
aConditions: 2-bromo-6-methoxynaphthalene (1.0 mmol), 1,4-dioxane (3 ml), K2CO3 (1.2 mmol), acrylate (1.2 mmol), catalyst (0.01 mmol).
b140°C.
c100°C.
dPercentage conversions were determined by GC based on 2-bromo-6-methoxynaphthalene.
The data in Table 3 show the results obtained from the
coupling of 2-bromo-6-methoxynaphthalene with substituted
styrenes under the previously determined optimal reaction
conditions. Despite the presence of an electron-donating sub-
stituent in the other ring, 2-bromo-6-methoxynaphthalene
gave complete conversion with substituted styrenes for the
1- and 4-catalyzed Heck coupling reactions (Table 3, entries
2–6). The 3-catalyzed reaction between 2-bromo-6-
methoxynaphthalene and 3-chlorostyrene also gave complete
conversion (Table 3, entry 3). Moderate conversions (20–58%) were
obtained when catalyst 2 was used for the coupling reaction of
2-bromo-6-methoxynaphthalene with styrene derivatives.
All the complexes were evaluated for Heck coupling with
activated and deactivated aryl bromides and a variety of acry-
lates. It was observed that catalyst 4 was a very effective catalyst
for the coupling of activated aryl bromides such as 3-bromo,
4-bromobenzaldehyde and 3-bromo, 4-bromoacetophenone
in relatively short time frames of 4 h, showing conversion
rates of 88–100%. When complex 1 or 3 was used as catalyst
for these coupling reactions, high conversions (59–100%)
were also observed, but in the presence of complex 2 only
moderate conversions were obtained after 5 h (Table 4,
entries 2, 3, 5, 6, 9, 10, 12, 13, 16, 17, 19, and 20). Additionally,
the use of complex 2 as a catalyst led to no conversion in the
reaction between 1-bromo-3-chlorobenzene and methyl acry-
late (Table 4, entry 1). It is noteworthy that complex 4 gave
complete conversion for 1-bromo-3-chlorobenzene, which
was deactivated by the ―Cl group (Table 4, entries 1, 8,
and 15). It also gave almost complete conversion for the other
reaction. Good conversions were obtained in cases where ethyl-
and butyl-substituted acrylates were used (Table 5, entries 2
and 3). In the case of methyl acrylate, only moderate conversions
were obtained (Table 5, entry 1).
Conclusions
In this research, several iminophosphine ligands and palladium(II)
1
complexes were prepared and characterized by FT-IR, H NMR,
31P NMR, 13C NMR, and 19F NMR spectroscopy. The palladium(II)
complexes were tested as catalysts for the Heck cross-coupling
reaction of bromobenzene with styrene. Under the determined
optimal reaction conditions, all complexes were evaluated in
the Heck coupling reaction with activated and deactivated aryl
bromides and a variety of styrene derivative and several
acrylates. The results show that complexes 1, 3, and 4 were
active, giving high conversions for the coupling reactions. The
higher activities of these complexes suggest that the
iminophosphine ligands are hemilabile. Complex 2 generally
gave low catalytic activities compared to the other catalysts,
due to the formation of palladium black.
Acknowledgments
The authors are grateful to the Çukurova University Scientific Re-
search Projects (FEF2011D9) and Associate Professor Mustafa
KELEŞ for providing financial support for this research.
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