Synthesis, characterization and catalytic activity of new aminomethyldiphosphine-Pd(II) complexes for Suzuki cross-coupling reaction

Article abstract of DOI:10.1002/aoc.3085

A new range of CF₃-substituted aminomethyldiphosphine (P - C - N) ligands ((C₆H₅)₂PCH₂) ₂NR (R = - C₆H₄(2-CF₃) (1), - C ₆H₄(3-CF₃) (1b) has been synthesized from 2-(trifluoromethyl)aniline and 3-(trifluoromethyl)aniline with diphenylphosphine. The aminomethyldiphosphine ligands were reacted with Pd(cod)Cl₂ to give corresponding metal complexes, PdLCl₂ (2a, 2b). The aminomethyldiphosphine-palladium compounds were characterized by utilizing several methods including NMR (¹H, ¹³C, ³¹P) and elemental analysis. These compounds were used as catalysts in Suzuki cross-coupling reaction of aryl chlorides and bromides. The effect of base was also investigated in this current project. CF₃-substituted aminomethyldiphosphine-palladium complexes were found to be efficient catalysts in Suzuki cross-coupling reaction of activated and deactivated aryl boronic acids.

Full text of DOI:10.1002/aoc.3085

Full Paper
Received: 16 August 2013
Revised: 4 October 2013
Accepted: 5 October 2013
Published online in Wiley Online Library: 26 November 2013
(wileyonlinelibrary.com) DOI 10.1002/aoc.3085
Synthesis, characterization and catalytic activity
of new aminomethyldiphosphine–Pd(II)
complexes for Suzuki cross-coupling
reaction
Mustafa Keleş* and Mustafa Kemal Yılmaz
A new range of CF3-substituted aminomethyldiphosphine (P―C―N) ligands ((C6H5)2PCH2)2NR (R = ―C6H4(2-CF3) (1a), ―C6H4
(3-CF3) (1b) has been synthesized from 2-(trifluoromethyl)aniline and 3-(trifluoromethyl)aniline with diphenylphosphine. The
aminomethyldiphosphine ligands were reacted with Pd(cod)Cl2 to give corresponding metal complexes, PdLCl2 (2a, 2b). The
aminomethyldiphosphine–palladium compounds were characterized by utilizing several methods including NMR (1H, 13C, 31P)
and elemental analysis. These compounds were used as catalysts in Suzuki cross-coupling reaction of aryl chlorides and bro-
mides. The effect of base was also investigated in this current project. CF3-substituted aminomethyldiphosphine–palladium
complexes were found to be efficient catalysts in Suzuki cross-coupling reaction of activated and deactivated aryl boronic
acids. Copyright © 2013 John Wiley & Sons, Ltd.
Keywords: phosphine; palladium; Suzuki cross-coupling reaction; aryl halide
complexes are easily synthesized and these compounds are effi-
cient catalysts for the Suzuki cross-coupling reaction.
The palladium-catalyzed Suzuki cross-coupling reactions have
Introduction
been increasingly employed for the formation of C―C bonds be-
tween aryl boronic acids and aryl halides.[1–4] In particular, this re- Experimental
action is widely used as key intermediates in fine chemistry, for
Materials and Methods
example pharmaceuticals, herbicides and natural products. Over
the past 40 years, the chemistry of the Suzuki cross-coupling re-
action has been the subject of intense study, and considerable
effort has been devoted the synthesis of ligands and catalysts.
It has been shown in the literature that choosing a solvent, cata-
lysts and temperature conditions are quite important factors in
increasing the yield of the product in the Suzuki reaction.[5–8] Pre-
vious studies showed that C―C bond formation is not achieved
without using bases in the Suzuki cross-coupling reaction.[9] Also
the genus of bases affects the conversion and increases the rate
of C―C coupling reaction. In the Suzuki reaction it was reported
that NaOAc, K2CO3, Cs2CO3, Na2CO3 and K3PO4 are used to deter-
mine optimum conditions for the Suzuki reaction.[10]
In general, the Suzuki reaction is carried out in the presence of
palladium–phosphine catalysts since they are highly active and
selective catalysts.[11–17] A range of catalysts have been synthesized
to improve catalytic activity, selectivity and stability for the Suzuki
reaction. Although phosphine ligands and their palladium com-
plexes are widely used to catalyze the Suzuki cross-coupling reac-
tion for a variety of substrates,[18–20] there are not many studies
concerning the CF3-substituted aminomethyldiphosphines[21] and
their applications in Suzuki-type reactions.
All reactions were conducted under an inert atmosphere of N2 or
Ar using conventional Schlenk glassware. Diethyl ether, toluene
and dichloromethane were dried using established procedures
and then immediately distilled under nitrogen atmosphere prior
to use. 2-(Trifluoromethyl)aniline and 3-(trifluoromethyl)aniline,
obtained from Sigma-Aldrich Chemie GmbH (Steinheim, Germany),
were used without further purification. [Pd(cod)Cl2] was prepared
as described in the literature.[22]
Elemental analysis was performed using a LECO CHNS 932 instru-
ment. The 1H NMR (400.1MHz) and 31P{1H} NMR (162 MHz) spectra
were recorded at 25°C in DMSO-d6 and CDCl3 on a Bruker NMR
spectrometer; 13C NMR were recorded on a Varian Mercury
100.6MHz NMR spectrometer. 31P{1H} NMR spectra were recorded
with complete proton decoupling and reported in ppm using 85%
H3PO4 as external standard. The coupling products were analyzed
by a PerkinElmer Clarus 500 series gas chromatograph equipped
with a flame ionization detector and a 30 m × 0.25 mm × 0.25 μm
film thickness β-Dex capillary column. Thin-layer chromatography
was used for monitoring the reactions.
*
Correspondence to: M. Keleş, Department of Chemistry, Faculty of Arts and Sci-
ences, Osmaniye Korkut Ata University, 80000 Osmaniye, Turkey. Email:
mkeles@osmaniye.edu.tr
In this study we have prepared new ―CF3-modified
aminomethyldiphosphine (P―C―N) ligands (1a, 1b) and their
palladium(II) complexes (2a, 2b) to be used in the Suzuki cross-
coupling of aryl halides with aryl boronic acids. The results dem-
onstrated that apart from aminomethyldiphosphine palladium
Department of Chemistry, Faculty of Arts and Sciences, Osmaniye Korkut Ata
University, 80000, Osmaniye, Turkey
Appl. Organometal. Chem. 2014, 28, 91–94
Copyright © 2013 John Wiley & Sons, Ltd.

M. Keleş and M. K. Yılmaz
Preparation of Ligands and Complexes
General Procedure for Suzuki Cross-Coupling
Preparation of ((Ph2PCH2)2NC6H4―2-(CF3)) (1a)
An oven-dried Schlenk flask was charged with base (2 mmol) and
organic solvent–H2O (3/3 mL) under nitrogen atmosphere
followed by aryl halide (1 mmol), aryl boronic acid (1.5 mmol)
and Pd(II) catalyst (1 mol%). The flask was then sealed under N2
atmosphere and placed in an oil bath pre-heated at 80 °C.
The reaction mixture was stirred and then allowed to cool to
room temperature. The reaction mixture was poured into water
(5 mL) and extracted with CHCl3 (3 × 20 mL). The extracts were
washed with brine and dried over MgSO4 and solvent was
evaporated.
A mixture of Ph2PH (1.5 mL, 8.0 mmol), HCHO (0.8 mL, 14 mmol),
and 2-(trifluoromethyl)aniline (0.65 g, 4 mmol) was refluxed for
2 h in toluene (10 mL). The reaction mixture was then allowed
to cool to room temperature. The product was extracted with
CH2Cl2, dried over MgSO4 and filtered off. The filtrate was
evaporated under reduced pressure until dryness to give the title
1
compound 1a, 1.65 g (74%). H NMR (400.1 MHz, CDCl3), δ ppm:
7.82–7.75 (m, 21H, CH, arom.), 7.46–7.41 (m, 1H, CH, arom.),
7.38–7.33(m, 1H, CH, arom.), 7.15–6.92 (m, 1H, CH, arom.), 4.04
(d, J = 4.3 Hz, 4H, CH2). 13C NMR (100.6 MHz, CDCl3), δ ppm:
149.19 (C1, ArC―N), 136.40 (d, JPC = 14.4 Hz), 133.15 (d, JPC = 18.8
Hz), 132.18 (C3), 131.86 (CH), 131.36 (d, JPC = 9.3 Hz), 130.79
(C4,CH), 129.32 (CH), 128.79 (d, JPC = 6.6 Hz), 125.03 (C6, C2),
122.32 (CF3) 55.67 (d, JPC = 13.1 Hz, N―CH2―P). 31P NMR
Results and Discussion
Ligands 1a and 1b were synthesized by treating
diphenylphosphine (HPPh2) with appropriate CF3-substituted
anilines according to the Mannich reaction. The Pd(II) complexes
of the aminomethyldiphosphine ligands (2a, 2b) were prepared
under argon atmosphere using Schlenk techniques as shown
in Scheme 1.
(162 MHz, CDCl3),
C33H28F3NP2: C, 71.09; H, 5.06; N, 2.51 %. Found: C, 70.43; H,
5.62; N, 2.62%.
δ
ppm: À18.84 (PPh2). Anal. calcd for
The ligand 1b was prepared as described in procedure 1a.
Preparation of ((Ph2PCH2)2NC6H4―3-(CF3)) (1b)
Characterization of CF3-Substituted Aminomethyldiphosphine
Ligands and their Pd(II) Complexes
Yield 1.60 g (71%).1H NMR (400.1 MHz, CDCl3), δ ppm: 7.55–7.44
(m, 20H, CH, arom.), 6.85–7.28 (m, 4H, CH, arom.), 3.84 (d,
J = 4.9 Hz., 4H, CH2). 13C NMR (100.6 MHz, CDCl3), δ ppm: 144.20
(C1, ArC―N), 132.63 (d, JPC = 13.8 Hz), 131.56 (d, JPC = 12.1 Hz),
131.35 (C3), 131.12 (CH), 130.71 (d, JPC = 11.4 Hz), 129.00 (C4, CH),
128.87 (CH) 127.92 (d, JPC = 7.1 Hz), 128.46 (C6, C2), 128.28 (CF3),
60.70 (d, JPC = 12.0 Hz, N―CH2―P). 31P NMR (162 MHz, CDCl3), δ
ppm: À19.25 (PPh2). Anal. calcd for C33H28F3NP2: C, 71.09; H,
5.06; N, 2.51%. Found: C, 70.14; H, 4.92; N, 2.84%.
The structures of compounds (1a–2b) were characterized by the
1H NMR, 13C NMR, 31P NMR and elemental analysis.
It was found that although the metal complexes (2a, 2b) are
very soluble in CH2Cl2, CHCl3, CH3CH2OH and acetone, they are
insoluble in diethyl ether and n-hexane. These complexes are sta-
ble both in air and in organic solvent. The 1H NMR spectra of the
ligands (1a, 1b) and their Pd(II) complexes (2a, 2b) showed that
the protons of the phenyl ring were at 6.92–7.95 ppm. The 1H
NMR spectrum of ligands and their Pd(II) complexes 1a–2b ap-
pear at 3.84–4.43 ppm, corresponding to the methylenic (PCH2N)
protons respectively. Additionally, there is no remarkable differ-
ence between the free ligands and their Pd(II) complexes in the
1H NMR spectra. The NCH2P signals of 2a and 2b slightly
shifted downfield when compared to the free ligands 1a
and 1b. As a result of this, the N atom was not coordinated
to Pd(II) as reported in the literature.[23,24] The 31P{1H} NMR
spectra of all compounds (1a–2b) manifested that a singlet
Preparation of [PdCl2 ((Ph2PCH2)2NC6H4―2-(CF3))] (2a)
To a solution of [Pd(cod)Cl2] (0.10 g, 0.35 mmol) in CH2Cl2 (10 mL)
was added 1a (0.20 g, 0.36 mmol). The mixture was stirred for 6 h
at reflux. Then, addition of diethyl ether caused the formation of
a yellow solid, which was filtered off and dried to give the title
compound 2a. Yield 0.17 g (80%), m.p. 158–159 °C. 1H NMR
(400.1 MHz, CDCl3), δ ppm: 7.95–7.71 (m, 20H, CH, arom.),
7.57–7.45 (m, 1H, CH, arom.), 7.40–7.35 (m, 1H, CH, arom.),
7.32–7.26 (m, 1H, CH, arom.), 4.40 (d, J = 1.8 Hz, 4H,
CH2). 13C NMR (100.6 MHz, CDCl3), δ ppm: 146.43 (C1,
ArC―N), 139.36 (C9), 132.23 (C5), 132.09 (C10, C14),
131.84 (C11, C12, C13), 131.77 (C3), 130.98 (C4), 128.56
(C6) 127.90 (CF3), 55.82 (C7, C8, N―CH2―P). 31P NMR
(162 MHz, CDCl3), δ ppm: 8.03 (Pd―PPh2). Anal. calcd
for C33H28Cl2F3NP2Pd: C, 53.94; H, 3.84; N, 1.91%. Found:
C, 55.01; H, 3.92; N, 2.14%.
The complex 2b was prepared as described for proce-
dure 2a.
P
R1
NH2
R1
6
toluene
reflux
7
R2
N
5
8 P
HPPh2
+
CH2O
+
R2
9
1
2
14
13
4
10
11
3
12
R1: CF3, R2: H (1a)
R1: H, R2: CF3 (1b)
Preparation of [PdCl2((Ph2PCH2)2NC6H4―3-(CF3))] (2b)
1
Yield 0.15 g (78%), m.p. 248–250 °C. H NMR (400.1MHz,
Ph2
Cl
P
CDCl3), δ ppm: 7.52–7.09 (m, 20H, CH, arom.), 7.88–7.70
Pd
PPh2
PPh2
R1
CH2Cl2
reflux
R1
Cl
(m, 4H, CH, arom.), 4.43 (d, J = 2.1Hz, 4H, CH2). 13C NMR
PPh2
R2
N
R2
N
[Pd(cod)Cl2]
+
(100.6 MHz, CDCl3), δ ppm: 148.82 (C1, ArC―N), 137.59
(C9), 132.37 (C5), 132.02 (C10, C14), 131.69 (C11, C12,C13),
130.81 (C2), 130.72 (C4), 129.06 (C6) 126.90 (CF3), 59.21
(C7, C8, N―CH2―P). 31P NMR (162 MHz, CDCl3), δ ppm:
9.56 (Pd―PPh2). Anal. calcd for C33H28Cl2F3NP2Pd: C,
R1: CF3, R2: H (2a)
R1: H, R2: CF3 (2b)
Scheme 1. Synthesis of CF3-substituted aminomethyldiphosphine ligands and
53.94; H, 3.84; N, 1.91%. Found: C, 54.74; H, 4.08; N, 2.10%. their Pd(II) complexes.
wileyonlinelibrary.com/journal/aoc
Copyright © 2013 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 91–94

Suzuki cross-coupling reactions by Phosphine-Pd(II) catalysts.
Table 1. 31P NMR data for ligands and Pd(II) complexes
acid are summarized in Tables 2 and 3. Our group has previously
studied the reaction of phenylboronic acid with bromobenzene
in different organic solvents and bases, e.g. DMF, toluene, 1,4-
dioxane, K2CO3, NaOAc and Cs2CO3. It was found that K2CO3
and NaOAc were useful bases in these reactions at 80 °C. Cs2CO3
is also an effective base in the reactions as shown in Table 2, but
it is an expensive compared to the other bases. The results in
Tables 2 and 3 illustrate that 2a shows slightly higher activity
than 2b.
Compound
δp (ppm)
Δδ (ppm)a
1a
1b
2a
2b
À18.8
À19.2
8.0
—
—
26.9
28.8
9.5
31P chemical shifts Δδ (ppm) = δ(complex) À δ (ligand).
a
According to the data presented in Table 3, under the same
reaction conditions catalysts 2a and 2b both exhibited excellent
activity and 99% biphenyl was obtained in the event of chloro-
benzene. These results show that both CF3-substituted
aminomethyldiphosphine–Pd(II) complexes (2a, 2b) are active
catalysts for the Suzuki cross-coupling reaction.
Finally, we checked the activity of complexes 2a and 2b in the
cross-coupling reaction of different phenylboronic acids and aryl
halide (Tables 4 and 5). As can be seen from Table 4, 2a and 2b
catalysts exhibited the highest catalytic activity. As is obvious
from Table 4, the Suzuki cross-coupling reaction displayed the
Pd(II) complexes of chelating bidentate ligands as efficient
catalysts. Owing to the electron-withdrawing nature of the
trifluoromethyl group and its being far away from the phospho-
rus atom, the electron density of the phosphorus center is not
affected very much. Therefore, the Suzuki reaction that was car-
ried out with aryl chloride gave good results. During the catalytic
resonance shifted downfield when compared to the uncoordinated
aminomethyldiphosphines, as shown in Table 1. The coordination
shift values of the complexes (Δ) depending on the metal centers
and the chemical structures of the ligands showed that the ligands
coordinated to Pd(II) via phosphorus atoms to give chelated
complexes.[25]
Elemental analysis for C, H and N of ligands 1a, 1b and Pd(II)
metal complexes 2a, 2b indicated that the metal–ligand ratio of
complexes was 1:1.
Suzuki Reaction
The catalytic activity of Pd(II) complexes was tested for the Suzuki
coupling reactions. The results obtained for the Suzuki reaction of
aryl bromides and chlorides in the presence of phenylboronic
Table 2. Palladium-catalyzed coupling of bromobenzene with
Table 3. Palladium-catalyzed coupling of chlorobenzene with
phenylboronic acida
phenylboronic acida
Entry Catalyst
Base
Solvent
Time (h) Yieldb (%)
Entry Catalyst
Base
Solvent
Time (h) Yieldb (%)
1
2a
2a
2a
2a
2a
2a
2a
2a
2a
2b
2b
2b
2b
2b
2b
2b
2b
2b
K2CO3
K2CO3
K2CO3
NaOAc
NaOAc
NaOAc
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
K2CO3
K2CO3
NaOAc
NaOAc
NaOAc
Cs2CO3
Cs2CO3
Cs2CO3
1,4-Dioxane
DMF
1
2
2
1
1
3
3
2
1
1
2
6
1
1
2
1
2
5
99
93
99
99
78
46
35
98
69
98
95
99
98
97
86
77
95
99
1
2a
2a
2a
2a
2a
2a
2a
2a
2a
2b
2b
2b
2b
2b
2b
2b
2b
2b
K2CO3
K2CO3
K2CO3
NaOAc
NaOAc
NaOAc
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
K2CO3
K2CO3
NaOAc
NaOAc
NaOAc
Cs2CO3
Cs2CO3
Cs2CO3
1,4-Dioxane
DMF
17
24
14
17
24
19
17
18
24
24
18
17
7
99
91
54
82
58
94
99
29
91
99
15
93
65
61
84
95
26
97
2
2
3
Toluene
1,4-Dioxane
DMF
3
Toluene
1,4-dioxane
DMF
4
4
5
5
6
Toluene
1,4-Dioxane
DMF
6
Toluene
1,4-Dioxane
DMF
7
7
8
8
9
Toluene
1,4-Dioxane
DMF
9
Toluene
1,4-Dioxane
DMF
10
11
12
13
14
15
16
17
18
10
11
12
13
14
15
16
17
18
Toluene
1,4-Dioxane
DMF
Toluene
1,4-Dioxane
DMF
18
31
24
18
14
Toluene
1,4-Dioxane
DMF
Toluene
1,4-Dioxane
DMF
Toluene
Toluene
aReaction conditions: aryl halide (1 mmol), phenylboronic acid
(1.2 mmol) base (1.2 mmol) and 0.01 mmol catalyst in 3/3 ml
organic solvent/H2O, 80 °C.
bAll reactions were monitored by gas chromatography and
aReaction conditions: aryl halide (1 mmol), phenylboronic acid
(1.2 mmol), base (1.2 mmol) and 0.01 mmol catalyst in 3/3 ml
organic solvent/H2O, 80 °C.
bAll reactions were monitored by gas chromatography and
yields are based on aryl halide.
yields are based on aryl halide.
Appl. Organometal. Chem. 2014, 28, 91–94
Copyright © 2013 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

M. Keleş and M. K. Yılmaz
Table 4. Palladium-catalyzed coupling of aryl halide with 2-substituted
Conclusions
phenylboronic acidsa
Pd(II) complexes with new CF3-substituted aminomethyldiphosphine
(P―C―N) ligands have been synthesized and characterized using
spectroscopic techniques. 31P{1H} NMR spectra of the complexes in-
dicate that coordination of the aminomethylphosphine ligand oc-
curs via two phosphorus atoms. The complexes have been tested
as catalysts for the Suzuki reaction. The results show that com-
plexes 2a and 2b catalyzed the reaction of olefin with aryl halide
in excellent yields.
In the next step, we have scheduled to synthesize ―C8F17-
included aminomethyldiphosphine ligands instead of ―CF3 and
their Pd(II) complexes. Additionally these complexes may be
examined in the C―C coupling reactions in supercritical CO2
solvent systems as a catalyst.
Entry
Catalyst
X
R
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
2a
2a
2a
2a
2b
2b
2b
2b
Cl
―CH3
C6H5
7
7
98
99
99
35
96
52
98
78
Cl
Br
Br
Cl
Cl
Br
Br
―CH3
C6H5
2
3
―CH3
C6H5
8
Acknowledgments
16
3
―CH3
C6H5
We thank Osmaniye Korkut Ata University for financial support.
We would also like to thank Mehmet Mart and Dr İbrahim Fazıl
Şengül for technical support.
3
aReaction conditions: aryl halide (1 mmol), phenylboronic acid
(1.2 mmol) base (1.2 mmol) and 0.01 mmol catalyst in 3/3 ml
DMF/H2O, 80 °C.
bAll reactions were monitored by gas chromatography and
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2
aReaction conditions: aryl halide (1 mmol), phenylboronic acid
(1.2 mmol) base (1.2 mmol) and 0.01 mmol catalyst in 3/3 ml
DMF/H2O, 80 °C.
bAll reactions were monitored by gas chromatography and
yields are based on aryl halide.
cycle, activation of the Pd(II) precursor by phenyl boronic acid is
also very rapid, even with very electron-rich ligands.
wileyonlinelibrary.com/journal/aoc
Copyright © 2013 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 91–94