Bis(imino)pyridine palladium(II) complexes as efficient catalysts for the Suzuki-Miyaura reaction in water

Article abstract of DOI:10.1002/aoc.1591

Bis(imino)pyridine palladium(II) complexes 3 and 4 of type [PdCl(L)PF ₆] are found to be efficient catalysts for Suzuki-Miyaura reactions of aryl halides and arylboronic acids. The reactions proceed smoothly to generate the corresponding biaryl compounds in moderate to excellent yields. The synthesis of various fluorinated biphenyl derivatives was successfully achieved by the complex 4 catalyzed the Suzuki-Miyaura reaction in the presence of surfactants bearing a long alkyl chain. Copyright

Full text of DOI:10.1002/aoc.1591

Full Paper
Received: 10 August 2009
Revised: 22 October 2009
Accepted: 22 October 2009
Published online in Wiley Interscience: 17 December 2009
(
www.interscience.com) DOI 10.1002/aoc.1591
Bis(imino)pyridine palladium(II) complexes as
efficient catalysts for the Suzuki–Miyaura
reaction in water
∗
Ping Liu , Mei Yan and Ren He
Bis(imino)pyridine palladium(II) complexes 3 and 4 of type [PdCl(L)PF6] are found to be efficient catalysts for Suzuki–Miyaura
reactionsofarylhalidesandarylboronicacids.Thereactionsproceedsmoothlytogeneratethecorrespondingbiarylcompounds
in moderate to excellent yields. The synthesis of various fluorinated biphenyl derivatives was successfully achieved by the
Jc oo hm np Wl e ixl e4 yc &a tSa ol yn zs e, dL t tdh .e Suzuki–Miyaura reaction in the presence of surfactants bearing a long alkyl chain. Copyright ꢀc 2009
Supporting information may be found in the online version of this article.
Keywords: bis(imino)pyridine; palladium(II); Suzuki–Miyaura reaction; water; liquid crystalline compounds
Introduction
Bruker DPX-400 spectrometer using TMS as internal standard and
CDCl3 as solvent. EI–mass spectra were measured on a LC/Q-TOF
MS (Micromass, UK). Dichloromethane was dried over CaH2,
distilled and stored under nitrogen. All other reagents were were
of analytical grade and used as received unless noted otherwise.
The synthesis of biaryl units in many kinds of compounds,[1,2]
including pharmaceuticals, herbicides and natural products, as
well as in the field of engineering materials, such as conducting
polymers, molecular wires and liquid crystals, has attracted
enormous interest from the chemistry community. The palladium-
catalyzed Suzuki–Miyaura reaction is the most important and
Synthesis of Complexes 3 and 4
efficient strategy for the construction of unsymmetrical biaryl
0.20 mmol of PdCl (CH CN) and 0.30 mmol of NH PF6 were
dissolved in 10 ml of CH Cl . The solution was stirred at room
2 2
2
3
2
4
compounds.[
3–6]
Phosphine-based ligands remain by far the most
[
7–13]
popular selection in this reaction.
However, most of the
temperature for 12 h followed by the addition of 0.20 mmol of
ligand. After 24 h, the reaction mixture was filtered, and ether
(100 ml) was added into the filtrate and a yellow solid was formed.
The yellow precipitate was filtered, washed with ether (2 × 10 ml)
and dried in vacuo to afford 3 or 4 as a yellow powder.
phosphine ligands are air- and moisture-sensitive, and P–C bond
degradation sometimes occurs at elevated temperatures, which
leads to palladium aggregation and eventually affects the overall
[
14]
catalytic performance.
Therefore, recently the application
of nitrogen-based ligands in the Pd-catalyzed Suzuki–Miyaura
reaction has opened up new opportunities, such as Schiff
3: Yield 74%. Anal. calcd for C H ClF N O PPd: C, 41.84; H,
3.51; N, 6.36; found: C, 41.37; H, 3.68; N, 6.35. H NMR (400 MHz,
2
3
23
6
3
2
1
bases,[
15–21]
aryloximes,
[22,23]
arylimines,
[24–28]
N-acylamidines,
[29]
CDCl ): δ 8.46 (t, J = 8.4 Hz, 1H, Py–Hp), 8.11 (d, J = 8.4 Hz, 2H,
3
guanidine,[ bis(oxazolinyl)pyrrole[31] and simple amines.
30]
[32–37]
Py–Hm), 7.07 (d, J = 9.2 Hz, 4H, Ar–H), 6.88 (d, J = 9.2 Hz, 4H,
1
3
Bis(imino)pyridine as tridentate ligands have received consider-
able attention over the past decade, mainly due to the discovery
of the high catalytic activity of their Fe and Co complexes in
CMe). C NMR (100 MHz,
Ar–H), 3.78 (s, 6H, OMe), 2.43 (s, 6H, N
ꢁ
ꢁ
d -DMSO): δ 19.06 (C5 and C5 ), 55.35 (C10 and C10 ), 113.66 (C8
6
ꢁ
ꢁ
ꢁ
and C8 ), 124.47 (C7 and C7 ), 129.25 (C2 and C2 ), 137.79 (C1),
[
38–41]
ꢁ
ꢁ
ꢁ
olefin polymerization.
To the best of our knowledge, few
142.77 (C6 and C6 ), 155.22 (C3 and C3 ), 158.60 (C9 and C9 ),
ꢁ
−1
investigations have been carried out on the synthesis and catalytic
activity of bis(imino)pyridine palladium(II) complexes.[42] In our
previous work, bis(imino)pyridine palladium (II) complexes of
types [PdCl(L)]2PdCl4 and [PdCl(L)]PdCl3 have been used suc-
cessfully to catalyze the Suzuki–Miyaura reaction in water.[
In this paper, we report the synthesis of new bis(imino)pyridine
palladium(II) complexes [PdCl(L)PF6], and their structure and
catalytic activity for the Suzuki–Miyaura reaction in water.
183.40 (C4 and C4 ). IR (KBr, cm ): 1635 (C N). HRMS (EI), m/z:
[M−PF ] , calculated for: 514.0514; found, 513.8875. m/z: [PF
+
−
]
6
6
calculated for: 144.9642; found, 145.0418.
4: Yield 75%. Anal. calcd for C H ClF N PPd· 0.25CH Cl :
2
5
27
6
3
2
2
43,44]
C, 44.76; H, 4.09; N, 6.20; found: C, 45.40; H, 4.22; N, 6.37. 1
H
NMR (400 MHz, CDC13
): δ 8.71 (t, J = 8.0 Hz, 1H, Py–Hp), 8.50
(d, J = 8.0 Hz, 2H, Py–Ho), 7.17–7.12 (m, 6H, Ar–H), 2.39 (s, 6H,
1
3
N
CMe), 2.60 (s, 12H, CMe). C NMR (100 MHz, d -DMSO): δ
6
Experimental
∗
Correspondence to: Ping Liu, State Laboratory of Fine Chemicals, Dalian
University of Technology, Dalian 116012, China.
E-mail: liuping1979112@yahoo.com.cn
Materials and Methods
Infrared spectra were obtained as KBr pellets on a Perkin–Elmer
FT–IR 430 spectrometer. H NMR spectral data were recorded on a
StateKeyLaboratoryofFineChemicals,DalianUniversityofTechnology,Dalian
116012, China
1
Appl. Organometal. Chem. 2010, 24, 131–134
Copyright ꢀc 2009 John Wiley & Sons, Ltd.

P. Liu, M. Yan and R. He
Scheme 1. Synthesis of bis(imino)pyridine palladium(II) complexes 3 and
4
.
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
1
1
1
7.62 (C5 and C5 ), 17.94 (C10 and C10 ), 127.75 (C2 and C2 ),
ꢁ
28.07 (C9 and C9 ), 129.26 (C7 and C7 ), 130.26 (C8 and C8 ),
42.56 (C1), 142.71 (C6 and C6 ), 154.33 (C3 and C3 ), 185.10 (C4
ꢁ
ꢁ
Figure 1. Structure of complex 4 at 30% probability level. Hydrogen atoms
are omitted for clarity.
ꢁ
−1
+
and C4 ). IR (KBr, cm ): 1632 (C N). HRMS (EI), m/z: [M − PF6]
−
calculated for: 510.0928; found: 509.9795; m/z: [PF6 ] calculated
for: 144.9642; found: 144.7618.
Table 1. Selected bond lengths (Å) and angles (deg) for complex 4
General Procedure for the Suzuki–Miyaura Reaction
Bond lengths
Bond angles
Amixtureofarylbromide(0.5 mmol),arylboronicacid(0.75 mmol),
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–N(3)
Pd(1)–Cl(1)
P(1)–F(11)
1.923(5)
2.034(5)
2.039(5)
2.267(2)
1.544(7)
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–N(3)
N(3)–Pd(1)–Cl(1)
N(2)–Pd(1)–Cl(1)
F(13)–P(1)–F(14)
80.0(2)
79.7(2)
K3PO4·3H2O (1.20 mmol) and complex 4 (0.50 mol%) in 2 ml of
◦
water was heated to 80 C and stirred under an air atmosphere
98.60(17)
101.63(16)
90.7(3)
for 1–3 h. When the reaction was completed, the mixture was
cooled to room temperature and extracted with ether (5 × 2 ml).
The combined extracts were dried over sodium sulfate, and
concentrated under vacuum. The residue was purified using a
silica gel column (petroleum as eluent) to give products.
◦
acid was investigated with K3PO4·3H2O as base at 80 C. Initially,
the model reaction proceeded smoothly in toluene to afford the
corresponding product 7a in 90% yield (Table 2, entry 1). Further
investigation revealed that the result could be improved when
water was used as solvent in the reaction (93 and 94%, Table 2,
entries 2 and 3). With complex 4 as the catalyst, a number of aryl
bromides and arylboronic acid were examined and the results are
summarized in Table 2. The electron-poor 4-bromoacetophenone
reacted with different arylboronic acids to give excellent yields
X-ray Crystallography
Single crystal of complex 4 was obtained by slow diffusion of
hexane into saturated dichloromethane solution. Suitable crystal
for X-ray diffraction was mounted on a glass fiber. Data collection
was performed on a Bruker Smart Apex CCD diffractometer us-
ing graphite monochromated Mo Kα radiation (λ = 0.71073 Å) at
2
73 K.ThediffractionframeswereintegratedusingtheSAINTpack-
◦
after 3 h of reaction at 80 C (96–98%, entries 4, 11, 15). The
age.Thestructurewassolvedbydirectmethodsusingtheprogram
SHELXS97. Structurerefinementbythefull-matrixleast-squareson
electron-rich 4-bromoanisole reacted with phenylboronic to also
give good yield after 5 h of reaction (85%, entry 5). Aryl bromides
containing an ortho-substituent also reacted effectively to furnish
the desired biaryl products in good yields (80%, entry 6). It is
noteworthy that the coupling reactions of water-soluble aryl
bromides, such as 4-bromophenol and 4-bromobenzoic acid,
with arylboronic acids were completed rapidly in excellent yields
for only 1 h (98 and 99%, respectively, entries 8 and 9). The cross-
coupling reactions of various aryl chlorides and arylboronic acids
have also been investigated in DMA (N,N-dimethylacetamide)
2
F was carried out with the program SHELXL97. All non-hydrogen
atoms of the complex were assigned anisotropic displacement
parameters. The hydrogen atoms were constrained to idealized
geometriesandassignedisotropicdisplacementparametersequal
to 1.2 times the Uiso values of their respective parent atoms.
Result and Discussion
◦
First, bis(imino)pyridine ligands 1 and 2 were synthesized ac-
at 100 C. The coupling reactions of aryl chlorides bearing an
[
45]
cording to literature methods. Bis(imino)pyridine palladium(II)
complexes 3 and 4 of type [PdCl(L)PF6] were prepared by reaction
of the mixture of PdCl2(CH3CN)2 and 1.5 equiv. of NH4 PF6 with
electron-withdrawing group, such as 4-CN, 4-COCH3 and 4-NO2,
with arylboronic acids gave biaryls in good yields ranging from 85
to 96% after 3 h of reaction (entries 16–18 and 20). However, the
electron-rich3-chloroanisolereactedwith4-methylphenylboronic
to give only 25% yield (entry 21), whereas 4-chloroanisole gave
no reaction under the same conditions (entry 19).
From the above results, we can conclude that the water-
solubility of aryl bromides has an obvious effect on the
Suzuki–Miyaura reaction in water. Therefore, when this catalytic
system was used to synthesize fluorinated biphenyl liquid
crystal compounds by the reaction of aryl bromide 6h with
4-fluorophenylboronic acid 5b, the coupling product 7n was not
obtained, probably because of the low solubility of aryl bromide
6h with a long alkyl chain in water (Table 3, entry 1). So it is
1
.0 equiv. of bis(imino)pyridine ligands in CH2Cl2 for 24 h at room
+
temperature (Scheme 1). Their structures contained one [PdLCl]
−
1
and one PF6 were initially confirmed by H NMR spectroscopy,
elemental analysis and HRMS(EI). The crystallographic analysis of
complex 4 revealed the expected Pd(II) distorted square planar
geometry with ligand 2. The proposed coordination pattern is dif-
ferent from the bis(imino)pyridine palladium complexes that have
been reported.[
46–49]
The crystal structure plot is shown in Fig. 1.
TheimportantbondlengthsandanglesaresummarizedinTable 1.
Next, the catalytic activity of complexes 3 and 4 in the
Suzuki–Miyaura reaction of 4-bromoanisole with phenylboronic
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Copyright ꢀc 2009 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2010, 24, 131–134

Bis(imino)pyridine palladium(II) complexes as efficient catalysts
Table 2. Suzuki–Miyaura reaction catalyzed by complex 4a,b
Entry
R1
R2, X
Product
Time (h)
Yield (%)c
1d
2e
3
H (5a)
4-OMe, Br (6a)
4-OMe, Br (6a)
4-OMe, Br (6a)
4-COMe, Br (6b)
4-Me, Br (6c)
7a
7a
7a
7b
7c
7d
7e
3f
3
3
3
3
5
5
5
1
1
3
3
1
1
3
3
3
3
3
3
3
3
90
93
94
96
85
80
90
99
98
91
96
97
98
94
98
96
93
88
0
H (5a)
H (5a)
4
H (5a)
5
H (5a)
6
H (5a)
2-Me, Br (6d)
4-F, Br (6e)
7
H (5a)
8
H (5a)
4-COOH, Br (6f)
4-OH, Br (6g)
4-OMe, Br (6a)
4-COMe, Br (6b)
4-COOH, Br (6f)
4-OH, Br (6g)
4-OMe, Br (6a)
4-COMe, Br (6b)
4-NO2, Cl (6h)
4-CN, Cl (6i)
9
H (5a)
7g
7h
7i
10
11
12
13
14
15
16
17
18
19
20
21
4-F (5b)
4-F (5b)
4-F (5b)
4-F (5b)
4-Me (5c)
4-Me (5c)
H (5a)
7g
7k
7l
7m
7n
7o
7i
H (5a)
H (5a)
4-COMe, Cl (6j)
4-OMe, Cl (6k)
4-COMe, Cl (6j)
3-OMe, Cl (6l)
H (5a)
7a
7i
4-Me (5c)
4-Me (5c)
85
25
7j
a
b
c
◦
Reaction conditions: aryl bromide 0.50 mmol, arylboronic acid 0.75 mmol, K3PO4·3H2O 1.20 mmol, 4 (0.50 mol%), H2O 2.0 ml, 80 C.
◦
Reaction conditions: aryl chloride 0.25 mmol, arylboronic acid 0.40 mmol, K3PO4·3H2O 0.50 mmol, 4 (0.25 mol%), DMA 2.0 ml, 100 C.
Isolated yields.
Toluene as solvent, complex 4 (0.50 mol%) as precatalyst.
Complex 3 (0.50 mol%) as precatalyst.
d
e
Table 3. Effect of surfactant on the Suzuki-Miyaura reactiona
Entry
Surfactant (mol%)
Yield (%)b
1
2
3
4
5
6
7
8
9
–
TBAB (25)
0
0
TBAI (25)
0
CTAB (25)
95
94
93
92
90
91
CTAB (5.0)
CTAB (2.5)
SDBS (2.5)
Sodium dodecane-1-sulfonate (2.5)
1-Hexadecylpyridinium chloride (2.5)
a
◦
Reaction conditions: aryl bromide 0.50 mmol, arylboronic acid 0.75 mmol, K3PO4.7H2O 1.20 mmol, 4 (0.5 mol%), H2O 2.0 ml, 80 C, 3 h.
Isolated yields.
b
necessary to add a suitable surfactant in this system. Next,
as TBAB and TBAI (entries 1 and 2). By contrast, when we
performed the reaction using different concentrations of CTAB
(hexadecyltrimethylammonium bromide) as the surfactant, good
yields were obtained (93–95%, entries 4–6). Other surfactants
we explored the effect of a variety of surfactants on the
coupling reaction (Table 3). The experiment result shows that
the surfactants with short alkyl chains are ineffective, such
Appl. Organometal. Chem. 2010, 24, 131–134
Copyright ꢀc 2009 John Wiley & Sons, Ltd.
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P. Liu, M. Yan and R. He
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ꢁ
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In conclusion, we have synthesized air- and moisture-stable
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gated their catalytic activity for the Suzuki–Miyaura reaction in
water. The synthesis of various fluorinated biphenyl derivatives
was successfully achieved using complex 4 in the presence of
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We gratefully acknowledge financial support of this work by the
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