A Highly Active Catalyst System for Suzuki-Miyaura Coupling of Aryl Chlorides

Article abstract of DOI:10.1021/acs.organomet.8b00883

A series of new Pd(II) complexes with simple structures were designed and synthesized for Suzuki-Miyaura coupling reactions of aryl chlorides. The new Pd(II) complexes contain bidentate amine ligands, and their structures were characterized by single-crystal X-ray diffraction. They are highly efficient for Suzuki-Miyaura coupling reactions of aryl chlorides with low catalyst loadings (0.01 mol %) in aqueous media at room temperature. Two possible reaction pathways involving a Pd^II/0/II and a Pd^II/IV/II catalytic cycle are proposed, and the mechanism was further investigated using density functional theory (DFT) calculations.

Full text of DOI:10.1021/acs.organomet.8b00883

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
A Highly Active Catalyst System for Suzuki−Miyaura Coupling of
Aryl Chlorides
Guiyan Liu,*,† Fangwai Han,† Chengxin Liu,† Hongli Wu,‡ Yongfei Zeng,† Rongjiao Zhu,‡ Xia Yu,†
Shuang Rao,† Genping Huang,*,‡ and Jianhui Wang*,‡
†Tianjin Key Laboratory of Structure and Performance for Functional, Molecules, Key Laboratory of Inorganic−Organic Hybrid
Functional, Material Chemistry (Ministry of Education), College of Chemistry, Tianjin Normal University, Tianjin, 300387, P. R.
China
‡Department of Chemistry, College of Science, Tianjin University, Tianjin, 300350, P. R. China
S
* Supporting Information
ABSTRACT: A series of new Pd(II) complexes with simple
structures were designed and synthesized for Suzuki−Miyaura
coupling reactions of aryl chlorides. The new Pd(II)
complexes contain bidentate amine ligands, and their
structures were characterized by single-crystal X-ray diffrac-
tion. They are highly efficient for Suzuki−Miyaura coupling
reactions of aryl chlorides with low catalyst loadings (0.01 mol
%) in aqueous media at room temperature. Two possible
reaction pathways involving a PdII/0/II and a PdII/IV/II catalytic
cycle are proposed, and the mechanism was further
investigated using density functional theory (DFT) calcu-
lations.
However, the use of its reductive product, N,N′-bis(2,4,6-
trimethylphenyl)ethane-1,2-diamine (BEDA), as a ligand to
construct metal complexes has rarely been reported.11 Herein,
the synthesis of simple Pd(II) complexes bearing a BEDA
ligand and their use for the Suzuki−Miyaura coupling reactions
of aryl chlorides is reported.
INTRODUCTION
■
The biphenyl motif is an important structural unit which
commonly exists in natural products and fine chemicals, such
as pharmaceuticals and herbicides.1 The Suzuki−Miyaura
cross-coupling (SMC) reaction is one of the most versatile
and powerful tools for producing substituted diphenyls.2
Typically, aryl bromides or iodides are applied to this reaction
under basic conditions in the presence of a metal catalyst.3
However, recently, the use of “unreactive” aryl chlorides as
coupling partners has attracted attention due to their low cost,
ready commercial availability, and diversity. Many efforts have
been made to develop highly efficient catalytic systems for the
smooth and efficient conversion of aryl chlorides, such as
Buchwald-type palladacycles,4 Organ-type PEPPSI-based pre-
catalysts,5 Nolan-type allyl-based precatalysts,6 and others7
(Figure 1).
However, the SMC reaction of aryl chlorides still presents
some challenges such as the need for elevated reaction
temperatures or high catalyst loadings. In recent years, our
group8 and others9 have reported some highly efficient catalyst
systems for SMC reactions of aryl chlorides, which function at
room temperature with low catalyst loadings (≤1 mol %) in
aqueous media. However, the preparation of auxiliary ligands
for these catalysts requires tedious synthetic steps and the
structures of these catalysts are quite complex. Thus, the
development of efficient catalytic systems with simple
structures is still an ongoing pursuit in this field.
RESULTS AND DISCUSSION
■
The synthetic route for the Pd(II) precatalysts is shown in
Scheme 1. First, N,N′-bis(2,4,6-trimethylphenyl)ethane-1,2-
diamine which is a bidentate ligand was reacted in THF at
reflux. The palladium(II) complex 1 was synthesized by
reacting BEDA with PdCl2. The complexes 2 and 3 were
obtained by halogen exchange.
Crystals of the palladium(II) complexes 1, 2, and 3 were
grown by slow evaporation of a mixed CH2Cl2/petroleum
ether solvent at −5 °C. The molecular structures of 1, 2, and 3
were determined by single X-ray crystallography and are
shown, respectively, in Figures 2, 3, and 4. The result showed
that these three complexes all have similar structures. The Pd
atom is coordinated with the N atoms to form a distorted five-
membered heterocyclic ring. Selected bond lengths and angles
are also given, respectively, in Figures 2, 3, and 4.
Initially, chlorobenzene (4A) and phenylboronic acid 5a
were chosen as model substrates to optimize the reaction
conditions for the palladium precatalysts (Table 1). The best
N,N′-Bis(2,4,6-trimethylphenyl)ethane-1,2-diimine, a biden-
Received: December 7, 2018
tate ligand, is often used to synthesize metal complexes.10
© XXXX American Chemical Society
A
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Figure 1. Previously reported typical examples of palladium(II) precatalysts and this work for Suzuki−Miyaura coupling reactions of aryl chlorides.
Scheme 1. Synthesis of Palladium(II) Precatalysts 1, 2, and
3
Figure 4. Molecular structure of 3 depicted in 50% thermal ellipsoids.
For clarity, the hydrogen atoms except N−H were omitted. Selected
bond distances (Å) and angles (deg): Pd1−N1, 2.114(6); Pd1−N2,
2.108(6); Pd1−I1, 2.5549(8); Pd1−I2, 2.5624(9); N1−Pd1−N2,
81.7(2); N2−Pd1−I1, 93.57(17); N2−Pd1−I2, 95.09(16); I1−Pd1−
I2, 89.64(3).
Table 1. Optimization of the Palladium Catalytic System for
a
the Suzuki−Miyaura Coupling Reaction of Chlorobenzene
Figure 2. Molecular structure of 1 depicted in 50% thermal ellipsoids.
For clarity, the hydrogen atoms except N−H were omitted. Selected
bond distances (Å) and angles (deg): Pd1−N1, 2.074(4); Pd1−N2,
f
2.067(4); Pd1−Cl1, 2.3015(13); Pd1−Cl2, 2.2997(13); N1−Pd1−
entry
base
solvent
yield (%)
N2, 83.80(17); N1−Pd1−Cl1, 91.11(13); N2−Pd1−Cl2, 92.48(12);
Cl1−Pd1−Cl2, 93.09(5).
1
2
3
4
5
6
7
8
9
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K2CO3
Na2CO3
KOH
CsCO3
K3PO4
K3PO4
K3PO4
K3PO4
H2O
75
45
55
65
95
60
80
85
90
95
95
45
80
MeOH
i-PrOH
MeOH/H2O (1:1)
i-PrOH/H2O (1:1)
i-PrOH/H2O (1:1)
i-PrOH/H2O (1:1)
i-PrOH/H2O (1:1)
i-PrOH/H2O (1:1)
i-PrOH/H2O (1:1)
i-PrOH/H2O (1:1)
i-PrOH/H2O (1:1)
i-PrOH/H2O (1:1)
b
10
11
12
c
d
Figure 3. Molecular structure of 2 depicted in 50% thermal ellipsoids.
For clarity, the hydrogen atoms except N−H were omitted. Selected
bond distances (Å) and angles (deg): Pd1−N1, 2.090(10); Pd1−N2,
2.098(10); Pd1−Br1, 2.3710(19); Pd1−Br2, 2.344(9); N1−Pd1−N2,
81.8(4); N1−Pd1−Br1, 94.5(3); N2−Pd1−Br2, 102.1(6); Br1−
Pd1−Br2, 80.1(6).
e
13
a
Reaction conditions: 4A (0.25 mmol), 5a (1.2 equiv), precatalyst 2
(0.01 mol %), base (2 equiv) in 0.8 mL of solvent, 25 °C, 3 h, in air.
Precatalyst 1 (0.01 mol %), 4.5 h. Precatalyst 3 (0.01 mol %), 6.5 h.
Pd-PEPPSI-IMes (0.01 mol %), 3 h. PdCl2 (2 mol %), 3 h. Isolated
yield.
b
c
d
e
f
catalytic system was found to be 0.01 mol % of catalyst with
K3PO4 in a mixed solvent of i-PrOH/water (1:1) at room
B
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Table 2. Catalytic Activities of Complexes 1 and 2 in Suzuki−Miyaura Coupling Reactions of Aryl Chlorides under the
a b
,
Optimized Conditions
a
Reactions condition: aryl chlorides (0.25 mmol, 1 equiv), arylboronic acid (1.2 equiv), precatalyst 1 and 2 (0.01 mol %), K3PO4 (0.5 mmol, 2
b
equiv) in i-PrOH/H2O (0.4 mL/0.4 mL) at room temperature. Isolated yields.
Figure 5. XPS spectra of the Pd 3d level and deconvolution peaks of the Pd species: experimental (black), deconvoluted (red), Pd(II) (green and
blue), Pd(0) (orange), and Pd(IV) (purple): (a) for precatalyst 1; (b) for precatalyst 1 after treatment with K3PO4 (2 equiv) in i-PrOH/H2O at
room temperature for 1 h; (c) for the above reaction system after adding chlorobenzene.
C
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Scheme 2. Proposed Mechanisms of Suzuki−Miyaura Coupling Reactions
temperature in air. With catalyst 2, the desired cross-coupling
product 6Aa was obtained in 3 h in 95% yield under these
conditions. When other solvents, such as H2O, MeOH, i-
PrOH, or MeOH/water (1:1), were used to replace i-PrOH/
water (1:1), the cross-coupling products were obtained in
yields of 45−75%. Replacing K3PO4 with other commonly
used bases, such as K2CO3, Na2CO3, KOH, and Cs2CO3, also
resulted in lower yields (60−90%). The chloride complex 1,
the iodide complex 3, Pd-PEPPSI-IMes, and PdCl2 were also
used as catalysts for similar transformations. Both 1 and 3
required longer reaction times than 2 (4.5 and 6.5 h versus 3 h,
respectively) to reach 95% yields. Compared with 2, Pd-
PEPPSI-IMes also has lower catalytic activity, and only a 45%
yield was achieved in 3 h. For PdCl2, increasing the loading of
catalyst to 2 mol %, 80% yield was achieved in 3 h.
With the optimized conditions in hand, we next turned our
attention toward the reaction scope (Table 2). Several aryl
halides and boronic acids were investigated using palladium
precatalysts 1 and 2. Using phenylboronic acid 5a as the
coupling partner, phenyl, 3-fluorophenyl, and 3-methylphenyl
chlorides were easily coupled and 6Aa−6Ca were prepared in
high yields (>95%) using the optimized conditions. The 3,5-
dimethylphenyl and 4-fluorophenyl chlorides took 7.5−10 and
12−15 h to provide 6Da and 6Ea in 95 and 96% yields,
respectively. For hindered aryl chlorides bearing −Me or −F
groups in the ortho positions, high yields (6Fa−6Ha, 94−
96%) were also achieved by prolonging the reaction time. For
4-methyl-3-fluorophenyl chloride and 3-methoxychloroben-
zene, only an 80% yield (6Ia) and a 70−75% yield (6Ja)
was obtained, respectively, when the reaction time was
prolonged to 36 h. However, for 2-chloropyridine and 2,6-
dimethylchlorobenzene, no products (6Ka and 6La) could be
obtained even prolonging the reaction time to 36 h.
products (6Am and 6An) could be obtained even prolonging
the reaction time to 36 h.
In order to understand the reaction process more clearly,
then, we studied the reaction mechanism. Surface composi-
tions of palladium species have been investigated by X-ray
photoelectron spectroscopy (XPS), which is one of the most
effective tools to identify the Pd species on heterogeneous
surfaces.12−14 The survey scan XPS spectrum of the precatalyst
1 (Figure 5a) showed the Pd 3d core-level lines were fitted
with two main peaks, where the Pd 3d5/2 peak at 338.2 eV was
assignable to the Pd(II) species.15 After the treatment with
K3PO4 in i-PrOH/H2O at room temperature for 1 h, the major
Pd 3d5/2 peak shifted to the binding energy at 338.0 eV, which
could be assigned to other Pd(II) species. However, another
Pd 3d5/2 peak was assigned to metallic palladium Pd(0).16 This
indicated that the new Pd species may have two different
transition states. By adding chlorobenzene into the above
Pd(II) species system, the partial Pd(II) 3d5/2 peak shifted to
the higher binding energy at 343.2 eV which indicated that the
Pd(IV) species were generated.17 Meanwhile, the Pd(0) peaks
disappeared.
On the basis of the above experimental results, two possible
mechanisms for the catalytic process of these palladium
complexes are proposed in Scheme 2. Reaction pathway I
involving a well-known accepted PdII/0/II catalytic cycle:18
First, an active Pd0 species A was generated which is analogous
to what was previously reported.19 The second step involves
the generation of intermediate species B in the presence of the
aryl halide. By adding arylboronic acid, intermediate C was
formed. Lastly, the coupling product was formed through a
reductive elimination reaction. Reaction pathway II involving a
new PdII/IV/II catalytic cycle: First, the precatalyst Pd(II)
complex was converted to the PdII species A′ by elimination of
HCl under basic conditions. This is considered to be the actual
active species. The PdII species A′ is stabilized through the
formation of N−Pd σ bonds. An oxidative addition of an aryl
halide to A′ generates the PdIV intermediate B′. A trans-
metalation of B′ in the presence of the arylboronic acid then
results in the formation of intermediate C′. Finally, a reductive
elimination of intermediate C′ gives the coupling product and
the catalytically active PdII species A′, which then undergoes
another catalytic cycle.
Next, a variety of arylboronic acids were explored (Table 2).
Reactions of chlorobenzene with 4-fluorophenyl, 4-chloro-
phenyl, and 4-methylphenyl boronic acid gave the coupling
products 6Ab, 6Ac, and 6Ad, respectively, in yields of 95−97%
within 5.5 h. Sterically hindered 2-methylphenyl and 2,5-
dimethylphenyl boronic acids also provided high yields (6Ae,
97%; 6Af, 96%) after 12−15 h. Other arylboronic acids with
various substituents, such as 3-fluorophenyl, 2-biphenyl, 4-
methoxyphenyl, 2-chlorophenyl, 2-fluorophenyl, and 2-methyl-
4-fluorophenyl, were also tolerated, providing 6Ag−6Al in high
yields of 90−98% after 15−32 h. However, for arylboronic
acids with a 4-aldehyde group or a 4-hydroxyl group, only trace
To validate the proposed mechanism, density functional
theory (DFT) calculations were performed at the B3LYP-
D3(BJ)/6-311+G(d,p)(SDD)//B3LYP/6-31G(d)(LAN-
L2DZ) level (see the Supporting Information for computa-
D
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Figure 6. Calculated energy profiles of the proposed reaction mechanisms. Energies are given in kcal/mol.
tional details). The calculated energy profiles in Figure 6 show
that the Pd0/PdII pathway begins with the formation of
intermediate INT1 through the coordination of chlorobenzene
to the Pd0 catalyst. A subsequent C−Cl oxidative addition
through transition state TS1 to form PdII species INT2 was
highly exergonic (relative to INT1) by 35.3 kcal/mol. The
coordination of K[PhB(OH)3]20 to the Pd center gives
intermediate INT3, from which intermediate INT4 can be
generated via the dissociation of KCl. The ensuing trans-
metalation occurs via transition state TS2, leading to the
formation of PdII complex INT5 and B(OH)3. Finally, the C−
C reductive elimination via transition state TS3 yields the
product-coordinated intermediate INT6. The PdII/PdIV path-
way was found to follow the same elementary steps as
compared with the Pd0/PdII pathway. The results show that,
for both possible pathways, the transmetalation is the rate-
determining step of the overall catalytic cycle. The energy
barriers of the Pd0/PdII pathway and the PdII/PdIV pathway
were calculated to be rather similar, being 19.8 and 18.8 kcal/
mol (relative to INT3 and INT3′), respectively. The
computations thus indicate that the proposed Pd0/PdII
pathway and PdII/PdIV pathway are both feasible under the
relatively mild reaction conditions employed.
complexes have a regular quadrilateral structure with only
slight distortions. The palladium complexes have excellent
stability which is due to the coordination of the Pd(II) to two
N atoms and two halogen atoms. The chloride complex 1 and
bromide complex 2 have high catalytic activities for SMC
reactions of inexpensive aryl chlorides and arylboronic acids
with low catalyst loadings (0.01 mol %) at room temperature.
Two possible reaction pathways involving a PdII/0/II catalytic
cycle and a PdII/IV/II catalytic cycle were proposed and verified
by XPS analysis and DFT calculations.
EXPERIMENTAL SECTION
■
General Procedures and Materials. Unless otherwise noted, all
reactions were performed under an atmosphere of dry N2 with oven-
dried glassware and anhydrous solvents. THF was distilled from
sodium benzophenone under a N2 atmosphere. CH2Cl2 was dried
over CaCl2 and distilled prior to use. All other solvents were dried
over 4−8 Å mesh molecular sieves (Aldrich). Reactions were
monitored by thin layer chromatography on 0.20 mm Yantai Dexin
silica gel plates (from Yantai Dexin Biotechnology Co., Ltd.), and
spots were detected with UV light. Silica gel (200−300 mesh) (from
Anhui Liang Chenchem Company, Ltd.) was used for flash
chromatography. Other chemicals or reagents were obtained from
commercial sources. NMR spectra were recorded with a Bruker
Avance III 400 MHz spectrometer. The X-ray crystallography data
was collected on a SuperNova, Dual, Cu at home/near, AtlasS2
diffractometer with graphite-monochromatized Mo Kα (Cu Kα)
radiation. Elemental analyses were determined in house using a
PerkinElmer 2400 CHN elemental analyzer. The X-ray photoelectron
CONCLUSIONS
■
In conclusion, a series of Pd(II) complexes bearing a bidentate
amine ligand have been designed and synthesized. The X-ray
diffraction spectra of the palladium complexes show that the
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spectroscopy (XPS) analysis was performed on an AXIS Ultra DLD
X-ray photoelectron spectrometer (Shimadzu, Japan).
4-Fluorobiphenyl (6Ea and 6Ab). 1H NMR (400 MHz, CDCl3) δ
(ppm): 7.52 (dd, J = 7.9, 2.5 Hz, 4H), 7.41 (t, J = 7.5 Hz, 2H), 7.33
(t, J = 7.3 Hz, 1H), 7.10 (t, J = 8.7 Hz, 2H). 13C NMR (100 MHz,
Synthesis of Complexes 1−3. The complexes were synthesized
according to the following general method: A flask was charged with
1,2-mesitylethylenediamine (0.36 mmol), PdCl2 (0.45 mmol), and 2
mL of dry THF. Then, the reaction mixture was allowed to warm to
55 °C and continued to stir for 18 h at this temperature. The resulting
mixture was then concentrated under a vacuum to give a yellow
residue, and the residue was recrystallized from CH2Cl2/petroleum
ether (2:1) to afford pure products.
CDCl3) δ (ppm): 162.4 (d, JC−F = 240.0 Hz), 140.2, 137.3 (d, JC−F
=
3.2 Hz), 128.7 (dd, JC−F = 10.6, 7.3 Hz), 126.9, 115.5 (d, JC−F = 20.0
Hz). 19F NMR (376 MHz, CDCl3) δ (ppm): −115.7 (s, 1F).
2,5-Dimethylbiphenyl (6Fa and 6Af). 1H NMR (400 MHz,
CDCl3) δ (ppm): 7.43−7.26 (m, 6H), 7.14 (d, J = 8.2 Hz, 1H), 7.05
(d, J = 5.8 Hz, 2H), 2.33 (s, 3H), 2.21 (s, 3H). 13C NMR (100 MHz,
CDCl3) δ (ppm): 142.0, 141.7, 135.1, 132.1, 130.5, 129.1, 128.7,
127.9, 127.1, 126.6, 20.8, 19.9.
1
Complex 1. Yellow solid. Yield: 90% (182 mg, 0.32 mmol). H
2-Methylbiphenyl (6Ga and 6Ae). 1H NMR (400 MHz, CDCl3) δ
(ppm): 7.38 (d, J = 8.0 Hz, 2H), 7.32 (t, J = 8.0 Hz, 3H), 7.25−7.23
(m, 4H), 2.26 (s, 3H). 13C NMR (100 MHz, CDCl3) δ (ppm): 141.9,
135.3, 130.2, 129.7, 129.1, 128.7, 128.0, 127.2, 126.7, 125.7, 20.4.
2-Fluorobiphenyl (6Ha and 6Ak). 1H NMR (400 MHz, CDCl3) δ
(ppm): 7.58−7.52 (m, 2H), 7.41 (t, J = 8.0 Hz, 3H), 7.35−7.24 (m,
2H), 7.18−7.09 (m, 2H). 13C NMR (100 MHz, CDCl3) δ (ppm):
159.7 (d, JC−F = 246.0 Hz), 141.2, 135.7, 130.7 (d, JC−F = 4.0 Hz),
129.0 (d, JC−F = 3.0 Hz), 128.1, 128.4, 127.6, 127.1 (d, JC−F = 8.0
Hz), 124.3 (d, JC−F = 4.0 Hz), 116.0 (d, JC−F = 22 Hz). 19F NMR
(376 MHz, CDCl3) δ (ppm): −117.9 (s, 1F).
NMR (400 MHz, DMSO-d6) δ (ppm): 6.90 (s, 2H, CHar), 6.78 (s,
2H, CHar), 6.17 (s, 2H, NH), 3.36 (s, 4H, CH), 2.36 (s, 6H, CH),
2.17 (s, 12H, CH). 13C NMR (100 MHz, DMSO-d6) δ (ppm): 140.1,
134.8, 131.2, 130.6, 129.9, 128.7, 53.0, 21.3, 20.1, 18.0. Analytical
Data. Calcd (found) for C20H28Cl2N2Pd: C, 50.70 (50.63); H, 5.96
(5.94); N, 5.91 (5.89).
Complex 2. Orange-red solid. Yield: 92% (98 mg, 0.15 mmol). 1H
NMR (400 MHz, DMSO-d6) δ (ppm): 6.90 (s, 2H, CHar), 6.80 (s,
2H, CHar), 6.18 (s, 2H, NH), 3.37 (s, 4H, CH), 2.37 (s, 6H, CH),
2.19−2.14 (m, 12H, CH). 13C NMR (100 MHz, DMSO-d6) δ (ppm):
140.7, 134.8, 131.2, 130.6, 129.8, 128.6, 53.0, 21.5, 20.1, 18.2.
Analytical Data. Calcd (found) for C20H28Br2N2Pd: C, 42.69 (42.71);
H, 5.02 (5.07); N, 4.98 (4.96).
3-Fluoro-4-methylbiphenyl (6Ia). 1H NMR (400 MHz, CDCl3) δ
(ppm): 7.54 (d, J = 7.7 Hz, 2H), 7.41 (t, J = 7.5 Hz, 2H), 7.32 (t, J =
7.3 Hz, 1H), 7.24−7.18 (m, J = 14.6, 7.2 Hz, 3H), 2.29 (s, 3H). 13C
NMR (100 MHz, CDCl3) δ (ppm): 161.1 (d, JC−F = 150.0 Hz), 140.7
(d, JC−F = 7.6 Hz), 139.9 (d, JC−F = 2.0 Hz), 131.6 (d, JC−F = 5.6 Hz),
128.8, 127.4, 126.8, 123.6 (d, JC−F = 17.3 Hz), 122.3 (d, JC−F = 3.2
Hz), 113.6, 113.3, 14.2 (d, JC−F = 3.3 Hz). 19F NMR (376 MHz,
CDCl3) δ (ppm): −117.3 (s, 1F).
Complex 3. Brown-red solid. Yield: 95% (190 mg, 0.34 mmol). 1H
NMR (400 MHz, DMSO-d6) δ (ppm): 6.89 (s, 2H, CHar), 6.83 (s,
2H, CHar), 6.07 (s, 2H, NH), 3.22 (s, 4H, CH), 2.20 (s, 6H, CH),
2.20−2.14 (m, 12H, CH). 13C NMR (100 MHz, DMSO-d6) δ (ppm):
141.3, 134.5, 131.1, 130.8, 129.7, 128.4, 52.6, 21.8, 20.1, 18.4.
Analytical Data. Calcd (found) for C20H28I2N2Pd: C, 36.58 (36.47);
H, 4.30 (4.32); N, 4.27 (4.28).
Optimization of the Reaction Conditions. A test tube was charged
with a mixture of phenylboronic acid (0.3 mmol), chlorobenzene
(0.25 mmol), base (0.5 mmol), and different solvent (0.8 mL). Then,
catalyst (0.01 mol %) was added and stirred at room temperature.
After 3 h, the mixture was extracted three times with CH2Cl2 (3 × 1
mL), dried over Na2SO4, filtered, and concentrated under a vacuum.
The products were further purified by flash chromatography on a
silica gel column.
3-Methoxybiphenyl (6Ja). 1H NMR (CDCl3, 300 MHz) δ (ppm):
7.59 (d, J = 6.6 Hz, 2H), 7.45−7.36 (m, 4H), 7.25−7.13 (m, 2H),
6.90 (d, J = 5.7 Hz, 1H), 3.84 (s, 3H). 13C NMR (100 MHz, CDCl3)
δ (ppm): 159.9, 142.7, 141.1, 129.8, 128.7, 127.4, 127.2, 119.7, 112.9,
112.6, 55.3.
1
4-Chlorobiphenyl (6Ac). H NMR (400 MHz, CDCl3) δ (ppm):
7.54−7.48 (m, 4H), 7.44−7.32 (m, 5H). 13C NMR (100 MHz,
CDCl3) δ (ppm): 139.9, 139.6, 133.3, 128.8, 128.8, 128.3, 127.5,
126.9.
1
4-Methylbiphenyl (6Ad). H NMR (400 MHz, CDCl3) δ (ppm):
General Procedure for Pd(II) Catalyzed Suzuki−Miyaura
Coupling Reaction of Aryl Halides with Arylboronic Acids. A
mixture of arylboronic acids (0.3 mmol), aryl halides (0.25 mmol),
and K3PO4 (0.5 mmol) was dissolved in i-PrOH/H2O (0.4 mL/0.4
mL). Then, precatalyst (0.01 mol %) was added and the reaction
mixture was stirred at room temperature. After completion of the
reaction, the mixture was extracted three times with CH2Cl2 (3 × 1
mL), dried over anhydrous Na2SO4, filtered, and concentrated under
a vacuum. The products were further purified by flash chromatog-
raphy on a silica gel column.
7.56 (d, J = 8.0 Hz, 2H), 7.48 (d, J = 8.0 Hz, 2H), 7.40 (t, J = 8.0 Hz,
2H), 7.30 (t, J = 8.0 Hz, 1H), 7.23 (d, J = 8.0 Hz, 2H), 2.37 (s, 3H).
13C NMR (100 MHz, CDCl3) δ (ppm): 141.1, 138.3, 137.0, 129.4,
128.7, 127.0, 126.9, 21.1.
1
2-Phenylbiphenyl (6Ah). H NMR (400 MHz, CDCl3) δ (ppm):
7.44−7.39 (m, 4H), 7.20−7.12 (m, 10H). 13C NMR (100 MHz,
CDCl3) δ (ppm): 141.5, 140.6, 130.6, 129.9, 127.9, 127.5, 126.5.
4-Methoxybiphenyl (6Ai). 1H NMR (400 MHz, CDCl3) δ (ppm):
7.53 (t, J = 8.9 Hz, 4H), 7.40 (t, J = 7.5 Hz, 2H), 7.30 (d, J = 7.3 Hz,
1H), 6.96 (d, J = 8.5 Hz, 2H), 3.82 (s, 3H). 13C NMR (100 MHz,
CDCl3) δ (ppm): 159.1, 140.7, 133.7, 128.6, 128.1, 126.7, 126.6,
114.1, 55.3.
Biphenyl (6Aa). 1H NMR (400 MHz, CDCl3) δ (ppm): 7.63 (d, J
= 8.0 Hz, 4H), 7.47 (t, J = 8.0 Hz, 4H), 7.37 (t, J = 8.0, 2H). 13C
NMR (100 MHz, CDCl3) δ (ppm): 141.2, 128.7, 127.2, 127.1.
3-Fluorobiphenyl (6Ba and 6Ag). 1H NMR (400 MHz, CDCl3) δ
(ppm): 7.52−7.46 (m, 3H), 7.35 (t, J = 8.0 Hz, 3H), 7.30−7.19 (m,
2H), 7.13−7.04 (m, 1H). 13C NMR (100 MHz, CDCl3) δ (ppm):
159.7 (d, JC−F = 240.0 Hz), 141.2, 135.7, 130.7 (d, JC−F = 3.5 Hz),
129.0 (d, JC−F = 2.9 Hz), 128.7, 128.4, 127.6, 127.1 (d, JC−F = 8.6
Hz), 121.1, 116.0 (d, JC−F = 20.0 Hz). 19F NMR (376 MHz, CDCl3)
δ (ppm): −113.1 (s, 1F).
1
2-Chlorobiphenyl (6Aj). H NMR (400 MHz, CDCl3) δ (ppm):
7.46−7.25 (m, 9H). 13C NMR (100 MHz, CDCl3) δ (ppm): 140.4,
139.3, 132.4, 131.3, 129.9, 129.4, 128.4, 128.0, 127.5, 126.7.
4-Fluoro-2-methylbiphenyl (6Al). 1H NMR (400 MHz, CDCl3) δ
(ppm): 7.43−7.32 (m, 3H), 7.29−7.25 (m, 2H), 7.19−7.16 (dd, J =
6.0, 8.4 Hz, 1H), 7.00−6.91 (m, 2H), 2.25 (s, 3H). 13C NMR (100
MHz, CDCl3) δ (ppm): 161.9 (d, JC−F = 245.3 Hz), 141.0, 137.9 (d,
JC−F = 3.1 Hz), 137.6 (d, JC−F = 7.7 Hz), 131.1 (d, JC−F = 8.2 Hz),
129.2, 128.1, 126.9, 116.7 (d, JC−F = 21.0 Hz), 112.4 (d, JC−F = 20.8
Hz), 20.6. 19F NMR (376 MHz, CDCl3) δ (ppm): −116.3 (s, 1F).
X-ray Crystal Structure Determinations. Single-crystal X-ray
diffraction data for complexes 1−3 were collected on a Super Nova,
Dual, Cu at home/near, Atlas S2 diffractometer. The crystals of
complexes 1−3 were kept, respectively, at 156.26(16), 100.00(10),
and 135.94(10) K during data collection. The structures were
resolved by direct method with the OLEX2 program21 and refined on
F2 with SHELXL.22 All nonhydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were generated geometrically.
1
3-Methylbiphenyl (6Ca). H NMR (400 MHz, CDCl3) δ (ppm):
7.58 (d, J = 8.0 Hz, 2H), 7.41 (dd, J = 16.0, 8.0 Hz, 4H), 7.33 (t, J =
8.0 Hz, 2H), 7.36 (d, J = 8.0 Hz, 1H), 2.42 (s, 3H). 13C NMR (100
MHz, CDCl3) δ (ppm): 141.4, 141.2, 138.3, 128.7, 128.7, 128.0,
127.2, 124.3, 21.5.
3,5-Dimethylbiphenyl (6Da). 1H NMR (400 MHz, CDCl3) δ
(ppm): 7.56 (d, J = 4.0 Hz, 2H), 7.39 (t, J = 8.0 Hz, 2H), 7.31 (dd, J
= 8.0, 4.0 Hz, 1H), 7.20 (s, 2H), 6.97 (s, 1H), 2.36 (s, 6H). 13C NMR
(100 MHz, CDCl3) δ (ppm): 141.5, 141.3, 141.3, 138.3, 129.0, 128.8,
128.7, 127.3, 127.3, 127.2, 127.1, 125.2, 21.5.
F
DOI: 10.1021/acs.organomet.8b00883
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Theoretical Calculations. All of the DFT calculations were
performed with the Gaussian 09 package.23 Geometry optimizations
were carried out using the B3LYP24 functional with a mixed basis set
of LANL2DZ25 for Pd and K and 6-31G(d) for other atoms.
Vibrational frequencies were computed analytically at the same level
of theory to confirm whether the structures are minima (no imaginary
frequencies) or transition states (only one imaginary frequency). Key
transition state structures were confirmed to connect corresponding
reactants and products by intrinsic reaction coordinate (IRC)
calculations.26 Solvation effects (solvent = generic, ε = 48.8) were
taken into account by performing single-point calculations with the
PCM model,27 and the atomic radii used for the PCM calculations
were specified using the UFF keyword. To obtain better accuracy,
energies of the optimized geometries were calculated using single-
point calculations with a larger basis set, which is SDD for Pd and K
and 6-311+G(d,p) for other atoms. The final free energies reported in
the article (ΔGsol) are the large basis set single-point energies with
gas-phase Gibbs free energy correction (at 298.15 K), solvation
correction, and dispersion correction using the DFT-D3(BJ) method
developed by Grimme and co-workers.28
Palladium-Catalyzed Cross-Coupling Reactions. Acc. Chem. Res.
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00883.
■
S
(4) Kinzel, T.; Zhang, Y.; Buchwald, S. L. A New Palladium
Precatalyst Allows for the Fast Suzuki-Miyaura Coupling Reactions of
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for the Most-Challenging Cross-Coupling Reactions. Angew. Chem.,
NMR spectra of compounds and complexes and X-ray
crystallographic analysis for 1−3 (PDF)
Cartesian coordinates (XYZ)
Accession Codes
CCDC 1842186−1842188 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Int. Ed. 2012, 51, 3314−3332. (b) Çalimsiz, S.; Sayah, M.; Mallik, D.;
Organ, M. G. Pd-PEPPSI-IPent: Low-Temperature Negishi Cross-
Coupling for the Preparation of Highly Functionalized, Tetra-ortho-
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(c) Organ, M. G.; Çalimsiz, S.; Sayah, M.; Hoi, K. H.; Lough, A. J. Pd-
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(6) (a) Chartoire, A.; Lesieur, M.; Falivene, L.; Slawin, A. M.;
Cavallo, L.; Cazin, C. S. J.; Nolan, S. P. [Pd(IPr*) (cinnamyl)Cl]: An
Efficient Pre-catalyst for the Preparation of Tetra-ortho-substituted
Biaryls by Suzuki-Miyaura Cross-Coupling. Chem. - Eur. J. 2012, 18,
4517−4521. (b) Marion, N.; Navarro, O.; Mei, J.; Stevens, E. D.;
Scott, N. M.; Nolan, S. P. Modified (NHC)Pd(allyl)Cl (NHC = N-
Heterocyclic Carbene) Complexes for Room-Temperature Suzuki-
Miyaura and Buchwald-Hartwig Reactions. J. Am. Chem. Soc. 2006,
128, 4101−4111. (c) Shi, S.; Nolan, S. P.; Szostak, M. Well-defined
Palladium(II)−NHC Precatalysts for Cross-coupling Reactions of
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AUTHOR INFORMATION
Corresponding Authors
*E-mail: guiyanliu2013@163.com.
*E-mail: gphuang@tju.edu.cn.
*E-mail: wjh@tju.edu.cn.
■
ORCID
Guiyan Liu: 0000-0001-9111-369X
Genping Huang: 0000-0002-2249-1248
Jianhui Wang: 0000-0003-2581-7247
Notes
The authors declare no competing financial interest.
(7) (a) Littke, A. F.; Fu, G. C. Palladium-catalyzed Coupling
Reactions of Aryl Chlorides. Angew. Chem. 2002, 114, 4350−4386;
Angew. Chem., Int. Ed. 2002, 41, 4176−4211. (b) Yin, L.; Liebscher, J.
Carbon-carbon Coupling Reactions Catalyzed by Heterogeneous
Palladium Catalysts. Chem. Rev. 2007, 107, 133−173. (c) Snelders, D.
J. M.; van Koten, G. Hexacationic Dendriphos Ligands in the Pd-
catalyzed Suzuki-Miyaura Cross-coupling Reaction: Scope and
Mechanistic Studies. J. Am. Chem. Soc. 2009, 131, 11407−11416.
(d) Konishi, S.; Iwai, T.; Sawamura, M. Organometallics 2018, 37,
1876. (e) Wang, T.; Xie, H.; Liu, L.; Zhao, W. X. N-heterocyclic
Carbene-Palladium(II) Complexes with Benzoxazole or Benzothia-
zole Ligands: Synthesis, Characterization, and Application to Suzuki-
Miyaura Cross-coupling Reaction. J. Organomet. Chem. 2016, 804,
73−79. (f) Wang, T.; Liu, L.; Xu, K.; Xie, H.; Shen, H.; Zhao, W. X.
Synthesis and Characterization of Trinuclear N-heterocyclic Car-
bene−palladium(II) Complexes and Their Applications in the Suzuki-
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ACKNOWLEDGMENTS
■
This work was supported by the Natural Science Foundation
of Tianjin (16JCYBJC19700, 16JCQNJC05600, and
16JCQNJC03200) and the National Natural Science Founda-
tion of China (Grant Nos. 21572155, 21503143, and
21771138).
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DOI: 10.1021/acs.organomet.8b00883
Organometallics XXXX, XXX, XXX−XXX