Highly bulky and stable geometry-constrained iminopyridines: Synthesis, structure and application in Pd-catalyzed Suzuki coupling of aryl chlorides

Article abstract of DOI:10.3762/bjoc.13.24

A series of bulky geometry-constrained iminopyridylpalladium chlorides were developed. The steric environment adjacent to the nitrogen atom in the pyridine rings and diimine parts enhanced the thermal stability of the palladium species. Bulkier groups at the imino group stabilized the palladium species and the corresponding palladium chlorides showed high activities in the coupling reaction of aryl chlorides.

Full text of DOI:10.3762/bjoc.13.24

Highly bulky and stable geometry-constrained iminopyridines:
Synthesis, structure and application in Pd-catalyzed Suzuki
coupling of aryl chlorides
Yi Lai1, Zhijian Zong1, Yujie Tang1, Weimin Mo1, Nan Sun1, Baoxiang Hu1,
Zhenlu Shen1, Liqun Jin*1,2, Wen-hua Sun*3 and Xinquan Hu*1,2
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2017, 13, 213–221.
1College of Chemical Engineering, Zhejiang University of Technology,
doi:10.3762/bjoc.13.24
Hangzhou 310032, P.R. China, 2State Key Laboratory for Oxo
Synthesis and Selective Oxidation, Lanzhou Institute of Chemical
Physics, Chinese Academy of Sciences, Lanzhou 730000, P.R. China
and 3Key laboratory of Engineering Plastics and Beijing National
Laboratory for Molecular Science, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100190, P.R. China
Received: 21 December 2016
Accepted: 19 January 2017
Published: 03 February 2017
Associate Editor: K. Itami
Email:
© 2017 Lai et al.; licensee Beilstein-Institut.
License and terms: see end of document.
Liqun Jin* - liqunjin@zjut.edu.cn; Wen-hua Sun* -
whsun@iccas.ac.cn; Xinquan Hu* - xinquan@zjut.edu.cn.
*
Corresponding author
Keywords:
aryl chloride; geometry-constrained; iminopyridyl; palladium; Suzuki
Abstract
A series of bulky geometry-constrained iminopyridylpalladium chlorides were developed. The steric environment adjacent to the
nitrogen atom in the pyridine rings and diimine parts enhanced the thermal stability of the palladium species. Bulkier groups at the
imino group stabilized the palladium species and the corresponding palladium chlorides showed high activities in the coupling reac-
tion of aryl chlorides.
Introduction
Palladium-promoted C–C coupling reactions are recognized as Targeting the handling and applicability of palladium catalysts,
one of the most powerful tools in organic syntheses, pharma- various species have been developed through the use of diversi-
ceutical processes and biological modifications [1-4]. The fied ligands [6-12].
achievement is largely beneficial to organic chemists for their
parallel contributions in Pd-catalyzed transformations as well as Typical ligands that successfully enhanced the reactivity of
for discovering new reactions. The improvement of the effi- palladium species towards the oxidative addition of aryl or alkyl
ciency of noble metal catalysts is still highly attractive from halides include phosphine ligands independently developed by,
both the academic and the industrial point of view [5]. for example, Buchwald [13-15], Hartwig [16,17], Fu [18-20],
213

Beilstein J. Org. Chem. 2017, 13, 213–221.
Kwong [21-23], Tang [24-27] and Lundgren [28], and
N-heterocyclic carbene ligands due to the inherent strong
sigma-donating property [29]. Alternatively, the palladacycles
reported by Herrmann and Beller in the 1990s [30] effectively
elongated the lifetime of the active Pd species through employ-
ing bidentate or multidentate ligands [31-36]. Meanwhile
nitrogen ligands are also widely used for palladium catalysts in
coupling reactions with the advantage of convenient synthetic
methods, easy functional group modifications and better
stability [37-43]. Pyridine, azole and imine-based N(sp2)
ligands received considerable attention, especially bidentate
Figure 1: The steric geometry-constrained iminopyridyl–palladium
complexes.
N,N-ligands. In general, most bidentate N,N(sp2) ligands expected to protect the active palladium center from decomposi-
comprise symmetrical frameworks, such as bipyridine [44-46], tion during the catalytic cycle. Nevertheless, multiple substitu-
biimidazole [47,48], and diimine [49-53]. Moreover imino- tions at Cb probably prohibit any tautomerization and result to
pyridines were attractive for a more straightforward preparation, increase the stability of iminopyridines and their palladium
the condensation of pyridine-2-carboxaldehyde or ketone and catalysts.
the relevant primary amines. By this work a wide variety of dif-
ferent substituents were introduced leading to a diversity with 6,7-Dihydroquinolin-8(5H)-one (1) and 2-chloro-6,7-dihydro-
regard to steric and electronic aspects [54-59].
quinolin-8(5H)-one (2) could be prepared in large amounts
following the previously reported synthetic procedures
Recently, we have developed a series of geometry-constrained [60,62,69-71]. Geminal dimethylation of 1 with NaH and MeI
iminopyridyl compounds [60-64] and their corresponding palla- in THF afforded 7,7-dimethyl-6,7-dihydroquinolin-8(5H)-one
dium complexes showed a good catalytic efficiency for both (3) easily in good yield. Meanwhile, the Ni-catalyzed Kumada
Suzuki and Heck cross-coupling reactions. The favorable effect coupling of 2 with methylmagnesium chloride produced
originated from the ring-fused framework being able to estab- 2-methyl-6,7-dihydroquinolin-8(5H)-one (4) efficiently with
lish a strained environment for better stability. Efficient quantitative yield. With compounds 1, 2, 3 and 4 in hand,
couplings were achieved with aryl bromides or iodides as sub- further condensations with different arylamines and direct coor-
strates, however, it is still not favored for the cheaper and more dination to PdCl2 in one pot smoothly in the presence of TsOH.
widely available aryl chloride substrates. For C–Cl bond activa- For this transformation, we found that vigorous stirring during
tion, the major efforts have focused on using extraordinarily the reaction was very important, which increased the yields
electron-rich ligands to promote the oxidative addition. We from medium to quantitative results [72]. Following a similar
assumed that the coupling of aryl chlorides could also be procedure as described in the Experimental section, complexes
furnished under high temperature, if the palladium catalyst is Pd1 to Pd5 were synthesized and could be isolated by simple
stable enough. The formation of palladium black was observed work-up (Scheme 1). All of these complexes have been fully
in reactions of aryl chlorides using the reported palladium cata- characterized and confirmed by NMR and HRMS, and the
lyst system, which inspired us to improve the thermal stability analyses are in good agreement with that of the previously re-
of the palladium complex. The steric environment adjacent to ported palladium complexes [72]. All of these complexes could
the nitrogen in pyridine rings and diimine parts enhanced the be stored open to air without any decomposition for several
thermal stability of metal species, albeit under harsh conditions months except Pd4. Their melting points [>240 °C] indicated
[
65-68]. Therefore, Figure 1 schematically illustrates various their high thermostability, especially Pd2 with a melting point
substituents of iminopyridines constraining the geometrical in- up to 325 °C.
fluence around the palladium center. In this report, the modifi-
cations using various substituents with different electronic and With these sterically hindered iminopyridine–palladium com-
steric factors have been explored, and fortunately thermally plexes Pd1 to Pd5 in hand, we firstly investigated their catalyt-
stable palladium chlorides are obtained demonstrating high ac- ic activity directly in Suzuki cross-coupling reactions with
tivities toward the coupling reaction of aryl chlorides.
chlorobenzene as the electrophile. The reactions were per-
formed under the previously reported conditions without any
change except at the higher reaction temperature. As shown in
Results and Discussion
According to Figure 1, the geometry-constrained iminopyridyl Table 1, using complex Pd1, which has exhibited an impres-
skeleton could be modified at three sites: Ca, Cb and Nc. Both sive efficiency in Pd-catalyzed Suzuki coupling of aryl bro-
the derivation of the Ca position and adjusting the imino part are mides, only delivered 18% conversion of chlorobenzene. The
214

Beilstein J. Org. Chem. 2017, 13, 213–221.
Scheme 1: Preparation of the bulky iminopyridyl–palladium complexes.
modification of the Cb position by importing two methyl groups coordination geometry around the palladium centre with a slight
of Pd1 to Pd3 did not give any improvement while with much distortion. Selected bond lengths and angles listed in Table 2
lower conversion. The efforts changing the steric and electronic suggest that both the imino double bond N3–C3 (1.304 Å) and
effect from the ortho-position of pyridyl (Pd4 and Pd5) also Pd–N3 (2.037 Å) were slightly longer than that of our previous
failed to promote C–Cl bond activation. To our delight, com- reported iminopyridyl–palladium complexes (1.27–1.30 Å,
plex Pd2, with a bulkier version of dipp (2,6-diisopropylphenyl) 2.02–2.03 Å, respectively) [57]. The structure clearly showed a
in the imino motif, displayed significant enhance with the flexible steric bulky effect from the replacement of two methyl
conversion up to 44%. The results in Table 1 and Figure 1 groups of iPr by phenyl rings and the palladium center could be
matched well with our proposal that improving the stability of protected very well.
palladium species favored C–Cl bond activation under higher
temperature.
With Pd2 as the catalyst, we then put our efforts on simply opti-
mizing the reaction conditions for the coupling between
Single crystals of complex Pd2 were obtained by slow diffu- chlorobenzene and 4-methylphenylboronic acid. We noticed
sion of diethyl ether to a saturated dichloromethane solution and that water could promote the conversion of chlorobenzene to
the molecular structure in solid state was determined by X-ray 62% which might be due to the better solubility of the base in
diffraction [73]. Presented in Figure 2, the molecular structure toluene/H2O (2.5:1) mixed solvents (Table 3, entry 1). Bases
and the predicted conformation was unambiguously confirmed. have been proven to play an important role in Suzuki coupling
The same as before, the complexes also exhibit square-planar reactions [74]. Then, in mixed solvents, various bases were ex-
Table 1: Pd-catalyzed coupling of chlorobenzene and 4-tolylboronic acid using Pd1–Pd5 as the catalyst.a
Cat.
Pd1
Pd2
Pd3
Pd4
Pd5
Conv.(%)b
18
44
5
4
18
aReaction conditions: chlorobenzene (1.0 mmol), 4-methylphenylboronic acid (1.2 mmol), toluene (3.0 mL), Pd catalyst (1 mol %), 18 h, purged with
N2 for 2 min. bConversions were determined by GC.
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Beilstein J. Org. Chem. 2017, 13, 213–221.
Table 2: Selected bond lengths [Å] and angles [°] for complexes Pd2.
Bond lengths (Å)
Bond angles (°)
Pd(1)–N(2) 2.036 (3)
Pd(1)–N(3) 2.038(2)
N(3)–Pd(1)–N(2) 80.45(9)
N(3)–Pd(1)–Cl(1) 174.33(7)
Pd(1)–Cl(2) 2.2772(10) N(3)–Pd(1)–Cl(2) 94.80(6)
Pd(1)–Cl(1) 2.2938(9)
N(2)–C(2) 1.373(4)
N(2)–C(41) 1.327(4)
N(2)–Pd(1)–Cl(2) 175.22(7)
N(2)–Pd(1)–Cl(2) 93.99(7)
Cl(2)–Pd(1)–Cl(1) 90.75(3)
N(3)–C(3)
N(3)–C(5)
1.304(3)
1.437(3)
to 140 °C could be an advantage for the reaction. Without any
other screening, we finally determined the reaction conditions
as following for the next substrates scope test: Pd2 (1 mol %),
toluene/H2O (5:1), 24 h, 140 °C.
With the optimized reaction conditions, a standard reaction in a
Figure 2: ORTEP drawing of Pd2 with thermal ellipsoids at 30% prob-
ability level. Hydrogen atoms and the solvent CH2Cl2 have been
omitted for clarity.
5
mmol scale between chlorobenzene and phenylboronic acid
was carried out and 64% isolated yield was obtained (Table 4,
entry 1). Subsequently, different aryl chlorides and arylboronic
amined (Table 3, entries 1–10). Compared with K2CO3, the acids were tested. The results were listed in Table 4. Aryl chlo-
other tested bases did not show any advantage. Increasing the rides with an electron-withdrawing functional group, such as
amount of base to 2.5 equivalents or elevating the temperature nitro (Table 4, entry 2), carbonyl (Table 4, entries 4–6), nitrile
Table 3: The optimization of conditions for Pd-catalyzed coupling reactions between chlorobenzene and phenylboronic acid a.
Entry
Base (equiv)
Temperature (°C)
Conversion.(%)b
1
2
3
4
5
6
7
8
9
K2CO3 (2.0)
Cs2CO3 (2.0)
t-BuOK (2.0)
NaOH (2.0)
DIPEA (2.0)
KOAc (2.0)
Na2CO3 (2.0)
NaF (2.0)
130
130
130
130
130
130
130
130
130
130
130
130
100
120
140
150
62
31
trace
16
NR
8
22
NR
NR
30
69
72
52
54
77
74
NaOAc (2.0)
EtONa (2.0)
K2CO3 (2.2)
K2CO3 (2.5)
K2CO3 (2.2)
K2CO3 (2.2)
K2CO3 (2.2)
K2CO3 (2.2)
10
11
12
13
14
15
16
aReaction conditions: chlorobenzene (1.0 mmol), 4-methylphenylboronic acid (1.2 mmol), toluene/H2O (2.5/0.5, v/v), Pd2 (1 mol %), 18 h, purged with
N2 for 2 min. bConversions were determined by GC. DIPEA = diisopropylethylamine.
216

Beilstein J. Org. Chem. 2017, 13, 213–221.
Table 4: Pd-catalyzed coupling between various aryl chlorides and arylboronic acids.a
Entry
1
ArCl
ArB(OH)2
Conv/Yield (%)b
3-1 71/64
1
-1
-2
2-1
2-1
2
3
3-2 64/58
3-3 99/99
1
2-1
2-1
1
-3
-4
4
5
3-4 86/85
3-5 82/69
1
2-1
1
1
1
1
1
-5
-6
-7
-8
-9
6
7
8
9
2-1
2-1
2-1
2-1
2-1
3-6 94/90
3-7 93/86
3-8 80/75
3-9 60/49
3-10 59/51
1
0
1
1
-10
-11
1
2-1
3-11 64/57
1
1
2
3
2-1
2-1
3-12 91/91
3-13 92/84
1
-12
-13
1
1
217

Beilstein J. Org. Chem. 2017, 13, 213–221.
Table 4: Pd-catalyzed coupling between various aryl chlorides and arylboronic acids.a (continued)
14
15
16
1-3
1-3
1-3
3-14 99/95
3-15 99/99
3-16 96/89
2-2
2-3
2-4
17
1-3
3-17 95/93
2-5
aReaction conditions: aryl chlorides (5.0 mmol), arylboronic acid (6.0 mmol), K2CO3 (11.0 mmol), toluene/H2O (10 mL/2 mL), Pd2 (1 mol %), 140 °C,
4 h, purged with N2 for 2 min. bConversions were determined by GC and yields were isolated results.
2
and CF3 (Table 4, entries 6 and 7) could be coupled with NMR multiplicities are abbreviated as follows: s = singlet,
-methylphenylboric acid in good to excellent yields. Aryl chlo- d = doublet, t = triplet, q = quartet, sept = septet, m = multiplet,
4
rides with an electron-donating functional group (Table 4, br = broad signal. Chemical shifts are given in ppm and are
entries 9 and 10) and steric hindered 2-chlorotoluene (Table 4, referenced to SiMe4 (1H, 13C) and all spectra were obtained at
entry 11), which are usually regarded as reluctant substrates due 25 °C in the solvent indicated. Coupling constants J are given in
to the sluggish oxidative addition of Pd(0) to aryl chlorides, Hz. GC analyses were performed on Agilent 6890 instrument
proceeded successfully with moderate yields. Heterocyclic aryl with FID detector using an HP-5 capillary column
chloride, for example, 2-chloropyridine, was also well tolerated (30 m × 0.32 mm (i.d.), 0.25 μ). High-resolution mass spectra
and 84% isolated yields was obtained (Table 4, entries 13). Dif- were recorded in the EI mode on Agilent 6210 TOF mass spec-
ferent arylboronic acids were also examined to react with trometry. Flash column chromatography was performed on
4
-chloroacetophenone in this system. No matter what kind of neutral SiO2 (200–300 mesh) with ethyl acetate/petroleum as
boronic acids were used: electron-deficient (Table 4, entry 14), eluent. Melting points were determined on BÜCHI M-565
electron-rich (Table 4, entries 15 and 16) or sterically hindered apparatus. X-ray crystallography were performed on a Bruker
(
Table 4, entry 17) arylboronic acids, high conversions and Smart Apex CCD area detector diffractometer using graphite-
excellent isolated yields were achieved.
monochromated Mo Kα radiation (λ = 0.71073 Å). Details of
the X-ray structure determinations and refinements are provi-
ded in Table 5. According to the synthetic procedures in the lit-
Conclusion
In summary, a series of geometrically-constrained iminopyri- erature, the organic compounds 1, 2, 3, and 4 were prepared in
dine–palladium complexes were prepared with various substitu- good yield [69,71,75].
ents. They promoted efficiently the Suzuki cross coupling of
aryl chlorides. To result good catalytic activities the importance Synthesis of Pd2
of bulkier groups at the imino moiety for the stabilization of the Toluene (100 mL) was added to a mixture of 6,7-dihydro-
palladium species was sown. A variety of aryl chlorides and quinolin-8(5H)-one (1.57 g, 11 mmol), 2,6-dibenzhydryl-4-
arylboronic acids were successfully coupled in high yields and methylaniline (5.27 g, 12 mmol), PdCl2 (1.77 g, 10 mmol) and
selectivity.
TsOH·H2O (0.95 g, 5 mmol). After being degassed by N2 for
2
3
min, the reaction mixture was sealed and stirred at 130 °C for
6 hours. Then the tube was allowed to cool to room tempera-
Experimental
General procedures
ture. After filtration and washing with toluene, the resulted
All reactions were carried out under air atmosphere unless residue was purified by column chromatography with dichloro-
otherwise noted. All 1H and 13C NMR spectra were recorded on methane as the eluent. The complex Pd2 was obtained as
a Bruker AVANCE III 500 MHz spectrometer in deuterated yellow solid (7.1 g, yield 95%). Mp (dec.) 325 °C. 1H NMR
solvents with tetramethylsilane (TMS) as internal standard. (CDCl3, 500 MHz) δ 9.42 (t, J = 3.4 Hz, 1H), 7.70 (d, J = 3.4
218

Beilstein J. Org. Chem. 2017, 13, 213–221.
Table 5: Crystal data and structure refinement for Pd2.
Identification code
Pd2
Identification code
Pd2
empirical formula
C42H34N2Cl2Pd·CH2Cl2 ρcalcg/cm3
1.4237
formula weight
829.00
orthorhombic
173
μ/mm−1
0.789
crystal system
F(000)
3373.8
temperature/K
radiation
Mo Kα (λ = 0.71073)
3.58 to 56.6
space group
Pbca
2θ range for data collection/o
index ranges
a/Å
18.996(3)
19.832(4)
20.531(4)
90
−24 ≤ h ≤25, −26 ≤ k ≤ 26, −27 ≤ l ≤ 23
66946
b/Å
reflections collected
independent reflections
data/restraints/parameters
goodness-of-fit on F2
final R indexes [I>=2σ (I)]
final R indexes [all data]
largest diff. peak/hole/e Å−3
c/Å
9585 [Rint = 0.0438, Rsigma = 0.0275]
9585/0/470
α/o
β/o
90
1.123
γ/o
90
R1 = 0.0412, wR2 = 0.1026
R1 = 0.0714, wR2 = 0.1295
1.09/−0.68
volume/Å3
Z
7735(2)
8
Hz, 2H), 7.63 (m, 16H), 7.30 (d, J = 7.4Hz, 4H), 6.72 (s, 2H), yellow solid (380 mg, yield 82%). Mp (dec.) 306 °C. Pd4
6
2
1
1
.22 (s, 2H), 2.14 (s, 5H), 0.48 (t, J = 6.5 Hz, 2H), 0.17 (m, decomposes slowly when exposed open to air. 1H NMR
H); 13C NMR (CDCl3, 125 MHz) δ 182.1, 151.9, 149.9, 143.2, (CDCl3, 500 MHz) δ 7.90 (d, J = 8.1 Hz, 1H), 7.69 (d, J = 8.1
42.4, 141.4, 140.3, 137.3, 137.0, 130.1, 129.9, 129.3, 129.0, Hz, 1H), 7.34 (d, J = 7.6 Hz, 1H), 7.20 (d, J = 7.6 Hz, 2H), 3.13
28.2, 127.0, 126.5, 53.6, 52.3, 31.6, 31.0, 27.6, 21.7, 19.8; (m, 2H), 3.03 (m, 2H), 2.44 (m, 2H), 1.93 (m, 2H), 1.44 (d,
HRMS (ESI+) m/z: [M – Cl + CH3CN]+ calcd for J = 6.7 Hz, 6H), 1.15 (d, J = 6.7 Hz, 6H); HRMS (ESI+) m/z:
C42H36ClN2Pd·CH3CN, 750.1874; found, 750.1897. [M − Cl + CH3CN]+ calcd for C21H25Cl2N2Pd·CH3CN,
5
24.0684; found, 524.0679.
Synthesis of Pd3
Using xylene as the solvent, and following a similar procedure Synthesis of Pd5:
to that described for Pd2 at 160 °C, resulted Pd3 with In a similar procedure to that described for Pd2 with 81% yield
2
5
7
4
9% yield as yellow powder. Mp 246 °C; 1H NMR (DMSO-d6, as yellow powder. Mp (dec.) 282 °C; 1H NMR (DMSO-d6,
00 MHz) δ 9.10 (d, J = 5.2 Hz, 1H), 8.22 (d, J = 7.8 Hz, 1H), 500 MHz) δ 8.05 (d, J = 7.8 Hz, 1H), 7.70 (d, J = 7.8 Hz, 1H),
.87 (m, 1H), 7.26 (m, 1H), 7.14 (d, J = 7.7 Hz, 2H), 3.06 (m, 7.30 (t, J = 8.1 Hz, 1H), 7.19 (t, J = 8.1 Hz, 2H), 3.11 (m, 2H),
H), 1.86 (t, J = 6.1 Hz, 2H), 1.45 (d, J = 6.7 Hz, 6H), 1.26 (d, 2.97 (d, J = 8.3 Hz, 5H), 2.40 (t, J = 6.0 Hz, 2H), 1.82 (t, J = 6.2
J = 6.7 Hz, 6H), 0.89 (s, 6H); 13C NMR (DMSO-d6, 125 MHz) Hz, 2H), 1.33 (d, J = 6.9 Hz, 5H), 1.10 (d, J = 6.8 Hz, 6H);
δ 181.7, 153.4, 150.2, 142.5, 140.7, 140.5, 139.6, 128.4, 128.3, 13C NMR (DMSO-d6, 125 MHz) δ 163.8, 151.6, 141.2, 140.9,
1
23.4, 42.5, 37.7, 29.3, 29.0, 27.4, 25.7, 24.8, 24.5, 23.7; 140.2, 139.8, 132.1, 127.9, 123.4, 31.9, 27.9, 27.7, 27.2, 23.6,
HRMS (ESI+) m/z: [M – Cl + CH3CN]+ calcd for 23.5, 21.0; HRMS (ESI+) m/z: [M – Cl + CH3CN]+ calcd for
C23H30ClN2Pd·CH3CN, 518.1392; found, 518.1378. C22H28ClN2Pd·CH3CN, 504.1235; found, 504.1231.
General procedure for Pd-catalyzed Suzuki
Synthesis of Pd4:
Toluene (4.0 mL) was added to a mixture of 2-chloro-6,7-dihy- cross-coupling reactions
droquinolin-8(5H)-one (181 mg, 1 mmol), 2,6-dibenzhydryl-4- To a Young tube, aryl chlorides (5.0 mmol), K2CO3 (1.5 g,
methylaniline (468 mg, 1.1 mmol), and TsOH·H2O (57 mg, 11 mmol), arylboric acid (6 mmol), complex Pd2 (37.5 mg,
0
.3 mmol). After degassed by N2 for 2 min, the reaction mix- 1 mol %), toluene (10 mL) and H2O (2 mL) were added. The
ture was sealed and stirred at 130 °C for 24 hours. Then the tube mixture was degassed for 2 min. Then, the sealed Young tube
was allowed to cool to room temperature and PdCl2 (160 mg, was set into the pre-heated 140 °C oil bath. After stirring for
0
2
.9 mmol) was added. After stirring at 50 °C for additional 24 hours, the Young tube was allowed to cool to room tempera-
4 hours, filtration and washing with toluene, the resulted ture. After filtration and extraction with toluene (50 mL), the
residue was purified by column chromatography with dichloro- resulted solution was concentrated under vacuum and the
methane as the eluent. The complex Pd4 was obtained as desired biaryl was isolated by column chromatography.
219

Beilstein J. Org. Chem. 2017, 13, 213–221.
2
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Supporting Information File 1
NMR spectra of palladium complexes and products.
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Acknowledgements
This work was supported by the National Natural Science Foun-
dations of China (21473160, 21376224 and 21603190). Jin also
thanks the support from Zhejiang University of Technology and
Qianjiang Scholar Program funded by Zhejiang Province.
doi:10.1002/anie.201002404
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Yee, N. K.; Senanayake, C. H. Org. Lett. 2011, 13, 1366–1369.
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