Room-temperature Suzuki-Miyaura cross-coupling reaction with α-diimine Pd(II) catalysts

Article abstract of DOI:10.1002/aoc.3365

An α-diimine Pd(II) complex containing chiral sec-phenethyl groups, {bis[N,N′-(4-methyl-2-sec-phenethylphenyl)imino]-2,3-butadiene}dichloropalladium (rac-C1), was synthesized and characterized. rac-C1 was applied as an efficient catalyst for the Suzuki-Miyaura cross-coupling reaction between various aniline halides and arylboronic acid in PEG-400-H₂O at room temperature. Among a series of aniline halides, rac-C1 did not catalyze the cross-coupling of aniline chlorides and fluorides but efficiently catalyzed the cross-coupling of aniline bromides and iodides with phenylboronic acid. The catalytic activity reduced slightly with increasing steric hindrance of the aniline bromides. The complexes {bis[N,N′-(4-fluoro-2,6-diphenylphenyl)imino]-2,3-butadiene}dichloropalladium and {bis[N,N′-(4-fluoro-2,6-diphenylphenyl)imino]acenaphthene}dichloropalladium were also found to be efficient catalysts for the reaction.

Full text of DOI:10.1002/aoc.3365

Full paper
Received: 24 May 2015
Revised: 17 June 2015
Accepted: 18 July 2015
Published online in Wiley Online Library: 16 September 2015
(wileyonlinelibrary.com) DOI 10.1002/aoc.3365
Room-temperature Suzuki–Miyaura cross-
coupling reaction with α-diimine Pd(II) catalysts
Fuzhou Wanga, Ryo Tanakaa, Zhengguo Caib, Yuushou Nakayamaa
and Takeshi Shionoa*
An α-diimine Pd(II) complex containing chiral sec-phenethyl groups, {bis[N,N′-(4-methyl-2-sec-phenethylphenyl)imino]-2,3-buta-
diene}dichloropalladium (rac-C1), was synthesized and characterized. rac-C1 was applied as an efficient catalyst for the
Suzuki–Miyaura cross-coupling reaction between various aniline halides and arylboronic acid in PEG-400–H2O at room temper-
ature. Among a series of aniline halides, rac-C1 did not catalyze the cross-coupling of aniline chlorides and fluorides but
efficiently catalyzed the cross-coupling of aniline bromides and iodides with phenylboronic acid. The catalytic activity reduced
slightly with increasing steric hindrance of the aniline bromides. The complexes {bis[N,N′-(4-fluoro-2,6-diphenylphenyl)imino]-
2,3-butadiene}dichloropalladium and {bis[N,N′-(4-fluoro-2,6-diphenylphenyl)imino]acenaphthene}dichloropalladium were also
found to be efficient catalysts for the reaction. Copyright © 2015 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: α-diimine Pd(II) complexes; Suzuki–Miyaura cross-coupling reaction; room temperature; aniline bromides
an internal standard. Infrared (IR) spectra were recorded with a
Digilab Merlin FTS 3000 FTIR spectrophotometer as KBr pellets.
Introduction
The Pd-catalyzed Suzuki–Miyaura cross-coupling reaction, the
cross-coupling of aryl halides with arylboronic acids, is one of the
most prevalent C–C bond forming processes for the synthesis
of biaryls.[1–4] Heterogeneous catalysts are preferred from the prac-
tical point of view.[5–9] However, homogeneous catalysts for
Suzuki–Miyaura cross-coupling reactions have also been developed
by the use of novel ligands.[10–20] Buchwald’s group synthesized a
very effective sulfonated phosphine ligand for these cross-coupling
reactions in aqueous media.[11] Gholinejad et al. reported a new
bulky diimine ligand for Suzuki cross-coupling reactions in water,
which gave excellent yields of aryl iodides and bromides with low
catalyst loading.[21] Most of these reactions were performed at ele-
vated temperatures (80–140°C) in traditional organic solvents.[22–30]
Recently, we reported bulky chiral ortho-sec-diphenethyl substituted
(Figs. 1(a) and (c))[31,32] and ortho-phenyl substituted (Figs. 1(b) and
(d))[33–35] α-diimine Ni(II) complexes that exhibited high activities to-
wards ethylene polymerization to produce highly branched polyethyl-
ene. In this context, we have become interested in the application of α-
diimine ligands to Pd(II) catalysts for the Suzuki–Miyaura cross-coupling
reaction. In the work reported here, an α-diimine Pd(II) complex con-
taining chiral sec-phenethyl groups was synthesized, and employed
as a catalyst for Suzuki–Miyaura cross-coupling reactions of various an-
iline halides and arylboronic acids at room temperature. For compari-
son, α-diimine Pd(II) complexes containing phenyl groups were also
used for the cross-coupling reaction.
Elemental analysis was carried out using a Flash EA 1112 micro-
analyzer. CH2Cl2 was pre-dried with 4 Å molecular sieves and
distilled from CaH2 under dry nitrogen. Ligand L1 was prepared in
the light of our recent publication (Fig. 1(a)).[31] Other chemicals were
commercially obtained and purified using common procedures.
Catalyst synthesis (scheme 1)
Synthesis of bis[N,N′-(4-methyl-2-sec-phenethylphenyl)imino]-1,2-dimethylethane
(L1)
Ligand L1 was synthesized according to our recent publication.[31]
Synthesis of {bis[N,N′-(4-methyl-2-sec-phenethylphenyl)imino]-2,3-butadiene}
dichloropalladium (rac-C1)
(MeCN)2PdCl2 (0.26 g, 1.0 mmol) and L1 (0.22 g, 0.40 mmol) were
placed in a Schlenk flask under nitrogen atmosphere. CH2Cl2 (30
ml) was added, and the reaction mixture was stirred at room temper-
ature for 24 h. The resulting suspension was filtered. The solvent was
removed under vacuum and the residue was washed with diethyl
ether (3 × 15 ml), and then dried under vacuum at room temperature
to afford complex rac-C1 (0.56 g, 86% yield). Anal. Calcd for
*
Correspondence to: Takeshi Shiono, Graduate School of Engineering, Hiroshima
University, Kagamiyama 1-4-1, Higashi-Hiroshima 739–8527, Japan.
E-mail: tshiono@hiroshima-u.ac.jp
Experimental
a Graduate School of Engineering, Hiroshima University, Kagamiyama 1-4-1,
General
Higashi-Hiroshima 739-8527, Japan
NMR spectra were recorded with a Varian Mercury Plus-400 instru-
ment in CDCl3 at ambient temperature using tetramethylsilane as
b State Key Lab of Chemical Fibers & Polymer Materials, College of Material Science
& Engineering, Donghua University, Shanghai 201620, China
Appl. Organometal. Chem. 2015, 29, 771–776
Copyright © 2015 John Wiley & Sons, Ltd.

F. Wang et al.
Figure 2. Structures of compounds a–h.
C10), 7.26 (s, 1H, proton of C4), 7.24 (s, 1H, proton of C2), 3.67
(s, 2H, –NH2), 2.59 (q, J = 7.6 Hz, 2H, protons of C11), 2.24 (s, 3H, pro-
tons of C13), 1.24 (t, J = 7.6 Hz, 3H, protons of C12). 13C NMR (400
MHz, CDCl3, δ, ppm): 141.64 (C6), 131.12 (C7), 129.56 (C3), 128.53
(C1), 127.67 (C2), 126.90 (C9), 126.50 (C8), 126.02 (C10), 125.00
(C4), 122.26 (C5), 24.34 (C11), 17.88 (C13), 13.08 (C12). Anal. Calcd
for C15H17N (%): C, 85.26; H, 8.11; N, 6.63. Found (%): C, 85.30; H,
8.17; N, 6.53.
Figure 1. Structure of our reported α-diimine Ni(II) and Pd(II) complexes.
1
2,6-Diethyl-4-phenylaniline (b): oily liquid (0.38 g, 84% yield). H
NMR (400 MHz, CDCl3, δ, ppm): 7.54–7.56 (m, 2H, protons of C6),
7.30–7.34 (m, 2H, protons of C7), 7.16–7.20 (m, 3H, protons of C2
and C8), 3.43 (s, 2H, –NH2), 2.41–2.46 (m, 4H, protons of C9),
1.19–1.22 (m, 6H, protons of C10). 13C NMR (400 MHz, CDCl3, δ,
ppm): 141.58 (C4), 140.96 (C5), 130.71 (C3), 128.33 (C7), 128.06
(C6), 126.20 (C8), 125.74 (C2), 124.50 (C1), 24.16 (C9), 12.84
(C10). Anal. Calcd for C16H19N (%): C, 85.28; H, 8.50; N, 6.22.
Found (%): C, 85.31; H, 8.42; N, 6.20.
2,6-Diisopropyl-4-phenylaniline (c): oily liquid (0.41 g, 81% yield).
1H NMR (400 MHz, CDCl3, δ, ppm): 7.46–7.56 (m, 2H, protons of
C6), 7.34–7.40 (m, 2H, protons of C7), 7.29 (s, 2H, protons of C2),
7.25 (t, J = 8.0 Hz, 1H, proton of C8), 3.79 (s, 2H, –NH2),
2.95–2.98 (m, 2H, protons of C9), 1.33 (d, J = 7.8 Hz, 12H, protons
of C10). 13C NMR (400 MHz, CDCl3, δ, ppm): 142.45 (C5), 132.68
(C4), 131.41 (C1), 128.62 (C3), 126.61 (C7), 125.96 (C6), 125.72
(C8), 121.92 (C2), 28.07 (C9), 22.43 (C10). Anal. Calcd for C18H23N
(%): C, 85.32; H, 9.15; N, 5.53. Found (%): C, 85.25; H, 9.19; N, 5.51.
4-Isopropyl-2,6-diphenylaniline (d): oily liquid (0.41 g, 72% yield).
1H NMR (400 MHz, CDCl3, δ, ppm): 7.53 (s, 4H, protons of C2), 7.39
(t, J = 7.6 Hz, 4H, protons of C7), 7.30 (t, J = 7.6 Hz, 2H, protons of
C8), 7.01 (s, 2H, protons of C6), 3.73 (s, 2H, –NH2), 2.85–2.90 (m,
1H, proton of C9), 1.28 (d, J = 7.2 Hz, 6H, protons of C10). 13C NMR
(400 MHz, CDCl3, δ, ppm): 140.04 (C4), 138.56 (C5), 130.08 (C3),
129.67 (C7), 129.31 (C6), 128.73 (C2), 128.16 (C8), 127.13 (C1),
32.99 (C9), 24.93 (C10). Anal. Calcd for C21H21N (%): C, 87.76; H,
7.37; N, 4.87. Found (%): C, 87.82; H, 7.31; N, 4.83.
2-Methyl-4,6-diphenylaniline (e): oily liquid (0.39 g, 75% yield).
1H NMR (400 MHz, CDCl3, δ, ppm): 7.50 (d, J = 8.4 Hz, 2H, protons
of C8), 7.37–7.44 (m, 4H, protons of C2, C9 and C4), 7.27–7.33 (m,
4H, protons of C13, C10 and C14), 7.16–7.21 (m, 2H, protons of
C12), 3.69 (s, 2H, –NH2), 2.22 (s, 3H, protons of C15). 13C NMR
(400 MHz, CDCl3, δ, ppm): 141.17 (C6), 141.12 (C7), 139.71 (C11),
131.02 (C2), 129.23 (C1), 128.85 (C9), 128.59 (C13), 128.34 (C8),
127.76 (C12), 127.24 (C10), 126.94 (C14), 126.43 (C3), 126.18
(C4), 122.77 (C5), 18.09 (C15). Anal. Calcd for C19H17N (%): C,
87.99; H, 6.61; N, 5.40. Found (%): C, 88.01; H, 6.56; N, 5.38.
Scheme 1. Synthesis of α-diimine Pd(II) complexes C1–C3.
C34H36Cl2N2Pd (%): C, 62.83; H, 5.58; N, 4.31. Found (%): C, 62.69; H,
5.48; N, 4.28. IR (KBr, cmꢀ1): 1647 (νC–N). Single crystals of complex
rac-C1 suitable for X-ray analysis were obtained at room temperature
by dissolving the palladium complex in CH2Cl2, followed by double
layering of the resulting solution with n-hexane.
General procedure for Suzuki cross-coupling reaction (scheme SI-2)
Aniline halide (2.00 mmol), arylboronic acid (2.1 mmol or 4.2 mmol),
K2CO3 (4.00 mmol) and Pd catalyst (0.04 mmol) were placed in a
100 ml flask and stirred at room temperature for 12 h in the pres-
ence of PEG-400–H2O. The mixture was extracted three times with
10 ml of diethyl ether. The combined organic phase was dried over
MgSO4, filtered and the solvent was removed. The residue was pu-
rified by chromatography on silica gel with petroleum ether–ethyl
acetate to afford the product.
Characterization of cross-coupling products (aryl-substituted
aniline derivatives)
The structures and numbering schemes for compounds a–h are
given in Fig. 2.
2-Methyl-6-ethyl-4-phenylaniline (a): oily liquid (0.36 g, 85% yield).
1H NMR (400 MHz, CDCl3, δ, ppm): 7.52–7.55 (m, 2H, protons of C8),
7.35–7.39 (m, 2H, protons of C9), 7.36 (t, J = 8.0 Hz, 1H, proton of
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Appl. Organometal. Chem. 2015, 29, 771–776

New Pd(II) chiral α-diimine-catalyzed Suzuki cross-coupling reaction
2-Chloro-4,6-diphenylaniline (f): oily liquid (0.45 g, 81% yield). 1H
NMR (400 MHz, CDCl3, δ, ppm): 7.43–7.45 (m, 3H, protons of C2
and C8), 7.38–7.39 (m, 3H, protons of C4 and C9), 7.28–7.32 (m,
4H, protons of C13, C14 and C10), 7.17–7.20 (m, 2H, protons of
C12), 4.11 (s, 2H, –NH2). 13C NMR (400 MHz, CDCl3, δ, ppm):
139.80 (C7), 139.61 (C6), 138.78 (C11), 131.51 (C9), 129.00 (C13),
128.95 (C3), 128.81 (C8), 128.73 (C12), 127.74 (C10), 127.47
(C14), 126.87 (C2), 126.73 (C1), 126.32 (C4), 119.90 (C5). Anal.
Calcd for C18H14ClN (%): C, 77.28; H, 5.04; N, 5.01. Found (%): C,
77.30; H, 5.01; N, 4.98.
chromatography on silica gel with petroleum ether–ethyl acetate
(Scheme SI-1). Compounds L1–L3 were well characterized using
IR and NMR spectroscopies and elemental analysis.
The corresponding palladium dichloride complexes C1–C3 were
obtained by the reaction of ligands L1–L3 with (MeCN)2PdCl2 in
CH2Cl2 at ambient temperature (Schemes 1 and SI-1). These com-
plexes were characterized using IR spectroscopy and elemental
analysis. The elemental analysis of complexes C1–C3 fits the molec-
ular structures obtained from the X-ray structural studies (see
below).
2,3-Dimethyl-4,6-diphenylaniline (g): oily liquid (0.40 g, 74% yield).
1H NMR (400 MHz, CDCl3, δ, ppm): 7.47–7.50 (m, 3H, protons of C4
and C12), 7.38–7.40 (m, 4H, protons of C9 and C8), 7.16–7.32 (m,
4H, protons of C10, C14 and C13), 3.74 (s, 2H, –NH2), 2.24 (s, 3H, pro-
tons of C16), 2.18 (s, 3H, protons of C15). 13C NMR (400 MHz, CDCl3,
δ, ppm): 140.76 (C6), 139.82 (C11), 138.78 (C7), 131.72 (C8), 129.13
(C13), 128.78 (C10), 128.05 (C9), 127.56 (C13), 127.14 (C2), 126.90
(C7), 127.42 (C1), 126.58 (5), 121.34 (C4), 20.01 (C16), 18.27 (C15).
Anal. Calcd for C20H19N (%): C, 87.87; H, 7.01; N, 5.12. Found (%):
C, 87.82; H, 6.97; N, 5.11.
X-ray crystallographic studies
The molecular structures of Pd(II) complexes C1–C3 were confirmed
using single-crystal X-ray diffraction. The coordination geometry
around the metal center is square planar for complexes C1–C3.
The structures of complexes C2 and C3 (Fig. SI-1, supporting
information)[34] have been reported previously.
The molecular structure of complex rac-C1 was determined and
the corresponding diagram is shown in Figure 3. Selected bond dis-
tances and angles are summarized in Table SI-2. The results of the
X-ray structure analysis of complex rac-C1 show that substituents
have a significant influence on coordination geometry. The struc-
ture of rac-C1 shows the expected bidentate coordination of the
diimine nitrogen atoms to the palladium center, forming distorted
square-planar coordination environments. In the solid state, the
most interesting feature of the ligand is the conformation of the
substituents attached to N1 and N2. These groups are rotated
about 180° from the position they must occupy to chelate metal
Pd. The two imino C¼N bonds have typical double bond character
with C9¼N1 bond lengths of 1.290 Å. The structure is similar to
those reported in the literature for other similar [PdCl2(α-diimine)]
and [NiBr2(α-diimine)] compounds characterized using X-ray dif-
fraction: {[4-F-2,6-Ph2C6H2N¼C(Me)]2PdCl2} (C2)[34] and {[4-Me-2-
PhCHMeC6H3N¼C(Me)]2NiBr2} (Fig. 1(a)).[31] In fact, the Pd–N and
Pd–Cl bond distances in rac-C1 (1.985–2.023 and 2.285–2.307 Å)
are similar to those reported for complex C2 (2.027 and 2.2732 Å).
3-Chloro-2-methyl-4,6-diphenylaniline (h): oily liquid (0.45 g, 76%
1
yield). H NMR (400 MHz, CDCl3, δ, ppm): 7.47–7.49 (m, 3H, pro-
tons of C4 and C8), 7.37–7.39 (m, 4H, protons of C9 and C13),
7.27–7.33 (m, 2H, protons of C10 and 14), 7.16–7.22 (m, 2H, pro-
tons of C12), 4.02 (s, 2H, –NH2), 2.12 (s, 3H, protons of C15). 13C
NMR (400 MHz, CDCl3, δ, ppm): 139.72 (C6), 139.41 (C11), 138.55
(C7), 129.81 (C2), 129.21 (C1), 128.95 (C3), 128.81 (C13), 128.73
(C9), 127.84 (C13), 127.43 (C8), 126.83 (C14), 126.71 (C10), 126.24
(C4), 120.10 (C5), 18.51 (C15). Anal. Calcd for C19H16ClN (%): C,
77.68; H, 5.49; N, 4.77. Found (%): C, 77.61; H, 5.53; N, 4.79.
X-ray structure determinations
Single crystals of complexes C1–C3 suitable for X-ray analysis were
obtained by dissolving the palladium complex in CH2Cl2, followed
by slow layering of the resulting solution with n-hexane. Data were
collected at 296(2) K using a Bruker SMART APEX diffractometer
with a CCD area detector and a graphite monochromator utilizing
Mo Kα radiation (λ = 0.71073 Å). The determination of crystal class
and unit cell parameters was carried out using the SMART program
package. The raw frame data were processed using SAINT and
SADABS to yield the reflection data file. The structures were solved
using the SHELXTL program. Refinement was performed on F2 an-
isotropically for all non-hydrogen atoms using the full-matrix
least-squares method. The hydrogen atoms were placed at the cal-
culated positions and were included in the structure calculation
without further refinement of the parameters. Crystal data, data col-
lection, and refinement parameters are listed in Table SI-1.
Results and discussion
Synthesis and characterization of Pd(II) complexes
Reaction of p-methylaniline with styrene at elevated temperature
(160°C) in the presence of CF3SO3H catalyst resulted in the corre-
sponding 4-methyl-2-sec-phenethylaniline 1. The α-diimine ligand
L1 was prepared by the condensation of 2 equiv. of the aniline with
1 equiv. of 2,3-butanedione, usually in the presence of a formic acid
catalyst (Scheme 1). The terphenyl α-diimine ligands L2 and L3
were subsequently prepared by refluxing a solution of 2,3-
butanedione/acenaphthoquinone and 4-fluoro-2,6-diphenylaniline
in benzene with catalytic p-toluenesulfonic acid, and purified by
Figure 3. Molecular structure of the chiral Pd(II) catalyst rac-C1 with 50%
probability level. Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and angles (°) for complexes: Pd1–N1, 1.985(13); Pd1–N2, 2.023
(14); Pd1–Cl1; 2.307(4); Pd1–Cl2, 2.285(4); N1–C9, 1.290(9); N2–C18, 1.24(2);
N1–C1, 1.476(19); N1–C16, 1.31(2); Cl2–Pd1–Cl1, 91.09(18); N2–Pd1–Cl2,
96.0(4); N2–Pd1–Cl1, 168.8(4); N1–Pd1–Cl1, 95.7(4); N1–Pd1–N2, 78.2(5);
C1–N1–Pd1, 124.8(10); C16–N1–Pd1, 121.1(10).
Appl. Organometal. Chem. 2015, 29, 771–776
Copyright © 2015 John Wiley & Sons, Ltd.
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F. Wang et al.
In addition, the Cl–Pd–Cl angle (91.09° for rac-C1) is also approxi-
mately the same as that for complex C2 (91.91°).
amount of water to increase the K2CO3 solubility can increase the
catalytic activity.
Using the optimized reaction conditions, we attempted to apply
the chiral catalyst rac-C1 to Suzuki cross-coupling reactions of
various aniline halides and arylboronic acids. Table 2 indicates that
the cross-coupling reactions of all aniline bromides proceed
smoothly to produce the desired phenyl-substituted aniline com-
pounds in high yields (79–95%). For example, reactions of
4-bromoaniline, 4-bromo-2-methylaniline, 4-bromo-2-ethylaniline,
4-bromo-2,6-dimethylaniline, 4-bromo-2-methyl-6-ethylaniline, 4-
bromo-2,6-diethylaniline and 4-bromo-2,6-diisopropylaniline as p-
bromoaniline derivatives with phenylboronic acid proceed well
and afford the desired products in 95, 90, 89, 86, 85, 84 and
81% isolated yields, respectively (Table 2, entries 1–6; Table 1,
entry 4). In addition, reactions of 2-bromoaniline, 2-bromo-4-
methylaniline and 2-bromo-4,6-dimethylaniline as o-bromoaniline
derivatives with phenylboronic acid proceed well and afford the
desired products in 85, 82 and 79% isolated yields, respectively
(Table 2, entries 7–9). The results indicate that the sterically hin-
dered aniline bromide prevents the reaction, and the catalytic ac-
tivity reduces slightly with increasing steric hindrance of the
aniline bromides.
Suzuki cross-coupling reaction
To examine the effect of the catalysts on the Suzuki reaction, the cross-
coupling reaction of 4-bromo-2,6-dimethylaniline and phenylboronic
acid was chosen as a model reaction. The reaction was conducted with
K2CO3 as base at room temperature for 12 h in PEG-400–H2O. The re-
sults are summarized in Table 1.
Table 1 reveals that the α-diimine Pd(II) complexes are effective
as catalysts for Suzuki cross-coupling. For comparison, the cross-
coupling reaction of 4-bromo-2,6-dimethylaniline and phenylboronic
acid was also performed with PdCl2, (MeCN)2PdCl2, Pd(OAc)2 and α-
diimine Pd(II) complexes under the established conditions. In the ab-
sence of ligands, only 43% yield of 2,6-dimethyl-4-phenylaniline is
obtained using PdCl2 (Table 1, entry 1). The yield of product increases
slightly when using (MeCN)2PdCl2 (50%; Table 1, entry 2), and the de-
sired product is afforded in 69% isolated yield with a regularly used
Pd(OAc)2/K2CO3 catalytic system at room temperature. However, in
the presence of the α-diimine palladium dichloride complexes, the
yield of product increases dramatically, to a range of 85–87% (Table 1,
entries 4–6). This is explained in that the activity increases because of
the increased reactivity and stability of the metal catalysts by use of
increasing efficacious supporting ligands.[10]
Having the most active precatalyst rac-C1 in hand, the solvent
was then optimized, employing the cross-coupling between
phenylboronic acid and 4-bromo-2,6-dimethylaniline as the bench-
mark reaction (Table 1, entries 6–9). Due to the steric hindrance and
solubility of substrates, reactions in neat water appear to be more
sensitive to steric bulk on the aryl bromide than in the PEG-400–
H2O system. Entries 7 and 9 show that the reaction does not pro-
ceed well when the reaction is conducted in PEG-400 alone or in
H2O alone. Surprisingly, the reaction proceeds smoothly, producing
the optimal yield, when PEG-400–H2O (30 ml/1.0 ml) is used as the
solvent (Table 1, entry 6 versus entries 7–9). The cross-coupling re-
action with the catalyst system in the process of adding a small
4-Chloroaniline and 4-fluoroaniline do not give products (Table 2,
entries 11 and 12). However, the catalyst enables the cross-coupling
of 4-bromoaniline and 4-iodoaniline with phenylboronic acid in
very high yields (>95%; Table 2, entries 6 and 10). When the reac-
tion is conducted at 100°C, a trace amount of product is observed
(Table 2, entry 13), which may be due to loss of activity of the poi-
soned catalyst rac-C1 in PEG-400–H2O at high temperature. There-
fore, it is demonstrated that the catalytic systems have great
Table 2. Suzuki cross-coupling reaction of various aniline halides and
arylboronic acids with catalyst rac-C1a
R
R
rac-C1
B(OH)2
X
K2CO3, PEG-400/H2O
NH2
NH2
Entry Arylboronic Aniline halide
acid
T
(°C)
Product
Product
yield
Table 1. Effect of catalyst and solvent on Suzuki cross-coupling
(%)b
R
X
R
Ar
reactiona
1
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
2,6-di-iPr 4-Br r.t. 2,6-di-iPr 4-Ph
2,6-di-Et 4-Br r.t. 2,6-di-Et 4-Ph
2-Et, 6-Me 4-Br r.t. 2-Et, 6-Me 4-Ph
81
84
2
Pd-Cat.
B(OH)2
Br
NH2
NH2
3
85
K2CO3, PEG-400/H2O
4
2-Et
2-Me
H
4-Br r.t.
4-Br r.t.
4-Br r.t.
2-Et
2-Me
H
4-Ph
4-Ph
4-Ph
89
Entry
Catalyst
Solvent
Yield
5
90
(%)b
6
95
PEG-400 (ml)
H2O (ml)
7
4,6-di-Me 2-Br r.t. 4,6-di-Me 2-Ph
79
1
2
3
4
5
6
7
8
9
PdCl2
30
30
30
30
30
30
31
15.5
0
1
1
43
50
69
85
87
86
46
64
12
8
4-Me
H
2-Br r.t.
2-Br r.t.
4-I r.t.
4-Cl r.t.
4-F r.t.
4-Br 100
4-Me
H
2-Ph
2-Ph
4-Ph
4-Ph
4-Ph
4-Ph
82
(MeCN)2PdCl2
Pd(OAc)2
C2
9
85
1
10
11
12
13
H
H
96
1
H
H
Trace
Trace
Trace
78
C3
1
H
H
rac-C1
rac-C1
rac-C1
rac-C1
1
H
H
0
14c NaphB(OH)2 2,6-di-Me 4-Br r.t. 2,6-di-Me 4-Naph
15c NaphB(OH)2 4,6-di-Me 2-Br r.t. 4,6-di-Me 2-Naph
15.5
31
65
aReaction conditions: Pd (0.04 mmol); aniline halide (2.00 mmol);
phenylboronic acid (2.1 mmol); K2CO3 (4.0 mmol); 12 h; solvent = PEG-
400–H2O (30 ml/1.0 ml).
aReaction conditions: Pd (0.04 mmol); 4-bromo-2,6-dimehylaniline (2.00
mmol); phenylboronic acid (2.10 mmol); K2CO3 (4.0 mmol); 12 h; room
temperature.
bIsolated yield.
bIsolated yield.
c1-Naphthylboronic acid (2.1 mmol).
wileyonlinelibrary.com/journal/aoc
Copyright © 2015 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2015, 29, 771–776

New Pd(II) chiral α-diimine-catalyzed Suzuki cross-coupling reaction
tolerance to a wide range of sensitive functional groups, such as F,
Cl and NH2, on aniline at room temperature.
activities of the α-diimine Pd(II) complexes in the Suzuki cross-
coupling reaction have a close correlation with the steric and elec-
tronic characteristics of the aniline bromides, and the catalytic activ-
ity reduces slightly with increasing steric hindrance of the aniline
bromides.
The cross-coupling of aniline bromides and 1-naphthylboronic
acid in PEG-400–H2O system was also studied at room temperature.
Entries 14 and 15 of Table 2 indicate that the cross-coupling reactions
of 4-bromo-2,6-dimethylaniline and 2-bromo-4,6-dimethylaniline
proceed smoothly to produce the desired 1-naphthyl-substituted
aniline products in 78 and 65% isolated yields, respectively. Due to
the steric hindrance and conjugation effect on the arylaniline, reac-
tions with phenylboronic acid appear more efficient than with 1-
naphthylboronic acid, as 2-bromo-4,6-dimethylaniline gives 79% of
the cross-coupling product with phenylboronic acid, while the yield
with 1-naphthylboronic acid is up to 65% (Table 2, entries 7 and 15).
Various aniline dibromides containing electron-withdrawing
Conclusions
Three α-diimine Pd(II) complexes containing chiral sec-phenethyl
and phenyl groups were prepared. These complexes were efficient
in catalyzing Suzuki–Miyaura cross-coupling reactions between var-
ious aniline halides and phenylboronic acids in PEG-400–H2O at
room temperature. Among a series of aniline halides (F, Cl, Br and
I), rac-C1 did not catalyze the cross-coupling of aniline chlorides
and fluorides but efficiently catalyzed the cross-coupling of aniline
bromides and iodides with phenylboronic acid. Interestingly, the
sterically hindered aniline bromide prevented the reaction, and
the catalytic activity reduced slightly with increasing steric hin-
drance of the aniline bromides. In addition, a series of new bulky
diphenyl-substituted aniline compounds were synthesized.
i
n
groups (F and Cl) and electron-donating groups (Me, Et, Pr, Bu)
were tested for the cross-coupling reaction using chiral catalyst
rac-C1 at room temperature (Table 3). The results show that the re-
actions give a series of new bulky diphenyl-substituted aniline com-
pounds in moderate yields, which is due to the bulkiness of
obstacles on the aryl ring of aniline (Table 3, entries 1–10).
We applied the chiral catalyst rac-C1 to the cross-coupling reac-
tion of phenylboronic acid with fluorochlorobromo-substituted an-
iline because fluoroaniline and chloroaniline do not react as evident
from Table 2. The reaction of 2,6-dibromo-3-chloro-4-fluoroaniline
with phenylboronic acid proceeds well and affords the correspond-
ing triphenyl products in 79% isolated yield (Table 3, entry 10).
Also, the reactions of 2,4-dibromo-6-chloroaniline, 2,4-dibromo-3-
chloro-2-methylaniline, 2,6-dibromo-4-chloroaniline and 2,6-dibro-
mo-4-fluoroaniline as halide-substituted aniline dibromides with
phenylboronic acid proceed well and afford the desired products
in 81, 77, 76 and 78% isolated yields, respectively (Table 3, entries 1,
2, 5 and 9). In addition, we studied the reactions of 2,4-dibromo-6-
methylaniline, 2,4-dibromo-5,6-dimethylaniline, 2,6-dibromo-4-
methylaniline, 2,6-dibromo-4-isopropylaniline and 2,6-dibromo-
4-butylaniline at room temperature. The desired triphenyls are
isolated in 75, 74, 72, 72 and 70% isolated yields, respectively, after
12 h (Table 3, entries 3, 4, 6–8). The data indicate that the catalytic
Acknowledgements
The authors are grateful to Tosoh-Finechem Co. Ltd for donating
the chemicals. The NMR measurements were made at the Natural
Science Center for Basic Research and Development (N-BARD), Hi-
roshima University.
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Supporting information
Additional supporting information may be found in the online ver-
sion of this article at the publisher’s web site.
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Appl. Organometal. Chem. 2015, 29, 771–776