Phosphine-free hydrazone-Pd complex as the catalyst precursor for a Suzuki-Miyaura reaction under mild aerobic conditions

Article abstract of DOI:10.1021/jo048107i

(Chemical Equation Presented) Glyoxal bis(N-methyl-N-phenylhydrazone) (1) and its related compounds such as 2-pyridinecarboxaldehyde N-methyl-N- phenylhydrazone (3) were prepared and examined as ligands for the Suzuki-Miyaura cross-coupling reaction of aryl halides and arylboronic acids. We found phosphine-free catalysts, such as Pd(OAc)₂/hydrazone ligand 1 or 3, to be efficient catalysts for a variety of substrates to produce the coupling products in good yields.

Full text of DOI:10.1021/jo048107i

Phosphine-Free Hydrazone-Pd Complex as the Catalyst
Precursor for a Suzuki-Miyaura Reaction under Mild Aerobic
Conditions
Takashi Mino,* Yoshiaki Shirae, Masami Sakamoto, and Tsutomu Fujita
Department of Applied Chemistry and Biotechnology, Faculty of Engineering, Chiba University,
1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
tmino@faculty.chiba-u.jp
Received October 26, 2004
Glyoxal bis(N-methyl-N-phenylhydrazone) (1) and its related compounds such as 2-pyridine-
carboxaldehyde N-methyl-N-phenylhydrazone (3) were prepared and examined as ligands for the
Suzuki-Miyaura cross-coupling reaction of aryl halides and arylboronic acids. We found phosphine-
free catalysts, such as Pd(OAc)2/hydrazone ligand 1 or 3, to be efficient catalysts for a variety of
substrates to produce the coupling products in good yields.
Introduction
In the past few years, great advances have been made
in developing active and efficient catalysts by modifying
traditional ligands and discovering new ones. Sterically
demanding, electron-rich phosphines, such as tri-tert-
butylphosphine, have shown high cross-coupling activi-
ties for a variety of substrates.4 In the meantime, new
types of ligands, such as heterocyclic carbenes,5 imine and
amine palladacycles,6 oxime palladacycles,7 diazabuta-
dienes,8 2-aryl-2-oxazolines,9 and simple amines,10 have
also emerged for use in the Suzuki-Miyaura cross-
coupling reaction.
The palladium-catalyzed Suzuki-Miyaura cross-cou-
pling reaction of aryl halides with arylboronic acids and
esters has become a common and convenient synthetic
method in organic chemistry for biaryl compounds.1 The
reaction has been applied to many areas,2 including
natural product synthesis.3 Triarylphosphine/Pd com-
plexes are commonly used as catalysts for the reaction.1a
(1) For reviewes, see: (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995,
95, 2457. (b) Stanforth, S. P. Tetrahedron 1998, 54, 263. (c) Suzuki, A.
Metal-Catalyzed Cross-Coupling Reactions; Diederich, F., Stang, P. J.,
Eds.; Wiley-VCH: Weinheim, Germany, 1998; pp 49-97. (d) Suzuki,
A. J. Organomet. Chem. 1999, 576, 147. (e) Llord-Williams, P.; Giralt,
E. Chem. Soc. Rev. 2001, 30, 145.
(2) For examples, see: (a) Patel, M.; Rodgers, J. D.; McHugh, R. J.,
Jr.; Johnson, B. L.; Cordova, B. C.; Klabe, R. M.; Bacheler, L. T.;
Erickson-Viitanen, S.; Ko, S. S. Bioorg. Med. Chem. Lett. 1999, 9, 3217.
(b) Wang, W.; Xiong, C.; Yang, J.; Hruby, V. J. Terahedron Lett. 2001,
42, 7717. (c) Vaz, B.; Rosana, R.; Nieto, M.; Paniello, A. I.; de Lera, A.
R. Terahedron Lett. 2001, 42, 7409. (d) Schomaker, J. M.; Delia, T. J.
J. Org. Chem. 2001, 66, 7125. (e) Wong, K.-T.; Huang, T. S.; Lin, Y.;
Wu, C.-C.; Lee, G.-H.; Peng, S.-M.; Chou, C. H.; Su, Y. O. Org. Lett.
2002, 4, 513.
(3) For examples, see: (a) Hobbs, P. D.; Upender, V.; Dawson, M. I.
Synlett 1997, 965. (b) Nicolaou, K. C.; Li, H.; Boddy, C. N. C.;
Ramanjulu, J. M.; Yue, T.-Y.; Natarajan, S.; Chu, X.-J.; Brase, S.;
Rubsam, F. Chem. Eur. J. 1999, 5, 2584. (c) Nicolaou, K. C.; Koumbis,
A. E.; Takayanagi, M.; Natarajan, S.; Jain, N. F.; Bando, T.; Li, H.;
Hughes, R. Chem. Eur. J. 1999, 5, 2622. (d) Kamikawa, K.; Watanabe,
T.; Daimon, A.; Uemura, M. Tetrahedron 2000, 56, 2325.
The synthesis and properties of palladium complexes
with hydrazone ligands have been previously reported,11
(4) (a) Littke, A. F.; Fu, G. C. Angew. Chem., Int. Ed. 1998, 37, 3387.
(b) Littke, A. F.; Dai, C.; Fu, G. C. J. Am. Chem. Soc. 2000, 122, 4020.
(5) (a) Herrmann, W. A.; Elison, M.; Fischer, J.; Kocher, C.; Artus,
G. R. J. Angew. Chem., Int. Ed. 1995, 34, 2371. (b) Weskamp, T.; Bohm,
V. P. W.; Herrmann, W. A. J. Organomet. Chem. 1999, 585, 348. (c)
Bohm, V. P. W.; Gstottmayr, C. W. K.; Weskamp, T.; Herrmann, W.
A. J. Organomet. Chem. 2000, 595, 186. (d) Zhang, C.; Huang, J.;
Trudell, M. L.; Nolan, S. P. J. Org. Chem. 1999, 64, 3804. (e) Zhang,
C.; Trudell, M. L. Terahedron Lett. 2000, 41, 595.
(6) (a) Weissan, H.; Milstein, D. Chem. Commun. 1999, 1901. (b)
Bedford, R. B.; Cazin, C. S. J. Chem. Commun. 2001, 1540.
(7) (a) Alonso, D. A.; Najera, C.; Pacheco, M. C. Org. Lett. 2000, 2,
1823. (b) Botella, L.; Najera, C. Angew. Chem., Int. Ed. 2002, 41, 179.
(8) Grasa, G. A.; Hillier, A. C.; Nolan, S. P. Org. Lett. 2001, 3, 1077.
(9) Tao, B.; Boykin, D. W. Terahedron Lett. 2002, 43, 4955.
(10) (a) Tao, B.; Boykin, D. W. J. Org. Chem. 2004, 69, 4330. (b)
Tao, B.; Boykin, D. W. Terahedron Lett. 2003, 44, 7993.
10.1021/jo048107i CCC: $30.25 © 2005 American Chemical Society
Published on Web 02/16/2005
J. Org. Chem. 2005, 70, 2191-2194
2191

Mino et al.
TABLE 1. Optimization of Reaction Conditions at
Room Temperaturea
TABLE 2. Suzuki-Miyaura Reaction of Aryl Bromide
with Arylboronic Acid at Room Temperature under
Aerobic Conditionsa
entry
base
solvent
Pd source
Pd(OAc)2
yield (%)b
1
2
Ca(OH)2
Na2CO3
K2CO3
Cs2CO3
CsF
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
DMF
59
53
73
88
42
33
48
41
5
59
99d
92d
59d
99d
DMF
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
PdCl2
3
DMF
4
DMF
5
DMF
6
1,4-dioxane
THF
7
8
PhMe
9
DMSO
10
11
12
13
14e
DMAc
DMF-H2Oc
DMF-H2Oc
DMF-H2Oc
DMF-H2Oc
PdCl2(MeCN)2
Pd(OAc)2
a Reaction conditions: 4-bromotoluene (1 mmol), phenylboronic
acid (1.5 mmol), base (2 mmol), solvent (3 mL), Pd-source (0.02
mmol), ligand 1 (0.03 mmol), 3 h. b GLC yields (2-methoxynaph-
thalene as internal standard; an average of two runs). c The
mixture of DMF (2 mL) and H2O (1 mL) was used as a solvent.
d Isolated yields. e This reaction was carried out under Ar.
and we expect hydrazone ligands to have advantages over
phosphine ligands due to their ease of synthesis and air
stability. We report here the Suzuki-Miyaura cross-
coupling reaction using glyoxal bis(N-methyl-N-phenyl-
hydrazone) (1) as a ligand of catalyst precursor.12
Results and Discussion
Optimization of Reaction Conditions. Glyoxal bis-
(methylphenylhydrazone) (1) was easily prepared from
glyoxal and 2 equiv of N-methyl-N-phenylhydrazine in
methanol. Using this hydrazone 1 as ligand, we applied
the coupling of 4-bromotoluene and phenylboronic acid
in the presence of Pd(OAc)2 under an aerobic atmosphere
at room temperature for finding out the optimum reaction
conditions (Table 1). The use of cesium carbonate as a
base led to higher yield for this reaction (entry 4 vs
entries 1-3 and 5). In the presence of cesium carbonate,
many commonly used solvents were tested (entries 4 and
6-10). The etheral solvents such as dioxane and THF or
nonpolar solvent toluene were not effective (entries 6-8).
The DMF-water system was preferred for this reaction
(entry 4 vs entry 11). Other palladium catalysts proved
to be less effective in this reaction (entries 12 and 13).
a Reaction conditions: aryl bromide (1 mmol), phenylboronic
acid (1.5 mmol), Pd(OAc)2 (2 mol %), ligand 1 (3 mmol %), Cs2CO3
(2 mmol), DMF (2 mL), H2O (1 mL), rt, 3 h. b Isolated yield. c This
reaction was carried out in 30 min. d This reaction was carried
out with 4 mol % of Pd(OAc)2 and 6 mol % of ligand 1 in 50 h.
e This reaction was carried out with 4 mol % of Pd(OAc)2 and 6
mol % of ligand 1 in 24 h.
Under argon atmosphere with the Pd(OAc)2/hydrazone
1 system, the reaction also proceeded to 99% at room
temperature (entry 14).
Suzuki-Miyaura Reaction at Room Temperature
under Aerobic Conditions. The effect of varying the
aryl bromide in the Suzuki-Miyaura reactions was
investigated by using phenylboronic acid as the substrate
at room temperature (Table 2). Using 4-substituted and
3-substituted aryl bromides led to good yields of the
(11) (a) Bombieri, G.; Caglioti, L.; Cattalini, L.; Forsellini, E.;
Gasparrini, F.; Graziani, R.; Vigato, P. A. J. Chem. Soc., Chem.
Commun. 1971, 1415. (b) Maresca, L.; Natile, G.; Cattalini, L.;
Gasparrini, F. J. Chem. Soc., Dalton Trans. 1975, 1602. (c) Mino, T.;
Imiya, W.; Yamashita, M. Synlett 1997, 583. (d) Bacchi, A.; Carcelli,
M.; Pelagatti, P.; Pelizzi, C.; Pelizzi, G.; Salati, C.; Sgarabotto, P. Inorg.
Chim. Acta 1999, 295, 171. (e) Mino, T.; Shiotsuki, M.; Yamamoto, N.;
Suenaga, T.; Sakamoto, M.; Fujita, T.; Yamashita, M. J. Org. Chem.
2001, 66, 1795 and references therein.
(12) Preliminary communication: Mino, T.; Shirae, Y.; Sakamoto,
M.; Fujita, T. Synlett 2003, 882.
2192 J. Org. Chem., Vol. 70, No. 6, 2005

Suzuki-Miyaura Reactions under Mild Aerobic Conditions
TABLE 3. Effect of Ligand under Low Catalyst Loading
Suzuki-Miyaura Reaction at Room Temperature under
Aerobic Conditionsa
TABLE 4. Suzuki-Miyaura Reaction of
4′-Chloroacetophenone with Phenylboronic Acid under
Aerobic Conditionsa
entry
1
Pd source/ligand
temp (°C)/time (h)
100/48
yield (%)b
67
Pd(OAc)2 (4 mol %)
1 (6 mol %)
2
3
Pd(OAc)2 (10 mol %)
1 (15 mol %)
Pd(OAc)2 (10 mol %)
3 (15 mol %)
100/8
100/8
66
35
a Reaction conditions: 4-Ac-PhCl (1 mmol), phenylboronic acid
(1.5 mmol), Pd(OAc)2, ligand, Cs2CO3 (2 mmol), DMF (2 mL), H2O
(1 mL). b Isolated yield.
SCHEME 1. Preparation of Palladium Complex 5
SCHEME 2. Suzuki-Miyaura Reaction with 5 as a
Catalyst
a Reaction conditions: 4-Ac-PhBr (1 mmol), phenylboronic acid
(1.5 mmol), Pd(OAc)2 (0.00005 mmol), ligand (0.000075 mmol),
Cs2CO3 (2 mmol), DMF (2 mL), H2O (1 mL), rt. b Determined by
1H NMR with 2-methoxynaphthalene as internal standard.
desired products (entries 1-7). Moreover, 2-substituted
aryl bromide and 1-bromonaphthalene also led to good
yields (entries 8-12). The reaction of 1-bromo-2-meth-
ylnaphthalene with phenylboronic acid resulted in a low
yield (entry 13). The effect of varying the arylboronic
acids was also investigated by using 4-bromotoluene as
the substrate at room temperature (entries 14-18). Using
4-substituted arylboronic acids led to moderate to good
yields of the desired products (entries 14 and 15).
2-Fluorophenylboronic acid and 1-naphthaleneboronic
acid also led to good yields (entries 16 and 18), but
2-formylphenylboronic acid led to a low yield (entry 17).
In addition to substituted aryl bromides, the reactions
with heterocyclic bromides led to the formation of the
desired products in moderate to good yields (entries 19-
21).
Low Catalyst Loading Suzuki-Miyaura Reac-
tion. Under low catalyst loadings with the Pd(OAc)2/
hydrazone 1 system (0.005 mol % Pd) (Table 3, entry 1),
it was necessary to use longer reaction times such as 24
h. We investigated the effect of ligand in the Suzuki-
Miyaura reaction of 4′-bromoacetophenone and phenyl-
boronic acid at room temperature. The reaction with
bishydrazone 2 prepared from 2,3-butanedione resulted
in a low yield (entry 2). On the other hand, similar
monohydrazone type ligand 3 gave a quantitative yield
with high turnover number (TON ) 19 800) after 24 h
(entry 3). Under the same conditions the desired product
was obtained in high yield with high turnover frequency
(TOF ) 5533 h-1) in only 3 h (entry 4). When the reaction
was carried out with ligand 4, a poor result was obtained
(entry 5).
Suzuki-Miyaura Reaction of Aryl Chloride. We
also attempted the coupling of 4′-chloroacetophenone and
phenylboronic acid in the presence of 4 mol % of Pd(OAc)2
using ligand 1 under an aerobic atmosphere at 100 °C.
It was necessary to use longer reaction times (entry 1).
With 10 mol % of Pd(OAc)2 the reaction gave a good yield
of the desired product after 8 h (entry 2). Unfortunately
ligand 3 was not effective in this reaction (entry 3).
Synthesis and Characterization of the Hydra-
zone-Palladium Complex. To investigate the nature
of the catalyst structure, a single red crystal of the Pd-
complex 5 was obtained from the reaction of glyoxal bis-
(methylphenylhydrazone) (1) and PdCl2(MeCN)2 in ace-
tonitrile under air (Scheme 1).
X-ray analysis of 5 showed the hydrazone-derived
palladacycle and the palladium atom bound to two
nitrogen atoms on the ligand. Additionally, the Pd-N
bonds are asymmetric with a difference of 0.262 Å. When
2 mol % of complex 5 was used as catalyst, the reaction
of 4-bromotoluene and phenylboronic acid was proceeded
smoothly in 99% yield for 3 h at room temperature
(Scheme 2).
Conclusions
It can be concluded that the Suzuki-Miyaura reaction
of aryl bromide and arylboronic acids can be performed
under mild phosphine-free conditions, based on Pd(OAc)2/
hydrazone 1 and its related compounds with cesium
carbonate in the DMF-water system under an aerobic
atmosphere at room temperature. Under low catalyst
loading conditions, ligand 3 gave a high turnover number
J. Org. Chem, Vol. 70, No. 6, 2005 2193

Mino et al.
3H), 6.91 (t, J ) 6.9 Hz, 1H), 7.24-7.40 (m, 7H), 7.49 (s, 1H),
7.69 (d, J ) 7.8 Hz, 2H); 13C NMR (CDCl3) δ 33.4, 115.6, 120.9,
126.4, 128.1, 129.0, 129.4, 132.2, 137.1, 148.2; EI-MS m/z (rel
intensity) 210 (M+, 100).
Bishydrazone-Pd-Catalyzed Suzuki-Miyaura Reac-
tion of Aryl Bromide with Arylboronic Acid. General
procedure: Under an atmosphere of air, aryl halide (1 mmol)
was added to the mixture of arylboronic acid (1.5 mmol),
palladium acetate (0.02 mmol), hydrazone 1 (0.03 mmol), and
Cs2CO3 (2 mmol) in N,N-dimethlyformamide (DMF) (2 mL)
and water (1 mL) at room temperature. The mixture was
stirred and monitored by TLC. In the case of entries 1-10,
Table 1, the yield was determined by GC (Shimadzu GC-14B
using CPB20-m25-025 column) with 2-methoxynaphthalene as
an internal standard. The mixture was diluted with ether and
water. The organic layer was washed with brine, dried over
MgSO4, and concentrated under reduced pressure. The residue
was purified by silica gel chromatography.
FIGURE 1. ORTEP plot of the Pd-complex 5.
2-Methyl-1-phenylnaphthalene (Table 2, entry 13): 24%
as a colorless liquid; 1H NMR (CDCl3) δ 2.23 (s, 3H), 7.21-
7.52 (m, 9H), 7.75-7.84 (m, 2H); 13C NMR (CDCl3) δ 20.8,
124.8, 125.8, 126.2, 127.0, 127.2, 127.8, 128.3, 128.4, 130.2,
132.0, 132.9, 133.1, 138.2, 139.8; EI-MS m/z (rel intensity) 218
(M+); HRMS (EI-MS) m/z calcd for C17H14 218.1096, found
218.1107.
(TON ) 19800) and a high turnover frequency (TOF )
5533 h-1). Pd(OAc)2/hydrazone 1 also shows a reactivity
of the Suzuki-Miyaura reaction with aryl chloride such
as that with 4′-chloroacetophenone at 100 °C.
Experimental Section
Preparation of Palladium Complex 5. A mixture of
hydrazone 1 (0.134 g, 0.5 mmol) in acetonitrile (15 mL) was
added to PdCl2(MeCN)2 (0.130 g, 0.5 mmol) and the mixture
was stirred for 24 h at room temperature. The mixture was
then filtered on Celite and concentrated under reduced pres-
sure. The red solid precipitated and was collected by filtration
and dried in vacuo (0.169 g, 0.41 mmol). Recrystallization from
hexane-chloroform gave 5 as a red solid for X-ray analysis.
Typical Procedure for the Preparation of Ligand. A
mixture of N-methyl-N-phenylhydrazine (1.22 g, 10 mmol) in
MeOH (3 mL) was added to 40 wt % of glyoxal in water (0.725
g, 5 mmol) at 0 °C. The mixture was stirred for 1 h at room
temperature. The yellow solid precipitated and was collected
by filtration, washed with water, and dried in vacuo. Recrys-
tallization from hexane-chloroform gave 1 as a yellow solid
(0.978 g, 3.68 mmol).
Glyoxal bis(N-methyl-N-phenylhydrazone) (1): 74%
yield; mp 216-217 °C; 1H NMR (CDCl3) δ 3.39 (s, 3H), 6.90-
6.96 (m, 2H), 7.30-7.32 (m, 8H), 7.51 (s, 2H); 13C NMR (CDCl3)
δ 33.4, 115.6, 120.8, 129.1, 133.8, 147.6; EI-MS m/z (rel
intensity) 266 (M+); HRMS (FAB-MS) m/z calcd for C16H18N4
266.1531, found 266.1508.
1
5: 82% yield; mp 170-171 °C; H NMR (DMSO-d6) δ 3.25
(s, 3H), 3.38 (s, 3H), 6.30-6.45 (m, 2H), 6.80-6.84 (m, 1H),
6.90-6.97 (m, 1H), 7.17-7.21 (m, 1H), 7.22-7.30 (m, 4H),
7.46-7.52 (m, 1H), 7.60-7.64 (m, 1H); 13C NMR (DMSO-d6) δ
33.3, 38.2, 108.7, 119.1, 119.3, 123.3, 125.1, 128.5, 128.9, 129.2,
135.1, 135.5, 137.3, 146.1, 152.7, 153.0; MS (FAB) m/z 406
(M+); HRMS (FAB-MS) m/z calcd for C16H17N435Cl106Pd
406.0180, found 406.0185.
2,3-Butanedion bis(N-methyl-N-phenylhydrazone) (2):
1317% as a light yellow solid; mp 99-100 °C; 1H NMR (CDCl3)
δ 2.30 (s, 6H), 3.24 (s, 6H), 6.93 (tt, J ) 1.0 and 7.3 Hz, 2H),
7.04 (dd, J ) 1.1 and 7.7 Hz, 4H), 7.30 (t, J ) 7.3 Hz, 4H); 13
C
Acknowledgment. This work was supported in part
by Grants-in-Aid for Scientific Research (No. 16750070)
from the Ministry of Education, Culture, Sports, Science
and Technology, Japan. We thank Prof. Katsuyuki
Ogura (Chiba University) for generously sharing the
Bruker DPX-300 system, and Prof. Kentaro Yamaguchi
(Chemical Analysis Center, Chiba University; presently
at Tokushima Bunri University) for performing the
X-ray diffraction analysis of 5.
NMR (CDCl3) δ 16.2, 43.4, 115.9, 120.8, 129.3, 151.4, 162.8;
EI-MS m/z (rel intensity) 294 (M+, 20).
2-Pyridinecarboxyaldehyde N-methyl-N-phenylhydra-
zone (3): 64% as a yellow solid; mp 67-68 °C; 1H NMR
(CDCl3) δ 3.46 (s, 3H), 6.98 (tt, J ) 1.2 and 7.0 Hz, 1H), 7.14
(ddd, J ) 1.1, 1.2 and 6.1 Hz 1H), 7.29-7.45 (m, 4H), 7.61 (s,
1H), 7.68 (dt, J ) 1.6 and 7.9 Hz, 1H), 8.02 (d, J ) 8.1 Hz
1H), 8.53 (qt, J ) 0.7 and 4.9 Hz, 1H); 13C NMR (CDCl3) δ
33.4, 115.6, 119.1, 121.3, 121.9, 129.1, 132.6, 136.2, 147.4,
149.0, 155.9; EI-MS m/z (rel intensity) 211 (M+, 19); HRMS
(FAB-MS) m/z calcd for C13H13N3 211.1109, found 211.1105.
Benzaldehyde N-methyl-N-phenylhydrazone (4):14 54%
Supporting Information Available: 1H and 13C NMR
spectra of all compounds and an X-ray crystallographic file
(CIF) for 5. This material is available free of charge via the
Internet at http://pubs.acs.org.
1
as a white solid; mp 104-105 °C; H NMR (CDCl3) δ 3.42 (s,
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JO048107I
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2194 J. Org. Chem., Vol. 70, No. 6, 2005