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Table 1
Suzuki coupling of aryl halides with phenyl boronic acid catalyzed by complexes 1 and 2a.
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Entry
X
R
Catalyst
(mol% Pd)
Yieldb (%)
1
2
3
4
5
6
7
8
Br
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
H
H
1 (0.5)
2 (0.5)
1 (0.5)
2 (0.5)
Pd(OAc)2/ImeoHCl (1/2)
2 (0.5)
2 (0.1)
2 (0.1)
2 (0.05)
2 (0.5)
97
99
95
98
87
96
98
99
99
13
32
86
p-CH3
p-CH3
p-CH3
o-CH3
p-COMe
p-NO2
p-NO2
H
9
10
11
12
H
p-NO2
2 (2.0)
2 (1.0)
a
Reaction conditions: aryl halides (0.5 mmol), PhB(OH)2 (0.75 mmol), Cs2CO3
(0.75 mmol), dioxane (5 mL), 100 °C, 12 h.
b
Isolated yields.
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bulky, benzannulated N-heterocyclic carbene with unusual intramolecular
C\H⋯Pd and Ccarbene⋯Br interactions and their catalytic activities, Organometallics
25 (2006) 3267–3274.
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Pd(II), Ni(II) complexes of N, N′-bis-(2,2-diethoxyethyl)imidazole-2-ylidene:
synthesis, structures, and their catalytic activity towards Heck reaction, J. Organomet.
Chem. 693 (2008) 3729–3740.
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rich cis-palladium(II) complexes with phosphine and carbene ligands as catalytic
precursors in Suzuki coupling reactions, Chem. Eur. J. 15 (2009) 405–417.
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catalysts bearing N-heterocyclic carbene ligands for the ring-opening metathesis
polymerization of cyclooctene, Adv. Synth. Catal. 344 (2002) 749–756.
[19] Characterization data for 1: m.p.=255–257 °C. Found (calcd) % for C35H31I2N2O2PPd:
C, 46.82 (46.56); H, 3.18 (3.46); N 3.35 (3.10). IR (KBr, cm−1): 2925, 1611, 1509,
1432, 1314, 1284, 1247, 1167, 1092, 1023, 831, 746, 728, 692, 679. ESI-MS (M-I)+
m/z: 775; 1H NMR (400 MHz, CDCl3, ppm): 7.91 (d, 4H, Ar–H), 7.42 (m, 6H, Ar–H),
7.26–7.34 (m, 11H, Ar–H), 7.05 (d, 4H, Ar–H), 3.92 (s, 6H, \OCH3).
[20] Characterization data for 2: m.p. 202–203 °C. Found (calcd) % for C38H37I2N2O2-
PPd: C, 48.63 (48.30); H, 3.67 (3.95); N 3.21 (2.96). IR (KBr, cm−1): 2922,
1609, 1511, 1442, 1246, 1118, 1174, 1095, 1023, 835, 807, 728, 709, 682. ESI-
MS (M-I)+ m/z: 818; 1H NMR (400 MHz, CDCl3, ppm): 7.93 (d, 4H, Ar–H),
7.26–7.31 (m, 8H, Ar–H), 7.06 (m, 10H, Ar–H), 3.93 (s, 6H, \OCH3), 2.33 (s, 9H,
\CH3).
such as 4-bromoacetophenone and 4-bromonitrobenzene, they could
be coupled very efficiently with a catalytic loading as low as 0.1 mol%
(entries 7–8). The catalytic loadings could be lowered to 0.05 mol%
without loss of activity (entry 9). We next investigated Suzuki cou-
pling of chlorobenzene under the same reaction conditions. However,
complex 2 was almost inactive under the above reaction conditions
(entry 10). Increasing catalyst loading to 2 mol% only gave 32% yield
(entry 11). For activated chlorides such as 4-chloronitrobenzene,
the yield of the coupled product could reach 86% by using 1 mol% of
2 (entry 12).
In conclusion, two new trans/cis N-heterocyclic carbene–phosphine
palladium(II) complexes have been prepared from the reaction of the
corresponding NHC dimers with phosphine ligands. Single-crystal
X-ray analysis confirms that there are intermolecular C\H⋯I and
C\H⋯O hydrogen bonds in the crystals of 1–2. These complexes are
efficient catalysts for the Suzuki reaction of aryl bromides.
Acknowledgments
[21] C. Horn, M. Scudder, I. Dance, Contrasting crystal supramolecularity for
[Fe(phen)3]I8 and [Mn(phen)3]I8: complementary orthogonality and complemen-
tary helicity, CrystEngComm 1 (2001) 1–8.
[22] L. Brammer, E.A. Bruton, P. Sherwood, Understanding the behavior of halogens as
hydrogen bond acceptors, Cryst. Growth Des. 1 (2001) 277–290.
We are grateful to the National Natural Science Foundation of China
(No. 20902043) and the Natural Science Foundation of Henan Province
and Henan Education Department, China (Nos. 102300410220 and
2009B150019) for financial support of this work.
[23] A. Nangia, Database research in the crystal engineering, CrystEngComm 4 (2002)
93–101.
[24] General procedure for the Suzuki reaction: Prescribed amounts of catalyst, aryl
halide (0.5 mmol), phenyl boronic acid (0.75 mmol), Cs2CO3 (0.75 mmol)
and dioxane (5.0 mL) were placed in a Schlenk tube under nitrogen. The mixture
was heated at 100 °C for 12 h, then cooled and quenched with water. The mixture
was extracted three times with CH2Cl2, then the combined organic layer was
washed with water, dried (MgSO4), and evaporated to dryness. The products were
isolated by flash chromatography on silica gel using petroleum ether as eluent and
analyzed by 1H NMR.
[25] C. Xu, J.F. Gong, G. Tao, Y.H. Zhang, Y.J. Wu, Cyclopalladated ferrocenylimine
complexes with dicyclohexylphosphinobiphenyl ligands: synthesis, crystal
structures and their use as highly efficient catalysts for Suzuki reaction of aryl
chlorides, J. Mol. Catal. A: Chem. 279 (2008) 69–76.
Appendix A. Supplementary material
CCDC 841990–841991 contain the supplementary crystallographic
data for 1–2, respectively. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.
can be found, in the online version, at doi:10.1016/j.inoche.2011.12.
009.
[26] C. Xu, Z.Q. Wang, Y.P. Zhang, X.M. Dong, X.Q. Hao, W.J. Fu, B.M. Ji, M.P. Song, Synthesis
and structural characterization of palladacycles with polydentate ligands via the
stepwise coupling route: palladacycles containing halide as efficient catalysts and
substrates, Eur. J. Inorg. Chem. (2011) 4878–4888.
[27] C. Xu, Y.X. Lu, X.H. Lou, Z.Q. Wang, W.J. Fu, B.M. Ji, Tri-p-tolylphosphine-
cyclopalladated ferrocenylpyrimidine complexes: synthesis, crystal structures,
catalytic activity, and a palladacycle cocrystallization adduct, Trans. Met. Chem.
36 (2011) 637–642.
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