Triazole-functionalized N-heterocyclic carbene complexes of palladium and platinum and efficient aqueous Suzuki-Miyaura coupling reaction

Article abstract of DOI:10.1002/asia.201000071

Imidazolium salts bearing triazole groups are synthesized via a copper catalyzed click reaction, and the silver, palladium, and platinum complexes of their N-heterocyclic carbenes are studied. [Ag₄(L1) ₄](PF₆)₄, [Pd(L1)Cl](PF₆), [Pt(L1)Cl](PF₆) (L1=3-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-1- (pyrimidin-2-yl)-1H-imidazolylidene), [Pd₂(L2)₂Cl ₂](PF₆)₂, and [Pd(L2)₂](PF ₆)₂ (L2=1-butyl-3-((1-(pyridin-2-yl)-1H-1,2,3-triazol-4- yl)methyl) imidazolylidene) have been synthesized and fully characterized by NMR, elemental analysis, and X-ray crystallography. The silver complex [Ag ₄(L1)₄](PF₆)₄ consists of a Ag ₄ zigzag chain. The complexes [Pd(L1)Cl](PF₆) and [Pt(L1)Cl](PF₆), containing a nonsymmetrical NCN' pincer ligand, are square planar with a chloride trans to the carbene donor. [Pd ₂(L2)₂Cl₂](PF₆)₂ consists of two palladium centers with CN₂Cl coordination mode, whereas the palladium in [Pd(L2)₂](PF₆)₂ is surrounded by two carbene and two triazole groups with two uncoordinated pyridines. The palladium compounds are highly active for Suzuki-Miyaura cross coupling reactions of aryl bromides and 1,1-dibromo-1-alkenes in neat water under an air atmosphere.

Full text of DOI:10.1002/asia.201000071

DOI: 10.1002/asia.201000071
Triazole-Functionalized N-Heterocyclic Carbene Complexes of Palladium
and Platinum and Efficient Aqueous Suzuki–Miyaura Coupling Reaction
Shaojin Gu,[a] Hui Xu,[a] Na Zhang,[a] and Wanzhi Chen*[a, b]
Abstract: Imidazolium salts bearing tri-
azole groups are synthesized via
copper catalyzed click reaction, and
the silver, palladium, and platinum
complexes of their N-heterocyclic car-
thesized and fully characterized by
NMR, elemental analysis, and X-ray
crystallography. The silver complex
chloride trans to the carbene donor.
[Pd2(L2)2Cl2](PF6)2 consists of two pal-
ladium centers with CN2Cl coordina-
tion mode, whereas the palladium in
a
ACHTUNGTRENNUNG
[Ag4(L1)4]
N
a Ag4
zigzag
[Pd(L2)2]ACHTNUTRGNEUNG(PF6)2 is surrounded by two
benes are studied. [Ag4(L1)4]
G
[Pd(L1)Cl]
containing a
pincer ligand, are square planar with a
R
G
carbene and two triazole groups with
two uncoordinated pyridines. The pal-
ladium compounds are highly active
for Suzuki–Miyaura cross coupling re-
actions of aryl bromides and 1,1-dibro-
mo-1-alkenes in neat water under an
air atmosphere.
[Pd(L1)Cl](PF6), [Pt(L1)Cl](PF6) (L1=
A
U
3-((1-benzyl-1H-1,2,3-triazol-4-yl)meth-
yl)-1-(pyrimidin-2-yl)-1H-imidazolyli-
dene),
[Pd2(L2)2Cl2]
N
Keywords: click chemistry N-
heterocyclic carbenes · palladium ·
platinum · Suzuki–Miyaura reaction
·
[Pd(L2)2]ACHTUNGTRENNUNG(PF6)2 (L2=1-butyl-3-((1-
(pyridin-2-yl)-1H-1,2,3-triazol-4-yl)me-
thyl)imidazolylidene) have been syn-
Introduction
of some biologically related substrates, such as proteins,
have to be performed in an aqueous phase.[3] Recently, a
few examples of the aqueous Suzuki–Miyaura reaction have
been reported.[4] For example, the oxime-derived palladacy-
cle complex was shown to be an efficient catalyst for the
Suzuki–Miyaura reaction of various aryl and heteroaryl
chlorides in water in the presence of tetra-n-butylammoni-
um bromide (TBAB).[5] Buchwald et al. demonstrated that
ligands containing sulfonated groups provide a highly active
catalyst system for Suzuki–Miyaura reaction in an aqueous
environment.[6] Very recently, it was discovered that pincer
CNC complexes of palladium carbenes also display good to
excellent catalytic activities for Suzuki–Miyaura reactions in
neat water.[7]
N-Heterocyclic carbenes (NHCs) are a class of appropri-
ate ligands for aqueous metal-catalyzed transformations
since metal complexes of NHCs show high thermal, air, and
moisture stability.[8] In this context, employing pincer-type li-
gands containing one or more NHC donating groups is a
good strategy since the tridentate coordination fashion
offers an additional stabilizing function.[9] NHC ligands have
higher donating capability and basicity than phosphine and
nitrogen ligands and demonstrate less labile properties than
P- and N-donor ligands. To achieve both high catalytic activ-
ity and stability, mixed tridentate donor ligands that com-
prise strong carbene carbon and relatively labile nitrogen
The development of transition-metal-catalyzed reactions in
an environmentally friendly and cheap reaction media is of
great importance for industrial applications.[1] Water, as a
non-flammable, safe, and cheap solvent compared to organic
solvents, has attracted attention for organic synthesis be-
cause the products may be readily separated from the aque-
ous layer and many reactions proceed with better selectivity
in an aqueous environment.[2] Suzuki coupling between an
organoboronic acid and a halide has been one of the most
widely employed protocols for the manufacture of biphenyls
and terphenyls owing to the good tolerance for various func-
tional groups. Exploration of aqueous catalysts is of impor-
tance not only because of the low cost and environmental
impact of using water, but also since the coupling reactions
[a] S. Gu, H. Xu, Dr. N. Zhang, Prof. Dr. W. Chen
Department of Chemistry
Zhejiang University
Hangzhou 310028 (P. R. China)
Fax : (+86)571-88273314
E-mail: chenwzz@zju.edu.cn
[b] Prof. Dr. W. Chen
State Key Laboratory of Elemento-organic Chemistry
Nankai University
Tianjing 300071 (P. R. China)
Chem. Asian J. 2010, 5, 1677 – 1686
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FULL PAPERS
donor atoms would be effective.[8c,10] Nonsymmetric pincer
ligands containing one or two NHC donors are more appro-
priate since they offer better opportunity to tune their ligat-
ing ability.[11] In this context, we have reported the synthesis
of nonsymmetric CC’C and NNC complexes of nickel and
palladium and their catalytic application in coupling reac-
tions.[12] We envisaged that the implementation of a click re-
action[13] in the synthesis of a functionalized carbene ligand
should lead to a novel ligand that features a carbene carbon
and a labile triazolyl donor. Surprisingly, the use of triazoles
as nitrogen donors in N, C(NHC) ligands has, to the best of
our knowledge, no literature precedent. Herein, we report
(i) the synthesis of a series of NHC ligands using click
chemistry; (ii) Ag, Pd, and Pt complexes of carbene-triazole
ligands; and (iii) the catalytic activity of nonsymmetrical
pincer palladium complexes in neat water.
The imidazolium salts 3a–d, each containing a triazole
group, were prepared via copper-catalyzed Huisgen cycload-
dition of 2a–c with azides in water (Scheme 1).[14] Subse-
quent anion exchange, by the addition of an excess of
NH4PF6, resulted in the isolation of imidazolium salts 3a–d
as white solids in excellent yields. The formation of triazole
was confirmed by the observation of a singlet at 9.11–
8.28 ppm in the H NMR spectra of 3a–d, assigned to the
proton of 1,2,3-triazole ring. The resonance signals of the
imidazolium protons appear at 10.29–9.25 ppm.
1
As shown in Scheme 2, treatment of 3-((1-benzyl-1H-
1,2,3-triazol-4-yl)methyl)-1-(pyrimidin-2-yl)-1H-imidazolium
hexafluorophosphate 3b with Ag2O in acetonitrile at 508C
Results and Discussion
Synthesis of Imidazolium Salts
Imidazolium salts, 3-alkyl-1-(prop-1-ynyl)-1H-imidazolium
bromides 2a–c, were obtained by direct reaction of 3-bro-
moprop-1-yne with the corresponding N-alkylimidazoles
1a–c (Scheme 1). Treatment of 3-bromoprop-1-yne with sol-
utions of 1a–c in dioxane at 1108C overnight led to the pre-
cipitation of the imidazolium salts, which were isolated as
solids for 2b and 2c and an oil for 2a in moderate to good
1
yields (50–78%). H NMR spectra of 2a–c show singlet sig-
nals at 10.25–9.47 ppm and triplet signals at 3.9–3.87 ppm,
characteristic of their acidic imidazolium protons and termi-
nal alkynyl protons, respectively.
Scheme 2. Synthesis of the Ag, Pd, and Pt complexes.
for 6 h afforded the silver-NHC
complex [Ag4(L1)4]ACTHNUTRGNENUG(PF6)4 4b
(L1=3-((1-benzyl-1H-1,2,3-tria-
zol-4-yl)methyl)-1-(pyrimidin-2-
yl)-1H-imidazolylidene).
The
formation of the Ag-carbene
complex was established by the
observation of
a
signal at
181.1 ppm in the 13C NMR
spectrum, which was assigned
to
the
imidazol-2-ylidene
carbon atoms, and by the ab-
sence of the resonance for the
Scheme 1. Synthesis of triazole-containing imidazolium salts.
2H-imidazolium proton in the
1H NMR spectrum. Colorless
crystals of complex 4b suitable
for an X-ray diffraction study were grown by slow diffusion
of diethyl ether into an acetonitrile solution. The details of
the molecular structure of 4b in the solid state were estab-
lished by an X-ray diffraction study.
Abstract in Chinese:
The silver–carbene complex 4b crystallizes in the triclinic
space group P-1. It is a cationic tetranuclear silver complex
consisting of a zigzag Ag4 chain. The molecular structure of
the cationic section is represented in Figure 1 along with the
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Chem. Asian J. 2010, 5, 1677 – 1686

N-Heterocyclic Carbene Complexes for Suzuki–Miyaura Coupling
ing loss of symmetry of the pyrimidine upon bonding to pal-
ladium.
Pale yellow crystals of 5b suitable for an X-ray diffraction
study were grown from an acetonitrile solution by addition
of diethyl ether. The molecular structure of 5b in the solid
state is depicted in Figure 2 along with the principal bond
Figure 1. ORTEP drawing of [Ag4(L1)4]ACHTNUTRGNEUGN(PF6)4 (4b). Thermal ellipsoids
are drawn at the 30% probability level. Hydrogen atoms and anions
have been removed for clarity. Selected bond distances (ꢁ) and angles
(8): Ag(1)–Ag(2) 3.0483(10), Ag(2)–Ag(3) 3.0346(10), Ag(3)–Ag(4)
3.0414(10), Ag(1)–C(4) 2.082(10), Ag(2)–C(21) 2.070(9), Ag(3)–C(55)
2.083(9), Ag(4)–C(38) 2.091(10), Ag(1)–N(8) 2.157(7), Ag(2)–N(1)
2.121(7), Ag(3)–N(15) 2.118(7), Ag(4)–N(22) 2.144(8); C(4)-Ag(1)-N8
178.1(3), C(21)-Ag(2)-N(1) 179.1(3), C(55)-Ag(3)-N(15) 177.6(3), C(38)-
Ag(4)-N(22) 178.3(3), Ag(3)-Ag(2)-Ag(1) 146.86(3), Ag(2)-Ag(3)-Ag(4)
148.13(3).
Figure 2. ORTEP drawing of [Pd(L1)Cl]PF6 (5b). Thermal ellipsoids are
drawn at the 30% probability level, and all hydrogen atoms and one
anion have been removed for clarity. Selected bond distances (ꢁ) and
angles (8): Pd(1)–C(4) 1.915(8), Pd(1)–N(1) 2.029(7), Pd(1)–N(6)
2.053(7), Pd(1)–Cl(1) 2.335(2); C(4)-Pd(1)-N(1) 86.5(3), C(4)-Pd(1)-N(6)
80.2(3), N(1)-Pd(1)-N(6) 166.6(3), C(4)-Pd(1)-Cl(1) 174.8(3), N(1)-Pd(1)-
Cl(1) 98.7(2), N(6)-Pd(1)-Cl(1) 94.6(2).
principal bond lengths and bond angles. The four silver
À
atoms are held together by four ligands with short Ag Ag
À
contacts, in which the Ag Ag bond distances are
À
3.0346(10)-3.0483(10) ꢁ. The Ag Ag distances are compara-
lengths and angles. In complex 5b, the geometry around the
metal is distorted square planar, with the imidazolylidene,
triazole, and pyrimidinyl rings lying in the molecular plane.
The phenyl ring extends out of the coordination plane. As
expected, 3-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-1-(pyri-
midin-2-yl)-1H-imidazolylidene is coordinated to palladium
in a tridentate fashion by one carbon atom and two nitrogen
atoms forming a nonsymmetric NCN pincer-type complex
with 5- and 6-membered fused metallacycles. The geometry
around Pd is distorted as illustrated by the N6-Pd-N1 and
C4-Pd-Cl1 angles being 166.6(3)8 and 174.8(3)8, respectively.
ble to the reported values in the silver-NHC cluster com-
plexes.[15,16] In the complex, the two external silver atoms
are each bicoordinated to one carbene carbon and one tria-
zole nitrogen atom in a slightly bent geometry with C-Ag-N
angles of 178.1(3)8 and 178.3(3)8. The two internal silver
atoms are also bicoordinated to a carbene carbon atom and
a triazole nitrogen atom, but in linear coordination geome-
try. The imidazole rings are essentially coplanar with their
attached pyrimidines, and they are perpendicular to the
plane of the triazole bonded to the same silver ion. The
À
À
Ag C bond distances are found in the range of 2.070(9)–
2.091(10) ꢁ, which is normal for silver carbene com-
The palladium-carbene distance Pd C(4) (1.915(8) ꢁ) is
shorter than those of normal PdII-NHC complexes (1.96 to
2.1 ꢁ),[19] but similar to the reported values (1.90 ꢁ) for pal-
ladium complexes consisting of tridentate N-heterocyclic
carbene ligands.[20]
plexes.[15]
Transmetallation via a preformed silver-NHC complex is
a practical and convenient method for the preparation of
other transition-metal-NHC complexes.[17] Following this
Similarly, the platinum-NHC complex [Pt(L1)Cl]
ACHTUNGTRENNUNG(PF6) 5c
strategy, treatment of 4b with Pd
at room temperature affords the palladium(II) complex
[Pd(L1)Cl](PF6) 5b in 87% yield (Scheme 2). The formation
G
could be obtained by treatment of 4b with Pt(cod)Cl2, as a
ACHTUNGTRENNUNG
1
light yellow solid in 86% yield. As expected, the H NMR
spectrum of 5c showed a characteristic set of three distinct
peaks for the pyrimidine protons, and disappearance of the
NCHN proton, confirming the coordination of the pyrimi-
dine group. The 13C NMR spectrum of 5c in [D6]DMSO ex-
hibits a resonance signal at 162.3 ppm ascribed to the car-
benic carbon atom, which is within the expected range for
platinum(II)-NHC complexes.
ACHTUNGTRENNUNG
of 5b was confirmed by the absence of the H NMR reso-
nance signal of the acidic imidazolium C2-H at 10.29 ppm.
The 13C NMR spectrum of 5b in [D6]DMSO exhibits a reso-
nance signal at 162.6 ppm ascribed to the carbenic carbon
atom, which is consistent with the reported values in the
range of 186.5–149.5 ppm for Pd-NHC complexes.[18] Chelate
formation was initially suggested by the appearance of three
distinct peaks for the pyrimidine protons which are absent
Light yellow crystals of 5c suitable for an X-ray diffrac-
tion study were grown from a DMF solution of 5c by addi-
tion of diethyl ether. The molecular structure of the com-
1
in the H NMR spectrum of the free imidazolium salt, show-
Chem. Asian J. 2010, 5, 1677 – 1686
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W. Chen et al.
FULL PAPERS
plex 5c in the solid state was determined by X-ray diffrac-
tion and is depicted in Figure 3 along with the principal
bond lengths and angles. Complex 5c is isostructural with its
tion. By reaction of the silver carbene complex, formed
in situ, with a half equivalent of [Pd
ACHTUNGTRENNUNG
nuclear palladium complex [Pd(L2)2]AHCTUNGTRENNUNG
The pale yellow solid was characterized by NMR and ele-
mental analysis. The 13C NMR spectrum of 5e in
[D6]DMSO shows a singlet at 161.9 ppm ascribed to the car-
benic carbon atom. In the 1H NMR spectrum, the methylene
groups of 5e show an AB splitting pattern at 6.09 and
5.83 ppm (J=16 Hz). For comparison, the corresponding
imidazolium salt showed a singlet at 5.65 ppm. This illus-
trates that rotation of the imidazole ring is prohibited upon
complexation. When one equivalent of [PdACTHNUGTRNEUNG(CH3CN)2Cl2]
was allowed to react with an acetonitrile solution of the
silver-NHC complex, a novel dinuclear palladium complex
5d was obtained as a pale yellow solid in 51% yield. In
1
both H and 13C NMR spectra of 5d, only one set of reso-
nance signals for the two ligands was observed illustrating
that they are completely equivalent in solution. In the
1H NMR spectrum of 5d, the methylene group shows only a
singlet at 5.72 ppm illustrating that the two protons attached
to each methylene are magnetically equivalent.
Crystals of 5d were obtained by slow diffusion of diethyl
ether into an acetonitrile solution of 5d. A structural draw-
ing is shown in Figure 4 along with the principal bond
lengths and angles. In the asymmetric unit, the complex con-
sists of two independent ligands and two independent palla-
dium atoms. Each palladium ion is coordinated by a triazole
nitrogen atom, a pyridine nitrogen atom, a NHC carbon
atom, and a chloride ion in a square planar geometry. The
Figure 3. ORTEP drawing of [Pt(L1)Cl]PF6 (5c). Thermal ellipsoids are
drawn at the 30% probability level. Hydrogen atoms and one anion have
been removed for clarity. Selected bond distances (ꢁ) and angles (8):
Pt(1)–C(2) 1.927(17), Pt(1)–N(5) 2.000(18), Pt(1)–N(3) 2.025(16), Pt(1)–
Cl(1) 2.352(4); C(2)-Pt(1)-N(5) 88.2(8), C(2)-Pt(1)-N(3) 79.1(7), N(5)-
Pt(1)-N(3) 167.3(6), C(2)-Pt(1)-Cl(1) 174.1(6), N(5)-Pt(1)-Cl(1) 97.6(5),
N(3)-Pt(1)-Cl(1) 95.0(4).
palladium analogue 5b. The central PtII ion is coordinated
by a triazole nitrogen atom, a pyrimidine nitrogen atom, a
NHC carbon atom, and a chloride ion in a square planar ge-
ometry. The small N5-Pt-N3 angle (167.3(6)8) is in accord-
ance with a pincer conformation consisting of 5- and 6-mem-
bered fused metallacycles.[21] Interestingly, although plati-
num N-heterocyclic carbene complexes are common, plati-
num(II) complexes with pincer ligands bearing NHC donors
À
pyridine rings are trans to the imidazolylidenes. The Pd N-
À
(triazole) bond trans to the chloride is shorter than the Pd
have not been reported.[22,23] The Pt C bond length of
À
1.927(17) ꢁ is shorter than other PtII-NHC complexes
(1.939–2.06 ꢁ).[23] The shorter Pt C distance might be
À
caused by the rigid structure of the tridentate ligands.
As shown in Scheme 3, we were able to obtain a dinuclear
palladium complex [Pd2Cl2(L2)2]ACTHNUTRGNEUNG(PF6)2 5d (L2=1-butyl-3-
((1-(pyridin-2-yl)-1H-1,2,3-triazol-4-yl)methyl)imidazolyli-
dene) and a mononuclear palladium complex [Pd(L2)2]
ACHTUNGTRENNUNG(PF6)2 5e from 3d in good yields via a carbene-transfer reac-
Figure 4. ORTEP drawing of [Pd2Cl2(L2)2]ACTHNUTRGNENUG(PF6)2 (5d). Thermal ellipsoids
are drawn at the 30% probability level, and all hydrogen atoms and
anions have been removed for clarity. Selected bond distances (ꢁ) and
angles (8): Pd(1)–C(24) 1.965(12), Pd(1)–N(2) 2.042(7), Pd(1)–N(4)
2.095(9), Pd(1)–Cl(1) 2.272(3), Pd(2)–C(9) 1.970(10), Pd(2)–N(8)
2.036(8), Pd(2)–N(10) 2.109(9), Pd(2)–Cl(2) 2.273(3); C(24)-Pd(1)-N(2)
96.5(3), C(24)-Pd(1)-N(4) 174.5(3), N(2)-Pd(1)-N(4) 78.7(3), C(24)-
Pd(1)-Cl(1) 87.2(3), N(2)-Pd(1)-Cl(1) 176.2(2), N(4)-Pd(1)-Cl(1) 97.7(2),
C(9)- Pd(2)-N(8) 94.9(3), C(9)-Pd(2)-N(10) 174.0(3), N(8)-Pd(2)-N(10)
79.1(3), C(9)-Pd(2)-Cl(2) 88.6(3), N(8)-Pd(2)-Cl(2) 176.4(2), N(10)-
Pd(2)-Cl(2) 97.4(2).
Scheme 3. Synthesis of [Pd2Cl2(L2)2]ACHTNUGTRENN(GU PF6)2 (5d) and [Pd (L2)2]CAHTUNGTREN(NUGN PF6) (5e).
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N-Heterocyclic Carbene Complexes for Suzuki–Miyaura Coupling
Table 2. Influence of catalyst loading on the Suzuki–Miyaura cross-cou-
pling of 4-bromoacetophenone and 4-bromoanisole.
NACHTUNGTRENNUNG(pyridine) bond trans to the carbene ligand owing to the
À
larger trans effect of the NHC ligand. The Pd Cl distances
are shorter than those in complex 5b. In the solid state mo-
lecular structure, the two imidazole rings are almost parallel
with a small dihedral angle of 10.298. The imidazolylidene
ring is nearly perpendicular to the pyridine ring bonded to
the same metal center lying in its coordination plane. The
dihedral angle between two coordination planes is 63.698.
R
Loading [mol%]
T [h]
Yield [%][b]
TON
COCH3
1
0.33
2
3
6
6
2
3
6
6
100
96
96
68
55
100
96
64
49
10
100
960
9600
68000
550000
100
10À1
10À2
10À3
10À4
1
OCH3
À
10À1
10À2
10À3
10À4
960
The palladium carbene distances, Pd(2) C(9)=1.970 (10) ꢁ
6400
49000
100000
À
and Pd(1) C(24)=1.965(12) ꢁ, lie within the normal range
of 1.95-2.10 ꢁ for palladium complexes.[19,24]
6
[a] Reaction conditions: aryl bromide 1.0 mmol, phenylboronic acid
1.5 mmol, K2CO3 2.0 mmol, H2O 1 mL, 1008C, in air. [b] Yield of isolated
product.
Catalytic Properties
The palladium complexes 5b, 5d, and 5e in the solid state
and in solution can be stored in air for months without ob-
servable decomposition. This encouraged us to examine
their catalytic efficiency for the coupling of 4-bromoaceto-
phenone and phenylboronic acid in neat water and an air at-
mosphere. The results are listed in Table 1. The reactions
creased to 0.01 mol%, the reaction still gave quantitative
conversion within 3 h. Further decrease of the catalyst load-
ing resulted in incomplete conversion even when the reac-
tion was extended to 24 h, although an extremely high turn-
over number could be reached. As expected, the coupling
reaction of the less active 4-bromoanisole requires a higher
catalyst loading to reach complete conversion.
Table 1. Effect of the bases in aqueous Suzuki–Miyaura cross-coupling of
4-bromoacetophenone and phenylboronic acid using 0.01 mol% 5b in
air.[a]
The promising catalytic behavior of 5b for the Suzuki–
Miyaura coupling of simple aryl bromides encouraged us to
explore its application in double coupling reactions of 1,1-di-
bromo-1-alkenes, which are readily available from alde-
hydes. The resulting tri-substituted alkenes are important in-
termediates in material science. The palladium/phosphine
catalyzed cross coupling of 1,1-dibromo-1-alkenes with aryl-
boronic acids or alkynyltrifluoroborate has been studied.[26]
A number of aliphatic and aromatic 1,1-dibromo-1-alkenes
can be converted to tri-substituted alkenes using phenylbor-
onic acid as the coupling partner. Trisubstituted alkenes
were obtained in good to excellent yields at 1008C in air.
The results are summarized in Table 3. All of the substrates
bearing either an electron donating group or an electron
withdrawing group at the para postion of the phenyl rings
could be applied. The coupling of heteroaryl substituted
alkene also afforded the desired product in excellent yield
(Table 3, entry 2). However, complex 5b demonstrated poor
reactivity for aliphatic 1,1-dibromodec-1-ene (Table 3,
entry 3). In the coupling reaction of 1-bromo-4-(2,2-dibro-
movinyl)benzene and 1-chloro-4-(2,2-dibromovinyl)benzene
Entry
Base
Yield%[b]
1
2
3
4
5
6
7
Na2CO3
K2PO4·3H2O
Cs2CO3
NaOH
KF
84
35
26
34
83
81
90
Et3N
K2CO3
[a] Reaction conditions: 4-acetylphenylbromide 1.0 mmol, phenylboronic
acid 1.5 mmol, Base 2.0 mmol, H2O 1 mL, 1008C. [b] GC yield.
were monitored by GC analysis after appropriate intervals
within 3 h. At a Pd loading of 0.01 mol% the effect of dif-
ferent bases was studied. When Na2CO3, KF, Et3N, and
K2CO3 were used, the coupling reactions gave satisfactory
yields of biphenyl. Much lower catalytic activities were ob-
served for K3PO4, Cs2CO3, and NaOH. It is noted that Pd-
and Ni-catalyzed Suzuki–Miyaura cross-couplings in organic
media often requires K3PO4 or Cs2CO3 as base.[11a,25] A com-
parative study shows that complexes 5b, 5d, and 5e display
similar activities for both electron poor and electron rich
aryl bromides at the same Pd loading and reaction condi-
tions. Complex 5b was chosen as the catalyst for a detailed
catalytic study of the aqueous coupling reaction, and K2CO3
was the base of choice.
To further examine the catalytic efficiency of 5b, the cou-
pling reactions of 4-acetylphenyl bromide and 4-bromoani-
sole with different catalyst loadings ranging from 1 to
10À4 mol% were performed. The results are listed in
Table 2. We found that the reaction of 4-acetylphenyl bro-
mide and phenylboronic acid in H2O under an air atmos-
phere could be complete within 20 min at 1008C with a cata-
lyst loading of 1.0 mol%. When the catalyst loading was de-
À
with phenylboronic acid, the C X bond at the para positions
are retained (Table 3, entries 4 and 5). Thus the resultant
products bear additional halides offering the opportunity for
the construction of more complex compounds. In fact, when
phenylboronic acid was replaced by 4-tolylboronic acid, the
coupling reaction of 1-bromo-4-(2,2-dibromovinyl)benzene
afforded
a mixture of 4-(2,2-di-p-tolylvinyl)-4’-methylbi-
phenyl and 4,4’-(2-(4-bromophenyl)ethene-1,1-diyl)bis(me-
thylbenzene) in 48% and 28% yields, respectively (Table 3,
entry 6). When the catalyst loading was increased to
0.03 mol%, 1-bromo-4-(2,2-dibromovinyl)benzene could be
converted to the triple coupling product in 81% yield
(Table 3, entry 7). Other phenylboronic acids bearing differ-
Chem. Asian J. 2010, 5, 1677 – 1686
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1681

W. Chen et al.
FULL PAPERS
Table 3. Double Suzuki–Miyaura coupling of 1,1-dibromo-1-alkene.[a]
Entry
1
Substrate
Product
Yield [%][b]
81
2
3
89
53
4
5
82
72
6
28:48
7[c]
81
78
8
1682
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ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1677 – 1686

N-Heterocyclic Carbene Complexes for Suzuki–Miyaura Coupling
Table 3. (Continued)
Entry
Substrate
Product
Yield [%][b]
9
82
10
11
81
79
12
13
78
84
14
77
[a] Reaction conditions: 1,1-dibromo-1-alkene 0.5 mmol, Pd 0.02 mol%, phenylboronic acid 2.25 mmol, K2CO3 2.25 mmol, H2O 2 mL, 1008C, in air, 12 h.
[b] Yield of isolated product. [c] 1,1-Dibromo-1-alkene 0.5 mmol, Pd 0.03 mol%, phenylboronic acid 3.5 mmol, K2CO3 4 mmol, H2O 2 mL, 1008C, in air.
ent functional groups and naphthylboronic acid also gave
the expected coupling products in good yields.
ture, and such properties make them promising catalyst pre-
À
cursors for C C bond formation.
Conclusions
Experimental Section
General
We have described (i) the synthesis of a series of NHC li-
gands containing triazole groups using click chemistry; and
(ii) structural characterization of Ag cluster 4b, pincer palla-
dium complex 5b, platinum complex 5c—containing a novel
nonsymmetrical NCNꢀ ligand, 3-((1-benzyl-1H-1,2,3-triazol-
4-yl)methyl)-1-(pyrimidin-2-yl)-1H-imidazol-3-iene (L1)—
and dinuclear palladium complex [Pd2Cl2{1-butyl-3-((1-(pyri-
din-2-yl)-1H-1,2,3-triazol-4-yl)methyl)imidazolyliden}2] 5d.
Palladium compound 5b was found to be highly active in
aqueous Suzuki–Miyaura cross-coupling reactions of 1,1-di-
bromo-1-alkenes in an air atmosphere at 1008C in neat
water. The complexes are all stable towards air and mois-
All chemicals were obtained from commercial suppliers and used without
further purification. 1-butyl-1H-imidazole (1a) was purchased from Alfa
Aesar. 2-(1H-imidazol-1-yl)pyrimidine (1b),[27] 1-mesityl-1H-imidazole
ACTHNUTRGNEUNG
(1c),[28] (azidomethyl)benzene,[29] 2-azidopyridine,[30] Pd(CH3CN)2Cl2,[31]
[32]
and Pt
N
were prepared according to known procedures. Ele-
mental analyses were performed on a Flash EA1112 instrument. 1H and
13C NMR spectra were recorded on Bruker Avance-400 (400 MHz) spec-
trometer. Chemical shifts (d) are expressed in ppm downfield to TMS at
d=0 ppm and coupling constants (J) are expressed in Hz.
Synthesis
3-(prop-2-ynyl)-1-(butyl-2-yl)-1H-imidazol-3-ium bromide (2a): To a solu-
tion of 1-butyl-1H-imidazole (2.28 g, 20 mmol) in 30 mL of dioxane was
Chem. Asian J. 2010, 5, 1677 – 1686
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1683

W. Chen et al.
FULL PAPERS
added 3-bromoprop-1-yne (2.60 g, 22 mmol). The mixture was refluxed at
1108C for 24 h. The mixture was evaporated to dryness and, after wash-
ing with dioxane and diethyl ether, the product was obtained as a yellow
triazole), 8.64 (d, 1H, J=4.0 Hz, pyridine), 8.17–8.15 (m, 2H, pyridine),
8.13 (t, 1H, J=1.6 Hz, NCHCHN), 7.96 (t, 1H, J=2.0 Hz, NCHCHN),
7.61–7.58 (m, 1H, pyridine),7.14 (s, 2H, Ar CH), 5.76 (s, 2H, CH2), 2.33
(s, 3H, CH3), 2.02 ppm (s, 6H, -CH3). 13C NMR (100 MHz, [D6]DMSO):
d=149.5, 148.7, 141.7, 140.8, 138.3, 134.8, 131.6, 129.7, 125.2, 124.7, 123.8,
122.6, 114.3, 44.7, 21.1, 17.4 ppm. Anal. calcd for C20H21F6N6P: C 48.98,
H 4.32, N 17.14; found: C 48.59, H 4.38, N 17.42.
1
oil. Yield: 3.00 g, 78%. H NMR (400 MHz, [D6]DMSO): d=9.47 (s, 1H,
NCHN), 7.93 (s, 1H, NCHCHN), 7.87 (s, 1H, NCHCHN), 5.27 (br, 2H,
-CH2-), 4.24 (t, 2H, J=7.2 Hz, CH2CH2CH2CH3), 3.87 (t, 1H, J=2.4 Hz,
CꢀCH), 1.79–1.72 (m, 2H, CH2CH2CH2CH3), 1.25–1.20 (m, 2H,
CH2CH2CH2CH3), 0.87 ppm (t, 3H, J=7.2 Hz, CH2CH2CH2CH3).
13C NMR (100 MHz, [D6]DMSO): d=136.4, 123.2, 122.6, 79.4, 76.4, 49.1,
39.1, 31.8, 19.1, 13.7 ppm.
1-butyl-3-((1-(pyridin-2-yl)-1H-1,2,3-triazol-4-yl)methyl)-1H-imidazol-3-
ium hexafluorophosphate (3d): The compound was prepared similarly as
for 3a from 2-azidopyridine (144 mg, 1.2 mmol), copper sulfate pentahy-
drate (12.5 mg, 0.05 mmol), sodium ascorbate (20 mg, 0.1 mmol), 3-butyl-
1-(prop-2-ynyl)-1H-imidazol-3-ium bromide 2a (242 mg, 1 mmol) in 2 mL
of water and tert-butyl alcohol (1:1). Yield: 286 mg, 67%. 1H NMR
(400 MHz, [D6]DMSO): d=9.30 (s, 1H, NCHN), 9.05 (s, 1H, triazole),
8.63 (d, 1H, J=4.8 Hz , pyridine), 8.16–8.14 (m,2H, pyridine), 7.87 (s,
1H, NCHCHN), 7.82(s, 1H, NCHCHN), 7.61–7.58 (m, 1H, pyridine),
5.65 (s, 2H,-CH2-), 4.18 (t, 2H, J=7.8 Hz, CH2CH2CH2CH3), 1.79–1.74
(m, 2H, CH2CH2CH2CH3), 1.31–1.24 (m, 2H, CH2CH2CH2CH3),
0.90 ppm (t, 3H, , J=7.2 Hz, CH2CH2CH2CH3). 13C NMR (100 MHz,
[D6]DMSO): d=149.5, 148.7, 142.0, 136.8, 125.1, 123.2, 123.1, 122.5,
114.2, 49.2, 44.0, 31.7, 19.2, 13.7 ppm. Anal. calcd for C15H19F6N6P:
C 42.06, H 4.47, N 19.62; found: C 42.35, H 4.40, N 19.42.
3-(prop-2-ynyl)-1-(pyrimidin-2-yl)-1H-imidazol-3-ium bromide (2b): The
compound was prepared similarly as for 2a from 2-(1H-imidazol-1-yl)-
pyrimidine (2.92 g, 20 mmol) and 3-bromoprop-1-yne (2.60 g, 22 mmol)
in 30 mL of dioxane. Yield: 3.70 g, 70%. 1H NMR (400 MHz,
[D6]DMSO): d=10.25 (s, 1H, NCHN), 9.07 (d, 2H, J=4.8 Hz, pyrimi-
dine), 8.50 (t, 1H, J=2.0 Hz, NCHCHN), 8.12 (t, 1H, J=2.0 Hz,
NCHCHN), 7.79 (t, 1H, J=4.8 Hz, pyrimidine), 5.42 (d, 2H, J=2.0 Hz,
CH2), 3.90 ppm (t, 1H, J=2.4 Hz, CꢀCH). 13C NMR (100 MHz,
[D6]DMSO): d=160.3, 152.2, 136.1, 123.8, 122.7, 119.7, 79.4, 75.9,
39.6 ppm. Anal. calcd for C10H9BrN4: C 45.30, H 3.42, N 21.13; found:
C 45.10, H 3.38, N 20.82.
3-mesityl-1-(prop-2-ynyl)-1H-imidazol-3-ium bromide (2c):[33] The com-
pound was prepared similarly as for 2a from 1-mesityl-1H-imidazole
(372 mg, 2.0 mmol) and 3-bromoprop-1-yne (260 mg, 2.2 mmol) in 10 mL
of dioxane. Yield: 304 mg, 50%. 1H NMR (400 MHz, [D6]DMSO): d=
9.58 (s, 1H, NCHN), 8.13 (t, 1H, J=1.6 Hz, NCHCHN), 7.99 (t, 1H, J=
1.6 Hz, NCHCHN), 8.12 (s, 2H, Ar CH), 5.32 (d, 2H, J=2.4 Hz, CH2),
3.89 (t, 1H, J=2.4 Hz, CꢀCH), 2.34 (s, 3H, CH3), 2.02 ppm (s, 6H,
CH3).
ACHTUNERGN[UNG Ag4(L1)4]AHCUTNGTRENN(GUN PF6)4 (4b): A solution of 3b (90 mg, 0.20 mmol) in acetoni-
trile (5 mL) was treated with Ag2O (24 mg, 0.10 mmol) at 508C. After
stirring for 6 h, the solution was filtered and concentrated to around
2 mL. Addition of diethyl ether (20 mL) resulted in the precipitation of a
1
white solid, which was isolated by filtration. Yield: 97 mg, 85%. H NMR
(400 MHz, [D6]DMSO): d=8.61 (d, 2H, J=4.4 Hz, pyrimidine), 8.55 (s,
1H, triazole), 8.22 (s, 1H, NCHCHN), 8.79 (s, 1H, NCHCHN), 7.49 (t,
1H, J=4.4 Hz, pyrimidine), 7.37 (br, 5H, Ar CH), 5.72 (s, 2H, CH2),
3-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-1-butyl-1H-imidazol-3-ium hex-
13
À
5.70 ppm (s, 2H, CH2). C NMR (100 MHz, [D6]DMSO): d=181.1 (Ag
afluorophosphate (3a):
A mixture of (azidomethyl)benzene (160 mg,
C), 159.5, 154.7, 143.3, 135.4, 129.4, 129.1, 128.9, 126.1, 123.9, 121.5, 120.8,
65.4, 54.4 ppm. Anal. calcd for C68H60F24N28P4Ag4·2H2O: C 35.25, H 2.78,
N 16.93; found: C 35.63, H 2.61, N 16.61.
1.2 mmol), copper sulfate pentahydrate (12.5 mg, 0.05 mmol) and sodium
ascorbate (20 mg, 0.1 mmol), 1-butyl-3-(prop-2-ynyl)-1H-imidazol-3-ium
bromide 2a (242 mg, 1 mmol) was added to water and tert-butyl alcohol
(2 mL, 1:1). The heterogeneous mixture was stirred vigorously for 24 h at
508C. The reaction mixture was diluted with water (20 mL), and the
yellow solution was added dropwise to an aqueous solution of NH4PF6.
The resulting white precipitate was collected by filtration and dried.
Yield: 313 mg, 70%. 1H NMR (400 MHz, [D6]DMSO): d=9.25 (s, 1H,
NCHN), 8.28 (s, 1H, triazole), 7.78 (s, 1H, NCHCHN), 7.77 (s,1H,
NCHCHN), 7.38–7.32 (m, 5H, Ar CH), 5.63 (s, 2H, CH2), 5.51 (s, 2H,
CH2), 4.17 (t, 2H, J=7.2 Hz, CH2CH2CH2CH3), 1.79–1.72 (m, 2H,
CH2CH2CH2CH3), 1.26–1.21 (m, 2H, CH2CH2CH2CH3), 0.89 ppm (t, 3H,
, J=7.2 Hz, CH2CH2CH2CH3); 13C NMR (100 MHz, [D6]DMSO): d=
141.2, 136.6, 136.1, 129.2, 128.7, 128.5, 124.9, 123.1, 53.4, 49.1, 44.1, 31.7,
19.2, 13.7 ppm. Anal. calcd for C17H22F6N5P: C 46.26, H 5.02, N 15.87;
found: C 46.01, H 4.98, N 15.66.
[Pd(L1)Cl]
(232 mg, 1.0 mmol) in 20 mL of acetonitrile was stirred at 508C. After
6 h, Pd(CH3CN)2Cl2 (520 mg, 2.0 mmol) was added and the mixture was
ACHTUGNTRNEN(UNG PF6) (5b): A mixture of 3b (900 mg, 2.0 mmol) and Ag2O
AHCTUNGTRENNUNG
stirred for another 8 h at room temperature. The filtrate was concentrat-
ed to around 5 mL. Addition of 50 mL of diethyl ether to the filtrate re-
sulted in the precipitation of a pale yellow solid, which was isolated by
filtration. Yield: 1.05 g, 87%. 1H NMR (400 MHz, [D6]DMSO): d=9.28
(s, 1H, pyrimidine), 9.18 (s, 1H, pyrimidine), 8.77 (s, 1H, triazole), 8.38
(d, 1H, J=2.4 Hz, NCHCHN), 7.97 (d, 1H, J=2.0 Hz, NCHCHN), 7.81
(t, 1H, J=5.2 Hz, pyrimidine), 7.44–7.40 (m, 5H, Ar CH), 5.86 (s, 2H,
CH2), 5.85 ppm (s, 2H, CH2). 13C NMR (100 MHz, [D6]DMSO): d=162.6
À
(Pd C), 159.8, 156.6, 152.8, 139.7, 134.5, 129.5, 129.4, 128.9, 126.5, 123.4,
121.1, 55.5, 46.3 ppm. Anal. calcd for C17H15ClF6N7PPd: C 44.07, H 3.48,
N 21.16; found: C 44.33, H 3.42, N 20.82.
3-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-1-(pyrimidin-2-yl)-1H-imida-
zol-3-ium hexafluorophosphate (3b): The compound was prepared simi-
larly as for 3a from (azidomethyl)benzene (1.60 g, 12 mmol), copper sul-
fate pentahydrate (125 mg, 0.5 mmol), sodium ascorbate (200 mg,
1 mmol), and 3-(prop-2-ynyl)-1-(pyrimidin-2-yl)-1H-imidazol-3-ium bro-
mide (2b) (2.65 g, 10 mmol) in water and tert-butyl alcohol (8 mL, 1:1).
Yield: 3.60 g, 78%. 1H NMR (400 MHz, [D6]DMSO): d=10.29 (s, 1H,
NCHN), 9.05 (d, 2H, J=4.4 Hz, pyrimidine), 8.47 (t, 1H, J=1.6 Hz,
NCHCHN), 8.34 (s, 1H, triazole), 7.99 (t, 1H, J=1.6 Hz, NCHCHN),
7.76 (t, 1H, J=4.8 Hz, pyrimidine), 7.38–7.33 (m, 5H, Ar CH), 5.68 (s,
2H, CH2), 5.64 ppm (s, 2H, CH2); 13C NMR (100 MHz, [D6]DMSO): d=
160.2, 152.2, 140.7, 136.4, 135.8, 128.9, 128.5, 128.2, 124.9, 124.0, 122.6,
119.6, 53.2, 44.6 ppm. Anal. calcd for C17H16N7PF6: C 44.07, H 3.48,
N 21.16; found: C 44.33, H 3.42, N 20.82.
[Pt(L1)Cl]
ACHTUNGTRENNUNG
from 3c (90 mg, 0.2 mmol), Ag2O (24 mg, 0.1 mmol), and PtACHTUNGTRENNUNG
(75 mg, 0.2 mmol) in 5 mL of acetonitrile. Yield: 120 mg, 86%. 1H NMR
(400 MHz, [D6]DMSO): d=9.48 (dd, 1H, J=6.0, 2.0 Hz, pyrimidine),
9.19 (dd, 1H, J=4.8, 2.0 Hz, pyrimidine), 8.79 (s, 1H, triazole), 8.36 (d,
1H, J=2.4 Hz, NCHCHN), 7.99 (d, H, J=2.0 Hz, NCHCHN), 7.82 (t,
1H, J=5.2 Hz, pyrimidine), 7.46–7.41 (m, 5H, Ar CH), 6.00 (s, 2H,
CH2), 5.85 ppm (s, 2H, CH2). 13C NMR (100 MHz, [D6]DMSO): d=162.3
À
(Pt C), 159.3, 158.3, 157.3, 139.5, 134.2, 129.5, 129.4, 128.9, 127.1, 122.9,
120.4, 55.7, 46.4 ppm. Anal. calcd for C17H15ClF6N7PPt: C 29.47, H 2.18,
N, 14.15; found: C 29.98, H 2.27, N 13.66.
AHCTUNGTRENNUNG
1-mesityl-3-((1-(pyridin-2-yl)-1H-1,2,3-triazol-4-yl)methyl)-1H-imidazol-
3-ium hexafluorophosphate (3c): The compound was prepared similarly
as for 3a from 2-azidopyridine (144 mg, 1.2 mmol), copper sulfate penta-
hydrate (12.5 mg, 0.05 mmol), sodium ascorbate (20 mg, 0.1 mmol), and
3-mesityl-1-(prop-2-ynyl)-1H-imidazol-3-ium bromide (2c) (305 mg,
1 mmol) in water and tert-butyl alcohol (2 mL, 1:1). Yield: 303 mg, 62%.
1H NMR (400 MHz, [D6]DMSO): d=9.56 (s, 1H, NCHN), 9.11 (s, 1H,
ACHTUNGTRENNUNG
added and the mixture was stirred for another 8 h at room temperature.
The filtrate was concentrated to around 2 mL. Addition of diethyl ether
(10 mL) to the filtrate resulted in the precipitation of a pale yellow solid,
which was isolated by filtration. Yield: 58 mg, 51%. 1H NMR (400 MHz,
[D6]DMSO): d=9.21 (s, 1H, triazole), 8.63 (d, 1H, J=4.4 Hz, pyridine),
8.19 (t, 1H, J=8.0 Hz, pyridine), 8.08 (d, 1H, J=4.4 Hz, pyridine), 7.67
1684
www.chemasianj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1677 – 1686

N-Heterocyclic Carbene Complexes for Suzuki–Miyaura Coupling
Table 4. Crystallographic data for complexes 4b, 5b, 5c, and 5d.
A
E
[Pd(L1)Cl]
N
[Pt(L1)Cl]
N
R
ACHTNUGERTN(NUGN PF6)2·2CH3CN
5b
5c
Formula
Fw
C68H62Ag4F24N28OP4
2298.82
C17H15ClF6N7PPd
604.18
C20H22ClF6N8OPPt
994.45
C34H42Cl2F12N14P2 Pd2
1220.46
Crystal system
Space group
a [ꢁ]
b [ꢁ]
c [ꢁ]
triclinic
P-1
triclinic
P-1
triclinic
P-1
triclinic
P-1
12.6432(12)
13.3920
15.8952
73.6150(10)
83.816(2)
86.537(2)
2565.7(5)
2
12.5731(13)
16.653(2)
22.756(2)
97.7750(10)
95.7140(10)
106.003(2)
4490.9(8)
2
7.3954(14)
9.6413(16)
15.539(2)
85.782(2)
80.1150(10)
77.5890(10)
1065.2(3)
2
7.4003(6)
9.7108(10)
19.335(18)
77.5160(10)
86.816(2)
77.2410(10)
1323.1(12)
2
a [8]
b [8]
g [8]
V [ꢁ3]
Z
Dcalcd [MgmÀ3
]
1.700
1.884
1.923
1.580
Reflections collected
Reflections independent, Rint
Goodness-of-fit on F2
R1, wR2 (I> 2s(I))
22930
15579, 0.0380
0.909
5319
3653, 0.0455
1.074
6611
4518, 0.0508
1.069
12514
8737, 0.0517
1.066
0.0653, 0.1475
0.0700, 0.1674
0.0893, 0.2233
0.0791, 0.1936
(br, 2H, pyridine and NCHCHN), 7.54 (s, 1H, NCHCHN), 5.72 (s, 2H,
CH2), 4.41 (t, 2H, J=6.6 Hz, -CH2CH2CH2CH3), 1.87–1.83 (m, 2H,
-CH2CH2CH2CH3), 1.32–1.27 (m, 2H, -CH2CH2CH2CH3), 0.93 ppm (t,
3H, J=7.6 Hz, -CH2CH2CH2CH3). 13C NMR (100 MHz, [D6]DMSO): d=
149.6, 147.8, 145.7, 141.1, 125.2, 124.3, 123.7, 122.3, 114.9, 50.4, 44.5, 33.2,
19.5, 13.9 ppm. Anal. calcd for C30H36Cl2F12N12P2Pd2: C 31.65, H 3.19,
N 14.77; found: C 31.70, H 3.16, N 14.36.
tural analyses are summarized in Table 4. CCDC 763107, CCDC 763108,
CCDC 763109, CCDC 763110 for 4b, 5b, 5c and 5d contains the supple-
mentary crystallographic data for this paper. This data can be obtained
free of charge from The Cambridge Crystallographic Data Centre at
www.ccdc.cam.ac.uk/data_request/cif.
[Pd(L2)2]
ACHTUNGTRENNUNG
from 3e (86 mg, 0.2 mmol), Ag2O (24 mg, 0.1 mmol), PdAHCTUNGTRENNUNG
(26 mg, 0.1 mmol) in 5 mL of acetonitrile. Yield: 46 mg, 48%. 1H NMR
(400 MHz, [D6]DMSO): d=9.47 (s, 1H, triazole), 8.70 (d, 2H, J=4.4 Hz,
pyridine), 8.19 (t, 1H, J=8.0 Hz, pyridine), 8.18 (td, 2H, J=8.4, 1.2 Hz,
pyridine), 7.97 (d, 2H, J=8.4 Hz, pyridine), 7.81 (d, 1H, J=1.6 Hz,
NCHCHN), 7.72–7.69 (m, 2H, pyridine), 7.56 (d, 1H, J=1.6 Hz,
NCHCHN), 6.09 (d, 2H, J=15.6 Hz, -CH2-), 5.84 (d, 2H, J=16.0 Hz,
-CH2-), 3.45 (br, 4H, 2ꢂCH2CH2CH2CH3), 1.68 (br, 2H,
CH2CH2CH2CH3), 1.34 (br, 2H, CH2CH2CH2CH3), 0.91 (brs, 2H,
CH2CH2CH2CH3), 0.72 (brs, 2H, CH2CH2CH2CH3), 0.45 ppm (t, 6H, J=
7.2 Hz, CH2CH2CH2CH3). 13C NMR (100 MHz, [D6]DMSO): d=161.9
Acknowledgements
The authors thank the National Natural Science Foundation of China
(20872129 and J0830413), the Fundamental Research Funds for the Cen-
tral Universities (2009QNA3004), and RFDP Foundation (200803350011)
for financial support.
[1] a) C. J. Li, T. H. Chan, Comprehensive Organic Reactions in Aque-
ous Media, 2nd ed., Wiley-VCH, Weinheim, 2007; b) B. Cornils,
W. A. Herrmann, Aqueous-Phase Organometallic Catalysis: Con-
cepts and Applications, 2nd ed., Wiley-VCH, Weinheim, 2004.
[2] a) C. J. Li, Chem. Rev. 1993, 93, 2023–2035; b) C. J. Li, Chem. Rev.
2005, 105, 3095–3165; c) A. Chanda, V. V. Fokin, Chem. Rev. 2009,
109, 725–748.
À
(Pd C), 149.8, 147.5, 143.3, 141.4, 126.8, 124.1, 123.4, 122.6, 114.9, 49.8,
44.4, 32.4, 19.6, 13.5 ppm. Anal. calcd for C30H36F12N12P2Pd: C 37.49,
H 3.78, N 17.49; found: C 37.75, H 3.81, N 17.40.
General procedure for the Suzuki–Miyaura coupling reaction: A Schlenk
tube was charged with 5b, aryl halide (1.0 mmol), phenylboronic acid
(1.5 mmol), K2CO3 (2.0 mmol), and H2O (1 mL) under an air atmos-
phere. After the mixture was stirred at 1008C for the required time, it
was extracted with EtOAc (3ꢂ10 mL), and the combined organic layer
was dried over anhydrous magnesium sulfate. After filtration, the solvent
was removed under vacuum, and the residue was purified by flash chro-
matography to give the desired product.
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X-ray Structural Determination
Single-crystal X-ray diffraction data were collected at 298(2) K on a Sie-
mens Smart/CCD area-detector diffractometer with a MoKa radiation
(l=0.71073 ꢁ) by using an w-2q scan mode. Unit-cell dimensions were
obtained with least-squares refinement. Data collection and reduction
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subjected to anisotropic refinement by full-matrix least squares on F2
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structures were calculated and allowed to ride on their respective C
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À
atoms with C H distances of 0.93–0.97 ꢁ and Uiso(H)=1.2–1.5Ueq(C).
Disordered solvent molecules that could not be modelled successfully
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solvent accessible void volume of 278.2 ꢁ3. Further details of the struc-
Chem. Asian J. 2010, 5, 1677 – 1686
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1685

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Received: January 25, 2010
Published online: May 25, 2010
1686
www.chemasianj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1677 – 1686