Synthesis and characterization of trinuclear N-heterocyclic carbene-palladium(II) complexes and their applications in the Suzuki-Miyaura cross-coupling reaction

Article abstract of DOI:10.1039/c6ra20852e

Five novel trinuclear N-heterocyclic carbene-palladium(ii) complexes 5a-e were conveniently synthesized through one-pot reactions of imidazolium salts, tridentate N-heterocycles {tris(4-(pyridin-4-yl)phenyl)amine or tris(4-(pyridin-3-yl)phenyl)amine} and palladium chloride in one step. All of the new complexes have been fully characterized by elemental analysis, ¹H, ¹³C NMR, and IR spectra. Among them, the molecular structures of complex 5d have been determined by X-ray single-crystal diffraction. Moreover, the obtained trinuclear palladium(ii) complexes were the effective catalyst precursors for the Suzuki-Miyaura coupling of aryl as well as benzyl chlorides with arylboronic acids. Under the optimal reaction conditions, the expected biaryl products were obtained in good to almost quantitative yields.

Full text of DOI:10.1039/c6ra20852e

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: T. Wang, L. Liu, K.
Xu, H. Xie, H. Shen and W. Zhao, RSC Adv., 2016, DOI: 10.1039/C6RA20852E.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Please do not adjust margins
RSC Advances
Page 1 of 8
View Article Online
DOI: 10.1039/C6RA20852E
Journal Name
ARTICLE
Synthesis and characterization of trinuclear N-heterocyclic
carbene-palladium(II) complexes and their applications in the
Suzuki-Miyaura cross-coupling reaction
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
a
a
a,b
DOI: 10.1039/x0xx00000x
Tao Wang , Lantao Liu* , Kai Xu , Huanping Xie , Hui Shen , Wen-Xian Zhao*
www.rsc.org/
Five novel trinuclear N-heterocyclic carbene-palladium(II) complexes 5a-e were conveniently synthesized through one-pot
reactions of imidazolium salts, tridentate N-heterocycles {tris(4-(pyridin-4-yl)phenyl)amine or tris(4-(pyridin-3-
yl)phenyl)amine} and palladium chloride in one step. All of the new complexes have been fully characterized by elemental
1
13
analysis, H, C NMR, and IR spectra. Among them, the molecular structures of complex 5d have been determined by X-
ray single-crystal diffraction. Moreover, the obtained trinuclear palladium(II) complexes were the effective catalyst
precursors for the Suzuki-Miyaura coupling of aryl as well as benzyl chlorides with arylboronic acids. Under the optimal
reaction conditions, the expected biaryl products were obtained in good to almost quantitative yields.
pyridine type ligands modified carbene palladium complexes
Introduction
as active catalysts for a series of catalytic reactions. Strassner
7
and co-workers explored the applications of the NHC-Pd(II)-
1
Since the pioneering work of Arduengo in the 1990s, a wide
variety of NHC-Pd complexes have been synthesized and
applied in catalytic reactions such as Buchwald-Hartwig
amination reactions, direct C-H bond arylation reactions, as
well as cross-coupling reactions including Heck, Hiyama, Stille,
Negishi, Suzuki-Miyaura, and Kumada-Tamao-Corriu(KTC)
2
-phenylimidazole complexes in Suzuki-Miyaura cross-coupling
reaction of aryl chlorides, providing the desired products in
excellent yields with low catalyst loading. Recently, Shao and
Lu have developed well-defined NHC-Pd(II)-1-methylimidazole
8
complexes, which can be easily prepared from commercially
2
2
available imidazolium salts, 1-methylimidazole, and PdCl from
reactions. In these transformations, it was found that the
a one-step process in good yields, and found them to be
efficient catalysts for the Suzuki-Miyaura coupling, arylation of
symmetric dialkyl ketones, direct C-H bond arylation reactions.
In our previous work, we reported the mononuclear N-
electronic properties and steric encumbrance of the NHC
ligands were crucial. During the past few years, a number of
modified carbene ligands such as IPr, IXy, IMes, SIPr, SIXy,
SIMes and the corresponding palladium complexes have been
successively designed and applied in organic reactions. In
addition to the NHC moieties, another strategy is to introduce
an ancillary ligand into the metal center, thereby enhancing
the potential for hemilability and heterometallation of the
carbene ligands. The ancillary ligands attached to the metal
core also played important roles in tuning the electronic and
steric properties of the coordination sphere. For example, The
heterocyclic
carbene-palladium(II)
complexes
with
benzoxazole or benzothiazole ligands, which were used as
effective catalysts for the Suzuki-Miyaura coupling of aryl as
9
well as benzyl chlorides with arylboronic acids. Very recently,
the obtained NHC-Pd complexes also applied to the Buchwald-
Hartwig amination of aryl chlorides with secondary or primary
1
0
amines under the same reaction conditions. While a series of
tertiary phosphine modified carbene palladium complexes
were used as effective catalysts for Suzuki cross-coupling and
3
4
5
6
groups of Organ, Tu, Thiel and Brenner reported the
1
1
other reactions.
Besides mononuclear N-heterocyclic
a.
carbene palladium complexes, the dinuclear N-heterocyclic
carbene complexes containing various bridging ligands have
attracted increasing attention in recent years. N-heterocycles
such as DABCO, pyrazine, and 4,4′-bipyridine have been the
School of Chemistry and Chemical Engineering, Henan Engineering Laboratory of
Green Synthesis for Pharmaceuticals, Shangqiu Normal University, Shangqiu,
Henan, 476000, People’s Republic of China.
College of Chemistry and Molecular Engineering, Zhengzhou University,
b.
Zhengzhou, Henan, 450052, People’s Republic of China.
Tel./Fax: +86 0370-2595126; e-mail: liult05@iccas.ac.cn or
zhwx2595126@163.com
Electronic supplementary information (ESI) available: H NMR and C NMR
spectra of the trinuclear palladium(II) complexes 5a-e, the catalysis products
12
most widely used bridging ligands in this field. Dinuclear
1
13
NHC-palladium complexes containing phosphine spacers have
also been reported to be active catalyst precursors for C-C and
13
8
and 10, characterization data of the catalysis products
for the Pd complex 5d. See DOI: 10.1039/x0xx00000x
8
and 10, and CIF files
C-N coupling reactions. Despite the impressive progress
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 2 of 8
View Article Online
DOI: 10.1039/C6RA20852E
ARTICLE
Journal Name
R1
R1
made so far in the N-heterocyclic carbene-palladium
complexes as catalysts, very little research has been reported
on trinuclear or multinuclear carbene-palladium complexes
bearing tridentate or multidentate bridging ligands.
Encouraged by the results mentioned above and also in
continuation of our interest in the construction of
functionalized complexes for organic synthesis, herein we
would like to report the facile synthesis and structural
characterization of five novel trinuclear N-heterocyclic
carbene-palladium(II) complexes bridged by tridentate N-
heterocycles (Scheme 1). Furthermore, as their preliminary
application, the resulting trinuclear NHC-palladium complexes
were used in the Suzuki-Miyaura coupling of aryl and benzyl
chlorides with arylboronic acids.
N
N
Cl
Cl
N
Pd
N
Pd
N
N
R1
N
N
R1
Cl
Cl
R1
N
N
N
Cl
+
+
PdCl2
K2CO3, THF
N
R1
N
N
Cl Pd Cl
5c: R1 = Bn (30%)
2
3
R1
R1
N
N
Results and discussion
Synthesis and characterization of the trinuclear N-heterocyclic
carbene-palladium(II) complexes
9
According to our previous report, the trinuclear N-
heterocyclic carbene-palladium(II) complexes
5
were
conveniently prepared through one-pot reactions of
imidazolium salts, tridentate N-heterocycles {tris(4-(pyridin-4-
yl)phenyl)amine or tris(4-(pyridin-3-yl)phenyl)amine} and
palladium chloride in one step as shown in Scheme 1. The
expected palladium(II) complexes
5 were isolated in good
yields (30-57%) and fully characterized by elemental analysis,
1
13
H NMR, C NMR, and IR spectra. In addition, the trinuclear N-
heterocyclic carbene-palladium(II) complexes are bench stable.
The molecular structures of Pd complex 5d was further
investigated by X-ray single crystal analysis. The molecules are
illustrated in Figures 1. The crystal structure of 5d showed a
trinuclear framework with tridentate N-heterocycle ligands
bridging across three square planar Pd(II) units. Each palladium
center in complex 5d is surrounded by an imidazolylidene, a
pyridine, and two chloro ligands in an almost squareplanar
fashion. The values of bond lengths and angles also compare
well to those of the related NHC-Pd(II) complexes with N-
Fig.1 Molecular structures of the trinuclear N-heterocyclic
carbene-palladium(II) complex 5d. Hydrogen atoms and
solvent molecules are omitted for clarity. Selected bond
lengths (Å) and angles (deg) in complex 5d
：Pd1-C1 1.986(5),
Pd1-N2 2.106(4), Pd1-Cl1 2.2784(15), Pd1-Cl2 2.3078(15); C1-
Pd1-Cl1 90.96(15), N2-Pd1-Cl1 89.56(12), C1-Pd1-Cl2
8
8.52(15), N2-Pd1-Cl2 91.09(12), C1-Pd1-N2 173.95(19), Cl1-
9, 14
containing compounds.
The Pd(1)-Ccarbene bond lengths
Pd1-Cl2 178.65(6).
(around 1.986 Å) in complex 5d are slightly shorter than that of
Pd(1)-N(2) (around 2.106 Å). The angles of Ccarbene-Pd(1)-N(2)
o
and Cl(1)-Pd(1)-Cl(2) are almost close to 180 , while the
Catalytic study
The cross-coupling of organic halides and organoboron
reagents, known as the Suzuki-Miyaura coupling has greatly
progressed, especially inspired by 2010 Nobel Prize in
chemistry. It has standed out as one of the most powerful and
convenient carbon-carbon bond-forming process in natural
Ccarbene-Pd(1)-Cl(1) angles, Ccarbene-Pd(1)-Cl(2) angles, N(2)-
Pd(1)-Cl(1) angles and N(2)-Pd(1)-Cl(2) angles are almost close
o
to 90 .
Scheme 1 Synthesis of trinuclear N-heterocyclic carbene-
15
products, advanced materials and organic synthesis.
palladium(II) complexes 5a-e
.
Although aryl chloridesare less reactive than aryl bromides and
aryl iodides, they are very desirable substrates for the coupling
reaction because of their economic reason of low cost,
availability and stability. As a result, the development of
known or new catalysts with excellent catalytic reactivity is in
great demand to allow the conversion of challenging aryl
chlorides. In the present study, we found that the obtained
trinuclear N-heterocyclic carbene-palladium(II) complexes
could exhibit high catalytic activities in the reaction. In the
2
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 3 of 8
View Article Online
DOI: 10.1039/C6RA20852E
Journal Name
ARTICLE
b
beginning the coupling of 1-chloro-4-methoxybenzene with
phenylboronic acid was chosen as a model to evaluate the
Entry
1
Cat.
Base
Solvent
PrOH/H O (1/2)
Yield (%)
94
t
i
i
i
i
i
i
i
i
i
5a
KO Bu
2
catalytic properties of complexes
i
5
in the mixed solvent of
2
3
4
5
6
7
8
5a
5a
5a
5a
5a
5a
5a
5a
5a
5a
5b
5c
5d
5e
I
2
Cs CO
3
PrOH/H O (1/2)
2
97
>99
96
75
35
41
31
90
73
86
92
90
95
91
35
56
71
85
PrOH (0.4 mL) and H O (0.8 mL) (Table 1). When 1.0 mol % of
t
complex 5a was used as catalyst, KO Bu, K
2
3
PO
4
, Cs
2
CO
3
or
K3PO4
PrOH/H O (1/2)
2
NaOH as the base, the corresponding biaryl product 8a was
NaOH
KOH
PrOH/H
PrOH/H
PrOH/H
PrOH/H
PrOH/H
PrOH/H
2
O (1/2)
2
O (1/2)
2
O (1/2)
O (1/2)
2
2
O (1/2)
2
O (1/2)
isolated in excellent yield (up to 99%) after 6 h (entries 1-4).
KOH was proved to be inferior base affording product in 75%
t
yield (entry 5). Other bases such as Na
Na HCO
word, base plays crucial role for the yield of the reaction.
2
CO
3
, NaO Bu or
Na
2
CO
3
2
3
afforded the product in low yield (entries 6-8). In a
t
1
6
NaO Bu
Product 8a was obtained in 90% yield when the reaction time
was reduced to 4 h (entry 9). When the mixed solvent of EtOH
and water was tested, the yield of the product decreased to
NaHCO
3
c
9
K
K
3
3
PO
4
4
10
PO
2
EtOH/H O (1/2)
73% (entry 10). And increasing the amount of water from 0.8
i
mL to 0.9 mL led to decreased yield (entry 11). Then the other
11
K3PO4
K3PO4
PrOH/H O (1/3)
2
four trinuclear N-heterocyclic carbene-palladium(II) complexes
i
i
i
i
i
i
i
i
12
13
14
PrOH/H O (1/2)
2
5
b-e were examined, and excellent yields were still achieved
90-95% yield, entries 12 15). Thus, the optimized conditions
include using complex 5a as the catalyst with K PO base and
PrOH mixed with two equal volume of water as the solvent at
K
K
K
K
K
K
3
3
3
3
3
3
PO
4
PO
4
PO
4
PO
4
PO
4
PO
4
PrOH/H
PrOH/H
PrOH/H
PrOH/H
PrOH/H
PrOH/H
2
O (1/2)
2
O (1/2)
2
O (1/2)
O (1/2)
2
2
O (1/2)
2
O (1/2)
(
−
3
4
i
o
15
16
8
0 C for 6 h. Fortunately, in our system, the trinuclear N-
heterocyclic carbene-palladium(II) complexes were found to
exhibit better catalytic activity than a related mononuclear
NHC-Pd(II) complex in the Suzuki-Miyaura coupling reaction.
For example, in the presence of 1 mol % of the mononuclear
17
II
d
1
8
I
d
N-heterocyclic carbene-palladium(II) complexes
I
(containing
19
II
K3PO4
2
PrOH/H O (1/2)
palladium 0.0025 mmol), very low yield of the corresponding
product 8a was obtained (entry 16). While the amount of
a
All reactions were carried out using 6a (0.25 mmol), 7a (0.375
mmol), base (2.0 equiv), Cat. (1.0 mol%) in solvent (1.2 mL) at
palladium complexes
I was further increased to 3 mol%
(containing palladium 0.0075 mmol), the yield slightly
o
b
c
d
0 C for 6 h. Isolated yields. Reaction time was 4 h. Cat. (3.0
8
mol%).
increased to 71% (entry 18). Similar results were also observed
when the Pd-PEPPSI complex II was used as the catalysts
(Table 1, entries 17 and 19).
With optimized conditions in hand, the generality and
limitation of the reactions between a variety of aryl chlorides
Table 1 Optimization of reaction conditions for the Suzuki- and aryl boronic acids was first tested. The results are shown
in Table 2. Gratifyingly, most of the coupling reaction
Miyaura reaction of 1-chloro-4-methoxybenzene with
proceeded rapidly and efficiently to provide the corresponding
phenylboronic acid catalyzed by the trinuclear NHC-Pd(II)
a
5
biaryl products in good to almost quantitative yields. Diverse
electronic and stericallyhindered substituents in the phenyl
ring of aryl chlorides were all tolerated in such transformation
and good results were obtained (entries 1-10). For instance,
electron-donating groups such as methoxy and methyl group
complexes
2
and electron-withdrawing group such as NO group are all
tolerated to give the corresponding products in good to almost
quantitative yields. It seems that the relative position of the
same substituents on the phenyl groups of aryl chlorides did
not affect the product yields apparently. For example, the
reaction was quite feasible with ortho-substituted aryl
chlorides when the phenylboronic acid was used (entries 3 and
6
). To our pleasure, heteroaromatic aryl chlorides such as 2-
chloropyridine and 3-chloropyridine were also good
substrates, giving corresponding products 8i-j in good to high
yields (entries 9-10). Based on the above satisfactory results,
kinds of arylboronic acids were also subjected to the optimal
conditions to test the generality and limitations (entries 11-
1
8). In most cases, the reaction worked well and approached
to corresponding products in good to almost quantitative
yields under identical conditions. For instance, electron-rich
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 4 of 8
View Article Online
DOI: 10.1039/C6RA20852E
ARTICLE
Journal Name
and electron-poor groups substituted boronic acids are all
tolerated to give the corresponding products in high yields.
However, sterically hindered boronic acid such as 2,6-
dimethylphenylboronic acid resulted in a significant decrease
in yield (entry 14). In fact, in the case of 3-pyridinylboronic acid
or 4-pyridinylboronic acid gave trace amounts of product
under the present reaction conditions (data not shown in
Table 2). The possible reason for the failure of cross-coupling
of pyridinylboronic acid was attributable to their susceptibility
to hydrolysis.
7
d
13
6a (4-OMe-C
6
6
H
H
4
4
)
)
8m
8n
99
57
(
2-Me-C H )
6
4
7e
2,6-Me
14
15
6a (4-OMe-C
(
2
-C
6
H
3
)
6a (4-OMe-C H )
6
4
7f (4-F-C H )
6 4
8o
8p
99
98
16
6a (4-OMe-C H )
7g (4-CF -C H )
3 6 4
6
4
7h
1-Naphthyl)
7i (2-Naphthyl)
17
6a (4-OMe-C
6
H
4
)
8q
8r
99
98
(
Inspired by these successful results, we then turned our
interest to such transformations using the benzyl chlorides as
the substrates. To our pleasure, the optimal reaction
conditions are also suitable for benzyl chlorides. As shown in
Table 3, all reactions proceed smoothly to afford
diarylmethanes in good to almost quantitative yields under
identical conditions. Particularly, when sterically hindered
boronic acids such as 2,6-dimethylphenylboronic acid were
used as the substrates, high yield of the corresponding product
was always observed (99% yield, entry 4). In these reactions,
electron-rich, and -neutral substituents on both substrates had
a detrimental effect on the catalytic activity instead. Overview,
the above results confirm that the present trinuclear N-
heterocyclic carbene-palladium(II) complexes are highly
efficient catalysts for the Suzuki-Miyaura coupling of aryl as
well as benzyl chlorides with arylboronic acids.
18
6 4
6a (4-OMe-C H )
a
All reactions were carried out using
mmol), K PO (2.0 equiv), Cat. 5a (1.0 mol%) in PrOH/H
1:2, 1.2 mL) at 80 C for 6 h. Isolated yields.
6
(0.25 mmol),
7
(0.375
O (V:V
i
3
4
2
o
b
=
Table 3 Substrate scope for the catalytic Suzuki-Miyaura
reaction of benzyl chlorides using the NHC-Pd(II) complex 5a as
the catalyst
a
3
2
b
Entry
1
9 (Ar )
7 (Ar )
Product
Yield (%)
> 99
Table 2 Substrate scope for the catalytic Suzuki-Miyaura
reaction of aryl chlorides using the NHC-Pd(II) complex 5a as
the catalyst
7
b
9a (Ph)
9a (Ph)
9a (Ph)
10a
a
(4-Me-C H )
6 4
7
c
2
3
10b
10c
99
99
(
6 4
3-Me-C H )
7
d
(
2-Me-C
H )
6 4
Yield
1
2
7e
Entry
6 (Ar )
7 (Ar )
Product
b
4
5
6
9a (Ph)
9a (Ph)
9a (Ph)
10d
10e
10f
99
75
81
(%)
(
2 6 3
2,6-Me -C H )
1
2
3
4
5
6
7
8
9
6a (4-MeO-C
6b (3-MeO-C
6c (2-MeO-C
6d (4-Me-C H )
6
H
4
)
)
7a (Ph)
7a (Ph)
7a (Ph)
7a (Ph)
7a (Ph)
7a (Ph)
7a (Ph)
7a (Ph)
7a (Ph)
7a (Ph)
8a
8b
8c
8d
8e
8f
> 99
> 99
98
7f (4-F-C
6 4
H )
6 4
H
7
g
6
H
4
)
(
4-CF
7h
-C
H
4
)
3
6
99
6
4
7
9a (Ph)
10g
99
6e (3-Me-C
6f (2-Me-C
6g (4-CH CO-C
6h (4-NO -C H )
6
H
4
)
99
(
1-Naphthyl)
7a (Ph)
t
6
H
4
)
94
8
9
9b (4- Bu-C
H
)
10h
10i
10j
10k
10l
87
99
96
72
66
6
4
3
6
H
4
)
8g
8h
8i
99
9c (4-Me-C H )
7a (Ph)
6
4
87
2
6
4
10
9d (3-Me-C H )
7a (Ph)
6
4
4
6i (2-Pyridyl)
6j (3-Pyridyl)
84
1
1
1
2
9e (2-Me-C
6
H
)
7a (Ph)
1
0
8j
99
9f (4-F-C
6
H
4
)
7a (Ph)
7
b
1
1
6a (4-OMe-C H )
8k
8l
> 99
99
6
4
a
(
4-Me-C H )
All reactions were carried out using
mmol), K PO
1:2, 1.2 mL) at 80 C for 6 h. Isolated yields.
9
(0.25 mmol),
7
(0.375
O (V:V
6
4
i
3
4
(2.0 equiv), Cat. 5a (1.0 mol%) in PrOH/H
2
7
c
o
b
=
1
2
6a (4-OMe-C
6
H
4
)
(
6 4
3-Me-C H )
4
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Page 5 of 8
RSC Advances
View Article Online
DOI: 10.1039/C6RA20852E
Journal Name
ARTICLE
Conclusions
Z
2
In summary, a new class of trinuclear N-heterocyclic carbene-
palladium(II) complexes as catalysts has been developed
successfully. These complexes are easy to prepare and their
structures can be readily modified as well. Furthermore, they
have revealed high activity in the catalytic Suzuki-Miyaura
coupling reaction. With a typical catalyst loading of 1.0 mol%,
a variety of electronically and structurally diverse aryl chlorides
as well as benzyl chlorides reacted effectively with arylboronic
acids, thus providing a convenient and alternative method for
space group
P-3
-3
D
calcd (g cm )
1.213
-
1
μ (mm )
0.572
o
θ range ( )
2.91-22.97
2540
F(000)
no. of data collected
no. of unique data
R(int)
104000
6182
the synthesis of biaryl products. Further modification of the
trinuclear N-heterocyclic carbene-palladium(II) complexes and
their applications in other reactions are in progress.
0.0832
R1 = 0.0524
final R indices
(
I > 2σ(I))
wR
= 0.0700
wR = 0.1471
1.029 and -0.694
2
= 0.1336
Experimental
R indices (all data)
R
1
General procedures
Reactions for the preparation of trinuclear N-heterocyclic
carbene-palladium(II) complexes as well as all the catalytic
reactions were carried out under nitrogen atmosphere.
Solvents were dried with standard methods and freshly
distilled prior to use if needed. Tris(4-(pyridin-4-
2
-3
Largest diff peak and hole (e·Å )
yl)phenyl)amine
3 and tris(4-(pyridin-3-yl)phenyl)amine 4 were
General procedure for the synthesis of trinuclear N-heterocyclic
carbene-palladium(II) complexes 5a-e
1
7
prepared according to the literature methods. All other
chemicals were used as purchased. Melting points were
measured on an XT4A melting point apparatus and are
uncorrected. IR spectra were collected on a Bruker VECTOR22
Under an N
0.33 mmol), tridentate N-heterocycles (0.1 mmol), PdCl
mg, 0.33 mmol) and K CO (45.6 mg, 0.33 mmol) was stirred in
2
atmosphere, the mixture of imidazolium salts
(
2
(58.5
1
13
2
3
spectrophotometer in KBr pellets. H and C NMR spectra
were recorded on a Bruker DPX 400 instrument using TMS as
an internal standard. Elemental analyses were measured on a
Thermo Flash EA 1112 elemental analyzer.
anhydrous THF (5 mL) under reflux for 12 h. After cooling,
filtration and evaporation, the residue was puried by
preparative TLC on silica gel plates eluting with CH Cl2 to
2
afford the corresponding trinuclear N-heterocyclic carbene-
palladium(II) complexes 5a-e.
Complex 5a: Pale yellow solid (124.1 mg, 57%). M.p.: 221-223
o
C. IR (KBr):
410, 1329, 1224, 944, 819, 803, 758, 703 cm . H NMR (400
MHz, CDCl ): 8.53 (d, J = 6.5 Hz, 2H, ArH), 7.49 (t, J = 7.7 Hz,
H, ArH), 7.37-7.34 (m, 6H, ArH), 7.24 (d, J = 6.6 Hz, 2H, ArH),
.13-7.09 (m, 4H, ArH), 3.22-3.15 (m, 4H, CH(CH ), 1.49 (d, J =
), 1.12 (d, J = 6.8 Hz, 12H, CH(CH
NMR (100 MHz, CDCl ): 155.2, 151.4, 148.8, 148.0, 146.7,
35.1, 130.2, 128.1, 125.0, 124.7, 124.0, 121.2, 28.7, 26.3, 23.3.
Anal. Calcd for C114H135Cl N Pd (2177.34): C, 62.89; H, 6.25; N,
ν 2963, 2917, 2866, 1595, 1521, 1489, 1466,
Table 4 Summary of crystallographic details for complex 5d
-
1 1
1
3
δ
Complex 5d
2
7
Empirical formula
Mr
114 6 3
C H135Cl N10Pd
3 2
)
1
3
2177.3367
173(2)
6.5 Hz, 12H, CH(CH
3
)
2
3
)
2
).
C
3
δ
temperature (K)
wavelength (Å)
crystal system
cryst size (mm)
a (Å)
1
0.71073
trigonal
6
10
3
6.43. Found: C, 62.59; H, 6.74; N, 6.38.
Complex 5b: Pale yellow solid (96.2 mg, 50%). M.p.: 224-227 C.
IR (KBr): 2954, 2919, 2856, 1597, 1519, 1488, 1434, 1408,
376, 1331, 1292, 1227, 927, 853, 819, 761, 730, 699 cm . H
NMR (400 MHz, CDCl ): 8.50 (d, J = 6.4 Hz, 2H, ArH), 7.39 (d,
J = 8.6 Hz, 2H, ArH), 7.24 (d, J = 6.6 Hz, 2H, ArH), 7.12-7.05 (m,
o
0.28 x 0.22 x 0.15
24.2624(8)
24.2624(8)
13.1013(4)
90
ν
-1 1
1
b (Å)
3
δ
c (Å)
1
3
o
8H, ArH), 2.37 (s, 18H, CH3). C NMR (100 MHz, CDCl3): δ
α ( )
1
1
53.0, 151.5, 148.8, 148.0, 139.2, 136.4, 135.1, 129.3, 128.2,
24.7, 124.2, 121.1, 21.2, 19.2. Anal. Calcd for C H Cl N Pd
3
o
β ( )
90
9
6
99
6
10
o
γ ( )
120
(
1924.86): C, 59.90; H, 5.18; N, 7.28. Found: C, 59.43; H, 5.65;
3
N, 7.22.
V (Å )
6679.0(4)
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 6 of 8
View Article Online
DOI: 10.1039/C6RA20852E
ARTICLE
Journal Name
o
Complex 5c: Pale yellow solid (57.2 mg, 30%). M.p.: 168-171 C. electrons per cell or approximately 1 water molecules per
IR (KBr):
414, 1327, 1290, 1222, 1187, 1027, 817, 740, 711 cm . H Pd(II) complex 5d was summarized in Table 4.
NMR (400 MHz, CDCl ): 8.99 (d, J = 5.3 Hz, 2H, ArH), 7.64-
.51 (m, 8H, ArH), 7.40-7.24 (m, 8H, ArH), 7.10-7.08 (m, 4H,
ν
3031, 2922, 2851, 1611, 1594, 1519, 1488, 1448, formula. Details of the crystal structure determination of the
-
1 1
1
3
δ
7
1
3
Acknowledgements
2 3
ArH), 6.28 (s, 4H, CH ). C NMR (100 MHz, CDCl ): δ 165.0,
1
1
C
51.3, 149.4, 148.3, 135.1, 134.6, 131.7, 128.9, 128.4, 128.2, We are grateful to the National Natural Sciences Foundation of
28.0, 124.9, 123.3, 121.6, 111.5, 53.2. Anal. Calcd for China (nos. U1404205, 21572126 and 21202095), the Program
for Science & Technology Innovation Talents in Universities of
Henan Province (14HASTIT016), Innovation Scientists and
Technicians Troop Construction Projects of Henan Province,
and Key Scientific and Technological Project of Henan Province
(152102410056) for financial support.
96
H
81Cl
6
N
10Pd
3
(1906.72): C, 60.47; H, 4.28; N, 7.35. Found: C,
0.13; H, 4.66; N, 7.30.
Complex 5d: Pale yellow solid (113.2 mg, 52%). M.p.: 228-231
6
o
C. IR (KBr):
408, 1320, 1219, 943, 817, 803, 756, 703 cm . H NMR (400
MHz, CDCl ): 8.78 (s, 1H, ArH), 8.50 (d, J = 4.6 Hz, 1H, ArH),
.70 (d, J = 7.8 Hz, 1H, ArH), 7.49 (t, J = 7.7 Hz, 2H, ArH), 7.36 (d,
ν 2965, 2913, 2862, 1585, 1520, 1484, 1465,
-1 1
1
3
δ
7
Notes and references
J = 7.7 Hz, 4H, ArH), 7.30 (d, J = 8.4 Hz, 2H, ArH), 7.16-7.11 (m,
1
A. J. Arduengo III, R. L. Harlow and M. Kline, J. Am. Chem. Soc.,
1991, 113, 361.
3 2
) ). C NMR (100 2 (a) F. E. Hahn and M. C. Jahnke, Angew. Chem. Int. Ed., 2008,
5H, ArH), 3.24-3.17 (m, 4H, CH(CH ) ), 1.51 (d, J = 6.4 Hz, 12H,
3 2
1
3
CH(CH
3
)
2
), 1.13 (d, J = 6.7 Hz, 12H, CH(CH
): 154.9, 149.8, 149.4, 147.4, 146.7, 136.7, 135.1,
31.3, 130.3, 128.1, 125.0, 124.8, 124.1, 123.8, 28.8, 26.3, 23.3.
4
2
7, 3122; (b) V. Nair, S. Vellalath and B. P. Babu, Chem. Soc. Rev.,
008, 37, 2691; (c) S. Diez-Gonzalez, N. Marion and Steven P.
MHz, CDCl
3
δ
1
Nolan, Chem. Rev., 2009, 109, 3612; (d) T. Droge and F. Glorius,
6 3
H135Cl N10Pd (2177.34): C, 62.89; H, 6.25; N, Angew. Chem. Int. Ed., 2010, 49, 6940; (e) G. C. Fortman and S.
Anal. Calcd for C114
.43. Found: C, 62.62; H, 6.59; N, 6.41.
Complex 5e: Pale yellow solid (78.9 mg, 41%). M.p.: 184-187 C.
IR (KBr): 2955, 2916, 2848, 1596, 1512, 1480, 1438, 1408,
6
P. Nolan, Chem. Soc. Rev.; 2011, 40, 5151; (f) D. Yuan and H. V.
Huynh, Molecules, 2012, 17, 2491; (g) S. Budagumpi, R. A. Haque
and A. W. Salman, Coordin. Chem. Rev.; 2012, 256, 1787; (h) R.
S. Menon, A. T. Biju and V. Nair, Chem. Soc. Rev.; 2015, 44, 5040.
o
ν
-1 1
1
387, 1331, 1294, 1223, 927, 855, 819, 767, 729, 696 cm . H 3 For selected examples, see: (a) C. J. O’Brien, E. A. B. Kantchev,
C. Valente, N. Hadei, G. A.Chass, A. Lough, A. C. Hopkinson and
M. G. Organ, Chem.-Eur. J., 2006, 12, 4743; (b) M. G. Organ, S.
3
NMR (400 MHz, CDCl ): δ 8.72 (s, 1H, ArH), 8.49 (d, J = 3.4 Hz,
1
H, ArH), 7.71 (d, J = 6.0 Hz, 1H, ArH), 7.33 (d, J = 6.8 Hz, 2H,
Avola, I. Dubovyk, N. Hadei, E. A. B. Kantchev, C. J. O’Brien and C.
ArH), 7.15-7.13 (m, 3H, ArH), 7.06 (s, 7H, ArH), 2.38 (s, 18H, Valente, Chem.-Eur. J., 2006, 12, 4749; (c) E. A. B. Kantchev, C. J.
1
3
O’Brien and M. G. Organ, Angew. Chem., Int. Ed., 2007, 46, 2768;
d) C. Valente, S. Baglione, D. Candito, C. J. O’Brien and M. G.
3 3
CH ). C NMR (100 MHz, CDCl ): δ 152.6, 149.8, 149.6, 147.4,
(
1
1
5
39.2, 136.4, 135.1, 129.3, 128.4, 124.7, 124.2, 123.7, 21.3,
Organ, Chem. Commun., 2008, 735; (e) G. Shore, S. Morin, D.
Mallik and M. G. Organ, Chem.-Eur. J., 2008, 14, 1351; (f) M. G.
Organ, M. Abdel-Hadi, S. Avola, I. Dubovyk, N. Hadei, E. A. B.
Kantchev, C. J. O’Brien, M. Sayah and C. Valente, Chem.-Eur. J.,
9.2. Anal. Calcd for C H Cl N Pd (1924.86): C, 59.90; H,
9
6
99
6
10
3
.18; N, 7.28. Found: C, 59.55; H, 5.63; N, 7.19.
General procedure for the catalytic Suzuki-Miyaura coupling
reaction
2
008, 14, 2443; (g) J. Nasielski, N. Hadei, G. Achonduh, E. A. B.
Kantchev, C. J. O. Brien, A. Lough and M. G. Organ, Chem. Eur. J.,
010, 16, 10844; (h) J. L. Farmer, M. Pompeo, A. J. Lough and M.
A Schlenk flask was charged with aryl chlorides (0.25 mmol),
2
arylboronic acids (0.375 mmol), trinuclear N-heterocyclic G. Organ, Chem. Eur. J., 2014, 20, 15790.
(a) T. Tu, W. Fang and J. Jiang, Chem. Commun., 2011, 47
12358; (b) T. Tu, Z. Sun, W. Fang, M. Xu, Y. Zhou, Org. Lett.,
012, 14, 4250; (c) W. Fang, Q. Deng, M. Xu and T. Tu, Org. Lett.,
. After cooling, the reaction mixture was 2013, 15, 3678; (d) Z. Liu, N. Dong, M. Xu, Z. Sun and T. Tu, J.
evaporated and the product was isolated by preparative TLC Org. Chem., 2013, 78, 7436; (e) S. Liu, Q. Deng, W. Fang, J. -F.
4
,
carbene-palladium(II) complex
5 (1 mol %), K PO (2.0 equiv),
3 4
i
2
PrOH (0.4 mL) and H O (0.8 mL). The mixture was stirred at 80
2
o
C for 6 h under N
2
Gong, M. -P. Song, M. Xu and T. Tu, Org. Chem. Front., 2014, 1,
on silica gel plates.
1
261.
F. Rajabi and W. R. Thiel, Adv. Synth. Catal., 2014, 356, 1873.
X-ray diffraction studies
5
Crystal of 5d (CCDC 1472981) was obtained by recrystallization 6 M. Teci, E. Brenner, D. Matt and L. Toupet, Eur. J. Inorg. Chem.;
2
7
3
8
013, 2841.
M. Micksch, M. Tenne and T. Strassner, Organometallics, 2014,
from CH
were collected on an Oxford diffraction Gemini
diffractometer with graphite-monochromated Mo
2 2
Cl /n-hexane at ambient temperature. Their data
E
3, 3966.
K
α
(a) H. -Y. Yin, M. -Y. Liu and L. -X. Shao, Org. Lett., 2013, 15
,
radiation (
λ
= 0.71073 Å). The structures were solved by 6042; (b) H. Lv, L. Zhu, Y. -Q.Tang and J. -M. Lu, Appl.
Organometal. Chem., 2014, 28, 27; (c) Z.- K. Xiao, H. -Y. Yin and J.
direct methods using the SHELXS-97 program, and all non-
hydrogen atoms were refined anisotropically on F2 by the full-
-M. Lu, Inorg. Chim. Acta., 2014, 423, 106; (d) X. -B. Shen, Y.
Zhang, W. -X. Chen, Z. -K. Xiao, T. -T. Hu and L. -X. Shao, Org.
matrix least-squares technique, which used the SHELXL-97 Lett., 2014, 16, 1984; (e) Z. -S. Gu, W. -X.Chen and L. -X. Shao, J.
1
crystallographic software package. The hydrogen atoms were
8
Org. Chem., 2014, 79, 5806; (f) Y. Zhang, S. -C. Yin and J. -M. Lu,
Tetrahedron, 2015, 71, 544.
included but not refined. Squeeze indicates a total solvent
3
accessible area volume of 124 Å , corresponding to about 12
9
2
T. Wang, H. Xie, L. Liu and W - X. Zhao, J. Organomet. Chem.,
016, 804, 73.
6
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 7 of 8
View Article Online
DOI: 10.1039/C6RA20852E
Journal Name
ARTICLE
1
0 T.Wang, K. Xu, L. Liu, H. Xie, Y. Li and W - X. Zhao, Transition
Met Chem., 2016, 41, 525.
1 For selected examples, see: (a) V. Jurcik, S. P. Nolan and C. S.
1
J. Cazin, Chem.-Eur. J., 2009, 15, 2509; (b) O. Diebolt, V. Jurcik, R.
Correa da Costa, P. Braunstein, L. Cavallo, S. P. Nolan, A. M. Z.
Slawin and C. S. J. Cazin, Organometallics, 2010, 29, 1443; (c) X.
Cai, S. Majumdar, G. C. Fortman, C. S. J. Cazin, A. M. Z. Slawin, C.
Lhermitte, R. Prabhakar, M. E. Germain, T. Palluccio, S. P. Nolan,
E. V. Rybak-Akimova, M. Temprado, B. Captain and C. D. Hoff, J.
Am. Chem. Soc., 2011, 133, 1290; (d) V. Jurčík, T. E. Schmid, Q.
Dumont, A. M. Z. Slawin and C. S. J. Cazin, Dalton Trans., 2012,
41, 12619; (e) J. Broggi, V. Jurcik, O. Songis, A. Poater, L. Cavallo,
A. M. Z. Slawin and C. S. J. Cazin, J. Am. Chem. Soc., 2013, 135,
588; (f) T. E. Schmid, D. C. Jones, O. Songis, O. Diebolt, M. R. L.
4
Furst, A. M. Z. Slawin and C. S. J. Cazin, Dalton Trans., 2013, 42
,
7345; (g) C. E. Hartmann, V. Jurčík, O. Songis and C. S. J. Cazin,
Chem. Commun., 2013, 49, 1005.
1
2
1
2
2 (a) Y. Han, H. V. Huynh and G. K. Tan, Organometallics, 2007,
6, 6447; (b) J. Yang and L.Wang, Dalton Trans., 2012, 41, 12031.
3 (a) J. Yang, P. Li, Y. Zhang and L. Wang, J. Organomet. Chem.,
014, 766, 73; (b) J. Yang, P. Li, Y. Zhang and L. Wang, Dalton
Trans., 2014, 43, 7166.
4 (a) M.-T. Chen, D. A. Vicic, M. L. Turner and O. Navarro,
1
Organometallics, 2011, 30, 5052; (b) L. Zhu, T.-T. Gao and L.-X.
Shao, Tetrahedron, 2011, 67, 5150; (c) P. Huang, Y. -X. Wang, H. -
F. Yu and J. -M. Lu, Organometallics, 2014, 33, 1587.
1
5 (a) N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457; (b)
A. Suzuki, J. Organomet. Chem., 1999, 576, 147; (c) J.-P. Corbet
and G. Mignani, Chem. Rev., 2006, 106, 2651; (d) N. Marion and
S. P. Nolan, Acc. Chem. Res., 2008, 41, 1440; (e) G. C. Fu, Acc.
Chem. Res., 2008, 41, 1555; (f) C. Valente, S. Calimsiz, K.-H. Hoi,
D. Mallik, M. Sayah and M. G. Organ, Angew. Chem. Int. Ed.,
2
1
1
2
1
012, 51, 3314.
6 K. Ouyang and Z. Xi, Acta Chim. Sinica, 2013, 71, 13.
7 C. Hua, P. Turner and D. M. D’Alessandro, Dalton Trans.,
013, 42, 6310.
8 (a) G. M.Sheldrick, SHELXS-97, Program for Crystal Structure
Solution; University of Göttingen, Göttingen, Germany, 1997. (b)
G. M. Sheldrick, SHELXL-97, Program for Crystal Structure
Refinement; University of Göttingen, Göttingen, Germany, 1997.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

RSC Advances
Page 8 of 8
View Article Online
DOI: 10.1039/C6RA20852E
Graphic abstract for the table of contents